ALBERT

Beschreibung: 〈p〉Publication date: 1 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 176〈/p〉 〈p〉Author(s): Hoheok Kim, Tatsuki Yamamoto, Yushi Sato, Junya Inoue〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We investigate the viability of establishing low-cost surrogate structure-property (S–P) linkages by introducing a Bayesian model selection method to extend the Materials Knowledge Systems (MKS) homogenization framework, which employs the n-point spatial correlation function, principal component analysis, and regression techniques. In particular, we place emphasis not only on choosing the important structural features but also on interpreting their implications for the property under consideration. First, the yield strengths of synthetic microstructures with various morphological characteristics are estimated by physics-based crystal plasticity simulation. Then, the dimension-reduced microstructural features are revealed by a combination of 2-point spatial correlations and principal component analysis. The Bayesian model selection method is further applied to establish a microstructure-to-yield-strength surrogate model. Finally, the model is validated with an independent dataset and its constituent features are interpreted with a morphology reconstruction based on a Monte Carlo algorithm. The method is found to be capable of interpreting the key microstructural features as well as modeling the mechanical response of a dual-phase metallic composite in consideration of the diverse microstructural factors.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645419304367-fx1.jpg" width="274" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 1 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 176〈/p〉 〈p〉Author(s): Denise C. Ford, David Hicks, Corey Oses, Cormac Toher, Stefano Curtarolo〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Metallic glasses are excellent candidates for biomedical implant applications due to their inherent strength and corrosion resistance. However, use of metallic glasses in structural applications is limited because bulk dimensions are challenging to achieve. Glass-forming ability (GFA) varies strongly with alloy composition and becomes more difficult to predict as the number of chemical species in a system increases. Here, we present a theoretical model — implemented in the AFLOW framework — for predicting GFA based on the competition between crystalline phases. The model is applied to biologically relevant binary and ternary systems. Elastic properties of Ca- and Mg-based systems are estimated for use in biodegradable orthopedic support applications. Alloys based on Ag〈sub〉0.33〈/sub〉Mg〈sub〉0.67〈/sub〉, Cu〈sub〉0.5〈/sub〉Mg〈sub〉0.5〈/sub〉, Cu〈sub〉0.37〈/sub〉Mg〈sub〉0.63〈/sub〉, and Cu〈sub〉0.25〈/sub〉Mg〈sub〉0.5〈/sub〉Zn〈sub〉0.25〈/sub〉, and in the Ag-Ca-Mg and Ag-Mg-Zn systems, are recommended for further study.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645419304380-fx1.jpg" width="500" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 1 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 176〈/p〉 〈p〉Author(s): Manuel J. Pfeifenberger, Vladica Nikolić, Stanislav Žák, Anton Hohenwarter, Reinhard Pippan〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The brittleness of tungsten at room temperature represents a severe challenge particularly for structural applications. Tungsten composites, consisting of foils or wires, overcome this low ductility by utilizing the remarkable mechanical properties of ultrafine grained tungsten materials. A comprehensive understanding of the fracture behaviour of these ultrafine grained tungsten materials is therefore essential for a further development of high performance structural composites. However, the dimensions of specimens used for classical fracture toughness experiments are not applicable to test all important crack growth directions in the case of thin foils and wires, especially, in the direction of the presumably lowest fracture toughness, which is along their characteristically elongated microstructure. Femtosecond laser processing allows to fabricate micro single leg bending specimens, which enable to properly evaluate the fracture toughness in this orientation. The fracture toughness value at crack initiation found for the foil is 2.4  〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"〉〈mtext〉MPa〈/mtext〉〈msqrt〉〈mtext〉m〈/mtext〉〈/msqrt〉〈/math〉, whereas for the wire a value of 5.3  〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"〉〈mtext〉MPa〈/mtext〉〈msqrt〉〈mtext〉m〈/mtext〉〈/msqrt〉〈/math〉 was determined. In both cases the results are significantly below the values reported for other orientations. This strongly anisotropic fracture behaviour is responsible for the reduced brittle to ductile transition temperature and the delamination induced toughening for crack orientations perpendicular to the elongated ultrafine grained structure. The distinct difference of the fracture toughness at crack initiation and the R-curve between wire and foil specimens could be primarily explained by the morphologies of the fracture surfaces, exhibiting significantly different roughnesses of the evolving crack paths.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645419304252-fx1.jpg" width="497" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 1 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 176〈/p〉 〈p〉Author(s): Peter Müllner〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Recent reports on highly mobile type II twin boundaries challenge the established understanding of deformation twinning and motivate this study. We consider the motion of twin boundaries through the nucleation and growth of disconnection loops and develop a mechanism-based model for twin boundary motion in the framework of isotropic linear elasticity. While such mechanisms are well established for type I and compound twins, we demonstrate based on the elastic properties of crystals that type II twin boundaries propagate in a similar way. Nucleation of a type I twinning disconnection loop occurs in a discrete manner. In contrast, nucleation of a type II twinning disconnection loop occurs gradually with increasing Burgers vector. The gradual nucleation of a type II disconnection loop accounts for the higher mobility of type II twin boundaries compared with type I twin boundaries. We consider the homogeneous nucleation of a disconnection loop, which is adequate for twinning in shape memory alloys with a low-symmetry crystal lattice. For the magnetic shape memory alloy Ni–Mn-Ga, the model predicts twinning stresses of 0.33 MPa for type II twinning and 4.7 MPa for type I twinning. Over a wide temperature range, the twinning stress depends on temperature only through the temperature dependence of the elastic constants, in agreement with experimental results.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645419304343-fx1.jpg" width="374" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: Available online 3 July 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia〈/p〉 〈p〉Author(s): Cuncai Fan, Qiang Li, Jie Ding, Yanxiang Liang, Zhongxia Shang, Jin Li, Ruizhe Su, Jaehun Cho, Di Chen, Yongqiang Wang, Jian Wang, Haiyan Wang, Xinghang Zhang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉There are increasing studies that show nanotwinned (NT) metals have enhanced radiation tolerance. However, the mechanical deformability of irradiated nanotwinned metals is a largely under explored subject. Here we investigate the mechanical properties of He ion irradiated nanotwinned Cu with preexisting nanovoids. In comparison with coarse-grained Cu, nanovoid nanotwinned (NV-NT) Cu exhibits prominently improved radiation tolerance. Furthermore, 〈em〉in situ〈/em〉 micropillar compression tests show that the irradiated NV-NT Cu has an ultrahigh yield strength of ∼ 1.6 GPa with significant plasticity. Post radiation analyses show that twin boundaries are decorated with He bubbles and thick stacking faults. These stacking fault modified twin boundaries introduce significant strengthening in NT Cu. This study provides further insight into the design of high-strength, advanced radiation tolerant nanostructured materials for nuclear reactor applications.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645419304331-fx1.jpg" width="307" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 1 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 176〈/p〉 〈p〉Author(s): Y. Kobayashi, J. Takahashi, K. Kawakami〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The influence of a pre-deformation with a true strain of 0.5 on the precipitation behavior during isothermal aging at 580 °C in ferritic steel containing 0.03C-0.1Ti-0.20Mn–3Al (mass %) was investigated. Atom probe tomography (APT) analysis revealed that titanium carbide (TiC) precipitates much earlier and more finely in pre-deformed steel than in steel without a pre-deformation. It was found that the precipitation sites of TiC are not only located on the dislocations but are also distributed homogeneously in a matrix in pre-deformed steel. In steel without a pre-deformation, coarse cementite first precipitates during the early stage of aging, and the cementite then dissolves owing to the subsequent precipitation of TiC. Meanwhile, in pre-deformed steel, cementite has difficulty precipitating, and carbon atoms are considered to segregate to high-density dislocations during the early stage of aging prior to the precipitation of TiC. A kinetic model that explains the difference between the precipitation behaviors of steel with and without a pre-deformation is proposed. Moreover, the difference observed between TiC particle strengthening in steel with and without a pre-deformation is discussed.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S135964541930429X-fx1.jpg" width="500" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 15 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 179〈/p〉 〈p〉Author(s): Chunguang Shen, Chenchong Wang, Xiaolu Wei, Yong Li, Sybrand van der Zwaag, Wei Xu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉With the development of the materials genome philosophy and data mining methodologies, machine learning (ML) has been widely applied for discovering new materials in various systems including high-end steels with improved performance. Although recently, some attempts have been made to incorporate physical features in the ML process, its effects have not been demonstrated and systematically analysed nor experimentally validated with prototype alloys. To address this issue, a physical metallurgy (PM) -guided ML model was developed, wherein intermediate parameters were generated based on original inputs and PM principles, e.g., equilibrium volume fraction (〈em〉V〈/em〉〈sub〉〈em〉f〈/em〉〈/sub〉) and driving force (〈em〉D〈/em〉〈sub〉〈em〉f〈/em〉〈/sub〉) for precipitation, and these were added to the original dataset vectors as extra dimensions to participate in and guide the ML process. As a result, the ML process becomes more robust when dealing with small datasets by improving the data quality and enriching data information. Therefore, a new material design method is proposed combining PM-guided ML regression, ML classifier and a genetic algorithm (GA). The model was successfully applied to the design of advanced ultrahigh-strength stainless steels using only a small database extracted from the literature. The proposed prototype alloy with a leaner chemistry but better mechanical properties has been produced experimentally and an excellent agreement was obtained for the predicted optimal parameter settings and the final properties. In addition, the present work also clearly demonstrated that implementation of PM parameters can improve the design accuracy and efficiency by eliminating intermediate solutions not obeying PM principles in the ML process. Furthermore, various important factors influencing the generalizability of the ML model are discussed in detail.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645419305452-fx1.jpg" width="500" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: Available online 20 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia〈/p〉 〈p〉Author(s): Hao Chen, Valery Levitas, Liming Xiong〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Molecular dynamics (MD) simulations of the amorphous band nucleation and growth ahead of the tip of a shuffle 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"〉〈mrow〉〈msup〉〈mrow〉〈mn〉60〈/mn〉〈/mrow〉〈mrow〉〈mi〉o〈/mi〉〈/mrow〉〈/msup〉〈/mrow〉〈/math〉 dislocation pileup at different grain boundaries (GBs) in diamond-cubic (dc) silicon (Si) bicrystal under shear are performed. Amorphization initiates when the local resolved shear stress reaches approximately the same value required for amorphization in a perfect single crystal (8.6-9.3GPa) for the same amorphization plane. Since the local stresses at the tip of a dislocation pileup increase when the number of dislocations in the pileup is increased, the critical applied shear stress 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.svg"〉〈mrow〉〈msub〉〈mrow〉〈mi〉τ〈/mi〉〈/mrow〉〈mrow〉〈mi〉a〈/mi〉〈mi〉p〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉 for the formation of an amorphous shear band significantly decreases with the dislocation accumulation at the GBs. In particular, when the number of the dislocations in a pileup increases from 3 to 8, the critical shear stress drops from 4.7GPa to 1.6GPa for both the 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si3.svg"〉〈mrow〉〈mtext〉Σ〈/mtext〉〈mn〉9〈/mn〉〈/mrow〉〈/math〉 and 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si4.svg"〉〈mrow〉〈mtext〉Σ〈/mtext〉〈mn〉19〈/mn〉〈/mrow〉〈/math〉 GBs and from 4.6GPa to 2.1GPa for the 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si5.svg"〉〈mrow〉〈mtext〉Σ〈/mtext〉〈mn〉3〈/mn〉〈/mrow〉〈/math〉 GB, respectively. After the formation of steps and disordered embryos at the GBs, the atomistic mechanisms responsible for the subsequent amorphous shear band formations near different GBs are found to distinct from each other. For a high-angle GB, such as 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si5.svg"〉〈mrow〉〈mtext〉Σ〈/mtext〉〈mn〉3〈/mn〉〈/mrow〉〈/math〉, an amorphous band propagates through the crystalline phase along the 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si6.svg"〉〈mrow〉〈mrow〉〈mo〉(〈/mo〉〈mrow〉〈mn〉112〈/mn〉〈/mrow〉〈mo〉)〈/mo〉〈/mrow〉〈/mrow〉〈/math〉 plane. For the 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si3.svg"〉〈mrow〉〈mtext〉Σ〈/mtext〉〈mn〉9〈/mn〉〈/mrow〉〈/math〉 GB, partial dislocations forming a stacking fault precede the formation of an amorphous band along the 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si7.svg"〉〈mrow〉〈mrow〉〈mo〉(〈/mo〉〈mrow〉〈mn〉110〈/mn〉〈/mrow〉〈mo〉)〈/mo〉〈/mrow〉〈/mrow〉〈/math〉 plane. For the 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si4.svg"〉〈mrow〉〈mtext〉Σ〈/mtext〉〈mn〉19〈/mn〉〈/mrow〉〈/math〉 GB, the one-layer stacking fault along the 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si8.svg"〉〈mrow〉〈mrow〉〈mo〉(〈/mo〉〈mrow〉〈mn〉111〈/mn〉〈/mrow〉〈mo〉)〈/mo〉〈/mrow〉〈/mrow〉〈/math〉 plane transforms into an interesting intermediate phase: a two-layer band with the atomic bonds being aligned along the 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si8.svg"〉〈mrow〉〈mrow〉〈mo〉(〈/mo〉〈mrow〉〈mn〉111〈/mn〉〈/mrow〉〈mo〉)〈/mo〉〈/mrow〉〈/mrow〉〈/math〉 plane (i.e., rotated by 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si9.svg"〉〈mrow〉〈msup〉〈mrow〉〈mn〉30〈/mn〉〈/mrow〉〈mrow〉〈mi〉o〈/mi〉〈/mrow〉〈/msup〉〈/mrow〉〈/math〉 with respect to the atomic bonds outside the band). This intermediate phase transforms to the amorphous band along the 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si8.svg"〉〈mrow〉〈mrow〉〈mo〉(〈/mo〉〈mrow〉〈mn〉111〈/mn〉〈/mrow〉〈mo〉)〈/mo〉〈/mrow〉〈/mrow〉〈/math〉 plane under a further shearing. The obtained results represent an atomic-level confirmation of the effectiveness of dislocation pileup at the nucleation site for various strain-induced phase transformations (PTs), and exhibit some limitations.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S135964541930535X-fx1.jpg" width="218" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 15 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 179〈/p〉 〈p〉Author(s): K. Sofinowski, M. Šmíd, I. Kuběna, S. Vivès, N. Casati, S. Godet, H. Van Swygenhoven〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A multi-phase Ti–6Al–4V prepared by electron beam melting and thermal post treatments has been shown to exhibit increased strength and ductility over standard wrought or hot isostatic pressed Ti–6Al–4V. The mechanical improvements are due to a prolonged, continuous work hardening effect not commonly observed in Ti alloys. 〈em〉In situ〈/em〉 x-ray diffraction and high resolution digital image correlation are used to examine the strain partitioning between the phases during tensile loading with post-mortem electron microscopy to characterize the deformation behavior in each phase. Specimens heat treated between 850 and 980 °C were tested and the effect of annealing temperature on the micromechanical response is discussed. It is shown that the work hardening is the result of composite load-sharing behavior between three mechanically distinct microstructures: large 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"〉〈mrow〉〈mi〉α〈/mi〉〈/mrow〉〈/math〉 lamellae and a martensitic region of fine acicular 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.svg"〉〈mrow〉〈mi〉α〈/mi〉〈mo〉'〈/mo〉〈/mrow〉〈/math〉 and a third phase not previously reported in this alloy.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S135964541930549X-fx1.jpg" width="500" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 15 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 179〈/p〉 〈p〉Author(s): Charlette M. Grigorian, Timothy J. Rupert〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Building on the recent discovery of tough nanocrystalline Cu-Zr alloys with amorphous intergranular films, this paper investigates ternary nanocrystalline Cu-Zr-Hf alloys with a focus on understanding how alloy composition affects the formation of disordered complexions. Binary Cu-Zr and Cu–Hf alloys with similar initial grain sizes were also fabricated for comparison. The thermal stability of the nanocrystalline alloys was evaluated by annealing at 950 °C (〉95% of the solidus temperatures), followed by detailed characterization of the grain boundary structure. All of the ternary alloys exhibited exceptional thermal stability comparable to that of the binary Cu-Zr alloy, and remained nanocrystalline even after two weeks of annealing at this extremely high temperature. Despite carbide formation and growth in these alloys during milling and annealing, the thermal stability of the ternary alloys is mainly attributed to the formation of thick amorphous intergranular films at high temperatures. Our results show that ternary alloy compositions have thicker boundary films compared to the binary alloys with similar global dopant concentrations. While it is not required for amorphous complexion formation, this work shows that having at least three elements present at the interface can lead to thicker grain boundary films, which is expected to maximize the previously reported toughening effect.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645419305439-fx1.jpg" width="400" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: Available online 22 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia〈/p〉 〈p〉Author(s): Hangfeng Zhang, Bin Yang, Haixue Yan, Isaac Abrahams〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Switchable ferroelectric/antiferroelectric ceramics are of significant interest for high power energy storage applications. Grain size control of this switching is an interesting approach to controlling polarization and hence dielectric properties. However, the use of this approach in technologically relevant ceramics is hindered by difficulty in fabricating dense ceramics with small grain sizes. Here an intermediate polar ferroelectric phase (〈em〉P〈/em〉2〈sub〉1〈/sub〉〈em〉ma〈/em〉) has been isolated in dense bulk sodium niobate ceramics by grain size control through spark plasma sintering methods. Our findings, supported by XRD, DSC, P-E (I-E) loops and dielectric characterization, provide evidence that the phase transition from the antiferroelectric (AFE) R-phase, in space group 〈em〉Pnmm〈/em〉, above 300 °C, to the AFE P-phase, in space group 〈em〉Pbma〈/em〉, at room temperature, always involves the polar intermediate 〈em〉P〈/em〉2〈sub〉1〈/sub〉〈em〉ma〈/em〉 phase and that the 〈em〉P〈/em〉2〈sub〉1〈/sub〉〈em〉ma → Pbma〈/em〉 transition can be suppressed by reducing grain size.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645419305506-fx1.jpg" width="296" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 15 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 179〈/p〉 〈p〉Author(s): M.J. Konstantinović, I. Uytdenhouwen, G. Bonny, N. Castin, L. Malerba, P. Efsing〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The thermal stability and the structure of solute-vacancy clusters formed by neutron irradiation are studied by means of positron annihilation spectroscopy and hardness measurements of post-irradiation annealed reactor pressure vessel steels with high and low Ni contents. Two distinct recovery stages were observed and assigned to (a) the dissolution of vacancy clusters at about 650 K, and (b) the dissolution of solute-vacancy clusters at about 750 K. In steels with high Ni content, hardening mainly recovers during the second stage. Atomistic and coarse grain models suggest that during this stage, the removal of vacancies from vacancy-solute clusters leads to complete cluster dissolution, which indicates that solute clusters are radiation induced.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645419305403-fx1.jpg" width="280" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 15 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 179〈/p〉 〈p〉Author(s): Hui Chen, Qingsong Wei, Yingjie Zhang, Fan Chen, Yusheng Shi, Wentao Yan〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The packing density of the powder layer plays a key role in the final quality of the parts fabricated via powder-bed-based (PBB) additive manufacturing. This paper presents a combined experimental and computational modeling study on the scraping type of powder-spreading process, in order to understand the fundamental mechanisms of the packing of the powder layer. The deposition mechanisms at the particulate scale, including particle contact stress and particle velocity, are investigated, using the discrete element method, while the macro-scale packing density is validated by experiments. It is found that there is a stress-dip at the bottom of powder pile scraped by the rake. This stress-dip makes the powder particles uniformly deposited. Three kinds of deposition mechanisms dominating the powder-spreading process are identified: cohesion effect, wall effect, and percolation effect. The cohesion effect, which leads to particle agglomerations and thus reduces the packing density, becomes stronger with the decrease of particle size. The wall effect, which leads to more vacancies in the powder layer, becomes stronger with the decrease of layer thickness or the increase of particle size. The percolation effect exists in bimodal powder particles, which leads to particle segregation within the powder layer and thus reduces the packing density. The three kinds of deposition mechanisms compete with each other during the powder-spreading process and make combined effects on the packing density of the powder layer.