ALBERT

Description: Using a controlled thermal simulator system, hybrid carbon nanotube-aluminum reinforced ZA27 composites were subjected to hot compression testing in the temperature range of 473-523 K with strain rates of 0.01-10 s −1 . Based on experimental results, a developed-flow stress model was established using a constitutive equation coupled with strain to describe strain softening arising from dynamic recrystallization. The intrinsic workability was further investigated by constructing three-dimensional (3D) processing maps aided by optical observations of microstructures. The 3D processing maps were constructed based on a dynamic model of materials to delineate variations in the efficiency of power dissipation and flow instability domains. The instability domains exhibited adiabatic shear band and flow localization, which need to be prevented during hot processing. The recommended domain is predicated to be within the temperature range 550-590 K and strain rate range 0.01-0.35 s −1 . In this state, the main softening mechanism is dynamic recrystallization. The results from processing maps agree well with the microstructure observations.

Description: This paper presents an integrated processing method that applies principal component analysis (PCA), artificial neural network (ANN), information entropy and information fusion technique to analyze acoustic emission signals for identifying fatigue damage in a steel structure. Firstly, PCA is used to build different data spaces based on the damage patterns. Input information from each sensor is diagnosed locally through ANN in the data space. The output of the ANNs is used for basic probability assignment. Secondly, the first fusion operation adopts Dempster-Shafer (D-S) evidence theory to combine the basic probability assignment value of ANNs in the different data space of a sensor. Finally, the fusion results of each sensor are combined by D-S evidence theory for the second fusion operation. In this paper, information entropy is used to calculate the uncertainty and construct basic probability assignment function. The damage identification method is verified through four-point bending fatigue tests of Q345 steel. Validation results show that the damage identification method can reduce the uncertainty of the system and has a certain extent of fault tolerance. Compared with ANN and ANN combined with information fusion methods, the proposed method shows a higher fatigue damage identification accuracy and is a potential for fatigue damage identification.

Description: In this study, Zn-Co-Mo coatings were deposited on the steel substrate from a citrate bath after adjusting pH, concentration, and current density. The morphology, the content of alloying elements, and the thickness of deposits were studied. Deposition behavior of these ternary coatings was examined by cathodic polarization and cyclic voltammetry (CV) techniques. The synthesized deposits were investigated by scanning electron microscopy (SEM), energy-dispersive x-ray (EDX) analysis, x-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization methods. The results showed that the deposition potential of Zn-Co-Mo alloy was feasible in negative potentials higher than about −1.25 V versus Ag/AgCl. Moreover, the corrosion behavior of these coatings was found to be related to the extent of Mo as well as the local anodes and cathodes. The amount of molybdenum in the Zn-Co-Mo coating varied from 2.6 to 14 wt.% as a result of changing the pH. Based on the experimental findings, a narrow range of pH values between 5 and 5.5 could contribute to the high quality of coating in conjunction with the corrosion resistant alloy. Besides, the coatings with Mo element could show a passive-like behavior in the anodic region.

Description: This work aims at studying the electrochemical behavior of annealed pure titanium (Ti) and nano-structured (NS) Ti coating in borate buffer solutions. Cathodic arc evaporation was successfully applied to deposit NS Ti coating. Samples were characterized by means of scanning electron microscope and x-ray diffraction. Potentiodynamic polarization tests, electrochemical impedance spectroscopy, and Mott-Schottky analysis were employed to discuss the electrochemical behavior of samples thoroughly. Electrochemical measurements showed that the deposited NS Ti coating offers a superior passivity in borate buffer solutions of pH 9.0 and 9.5. Mott-Schottky analysis revealed that all passive films are of n-type semiconducting nature in these alkaline solutions and the deposition process did not alter the semiconducting type of passive films formed on samples. Additionally, this analysis showed that the NS Ti coating possessed lower levels of donor densities. Finally, all electrochemical tests showed that passive behavior of the NS Ti samples was superior, mainly due to the formation of thicker and less defective passive films.

Description: Using a multi-technique approach, we explore the effect of Er doping on the mechanical properties and phase transition temperature of polycrystalline Co-Ni-Al alloy. The un-doped alloy exhibits poor mechanical properties and a very low phase transition temperature. Therefore, the alloy could not obtain the apparent magnetic-field-induced strain. We show that the microstructure is typical of a multi-phase structure at room temperature. Within the grain boundary, a γ phase exists and is shown to continuously grow surrounding the matrix as the Er is being doped. This results in the appearance of Co 2 Er in the γ phase when Er rises above 0.5 at.%. The phase transformation temperature clearly increases with doping and reaches room temperature when doping is at 1 at.% Er. The yield stress and ductility of the alloy increased remarkably at first and then slightly decreased with further doping. The sample exhibits an interesting shape memory effect that is enhanced by Er doping or thermo-mechanical cycles.

Description: Dispersion-strengthened Cu-Al 2 O 3 materials have been studied over recent years to find an optimum processing route to obtain a high strength, thermal-stable copper alloy designed for modern applications in electrical engineering. The study analyses the influence of 1 vol.% of alumina content on strengthening the copper matrix. Microstructure of the Cu-Al 2 O 3 composite was studied by x-ray diffraction as well as scanning and transmission electron microscopy. The composite shows a homogeneous, thermal-stable nanostructure up to 900 °C due to dispersed alumina nanoparticles. The particles effectively strengthen crystallite/grain boundaries in processes of powder consolidation and annealing of the compact. In contrast to monolithic Cu, the Cu-1 vol.% Al 2 O 3 exhibits more than double strength and hardness. The nanocrystalline matrix and the low amount of alumina particles result in a yield strength of 288 MPa and a ductility of 15% which is a good combination for practical utilization of the material.

