ALBERT

Description: High-entropy alloys (HEAs) are a class of alloys that are being considered for a number of applications. In the present study, the microstructures and 1050°C oxidation behaviors of two HEAs, Al 10 Cr 22.5 Co 22.5 Ni 22.5 Fe 22.5 (at.%) and Al 20 Cr 25 Co 25 Ni 25 Si 5 have been investigated along with Al 15 Cr 10 Co 35 Ni 35 Si 5 , which is a high-temperature shape-memory alloy. Oxide formation occurred via selective oxidation in a manner that was consistent with the oxide formation model devised by Giggins and Pettit for model Ni-Cr-Al alloys. The lower Al content alloy formed an external Cr 2 O 3 scale and an internal subscale consisting of Al 2 O 3 and AlN precipitates. The higher Al content alloys exhibited smaller mass gains and formed external Al 2 O 3 scales without any internal oxidation of the alloys.

Description: Integrated computational materials engineering approaches to alloy development leverage the hierarchical, interconnected nature of materials systems to rapidly optimize material performance. Particular emphasis is placed on the use of predictive models and simulation tools to elucidate fundamental relationships within the processing-structure-processing materials paradigm. For the current work, computational simulation results were used in combination with mechanistic, science-based models to assist alloy design. Two case studies are presented as illustrative examples that focus on high-temperature magnesium (Mg) alloy development. Solid solution strengthening potency and solute-based effects on creep rate were discussed in the first case study to guide strategies for solute selection in alloy development. This analysis was completed through the identification of composition-sensitive microstructural parameters that were subsequently evaluated in a predictive fashion. The second case study used computational thermo-kinetic simulations to evaluate Mg alloy precipitate systems for their ability to nucleate a high number density of coarsening-resistant particles. This nucleation and growth analysis was then applied to a Mg-Sn-Al alloy to highlight the utility of the current methodology in predicting multicomponent alloy precipitation behavior. This paper ultimately seeks to provide insight into an integrative approach that captures the important underlying material physics through relationships parameterized by descriptive thermodynamic and kinetic factors, where these factors can be readily calculated with a commercially available suite of computational tools in concert with accessible data in the literature.

Description: After the post heat-treatment (PHT) process of powder metallurgy carbon nanotubes (CNT)/Al composites, micro-cracks were observed in the composites, leading to greatly degraded mechanical properties. To understand and suppress the crack formation, an in situ observation of CNT/Al composites was performed at elevated temperatures. PHT was also applied to various bulk pure Al and CNT/Al composites fabricated under different processes. It was observed that the composites consolidated by hot-extrusion might form micro-cracks, but those consolidated by spark plasma sintering (SPS) showed no crack after PHT. A high-temperature SPS process before hot-extrusion was effective to prevent crack formation. The release of residual stress in severe plastic deformed (SPD) materials was responsible for the cracking phenomena during the PHT process. Furthermore, a good particle bonding was essential and effective to suppress cracks for SPD materials in the PHT process.

Description: Physical and statistical models are combined to describe and design magnesium and high entropy alloys. A principal component analysis is applied to merge material datasets, and it is shown that limits in properties can be envisaged. Extrapolation techniques can be employed to devise properties of non-existing alloys, such as specific heat capacity, melting point and Young’s modulus. These in turn can be input to physical models to predict, for example, yield strength and modulus of toughness. The tools described herein can readily be used for materials discovery, and are being implemented in the Accelerated Metallurgy project.

Description: In this article, we study the physical and mechanical properties of lutetium, which will be compared with the elements of the third-row transition metals (Cs, Ba, Hf, Ta, W, Re, Os, Ir, Pt, Au, Tl, Pb, and Bi). Data mining is an ideal approach for analyzing the information and exploring the hidden knowledge among the data. The purpose of the data mining scheme is to identify and classify the effects of the relationships existing between properties. The results of the investigation are presented by means of multivariate modeling methods, such as the principal component analysis and the partial least squares regression to discover the implicit, yet meaningful, relationship between the elements of the data set, and to locate correlations between the properties of the materials. In this study, we present a data mining approach to discover such unusual correlations between properties of the elements. When comparing the properties of the transition metals with those of lutetium, our results show that lutetium shares many properties and similarities with the transition metals of the sixth row in the periodic table and can be well described as a transition metal.

Description: Graphene is a two-dimensional nanomaterial that has unique electrical, mechanical, thermal, and optical properties. For realizing the practical applications of graphene, one of the major challenges lies in cost-effective production of graphene-based nanomaterials at a large scale. Significant research efforts have been demonstrated in regard to scalable manufacturing of graphene and show strong potential for their commercialization and industrialization. Here, we review the state-of-the-art techniques developed for the scalable production of graphene. This review mainly discusses the top-down techniques including exfoliation of bulk graphite and chemical reduction of graphene oxide. Critical comparison for graphene quality, structure, and yields for different techniques is discussed and specific examples are described in detail.

Description: Graphene is critical for applications in electronics, optical devices, thermal management, energy, and biosystems, while at the same time cost-effective and large-scale production of graphene is a challenge. In this regard, vapor phase graphene synthesis is a bottom-up approach, which could be compatible with device industry fabrication methods. Here, we review the state-of-the-art techniques developed for the scalable production of graphene in bottom-up approaches. These mainly include the epitaxial growth and chemical vapor deposition methods. Product quality, structure, and yields for different graphene growth techniques are discussed and specific examples are described. The article also emphasizes promising methods for scalable graphene production but still needing a deeper research understanding.

Description: Molecular vibrational spectroscopy is an important method to study the atomic structure of graphene oxide. To investigate the effect of oxidation on the structural and spectroscopic properties of graphene, pseudo-potential density functional theory calculations were applied. Several models were considered, covering the most relevant functional groups that have been postulated to decorate the surface of graphene layer on carbon materials. Different arrangements of these units produced a range of vibrational spectra. The results suggested the possibility of creating and tuning graphene’s spectroscopic properties by varying the oxidation levels and the relative position of epoxy and hydroxyl functional groups on the surface. Spectra characteristics for local structures from this work shed light on the structural and vibrational properties of graphene oxide, which could be very helpful for experimental groups to further understand the structure of graphene oxide and reduce graphene oxide.

Description: Increasing the efficiency of natural gas reciprocating engines will require materials with better mechanical and corrosion resistance at high temperatures. One solution to increase the lifetime of exhaust valves is to apply an aluminide coating to prevent corrosion assisted fatigue cracking, but the impact of the coating on the valve material mechanical properties needs to be assessed. In addition to cyclic oxidation testing in dry and humid air at 800°C, creep and high cycle fatigue (HCF) testing were conducted at 816°C on bare and slurry or pack-coated 31V alloy. The coated and bare creep specimens exhibited very similar creep rupture lives, as long as the specimens were annealed according to the 31V standard heat treatment before testing. The HCF behavior of the pack-coated alloy was close to the behavior of the bare alloy, but fatigue lifetimes of slurry-coated 31V specimens had higher variability. Aluminide coatings have the potential to improve the valve performance at high temperature, but the coating deposition process needs to be tailored for the substrate standard heat treatment.

Description: Recent research on ancient ferrous artefacts belonging to different historical periods has indicated significant differences in various parameters characterizing the slags entrapped in these artefacts, in cases where they were obtained by using different production methods. Such differences have been observed by comparing “ancient period” artefacts with “subsequent period” artefacts. “Ancient period” products were obtained by direct reduction of iron ore, without carburizing and at temperatures below the melting point of the reduced sponge iron. In the “subsequent period”, the indirect process started to be introduced, with the production, in a first reduction stage, of a liquid cast iron that had to be converted to wrought iron during a second fining operation. The understanding of the characterizing parameters of the slags has in fact progressed to the point where they represent a useful tool not only for inferring the origins of the starting ore but also for distinguishing between direct or indirect production. In the present research work, an accurate study of the entrapped slags has been carried out on an artefact from the Val Gabbia III site, identified in previous studies as a miner’s chisel. This study aims to carry out further metallurgical investigation into the miner’s chisel microstructure and the entrapped slags in order to help ascertain which production method was in use at the Val Gabbia III site; in fact, based on the intrinsic characteristics of the chisel, and the fact that the site where it was found, i.e. layers of the V–VI cent AD in Val Gabbia III site, was characterized by the presence of an almost 3.5 kg cast iron block, previous investigators were led to suppose that it may be a very early site of indirect iron smelting. While the slag characterizing parameters obtained in the present investigation appear to be consistent with published results related to the direct method, the discussion on the relationship between the indirect method production effects on entrapped slag and the experimental findings substantiate, although not definitively, the hypothesis that the production method of the miner’s chisel is indirect.