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645419305427-fx1.jpg" width="264" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 15 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 179〈/p〉 〈p〉Author(s): Qi-Nan Han, Shao-Shi Rui, Wenhui Qiu, Xianfeng Ma, Yue Su, Haitao Cui, Hongjian Zhang, Huiji Shi〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The effect of crystal orientation on fretting fatigue induced crack initiation and dislocation distribution is studied by in-situ SEM observation and electron back-scattered diffraction (EBSD) in this paper. Cracks and slip lines are observed in the fretting contact area of Ni-based single-crystal (NBSX) superalloys. The in-situ SEM observation captures different crack and slip line behaviors under different crystal orientations. The EBSD analysis results show obvious misorientation and orientation deviation in the fretting contact area. For both crystal orientations, the geometrically necessary dislocation (GND) density distributions in the contact area are obtained by using Hough-based EBSD methods. The peak position of grain reference orientation deviation (GROD) and GND density matches with the fretting fatigue crack formation position. EBSD analysis shows that the dislocation density distribution on each slip system is closely related to the crack initiation direction. The direction of slip system with the maximum dislocation density agrees with the crack initiation direction obtained by in-situ observation.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645419305476-fx1.jpg" width="448" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 15 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 179〈/p〉 〈p〉Author(s): Jinghao Xu, Hans Gruber, Dunyong Deng, Ru Lin Peng, Johan J. Moverare〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Additive manufacturing (AM) of high γ′ strengthened Nickel-base superalloys, such as IN738LC, is of high interest for applications in hot section components for gas turbines. The creep property acts as the critical indicator of component performance under load at elevated temperature. However, it has been widely suggested that the suitable service condition of AM processed IN738LC is not yet fully clear. In order to evaluate the short-term creep behavior, slow strain rate tensile (SSRT) tests were performed. IN738LC bars were built by laser powder-bed-fusion (L-PBF) and then subjected to hot isostatic pressing (HIP) followed by the standard two-step heat treatment. The samples were subjected to SSRT testing at 850 °C under strain rates of 1 × 10〈sup〉−5〈/sup〉/s, 1 × 10〈sup〉−6〈/sup〉/s, and 1 × 10〈sup〉−7〈/sup〉/s. In this research, the underlying creep deformation mechanism of AM processed IN738LC is investigated using the serial sectioning technique, electron backscatter diffraction (EBSD), transmission electron microscopy (TEM). On the creep mechanism of AM polycrystalline IN738LC, grain boundary sliding is predominant. However, due to the interlock feature of grain boundaries in AM processed IN738LC, the grain structure retains its integrity after deformation. The dislocation motion acts as the major accommodation process of grain boundary sliding. Dislocations bypass the γ′ precipitates by Orowan looping and wavy slip. The rearrangement of screw dislocations is responsible for the formation of subgrains within the grain interior. This research elucidates the short-creep behavior of AM processed IN738LC. It also shed new light on the creep deformation mechanism of additive manufactured γ′ strengthened polycrystalline Nickel-base superalloys.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645419305464-fx1.jpg" width="500" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 15 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 179〈/p〉 〈p〉Author(s): Garth C. Egan, Tae Wook Heo, Amit Samanta, Geoffrey H. Campbell〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We report a novel mechanism for explosive crystallization in amorphous germanium (a-Ge), which operates through liquid-mediated nucleation occurring under extreme thermal gradient conditions. The crystallization kinetics of sputter-deposited films with thicknesses ranging from 30 to 150 nm were characterized using 〈em〉in situ〈/em〉 movie-mode dynamic transmission electron microscopy (MM-DTEM). After localized heating from a short laser pulse, explosive liquid phase nucleation (LPN) was observed to occur during the early stage (〈2 μs) of crystallization in the thicker (〉50 nm) films deposited on silicon nitride substrates. The crystallization front propagated at ∼12–15 m/s and produced nanocrystalline microstructure with ∼50 nm grains. A mechanism involving the existence of a relatively thick (〉100 nm) transient liquid layer and a high nucleation rate is proposed to explain the behavior. The key thermodynamic and kinetic features as well as the feasibility of the mechanism are further explored by employing parametric and systematic phase-field modeling and simulations.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645419305385-fx1.jpg" width="418" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 15 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 179〈/p〉 〈p〉Author(s): Le Van Lich, Minh-Tien Le, Tinh Quoc Bui, Thanh-Tung Nguyen, Takahiro Shimada, Takayuki Kitamura, Trong-Giang Nguyen, Van-Hai Dinh〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A reversal of polarization vortexlike domains in ferroelectric nanostructures plays important roles for next generations of electronic nanodevices. However, a direct switching of the polarization vortexlike domains in ferroelectrics is a nontrivial task since the toroidal moment is conjugated to a curled electric field rather than a homogeneous one. This work is dedicated to developing an approach to directly switch the toroidal ordering under an irrotational (homogeneous) electric field with the use of compositionally graded ferroelectric (cgFE) nanodots. The variation in material compositions induces an additionally broken spatial inversion symmetry at a scale beyond unit-cell level, giving rise to a formation of asymmetric flux-closure domain (FCD) in a cgFE nanodot. More interestingly, such an asymmetric character facilitates to a switch of FCD by an irrotational electric field. In particular, the rotation of polarization can be directly switched from counter-clockwise to clockwise rotations and vice versa without a formation of intermediate domain structures during the switching process. This switching behavior is distinguished from that in homogeneous counterparts. We further demonstrate that the variation in material compositions tailors the distributions of electrostatic and total free energies in the cgFE nanodot that can control the annihilation/initiation process of FCD under irrotational electric field, providing fundamental reason for the direct switching of the toroidal moment. Another interesting issue is found that both the amplitude and frequency of applied electric field strongly affect the switching behavior of FCD in cgFE nanodot.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645419305373-fx1.jpg" width="459" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 15 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 179〈/p〉 〈p〉Author(s): Dipak Kumar Khatua, Anupam Mishra, Naveen Kumar, Gobinda Das Adhikary, Uma Shankar, Bhaskar Majumdar, Rajeev Ranjan〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Driven by environmental concerns and governmental directives, a sustained research effort in the last decade and half has led to the development of lead-free alternatives which can potentially replace the commercial lead-based piezoceramics in niche applications. Na〈sub〉0.5〈/sub〉Bi〈sub〉0.5〈/sub〉TiO〈sub〉3〈/sub〉 (NBT)-based lead-free piezoceramics have found acceptance as promising lead-free transducers in high power ultrasonic devices. An issue of concern however is the low depolarization temperature which limits the device's tolerance for temperature rise during operation. While several strategies have been reported to improve thermal depolarization in NBT-based piezoceramics, there is a lack of consensus regarding the most fundamental factor/mechanism which enhances the depolarization temperature. In this paper we unravel a coupled microstructural-structural mechanism which controls the thermal depolarization in NBT-based piezoceramics. First, we demonstrate the phenomenon of a considerable increase in the depolarization temperature, without significantly losing the piezoelectric property in unmodified NBT by increasing the grain size. We then establish a grain size controlled structural mechanism and demonstrate that the rise in depolarization temperature is primarily associated with the bigger grains allowing relatively large lattice distortion to develop in the poling stabilized long range ferroelectric phase. We reconfirmed the validity of this mechanism in the model morphotropic phase boundary (MPB) composition 0.94Na〈sub〉0.5〈/sub〉Bi〈sub〉0.5〈/sub〉TiO〈sub〉3〈/sub〉-0.06BaTiO〈sub〉3〈/sub〉. For the sake of generalization, we demonstrate that the same mechanism is operative in another lead-based relaxor-ferroelectric system 0.62PbTiO〈sub〉3〈/sub〉-0.38Bi(Ni〈sub〉0.5〈/sub〉Hf〈sub〉0.5〈/sub〉)O〈sub〉3〈/sub〉. Our study provides the fundamental structural basis for understanding thermal depolarization delay in relaxor ferroelectric based piezoceramics.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645419305348-fx1.jpg" width="240" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 1 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 178〈/p〉 〈p〉Author(s): Hao Sun, Shaohua Fu, Chichi Chen, Zhirui Wang, Chandra Veer Singh〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Nickel carbonyl vapor deposition (CVD) is a high-efficiency process used to produce nickel shell molds with high yield strength, reasonable ductility, and strong corrosion resistance. Such advantageous properties arise from the nanocrystals and nanotwins inside CVD nickel. However, the nanotwins do not persist at high temperatures, transforming into dislocation cells after 40-min annealing at 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"〉〈mrow〉〈mn〉800〈/mn〉〈mspace width="0.25em"〉〈/mspace〉〈mo〉°C〈/mo〉〈/mrow〉〈/math〉. Using experimental examinations and computational simulations, we investigated the kinetics of the annealing-induced detwinning in CVD nickel. TEM examinations showed that detwinning is realized by incoherent twin boundary (ITB) migration; meanwhile, plentiful dislocations are generated from coherent twin boundaries (CTBs). Our theoretical analysis revealed that these dislocations are necessary for the formation of the ITBs. Next, using molecular dynamics simulations, we found that the dislocations nucleated from CTBs during annealing are intrinsic grain boundary dislocations (IGBDs). Driven by the internal stress intensified by grain growth in the nanocrystalline regime, the IGBDs can separate from CTBs due to creep at 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"〉〈mrow〉〈mn〉800〈/mn〉〈mspace width="0.25em"〉〈/mspace〉〈mo〉°C〈/mo〉〈/mrow〉〈/math〉, resulting in a higher dislocation density inside the twin lamella than that of the outside. These dislocations can trigger the formation of ITBs. Overall, unlike grain growth, stress is necessary for detwinning, so a monolithic nanotwin structure should be more stable than the nanotwins inside a nanocrystalline matrix.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645419305208-fx1.jpg" width="500" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 1 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 178〈/p〉 〈p〉Author(s): Zefeng Yu, Chenyu Zhang, Paul M. Voyles, Lingfeng He, Xiang Liu, Kelly Nygren, Adrien Couet〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Proton irradiation induced Nb redistribution in Zr-xNb alloys (x = 0.4, 0.5, 1.0 wt%) has been investigated using scanning transmission electron microscopy/energy dispersive X-ray spectroscopy (STEM/EDS). Zr-xNb alloys are mainly composed of Zr matrix, native Zr–Nb–Fe phases, and β-Nb precipitates. After 2 MeV proton irradiation at 350 °C, a decrease of Nb content in native precipitates, as well as irradiation-induced precipitation of Nb-rich platelets (135 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"〉〈mrow〉〈mo〉±〈/mo〉〈/mrow〉〈/math〉 69 nm long and 27 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"〉〈mrow〉〈mo〉±〈/mo〉〈/mrow〉〈/math〉 12 nm wide) were found. Nb-rich platelets and Zr matrix form the Burgers orientation relationship, [〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.svg"〉〈mrow〉〈mn〉1〈/mn〉〈mrow〉〈mover accent="true"〉〈mn〉1〈/mn〉〈mo〉¯〈/mo〉〈/mover〉〈/mrow〉〈mn〉1〈/mn〉〈/mrow〉〈/math〉]//[〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si3.svg"〉〈mrow〉〈mn〉2〈/mn〉〈mrow〉〈mover accent="true"〉〈mn〉1〈/mn〉〈mo〉¯〈/mo〉〈/mover〉〈/mrow〉〈mrow〉〈mover accent="true"〉〈mn〉1〈/mn〉〈mo〉¯〈/mo〉〈/mover〉〈/mrow〉〈mn〉0〈/mn〉〈/mrow〉〈/math〉] and (011)//(0002). The platelets were found to be mostly coherent with the matrix with a few dislocations near the ends of the precipitate. The coherent strain field has been measured in the matrix and platelets by the 4D-STEM technique. The growth of Nb-rich platelets is mainly driven by coherency and dislocation-induced strain fields. Irradiation may both enhance the diffusion and induce segregation of interstitial Nb to the ends of the irradiation induced platelets, further facilitating their growth.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645419305221-fx1.jpg" width="250" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 1 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 178〈/p〉 〈p〉Author(s): Gi-Dong Sim, Kelvin Y. Xie, Kevin J. Hemker, Jaafar A. El-Awady〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Here, an experimental study utilizing 〈em〉in-situ〈/em〉 scanning electron microscopy (SEM) micro-compression testing and post-mortem transmission electron microscopy (TEM) imaging is presented to quantify the effect of temperature on the transition in deformation modes in twin-oriented Mg single crystals. Single crystal micropillars were fabricated using FIB milling, then tested by 〈em〉in-situ〈/em〉 SEM micro-compression from 20 °C to 225 °C. It is observed that plasticity in the deformed Mg microcrystals at temperatures at and below 100 °C is governed by 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"〉〈mrow〉〈mo stretchy="true"〉{〈/mo〉〈mn〉10〈/mn〉〈mrow〉〈mover accent="true"〉〈mn〉1〈/mn〉〈mo〉¯〈/mo〉〈/mover〉〈/mrow〉〈mn〉2〈/mn〉〈mo stretchy="true"〉}〈/mo〉〈/mrow〉〈/math〉 extension twinning. However, an anomalous increase of the flow stresses is observed at 100 °C, which is likely due to paucity of dislocation sources that are required to promote twin boundary migration. At 150 °C and above, extension twinning is suppressed and a continuous plastic flow and strain softening induced by prismatic dislocation mediated plasticity is observed. By comparing the current results with those from bulk scale studies for other hexagonal-closed-pack single crystals (e.g. titanium (Ti) and zirconium (Zr)), a general trend for the effect of temperature on the transition in deformation modes in HCP materials is proposed.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645419305245-fx1.jpg" width="500" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 1 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 178〈/p〉 〈p〉Author(s): X.C. Tang, C. Li, H.Y. Li, X.H. Xiao, L. Lu, X.H. Yao, S.N. Luo〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A special spallation morphology in bulk metallic glass, named as the “cup-cone” structure, is of particular interest since it manifests a unique “ductile–brittle” transition. To gain insights into the underlying mechanism for the formation of a cup-cone structure, we conduct planar impact experiments at various impact velocities, as well as finite element method analysis. Spall strength increases with increasing impact velocity. Scanning electron microscopy and X-ray computed tomography are performed on postmortem samples to characterize cup-cone structures; their average size and spacing decrease as impact velocity increases, and they dominate fracture morphology at high impact velocities. Cups and cones are generally distributed on the side away from and on the side closer to the target free surface, respectively. The initial nucleation sites of voids become the conical vertices of cup-cones, and the subsequent nucleation sites form along the conical surface and coalesce into the cracks and fracture surfaces.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645419305087-fx1.jpg" width="287" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 1 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 178〈/p〉 〈p〉Author(s): Satoshi Okamoto, Kazunori Miyazawa, Takahiro Yomogita, Nobuaki Kikuchi, Osamu Kitakami, Kentaro Toyoki, David Billington, Yoshinori Kotani, Tetsuya Nakamura, Taisuke Sasaki, Tadakatsu Ohkubo, Kazuhiro Hono, Yukio Takada, Takashi Sato, Yuji Kaneko, Akira Kato〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A Ga-doped Nd-Fe-B sintered magnet has attracted significant attention as a heavy-rare-earth-free high-performance magnet. We have studied the temperature dependent magnetization reversal process of a Ga-doped Nd-Fe-B sintered magnet based on the first-order reversal curve (FORC) analysis. The FORC diagram pattern of the Ga-doped Nd-Fe-B sintered magnet changes from single spot in the high field region at room temperature to double spots in the low and high field regions at 200 °C, indicating that the dominant magnetization reversal process changes from single domain type to multidomain type. The single domain magnetization reversal at room temperature is well confirmed by using the soft X-ray magnetic circular dichroism microscopy observation. This change in the magnetization reversal process is well discussed by the temperature dependent local demagnetization field and the saturation field of multidomain state. Moreover, we have demonstrated the quantitative analysis of the FORC diagram pattern, which makes a deeper understanding of the magnetization reversal process of the Ga-doped Nd-Fe-B sintered magnet.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645419305063-fx1.jpg" width="500" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 1 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 178〈/p〉 〈p〉Author(s): Sumeet Mishra, Manasij Yadava, Kaustubh N. Kulkarni, N.P. Gurao〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A new methodology for analyzing strain hardening behavior of face centered cubic materials based on transition from restricted glide/single slip to multiple slip has been developed. The proposed modification considers strain dependence of orientation factor spanning between lower bound iso-stress Sachs model and upper bound iso-strain Taylor model. The modifications are suitably incorporated in the classical two internal variable model to develop a new slip activity based strain hardening model. The proposed model is shown to be performing better than the existing one parameter forest strengthening model and two internal variable model in predicting strain hardening behavior in the presence of wide range of microstructural features such as solutes, semi-coherent and incoherent precipitates, grain sizeand twins. Experimental validation of the proposed concept of transition in slip behavior is shown in terms of evolution of dislocation density and character from X-ray diffraction and surface roughness, slip lines and micro-texture from in-situ electron back scatter diffraction tests.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S135964541930504X-fx1.jpg" width="257" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 15 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 179〈/p〉 〈p〉Author(s): B. Christiaen, C. Domain, L. Thuinet, A. Ambard, A. Legris〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The growth of zirconium alloys under irradiation is a phenomenon experimentally identified and associated with the development beyond a threshold dose of dislocation loops with vacancy character having a Burgers vector with a component parallel to the c axis. In this work, by combining atomic simulations (DFT and empirical potential) and continuous modeling, we show that prismatic stacking fault pyramids or bipyramids whose base rests on the basal plane of the hcp structure are likely precursors to the formation of ‹c› vacancy loops. In other words, these would not be formed by progressive accretion of vacancies but rather by collapse of the pyramids or bipyramids beyond a certain size. This mechanism could explain the fact that the ‹c› vacancy loops are never observed below a size of the order of 10 nm and their appearance at high fluence.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645419304707-fx1.jpg" width="389" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 1 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 178〈/p〉 〈p〉Author(s): P.E. Seiler, H.C. Tankasala, N.A. Fleck〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Additive manufacture and rapid prototyping are versatile methods for the generation of lattice materials for applications in the creep regime. However, these techniques introduce defects that can degrade the macroscopic creep strength. In the present study, the uniaxial tensile response of two-dimensional PMMA lattices is measured in the visco-plastic regime: tests are performed at 100 °C which is slightly below the glass transition temperature 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"〉〈mrow〉〈msub〉〈mrow〉〈mi〉T〈/mi〉〈/mrow〉〈mrow〉〈mtext〉g〈/mtext〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉 of PMMA. Both 〈em〉as-manufactured〈/em〉 defects (Plateau borders and strut thickness variation) and 〈em〉as-designed〈/em〉 defects (missing cell walls, solid inclusions, and randomly perturbed joints) are introduced. The dispersion in macroscopic strength is measured for relative densities in the range of 0.07–0.19. It is observed that initial failure of the lattice is diffuse in nature: struts fail at a number of uncorrelated locations, followed by the development of a single macroscopic crack transverse to the loading direction. In contrast, the same PMMA lattice fails in a correlated, brittle manner at room temperature. An FE study is performed to gain insight into the diffuse failure mode and the role played by 〈em〉as-manufactured〈/em〉 defects, including the dispersion in tensile strength of individual struts of the lattice. A high damage tolerance to 〈em〉as-designed〈/em〉 defects is observed experimentally: there is negligible knock-down in strength due to the removal of cell walls or to the presence of solid inclusions. These findings aid the design and manufacture of damage tolerant lattices in the creep regime.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉Elastic-brittle versus visco-plastic failure ofPMMA lattices.〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645419305026-fx1.jpg" width="229" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 15 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 177〈/p〉 〈p〉Author(s): Christopher A. Schuh〈/p〉