Description: The influence of Cu nanoparticles addition on microstructure and mechanical properties of Sn0.7Ag0.5Cu-BiNi/Cu solder joint after reflow and isothermal aging has been investigated in this study. Experimental results indicate that the addition of Cu nanoparticles suppresses the growth of intermetallic compound (IMC) layer at the interface after reflow and aging. Moreover, the bulk solder appears with refined microstructure after adding Cu nanoparticles. In addition, solder joints containing Cu nanoparticles display higher microhardness due to the dispersive distribution of Cu nanoparticles as well as the refined IMC particles. The addition of 0.1% Cu nanoparticles can improve the microhardness by 16% compared with the noncomposite. However, the existing porosity in the solder exerts a negative effect on microhardness and shear strength. The mechanism of porosity formation has been discussed in detail. Porosity increases markedly with increasing Cu nanoparticles proportion.

Description: Hot deformation behavior of a Fe-24Cr-22Ni-7Mo-0.5N superaustenitic stainless steel was investigated by hot compression tests in a wide temperature range of 950-1250 °C and strain rate range of 0.001-10 s −1 . The flow curves show that the flow stress decreases as the deformation temperature increases or the strain rate decreases. The processing maps developed on the basis of the dynamic materials model and flow stress data were adopted to optimize the parameters of hot working. It was found that the strain higher than 0.2 has no significant effect on the processing maps. The optimum processing conditions were in the temperature range of 1125-1220 °C and strain rate range of 0.1-3 s −1 . Comparing to other stable domains, microstructural observations in this domain revealed the complete dynamic recrystallization (DRX) with finer and more uniform grain size. Flow instability occurred in the domain of temperature lower than 1100 °C and strain rate higher than 0.1 s −1 .

Description: In this paper, the structure formation during the plastic deformation of polycrystalline nickel and aluminum based alloy 2024-T3 is investigated. The possibility of the relaxation and synergetic structure formation is examined. It is shown the deformation softening to be due to the crystallization of the amorphous structure of hydrodynamics flow channels (synergetic structure) HC as micrograins and their subsequent growth. The possible mechanism of micrograins’ growth is proposed. The deformation processes change the phase composition of the multiphase alloy 2024-T3. It is shown by the quantitative analysis of the structures which were deformed in different regimes of the alloy samples. A method for increasing of the fatigue life through a dynamic pre-deformation is suggested.

Description: In the present investigation, an attempt has been made to join Hastelloy C-276 nickel-based superalloy and AISI 321 austenitic stainless steel using ERNiCrMo-4 filler. The joints were fabricated by continuous and pulsed current gas tungsten arc welding processes. Experimental studies to ascertain the structure-property co-relationship with or without pulsed current mode were carried out using an optical microscope and scanning electron microscope. Further, the energy-dispersive spectroscope was used to evaluate the extent of microsegregation. The microstructure of fusion zone was obtained as finer cellular dendritic structure for pulsed current mode, whereas columnar structure was formed with small amount of cellular structure for continuous current mode. The scanning electron microscope examination witnessed the existence of migrated grain boundaries at the weld interfaces. Moreover, the presence of secondary phases such as P and μ was observed in continuous current weld joints, whereas they were absent in pulsed current weld joints, which needs to be further characterized. Moreover, pulsed current joints resulted in narrower weld bead, refined morphology, reduced elemental segregation and improved strength of the welded joints. The outcomes of the present investigation would help in obtaining good quality dissimilar joints for industrial applications and AISI 321 ASS being cheaper consequently led to cost-effective design also.

Description: The performance of dry self-lubricating bulk materials is directly related to microstructural aspects such as solid lubricant chemical composition and distribution. In this paper, dry powder mixtures were prepared from iron powder and 9-16.5 vol.% of solid lubricants (graphite and MoS 2 ), both combined and isolated. The results showed that interactions and reactions occurred during processing, either between the solid lubricants or between the lubricants and the matrix, generating carbides and sulfides. On account of that, the lubricant distribution in the microstructure is greatly altered, and the microhardness, friction coefficient and wear rate are increased. The best results were achieved by adequate powder particle size, solid lubricant content and sintering temperature control. In the composite containing 9%MoS 2  + 2.5%C, values of friction coefficient and wear rate lower than 0.08 and 8 × 10 −6  mm 3  N −1  m −1 were reached.

Description: Oxide dispersion strengthened (ODS) ferritic steels are candidates for cladding tubes in fast breeder nuclear reactors. In this study, an 18%Cr ODS ferritic steel was prepared through powder forging route. Elemental powders with a nominal composition of Fe-18Cr-2 W-0.2Ti (composition in wt.%) with 0 and 0.35% yttria were prepared by mechanical alloying in a Simoloyer attritor under argon atmosphere. The alloyed powders were heated in a mild steel can to 1473 K under flowing hydrogen atmosphere. The can was then hot forged. Steps of sealing, degassing and evacuation are eliminated by using powder forging. Heating ODS powder in hydrogen atmosphere ensures good bonding between alloy powders. A dense ODS alloy with an attractive combination of strength and ductility was obtained after re-forging. On testing at 973 K, a loss in ductility was observed in yttria-containing alloy. The strength and ductility increased with increase in strain rate at 973 K. Reasons for this are discussed. The ODS alloy exhibited a recrystallized microstructure which is difficult to achieve by extrusion. No prior particle boundaries were observed after forging. The forged compacts exhibited isotropic mechanical properties. It is suggested that powder forging may offer several advantages over the traditional extrusion/HIP routes for fabrication of ODS alloys.