Description: Integrated computational materials engineering (ICME) approaches to composition and thickness profiles of sputtered thin-film samples are the key to expediting materials exploration for these materials. Here, an ICME-based semi-empirical approach to modeling the thickness of thin-film samples deposited via magnetron sputtering is developed. Using Yamamura’s dimensionless differential angular sputtering yield and a measured deposition rate at a point in space for a single experimental condition, the model predicts the deposition profile from planar DC sputtering sources. The model includes corrections for off-center, tilted gun geometries as well as shadowing effects from gun chimneys used in most state-of-the-art sputtering systems. The modeling algorithm was validated by comparing its results with experimental deposition rates obtained from a sputtering system utilizing sources with a multi-piece chimney assembly that consists of a lower ground shield and a removable gas chimney. Simulations were performed for gun-tilts ranging from 0° to 31.3° from the vertical with and without the gas chimney installed. The results for the predicted and experimental angular dependence of the sputtering deposition rate were found to have an average magnitude of relative error of  \( 4.14\% \pm 3.02\% \) for a 0°–31.3° gun-tilt range without the gas chimney, and \( 2.12\% \pm 1.71\% \) for a 17.7°–31.3° gun-tilt range with the gas chimney. The continuum nature of the model renders this approach reverse-optimizable, providing a rapid tool for assisting in the understanding of the synthesis-composition-property space of novel materials.

Description: We report a scalable manufacturing approach to produce nano-porous metal oxide films and the dopant variants using a block-copolymer template combined with a sol–gel solution processing approach. The refractive index of the film can be tailored to 1.2–2.4 by 3D nanostructuring in the sub-wavelength regime at scales of 20 nm or less. Based on this approach, this paper reports the synthesis of nanoporous palladium (Pd)-doped titanium dioxide (TiO 2 ) film with refractive index matching the optical fiber material, and its importance on D-shaped fiber Bragg grating for hydrogen sensing at extremely high temperature up to 700°C. The sensor is based on evanescent field interaction in hydrogen-sensitive cladding. The flat side of D-shaped fiber grating was etched to remove a residual 4 μm cladding material, and thermally stabilized for high-temperature requirements. The peak intensity change of the fiber Bragg wavelength was observed with different hydrogen concentrations from 0.25 vol.% H 2 /N 2 to 5 vol.% H 2 /N 2 . The experimental result shows that the sensor’s hydrogen response is reversible and fast. The response time of the hydrogen sensor is 〈8 s.

Description: Phase-field crystal (PFC) is a model with atomistic-scale details acting on diffusive time scales. PFC uses the density field as its order parameter, which takes a constant value in the liquid phase and a periodic function in the solid phase. PFC naturally takes into account elasticity, solid–liquid interface free energy, surface anisotropy, and grain boundary free energy by using this single-order parameter in modeling of coexisting solid–liquid structures. In this article, the recent advancements in PFC modeling of materials nanostructures are reviewed, which includes an overview of different PFC models and their applications, and the numerical algorithms developed for solving the PFC governing equations. A special focus is given to PFC models that simulate coexisting solid–liquid structures. The quantitative PFC models for solid–liquid structures are reviewed, and the methods for determining PFC model parameters for specific materials are described in detail. The accuracy of different PFC models in calculating the solid–liquid interface properties is discussed.

Description: One key aspect of any integrated computational materials engineering approach is the integration of experiments that provide critical information for the modeling activities. This article describes, using case studies, three examples of critical experiments that have been conducted in an integrated fashion with modeling activities for titanium alloys, providing valuable information in an accelerated manner. The first has been used to identify key microstructural features associated with fracture toughness in Ti-6Al-4V and integrates artificial neural networks and various experimental techniques. The second is associated with defect accumulation in highly constrained titanium structures and integrates a highly innovative characterization technique (precession electron diffraction) and dislocation dynamics. The third is a high-throughput combinatorial technique to understand the oxidation behavior of titanium alloys and couples the experimental effort with the CALPHAD approach.

Description: This article reflects on the presentations made during the Metal and Polymer Matrix Composites symposium at Materials Science and Technology 2013 (MS&T’13) held in Montreal (Quebec, Canada) from October 27 to 31. The symposium had three sessions on metal matrix composites and one session on polymer matrix composites containing a total of 23 presentations. While the abstracts and full-text papers are available through databases, the discussion that took place during the symposium is often not captured in writing and gets immediately lost. We have tried to recap some of the discussion in this article and hope that it will supplement the information present in the proceedings. The strong themes in the symposium were porous composites, aluminum matrix composites, and nanocomposites. The development of processing methods was also of interest to the speakers and attendees.

Description: This scientific investigation on metal artwork is meant to expand knowledge regarding the technical skills developed by artists in sculpture manufacturing. Moreover all the gathered data support the speculation about the motivations behind the choices of certain material or a specific manufacturing method (e.g., economic or technical reasons, or both). The subject of this study is the Virtues sculptural group made at the end of the XVI century by Giambologna to decorate the Grimaldi Chapel in the church of San Francesco di Castelletto (Genoa, Italy). Six life-size statues depicting Charity, Justice, Hope, Fortitude, Faith, and Temperance (i.e., the artwork discussed in this article); seven bas-reliefs; and six winged representations of putti are what remains of the original monumental project. X-ray fluorescence, a nondestructive investigation method, was applied to determine the chemical nature of the metallic substrate and of the “artistic” and natural patinas. The achieved results allowed for distinguishing variations in the content of the major alloying elements that might correspond to a motivated will of the artist connected to technical and aesthetic aims: the production of defect-free and golden bronze artifacts.

Description: Induction sintering was developed as an alternative method to conventional sintering to sinter iron-based powder metal (PM) compacts. Several compositions of compact such as pure iron, 3 wt.% copper mixed iron, or 3 wt.% bronze mixed iron were sintered by using induction sintering machines with 12 kW power and 30 kHz frequency. The mechanical properties, microstructural properties, densities, and microhardness values were investigated for both processes. Iron-based PM compacts sintered at 1120°C by induction in 8.33 min (500 s) were found to be similar to those sintered conventionally in 30 min. The results were compared with the experimental studies.

Description: Shredder residue is the by-product remaining after ferrous and nonferrous metals have been recovered from the processing of vehicles, white goods, and peddler scrap. Shredder residue consists of glass, plastics, rubber, dirt, and small amounts of metal. It is estimated that 5–7 million tons of this shredder residue are landfilled each year in the United States. Technical advancements, coupled with European Union directives and the economic climate, have transformed the recycling of shredder residue in Europe. In the United States, however, regulatory controls and the cheap cost of landfill have worked against the advancement of recycling and recovery of this resource. The Argonne National Laboratory, which is funded by the U.S. Department of Energy, has investigated the effectiveness of recycling shredder residue into polymers. Other research has examined the use of shredder residue in waste-to-energy applications. To improve our ability to process and recycle shredder residue, an investigation of the regulatory, economic, and technological challenges was undertaken. The objective was to conduct a comprehensive review of work done to date, to document the composition of typical shredder output and to identify potential recoverable items (residual metals, plastics, rubber, foam, etc.). Along with uncovering potential new markets, the research would identify the technical, regulatory, and economic barriers to developing those markets.

Description: After more than 80 years of practical experience and despite many noted research efforts, theories that rigorously explained the formation of the silicon eutectic phases and the modification of the morphology of those phases by specific chemical additives remained elusive. Almost all papers related to the growth and modification of silicon in casting Al-Si alloys refer to the importance of twinning and a mechanism called a twin-plane reentrant edge. However, a review paper containing detailed information on how the parallel twins are formed in a crystal during melt growth, why the twins are generated parallel to each other, what is the prerequisite for growing a facetted dendrite, and how effective are various rare earth elements is missing in the literature. A comprehensive review is conducted on the models proposed for the flaky silicon growth including twin-plane reentrant edge and the models proposed for eutectic modification: impurity induced twinning and restricted growth theory. Furthermore, the papers with focus on modifying efficiency of the rare-earth metals have been reviewed.