Beschreibung: 〈p〉Publication date: 15 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 179〈/p〉 〈p〉Author(s): N. Almirall, P.B. Wells, T. Yamamoto, K. Wilford, T. Williams, N. Riddle, G.R. Odette〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Mn-Ni-Si intermetallic precipitates (MNSPs) that are observed in some Fe-based alloys following thermal aging and irradiation are of considerable scientific and technical interest. For example, large volume fractions (f) of MNSPs form in reactor pressure vessel low alloy steels irradiated to high fluence, resulting in severe hardening induced embrittlement. Nine compositionally-tailored small heats of low Cu RPV-type steels, with an unusually wide range of dissolved Mn (0.06–1.34 at.%) and Ni (0.19–3.50 at.%) contents, were irradiated at ≈ 290 °C to ≈ 1.4 × 10〈sup〉20〈/sup〉 n/cm〈sup〉2〈/sup〉 at an accelerated test reactor flux of ≈3.6 × 10〈sup〉12〈/sup〉 n/cm〈sup〉2〈/sup〉-s (E 〉 1 MeV). Atom probe tomography shows Mn-Ni interactions play the dominant role in determining the MNSP f, which correlates well with irradiation hardening. The wide range of alloy compositions results in corresponding variations in precipitates chemistries that are reasonably similar to various phases in the Mn-Ni-Si projection of the Fe based quaternary. Notably, f scales with ≈ Ni〈sup〉1.6〈/sup〉Mn〈sup〉0.8〈/sup〉. Thus f is modest even in advanced high 3.5 at.% Ni steels at very low Mn (Mn starvation); in this case Ni-silicide phase type compositions are observed.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645419305397-fx1.jpg" width="415" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: Available online 14 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia〈/p〉 〈p〉Author(s): Bar Danino, Gil Gur-Arieh, Doron Shilo, Dan Mordehai〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Ferroic materials typically exhibit a microstructure that contains twins or domains separated by twin boundaries (walls). The deformation of these materials is governed by twin boundary motion under mechanical/electrical/magnetic driving force. The Landau-Ginzburg model is a widely accepted phenomenological model used to describe twin boundary properties. However, it is incapable of describing energy barriers for motion due to the lack of atomistic description. In this work, we present a model interatomic potential for studying the relations between the lattice barrier for twin boundary motion and measurable material properties. The interatomic potential emulates the continuum Landau-Ginzburg model and reproduces known results of twin boundary thickness and energy as a function of the model parameters. An atomic model system is constructed, with a single twin boundary separating crystals of different orientations and we employ the Nudged Elastic Band method to calculate the energy barriers for the motion of twin boundaries with different thicknesses under different externally-applied shear stresses. The results are summarized in a closed-form expression relating the energy barriers with material properties and the external loading. The energy barrier function extends the Landau-Ginzburg model and allows treating the motion of twin boundary as a thermally activated process.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645419305282-fx1.jpg" width="446" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 15 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 179〈/p〉 〈p〉Author(s): Hongping Li, Mitsuhiro Saito, Chunlin Chen, Kazutoshi Inoue, Kazuto Akagi, Yuichi Ikuhara〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Metal/oxide heterointerfaces are ubiquitous in functional materials, and their microstructures frequently govern the macroscopic properties. It has been believed that the interfacial interactions are very weak at incoherent interfaces with large mismatches. Combining atomic-resolution scanning transmission electron microscopy with density functional theory calculations, we investigated the interaction and bonding reconstruction at Pd/ZnO{0001} interfaces, which have large mismatches. Molecular beam epitaxy was employed to grow Pd films on clean Zn-terminated ZnO(0001) and O-terminated ZnO(000〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"〉〈mrow〉〈mover accent="true"〉〈mn〉1〈/mn〉〈mo〉¯〈/mo〉〈/mover〉〈/mrow〉〈/math〉) polarized surfaces. Atomically sharp Zn-terminated interfaces formed on both substrates, and the large lattice misfits between them were not strongly accommodated, suggesting the formation of incoherent regions. The interfacial atoms were located almost at bulk lattice points in the stoichiometric Zn-terminated Pd(111)/ZnO(0001) structure, whereas the interfacial Pd and Zn atoms underwent relatively large relaxations on the interfacial plane in the nonstoichiometric Zn-terminated Pd(111)/ZnO(〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.svg"〉〈mrow〉〈mn〉000〈/mn〉〈mrow〉〈mover accent="true"〉〈mn〉1〈/mn〉〈mo〉¯〈/mo〉〈/mover〉〈/mrow〉〈/mrow〉〈/math〉) interface. Effective Pd–Zn chemical bonds were formed across both interfaces, but the bonding mechanisms were quite different, depending on the local atomic geometry. The Pd–Zn bonds exhibited site-dependent characteristics and gradually transitioned from covalent to ionic at the Pd(111)/ZnO(0001) interface, whereas most of Pd–Zn bonds exhibited strong covalent behavior at the Pd/ZnO(〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.svg"〉〈mrow〉〈mn〉000〈/mn〉〈mrow〉〈mover accent="true"〉〈mn〉1〈/mn〉〈mo〉¯〈/mo〉〈/mover〉〈/mrow〉〈/mrow〉〈/math〉) interface. The adhesive energies indicated that the Zn-terminated Pd/ZnO(〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.svg"〉〈mrow〉〈mn〉000〈/mn〉〈mrow〉〈mover accent="true"〉〈mn〉1〈/mn〉〈mo〉¯〈/mo〉〈/mover〉〈/mrow〉〈/mrow〉〈/math〉) interface is energetically preferable to the Zn-terminated Pd/ZnO(0001) interface. Thus, the interfacial interaction can be strong and direct metal–metal interactions can play a critical role in metal/oxide heterointerfaces with large mismatches, opening up a new avenue for understanding the origins of interface-related issues.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645419305300-fx1.jpg" width="344" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 1 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 178〈/p〉 〈p〉Author(s): Keita Nomoto, Hiroshi Sugimoto, Xiang-Yuan Cui, Anna V. Ceguerra, Minoru Fujii, Simon P. Ringer〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Boron (B) and phosphorous (P) co-doped colloidal silicon nanocrystals (Si NCs) have unique size-dependent optical properties, which lead to potential applications in optoelectronic and biomedical applications. However, the microstructure of the B and P co-doped colloidal Si NCs – in particular, the exact location of the dopant atoms in real space, has not been studied. A lack of understanding of this underlying question limits our ability to better control sample fabrication, as well as our ability to further develop the optical properties. To study the microstructure, a process enabling atom probe tomography (APT) of colloidal Si NCs was developed. A dispersion of colloidal Si NCs in a SiO〈sub〉2〈/sub〉 sol-gel solution and a low temperature curing are demonstrated as the key sample preparation steps. Our APT results demonstrate that a B-rich region exists at the surface of the Si NCs, while P atoms are distributed within the Si NCs. First principles density functional theory calculations of a Si NC embedded in SiO〈sub〉2〈/sub〉 matrix reveal that P atoms, which always prefer to reside inside a Si NC, significantly influence the distribution of B atoms. Specifically, P atoms lower the B diffusion barrier at Si/SiO〈sub〉2〈/sub〉 interface and stabilize B atoms to reside within individual Si NCs. We propose that the B-modified surface changes the chemical properties of the Si NCs by (i) offering chemical resistance to attack by HF and (ii) enabling dispersibility in solution without aggregation.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645419305233-fx1.jpg" width="205" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 15 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 179〈/p〉 〈p〉Author(s): Arthur S. Nishikawa, Goro Miyamoto, Tadashi Furuhara, André P. Tschiptschin, Hélio Goldenstein〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The modification of the matrix of ductile cast irons by heat treatments has been of interest of researchers for many years. Among these treatments, in the last years the Quenching & Partitioning (Q&P) process has emerged as a viable way to produce microstructures containing controlled amounts of martensite and retained austenite, providing a good combination of strength and ductility. In this work, the different mechanisms of phase transformations occurring during the Q&P heat treatment applied to a ductile cast iron alloy is investigated. Microsegregation, inherent to cast irons, was analyzed by means of Electron Probe Microanalysis (EPMA). Microstructural characterization was performed with Scanning Electron Microscopy (SEM) and Electron Backscattered Diffraction (EBSD), while kinetics of carbon redistribution and competitive reactions were studied using dilatometry and in situ synchrotron X-ray diffraction. It was found that either transition carbides or cementite precipitate in martensite depending on the partitioning temperature. Despite of carbides precipitation, evidence of carbon partitioning from martensite to austenite was obtained. Formation of bainitic ferrite occurs during the partitioning step, further contributing to carbon enrichment of austenite. The experimental results are compared with a local field model that computes the local kinetics of carbon redistribution by simultaneously considering carbides precipitation and growth of bainitic ferrite. Results showed that kinetics of carbon partitioning from martensite to austenite depends on the carbides free energy. More stable carbides do not dissolve and prevent the escape of carbon from martensite. Fast carbon partitioning occurs by dissolution of less stable carbides, but it is slowed down as growth of bainitic ferrite proceeds. This result is explained by the overlapping of the diffusion fields (soft impingement) of the carbon partitioned from martensite and the carbon rejected from growth of bainitic ferrite.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645419305038-fx1.jpg" width="346" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 1 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 178〈/p〉 〈p〉Author(s): P. Tozman, Y.K. Takahashi, H. Sepehri-Amin, D. Ogawa, S. Hirosawa, K. Hono〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Zr is one of the essential elements to stabilize the ThMn〈sub〉12〈/sub〉 structure in rare earth (R) transition metal (M) hard magnetic compounds, RM〈sub〉12〈/sub〉. In this work, the effects of Zr on the intrinsic hard magnetic properties of (Sm〈sub〉1-x〈/sub〉 Zr〈sub〉x〈/sub〉)(Fe〈sub〉0.8〈/sub〉Co〈sub〉0.2〈/sub〉)〈sub〉12〈/sub〉 compounds are investigated using epitaxially grown thin films. The increase of Zr substitution for Sm from 〈em〉x〈/em〉 = 0 to 0.26 for (Sm〈sub〉1-x〈/sub〉 Zr〈sub〉x〈/sub〉)(Fe〈sub〉0.8〈/sub〉Co〈sub〉0.2〈/sub〉)〈sub〉12〈/sub〉 increases saturation magnetization (μ〈sub〉0〈/sub〉〈em〉M〈/em〉〈sub〉s〈/sub〉) from 1.78 T to 1.90 T, the highest value reported for hard magnetic compounds. The largest μ〈sub〉0〈/sub〉〈em〉H〈/em〉〈sub〉a〈/sub〉 and 〈em〉T〈/em〉〈sub〉〈em〉c〈/em〉〈/sub〉 for Zr-doped samples were found to be 9.8 T and 671 K for 〈em〉x〈/em〉 = 0.18 which is superior to those for Nd〈sub〉2〈/sub〉Fe〈sub〉14〈/sub〉B. Sm-rich Sm〈sub〉1.30〈/sub〉Zr〈sub〉0.27〈/sub〉(Fe〈sub〉0.8〈/sub〉Co〈sub〉0.2〈/sub〉)〈sub〉12,〈/sub〉 obtained as sub-μm thick films, has remanence, μ〈sub〉0〈/sub〉〈em〉M〈/em〉〈sub〉r〈/sub〉 of 1 T, which appears to be useful for near-field applications such as micro-electro-machines and magnetic recording media if microstructure can be optimized to obtain a sufficient coercivity.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645419305051-fx1.jpg" width="441" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 15 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 179〈/p〉 〈p〉Author(s): X. Lu, D. Wang, D. Wan, Z.B. Zhang, N. Kheradmand, A. Barnoush〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The susceptibility of age-hardened nickel-based Alloy 718 to hydrogen embrittlement was studied by the controlled electrochemical charging combined with slow strain-rate tensile tests (SSRT) and advanced characterization techniques. We proposed some novel ideas of explaining hydrogen embrittlement mechanisms of the studied material in regard to two cracking morphologies: transgranular and intergranular cracking. It is for the first time to report that electrochemical charging alone could cause slip lines, surface and subsurface cracks on nickel-based superalloys. The formation of pre-damages was discussed by calculating the hydrogen concentration gradient and the internal stress generated during cathodic charging. Pre-damages were proved to result in transgranular cracks and lead to the evident reduction of mechanical properties. In addition, the STRONG (Slip Transfer Resistance of Neighbouring Grains) model was used to analyze the dependence of hydrogen-assisted intergranular cracking on the microscopic incompatibility of the grain boundaries. The results show that in the presence of hydrogen, grain boundaries with a lower dislocation slip transmission are more prone to cracking during loading and vice versa.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645419305324-fx1.jpg" width="500" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 15 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 179〈/p〉 〈p〉Author(s): Amin Nozariasbmarz, Mahshid Hosseini, Daryoosh Vashaee〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We report that microwave radiation can decompose continuous solid-solution materials into their constituent phases – a process that is thermodynamically unfavorable at equilibrium. A detailed analysis of the interaction of the electromagnetic wave with the material showed that a strong ponderomotive force preferentially separates the constituent phases via an enhanced mass transport process amplified particularly near the interfaces. The proof of concept experiments showed that the material, whether it is a solid-solution of two elements, e.g. (Si〈sub〉1-x〈/sub〉Ge〈sub〉x〈/sub〉), or two compounds, e.g. (Bi〈sub〉2〈/sub〉Te〈sub〉3〈/sub〉)〈sub〉1-x〈/sub〉(Sb〈sub〉2〈/sub〉Te〈sub〉3〈/sub〉)〈sub〉x〈/sub〉, decomposes into the constituent phases when radiated by a polarized microwave field. The dissolution happens in the bulk of the material and even below the melting point. The degree of decomposition can be controlled by radiation parameters to produce structures composed of gradient phases of the solid-solution. This offers a novel and facile method for synthesizing gradient composite and complex structures for application in thermoelectricity as well as fabrication of core-shell structures for catalysts and biomedical applications.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645419305294-fx1.jpg" width="306" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 1 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 178〈/p〉 〈p〉Author(s): Anh Tran, Hoang Tran〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Microstructure reconstruction problems are usually limited to the representation with finitely many number of phases, e.g. binary and ternary. However, images of microstructure obtained through experimental, for example, using microscope, are often represented as a RGB or grayscale image. Because the phase-based representation is discrete, more rigid, and provides less flexibility in modeling the microstructure, as compared to RGB or grayscale image, there is a loss of information in the conversion. In this paper, a microstructure reconstruction method, which produces images at the fidelity of experimental microscopy, i.e. RGB or grayscale image, is proposed without introducing any physics-based microstructure descriptor. Furthermore, the image texture is preserved and the microstructure image is represented with continuous variables (as in RGB or grayscale images), instead of binary or categorical variables, which results in a high-fidelity image of microstructure reconstruction. The advantage of the proposed method is its quality of reconstruction, which can be applied to any other binary or multiphase 2D microstructure. The proposed method can be thought of as a subsampling approach to expand the microstructure dataset, while preserving its image texture. Moreover, the size of the reconstructed image is more flexible, compared to other machine learning microstructure reconstruction method, where the size must be fixed beforehand. In addition, the proposed method is capable of joining the microstructure images taken at different locations to reconstruct a larger microstructure image. A significant advantage of the proposed method is to remedy the data scarcity problem in materials science, where experimental data is scare and hard to obtain. The proposed method can also be applied to generate statistically equivalent microstructures, which has a strong implication in microstructure-related uncertainty quantification applications. The proposed microstructure reconstruction method is demonstrated with the UltraHigh Carbon Steel micrograph DataBase (UHCSDB).〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645419305178-fx1.jpg" width="322" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 15 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 179〈/p〉 〈p〉Author(s): O.I. Gorbatov, A.Yu Stroev, Yu.N. Gornostyrev, P.A. Korzhavyi〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The strengthening by coherent, nano-sized particles of metastable phases (pre-precipitates) continues to be the main design principle for new high-performance aluminium alloys. To describe the formation of such pre-precipitates in Al–Cu, Al–Mg, Al–Zn, and Al–Si alloys, we carry out cluster expansions of 〈em〉ab initio〈/em〉 calculated energies for supercell models of the dilute binary Al-rich solid solutions. Effective cluster interactions, including many-body terms and strain-induced contributions due to the lattice relaxations around solute atoms, are thus systematically derived. Monte Carlo and statistical kinetic theory simulations, parameterized with the obtained effective cluster interactions, are then performed to study the early stages of decomposition in the binary Al-based solid solutions. We show that this systematic approach to multi-scale modelling is capable of incorporating the essential physical contributions (usually referred to as atomic size and electronic structure factors) to the free energy, and is therefore able to correctly describe the ordering temperatures, atomic structures, and morphologies of pre-precipitates in the four studied alloy systems.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S135964541930521X-fx1.jpg" width="361" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 15 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 179〈/p〉 〈p〉Author(s): T. Glechner, R. Hahn, T. Wojcik, D. Holec, S. Kolozsvári, H. Zaid, S. Kodambaka, P.H. Mayrhofer, H. Riedl〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Using a combination of density functional theory calculations and nanomechanical testing of sputter-deposited, 110-oriented Ta〈sub〉0.47〈/sub〉C〈sub〉0.34〈/sub〉N〈sub〉0.19〈/sub〉 thin films, we show that non-metal alloying – substituting C with N atoms – in TaC results in a super-hard material with enhanced ductility. Based on the calculated elastic constants, with Pugh and Pettifor criteria for ductile character, we predict that stoichiometric and sub-stoichiometric Ta-C-N alloys are more ductile than Ta-C compounds. From nanoindentation of the as-deposited coating, we measure hardness of 43 ± 1.4 GPa. 〈em〉In situ〈/em〉 scanning electron microscopy (SEM) based micro-compression of cylindrical pillars, prepared via focused ion beam milling of the coating, revealed that Ta-C-N alloys are ductile and undergo plastic deformation with a yield strength of 17 ± 1.4 GPa. The post-compression SEM images of the pillars show {111} 〈〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"〉〈mrow〉〈mn〉01〈/mn〉〈mrow〉〈mover accent="true"〉〈mn〉1〈/mn〉〈mo〉¯〈/mo〉〈/mover〉〈/mrow〉〈/mrow〉〈/math〉〉 as the active slip system operating during compression. Additional 〈em〉in situ〈/em〉 SEM based cantilever tests suggest that the Ta-C-N films exhibit superior fracture toughness compared to Ta-C coatings. Our results provide a new perspective on the role of alloying on the mechanical behavior of ultra-high temperature compounds such as transition-metal carbides.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645419305257-fx1.jpg" width="490" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 1 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 178〈/p〉 〈p〉Author(s): Zhen Zhang, Ningbo Liao, Hongming Zhou, Wei Xue〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The combination of silicon and carbon layers exhibits superior lithium capacity and rate performance; however, the corresponding lithiation mechanism on the atomic-scale is not clear. In this work, the impact of the carbon layer on the electrochemical performance of silicon-carbon film systems as the lithium anode is investigated by a combination of experiments and first principles calculations. Experimental results show that the sample with the thickest carbon layer presents the smallest first cycle discharge capacities (2814 mAhg〈sup〉−1〈/sup〉); however, this sample also results in the largest capacity retentions after 100 cycles (69%) and the rate capability test (48.4%). Based on first principles calculations, the average length of the Li–Si bond near the silicon-carbon interface is significantly shorter than that in silicon, indicating an irreversible capacity loss. The structure with the largest carbon layer thickness corresponds to enhanced reversible capacity, electronic conductivity and lithium diffusion coefficient, which is consistent with experimental results. Our calculations provide a deeper understanding of irreversible capacity loss and how the primary nanostructure contributes to superior rate performance for silicon-carbon film anode materials.