Description: Investigation on the electrochemical behavior and corrosion product films formed on three 90Cu-10Ni tubes designated as Tubes A, B and C from three different manufacturers with different service lives were carried out using electrochemical techniques, SEM, XRD and XPS after immersion in 3.5 wt.% NaCl solution. The results of polarization curve measurements showed noticeable decrease in the corrosion current densities ( I corr ) of the three tubes with immersion time, and the I corr of Tube C was comparatively lower than those of Tubes A and B at early immersion period. EIS measurements revealed duplex film layers on the surface of the samples with the inner film formation occurring at different times for different tubes as the film resistance R f2 revealed the formation of the inner compact layer in Tube C after 15-day immersion and in Tubes A and B after 30 days. Tube C showed better corrosion resistance which is due to early formation of the inner compact oxide film. The XPS analysis revealed Ni enrichment on the surface film of the three samples but Ni depletion as the immersion time is increased.

Description: Iron-aluminum oxides in the red soil have a significant impact on the corrosion behavior of the metal for grounding grids. Effects of iron-aluminum oxides on the corrosion behavior of the cross section of copper-clad steel in the red soil have been investigated using electrochemical impedance spectroscopy and Tafel polarization. All the data indicate that the iron-aluminum oxides can promote the corrosion of copper-clad steel in the red soil. The corrosivity of the red soil greatly increases after iron-aluminum oxides are added into the soil. Iron-aluminum oxides promote galvanic corrosion of copper-clad steel and increase the corrosion degree of the center steel layer. The iron-aluminum oxides stimulate corrosion process of copper-clad steel acting as a cathodic depolarizing agent. XRD results further validate that the corrosion products of the copper-clad steel bar mainly consist of Fe 3 O 4 and Cu 2 O.

Description: The effects of die channel angle (Φ) in hot (~623 K) equi-channel angular pressing (ECAP) on microstructure, and tensile and compressive flow properties of AZ80 Mg alloy were investigated. Two solid ECAP dies, having Φ of (1) dual 60° and 120° in a single die and (2) 90° in another die, were designed for this purpose. Grain refinement with more than 40% reduction in average grain size along with submicron size second-phase β-precipitates was achieved after single-pass ECAP. A great variation in β-Mg 17 Al 12 phase morphology with increasing flow stresses in tension and compression are found with decreasing value of angle Φ. There found an increasing effect on strain to failure with decrease in porosity and second-phase precipitate modification. However, there appears flow asymmetry between tension and compression with the latter exhibiting greater flow stress and strain to failure.

Description: Recently, aerospace industries have shown increasing interest in forming limits of Inconel 718 sheet metals, which can be utilised in designing tools and selection of process parameters for successful fabrication of components. In the present work, stress-strain response with failure strains was evaluated by uniaxial tensile tests in different orientations, and two-stage work-hardening behavior was observed. In spite of highly preferred texture, tensile properties showed minor variations in different orientations due to the random distribution of nanoprecipitates. The forming limit strains were evaluated by deforming specimens in seven different strain paths using limiting dome height (LDH) test facility. Mostly, the specimens failed without prior indication of localized necking. Thus, fracture forming limit diagram (FFLD) was evaluated, and bending correction was imposed due to the use of sub-size hemispherical punch. The failure strains of FFLD were converted into major-minor stress space ( σ -FFLD) and effective plastic strain-stress triaxiality space ( η EPS-FFLD) as failure criteria to avoid the strain path dependence. Moreover, FE model was developed, and the LDH, strain distribution and failure location were predicted successfully using above-mentioned failure criteria with two stages of work hardening. Fractographs were correlated with the fracture behavior and formability of sheet metal.

Description: Service lifetime of ethylene propylene diene monomer (EPDM) rubber at room temperature (25 °C) was estimated based on accelerated aging tests. The study followed sealing stress loss on compressed cylinder samples by compression stress relaxation methods. The results showed that the cylinder samples of EPDM can quickly reach the physical relaxation equilibrium by using the over-compression method. The non-Arrhenius behavior occurred at the lowest aging temperature. A significant linear relationship was observed between compression set values and normalized stress decay results, and the relationship was not related to the ambient temperature of aging. It was estimated that the sealing stress loss in view of practical application would occur after around 86.8 years at 25 °C. The estimations at 25 °C based on the non-Arrhenius behavior were in agreement with compression set data from storage aging tests in natural environment.

Description: The composite coatings containing HBN were prepared on 2024 aluminum alloy by microarc oxidation in the electrolyte with nano-HBN particles. The microstructure, surface roughness, phase composition, hardness, adhesion strength and wear resistance of composite coatings were analyzed by SEM, EDS, laser confocal microscope, XRD, Vickers hardness tester, scratch test and ball-on-disc abrasive tests. The results revealed that composite coatings were mainly composed of γ-Al 2 O 3 , α-Al 2 O 3 , mullite and HBN. With increasing the content of HBN particles in the electrolyte, the size and number of the pores on the surface of composite coatings decreased significantly. Compared to the MAO coatings without HBN, the composite coatings exhibited better wear resistance, as demonstrated by the lower friction coefficient and the lower wear rate.