Description: Commercial nuclear energy has been used for over 6 decades; however, to date, none of the 30+ countries with nuclear power has opened a repository for high-level waste (HLW). All countries with nuclear waste plan to dispose of it in metallic containers located in underground geologically stable repositories. Some countries also have liquid nuclear waste that needs to be reduced and vitrified before disposition. The five articles included in this topic offer a cross section of the importance of alloy selection to handle nuclear waste at the different stages of waste processing and disposal.

Description: This article deals with the development of fine-grained high-strength low-alloy (HSLA) magnesium alloys intended for use as biodegradable implant material. The alloys contain solely low amounts of Zn and Ca as alloying elements. We illustrate the development path starting from the high-Zn-containing ZX50 (MgZn5Ca0.25) alloy with conventional purity, to an ultrahigh-purity ZX50 modification, and further to the ultrahigh-purity Zn-lean alloy ZX10 (MgZn1Ca0.3). It is shown that alloys with high Zn-content are prone to biocorrosion in various environments, most probably because of the presence of the intermetallic phase Mg 6 Zn 3 Ca 2 . A reduction of the Zn content results in (Mg,Zn) 2 Ca phase formation. This phase is less noble than the Mg-matrix and therefore, in contrast to Mg 6 Zn 3 Ca 2 , does not act as cathodic site. A fine-grained microstructure is achieved by the controlled formation of fine and homogeneously distributed (Mg,Zn) 2 Ca precipitates, which influence dynamic recrystallization and grain growth during hot forming. Such design scheme is comparable to that of HSLA steels, where low amounts of alloying elements are intended to produce a very fine dispersion of particles to increase the material’s strength by refining the grain size. Consequently our new, ultrapure ZX10 alloy exhibits high strength (yield strength R p  = 240 MPa, ultimate tensile strength R m  = 255 MPa) and simultaneously high ductility (elongation to fracture A  = 27%), as well as low mechanical anisotropy. Because of the anodic nature of the (Mg,Zn) 2 Ca particles used in the HSLA concept, the in vivo degradation in a rat femur implantation study is very slow and homogeneous without clinically observable hydrogen evolution, making the ZX10 alloy a promising material for biodegradable implants.

Description: In this article, the surface characterization of graphite-based coatings deposited on metallic substrates at ambient temperature via a modified micro-blasting process technique named CoBlast™ is reported. The coated metals were characterized using scanning electron microscopy, energy-dispersive x-ray spectroscopy, x-ray diffractometer, and x-ray photoelectron spectroscopy. Surface roughness and contact angles were also evaluated. The results showed that the coated layer irrespective of the substrate type was hydrophobic and consisted of graphite, the grit material, and surface oxides, while surface roughness values varied from one substrate to the other. Implications of the resulting surface properties in relation to wear and corrosion applications are highlighted.

Description: Diamond/metal composites are very attractive materials for electronics because their excellent thermal properties make them suitable for use as heat sink elements in multifunctional electronic packaging systems. To enlarge the potential applications of these composites, current efforts are mainly focused on investigating different ways to improve the contact between metal and diamond. In the present work, a theoretical study has been carried out to determine the differences between the interfacial thermal conductance of aluminum/diamond and aluminum/graphite interfaces. Additionally, diamond particles were surface modified with oxygen to observe how it affects the quality of the diamond surface. The characterization of the surface of diamonds has been performed using different surface analysis techniques, especially x-ray photoelectron spectroscopy and temperature-programmed desorption.

Description: All materials (including conductors) possess the so-called quantum capacitance, which is present in series with the traditional geometric (electrostatic) capacitance. It is usually a large positive quantity and therefore irrelevant for most materials except for nanostructures. Quantum capacitance has been found to reduce the overall capacitance of nanostructures compared with what is predicted by classical electrostatics. One of many tantalizing recent physical revelations about quantum capacitance is that it can posses a negative value, hence, allowing for the possibility of enhancing (sometimes dramatically) the overall capacitance in some particular material systems—beyond the scaling predicted by classical electrostatics. We provide here a short overview of this subject and review some recent developments.

Description: Hierarchically organized nanostructures were fabricated by growing SnO 2 nanoparticles on a fluorine-doped tin oxide/glass substrate via a laser ablation method. Cauliflower-like clusters consisting of agglomerated nanoparticles were deposited and aligned with respect to the substrate with a large internal surface area and open channels of pores. The morphological changes of SnO 2 nanostructured films were investigated as a function of the oxygen working pressure in the range of 100–500 mTorr. A nanostructured scaffold prepared at an oxygen working pressure of 100 mTorr exhibited the best photoelectrochemical (PEC) performance. A Ti:Fe 2 O 3 -SnO 2 nanostructured photoanode showed the photocurrent that was 34% larger than that of a Ti:Fe 2 O 3 flat photoanode when the amount of Ti:Fe 2 O 3 sensitizer was identical for the two photoanodes. The larger surface area and longer electron lifetime of the Ti:Fe 2 O 3 -SnO 2 nanostructured photoanode explains its improved PEC performance.

Description: Previous studies indicated that the availability of mixed shredded aluminum scrap from end-of-life vehicles (ELV) is likely to surpass the capacity of secondary castings to absorb this type of scrap, which could lead to a scrap surplus unless suitable interventions can be identified and implemented. However, there is a lack of studies analyzing potential solutions to this problem, among others, because of a lack of component- and alloy-specific information in the models. In this study, we developed a dynamic model of aluminum in the global vehicle stock (distinguishing 5 car segments, 14 components, and 7 alloy groups). The forecasts made up to the year 2050 for the demand for vehicle components and alloy groups, for the scrap supply from discarded vehicles, and for the effects of different ELV management options. Furthermore, we used a source-sink diagram to identify alloys that could potentially serve as alternative sinks for the growing scrap supply. Dismantling the relevant components could remove up to two-thirds of the aluminum from the ELV stream. However, the use of these components for alloy-specific recycling is currently limited because of the complex composition of components (mixed material design and applied joining techniques), as well as provisions that practically prevent the production of safety-relevant cast parts from scrap. In addition, dismantling is more difficult for components that are currently penetrating rapidly. Therefore, advanced alloy sorting seems to be a crucial step that needs to be developed over the coming years to avoid a future scrap surplus and prevent negative energy use and emission consequences.

Description: Electrical resistance of polymer-supported thin metal films subjected to cyclic tensile loading typically is expected to grow with the cycle number due to fatigue-induced damage. Here it is demonstrated that electrical resistance can also decrease with the cycle number. Using electron backscatter diffraction analysis, it is shown that significant strain-induced, room-temperature grain coarsening is responsible for the resistance decrease. Grain coarsening has a vital effect on the electrical stability of metal films in a low-cycle fatigue regime.

Description: This study presents an overview of commonly used electronic materials and nanocoatings, as well as the evolution and significance of emissivity of commonly used electronic materials and nanocoatings. In addition, some key issues are addressed, such as accurate temperature measurements during materials processing and control as well as thermal management in high-power electronic device applications. Case studies of the optical properties of bulk materials, multilayered structures, and electronic devices, mainly bolometers, are discussed and analyzed for optimization.

Description: The radio frequency plasma synthesis of nitrogen clusters stabilized on carbon nanotube sheets has been demonstrated under various conditions. Characterization of the samples produced has been carried out using micro-Raman and attenuated total reflectance-Fourier transform infrared spectroscopy. Initial investigations of the sample morphologies and compositions have also been performed using scanning electron microscopy combined with energy-dispersive x-ray analysis and transmission electron microscopy. The spectroscopic results, together with density functional theory calculations, suggest that a linear chain nitrogen cluster is formed under the plasma conditions employed and is stabilized most likely inside the walls of the carbon nanotubes that are used as substrates during the synthesis.

Description: The microstructure of Allvac 718 Plus (718 Plus; ATI, Pittsburgh, PA, USA) superalloy was examined after linear friction welding (LFW) and after standard postweld heat treatment (PWHT). The liquid phase reaction of second-phase precipitates, which are known to constitutionally liquate during conventional fusion welding, was observed in the thermomechanically affected zone (TMAZ) of the welded material. These phases included MC-type carbides, Ti-rich carbonitrides, and δ phase precipitates. This observation is contrary to the general assumption that LFW is a completely solid-state joining process. However, unlike conventional fusion welding processes that cause heat-affected zone liquation cracking in 718 Plus and many other superalloys, the LFW process did not cause cracking in 718 Plus superalloy despite the liquation of precipitates. This absence of cracking during joining is attributed to the applied compressive stress during the forging stage of the LFW process. Also, no cracking was observed after PWHT, although PWHT resulted in a microstructure that had a nonhomogeneous distribution of precipitates in the weld and the TMAZ.