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645419305191-fx1.jpg" width="393" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 1 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 178〈/p〉 〈p〉Author(s): J. Narayan, A. Bhaumik, A. Haque〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We report pseudo-topotactic growth of single-crystal diamond fibers by nanosecond laser melting of amorphous carbon nanofibers (CNFs) and crystalline multi-wall carbon nanotubes (MWCNTs). A rapid laser melting in a super undercooled state and subsequent quenching convert the tips of CNFs and MWCNTs into phase-pure 〈110〉 nanodiamonds along the growth directions. Subsequent laser pluses melt regions below 〈110〉 nanodiamonds that provide seeds for epitaxial growth. By repeating this process, the length of 〈110〉 nanodiamond fibers can be increased, as each pulse results in ∼50 nm nanodiamond region, depending upon the initial size of CNFs and MWCTs. This conversion process can be carried at ambient temperature and pressure in air. The epitaxial nature of 〈110〉 nanodiamond fibers has been confirmed by systematic electron-back-scatter-diffraction studies along the fiber in high-resolution scanning electron microscopy, and high-resolution TEM imaging and diffraction. The nature of C–C bonding characteristics was studied by high-resolution electron-energy-loss spectroscopy to establish the formation of diamond phase by the characteristic peak at 292 eV for sp〈sup〉3〈/sup〉 bonding (σ〈sup〉∗〈/sup〉), and absence of 284 eV peak for sp〈sup〉2〈/sup〉 (π〈sup〉∗〈/sup〉) graphitic bonding. The characteristic diamond Raman peak at 1332 cm〈sup〉−1〈/sup〉 is found to downshift to 1321 cm〈sup〉−1〈/sup〉 because of phonon confinement in nanodiamonds associated with nanofibers. These nanodiamond structures can be doped with both n- and p-type dopants with concentrations far higher than thermodynamic solubility limit due to solute trapping during quenching from the liquid phase. Thus, these nanodiamond structures provide ideal platform for nanosensing, computing and communication, including efficient field emitting devices.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S135964541930518X-fx1.jpg" width="237" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: Available online 8 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia〈/p〉 〈p〉Author(s): Diwakar P. Naragani, Paul A. Shade, Peter Kenesei, Hemant Sharma, Michael D. Sangid〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The small fatigue crack (SFC) growth regime in polycrystalline alloys is complex due to the heterogeneity in the local micromechanical fields, which result in high variability in crack propagation directions and growth rates. In this study, we employ a suite of techniques, based on high-energy synchrotron-based X-ray experiments that allow us to track a nucleated crack, propagating through the bulk of a Ni-based superalloy specimen during cyclic loading. Absorption contrast tomography is used to resolve the intricate 3D crack morphology and spatial position of the crack front. Initial near-field high-energy X-ray diffraction microscopy (HEDM) is used for high-resolution characterization of the grain structure, elucidating grain orientations, shapes, and boundaries. Cyclic loading is periodically interrupted to conduct far-field HEDM to determine the centroid position, average orientation, and average lattice strain tensor for each grain within the volume of interest. Reciprocal space analysis is used to further examine the deformation state of grains that plasticize in the vicinity of the crack. Analysis of the local micromechanical state in the grains ahead of the crack front is used to rationalize the advancing small crack path and growth rate. Specifically, the most active slip system in a grain, determined by the maximum resolved shear stress, aligns with the crack growth direction; and the degree of microplasticity ahead of the crack tip helps to identify directions for potential occurrences of crack arrest or propagation. The findings suggest that both the slip system level stresses and microplasticity events within grains are necessary to get a complete description of the SFC progression. Further, this detailed dataset, produced by a suite of X-ray characterization techniques, can provide the necessary validation, at the appropriate length-scale, for SFC models.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645419305075-fx1.jpg" width="270" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 1 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 178〈/p〉 〈p〉Author(s): Sam Bakhtiari, Jefferson Zhe Liu, Yinong Liu, Hong Yang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Ti〈sub〉50〈/sub〉Ni〈sub〉50-x〈/sub〉Cu〈sub〉x〈/sub〉 alloys are observed to exhibit multiple martensitic transformations from B2 to an orthorhombic B19 and a monoclinic B19′ phase. In addition, DFT calculations have predicted a B19ʺ phase with a higher monoclinic angle as the thermodynamically stable ground state. This study investigated the effects of Cu content and shear stress on the monoclinic angles, phase stabilities of the various martensites, the minimum energy pathways, and the relative total energies among the phases in this pseudo-equiatomic Ti(Ni〈sub〉50-x〈/sub〉Cu〈sub〉x〈/sub〉) system. A new monoclinic phase (B19〈sub〉M〈/sub〉) with a monoclinic angle lower than that of B19′ was found at above a critical Cu content. This confirms the formation of an intermediate phase in the martensitic transformation sequence of the pseudo-equiatomic Ti(Ni〈sub〉50-x〈/sub〉Cu〈sub〉x〈/sub〉) system but contradicts the crystal structure of the experimentally observed phase. It was found that the monoclinic angles of both B19〈sub〉M〈/sub〉 and B19ʺ decrease with increasing the magnitude of an opposing shear stress to their monoclinic distortion. At above certain critical values of the opposing shear stress, the B19〈sub〉M〈/sub〉 and B19ʺ phases destabilise and transform to lower monoclinic angle phases. In addition, the evidence suggests that the experimentally observed monoclinic B19′ phase is in fact a distorted B19ʺ with a reduced monoclinic angle under an opposing shear stress. With the same argument, the experimentally reported B19 phase is a metastable phase formed under the effect of an opposing shear stress to the monoclinic distortion of B19〈sub〉M〈/sub〉.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645419304987-fx1.jpg" width="254" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 1 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 164〈/p〉 〈p〉Author(s): Bernard Gaskey, Ian McCue, Alyssa Chuang, Jonah Erlebacher〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A major challenge in the synthesis of high surface area metals via subtractive processes such as dealloying is maintaining the mechanical integrity of the resulting porous materials. This problem is especially apparent in liquid metal dealloying, in which high-temperature selective dissolution in a molten metal bath leads to bicontinuous porosity formation. In liquid metal dealloying of polycrystalline alloys, grain boundary separation leads to the detachment of individual grains. In this work, we show that addition of small amounts of silicon to Nb〈img src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"〉Ti or Ta〈img src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"〉Ti parent alloys leads to the generation of self-assembled arrays of intermetallic (niobium silicide or tantalum silicide) plates that are structurally merged with the usual bicontinuous porosity seen in dealloying. These silicide plates pass through grain boundaries and hold the niobium or tantalum network intact without strongly affecting the microstructural evolution during dealloying. Our approach yields a mechanically robust porous metal-intermetallic composite, which can be further processed to form tertiary materials via re-impregnation by a new third phase. The materials design strategy introduced here can be generalized to serve as a platform to form dense multiphase nanocomposites.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S135964541830867X-fx1.jpg" width="500" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 1 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 164〈/p〉 〈p〉Author(s): Yafeng Chen, Fei Meng, Guangyao Li, Xiaodong Huang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The Dirac-like cones underlie many unique properties of photonic crystals (PhCs). This paper aims to design fabrication-friendly PhCs with Dirac-like cones for transverse magnetic (TM) modes and transverse electric (TE) modes at different specific frequencies. By maximizing the minimum of a collection of the local density of states corresponding to different judiciously selected sources, this paper demonstrates that Dirac-like cones formed by the degeneracy of a doubly degenerate mode and a single mode at different desired frequencies are successfully obtained. The exotic wave manipulation properties associated with Dirac-like cones, such as cloaking, wavefront shaping and tunneling through bent channels, are exhibited based on the optimized structures. This paper also demonstrates that the proposed method could be used for the design of PhCs with one Dirac-like cone at 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈mi〉ω〈/mi〉〈/mrow〉〈/math〉, and one monopolar band at 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.gif" overflow="scroll"〉〈mrow〉〈mn〉2〈/mn〉〈mi〉ω〈/mi〉〈/mrow〉〈/math〉 at the Γ point, and PhCs with third order Dirac-like cones, which have potential applications in nonlinear optics. All topological patterns of the optimized PhCs are reported and have regular and smooth features, meaning they can be readily fabricated.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418308681-fx1.jpg" width="415" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 1 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 164〈/p〉 〈p〉Author(s): Y. Wang, C.M. Fang, L. Zhou, T. Hashimoto, X. Zhou, Q.M. Ramasse, Z. Fan〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Al-Ti-B based master alloys have been widely used for grain refining of Al-alloys in industry for many decades. However, the effectiveness of such grain refiners is severely compromised when a few hundred ppm of Zr is present in the Al melt, and this phenomenon is referred to as Zr poisoning in the literature. So far the exact mechanisms for Zr poisoning are not clear albeit significant research effort on the subject in the last few decades. In this work we investigated the mechanism for Zr poisoning through extensive examinations of the Al/TiB〈sub〉2〈/sub〉 interface using the state-of-the-art electron microscopy and 〈em〉ab initio〈/em〉 molecular dynamics simulations. We found that the presence of Zr in Al melts leads to (i) the dissolution of the Al〈sub〉3〈/sub〉Ti 2-dimensional compound (2DC) formed on the (0 0 0 1) TiB〈sub〉2〈/sub〉 surface during the grain refiner production process; and (ii) the formation of an atomic monolayer of Ti〈sub〉2〈/sub〉Zr 2DC on the (0 0 0 1) TiB〈sub〉2〈/sub〉 surface, which replaces the original Ti-terminated TiB〈sub〉2〈/sub〉 basal surface. This monolayer of Ti〈sub〉2〈/sub〉Zr not only has large lattice misfit (4.2%) with α-Al, but also is atomically rough, rendering the TiB〈sub〉2〈/sub〉 particles impotent for heterogeneous nucleation of α-Al. This work, in combination of our previous work, demonstrates that heterogeneous nucleation can be effectively manipulated, either enhanced or impeded, by chemical segregation of selected alloying/impurity elements at the liquid/substrate interface.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉(a, b) High resolution STEM HAADF images showing an atomic monolayer of Ti〈sub〉2〈/sub〉Zr 2-dimensional compound (2DC) on (0 0 0 1) surface of TiB〈sub〉2〈/sub〉 being viewed along (a) [1 1 -2 0]TiB〈sub〉2〈/sub〉 and (b) [1 0 -1 0]TiB〈sub〉2〈/sub〉 direction respectively, and (c) 3D construction of the Ti〈sub〉2〈/sub〉Zr 2DC on top of TiB〈sub〉2〈/sub〉.〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418308668-fx1.jpg" width="205" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 1 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 164〈/p〉 〈p〉Author(s): Yi Huang, Piotr Bazarnik, Diqing Wan, Dan Luo, Pedro Henrique R. Pereira, Malgorzata Lewandowska, Jin Yao, Brian E. Hayden, Terence G. Langdon〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Metal matrix nanocomposites were fabricated by high-pressure torsion (HPT) using 5% graphene nanoplates as a reinforcement contained within an Al matrix. Powders were mixed and compacted at room temperature and then processed by HPT at three different temperatures of 298, 373 and 473 K. After processing, microstructural observations were undertaken to reveal the distributions of graphene in the matrix, the grain refinement in the aluminium and the nature of the graphene-aluminium interfaces. Tests were performed to measure the microhardness, the tensile stress-strain curves and the electrical conductivity. The results show that processing by HPT is advantageous because it avoids the sintering and high temperature deformation associated with other processing routes.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S135964541830870X-fx1.jpg" width="245" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 15 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 163〈/p〉 〈p〉Author(s): 〈/p〉

Beschreibung: 〈p〉Publication date: 1 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 164〈/p〉 〈p〉Author(s): M. Bonvalet, X. Sauvage, D. Blavette〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Both continuous and discontinuous precipitation is known to occur in CuAg alloys. The precipitation of Ag-rich phase has been experimentally investigated by atom probe tomography and transmission electron microscopy after ageing treatment of Cu-5%wtAg at 440 °C during 30’. Both continuously and discontinuously formed precipitates have been observed. The precipitates located inside the grains exhibit two different faceted shapes: tetrahedral and platelet-shaped precipitates. Dislocations accommodating the high misfit at the interface between the two phases have also been evidenced. Based on these experimental observations, we examine the thermodynamic effect of these dislocations on the nucleation barrier and show that the peculiar shapes are due to the interfacial anisotropy. The appropriate number of misfit dislocations relaxes the elastic stress and lead to energetically favorable precipitates. However, due to the large misfit between the parent and precipitate phases, discontinuous precipitation that is often reported for CuAg alloys can be a lower energetic path to transform the supersaturated solid solution. We suggest that the presence of vacancy clusters may assist intragranular nucleation and decrease the continuous nucleation barrier. We eventually propose qualitative thermodynamic and kinetic justifications accounting for the relative importance of homogeneous and discontinuous precipitation modes as a function of temperature.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418308656-fx1.jpg" width="315" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 1 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 164〈/p〉 〈p〉Author(s): C. Suwanpreecha, J. Perrin Toinin, R.A. Michi, P. Pandee, D.C. Dunand, C. Limmaneevichitr〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Dilute Al〈img src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"〉Sc alloys (〈0.4 wt% Sc) are creep-resistant up to ∼300 °C owing to coherent, nanosize Al〈sub〉3〈/sub〉Sc particles created by solid-state precipitation. By contrast, eutectic Al〈img src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"〉Ni alloys (Al-6 wt.% Ni) derive their high strength at elevated temperature from Al〈sub〉3〈/sub〉Ni microfibers formed during solidification. Here, we investigate ternary Al〈img src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"〉6Ni-0.2Sc and Al〈img src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"〉6Ni-0.4Sc alloys with both types of strengthening precipitates (Al〈sub〉3〈/sub〉Sc and Al〈sub〉3〈/sub〉Ni) and compare them to binary Al〈img src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"〉6Ni, Al-0.2Sc and Al-0.4Sc alloys with a single population of precipitates. Kinetics of Al〈sub〉3〈/sub〉Sc and Al〈sub〉3〈/sub〉Ni precipitation and coarsening are studied via hardness measurements during isochronal and isothermal aging; the two phases resist coarsening up to 475 and 350 °C, respectively, upon short term exposures (1 h isochronal steps). No noticeable effect of Sc is observed on the Al〈sub〉3〈/sub〉Ni micro-fiber composition and hardening in the alloy. Similarly, Ni does not significantly affect the hardening provided by the Al〈sub〉3〈/sub〉Sc precipitates, despite the presence of 0.14–0.17 at.% Ni in the Al〈sub〉3〈/sub〉Sc nano-precipitates. The strengthening contributions of the Al〈sub〉3〈/sub〉Ni and Al〈sub〉3〈/sub〉Sc phases at ambient temperature are cumulative in the ternary alloys. For creep deformation at 300 °C, all alloys show a creep threshold stress, indicating that both types of precipitates impede dislocation motion. The ternary Al〈img src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"〉Ni〈img src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"〉Sc alloys show higher creep threshold stresses than their binary counterparts, also consistent with cumulative strengthening effects of precipitation strengthening (from Al〈sub〉3〈/sub〉Sc nano-precipitates) and load transfer (from Al〈sub〉3〈/sub〉Ni micro-fibers).〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418308693-fx1.jpg" width="500" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: Available online 30 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia〈/p〉 〈p〉Author(s): Manon Bonvalet-Rolland, Thomas Philippe, John Ågren〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Nucleation kinetics in a multicomponent supersaturated solid solution is examined. Attachment rate of atoms to a nucleus of a size close to the critical one is determined combining a thermodynamic extremum principle and the Fokker-Planck equation. Two limiting cases are examined; when bulk diffusion controls the nucleation kinetics and when the process is limited by the interfacial mobility. The mixed regime is also treated. Moreover, the growth law in multicomponent alloys is derived in the general case, when both mechanisms are considered. Additionally, the attachment rate is derived, in the classical framework, from a new macroscopic growth equations and the fundamental role of the interfacial mobility is examined. These new general expressions, for the attachment rates and the growth laws, determined either applying the thermodynamic extremum principle or derived from the classical formalism are found to be consistent.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645419301740-fx1.jpg" width="397" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: Available online 29 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia〈/p〉 〈p〉Author(s): Wei Chen, Shuo Cao, Wenjuan Kou, Jinyu Zhang, Yue Wang, You Zha, Yan Pan, Qingmiao Hu, Qiaoyan Sun, Jun Sun〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The ductile-to-brittle transition is commonly observed in metastable 〈em〉β〈/em〉-titanium (Ti) alloys containing 〈em〉ω〈/em〉-precipitates, while the fundamental understanding on 〈em〉ω〈/em〉-embrittlement hitherto remains elusive. In this work, the prototypical Ti-20wt.% Mo metastable 〈em〉β〈/em〉-Ti alloy has been systematically investigated by coupling experiments and first-principles calculation to eliminate this puzzle. It is shown that the structural evolution of 〈em〉ω〈/em〉-phase controls the deformation mechanism transition of twinning-to-slip in Ti-Mo alloy, being the origin of ductile-to-brittle transition of this alloy. The initial trigonal 〈em〉ω〈/em〉-structure continuously collapses to hexagonal 〈em〉ω〈/em〉-structure (structural collapse) whilst Mo-atoms is rejected out concurrently (stoichiometric varieties), both leading to hardening of 〈em〉ω〈/em〉-precipitates. This self-hardening of 〈em〉ω〈/em〉-precipitates was further rationalized in terms of the enhanced propensity for a covalent character of the atomic bond demonstrated by the electronic density of states (DOS) from first-principles calculation. Specifically, the self-hardening behavior of 〈em〉ω〈/em〉-precipitates promotes dislocation slip on isolated planes in lieu of correlative slip on successive planes inside 〈em〉ω1〈/em〉-variant, while dislocations are completely blocked ahead 〈em〉ω2/ω3/ω4-〈/em〉variants. This in turn renders the transition from deformation twinning that contributes to great macro-plasticity to ordinary dislocation slip that contributes to localized deformation bands in the present Ti-Mo alloy.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645419301776-fx1.jpg" width="377" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: Available online 28 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia〈/p〉 〈p〉Author(s): Elizaveta Y. Plotnikov, Zugang Mao, Sung-Il Baik, Mehmet Yildirim, Yongsheng Li, Daniel Cecchetti, Ronald D. Noebe, Georges Martin, David N. Seidman〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The temporal evolution of ordered γ’(L1〈sub〉2〈/sub〉)-precipitates precipitating in a disordered γ(f.c.c.) matrix is studied in extensive detail for a Ni-12.5 Al at.% alloy aged at 823 K (550 〈sup〉o〈/sup〉C), for times ranging from 0.08 to 4096 h. Three-dimensional atom-probe tomography (3-D APT) results are compared to monovacancy-mediated lattice-kinetic Monte Carlo (LKMC〈sub〉1〈/sub〉) simulations on a rigid lattice, which include monovacancy-solute binding energies through 4〈sup〉th〈/sup〉 nearest-neighbor distances, for the same mean composition and aging temperature. The temporal evolution of the measured values of the mean radius, 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈mrow〉〈mo〉〈〈/mo〉〈mrow〉〈mi〉R〈/mi〉〈mrow〉〈mo〉(〈/mo〉〈mi〉t〈/mi〉〈mo〉)〈/mo〉〈/mrow〉〈/mrow〉〈mo〉〉〈/mo〉〈/mrow〉〈/mrow〉〈/math〉, number density, aluminum supersaturations, and volume fraction of the γ’(L1〈sub〉2〈/sub〉)-precipitates are compared to the predictions of a modified version of the Lifshitz-Slyozov diffusion-limited coarsening model due to Calderon, Voorhees et al. The resulting experimental rate constants are used to calculate the Gibbs interfacial free-energy between the γ(f.c.c.)