Description: Mechanically induced solid-state mixing, using high-energy ball milling technique, was employed for preparing WC/7 wt.% (10Cr/4Cr) solid-solution powders. The solid-solution powders obtained after 50 h of milling were mechanically mixed for 50 h together with small weight fractions (0-7 wt.%) of (ZrO 2  + 1.5 wt.% Y 2 O 3 ) powders. The powders were then consolidated in vacuum under a uniaxial pressure of 30 MPa at 1250 °C, using spark plasma sintering. The consolidated bulk samples were nearly full dense and maintained their nanocrystalline structure after this consolidation step. The results showed that the consolidated samples over the entire range of ZrO 2 concentrations (0–7 wt.%) had low values for Young’s modulus (297–318 GPa) due to their nanocrystalline structures. Moreover, the WC/7 wt.% (10Cr/4Cr)/7(ZrO 2 -1.5 mol.% Y 2 O 3 ) showed excellent wear resistance, indexed by its low-value friction coefficient (~0.29).

Description: TA15 and Ti2AlNb alloys were joined by diffusion welding. The influence of holding time on morphology and mechanical properties of the joint was studied under two conditions of different bonding pressure and temperature. The interface structure was analyzed by BSE and EDS. The mechanical properties of joints were tested. The results show that the typical interfacial microstructure consists of lath α-phase (TA15 alloy)/flake α phase + α-interfacial phase + α2 phase/B2-rich phase/Ti2AlNb alloy. When bonding at 920 °C and 15 MPa with increasing holding time, the interface microstructure evolves into flake α phase and distributes as a basket-weave and the interfacial coarse spherical α phase distributes as a line. α2 phase and O phase disappear gradually while the content of the B2 phase increases. The tensile strength of the joints is 870, 892 and 903 MPa, for 120, 150 and 210 min holding time, respectively, while the elongation rises as well. When bonding at 940 °C and 10 MPa with increasing holding time, the interfacial area includes more Widmanstatten structure and B2 phase. The tensile strength of joints decreases from 921 to 908 MPa, while the elongation increases from 12 to 15.5%, for holding 120 and 210 min, respectively. The tendency of plastic fracture also increases with holding time for both temperature-pressure combinations.

Description: The aim of this research was to investigate the effects of casting size (10-210 mm) on the microstructure and mechanical properties of spheroidal (SGI) and compacted (CGI) graphite cast irons. A comparison of the experimental mechanical data with those specified by ISO standards is presented and discussed. The study highlighted that the microstructure and mechanical properties of SGI (also known as ductile or nodular cast iron) are more sensitive to casting size than CGI (also known as vermicular graphite cast irons). In particular, in both types of cast iron, hardness, yield strength and ultimate tensile strength decreased, with increasing casting size, by 27% in SGI and 17% in CGI. Elongation to failure showed, instead, an opposite trend, decreasing from 5 to 3% in CGI, while increasing from 5 to 11% in SGI. These results were related to different microstructures, the ferritic fraction being more sensitive to the casting size in SGI than CGI. Degeneration of spheroidal graphite was observed at casting size above 120 mm. The microstructural similarities between degenerated SGI and CGI suggested the proposal of a unified empirical constitutional law relating the most important microstructural parameters to the ultimate tensile strength. An outstanding result was also the finding that standard specifications underestimated the mechanical properties of both cast irons (in particular SGI) and, moreover, did not take into account their variation with casting size, at thicknesses over 60 mm.

Description: Rolling contact fatigue (RCF) of a nitrided ductile cast iron was investigated. Flat washers machined from a pearlitic ductile cast iron bar were quenched and tempered to maximum hardness, ground, polished and divided into four groups: (1) specimens tested as quenched and tempered; (2) specimens plasma-nitrided for 8 h at 400 °C; (3) specimens plasma-nitrided and submitted to a diffusion process for 16 h at 400 °C; and (4) specimens submitted to a second tempering for 24 h at 400 °C. Hardness profiles, phase analyses and residual stress measurements by x-ray diffraction, surface roughness and scanning electron microscopy were applied to characterize the surfaces at each step of this work. Ball-on-flat washer tests were conducted with a maximum contact pressure of 3.6 GPa, under flood lubrication with a SAE 90 API GL-5 oil at 50 °C. Test ending criterion was the occurrence of a spalling. Weibull analysis was used to characterize RCF’s lifetime data. Plasma-nitrided specimens exhibited a shorter RCF lifetime than those just quenched and tempered. The effects of nitriding on the mechanical properties and microstructure of the ductile cast iron are discussed in order to explain the shorter endurance of nitrided samples.

Description: In the present study, St37 low-carbon steel and 304 stainless steel were welded successfully, with the thickness of 2 mm, by a friction stir spot welding process carried out at the tool dwell time of 6 s and two different tool rotational speeds of 630 and 1250 rpm. Metallographic examinations revealed four different zones including SZ and HAZ areas of St37 steel and SZ and TMAZ regions of 304 stainless steel in the weld nugget, except the base metals. X-ray diffraction and energy-dispersive x-ray spectroscopy experiments were used to investigate the possible formation of such phases as chromium carbide. Based on these experiments, no chromium carbide precipitation was found. The recrystallization of the weld nugget in the 304 steel and the phase transformations of the weld regions in the St37 steel enhanced the hardness of the weld joint. Hardness changes of joint were acceptable and approximately uniform, as compared to the resistance spot weld. In this research, it was also observed that the tensile/shear strength, as a crucial factor, was increased with the rise in the tool rotational speed. The bond length along the interface between metals, as an effective parameter to increase the tensile/shear strength, was also determined. At higher tool rotational speeds, the bond length was found to be improved, resulting in the tensile/shear strength of 6682 N. Finally, two fracture modes were specified through the fracture mode analysis of samples obtained from the tensile/shear test consisting of the shear fracture mode and the mixed shear/tensile fracture mode.