Description: Metal matrix syntactic foam (MMSF) blocks were produced by an inert gas-assisted pressure infiltration technique. MMSFs are advanced hollow sphere reinforced-composite materials having promising application in the fields of aviation, transport, and automotive engineering, as well as in civil engineering. The produced blocks were investigated in free and constrained compression modes, and besides the characteristic mechanical properties, their deformation mechanisms and failure modes were studied. In the tests, the chemical composition of the matrix material, the size of the reinforcing ceramic hollow spheres, the applied heat treatment, and the compression mode were considered as investigation parameters. The monitored mechanical properties were the compressive strength, the fracture strain, the structural stiffness, the fracture energy, and the overall absorbed energy. These characteristics were strongly influenced by the test parameters. By the proper selection of the matrix and the reinforcement and by proper design, the mechanical properties of the MMSFs can be effectively tailored for specific and given applications.

Description: Trimodal composites, consisting of nanocrystalline or ultrafine grains (UFGs), coarse grains (CGs), and ceramic particles, were originally formulated to achieve combinations of physical and mechanical properties that are unattainable with the individual phases, such as strength, ductility, and high-strain-rate deformation. The concept of a trimodal structure is both scientifically novel as well as technologically promising because it provides multiple controllable degrees of freedom that allow for extensive microstructure design. The UFGs provide efficient obstacles for dislocation movement, such as grain boundaries and other crystalline defects. The size, distribution, and spatial arrangement of the CGs can be controlled to provide plasticity during deformation. The size, morphology, and distribution of the reinforcement particles can be tailored to attain various engineering and physical properties. Moreover, the interfaces that form among the various phases also help determine the overall behavior of the trimodal composites. In this article, a review is provided to discuss the selection and design of each component in trimodal Al composites. The toughening and strengthening mechanisms in the trimodal composite structure are discussed, paying particular attention to strategies that can be implemented to tailor microstructures for optimal mechanical behavior. Recent results obtained with high-performance trimodal Al composites that contain nanometric reinforcements are also discussed to highlight the ability to control particle–matrix interface characteristics. Finally, a perspective is provided on potential approaches that can be explored to develop the next generation of trimodal composites, and interesting scientific paradigms that evolve from the proposed design strategies are discussed.

Description: Phase transformation from austenite to ferrite is an important process to control the microstructures of steels. To obtain finer ferrite grains for enhancing its mechanical property, various thermomechanical processes followed by static ferrite transformation have been carried out for austenite phase. This article reviews the dynamic transformation (DT), in which ferrite transforms during deformation of austenite, in a 6Ni-0.1C steel recently studied by the authors. Softening of flow stress was caused by DT, and it was interpreted through a true stress–true strain curve analysis. This analysis predicted the formation of ferrite grains even above the Ae 3 temperature (ortho-equilibrium transformation temperature between austenite and ferrite), where austenite is stable thermodynamically, under some deformation conditions, and the occurrence of DT above Ae 3 was experimentally confirmed. Moreover, the change in ferrite grain size in DT was determined by deformation condition, i.e., deformation temperature and strain rate at a certain strain, and ultrafine ferrite grains with a mean grain size of 1  μ m were obtained through DT with subsequent dynamic recrystallization of ferrite.

Description: The tensile and low-cycle fatigue deformation and α ′-martensitic transformation behavior of three austenitic steels with varied silicon, aluminum, and nickel levels were characterized using mechanical testing and transmission electron microscopy. Silicon alloying promoted deformation twinning and high work-hardening rates in tension by lowering the stacking fault energy (SFE). Deformation twins and their intersections served as martensite nucleation sites in tension. Martensitic transformation was maximized in the alloy with a low SFE, which increased the alloy capacity to form strain-induced nucleation sites, and low nickel content, which increased the thermodynamic driving force for martensite formation. In fatigue loading, martensite nucleation occurred on localized austenite shear bands composed of dissociated dislocations that form in the cyclically stabilized portion of the fatigue life. The shear bands occurred in all materials irrespective of the SFE. The extent of martensitic transformation in fatigue is apparently dictated more by thermodynamic driving force for transformation and not by SFE. In both tension and fatigue, martensite formation led to strain hardening.

Description: The effect of different amounts of boron, in the form of AlB 2 particles, as well as zinc concentration in a gravity cast Al-B-Zn composite, was studied and related to the absorbed energy upon fracture during Charpy impact experiments. In addition, the authors correlated the composite Brinell hardness with the quantitative assessment of brittle and ductile fracture areas of the Charpy fractured specimens and found that increasing AlB 2 particle concentration resulted in a reduction of absorbed impact energy. Although larger zinc levels produced somewhat similar results, the AlB 2 effect was prevalent. The energy absorption upon impact reached a maximum when no particles were present; conversely, the lowest amount of absorbed energy corresponded to a composite with a composition of 15 wt.% Zn and 8% in volume of AlB 2 , i.e., the highest concentration of AlB 2 and zinc studied. Raising the amount of AlB 2 as well as zinc, as expected, resulted in higher Brinell hardness. A statistical analysis allowed studying of the particle size distribution, whereas values for crack tip opening displacement were subsequently calculated for the range of particle sizes found and the corresponding AlB 2 particle volume percent. Higher porosity values were measured for larger AlB 2 volume percent. Finally, analyses of fracture surfaces corroborated that brittle fracture was favored in composites with higher amounts of AlB 2 and zinc.

Description: A new class of Ni-Ti-C-based metal-matrix composites has been developed using the laser-engineered net shaping™ process. These composites consist of an in situ formed and homogeneously distributed titanium carbide (TiC) phase reinforcing the nickel matrix. Additionally, by tailoring the Ti/C ratio in these composites, an additional graphitic phase can also be engineered into the microstructure. Serial-sectioning, followed by three-dimensional reconstruction of the microstructure in these composites, reveals homogeneously distributed primary and eutectic titanium carbide precipitates as well as a graphitic phase encompassing the primary carbides within the nickel matrix. The morphology and spatial distribution of these phases in three dimensions reveals that the eutectic carbides form a network linked by primary carbides or graphitic nodules at the nodes, which suggests interesting insights into the sequence of phase evolution. These three-phase Ni-TiC-C composites exhibit excellent tribological properties, in terms of an extremely low coefficient of friction while maintaining a relatively high hardness.

Description: Many materials are known to deform under shear in an intermittent way with slip avalanches detected as acoustic emission and serrations in the stress–strain curves. Similar serrations have recently been observed in a new class of materials, called high-entropy alloys (HEAs). Here, we discuss the serration behaviors of several HEAs from cryogenic to elevated temperatures. The experimental results of slow compression and tension tests are compared with the predictions of a slip-avalanche model for the deformation of a broad range of solids. The results shed light on the deformation processes in HEAs. Temperature effects on the distributions of stress drops and the decrease of the cutoff (i.e., of the largest observed slip size) for increasing temperature qualitatively agree with the model predictions. The model is used to quantify the serration characteristics of HEAs, and pertinent implications are discussed.

Description: The proposal of configurational entropy maximization to produce massive solid-solution (SS)-strengthened, single-phase high-entropy alloy (HEA) systems has gained much scientific interest. Although most of this interest focuses on the basic role of configurational entropy in SS formability, setting future research directions also requires the overall property benefits of massive SS strengthening to be carefully investigated. To this end, taking the most promising CoCrFeMnNi HEA system as the starting point, we investigate SS formability, deformation mechanisms, and the achievable mechanical property ranges of different compositions and microstructural states. A comparative assessment of the results with respect to room temperature behavior of binary Fe-Mn alloys reveals only limited benefits of massive SS formation. Nevertheless, the results also clarify that the compositional requirements in this alloy system to stabilize the face-centered cubic (fcc) SS are sufficiently relaxed to allow considering nonequiatomic compositions and exploring improved strength–ductility combinations at reduced alloying costs.