- and γ’(L1〈sub〉2〈/sub〉)-phases, which enter the model〈em〉,〈/em〉 using data from two thermodynamic databases, and its value is compared to all exiting values. The diffusion coefficient for coarsening is calculated utilizing the same rate-constants and compared to all archival diffusivities, 〈em〉not determined from coarsening experiments, and it is demonstrated to be the inter-diffusivity,〈/em〉 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.gif" overflow="scroll"〉〈mrow〉〈mover accent="true"〉〈mi〉D〈/mi〉〈mo〉˜〈/mo〉〈/mover〉〈/mrow〉〈/math〉〈em〉, of Ni and Al.〈/em〉 The monovacancy-mediated LKMC〈sub〉1〈/sub〉 simulation results are in good agreement with our 3-D APT data. The compositional interfacial width, for the {100}-interface, between the γ(f.c.c.)- and γ’(L1〈sub〉2〈/sub〉)-phases, decreases continuously with increasing aging time and 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈mrow〉〈mo〉〈〈/mo〉〈mrow〉〈mi〉R〈/mi〉〈mrow〉〈mo〉(〈/mo〉〈mi〉t〈/mi〉〈mo〉)〈/mo〉〈/mrow〉〈/mrow〉〈mo〉〉〈/mo〉〈/mrow〉〈/mrow〉〈/math〉, both for the 3-D APT results and the monovacancy-mediated LKMC〈sub〉1〈/sub〉 simulations, in disagreement with an 〈em〉ansatz〈/em〉 intrinsic to the trans-interface diffusion-controlled coarsening model, which assumes the exact opposite trend for binary alloys.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645419301594-fx1.jpg" width="255" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: Available online 26 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia〈/p〉 〈p〉Author(s): Chenxi Wang, Xiaoming Yang, Zujian Wang, Chao He, Xifa Long〈/p〉 〈div xml:lang="en"〉 〈h5〉ABSTRACT〈/h5〉 〈div〉〈p〉Switching behavior is a general feature in ferroelectrics. The related fatigue effects influenced by defect dipoles in ferroelectrics are still controversial that is focused on the positive and negative effects of oxygen vacancies. Here, we report the polarization switching behavior of acceptor-doped ceramics using the first-order reversal curve (FORC) approach, especially for the abnormal self-rejuvenation effect and the enhanced fatigue endurance in acceptor-doped ceramics. The reversible and irreversible components under electric field in the ceramics were distinguished by the FORC distribution of ideal “hysteron”. The abnormal self-rejuvenation behavior stemmed from dispersive response of hysteron for undoped samples while from the redistribution of defect dipoles for acceptor-doped samples. The self-rejuvenation was induced mainly by the irreversible component. For the fatigue effect, the pinning of domain walls was not the main reason. The re-annealing treatment for a fatigued sample weakened the interactions between the spontaneous polarizations and defect dipoles, but enhanced the dispersion of coercive field. The enhancement of fatigue endurance came from the phase stability of structure in acceptor-doped ceramics, while complex phase evolution existed in undoped ceramic with weak fatigue endurance. Our study shed new light on the interactions between spontaneous polarization and defect dipoles under repetitive AC electric field.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645419301764-fx1.jpg" width="491" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 165〈/p〉 〈p〉Author(s): O. El-Atwani, E. Esquivel, E. Aydogan, E. Martinez, J.K. Baldwin, M. Li, B.P. Uberuaga, S.A. Maloy〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Nanocrystalline metals are often postulated as irradiation tolerant materials due to higher grain boundary densities. The efficiency of these materials in mitigating irradiation damage is still under investigation. Here, we present an in-situ transmission electron microscopy with ion irradiation study on equiaxed 35 nm grained tungsten (NCW-35 nm) and compare its radiation tolerance, in terms of dislocation loop damage, to several other grades of tungsten with different grain sizes at two temperatures (RT and 1073 K). The NCW-35 nm was shown to possess significant higher radiation tolerance in terms of loop damage. As demonstrated by Kinetic Monte Carlo simulations, at least part of the higher radiation tolerance of the small grains is due to higher interstitial storage (at the grain boundaries) and defect recombination (in the grain interiors) in the small grain material. In addition, experimental observations reveal rapid and efficient dislocation loop absorption by the grain boundaries and this is considered the dominant factor for mass transport to the boundaries during irradiation, enabling the remarkable radiation tolerance of 35 nm grained tungsten. This study demonstrates the possibility of attaining high radiation tolerant materials, in terms of dislocation loop damage, by minimizing grain sizes in the nanocrystalline regime.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉The response of different tungsten material grades to 1 MeV Kr〈sup〉+2〈/sup〉 heavy ion irradiation at different conditions.〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418309005-fx1.jpg" width="235" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 165〈/p〉 〈p〉Author(s): Rafael Herschberg, Chu-Chun Fu, Maylise Nastar, Frédéric Soisson〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The diffusion of C in Fe〈img src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"〉Cr solid solutions is modelled and compared to experimental data. A set of binding energies and migration barriers for C diffusion in different local chemical environments are first calculated using density functional theory. A pair interaction model is developed in order to reproduce these data and predict the migration barriers in other environments. The diffusion model is then implemented in a kinetic Monte Carlo method to simulate tracer diffusion experiments, using a standard procedure, and internal friction experiments, using a novel method. Simulations of internal friction show a unique Snoek peak in the whole concentration range, between pure iron and pure chromium. The average migration barrier for C diffusion in Fe〈img src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"〉Cr alloys is found to increase progressively with the Cr concentration, with a small rate below 6 %Cr. In Cr-rich alloys, the effective migration barrier for C diffusion is found to be larger in tracer diffusion than in the internal friction simulations. We conclude that the effective migration barrier extracted from tracer diffusion is closely related to trapping effects of C atoms in Fe-rich local environments, whereas the migration barrier associated with internal friction is mainly controlled by the migration barriers of the most probable configurations, as it is clearly shown in the Cr-rich domain.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉Tracer diffusion and Internal Friction experiments were simulated via AKMC and compared with the available experimental data. A new model for the Internal Friction was developed and it was also compared with a previous model found in the experimental literature.〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418309017-fx1.jpg" width="426" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 1 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 164〈/p〉 〈p〉Author(s): Lin Zhou, Fanqiang Meng, Shihuai Zhou, Kewei Sun, TaeHoon Kim, Ryan Ott, Ralph Napolitano, Matthew J. Kramer〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Phase selection and growth of materials far from equilibrium provides fertile ground for novel phases and morphologies since a multitude of different pathways may be energetically accessible. In this study, a complex metastable devitrification of Al〈sub〉60〈/sub〉Sm〈sub〉11〈/sub〉 (ε-phase) from its amorphous precursor is discovered using a combination of 〈em〉in-situ〈/em〉 high-energy X-ray diffraction (HEXRD), providing insight into the average bulk behavior, and 〈em〉in-situ〈/em〉 aberration corrected scanning transmission electron microscopy, revealing the atomic scale mechanisms of growth and their dynamics. We have found that non-equilibrium chemical partitioning disrupts the nominal planer growth by formation of nanoscale Al enriched regions inhomogeneously segregated at the ε/glass interface, to locally balance the compositionally dependent driving force and the associated diffusional burden imposed on its grain growth. These Al-rich regions form 〈em〉fcc〈/em〉-Al-rich nanocrystallites epitaxially with the ε-phase, modifying ε/glass interface mobility and creating a crenulated growth front. This new mechanism offers a pathway for fabricating alloy structures with nanoprecipitate dispersions through a meta-stable phase transition.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418309030-fx1.jpg" width="395" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 165〈/p〉 〈p〉Author(s): S. Wang, J. Kang, Z. Guo, T.L. Lee, X. Zhang, Q. Wang, C. Deng, J. Mi〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The fatigue fragmentation of dendritic structures of a SCN-5〈em〉wt〈/em〉.% Camphor transparent alloy in an ultrasound field was investigated systematically using high-speed imaging. Dynamic interactions between oscillating ultrasonic bubbles and the primary and secondary dendrites were observed and recorded. High speed images show that when an ultrasound bubble was trapped inside an interdendritic region, the oscillation of the bubble can cause cyclic bending of the dendritic arms. Consequently, a fatigue type crack initiated at the arm root and propagated through the dendrite, causing the dendrite to fragment, i.e. dendritic fragmentation. From the recorded videos, the cycle numbers for the fatigue fragmentation were extracted, then, the fatigue strength and fatigue life of the SCN-5〈em〉wt〈/em〉.% Camphor transparent alloy were calculated. Results showed that the cyclic fatigue load cause a crack initiating on a SCN dendrite at a much lower stress level than its tensile strength under high frequent oscillation.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418309303-fx1.jpg" width="260" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 165〈/p〉 〈p〉Author(s): T. Mukhopadhyay, S. Adhikari, A. Alu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉An insightful mechanics-based concept is developed for probing the frequency-dependence in in-plane elastic moduli of microstructured lattice materials. Closed-form expressions for the complex elastic moduli are derived as a function of frequency by employing the dynamic stiffness matrix of beam elements, which can exactly capture the sub-wavelength scale dynamics. It is observed that the two Poisson's ratios are not dependent on the frequency of vibration, while the amplitude of two Young's moduli and shear modulus increase significantly with the increase of frequency. The variation of frequency-dependent phase of the complex elastic moduli is studied in terms of damping factors of the intrinsic material. The tunable frequency-dependent behaviour of elastic moduli in lattice materials could be exploited in the pseudo-static design of advanced engineering structures which are often operated in a vibrating environment. The generic concepts presented in this paper introduce new exploitable dimensions in the research of engineered materials for potential applications in various vibrating devices and structures across different length-scales.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418308887-fx1.jpg" width="500" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 165〈/p〉 〈p〉Author(s): Weiwei Sun, Hossein Ehteshami, Paul R.C. Kent, Pavel A. Korzhavyi〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉To date, the mechanism of Ti atom self-diffusion is unproven. Prior theoretical work mostly focused on Ti vacancy based mediators, but these do not reproduce the experimental activation energy or entropy. In this work, in density functional theory calculations, Ti interstitials and related defect complexes are systematically considered as possible mediators of Ti self-diffusion. Among these defects, the defect complex of two C vacancies tightly bound to a Ti dumbbell is found to have the lowest formation energy. A sustainable migration of the complex, in a translational or rotational fashion, is enabled in the presence of another (free) carbon vacancy nearby the complex, and thus the rate of Ti self-diffusion by this mechanism is dependent on the concentration of carbon vacancies. The calculated activation energy of the complex agrees well with the experimental value in TiC〈sub〉0.97〈/sub〉. Similar analyses of the Ti self-diffusion mechanisms mediated by Ti interstitials or dumbbells yield much higher activation energies, but the corresponding migration energies are evaluated to be less than 1 eV, which suggests they can be possible mediators of the radiation-enhanced Ti self-diffusion in TiC. To fully enable the comparison with experiments that are typically conducted at temperatures as high as 2500 K, we also consider the temperature dependent vibrational contribution to the activation energy of the defect complex. The vibrational contribution imposes an additive effect on the defect formation energy, while the migration energies are lowered due to the thermal expansion of the lattice. When combined, these factors give an excellent agreement with the experiments. This work gives strong support to the concept that Ti interstitial based defect complexes are likely diffusion mediators for Ti atom self-diffusion in TiC, further establishes a solid basis for large-scale modeling, and may eventually pave the way to accurately predicting defect-controlled diffusional processes.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉Schematic diagrams showing pathways of vacancy-assisted translational (a) and rotational (b) migration of a Ti〈sub〉D〈/sub〉” defect complex. The blue spheres represent Ti atoms with the marked purple spheres for the defect complex, and brown spheres for C atoms. The pathway is marked by the dashed line, with an arrow used to highlight the migration orientation. Images from the left to the right correspond, to the the initial state, the transition state (saddle point), and the final state, respectively.〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418309339-fx1.jpg" width="310" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 165〈/p〉 〈p〉Author(s): I. Dirba, H. Sepehri-Amin, T. Ohkubo, K. Hono〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉SmFe〈sub〉12〈/sub〉-based compounds possess promising intrinsic magnetic properties, even superior to those of Nd〈sub〉2〈/sub〉Fe〈sub〉14〈/sub〉B phase at elevated temperatures. However, the remaining challenge is to demonstrate that those intrinsic properties can be further developed into practically relevant extrinsic ones by proper processing. Here we have employed hydrogenation disproportionation desorption recombination (HDDR) process for preparation of ultrafine-grained SmFe〈sub〉12〈/sub〉-based alloys with the tetragonal ThMn〈sub〉12〈/sub〉-type crystal structure. The effect of alloying elements and grain boundary phase on disproportionation rate is investigated and experimental HDDR process phase diagram is proposed. Due to the high vapor pressure of Sm as well as the competing phases, recombination into phase-pure samples can be realized only in a narrow processing parameters window. The resultant phase constitutions, chemical composition, microsctructure and crystallographic relations at different process steps are discussed.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S135964541830942X-fx1.jpg" width="473" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 165〈/p〉 〈p〉Author(s): Xuan Quy Tran, Min Hong, Hiroshi Maeno, Youichirou Kawami, Takaaki Toriyama, Kevin Jack, Zhi-Gang Chen, Jin Zou, Syo Matsumura, Matthew S. Dargusch〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The GeTe-based system has long been considered as a promising candidate system for various functional applications; many of which are directly related to the polymorphic phase transformation in their crystalline forms. Consequently, the microstructure underlying their intriguing phase transition has been the subject of numerous studies. Here we provide real-time observation of the microstructural changes associated with the reversible pseudo-cubic (or rhombohedral) to cubic GeTe phase transition using high-voltage transmission electron microscopy (HV-TEM) operating at 1,250 kV and complementary high-temperature X-ray diffraction (XRD). As a result of the phase transition, the pseudo-cubic GeTe domain's configuration significantly changes from its original band-like to a spike-like morphology with a different orientation after a heating/cooling cycle. The coefficients of thermal expansion (CTE) properties as a function of temperature are also explored in relation to the GeTe phase transition.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418309364-fx1.jpg" width="362" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 165〈/p〉 〈p〉Author(s): Mojtaba Salehi, Saeed Maleksaeedi, Sharon Mui Ling Nai, Ganesh Kumar Meenashisundaram, Min Hao Goh, Manoj Gupta〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Several metallurgical issues arise during melting and solidification-based additive manufacturing (AM) methods which limit their use to only a few alloys. This study shows how capillarity-driven bridging can serve as a new and rapid tool of assembling powder particles into 3D structures providing the least metallurgical complexity. According to the established conceptual framework, in-situ binding agent can be derived autogenously from selective interactions of a liquid solvent with superficial layer of powder particles to form in-situ solid interparticle bridges which enables AM at ambient conditions. Magnesium (Mg) is the most difficult engineering metal to handle in all 3D AM processes in view of its intrinsic properties. Supported by transmission and scanning electron microscopies together with Fourier transform infrared and Raman spectroscopy, the introduced 3D printing concept is readily accomplished for Mg alloys by conversion of MgO film, inevitably existing on the outermost layer of Mg powder, into interparticle bridges. In the absence of pyrolysis-adapted sintering profile, these bridges fully decompose during the following sintering step which result in functional Mg parts with chemical composition same as the starting Mg powder with zero contamination, according to chemical and thermal analysis results. The introduced capillary-mediated binding of particles is simple and generic that could be extended to additively manufacture other metals, ceramics and found applications in other traditional ex-situ binder-based processes.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418309388-fx1.jpg" width="250" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 165〈/p〉 〈p〉Author(s): Yongjie Wang, R. Hrubiak, S. Turczyński, D.A. Pawlak, M. Malinowski, D. Włodarczyk, K.M. Kosyl, W. Paszkowicz, H. Przybylińska, A. Wittlin, A. Kaminska, Ya Zhydachevskyy, M.G. Brik, Li Li, Chong-Geng Ma, A. Suchocki〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉High pressure studies of monoclinic yttrium aluminum oxide single crystals (Y〈sub〉4〈/sub〉Al〈sub〉2〈/sub〉O〈sub〉9〈/sub〉 -YAM) doped with Ce〈sup〉3+〈/sup〉 ions grown by micro-pulling-down method are reported. The results of absorption measurements in the mid-infrared prove the existence of four different sites in which Ce〈sup〉3+〈/sup〉 ions substitute Y ions, in accordance with the crystallographic structure of YAM. The lowest 5d level of Ce〈sup〉3+〈/sup〉 is located very close to the bottom of the conduction band for two of four Ce〈sup〉3+〈/sup〉 related centers at ambient pressure, which results in strong temperature quenching of their luminescence. Two other Ce〈sup〉3+〈/sup〉 centers do not emit at ambient pressure since their 5d levels are resonant with the conduction band. Application of high pressure above 11 GPa restores their luminescence. Consequences of such energy structure of various Ce〈sup〉3+〈/sup〉 sites in YAM for the Dorenbos theory are discussed. The bandgap energy of YAM is found to be 5.93 eV, which is the smallest out of the three yttrium aluminum oxides. High-pressure synchrotron angle dispersive x-ray diffraction and Raman scattering measurements identify a phase transition occurring at pressures between 8 and 11 GPa, which has martensitic character. The second phase transition to another structure (likely with hexagonal symmetry) occurs at a pressure around 16 GPa.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418309340-fx1.jpg" width="277" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 165〈/p〉 〈p〉Author(s): Nico Neuber, Oliver Gross, Miriam Eisenbart, Alexander Heiss, Ulrich E. Klotz, James P. Best, Mikhail N. Polyakov, Johann Michler, Ralf Busch, Isabella Gallino〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Effective strategies to improve the tarnishing resistance of the 18 K (karat) gold-based bulk glass-forming composition Au〈sub〉49〈/sub〉Ag〈sub〉5.5〈/sub〉Pd〈sub〉2.3〈/sub〉Cu〈sub〉26.9〈/sub〉Si〈sub〉16.3〈/sub〉 were recently found, with the addition of Ga at the expense of Cu and a sufficient reduction of Si. However, the modification of the alloy is accompanied by a reduction of the glass-forming ability (GFA) from 5 to 2 mm in terms of the critical casting thickness, and eventually collapses for Ga contents higher than about 9 at%. In this work, thermodynamic and kinetic studies of the newly discovered 18 K Au-Ag-Pd-Cu-Ga-Si system shed light on the reason for the loss in GFA with increasing Ga content. Investigations of the liquid kinetics in terms of viscosity and transition time, assessed by three-point beam bending and the T〈sub〉g〈/sub〉-shift method, reveal an unexpected change of the fragility to stronger liquid kinetics with increasing Ga concentration, which is usually attributed to an increase in the GFA. Thermodynamic considerations based on specific heat capacity measurements reveal, in contrast, an ascending driving force for crystallization with an increasing Ga-content, accountable for the drop in GFA. Therefore, a Ga-rich melt beyond the threshold concentration of 9 at% is not desirable for the production of bulk metallic glasses (BMGs) from the liquid state. With the intention to outrun this barrier, while preserving the amorphous structure, Ga-ion implantation with a liquid metal focused ion beam source is used as a post-processing routine for a cast Ga-containing 18 K Au-BMG. Hence, the thermodynamic borderline concentration is successfully crossed with additional tremendous improvement of the tarnishing resistance in the Ga-enriched areas.