Description: Superinvar Fe-31Ni-5Co alloy (SI) and Co-20Cr-15W-10Ni superalloy (SA) are used in space applications. Similar metal (SI-SI and SA-SA) joints as well as dissimilar metal (SA-SI) joints of these alloys have been made using electron beam welding (EBW) technique. Extensive characterization of these weldments has been carried out using optical and electron microscopy, microhardness measurements and tensile testing at ambient and cryogenic temperatures. It has been observed that weld efficiency is 100% for similar metal joints, whereas it is governed by base metal properties of the alloy having lower strength for dissimilar metal joint. Weld efficiency of SA-SI/EBW joint is comparable with base metal of lower strength indicating no detrimental formation of intermetallic/brittle phase. Microhardness of the SA-SI/EBW joint is found to be representative of the respective base metal properties with no sudden variation across the SA/SI interface in the weldment indicating good dilution in the weld. This has been confirmed through energy-dispersive spectrum using x-rays (EDX) showing the presence of Fe near the superalloy weldment interface and the presence of Cr and W near the superinvar weldment interface. Increase in strength and decrease in ductility of base metals are observed for all types of joints when tested at cryogenic temperature (77 K) vis-à-vis at ambient temperature. Fracture features of the failed surface of SA-SI/EBW joint are found to be similar to that of the SI-SI/EBW joint. Microhardness, mechanical properties and fracture analysis confirm that failure of dissimilar metal joint takes place toward lower strength base metal, i.e., superinvar.

Description: The effect of hydrogen charging on the stress corrosion cracking (SCC) behavior of 2205 duplex stainless steel (DSS) under 3.5 wt.% NaCl thin electrolyte layer was investigated on precharged samples through hydrogen determination, electrochemical measurement, and slow strain rate tensile test. Results show that hydrogen charging weakens the passive film without inducing any obvious trace of localized anodic dissolution. Therefore, hydrogen charging increases the SCC susceptibility of 2205 DSS mainly through mechanism of hydrogen embrittlement rather than mechanism of localized anodic dissolution. 2205 DSS shows a more susceptibility to hydrogen under the TEL when hydrogen charging current density (HCCD) is between 20 and 50 mA cm −2 . The increasing trend is remarkable when hydrogen charging current density increases from 20 to 50 mA cm −2 and fades after 50 mA cm −2 .

Description: An experimental investigation on the effects of post-annealing treatments on the microstructure, mechanical properties and corrosion behavior of direct metal laser sintered Ti-6Al-4V alloys has been conducted. The microstructure and phase evolution as affected by annealing treatment temperature were examined through scanning electron microscopy and x-ray diffraction. The tensile properties and Vickers hardness were measured and compared to the commercial Grade 5 Ti-6Al-4V alloy. Corrosion behavior of the parts was analyzed electrochemically in simulated body fluid at 37 °C. It was found out that the as-printed parts mainly composed of non-equilibrium α′ phase. Annealing treatment allowed the transformation from α′ to α phase and the development of β phase. The tensile test results indicated that post-annealing treatment could improve the ductility and decrease the strength. The as-printed Ti-6Al-4V part exhibits inferior corrosion resistance compared to the commercial alloy, and post-annealing treatment can reduce its susceptibility to corrosion by reducing the two-phase interface area.

Description: The ternary Ni- x Al- y Ti ( x , y in wt.%) nanocomposite protective coatings were electroplated on carbon nanotubes (CNT)/Al composite by the co-deposition of Al and Ti particles at several current densities. The dependences of microstructure, microhardness, residual stress, and corrosion resistance of the ternary nanocomposite coating on current density were investigated. The results showed that the embedded Al and Ti particles caused the crystallite refinement and the decrease of [200] fiber texture of nanocrystalline Ni matrix when current density decreased. The microstructure evolution endowed the ternary nanocomposite coating with high microhardness and corrosion resistance. The surface residual stress of the ternary nanocomposite coating increased with decreasing current density.

Description: The corrosion behavior of low-C medium-Mn steel in simulated marine immersion and splash zone environment was studied by static immersion corrosion experiment and wet-dry cyclic corrosion experiment, respectively. Corrosion rate, corrosion products, surface morphology, cross-sectional morphology, elemental distribution, potentiodynamic polarization curves and electrochemical impedance spectra were used to elucidate the corrosion behavior of low-C medium-Mn steel. The results show that corrosion rate in immersion zone is much less than that in splash zone owing to its relatively mild environment. Manganese compounds are detected in the corrosion products and only appeared in splash zone environment, which can deteriorate the protective effect of rust layer. With the extension of exposure time, corrosion products are gradually transformed into dense and thick corrosion rust from the loose and porous one in these two environments. But in splash zone environment, alloying elements of Mn appear significant enrichment in the rust layer, which decrease the corrosion resistance of the steel.