Description: In Si and FeSi production, the main Si source is SiO 2 , in the form of quartz. Reactions with SiO 2 generate SiO gas that further reacts with SiC to Si. During heating, quartz will transform to other SiO 2 modifications with cristobalite as the stable high-temperature phase. Transformation to cristobalite is a slow process. Its rate has been investigated for several industrial quartz sources and has been shown to vary considerably among the different quartz types. Other differences in behavior during heating between these quartz sources, such as softening temperature and volume expansion, have also been studied. The quartz-cristobalite ratio will affect the rate of reactions involving SiO 2 . The industrial consequences and other implications of the observed difference between quartz types are discussed. Initial studies of industrial quartz were published by Ringdalen et al. In the current work, a new experimental method has been developed, and an investigation of several new quartz sources has confirmed the earlier observed large variation between different sources. The repeatability of the data has been studied and the effect of gas atmosphere investigated. The results from the earlier work are included as a basis for the discussion.

Description: The terminology Wootz for the legendary Indian crucible steel was first introduced by Helenus Scott in his letter to Joseph Banks, the then President of the Royal Society, London, in 1794. He stated several salient features of this steel in his letter. During the period 1794–1796, Banks received approximately 200 lbs. of this steel from Scott. Banks assigned several professionals to carry out experimental work on Indian crucible steel. One such important person was the famous surgical instrument maker, cutler and metallurgist of his time, James Stodart. Stodart experimented extensively with the Indian crucible steel, and was its great admirer. It has been shown, along with corroborative documentary evidence, that the original word for this steel was Sanskrit word “ utsa ”. This was erroneously transliterated in Roman script as Wootz by Scott in his letter to Banks. It was James Stodart, who preserved the Sanskrit word “ utsa ” written in Devanāgarī script on his trade card for future generation. The reason for using this word for the Indian crucible steel has also been discussed.

Description: Nuclear energy is a mature technology with a small carbon footprint. However, work is needed to make current reactor technology more accident tolerant and to allow reactor fuel to be burned in a reactor for longer periods of time. Optimizing the reactor fuel performance is essentially a materials science problem. The current understanding of fuel microstructure have been limited by the difficulty in studying the structure and chemistry of irradiated fuel samples at the mesoscale. Here, we take advantage of recent advances in experimental capabilities to characterize the microstructure in 3D of irradiated mixed oxide (MOX) fuel taken from two radial positions in the fuel pellet. We also reconstruct these microstructures using Idaho National Laboratory’s MARMOT code and calculate the impact of microstructure heterogeneities on the effective thermal conductivity using mesoscale heat conduction simulations. The thermal conductivities of both samples are higher than the bulk MOX thermal conductivity because of the formation of metallic precipitates and because we do not currently consider phonon scattering due to defects smaller than the experimental resolution. We also used the results to investigate the accuracy of simple thermal conductivity approximations and equations to convert 2D thermal conductivities to 3D. It was found that these approximations struggle to predict the complex thermal transport interactions between metal precipitates and voids.

Description: In response to the increasing temperature capability of the structural materials required for advanced gas turbine engines, new alloying concepts are required to develop materials with properties that are significantly better than existing nickel-base superalloys. Recent investigations have focused on the development of polycrystalline, ternary eutectic γ - γ ′- δ Ni-base superalloys that use large volume fractions of the intermetallic δ phase to provide composite strengthening. While compositional changes enabled the formation of the δ phase precipitates, in some alloys an additional precipitate phase η was formed. As the effects of these phases on high-temperature mechanical properties are not well quantified, a better understanding of the thermodynamics and kinetics associated with the formation of these δ and η phase precipitates is required for future designs of Ni-base superalloys. A set of experimental alloys was investigated to understand the formation of the δ and η phase precipitates in Ni-base superalloys. When the alloy chemistry was observed to exhibit a compositional ratio of Al/(Nb+Ta+Ti) less than 1, δ and/or η phase precipitates formed, whereas a ratio greater than 1 resulted in conventional γ - γ ′ microstructures. For alloys in which δ and/or η phase precipitates were formed, the prevalent phase could be determined by evaluating the compositional ratio for (Nb+Ta)/(Al+Ti). Alloys that had ratios greater than 1 were largely composed of δ phase precipitates, whereas a ratio less than 1 resulted in the predominance of the η phase precipitates.

Description: The dependence of the solidification temperature on the concentration x of impurity atoms, M, of Sn-M x alloys after cooling from the melt was measured separately for M = Co, Ni, Ag, and Cu. For a comparison, similar measurements were performed on SAC305-Ni x alloys. Large variations in undercooling were observed. It was found that the Ag atoms dissolved in the Sn-Ag melt significantly lowered undercooling, although the presence of Ag 3 Sn intermetallic compounds did not. While Cu 6 Sn 5 intermetallic compounds in Sn-Cu melts did not significantly lower undercooling, the undercooling of a Sn-Cu melt in contact with a Cu interface was significantly reduced. The addition of Ni to Pb-free solder SAC305 caused a factor of two reduction in the undercooling, similar to that observed after the addition of Ni to high-purity Sn.

Description: Reducing the density of steels is a novel approach for weight reduction of automobiles to improve fuel efficiency. In this overview article, strategies for the development of lightweight steels are presented with a focus on bulk ferrous alloys. The metallurgical principles of these steels and their mechanical properties of relevance to automotive applications are discussed. Some of the engineering aspects highlighting the possible problems related to mass production of these steels are also considered. Application prospects of these steels vis-à-vis standard automotive steels are shown.

Description: In situ transmission electron microscopy observation of polycrystalline UO 2 (with average grain size of about 5  µ m) irradiated with Kr ions at 600°C and 800°C was conducted to understand the radiation-induced dislocation evolution under the influence of grain boundaries. The dislocation evolution in the grain interior of polycrystalline UO 2 was similar under Kr irradiation at different ion energies and temperatures. As expected, it was characterized by the nucleation and growth of dislocation loops at low irradiation doses, followed by transformation to extended dislocation lines and tangles at high doses. For the first time, a dislocation-denuded zone was observed near a grain boundary in the 1-MeV Kr-irradiated UO 2 sample at 800°C. The denuded zone in the vicinity of grain boundary was not found when the irradiation temperature was at 600°C. The suppression of dislocation loop formation near the boundary is likely due to the enhanced interstitial diffusion toward grain boundary at the high temperature.

Description: This article describes the results of a whisker formation study on SAC305 assemblies, evaluating the effects of lead-frame materials and cleanliness in different environments: low-stress simulated power cycling (50–85°C thermal cycling), thermal shock (–55°C to 85°C), and high temperature/high humidity (85°C/85% RH). Cleaned and contaminated small outline transistors, large leaded quad flat packs (QFP), plastic leaded chip carrier packages, and solder balls with and without rare earth elements (REE) were soldered to custom designed test boards with Sn3Ag0.5Cu (SAC305) solder. After assembly, all the boards were cleaned, and half of them were recontaminated (1.56  µ g/cm 2 Cl − ). Whisker length, diameter, and density were measured. Detailed metallurgical analysis on components before assembly and on solder joints before and after testing was performed. It was found that whiskers grow from solder joint fillets, where the thickness is less than 25  µ m, unless REE was present. The influence of lead-frame and solder ball material, microstructure, cleanliness, and environment on whisker characteristics is discussed. This article provides detailed metallurgical observations and select whisker length data obtained during this multiyear testing program.

Description: Recent results on irradiated UO 2 by Raman spectroscopy evidenced Raman lines that are characteristic of irradiation-induced defects. Three main mechanisms are identified to explain their origin: resonant Raman, formation of new molecular entities, or breakdown in symmetry. Arguments are given to consider breakdown in symmetry as the predominant mechanism. A tentative description of the defects at the origin of this symmetry breakdown is proposed in terms of coordination polyhedrons of uranium. This discussion led us to consider that the Raman defect modes could be related to area with different stoichiometry.

Description: The suitability of using aluminum dross waste and kaolin to produce refractory bricks is experimentally studied. Thirty brick samples of different blends are produced, dried at 30°C, dried further at 110°C, and fired at 1200°C. The firing temperature point, bulk density, apparent porosity, thermal conductivity, thermal shock, loss on ignition, permeability, shatter index, and shrinkage of the bricks blends are determined. The results show that some blend samples have good refractory characteristics with mixing ratio 4:1:2 (representing weight in grams of aluminum dross, plastic clay, and kaolin, respectively). The evaluations of studied properties reveal the possibility for aluminum dross waste to be used as matrix in refractory bricks.