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418309285-fx1.jpg" width="259" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 165〈/p〉 〈p〉Author(s): Damien Texier, Jean-Charles Stinville, McLean P. Echlin, Stéphane Pierret, Patrick Villechaise, Tresa M. Pollock, Jonathan Cormier〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Fatigue cracks initiating from surface and sub-surface non-metallic inclusions (NMIs) have recently been demonstrated to be a necessary but not sufficient explanation for atypically short low-cycle fatigue life in Inconel 718 alloy at intermediate temperature. Therefore, the early stages of short crack propagation from surface NMIs were investigated in a crystallographic and two-dimensional versus three-dimensional morphological manner after room temperature low cycle fatigue (LCF) testing. In the present investigation, NMIs were purposely pre-cracked using different techniques to suppress the natural crack initiation period and thus the incubation period prior to the early stages of crack propagation. Under such fatigue testing conditions, different mechanisms of crack transmission from pre-cracked NMIs were identified: (i) no propagation, (ii) NMI/adjacent metallic grain interfacial debonding, (iii) transgranular crack propagation within the adjacent metallic grain. Focused-ion-beam cross-section observations of numerous fatigue tested NMIs aimed to define a morphological criterion for non-propagating NMIs. Large cracked NMIs at the surface (〈em〉2c〈/em〉) with limited extension into the depth (〈em〉a〈/em〉) did not propagate under such fatigue conditions for 2〈em〉c/a〈/em〉 ratio higher than 3. Furthermore, specific crystallographic relationships between NMIs and the adjacent metallic grain explained different crack propagation configurations from pre-cracked NMIs, 〈em〉i.e.〈/em〉 interfacial debonding and transgranular crack propagation involving single or multiple-slip activity.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418309273-fx1.jpg" width="494" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 166〈/p〉 〈p〉Author(s): Thomas Edward James Edwards, Fabio Di Gioacchino, Amy Jane Goodfellow, Gaurav Mohanty, Juri Wehrs, Johann Michler, William John Clegg〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The distribution of strain in hard mode oriented lamellar stacks of the two-phase γ-TiAl/α〈sub〉2〈/sub〉-Ti〈sub〉3〈/sub〉Al alloy Ti-45Al-2Nb-2Mn (at.%)-0.8 vol% TiB〈sub〉2〈/sub〉 was measured at several temperatures up to 633 °C by 〈em〉in situ〈/em〉 micropillar compression, complemented by electron backscatter diffraction orientation mapping and digital image correlation strain mapping of a thermally stable surface Pt speckle pattern. Post-mortem transmission electron microscopy further identified the finest scale deformation structures. It was found that slip and twinning transverse to the lamellae operates within discreet bands that zigzag across the lamellar structure. The shear strain within each band is approximately constant across the pillar width. This is inconsistent with current energetic models for transverse twin formation in γ-TiAl, which assume independent, non-interacting twins. This is explained using a mathematical formulation for the stress required to operate this transverse mechanical twinning as a function of strain. This study has elucidated how the multi-scale combination of several transverse twinning systems on different {111} planes in γ-TiAl lamellae can relieve the elastic stresses generated at a lamellar interface by the primary (highest Schmid factor) twinning system. It is thought that the facilitation of this mechanism will promote the ductilisation of lamellar γ-TiAl alloys. This is crucial for an increased damage tolerance and ease of component manufacture, leading to a more widespread use of γ-TiAl alloys.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418309261-fx1.jpg" width="461" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 166〈/p〉 〈p〉Author(s): Sinan S. Faouri, Ali Mostaed, Julian S. Dean, Dawei Wang, Derek C. Sinclair, Shiyu Zhang, William G. Whittow, Yiannis Vardaxoglou, Ian M. Reaney〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Ceramics-ceramic composites in series (1-〈em〉x〈/em〉)Li〈sub〉2〈/sub〉MoO〈sub〉4〈/sub〉-〈em〉x〈/em〉BaFe〈sub〉12〈/sub〉O〈sub〉19〈/sub〉 (LMO-BF12, 0.00 ≤ 〈em〉x〈/em〉 ≤ 0.15) have been cold sintered at 120 °C and their structure and properties characterized. X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) confirmed that compositions were dual phase and had a dense microstructure. Composites in the 〈em〉x〈/em〉BF12-(1-〈em〉x〈/em〉)LMO (0.0 ≤ 〈em〉x〈/em〉 ≤ 0.15) series resonated at MW frequencies (∼6 GHz) with 5.6≤〈em〉ε〈/em〉〈sub〉〈em〉r〈/em〉〈/sub〉 ≤ 5.8 and 〈em〉Qf〈/em〉 = 16,000–22,000 GHz, despite the black colour of compositions with 〈em〉x〈/em〉 〉 0. The permeability of the composites was measured in the X band (∼8 GHz) and showed an increase from 0.94 (〈em〉x〈/em〉 = 0.05) to 1.02 (〈em〉x〈/em〉 = 0.15). Finite element modelling revealed that the volume fraction of BF12 dictates the conductivity of the material, with a percolation threshold at 10 vol% BF12 but changes in 〈em〉ε〈/em〉〈sub〉〈em〉r〈/em〉〈/sub〉 as a function of 〈em〉x〈/em〉 were readily explained using a series mixing model. In summary, these composites are considered suitable for the fabrication of dual mode or enhanced bandwidth microstrip patch antennas.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418310085-fx1.jpg" width="500" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 166〈/p〉 〈p〉Author(s): X.F. Kong, I.J. Beyerlein, Z.R. Liu, B.N. Yao, D. Legut, T.C. Germann, R.F. Zhang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Low-energy structures of bimetal interfaces commonly occur in nature, yet higher energy forms, made by deviations in the interface plane, are also likely. While these variants may occur less frequently, they can still play an important role in the response of the material under deformation, by acting as preferential sites for defect formation and boundary motion. Here, using atomic-scale simulation and interface defect theory and considering two bimetal systems, Cu/Ag and Cu/Nb, we show that high-energy interfaces can achieve a local, low-energy state by forming atomic-scale serrations and that the predicted size and location of the serrations are consistent with experimental observation. For several distinct strain states, we reveal that interfaces with atomic-scale serrations bear both higher barriers for dislocation nucleation and higher resistances to interfacial shear compared to their planar interface variants. This desirable combination is not a characteristic of the more commonly studied low-energy interfaces, which typically possess a high nucleation barrier and low sliding resistance. We explain, through an analysis of the misfit dislocation structure, that the serrations alter the number of dislocations emitted, change the favorable slip systems, and alleviate the stress concentrations generated by misfit dislocations. An interface engineering strategy is then proposed for designing atomically serrated interfaces to improve mechanical strength and hinder localization and creep of metallic nanomaterials.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418310024-fx1.jpg" width="265" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 166〈/p〉 〈p〉Author(s): Zijiang Yang, Yuksel C. Yabansu, Dipendra Jha, Wei-keng Liao, Alok N. Choudhary, Surya R. Kalidindi, Ankit Agrawal〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Data-driven methods are attracting growing attention in the field of materials science. In particular, it is now becoming clear that machine learning approaches offer a unique avenue for successfully mining practically useful process-structure-property (PSP) linkages from a variety of materials data. Most previous efforts in this direction have relied on feature design (i.e., the identification of the salient features of the material microstructure to be included in the PSP linkages). However due to the rich complexity of features in most heterogeneous materials systems, it has been difficult to identify a set of consistent features that are transferable from one material system to another. With flexible architecture and remarkable learning capability, the emergent deep learning approaches offer a new path forward that circumvents the feature design step. In this work, we demonstrate the implementation of a deep learning feature-engineering-free approach to the prediction of the microscale elastic strain field in a given three-dimensional voxel-based microstructure of a high-contrast two-phase composite. The results show that deep learning approaches can implicitly learn salient information about local neighborhood details, and significantly outperform state-of-the-art methods.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418309960-fx1.jpg" width="500" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 166〈/p〉 〈p〉Author(s): Paraskevas Kontis, Aleksander Kostka, Dierk Raabe, Baptiste Gault〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The microstructural and compositional evolution of intergranular carbides and borides prior to and after creep deformation at 850 °C in a polycrystalline nickel-based superalloy was studied. Primary MC carbides, enveloped within intergranular γ′ layers, decomposed resulting in the formation of layers of the undesirable η phase. These layers have a composition corresponding to Ni〈sub〉3〈/sub〉Ta as measured by atom probe tomography and their structure is consistent with the D0〈sub〉24〈/sub〉 hexagonal structure as revealed by transmission electron microscopy. Electron backscattered diffraction reveals that they assume various misorientations with regard to the adjacent grains. As a consequence, these layers act as brittle recrystallized zones and crack initiation sites. The composition of the MC carbides after creep was altered substantially, with the Ta content decreasing and the Hf and Zr contents increasing, suggesting a beneficial effect of Hf and Zr additions on the stability of MC carbides. By contrast, M〈sub〉5〈/sub〉B〈sub〉3〈/sub〉 borides were found to be microstructurally stable after creep and without substantial compositional changes. Borides at 850 °C were found to coarsen, resulting in some cases into γ′- depleted zones, where, however, no cracks were observed. The major consequences of secondary phases on the microstructural stability of superalloys during the design of new polycrystalline superalloys are discussed.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S135964541830990X-fx1.jpg" width="498" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 166〈/p〉 〈p〉Author(s): Jinming Guo, María Jazmin Duarte, Yong Zhang, Andrea Bachmaier, Christoph Gammer, Gerhard Dehm, Reinhard Pippan, Zaoli Zhang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Light elements play a crucial role on the microstructure and properties of conventional alloys and steels. Oxygen is one of the light elements which is inevitably introduced into nanocrystalline alloys during manufacturing. Here, we report that severe plastic deformation can fragment the oxides formed in powder processing and eventually cause oxygen dissolution in the matrix. A comparative investigation on Cu-Fe nanocrystalline alloys generated from different initial materials, blended powders and arc-melted bulk materials which have different oxygen contents, reveals that fragmented oxides at grain boundaries effectively decrease the grain boundary mobility, markedly facilitating grain refinement. In contrast, those oxygen atoms dissolved as interstitials in the Cu-Fe matrix lead to lattice expansion and significant decrease of stacking fault energy locally as validated by density functional theory. Such oxygen-mediated microstructure gives rise to enhanced strength and superior structural stability. The remarkable tailoring effect of oxygen can be employed to engineer nanocrystalline materials with desired properties for different applications.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418309911-fx1.jpg" width="369" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 166〈/p〉 〈p〉Author(s): Daniel Gaertner, Katrin Abrahams, Josua Kottke, Vladimir A. Esin, Ingo Steinbach, Gerhard Wilde, Sergiy V. Divinski〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉The diffusion kinetics in a CoCrFeMnNi high entropy alloy is investigated by a combined radiotracer–interdiffusion experiment applied to a pseudo-binary Co〈sub〉15〈/sub〉Cr〈sub〉20〈/sub〉Fe〈sub〉20〈/sub〉Mn〈sub〉20〈/sub〉Ni〈sub〉25〈/sub〉/Co〈sub〉25〈/sub〉Cr〈sub〉20〈/sub〉Fe〈sub〉20〈/sub〉Mn〈sub〉20〈/sub〉Ni〈sub〉15〈/sub〉 couple. As a result, the composition-dependent tracer diffusion coefficients of Co, Cr, Fe and Mn are determined. The elements are characterized by significantly different diffusion rates, with Mn being the fastest element and Co being the slowest one. The elements having originally equiatomic concentration through the diffusion couple are found to reveal up-hill diffusion, especially Cr and Mn. The atomic mobility of Co seems to follow a S-shaped concentration dependence along the diffusion path. The experimentally measured kinetic data are checked against the existing CALPHAD-type databases.〈/p〉 〈p〉In order to ensure a consistent treatment of tracer and chemical diffusion a generalized symmetrized continuum approach for multi-component interdiffusion is proposed. Both, tracer and chemical diffusion concentration profiles are simulated and compared to the measurements. By using the measured tracer diffusion coefficients the chemical profiles can be described, almost perfectly, including up-hill diffusion.〈/p〉 〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418309832-fx1.jpg" width="273" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 166〈/p〉 〈p〉Author(s): Toby Francis, Ian Chesser, Saransh Singh, Elizabeth A. Holm, Marc De Graef〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We propose a representation of grain boundaries on the unit octonion 7-sphere. This representation comes with algebraic and computational tools for comparing and interpolating between grain boundaries. We derive a geodesic metric based on the inner product between unit octonions, which themselves consist of pairs of quaternions describing the grain orientations in the reference frame of the grain boundary plane. We show how the metric behaves under the application of a number of symmetries: grain exchange symmetry; 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈mi〉U〈/mi〉〈mrow〉〈mo stretchy="true"〉(〈/mo〉〈mrow〉〈mn〉1〈/mn〉〈/mrow〉〈mo stretchy="true"〉)〈/mo〉〈/mrow〉〈/mrow〉〈/math〉 symmetry around the grain boundary normal; the no-boundary condition; and crystal symmetry. We show that this metric reproduces the Mackenzie distribution in the no-boundary case, and correctly determines the angular distances between grain boundaries with a common normal or misorientation. We provide a graphical representation of the mapping of quaternion pairs onto the octonion unit sphere, and describe a number of practical computations in the Supplementary Material accompanying this paper.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418309844-fx1.jpg" width="454" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: Available online 11 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia〈/p〉 〈p〉Author(s): Michihiko Nagumo, Kenichi Takai〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Recent studies on hydrogen enhancement of the strain-induced generation of vacancies, i.e. the HESIV mechanism, and its role in hydrogen embrittlement (HE) of steels are overviewed. A high density of vacancies and their clustering have been detected by newly developed low temperature hydrogen thermal desorption spectroscopy and positron lifetime measurements. The promotion of crack nucleation and growth is ascribed to the evolution of damage associated with intense strain localization, and characteristic features of HE such as dependence on the microstructures of steels and test conditions are consistent with the HESIV mechanism. The predominant and supplementary roles of vacancies and hydrogen, respectively, in premature fracture are demonstrated by experiments devised to separate each contribution. A constitutive relation for porous materials is applicable to describe mechanistic effects of the HESIV mechanism on crack growth resistance and strain localization. The sequential void nucleation, growth and link mechanism in nanoscale are suggested.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418309558-fx1.jpg" width="272" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 165〈/p〉 〈p〉Author(s): Shun Xu, Ping Zhou, Guisen Liu, Dawu Xiao, Mingyu Gong, Jian Wang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Shock loading causes complicated twinning processes in Ti and Ti alloys. In this work, two types of {10〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈mover accent="true"〉〈mn〉1〈/mn〉〈mo〉¯〈/mo〉〈/mover〉〈/mrow〉〈/math〉2} sequential twinning processes are for the first time reported according to electron backscatter diffraction (EBSD) characterization of titanium sheets that are subjected to shock loading. One is described as {11〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.gif" overflow="scroll"〉〈mrow〉〈mover accent="true"〉〈mn〉2〈/mn〉〈mo〉¯〈/mo〉〈/mover〉〈/mrow〉〈/math〉1}〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si3.gif" overflow="scroll"〉〈mrow〉〈mo〉⇒〈/mo〉〈/mrow〉〈/math〉P〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si4.gif" overflow="scroll"〉〈mrow〉〈mo〉→〈/mo〉〈/mrow〉〈/math〉{10〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈mover accent="true"〉〈mn〉1〈/mn〉〈mo〉¯〈/mo〉〈/mover〉〈/mrow〉〈/math〉2} (〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si5.gif" overflow="scroll"〉〈mrow〉〈msubsup〉〈mrow〉〈mi〉T〈/mi〉〈/mrow〉〈mrow〉〈mi〉i〈/mi〉〈/mrow〉〈mrow〉〈mi〉I〈/mi〉〈mi〉I〈/mi〉〈/mrow〉〈/msubsup〉〈mo〉⇒〈/mo〉〈mtext〉P〈/mtext〉〈mo〉→〈/mo〉〈msubsup〉〈mrow〉〈mi〉T〈/mi〉〈/mrow〉〈mrow〉〈mi〉j〈/mi〉〈/mrow〉〈mrow〉〈mi〉I〈/mi〉〈/mrow〉〈/msubsup〉〈/mrow〉〈/math〉), i.e., {10〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈mover accent="true"〉〈mn〉1〈/mn〉〈mo〉¯〈/mo〉〈/mover〉〈/mrow〉〈/math〉2} sequential twinning is activated in the parent grain (P) along with {11〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.gif" overflow="scroll"〉〈mrow〉〈mover accent="true"〉〈mn〉2〈/mn〉〈mo〉¯〈/mo〉〈/mover〉〈/mrow〉〈/math〉1} twins. The other is described as {11〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.gif" overflow="scroll"〉〈mrow〉〈mover accent="true"〉〈mn〉2〈/mn〉〈mo〉¯〈/mo〉〈/mover〉〈/mrow〉〈/math〉2}〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si3.gif" overflow="scroll"〉〈mrow〉〈mo〉⇒〈/mo〉〈/mrow〉〈/math〉{11〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.gif" overflow="scroll"〉〈mrow〉〈mover accent="true"〉〈mn〉2〈/mn〉〈mo〉¯〈/mo〉〈/mover〉〈/mrow〉〈/math〉4}〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si4.gif" overflow="scroll"〉〈mrow〉〈mo〉→〈/mo〉〈/mrow〉〈/math〉{10〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈mover accent="true"〉〈mn〉1〈/mn〉〈mo〉¯〈/mo〉〈/mover〉〈/mrow〉〈/math〉2} (〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si6.gif" overflow="scroll"〉〈mrow〉〈msubsup〉〈mrow〉〈mi〉C〈/mi〉〈/mrow〉〈mrow〉〈mi〉i〈/mi〉〈/mrow〉〈mrow〉〈mi〉I〈/mi〉〈/mrow〉〈/msubsup〉〈mo〉⇒〈/mo〉〈msubsup〉〈mrow〉〈mi〉C〈/mi〉〈/mrow〉〈mrow〉〈mi〉j〈/mi〉〈/mrow〉〈mrow〉〈mi〉I〈/mi〉〈mi〉I〈/mi〉〈/mrow〉〈/msubsup〉〈mo〉→〈/mo〉〈msubsup〉〈mrow〉〈mi〉T〈/mi〉〈/mrow〉〈mrow〉〈mi〉k〈/mi〉〈/mrow〉〈mrow〉〈mi〉I〈/mi〉〈/mrow〉〈/msubsup〉〈/mrow〉〈/math〉), i.e., {10〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈mover accent="true"〉〈mn〉1〈/mn〉〈mo〉¯〈/mo〉〈/mover〉〈/mrow〉〈/math〉2} secondary twinning is stimulated inside {11〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.gif" overflow="scroll"〉〈mrow〉〈mover accent="true"〉〈mn〉2〈/mn〉〈mo〉¯〈/mo〉〈/mover〉〈/mrow〉〈/math〉4} twin by co-zone {11〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.gif" overflow="scroll"〉〈mrow〉〈mover accent="true"〉〈mn〉2〈/mn〉〈mo〉¯〈/mo〉〈/mover〉〈/mrow〉〈/math〉2} twin. A statistical analysis according to EBSD characterization reveals the well-defined crystallographic relations between sequential {10〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈mover accent="true"〉〈mn〉1〈/mn〉〈mo〉¯〈/mo〉〈/mover〉〈/mrow〉〈/math〉2} twin variants and the primary/incoming twins, i.e., 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si7.gif" overflow="scroll"〉〈mrow〉〈msubsup〉〈mrow〉〈mi〉T〈/mi〉〈/mrow〉〈mrow〉〈mi〉i〈/mi〉〈/mrow〉〈mrow〉〈mi〉I〈/mi〉〈mi〉I〈/mi〉〈/mrow〉〈/msubsup〉〈mo〉⇒〈/mo〉〈mtext〉P〈/mtext〉〈mo〉→〈/mo〉〈msubsup〉〈mrow〉〈mi〉T〈/mi〉〈/mrow〉〈mrow〉〈mi〉i〈/mi〉〈/mrow〉〈mrow〉〈mi〉I〈/mi〉〈/mrow〉〈/msubsup〉〈mspace width="0.25em"〉〈/mspace〉〈mi〉o〈/mi〉〈mi〉r〈/mi〉〈mspace width="0.25em"〉〈/mspace〉〈msubsup〉〈mrow〉〈mi〉T〈/mi〉〈/mrow〉〈mrow〉〈mi〉i〈/mi〉〈mo〉+〈/mo〉〈mn〉1〈/mn〉〈/mrow〉〈mrow〉〈mspace width="0.25em"〉〈/mspace〉〈mspace width="0.25em"〉〈/mspace〉〈mi〉I〈/mi〉〈/mrow〉〈/msubsup〉〈/mrow〉〈/math〉 and 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si8.gif" overflow="scroll"〉〈mrow〉〈msubsup〉〈mrow〉〈mi〉C〈/mi〉〈/mrow〉〈mrow〉〈mi〉i〈/mi〉〈/mrow〉〈mrow〉〈mi〉I〈/mi〉〈/mrow〉〈/msubsup〉〈mo〉⇒〈/mo〉〈msubsup〉〈mrow〉〈mi〉C〈/mi〉〈/mrow〉〈mrow〉〈mi〉i〈/mi〉〈mo〉+〈/mo〉〈mn〉3〈/mn〉〈/mrow〉〈mrow〉〈mi〉I〈/mi〉〈mi〉I〈/mi〉〈/mrow〉〈/msubsup〉〈/mrow〉〈/math〉 → 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si9.gif" overflow="scroll"〉〈mrow〉〈msubsup〉〈mrow〉〈mi〉T〈/mi〉〈/mrow〉〈mrow〉〈mi〉i〈/mi〉〈/mrow〉〈mrow〉〈mi〉I〈/mi〉〈/mrow〉〈/msubsup〉〈/mrow〉〈/math〉 or 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si10.gif" overflow="scroll"〉〈mrow〉〈msubsup〉〈mrow〉〈mi〉T〈/mi〉〈/mrow〉〈mrow〉〈mi〉i〈/mi〉〈mo〉+〈/mo〉〈mn〉1〈/mn〉〈/mrow〉〈mrow〉〈mspace width="0.25em"〉〈/mspace〉〈mi〉I〈/mi〉〈/mrow〉〈/msubsup〉〈/mrow〉〈/math〉. We proposed and examined two sequential twinning mechanisms, (i) emissary twinning disconnections at steps along twin boundary for the first case and (ii) shear transformation into the primary twin for the second case, based on dislocation theory and the deformation accommodation ability of the sequential {10〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈mover accent="true"〉〈mn〉1〈/mn〉〈mo〉¯〈/mo〉〈/mover〉〈/mrow〉〈/math〉2} twinning to the shear deformation of the primary/incoming twin. Crystal plasticity modelling is performed to calculate the local stress field associated with the proposed twinning mechanisms. The results demonstrate that the preferred twin variant observed in experiments has the maximum resolved shear stress among the six twin variants. Our work suggests that complicated twinning processes under shock loading obey crystallographic relations according to deformation accommodation ability. The findings from this study can be implemented into meso-/macro-scale crystal plasticity models for predicting mechanical behaviors and texture evolution of polycrystalline aggregates of hexagonal materials.