Description: In this work, we describe a method to improve the bonding of an immiscible Mg/steel system using Ni as an interlayer by coating it on the steel surface. Laser welding-brazing of AZ31B Mg alloy to Ni-coated Q235 steel using Mg-based filler was performed in a lap configuration. The influence of laser power on the weld characteristics, including joint appearance, formation of interfacial reaction layers and mechanical properties was investigated. The results indicated that the presence of the Ni-coating promoted the wetting of the liquid filler metal on the steel surface. A thermal gradient along the interface led to the formation of heterogeneous interfacial reaction layers. When using a low laser power of 1600 W, the reaction products were an FeAl phase in the direct laser irradiation zone, an AlNi phase close to the intermediate zone and mixtures of AlNi phase and an (α-Mg + Mg 2 Ni) eutectic structure near the interface at the seam head zone. For high powers of more than 2000 W, the FeAl phase grew thicker in the direct laser irradiation zone and a new Fe(Ni) transition layer formed at the interface of the intermediate zone and the seam head zone. However, the AlNi phase and (α-Mg + Mg 2 Ni) eutectic structure were scattered at the Mg seam. All the joints fractured at the fusion zone, indicating that the improved interface was not the weakest joint region. The maximum tensile-shear strength of the Mg/Ni-coated steel joint reached 190 N/mm, and the joint efficiency was 70% with respect to the Mg alloy base metal.

Description: Mg-6wt.%Al-1wt.%Sn alloys under different conditions are prepared. Primary magnesium-air batteries are assembled using such experimental Mg-Al-Sn alloys as anodes. The discharge behaviors of different alloys are investigated in 3.5 wt.% NaCl solution. The results show that the solution treatment can facilitate the homogeneous distribution of alloy elements and reduce the accumulation of discharge products. The magnesium-air battery based on the solution-treated Mg-Al-Sn anode presents higher operating voltage and more stable discharge process than those on the as-cast and the aged ones. Although the solution treatment cannot effectively improve the capacity density and the anodic efficiency of the experimental Mg-Al-Sn alloy, it is an effective approach to increasing the power and the energy density during discharge process. Especially at the applied current density of 30 mA cm −2 for 5 h, the solution-treated anode supplies 1.212 V average operating voltage, the anode energy density reaches 1527.2 mWhg −1 , while the cast one is 1481.3 mWhg −1 and the aged one is 1478.8 mWhg −1 .

Description: In this work, we address two of the main challenges encountered in constitutive modeling of the thermomechanical behaviors of actuation-based shape memory alloys. Firstly, the complexity of behavior under cyclic thermomechanical loading is properly handled, particularly with regard to assessing the long-term dimensional stability. Secondly, we consider the marked differences in behavior distinguishing virgin-versus-trained SMA material. To this end, we utilize a set of experimental data comprehensive in scope to cover all the anticipated operational conditions for one and same SMA alloy, having a specific chemical composition with fixed heat treatment. More specifically, this includes twenty-four different tests from the recent SMA experimental literature for the Ni 49.9 Ti 50.1 material having austenite finish temperature above 100 °C. Under all the different conditions investigated, the model results were found to be in very good agreement with the experimental measurements.

Description: Superhydrophobic (SHP) coatings on titanium were developed using a two-step method involving anodization and coating with silane. The robustness of the SHP coatings was assessed by sonication and water impact tests. The adhesion of the coatings was evaluated by ASTM standard tape test. After evaluating the stability, the durability of superhydrophobic coatings developed on titanium was tested in seawater. The long-term immersion in seawater showed minimal reduction in water contact angle (WCA) after the immersion. Antibacterial activity of the SHP coatings after long-term exposure in seawater and bacterial pure cultures were also evaluated. The present study aims to evaluate the stability, durability and shelf life of the SHP coatings developed on Ti using silanes for long-term practical applications.

Description: In the present paper, the aging precipitation and coarsening of disk-like δ-Ni 2 Si particles in Cu and Cu-10Zn alloys aged at 450 °C have been investigated by hardness, electric resistivity measurement and transmission electron microscopy observation. The coarsening dynamics of the average diameter of the δ-Ni 2 Si particles coincides with the t 1/3 time law for both alloys. The coarsening of the diminution of supersaturation related to aging time t coincides with the t −1/3 time rule. Adding Zn to the Cu-Ni-Si alloy increases the growth and coarsening rate of the particles mainly because of the increased diffusivity D of the δ-Ni 2 Si particles in the matrix. The value of D of the δ-Ni 2 Si particles in the Cu-xZn ( x  = 0, 10 wt.%) matrix and the Cu/δ-Ni 2 Si interfacial energy γ are independently calculated by using the Lifshitz–Slyozov–Wagner theory which was extended to include disk-like particles by Boyd and Nicholson. The values of D and γ increase from 0.77 × 10 −19 to 2.21 × 10 −19  m 2 /s and 0.19 to 0.63 J/m 2 , respectively, when Zn is added to the Cu-Ni-Si alloy. These calculations and the analysis show that the properties of Cu-Ni-Si-Zn alloy can significantly be enhanced by reducing the aging temperature.

Description: The aim of this study was to investigate the effects of welding current and welding time on the microstructure and mechanical properties of welding joints. To this end, two dissimilar materials, austenitic stainless steel alloy SUS301L and aluminum alloy 6063-T6, were welded together via intermediate frequency resistance spot welding. A thick, two-layered intermetallic compound layer containing FeAl 3 and Fe 2 Al 5 phases was formed at the SUS301L/6063-T6 interface. As the welding current and welding time increased, the nugget diameter increased, the interfacial layer structure became coarser, the thickness of the interfacial intermetallic compound increased, and the tensile shear load of the weld joints had an increased welding tendency in stainless steel/aluminum joints. The nugget diameter reached 5.4 mm, and the maximum tensile shear load reached 1783 N at 7 kA for 200 ms of welding time. The resistance spot welded joint exhibited an interfacial fracture mode in the welded joint. The crack initiated at the interfacial intermetallic compound layer near the aluminum alloy side and spread through the interfacial layer, as well as through the aluminum alloy fusion zone near the interface.