Description: The salt removal from black dross by thermal treatment has experimentally been studied under different conditions in both a stationary resistance furnace and in a laboratory scale rotary furnace. The experiments were designed based on partial pressure calculations using the Thermo-Calc software (Thermo-Calc Software, Stockholm, Sweden). The salt removal efficiency was evaluated by scanning electron microscope (SEM) energy-dispersive x-ray spectroscopy and x-ray diffraction analyses, and the optimum conditions for treatment established, i.e., temperature, gas flow rate, holding time, rotation rate, and sample size. The overall degree of chloride removal was established to increase as a function of time and temperature, as well as by reduced pressure. Under atmospheric pressure, the highest degree of chloride removal from a 20 g sample was obtained after 10 h at 1523 K resulting in a 98% removal and a final chloride content of 0.3 wt.% in the residue. Under reduced pressure, the chloride concentrate was lowered to 0.2 wt.% after thermal treatment of a 20 g sample at 1473 K for 8 h. In the case of 200 g samples treated in a rotary furnace, the chloride concentrate was 2.5 wt.% after 14 h at 1523 K, representing a removal of 87%. Below 0.3 wt.% chloride content, the material is deemed a nonhazardous waste.

Description: The etching treatment is an important process step in influencing the surface quality of anodized aluminum alloy extrusions. The aim of etching is to produce a homogeneously matte surface. However, in the etching process, further surface imperfections can be generated on the extrusion surface due to uneven materials loss from different microstructural components. These surface imperfections formed prior to anodizing can significantly influence the surface quality of the final anodized extrusion products. In this article, various factors that influence the materials loss during alkaline etching of aluminum alloy extrusions are investigated. The influencing variables considered include etching process parameters, Fe-rich particles, Mg-Si precipitates, and extrusion profiles. This study provides a basis for improving the surface quality in industrial extrusion products by optimizing various process parameters.

Description: The new aluminum electrolysis technology based on inert electrodes has received much interest for several decades because of the environment and energy advantages. The key to realize this technique is the inert anode. This article presents China’s recent developments of NiFe 2 O 4 -based cermet inert anodes, which include the optimization of material performance, the joint between the cermet inert anode and metallic bar, as well as the results of 20 kA pilot testing for a large-size inert anode group. The problems NiFe 2 O 4 -based cermet inert anodes face are also discussed.

Description: In 2006, a new-ordered L1 2 phase, Co 3 (Al,W), was discovered that can form coherently in a face-centered cubic (fcc) A1 Co matrix. Since then, a community has developed that is attempting to take these alloys forward into practical applications in gas turbines. A new candidate polycrystalline Co-Ni γ / γ ′ superalloy, V208C, is presented that has the nominal composition 36Co-35Ni-15Cr-10Al-3W-1Ta (at.%). The alloy was produced by conventional powder metallurgy superalloy methods. After forging, a γ ′ fraction of ~56% and a secondary γ ′ size of 88 nm were obtained, with a grain size of 2.5  μ m. The solvus temperature was 1000°C. The density was found to be 8.52 g cm −3 , which is similar to existing Ni alloys with this level of γ ′. The alloy showed the flow stress anomaly and a yield strength of 920 MPa at room temperature and 820 MPa at 800°C, similar to that of Mar-M247. These values are significantly higher than those found for either conventional solution and carbide-strengthened Co alloys or the γ / γ ′ Co superalloys presented in the literature thus far. The oxidation resistance, with a mass gain of 0.08 mg cm −2 in 100 h at 800°C, is also comparable with that of existing high-temperature Ni superalloys. These results suggest that Co-based and Co-Ni superalloys may hold some promise for the future in gas turbine applications.

Description: Fluoride cycling within a smelter has been examined as a function of alumina properties. Using an experimental configuration in which the two ends of a single potline were operated with different aluminas, quantitative measurements were made of fluoride evolution from the pots, and hydrogen fluoride (HF) levels at the scrubber and stack. Correlations were then examined with specific alumina properties, once environmental factors and other baseline effects had been considered. Although the phase analysis, including both residual gibbsite and alumina structural hydroxide content, is correlated with HF generation, local weather conditions (primarily humidity) also have a major influence on fluoride evolution. Importantly, HF concentrations at the scrubber (measured in the gas phase at the outlet to the gas treatment center), as a proxy for the kinetics of the scrubbing process, support the importance of alumina pore size distribution as opposed to simply specific surface area. This is also found to be true in the independent analysis of bath acidity, indicating a more general but extremely important influence of alumina porosity on the entire fluoride cycle. The study provides insight into the impacts of a range of typically unreported alumina properties on smelter performance and strongly supports the presence of kinetically inaccessible porosity in pores narrower than ~3 nm in alumina.

Description: The shot-peening process is currently employed in most industries to improve the longevity of components by inhibiting crack initiation as well as crack growth at the surface. The protective effect of shot peening has been mainly attributed to compressive stresses within the deformed layer. Intensive research has been carried out to quantify the near-surface residual stresses on entry into service and evolution throughout life. In nickel-base superalloys, the focus of research on the effects of shot-peening has performed using x-rays from either laboratory or synchrotron-based sources. However, this approach cannot evaluate in detail the deformation mechanisms nor the role of the γ ′ precipitates in a nickel-base superalloy; the latter is responsible for its unique properties. Our study uses a complementary range of techniques to investigate in detail the microstructure and deformation mechanisms associated with shot-peening in a coarse-grained nickel-based superalloy strengthened with coherent γ ′ precipitates. These include scanning electron microscopy and transmission electron microscopy, nanoindentation and micropillar compression. Accurate mapping of the dislocation structure produced throughout the deformed layers have been performed. Using an unconventional specimen preparation technique, it provides the basis for a more complete interpretation of how shot-peening inhibits fatigue cracking.

Description: With no agreed-on definition of critical materials, product and process designers have been unable to systematically address the critical materials issue. Using a comprehensive methodology, we have determined the criticality of 62 metals and metalloids—approximately two-thirds of the periodic table. We illustrate how the analyses were performed, provide an overview of criticality at the global level for all elements, and then present examples of how the criticality information could be used in making material-related choices in product and process design.

Description: Two individual high-pressure die casting geometries were developed to study the influence of process parameters and alloy composition on the distortion behavior of aluminum alloy castings. These geometries, a stress lattice and a V-shaped lid, tend to form residual stress due to a difference in wall thickness and a deliberate massive gating system. Castings were produced from two alloys: AlSi12(Fe) and AlSi10MnMg. In the experimental castings, the influence of important process parameters such as die temperature, ejection time, and cooling regime was examined. The time evolution of process temperatures was measured using thermal imaging. Subsequent to casting, distortion was measured by means of a tactile measuring device at ambient temperatures. The measured results were compared against a numerical process and stress simulations of the casting, ejection, and cooling process using the commercial finite element method software ANSYS Workbench. The heat transfer coefficients were adapted to the temperature distributions of the die, and the castings were observed by thermal imaging. A survey of the results of the comparison between simulation and experiment is given for both alloys.

Description: Slag freeze linings, the formation of protective deposit layers on the inner walls of furnaces and reactors, are increasingly used in industrial pyrometallurgical processes to ensure that furnace integrity is maintained in these aggressive, high-temperature environments. Most previous studies of freeze-linings have analyzed the formation of slag deposits based solely on heat transfer considerations. These thermal models have assumed that the interface between the stationary frozen layer and the agitated molten bath at steady-state deposit thickness consists of the primary phase, which stays in contact with the bulk liquid at the liquidus temperature. Recent experimental studies, however, have clearly demonstrated that the temperature of the deposit/liquid bath interface can be lower than the liquidus temperature of the bulk liquid. A conceptual framework has been proposed to explain the observations and the factors influencing the microstructure and the temperature of the interface at steady-state conditions. The observations are consistent with a dynamic steady state that is a balance between (I) the rate of nucleation and growth of solids on detached crystals in a subliquidus layer as this fluid material moves toward the stagnant deposit interface and (II) the dissolution of these detached crystals as they are transported away from the interface by turbulent eddies. It is argued that the assumption that the interface temperature is the liquidus of the bulk material represents only a limiting condition, and that the interface temperature can be between T liquidus and T solidus depending on the process conditions and bath chemistry. These findings have implications for the modeling approach and boundary conditions required to accurately describe these systems. They also indicate the opportunity to integrate considerations of heat and mass flows with the selection of melt chemistries in the design of future high temperature industrial reactors.