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418309595-fx1.jpg" width="244" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 165〈/p〉 〈p〉Author(s): Xiaodong Tan, Dirk Ponge, Wenjun Lu, Yunbo Xu, Xiaolong Yang, Xi Rao, Di Wu, Dierk Raabe〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We applied a hot rolling direct quenching and partitioning (HDQ&P) process to a low-C low-Si Al-added steel and obtained a Q&P steel containing 40 vol % of ferrite. Microstructure characterization was performed by means of SEM, EBSD, TEM and XRD. Atomic-scale characterization of carbon partitioning among the phases was carried out by atom probe tomography (APT). The carbon distribution in the retained austenite and near the martensite/retained austenite interfaces was quantitatively analyzed to study its partitioning behavior. The macroscopic strain distribution evolution across the tensile sample surface was investigated using macro digital image correlation (DIC) analysis. Combining these results with joint micro-DIC and EBSD analysis during quasi in-situ tensile testing, we investigated the strain partitioning among the different phases and the TRIP effect. Coupling of these results enabled us to reveal the relation among carbon partitioning, strain partitioning and the TRIP effect. The large blocky retained austenite with a side length of about 300–600 nm located near the ferrite/martensite (F/M) interfaces has low stability and transforms to martensite during the early deformation stages, i.e. at average strain below 21%. The retained austenite films in the centers of the martensite regions are more stable. The carbon distribution in both, the martensite and the retained austenite are inhomogeneous, with 0.5–2.0 at. % in the martensite and 4.0–7.5 at. % in the retained austenite. Strong carbon concentration gradients of up to 1.1 at. %/nm were observed near the martensite/retained austenite interfaces. The large blocky retained austenite (300–600 nm in side length) near the F/M interfaces has 1.5–2.0 at. % lower carbon content than that in the narrow retained austenite films (20–150 nm in thickness). The ferrite is soft and deforms prior to the martensite. The strain distribution in ferrite and martensite is inhomogeneous, varying by up to 20% within the same phase at an average strain of about 20%. Ferrite deformation is the main origin of ductility of the material. The balance between ferrite fraction and martensite morphology controls the TRIP effect and its efficiency in reaching a suited combination of strength and ductility. Reducing the ferrite volume fraction and softening the martensite by coarsening and polygonization can enhance the strain carried by the martensite, thus promoting more retained austenite in the martensite regions enabling a TRIP effect. The enhancement of the TRIP effect and the decrease of the strain contrast between ferrite and martensite jointly optimize the micromechanical deformation compatibility of the adjacent phases, thus improving the material's ductility.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418309613-fx1.jpg" width="379" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 166〈/p〉 〈p〉Author(s): T. Müller, M.W. Kapp, A. Bachmaier, P. Felfer, R. Pippan〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A new ultrahigh-strength structure is created by severe plastic deformation of a martensitic 0.1 wt.-% C steel using high pressure torsion (HPT) at room temperature. Tensile tests reveal an ultimate tensile strength of 2.4 ± 0.1 GPa after an equivalent strain of ε〈sub〉vM〈/sub〉 = 7.5 – to our knowledge the highest tensile strength ever reported for a carbon steel with such low carbon content. During HPT, a lamellar microstructure is formed with decreasing lamellar spacing for increasing plastic strain. Micropillar compression tests give crucial insights into the mechanical properties, which are correlated to the deformation behavior of this material. Strong similarities compared to HPT-treated pearlitic steel are found in spite of the large differences concerning both carbon content and phase composition. The possibilities and limits of strength maximization in carbon steels are evaluated and discussed.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418309704-fx1.jpg" width="500" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 165〈/p〉 〈p〉Author(s): Sida Liu, Keke Chang, Stanislav Mráz, Xiang Chen, Marcus Hans, Denis Music, Daniel Primetzhofer, Jochen M. Schneider〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Metastable titanium aluminum nitride coatings are widely applied in cutting and forming applications. Although it is generally accepted that the phase formation of metastable TiAlN is governed by kinetic factors, modeling attempts today are based solely on energetics. In this work, the metastable phase formation of TiAlN is predicted based on one combinatorial magnetron sputtering experiment, the activation energy for surface diffusion, the critical diffusion distance, as well as thermodynamic calculations. The phase formation data obtained from further combinatorial growth experiments varying chemical composition, deposition temperature, and deposition rate are in good agreement with the model. Furthermore, it is demonstrated that a significant extension of the predicted critical solubility range is enabled by taking kinetic factors into account. Explicit consideration of kinetics extends the Al solubility limit to lower values, previously unobtainable by energetics, but accessible experimentally.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418309467-fx1.jpg" width="398" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 166〈/p〉 〈p〉Author(s): Ellen L.S. Solomon, Anirudh Raju Natarajan, Arunabha Mohan Roy, Veera Sundararaghavan, Anton Van der Ven, Emmanuelle A. Marquis〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Alloying Mg with rare-earth elements, such as Nd, Gd, or Y, enables hardening from the precipitation of metastable coherent phases during aging at low temperatures. While the aging potential of binary Mg-Nd alloys is relatively limited due to the nucleation of coarse β〈sub〉1〈/sub〉 and β precipitates at the expense of the strengthening β‴ precipitates, binary Mg-Y alloys exhibit exceptional stability of the strengthening coherent β〈sub〉S〈/sub〉′ phase when aged at 200 °C. Through combination of high-resolution characterization, density functional theory calculations, and finite-element elasticity studies, we demonstrate that the strengthening β〈sub〉S〈/sub〉’ phase is thermodynamically stable at low temperatures (as opposed to metastable as in other Mg-RE binaries) and that misfit strains play a key role in not only controlling precipitate structure and morphology but also their unusual evolution into an interconnected network.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418309686-fx1.jpg" width="499" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 166〈/p〉 〈p〉Author(s): Masakazu Tane, Haruki Okuda, Fumihiko Tanaka〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Nanocomposite microstructures dominating the anisotropic elastic properties in carbon fibers were studied, to construct a micromechanics model that can explain the anisotropic elastic properties of carbon fibers. Aluminum-based composites containing five types of carbon fibers were prepared, and their anisotropic elastic properties were measured using resonant ultrasound spectroscopy combined with electromagnetic acoustic resonance. Then, all the independent elastic stiffness components of the carbon fibers were extracted from those of the composites using a composite model based on Eshelby's inclusion theory, Mori–Tanaka mean-field theory, and effective-medium approximation. Moreover, we newly developed a nanocomposite microstructure model that can fully reproduce all the anisotropic constants of carbon fibers exhibiting a wide variety of Young's moduli. In the developed model, the microstructures of carbon fibers were approximated as nanocomposites comprised of an amorphous carbon matrix and graphite-crystal inclusions that are aggregations of graphite nanocrystallites. Based on this nanocomposite microstructure model, the shape of the graphite-crystal inclusions and the elastic properties of the amorphous carbon matrix were analyzed, considering the volume fraction and orientation of the graphite nanocrystallites, as determined using X-ray diffraction. The analysis revealed that the shapes of the graphite-crystal inclusions are flat ellipsoids elongated along the fiber axis, and the aspect ratio of the graphite-crystal inclusions dominantly affects the anisotropy in the Young's modulus. This indicates that the graphite nanocrystallites are connected along the in-plane directions of the graphitic layers, and not the shape of nanocrystallites but their two-dimensional connectivity dominates the anisotropic elastic modulus in carbon fibers.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418309716-fx1.jpg" width="500" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 165〈/p〉 〈p〉Author(s): Binbin Jiang, Chunjin Chen, Xuelu Wang, Hao Wang, Weizhen Wang, Hengqiang Ye, Kui Du〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Interstitial compounds are widely used to improve stiffness, modulus, strength and wear resistance of alloys owing to their high strength and stiffness. Understanding defect evolution and phase transformation processes in interstitial compounds during deformation would therefore provide important guidance for further enhancement of alloy properties. Here, we observed and analyzed the various deformation-induced defects in an NbB crystal using aberration-corrected electron microscopy combined with density functional theory simulations. We identified stable defects such as stacking faults and deformation twins on {110} planes, and (020)[101] planar faults. The stability originates from preservation of the dodecahedron building blocks and B-B covalent bonds. In contrast for the case of (020)[100] planer faults, the crystal structure at planar faults is significantly altered and the B-B bonds are broken, resulting in a deformation-induced phase transition from NbB to Nb phase. These results provide insights on the deformation processes of complex interstitial compounds in general.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418309534-fx1.jpg" width="245" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 165〈/p〉 〈p〉Author(s): Deep Choudhuri, Bharat Gwalani, Stephane Gorsse, Mageshwari Komarasamy, Srinivas A. Mantri, Srivilliputhur G. Srinivasan, Rajiv S. Mishra, Rajarshi Banerjee〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Twinning is a key deformation mechanism in face-centered-cubic (fcc)-based and some body-centered-cubic (bcc)-based alloys, which imparts excellent strength-ductility combination by increasing strain-hardenability. Typically, twinning in fcc-based alloys increases when the stacking fault energy is lowered via changes in composition. The present study clearly demonstrates that deformation twinning can be enhanced when hard-intermetallic compounds like ordered B2 and sigma phases form in the fcc matrix of a high entropy alloy (HEA), leading to an excellent combination of strength, ductility, and strain-hardenability. Such a combination of properties was achieved by exploiting the novel and often unusual phase stability regimes that can be accessed in these complex concentrated HEAs. The present study exploits a unique three-phase mixture of recrystallized fine-grained fcc + B2 + sigma in a prototypical Al〈sub〉0.3〈/sub〉CoCrFeNi HEA to demonstrate this effect. Coupling transmission electron microscopy and molecular dynamics simulations revealed that B2 grains enhance deformation twinning by raising the local stress levels, consequently forming substantially thicker twins as compared to the single fcc-phase condition of Al〈sub〉0.3〈/sub〉CoCrFeNi. The local stresses were further accommodated via nano-twinning, limited B2 plasticity, and highly restricted micro-cracks in and around the sigma grains.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418309522-fx1.jpg" width="500" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 166〈/p〉 〈p〉Author(s): David Kleiven, Olve L. Ødegård, Kari Laasonen, Jaakko Akola〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The Cluster Expansion formalism based on Density Functional Theory (DFT) simulation data has been applied for Al〈img src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"〉Mg alloys with high accuracy (〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈mo〉∼〈/mo〉〈mn〉1〈/mn〉〈/mrow〉〈/math〉 meV/atom). The atomistic simulations are used to model the Al〈img src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"〉Mg phase diagram, phase boundaries and the initial solute clustering at different compositions and temperatures. The obtained free energies of formation for the FCC, HCP and 〈em〉γ〈/em〉-phase are in accordance with the experimental phase diagram. The calculations demonstrate the formation of Guinier-Preston (GP) zones of 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.gif" overflow="scroll"〉〈mrow〉〈msub〉〈mrow〉〈mtext〉Al〈/mtext〉〈/mrow〉〈mrow〉〈mn〉3〈/mn〉〈/mrow〉〈/msub〉〈mtext〉Mg〈/mtext〉〈/mrow〉〈/math〉 (L〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si3.gif" overflow="scroll"〉〈mrow〉〈msub〉〈mrow〉〈mn〉1〈/mn〉〈/mrow〉〈mrow〉〈mn〉2〈/mn〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉 phase) within the Al matrix under varying conditions. The computed transition temperatures where the ordered structures dissolve are approximately 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si4.gif" overflow="scroll"〉〈mrow〉〈mn〉50〈/mn〉〈mspace width="0.25em"〉〈/mspace〉〈mtext〉K〈/mtext〉〈/mrow〉〈/math〉 higher than experimental data. The free energy barriers associated with the formation of GP-zones increase as the solute (Mg) concentrations are reduced and the temperature is increased.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418310012-fx1.jpg" width="411" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 166〈/p〉 〈p〉Author(s): Cun-hong Yin, Yi-long Liang, Yu Liang, Wei Li, Ming Yang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Dry sliding wear tests of steel disks of various compositions were performed with consideration of the effects of microstructure, shear strain and shear strain rate using a ball-on-disk tester with a tungsten carbide ball under ambient atmosphere and room temperature. We found a severe–mild wear transition phenomenon, which we called self-lubrication, and categorized friction behavior into two regimes: a high-friction regime and a low-friction regime. However, self-lubrication occurs only at specific strain levels and rates related to materials with martensite and pearlite structures. We characterized the microstructures of the worn surface, subsurface and matrix and found a thin self-lubricating layer composed of nano-oxide particles with sizes in the range 6–20 nm attached to the surface. The formation of these nano-oxide particles is controlled by lamellar structure (martensite or pearlite) nano-lamination, oxidation and solid-state amorphization during dry sliding. The high density of geometrically necessary dislocations and defects induced by plastic deformation under wear shear strain levels and rates is important in the formation of nano-lamellar microstructures and amorphous oxide. These results both clarify nano-lamellar microstructure solid-state amorphization and oxidation behavior and reveal the mechanism of self-lubricating layer formation observed in this work.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418310000-fx1.jpg" width="487" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 166〈/p〉 〈p〉Author(s): Siddharth Gupta, Adele Moatti, Anagh Bhaumik, Ritesh Sachan, Jagdish Narayan〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Localized charge injection by formation of vacancies provides an attractive platform for the development of multifunctional nanomaterials with direct implications in spintronics. However, further progress in spintronics critically depends on a deeper understanding of polaronic interactions between the localized charge states. This report is focused on TiN metallic system, which exhibits Pauli paramagnetism due to the absence of unpaired localized spin states. Here, nitrogen vacancies (V〈sub〉N〈/sub〉) are used as a variable to tune the magnetic properties of epitaxial TiN thin films by thermal annealing in high-vacuum and N〈sub〉2〈/sub〉 environment. Systematic introduction of V〈sub〉N〈/sub〉 generates robust magnetic ordering in vacuum-annealed TiN〈sub〉1-x〈/sub〉 films, with Curie temperature (〈em〉T〈/em〉〈sub〉〈em〉C〈/em〉〈/sub〉) ∼700 K, and saturation magnetization (〈em〉M〈/em〉〈sub〉〈em〉s〈/em〉〈/sub〉) at absolute zero of 13.6 emu g〈sup〉−1〈/sup〉. The signature spin-glass behavior below the irreversibility temperature (〈em〉T〈/em〉〈sub〉〈em〉ir〈/em〉〈/sub〉 ∼40 K) indicates the Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling interactions between the unpaired localized spin-states. Through spatially resolved electron energy-loss spectroscopy, we have determined the generation of unpaired localized spins at Ti〈sup〉+2〈/sup〉 polarons with ∼12 ± 2 at.% V〈sub〉N〈/sub〉 in TiN〈sub〉1-x〈/sub〉 films. Such a large concentration of V〈sub〉N〈/sub〉 results in increased spin stiffness and high 〈em〉T〈/em〉〈sub〉〈em〉C〈/em〉〈/sub〉. These findings open a definitive pathway for tuning the magnetic nature of metallic materials for spintronic applications.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418309923-fx1.jpg" width="422" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 166〈/p〉 〈p〉Author(s): Jiang Yi, Yanlin Jia, Yuyuan Zhao, Zhu Xiao, Kejian He, Qi Wang, Mingpu Wang, Zhou Li〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Cu〈img src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"〉Ni〈img src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"〉Si alloys have been widely applied in electronic and electrical industries. The precipitation behavior of some of the Cu〈img src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"〉Ni〈img src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"〉Si alloys is still not well understood. In this study, the precipitation behavior of the Cu-3.0Ni-0.72Si alloy aged at 600 °C for different times was investigated by transmission electron microscopy, atom probe tomography and phenomenological theory of precipitation crystallography. A new orientation relationship (OR) between the precipitates and the Cu matrix was found in the over-aged condition and a coarsening mechanism of the metastable precipitates was put forward. The two- and three-dimension invariant line theories were successfully applied in interpreting the evolution of the ORs and the morphologies in the Cu/δ-Ni〈sub〉2〈/sub〉Si (Cu/δ) system. At the early stage of aging, the fine metastable δ’-(Cu, Ni)〈sub〉2〈/sub〉Si precipitates are coherent with the Cu matrix, with a quasi-Bain OR of (110)〈sub〉Cu〈/sub〉||(100)〈sub〉δ′〈/sub〉 and [001]〈sub〉Cu〈/sub〉||[001]〈sub〉δ′〈/sub〉, and four pairs of parallel conjugate planes: (〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si91.gif" overflow="scroll"〉〈mrow〉〈mover accent="true"〉〈mrow〉〈mn〉1〈/mn〉〈/mrow〉〈mo stretchy="true"〉¯〈/mo〉〈/mover〉〈/mrow〉〈/math〉〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si91.gif" overflow="scroll"〉〈mrow〉〈mover accent="true"〉〈mrow〉〈mn〉1〈/mn〉〈/mrow〉〈mo stretchy="true"〉¯〈/mo〉〈/mover〉〈/mrow〉〈/math〉1)〈sub〉Cu〈/sub〉||(〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si93.gif" overflow="scroll"〉〈mrow〉〈mover accent="true"〉〈mrow〉〈mn〉3〈/mn〉〈/mrow〉〈mo stretchy="true"〉¯〈/mo〉〈/mover〉〈/mrow〉〈/math〉01)〈sub〉δ′〈/sub〉, (111)〈sub〉Cu〈/sub〉||(301)〈sub〉δ′〈/sub〉, (〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si91.gif" overflow="scroll"〉〈mrow〉〈mover accent="true"〉〈mrow〉〈mn〉1〈/mn〉〈/mrow〉〈mo stretchy="true"〉¯〈/mo〉〈/mover〉〈/mrow〉〈/math〉11)〈sub〉Cu〈/sub〉||(021)〈sub〉δ′〈/sub〉, and (1〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si91.gif" overflow="scroll"〉〈mrow〉〈mover accent="true"〉〈mrow〉〈mn〉1〈/mn〉〈/mrow〉〈mo stretchy="true"〉¯〈/mo〉〈/mover〉〈/mrow〉〈/math〉1)〈sub〉Cu〈/sub〉||(0〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si92.gif" overflow="scroll"〉〈mrow〉〈mover accent="true"〉〈mrow〉〈mn〉2〈/mn〉〈/mrow〉〈mo stretchy="true"〉¯〈/mo〉〈/mover〉〈/mrow〉〈/math〉1)〈sub〉δ’〈/sub〉. The precipitates have a δ-Ni〈sub〉2〈/sub〉Si structure, with some Ni atoms substituted by Cu atoms. During growth, the core region of the metastable δ’-(Cu,Ni)〈sub〉2〈/sub〉Si precipitate transforms into stable δ-Ni〈sub〉2〈/sub〉Si, with a quasi-NW OR of (〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si91.gif" overflow="scroll"〉〈mrow〉〈mover accent="true"〉〈mrow〉〈mn〉1〈/mn〉〈/mrow〉〈mo stretchy="true"〉¯〈/mo〉〈/mover〉〈/mrow〉〈/math〉11)〈sub〉Cu〈/sub〉||(021)〈sub〉δ〈/sub〉 and [110]〈sub〉Cu〈/sub〉||[100]〈sub〉δ〈/sub〉, while a layer of metastable δ’- (Cu, Ni)〈sub〉2〈/sub〉Si still exists around the core. With prolonging aging time, the δ-Ni〈sub〉2〈/sub〉Si precipitates with the OR of (〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si91.gif" overflow="scroll"〉〈mrow〉〈mover accent="true"〉〈mrow〉〈mn〉1〈/mn〉〈/mrow〉〈mo stretchy="true"〉¯〈/mo〉〈/mover〉〈/mrow〉〈/math〉11)〈sub〉Cu〈/sub〉||(021)〈sub〉δ〈/sub〉 and [110]〈sub〉Cu〈/sub〉||[100]〈sub〉δ〈/sub〉 grow two-dimensionally to form a plate-like shape, while those with the OR of (111)〈sub〉Cu〈/sub〉||(301)〈sub〉δ〈/sub〉 and [〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si91.gif" overflow="scroll"〉〈mrow〉〈mover accent="true"〉〈mrow〉〈mn〉1〈/mn〉〈/mrow〉〈mo stretchy="true"〉¯〈/mo〉〈/mover〉〈/mrow〉〈/math〉10]〈sub〉Cu〈/sub〉||[010]〈sub〉δ〈/sub〉 grow one-dimensionally to form a fiber-like shape.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418309984-fx1.jpg" width="441" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 166〈/p〉 〈p〉Author(s): Luchan Zhang, Yang Xiang, Jian Han, David J. Srolovitz〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉High-entropy alloys (HEAs), i.e., single-phase, (nearly) equiatomic multicomponent, metallic materials, are associated with novel mechanical properties, such as high strength, fracture resistance etc. In this paper, a stochastic Peierls-Nabarro (PN) model is proposed to understand how random site occupancy affects intrinsic strength. The stochastic PN model accounts for the randomness in the composition, characterized by both the standard deviation of the perturbation in the interplanar potential and the correlation length within the spatial compositional distribution. The model presented includes the effects of non-uniform compositional distribution both in the direction of dislocation glide and along a dislocation line to predict overall dislocation glide resistance. The model predicts the intrinsic strength of HEAs as a function of the standard deviation and the correlation length of the randomness. We find that, in most of the parameter space, the compositional randomness in an HEA gives rise to an intrinsic strength that far exceeds that of any of the pure metals from which the HEA is composed. This approach provides a fundamental explanation to the origin of the high strength of HEAs.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418309820-fx1.jpg" width="266" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 166〈/p〉 〈p〉Author(s): I.R. Souza Filho, A. Kwiatkowski da Silva, M.J.R. Sandim, D. Ponge, B. Gault, H.R.Z. Sandim, D. Raabe〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Austenite (γ) reversion in a cold-rolled 17.6 wt.