Description: In this work, the effect of alloying element Zn on microstructure and prosperity of 5083 Al alloy was investigated. The grain sizes of 5083 and 5083 + Zn alloys were refined to 〈200 nm by appropriate rolling processes. The microhardness and tensile tests were conducted. The results showed that the dislocation density evaluated by microhardness of rolled 5083 + Zn alloys increases from 1.90 × 10 13 to 2.57 × 10 13 with increasing Zn contents. The tensile tests showed that the ultimate tensile strength of rolled 5083 alloy doubled when Zn was introduced, while the uniform elongation pronounced decreased. The yield strength of 5083 + Zn alloys increases with Zn contents. However, the strain hardening rate for the rolled alloys was decreased with increasing Zn contents. Solid solution strengthen and precipitation strengthen due to addition of Zn were responsible for the increase in yield strength and ultimate tensile strength.

Description: Due to their unusual mechanical, chemical, physical, optical, and biological properties, nearly spherical-like nanodiamonds have received much attention as desirable advanced nanomaterials for use in a wide spectrum of applications. Although, nanodiamonds can be successfully synthesized by several approaches, applications of high temperature and/or high pressure may restrict the real applications of such strategic nanomaterials. Distinct from the current preparation approaches used for nanodiamonds preparation, here we show a new process for preparing ultrafine nanodiamonds (3-5 nm) embedded in a homogeneous amorphous-carbon matrix. Our process started from high-energy ball milling of commercial graphite powders at ambient temperature under normal atmospheric helium gas pressure. The results have demonstrated graphite-single wall carbon nanotubes-amorphous-carbon-nanodiamonds phase transformations carried out through three subsequent stages of ball milling. Based on XRD and RAMAN analyses, the percentage of nanodiamond phase + C60 (crystalline phase) produced by ball milling was approximately 81%, while the amorphous phase amount was 19%. The pressure generated on the powder together the with temperature increase upon the ball-powder-ball collision is responsible for the phase transformations occurring in graphite powders.

Description: In this paper, processes occurring during heat treatment of the diamond-Ti compound composites without Co addition were investigated and compared with commercial PCD. Three types of materials were prepared. The first material was sintered using the mixture containing diamond and 10 mass% of TiC, the second material was prepared using diamond powder and 10 mass% of Ti-Si-C, and the third composite was sintered using the addition of 10 mass% of TiB 2 . During the research, it was proved that TiO 2 formation contributes to material swelling and WO 3 (W is present from the milling process) causes a significant increase in coefficient of friction. TiC and Ti-Si-C bonded materials are very susceptible to this process of oxidation; their hardness drops absolutely after wear test at 600 °C. The diamond composite with TiB 2 is the most resistant to oxidation from investigated materials.

Description: Although multiwall carbon nanotubes (MWCNT) are promising materials to strengthen lightweight aluminum matrix composites, their dispersion into the metallic matrix is challenge. In the present work, MWCNT were dispersed into age-hardenable AA6061 aluminum alloy by high-energy ball milling and the blend was subsequently hot-extruded. The composite bars obtained were heat-treated by solution heat treatment at 520 °C and artificially aged at 177 °C for 8 h, in order to reach the T6 temper. Special attention was given to the integrity of the MWCNT along the entire composite production. The microstructure of the obtained bars was evaluated by optical and scanning electron microscopy, and the mechanical properties were evaluated by Vickers microhardness tests. Raman spectroscopy, x-ray diffraction and transmission electron microscopy were employed to evaluate the structural integrity of MWCNT. It was found that milling time is critical to reach a proper dispersion of the reinforcing phase. The composite hardness increased up to 67% with the dispersion of 2% in weight of MWCNT, when comparing with un-reinforced bars produced by similar route. However, age hardening was not observed in composite bars after heat treatment. It was also found that MWCNT continuously degraded along the process, being partially converted into Al 4 C 3 in the final composite.

Description: Wear behavior of a harmonic structured 304L austenitic stainless steel with periodically distributed fine and coarse grains was examined and compared with a sintered non-harmonic structured 304L stainless steel and a low carbon conventional 304 stainless steel using fretting wear tests at varying loads in ball-on-flat contact configuration. Characterization was accomplished using scanning electron microscope, energy-dispersive spectroscopy, optical profilometry and Raman spectroscopy. Coefficient of friction and wear volume were minimum at intermediate normal load of 5 N, whereas maximum at 10 N for the harmonic stainless steel compared to other two steels. Harmonically distributed fine- and coarse-grained structure attributes to the higher wear rate of the harmonic structured steel at higher load because of differential interaction of the ball with the harmonically distributed hard (fine) and relatively soft (coarse) regions.

Description: A SiC nanoparticle toughened-SiC/MoSi 2 -SiC functionally graded oxidation protective coating on graphite was prepared by reactive melt infiltration (RMI) at 1773 and 1873 K under argon atmosphere. The phase composition and anti-oxidation behavior of the coatings were investigated. The results show that the coating was composed of MoSi 2 , α-SiC and β-SiC. By the variations of Gibbs free energy (calculated by HSC Chemistry 6.0 software), it could be suggested that the SiC coating formed at low temperatures by solution-reprecipitation mechanism and at high temperatures by gas-phase reactions and solution-reprecipitation mechanisms simultaneously. SiC nanoparticles could improve the oxidation resistance of SiC/MoSi 2 -SiC multiphase coating. Addition of SiC nanoparticles increases toughness of the coating and prevents spreading of the oxygen diffusion channels in the coating during the oxidation test. The mass loss and oxidation rate of the SiC nanoparticle toughened-SiC/MoSi 2 -SiC-coated sample after 10-h oxidation at 1773 K were only 1.76% and 0.32 × 10 −2  g/cm 3 /h, respectively.