Description: The formation energy of cation antisites in pyrochlores (A 2 B 2 O 7 ) has been correlated with the susceptibility to amorphize under irradiation, and thus, density functional theory calculations of antisite energetics can provide insights into the radiation tolerance of pyrochlores. Here, we show that the formation energy of antisite pairs in titanate pyrochlores, as opposed to other families of pyrochlores (B = Zr, Hf, or Sn), exhibits a strong dependence on the separation distance between the antisites. Classical molecular dynamics simulations of collision cascades in Er 2 Ti 2 O 7 show that the average separation of antisite pairs is a function of the primary knock-on atom energy that creates the collision cascades. Together, these results suggest that the radiation tolerance of titanate pyrochlores may be sensitive to the irradiation conditions and might be controllable via the appropriate selection of ion beam parameters.

Description: Precipitates in bulk p-type thermoelectric materials, PbTe-SrTe and PbTe-PbS, are studied using three-dimensional (3-D) atom-probe tomography (APT). APT is capable of characterizing chemically materials in 3-D with subnano-scale spatial resolution on an atom-by-atom basis, which enables us to characterize secondary phases in the PbTe matrix as well as the dopant distributions at different imperfections. We demonstrate that APT provides accurate information about the compositions and morphologies of nanoprecipitates. In the PbTe-SrTe system, different morphology of precipitates is observed and the SrTe composition is confirmed. Also, segregation of Na dopants at mesoscale imperfections, dislocations and grain boundaries, and at matrix/precipitate interfaces is observed. In the PbTe-PbS system, PbS precipitates are observed. The PbS precipitates exhibit faceting, and have a morphology that depends on the bulk Na concentration. A predominance of {100} faceted precipitates is observed for 2 mol.% Na. Using 3-D APT, we demonstrate that Na segregation at matrix/precipitate interfaces is most likely responsible for the change in their morphologies, which occurs by reducing the interfacial free energy of {100} facets.

Description: We present a self-contained review of the discrete dislocation dynamics (DDD) method for the numerical investigation of plasticity in crystals, focusing on recent development and implementation progress. The review covers the theoretical foundations of DDD within the framework of incompatible elasticity, its numerical implementation via the nodal method, the extension of the method to finite domains and several implementation details. Applications of the method to current topics in micro-plasticity are presented, including the size effects in nano-indentation, the evolution of the dislocation microstructure in persistent slip bands, and the phenomenon of dislocation avalanches in micro-pillar compression.

Description: The design, manufacture, and experimental analysis of structural materials capable of operation in the high temperatures, corrosive environments, and radiation damage spectra of future reactor designs remain one of the key pacing items for advanced reactor designs. The most promising candidate structural materials are vanadium-based refractory alloys, silicon carbide composites and oxide dispersion strengthened steels. Of these, oxide dispersion strengthened steels are a likely near-term candidate to meet required demands. This paper reviews different variants of oxide dispersion strengthened steels and discusses their capability with regard to high-temperature strength, corrosion resistance, and radiation damage resistance. Additionally, joining of oxide dispersion strengthened steels, which has been cited as a limiting factor preventing their use, is addressed and reviewed. Specifically, friction stir welding of these steels is reviewed as a promising joining method for oxide dispersion strengthened steels.

Description: Thermochemical liquefaction processing of biomass to produce bio-derived fuels (e.g., gasoline, jet fuel, diesel, home heating oil, etc.) is of great recent interest as a renewable energy source. Approaches under investigation include direct liquefaction, hydrothermal liquefaction, hydropyrolysis, fast pyrolysis, etc., to produce energy dense liquids that can be utilized as produced or further processed to provide products of higher value. An issue with bio-oils is that they tend to contain significant concentrations of organic oxygenates, including acids, which make the bio-oil a potential source of corrosion issues in transport, storage, and use. Efforts devoted to modified/further processing of bio-oils to make them less corrosive are currently being widely pursued. Another issue that must also be addressed in bio-oil liquefaction is potential corrosion issues in the process equipment. Depending on the specific process, bio-oil liquefaction production temperatures are typically in the 300–600°C range, and the process environment can contain aggressive sulfur and halide species from both the biomass used and/or process additives. Detailed knowledge of the corrosion resistance of candidate process equipment alloys in these bio-oil production environments is currently lacking. This paper summarizes recent, ongoing efforts to assess the extent of corrosion of bio-oil process equipment, with the ultimate goal of providing a basis for the selection of the lowest cost alloy grades capable of providing the long-term corrosion resistance needed for future bio-oil production plants.

Description: The development of oxide dispersion strengthened ferrous alloys has shown that microstructures designed for excellent irradiation resistance and thermal stability ideally contain stable nanoscale precipitates and dislocation sinks. Based upon this understanding, the microstructures of conventionally manufactured ferritic and ferritic-martensitic steels can be designed to include controlled volume fractions of fine, stable precipitates and dislocation sinks via specific alloying and processing paths. The concepts proposed here are categorized as advanced high-Cr ferritic-martensitic (AHCr-FM) and novel tailored precipitate ferritic (TPF) steels, which have the potential to improve the in-reactor performance of conventionally manufactured alloys. AHCr-FM steels have modified alloy content relative to current reactor materials (such as alloy NF616/P92) to maximize desirable precipitates and control phase stability. TPF steels are designed to incorporate nickel aluminides, in addition to microalloy carbides, in a ferritic matrix to produce fine precipitate arrays with good thermal stability. Both alloying concepts may also benefit from thermomechanical processing to establish dislocation sinks and modify phase transformation behaviors. Alloying and processing paths toward designed microstructures are discussed for both AHCr-FM and TPF material classes.

Description: A variety of commercial slurries are available to aluminize the surfaces of nickel-based superalloys; however, they have three main disadvantages. First, the phosphates and chromates or halides used as binders or to activate the diffusion species are environmentally harmful and toxic; second, the slurry coatings can only produce high-aluminum-activity coatings which form precipitate-rich coatings that are detrimental to adherence. Finally, these coatings are limited to the incorporation of aluminum and silicon, whereas the co-deposition of other elements such as chromium or cobalt has not been achieved so far. In this work, the limitations of slurry coatings have been overcome by carefully designing the powder composition and controlling the process to produce co-deposition coatings with chromium, cobalt, or nickel by using nontoxic water-based slurries. This also opens an effective way to control Al activity and to produce low-activity aluminized coatings for the first time when using the slurry technique. These results expand the application range of slurry coatings so they can also be applied under ambient atmosphere, making it possible to fully coat aero engine pieces or large-scale industrial components, providing all properties that are usually only achieved by using more complex and expensive methods such as chemical vapor deposition. Furthermore, these new coatings offer unique advantages that can be very favorable especially as a repairing technique.

Description: Fe-substituted superconducting thin BiSrCaCuO rods with nominal compositions of Bi 2 Sr 2 Ca 1 Cu 2− x Fe x O 8+ δ ( x  = 0, 0.01, 0.03, 0.05, and 0.1) were fabricated using the laser floating zone technique at two different growth speeds, 15 mm h −1 and 30 mm h −1 . The influences of growth speed and Fe substitution on the grain alignment in the rods were evaluated by means of x-ray pole figure studies. The obtained results showed that both applied growth speed and Fe substitution play a crucial role on grain alignment, which is strongly connected with the current-carrying capacity of the rods. It was found that the rods grown at 15 mm h −1 (G15) have stronger orientation than the rods grown at 30 mm h −1 (G30). However, in contrast to the G15 rods, an increased substitution rate improved the orientation of the G30 rods. Another important observation is that the increase on the substitution caused a decrease on the grain size of all the rods. The decrease of critical temperature values of the rods upon substitution was ascribed to both grain size effect and formation of a nonsuperconducting Fe-rich phase detected in scanning electron microscope/energy-dispersive x-ray analyses. The thermal conductivity values of the G15 and G30 rods were found to be in the range of 0.9–1.9 and 1.1–1.18 W m −1  K −1 at 150 K, respectively. The higher values of figure of merit ( ZT ), at all temperature ranges, were obtained from the highest substituted rods ( x  = 0.1) for both of the applied growth speeds. In addition, it was observed that the ZT of G30 rods are up to three times higher than that of G15 ones.