% Mn steel was tracked by means of dilatometry and 〈em〉in-situ〈/em〉 magnetic measurements during slow continuous annealing. A splitting of the γ-reversion into two stages was observed to be a result of strong elemental partitioning between γ and α′-martensite during the low temperature stage between 390 and 575 °C. Atom probe tomography (APT) results enable the characterization of the Mn-enriched reversed-γ and the Mn-depleted remaining α′-martensite. Because of its lower Mn content, the reversion of the remaining α′-martensite into austenite takes place at a higher temperature range between 600 and 685 °C. APT results agree with partitioning predictions made by thermo-kinetic simulations of the continuous annealing process. The critical composition for γ-nucleation was predicted by thermodynamic calculations (Thermo-Calc) and a good agreement was found with the APT data. Additional thermo-kinetic simulations were conducted to evaluate partitioning-governed γ-growth during isothermal annealing at 500 °C and 600 °C. Si partitioning to γ was predicted by DICTRA and confirmed by APT. Si accumulates near the moving interface during γ-growth and homogenizes over time. We used the chemical composition of the remaining α′-martensite from APT data to calculate its Curie temperature (T〈sub〉Curie〈/sub〉) and found good agreement with magnetic measurements. These results indicate that elemental partitioning strongly influences not only γ-reversion but also the T〈sub〉Curie〈/sub〉 of this steel. The results are important to better understand the thermodynamics and kinetics of austenite reversion for a wide range of Mn containing steels and its effect on magnetic properties.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418309972-fx1.jpg" width="500" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 166〈/p〉 〈p〉Author(s): Jin Hyeok Choi, Min Chul Jo, Hyungsoo Lee, Alireza Zargaran, Taejin Song, Seok Su Sohn, Nack J. Kim, Sunghak Lee〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Austenitic high-Mn steels have been nominated as desirable ultra-high-strength cold-rolled steels whose mechanical properties are greatly improved by powerful deformation mechanisms of transformation- and twinning-induced plasticity (TRIP and TWIP). In this study, an austenitic high-Mn TRIP steel was suggested to achieve a good strength-ductility balance, and 1–2 wt.% Cu was added as an element for increasing stacking fault energy (SFE) as well as an austenite stabilizer to exploit a transition from TRIP to TWIP. The non-Cu-added steel showed the highest yield and tensile strengths (502 MPa and 1137 MPa, respectively) and the lowest elongation (34.6%) with a serrated flow. Yield and tensile strengths decreased with increasing Cu content, while the elongation was the highest in the 1%-Cu-added steel. TRIP and TWIP mechanisms showed good agreements with calculated SFEs in consideration of (Mn,Cu)-segregated bands. In the non-Cu-added steel, the TRIP occurred step by step as localized deformation bands passed through the specimen gage section to activate the serrated flow, which were reduced (or improved) by the transition from TRIP to TWIP with increasing Cu content. In the 1%-Cu-added steel, overall tensile properties were improved (yield strength; 461 MPa, tensile strength; 1093 MPa, elongation; 65.1%) as both TRIP and TWIP were well homogenized to produce synergic effects.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418309959-fx1.jpg" width="449" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 165〈/p〉 〈p〉Author(s): Peng Li, Yu Huan, Weiwei Yang, Fangyuan Zhu, Xiaolong Li, Xingmin Zhang, Bo Shen, Jiwei Zhai〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Lead-free piezoelectric ceramics are urgently needed in the field of electromechanical conversion devices due to the restriction on the use of lead-based ceramics. In this study, the polymorphic phase boundary (PPB) were tuned by incorporating different concentration of (Bi〈sub〉0.5〈/sub〉K〈sub〉0.5〈/sub〉)HfO〈sub〉3〈/sub〉 into the matrix (K〈sub〉0.5〈/sub〉Na〈sub〉0.5〈/sub〉)(Nb〈sub〉0.965〈/sub〉Sb〈sub〉0.035〈/sub〉)O〈sub〉3〈/sub〉〈img src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"〉CaZrO〈sub〉3〈/sub〉, and the 〈00〈em〉l〈/em〉〉〈sub〉c〈/sub〉 crystallographic texture was realized by templated grain growth method. The maximal 〈em〉d〈/em〉〈sub〉33〈/sub〉 (∼550 pC/N) and 〈em〉k〈/em〉〈sub〉p〈/sub〉 (∼72%) were achieved in the 〈00〈em〉l〈/em〉〉〈sub〉c〈/sub〉 textured ceramics with composition around rhombohedral-orthorhombic-tetragonal (R-O-T) phase boundary. It is proposed that the enhanced piezoelectricity should be ascribed to several combined effects, which primarily contain the R-O-T phase boundary facilitating polarization rotation, the crystallographic orientation induced intrinsic piezoelectric anisotropy, electric-field-induced lattice distortion and phase transitions, and NaNbO〈sub〉3〈/sub〉 seed-crystal-driven nanodomain structures. This work provides an effective solution to enhance piezoelectric properties by simultaneous tailoring polymorphic phase boundary and using crystallographic texture in potassium-sodium niobate based piezoelectric ceramics. We believe that the simple solution and design principle can also be applied to other piezoelectric ceramic systems, no matter lead-based or lead-free.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉Superior piezoelectric properties (〈em〉d〈/em〉〈sub〉33〈/sub〉∼550 pC/N, 〈em〉k〈/em〉〈sub〉p〈/sub〉∼72%) were achieved by simultaneous tailoring polymorphic phase boundary and using crystallographic texture in lead-free KNN-based piezoelectric ceramics. The excellent piezoelectric properties benefit mainly from crystallographic orientation induced intrinsic piezoelectric anisotropy, high polarization efficiency, electric-field-induced lattice distortion and NaNbO〈sub〉3〈/sub〉 seed-crystal-driven nanodomain structure. These piezoelectric properties in conjunction with high Curie temperature (〈em〉T〈/em〉〈sub〉c〈/sub〉∼256 °C) in KNN-based ceramics are comparable to that of commercial PZT ceramics.〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418309662-fx1.jpg" width="223" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 166〈/p〉 〈p〉Author(s): Emil Annevelink, Elif Ertekin, Harley T. Johnson〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We describe grain boundary structure and migration in graphene using the concept of dislocations in the displacement shift complete lattice. The equivalence of displacement shift complete lattice dislocations and grain boundary kinks in graphene is shown both topologically and energetically. Topologically, a grain boundary kink and a displacement shift complete lattice dislocation both translate the coincident site lattice. The energetic equivalence is established through comparison of atomistic and continuum elasticity models of metastable states to show that DSC dislocations are well-described by elasticity theory. The continuum results are fitted to the atomistic results with one adjustable parameter, the DSC dislocation core radius. The atomistic results reveal that low sigma boundaries have large energy barriers to grain boundary motion, which match continuum results obtained for smaller core radii dislocations. The larger energy barriers for low sigma boundaries are consistent with experimental results reporting isolated, low sigma boundaries in grown graphene. The trends in the dislocation Burgers vector and fitted core radii across grain boundaries of different misorientation are expressed in a unified model. The analysis provides a framework for understanding grain boundary motion in graphene and can serve as a basis for engineering the atomic structure of graphene.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418309728-fx1.jpg" width="479" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 166〈/p〉 〈p〉Author(s): Hamzeh Kashani, Mingwei Chen〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Dealloyed nanoporous metals are emerging as a new class of structural and functional materials for a wide range of applications. Nevertheless, the dealloying process usually leads to significant volume shrinkage, large internal stresses, surface oxidation, stress-corrosion cracking and thereby extensive fabrication flaws. This is particularly serious for nanoporous non-noble metals because of their high affinity with oxygen and resulting serious oxidation. Therefore, dealloyed nanoporous metals usually have poor mechanical performances, particularly, under tension which is highly sensitive to flaws. Consequently, high tensile strength has not been achieved from technically-important and economic nanoporous transition metals, such as Ni and Cu. In this study we report flaw-free nanoporous Ni fabricated by utilizing an ultrafine grained precursor alloy, high-temperature dealloying and post-dealloying annealing. The resulting nanoporous Ni shows an excellent tensile strength, which is one order of magnitude higher than all reported tensile strengths of dealloyed nanoporous metals. The strong and ductile nanoporous Ni developed in this study can be scaled up for large-scale structural and functional applications where tensile properties are required.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418310073-fx1.jpg" width="363" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 166〈/p〉 〈p〉Author(s): Luis A. Marqués, María Aboy, Manuel Ruiz, Iván Santos, Pedro López, Lourdes Pelaz〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉By using classical molecular dynamics simulations and a novel technique to identify defects based on the calculation of atomic strain, we have elucidated the detailed mechanisms leading to the anomalous generation and growth of {001} loops found after ultra-fast laser annealing of ion-implanted Si. We show that the building block of the {001} loops is the very stable Arai tetra-interstitial [N. Arai, S. Takeda, M. Kohyama, Phys. Rev. Lett. 78, 4265 (1997)], but their growth is kinetically prevented within conventional Ostwald ripening mechanisms under standard processing conditions. However, our simulations predict that at temperatures close to the Si melting point, Arai tetra-interstitials directly nucleate at the boundaries of fast diffusing self-interstitial agglomerates, which merge by a coalescence mechanism reaching large sizes in the nanosecond timescale. We demonstrate that the crystallization of such agglomerates into {001} loops and their subsequent growth is mediated by the tensile and compressive strain fields that develop concurrently around the loops. We also show that further annealing produces the unfaulting of {001} loops into perfect dislocations. Besides, from the simulations we have fully characterized the {001} loops, determining their atomic structure, interstitial density and formation energy.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418310036-fx1.jpg" width="369" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 166〈/p〉 〈p〉Author(s): Jose F. Gómez-Cortés, María L. Nó, Isabel Ruíz-Larrea, Tomasz Breczewski, Angel López-Echarri, Christopher A. Schuh, Jose M. San Juan〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Micro and nano pillars of Copper-based shape memory alloys (SMAs) with feature sizes between about 2 μm and 250 nm are known to exhibit ultra-high mechanical damping due to the nucleation and motion of stress-induced martensite interfaces during superelastic straining. While this behavior could be extremely useful to protect micro electro-mechanical systems (MEMS) against vibrations in aggressive environments, a fundamental question must yet be answered in order to envisage further applications, namely, whether this damping is reproducible and stable over long times and many cycles, or whether the damping is a signal of accumulating damage that could compromise long-term usage. In the present paper this crucial question is answered; we show that micropillar arrays of Cu-Al-Ni SMAs exhibit a completely recoverable and reproducible superelastic response, with an ultra-high damping loss factor η 〉 0.1, or even higher for sub-micrometer pillars, η 〉 0.2, even after thousands of cycles (〉5000) and after long times spanning more than four years. Furthermore, the first high-frequency tests on such nanoscale SMAs show that their superelastic response is very fast and relevant to ultra-high damping even at frequencies as high as 1000 Hz. This paves the way for the design of micro/nano dampers, based on SMAs, to improve the reliability of MEMS in noisy environments.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418309947-fx1.jpg" width="500" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 166〈/p〉 〈p〉Author(s): G. Rogl, K. Yubuta, V.V. Romaka, H. Michor, E. Schafler, A. Grytsiv, E. Bauer, P. Rogl〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉With a small gap in the density of states and a substantially semiconducting behavior half Heusler alloys have drawn attention as thermoelectric materials. For this study we have selected Hf-free compounds, Ti〈sub〉0.5〈/sub〉Zr〈sub〉0.5〈/sub〉NiSn, Ti〈sub〉0.5〈/sub〉Zr〈sub〉0.5〈/sub〉NiSn (with a densification aid (DA)) and Ti〈sub〉0.5〈/sub〉Zr〈sub〉0.5〈/sub〉NiSn〈sub〉0.98〈/sub〉Sb〈sub〉0.02〈/sub〉 as well their parent alloys TiNiSn and ZrNiSn as cheap thermoelectrics. Electrical resistivity, thermal conductivity and specific heat were evaluated below room temperature (4.2–300 K) in order to get insight into the mechanism of transport properties. SEM and TEM investigations as well as DFT (density functional theory) calculations accompany this research. The fine-grained epitaxial microstructure with a large number of dislocations warrants a low thermal conductivity at ultralow values (∼30 mW/cmK at 300 K) at a narrow band gap with a sufficiently high density of states at the Femi level. High order of components mixing strongly affects the stability of the solid solutions by the configuration entropy term, which causes a shrinkage of the miscibility gap. For the electronic density of states (DOS) the split Zr band and impurity Ni band induce a significant reduction of the effective energy gap and thus explain n-type of conductivity of the compounds and solid solutions studied.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418309935-fx1.jpg" width="480" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 166〈/p〉 〈p〉Author(s): R. Kumar, J. Villanova, P. Lhuissier, L. Salvo〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Cavity growth during high temperature deformation has been extensively studied theoretically, but experimental investigation of nucleation and early stages of growth has been limited. In this work, 〈em〉in situ〈/em〉 nanotomography investigation of cavity nucleation and growth during high temperature deformation (7.9 MPa, 698 K), has been carried out in Al −3.6 wt% Cu alloy. This model alloy allows controlled generation of second phase particles to promote cavity nucleation and has hence been chosen for the study. Fast 3D imaging using synchrotron X-Rays with 100 nm pixel size and scan time of 7 s has been done to track nucleation and volumetric growth of individual cavities during deformation. Using this, change in shape of cavities with straining has been studied. Also, the change of volumetric cavity growth rate vs equivalent radius of individual cavities has been compared to existing models of cavity growth by diffusion and plasticity. It was seen that several pre-existing porosities were present in the alloy, while very few cavity nucleations were observed. The experimental data of growth rate matched well with the studied models and it was concluded that cavities initially grew by diffusion, while the growth mechanism changed to plasticity near failure.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418309625-fx1.jpg" width="500" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 166〈/p〉 〈p〉Author(s): Chu Lun Alex Leung, Sebastian Marussi, Michael Towrie, Robert C. Atwood, Philip J. Withers, Peter D. Lee〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Understanding defect formation during laser additive manufacturing (LAM) of virgin, stored, and reused powders is crucial for the production of high quality additively manufactured parts. We investigate the effects of powder oxidation on the molten pool dynamics and defect formation during LAM. We compare virgin and oxidised Invar 36 powder under overhang and layer-by-layer build conditions using 〈em〉in situ〈/em〉 and 〈em〉operando〈/em〉 X-ray Imaging. The oxygen content of the oxidised powder was found to be 〈em〉ca.〈/em〉 6 times greater (0.343 wt.%) than the virgin powder (0.057 wt.%). During LAM, the powder oxide is entrained into the molten pool, altering the Marangoni convection from an inward centrifugal to an outward centripetal flow. We hypothesise that the oxide promotes pore nucleation, stabilisation, and growth. We observe that spatter occurs more frequently under overhang conditions compared to layer-by-layer conditions. Droplet spatter can be formed by indirect laser-driven gas expansion and by the laser-induced metal vapour at the melt surface. Under layer-by-layer build conditions, laser re-melting reduces the pore size distribution and number density either by promoting gas release from keyholing or by inducing liquid flow, partially or completely filling pre-existing pores. We also observe that pores residing at the track surface can burst during laser re-melting, resulting in either formation of droplet spatter and an open pore or healing of the pore via Marangoni flow. This study confirms that excessive oxygen in the powder feedstock may cause defect formation in LAM.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉Using a laser additive manufacturing process replicator with 〈em〉in situ〈/em〉 and 〈em〉operando〈/em〉 X-ray imaging (a) permits capturing the formation of (b) porosity and (c) spatter during laser-matter interaction. In addition, we performed post mortem X-ray computed tomography analysis (d) reveal two types of pores inside the melt track: (i) open pores and (ii) closed pores.〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418309698-fx1.jpg" width="500" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 166〈/p〉 〈p〉Author(s): Zhifeng Huang, Fei Chen, Qiang Shen, Lianmeng Zhang, Timothy J. Rupert〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Most research on nanocrystalline alloys has been focused on planned doping of metals with other metallic elements, but nonmetallic impurities are also prevalent in the real world. In this work, we report on the combined effects of metallic dopants and nonmetallic impurities on grain boundary energy and strength using first-principles calculations, with a Σ5 (310) grain boundary in Cu chosen as a model system. We find a clear correlation between the grain boundary energy and the change in excess free volume of doped grain boundaries. A combination of a larger substitutional dopant and an interstitial impurity can fill the excess free volume more efficiently and further reduce the grain boundary energy. We also find that the strengthening effects of dopants and impurities are dominated by the electronic interactions between the host Cu atoms and the two types of dopant elements. For example, the significant competing effects of metal dopants such as Zr, Nb, and Mo with impurities on the grain boundary strength are uncovered from the density of states of the 〈em〉d〈/em〉 electrons. As a whole, this work deepens the field's understanding of the interaction between metallic dopants and nonmetallic impurities on grain boundary properties, providing a guide for improving the thermal stability of materials while avoiding embrittling effects.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418309819-fx1.jpg" width="330" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 165〈/p〉 〈p〉Author(s): E. Francis, R. Prasath Babu, A. Harte, T.L. Martin, P. Frankel, D. Jädernäs, J. Romero, L. Hallstadius, P.A.J. Bagot, M.P. Moody, M. Preuss〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Detailed analysis was carried out on proton and a neutron irradiated Nb-containing Zr-alloy to study the evolution of dislocation loop size and densities as well as the formation and evolution of irradiation-induced precipitation/clustering. The results obtained here have been contrasted against previously published work on a Nb-free Zr-alloy [1, 2] to investigate the mechanistic reason for the improved resistance to irradiation-induced growth of Nb-containing Zr alloys. The combined use of bright field scanning transmission electron microscopy, ultra-high-resolution energy dispersive spectroscopy and atom probe tomography analysis provides evidence of evenly distributed radiation-induced Nb clusters that have formed during the early stage of proton irradiation and Fe-rich nano-rods near Fe-containing second phase particles. The former seems to have a profound effect on 〈a〉 loop and subsequent 〈c〉 loop formation, keeping 〈a〉 loop size small but number density high while 〈c〉 loops seem to initially form at similar dose levels compared to a Nb-free alloy but 〈c〉 loop line density does not increase during further irradiation. It is hypothesized that the formation of the Nb nano-precipitates/clusters significantly hinders mobility and growth of 〈a〉 loops, resulting in a small size, high number density and limited ability of 〈a〉 loops to arrange along basal traces compared to Nb-free Zr-alloys. It is suggested that it is the limited 〈a〉 loop arrangement that slows down 〈c〉 loop formation and the root cause for the high resistance of Nb-containing Zr-alloys to irradiation-induced growth.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418309637-fx1.jpg" width="250" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia, Volume 165〈/p〉 〈p〉Author(s): Nathan Beets, Diana Farkas, Sean Corcoran〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We report a series of atomistic virtual mechanical tests on digitally created samples of nanoporous gold with 60% porosity, and average ligament diameters varying from 5.5 nm to 14.4 nm. Corresponding tests were also conducted for nanowires of equivalent surface to volume ratio and crystalline orientation. The validity of the Gibson-Ashby (G-A) scaling relations for the elastic and plastic behavior of the NP-Au structures is discussed. Tension/compression asymmetry in the plastic behavior was observed in both the nanoporous samples as well as the nanowires. Consistent with previous experimental and computational studies, the asymmetry becomes increasingly evident for the smaller ligament diameters, clearly pointing to capillary effects for large surface to volume ratios. Based on the present simulation results, a simple analytical model is presented for predicting the tension/compression asymmetry. The effects of internal ligament stresses on the deformation mechanisms and dislocation activity in the NP-Au structures are also discussed.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645418309480-fx1.jpg" width="500" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