Description: Slag properties, such as electrical conductivity, thermal conductivity, density, viscosity, and surface tension, and the prediction of these properties play an important role in melting and metal refining. Optical basicity depends on the electronegativity of the ions of an individual oxide. This feature represents the bonding characteristics, ionization ability, ion size, and consequently the mobility of free ions inside the slag. These properties affect the electrical conductivity of slags. Therefore, in the current study, various slags containing mainly CaF 2 and various oxides were prepared. The optical basicity value of each slag was calculated and their electrical conductivities were measured between 1450°C and 1600°C. The relationship between the optical basicity and the measured properties were discussed. It was observed that increasing optical basicity increases the electrical conductivity as well as the temperature. Thus, a new model for predicting electrical conductivity of slags was built between 1450°C and 1600°C depending on optical basicity and temperature.

Description: In this paper, a sensitivity and general uncertainty analysis is performed related to the modified embedded-atom method (MEAM) potential calibration of pure aluminum for data garnered from lower length scale (ab initio) simulations. Input uncertainties were quantified from 95% normal distribution confidence intervals of the various calibrated MEAM potential parameters from Part A of this study. A perturbation method was used to quantify the MEAM sensitivities to input parameters. The input uncertainties and sensitivities were then combined in a general uncertainty propagation analysis method. The results of the sensitivity analysis show that all the MEAM parameters interdependently influence all MEAM model outputs to varying degrees, allowing for the definition of an ordered calibration procedure to target specific MEAM outputs. In relation to the generalized stacking fault energy (GSFE) curve, the coefficient of the embedding function related to the background electron density, asub, was the most influential parameter related to the first peak. The first peak of the GSFE curve is related to unstable dislocations, in effect dislocation nucleation, and the first trough is related to stable dislocations. This connection of tying asub to the dislocation nucleation and motion was not obvious before this study indicating the power of the sensitivity and uncertainty method that was employed.

Description: Aluminide coatings were applied to the surfaces of several austenitic stainless steels—UNS S30300, S30400, S30900, S31000, and S31600 (Type 303, 304, 309, 310, and 316)—by the halide activated pack cementation process. The coating compositions, microstructures, and hardness were determined for the different steels coated at 850°C for 25 h. The stability of the austenite phase for each type of steel was calculated by determining the ratio of the nickel to the chromium equivalents based on their nominal compositions. The thickness of the inner diffusion zone in the coating was shown to be inversely related to the austenite stability of the steels. Microhardness measurements were obtained across the coating thickness and into the substrate. The hardness values followed the same trends as the aluminum composition profile into the substrate.

Description: Density reduction of automotive steels is needed to reduce fuel consumption, thereby reducing greenhouse gas emissions. Aluminum addition has been found to be effective in making steels lighter. Such an addition does not change the crystal structure of the material. Steels modified with aluminum possess higher strength with very little compromise in ductility. In this work, different compositions of Fe-Al systems have been studied so that the desired properties of the material remain within the limit. A density reduction of approximately 10% has been achieved. The specific strength of optimal Fe-Al alloys is higher than conventional steels such as ultra-low-carbon steels.

Description: Significant amounts of electric arc furnace dust originating from steel production are recycled every year by the Waelz process, despite the fact that this type of process has several disadvantages. One alternative method would be the recovery of very high-quality ZnO as well as iron and even chromium in the two-step dust recycling process, which was invented to treat special waste for the recovery of heavy metal-containing residues. The big advantage of that process is that various types of residues, especially dusts, can be treated in an oxidizing first step for cleaning, with a subsequent reducing step for the metal recovery. After the treatment, three different fractions—dust, slag, and an iron alloy, can be used without any limitations. This study focuses on the development of the process along with some thermodynamic considerations. Moreover, a final overview of mass balances of an experiment performed in a 100-kg top blowing rotary converter with further developments is provided.

Description: This article presents a study of the effects of process parameters in bulk-forming bimetallic watchcase components using finite-element (FE) simulation. This study aimed to determine the suitable forming temperature T and ram speed S for attaining the complete die filling of bimetals. A complicated watchcase component made of 3-mm-thick AISI 316L stainless steel (SS316L) and 6-mm-thick 6063 aluminum alloy (AA6063) was used as the example. The processes were simulated with T of 400°C, 500°C, 600°C, 700°C, 800°C, and 900°C and S of 20 mm/s, 40 mm/s, and 60 mm/s. Although the AA6063 was not heated in the beginning, it flowed faster than the SS316L during the process, and hence, the incomplete die filling was found mainly in the SS316L region. To avoid the incomplete die filling and strengthen the intermetallic bond between two dissimilar metals, the T of 900°C was suggested. The S of 40 mm/s was recommended also because this could save much forming energy and prevent the damage of tools. The experimental verification was carried out under process conditions that were employed in the simulations. An infrared thermal imaging camera and a 300-ton mechanical press were used to monitor the T and testify the bulk-forming operation, respectively. The data acquired from the experiments, on average, agreed strongly with those predicted by the simulations. On the basis of the results in this study, engineers can gain a better understanding of bulk-forming bimetallic components and be able to determine the T and S efficiently for similar processes.

Description: Concepts of Fe-Al-Mn-C-based lightweight steels are fairly simple, but primary metallurgical issues are complicated. In this study, recent studies on lean-composition lightweight steels were reviewed, summarized, and emphasized by their microstructural development and mechanical properties. The lightweight steels containing a low-density element of Al were designed by thermodynamic calculation and were manufactured by conventional industrial processes. Their microstructures consisted of various secondary phases as κ -carbide, martensite, and austenite in the ferrite matrix according to manufacturing and annealing procedures. The solidification microstructure containing segregations of C, Mn, and Al produced a banded structure during the hot rolling. The (ferrite + austenite) duplex microstructure was formed after the annealing, and the austenite was retained at room temperature. It was because the thermal stability of austenite nucleated from fine κ -carbide was quite high due to fine grain size of austenite. Because these lightweight steels have outstanding properties of strength and ductility as well as reduced density, they give a promise for automotive applications requiring excellent properties.

Description: Niobium-based alloys are well-established refractory materials; as a result of their high melting temperature and good creep properties, these alloys find their applications in nuclear reactors. The present study deals with a microstructural response of these materials during hot working. The evolution of microstructure and texture during high-temperature deformation has been investigated in the temperature range 1500–1700°C and strain rate range of 0.001–0.1 s −1 . For each deformed sample, the microstructure has been examined in detail. The microstructural features clearly revealed the formation of a substructure and the occurrence of dynamic recrystallization in a proper temperature-strain rate window. At low strain rates, the necklace structure formation was more prominent.

Description: The traditional artificial recognition methods for the blast furnace dust composition have several disadvantages, including a great deal of information to dispose, complex operation, and low working efficiency. In this article, a multifeature analysis method based on comprehensive image-processing techniques was proposed to automatically recognize the blast furnace dust composition. First, the artificial recognition and feature analysis, which included image preprocessing, Harris corner feature, Canny edge feature, and Ruffle feature analysis, was designed to build the template image, so that any unknown dust digital image could be tested. Second, the composition of coke, microvariation pulverized coal, vitric, ash, and iron from dust would be distinguished according to their different range of values based on the multifeature analysis. The method is valid for recognizing the blast furnace dust composition automatically, and it is fast and has a high recognition accuracy.

Description: The Outokumpu flash smelting process is a very successful technology for copper extraction from sulfide concentrate. Numerical simulation has been used for several decades in the analysis and evaluation of the smelting process. However, significant delay in the particle ignition was found in computations of flash furnaces that had great expansion in their productivity. A study was thereafter carried out to investigate how the gaseous flows influence the particle dispersion and combustion. A momentum ratio was defined to describe the effective portion of the pressure forces caused by the lateral and the vertical gaseous flows. Simulations were carried out with Fluent 6.3 (Fluent Inc. The software package is now known as Ansys Fluent of Ansys Inc.) for cases with different momentum ratios as well as of the same momentum value. A detailed analysis and discussion of influences of the gaseous momentum on the particle dispersion are presented. The result reveals that a large momentum ratio combined with large amount of distribution air is helpful for good particle dispersions and thus quicker combustions. Also the process air is found to perform a constraint influence on the particle dispersions, particularly for those of medium and small sizes.