Description: In this research, we studied low velocity impact response of homogenous basalt fiber-reinforced polymer (BFRP) composites and then compared the impact key parameters with carbon fiber-reinforced polymer (CFRP) homogenous composites. BFRPs and CFRPs were fabricated by vacuum-assisted resin transfer molding (VARTM) method. Fabricated composites included 60% fiber and 40% epoxy matrix. Basalt and carbon fibers used as reinforcement materials were weaved in 2/2 twill textile tip in the structures of BFRP and CFRP composites. We also utilized the energy profile method to determine penetration and perforation threshold energies. The low velocity impact tests were carried out in 30, 60, 80, 100, 120 and 160 J energy magnitudes, and impact response of BFRPs was investigated by related force-deflection, force-time, deflection-time and absorbed energy-time graphics. The related impact key parameters such as maximum contact force, absorbed energy, deflection and duration time were compared with CFRPs for various impact energy levels. As a result, due to the higher toughness of basalt fibers, a better low velocity impact performance of BFRP than that of CFRP was observed. The effects of fabrication parameters, such as curing process, were studied on the low velocity impact behavior of BFRP. The results of tested new fabricated materials show that the change of fabrication process and curing conditions improves the impact behavior of BFRPs up to 13%.

Description: The current work analyzes the effect of the dynamic change in strain rate during tensile loading of a mild steel on its mechanical and stress corrosion behavior in 3.5 wt.% NaCl solution. The sample experiences high strain rate (10 −2  s −1 ) up to 10, 15 and 20% of total deformation and then very low strain rate of 10 −6  s −1 till fracture without any unloading in between. The behavioral characteristics of the steel under these circumstances are found to be different from that exhibited during complete loading till fracture both at high and slow strain rates separately. Total strain increases with the increase in the strain at which change in strain rate happens, and this is attributed to the generation of large number of dislocations at higher strain rate and subsequently release of dislocation at low strain rate during change over due to more time available for dynamic recovery. This observation is common for both in air and corrosive environment. One unique observation in this study is the higher total strain and lower strength observed during dynamic change in strain rate in the corrosive environment compared to that in air, which is attributed to the hydrogen-induced plasticity mechanism.

Description: In this paper, an amorphous Ni-W coating was electrodeposited on the low-carbon steel and then annealed in hydrogen and argon atmosphere. Their characterization was carried out using scanning electron microscopy and x-ray diffraction. The corrosion characterization was carried out using the potentiodynamic polarization (Tafel) and electrochemical impedance spectroscopy. The results show that microcracks inevitably exist on the surface of Ni-W coating when annealed at 750 °C or higher temperature. After annealing treatment, amorphous structure transforms to crystalline and some new phases are precipitated, which is significantly affected by the annealing temperature and atmosphere. The microhardness of annealed Ni-W coatings is much higher than that of as-deposited coating, while an adverse corrosion performance is observed for the annealed Ni-W coatings. The coating annealed in hydrogen at 500 °C shows a huge improvement in hardness and a fairly acceptable corrosion resistance compared with the as-deposited Ni-W coating.

Description: In this study, alumina-silica composite coating was coated on an aluminum substrate by the plasma electrolytic oxidation technique at 30 °C and current density of 20 A dm −2 for 30, 60, and 90 min. Microstructure of the coatings was evaluated by an atomic force microscope and a scanning electron microscope. X-ray diffraction analysis was employed to evaluate the phase analysis of the coatings. In addition, corrosion behavior of the coated and uncoated samples was investigated by using potentiodynamic polarization and electrochemical impedance spectroscopy tests in a 3.5 wt.% NaCl solution at 25 °C. Results showed that, by increasing the coating time, the coating thickness and porosity size were increased. However, the number of porosities was decreased by increasing the coating time. Phase analysis results revealed that the coating was mainly composed of mullite, alumina, and silica. Moreover, the results of the corrosion tests indicated that the alumina-silica composite coating formed by the plasma electrolytic oxidation technique considerably improved the corrosion resistance. The sample coated for 60 min showed a better corrosion resistance in comparison with other samples coated for 30 and 90 min.

Description: FeCrMoVTi x ( x values represent the molar ratio, where x  = 0, 0.5, 1.0, 1.5, and 2.0) high-entropy alloys were prepared by a vacuum arc melting method. The effects of Ti element on the microstructure and room-temperature mechanical properties of the as-cast FeCrMoVTi x alloys were investigated. The results show that the prepared alloys exhibited typical dendritic microstructure and the size of the microstructure became fine with increasing Ti content. The FeCrMoV alloy exhibited a single body-centered cubic structure (BCC1) and the alloys prepared with Ti element exhibited BCC1 + BCC2 mixed structure. The new BCC2 phase is considered as (Fe, Ti)-rich phase and was distributed in the dendrite region. With the increase of Ti content, the volume fraction of the BCC2 phase increased and its shape changed from a long strip to a network. For the FeCrMoV alloy, the fracture strength, plastic strain, and hardness reached as high as 2231 MPa, 28.2%, and 720 HV, respectively. The maximum hardness of 887 HV was obtained in the FeCrMoVTi alloy. However, the fracture strength, yield stress, and plastic strain of the alloys decreased continuously as Ti content increased. In the room-temperature compressive test, the alloys showed typical brittle fracture characteristics.

Description: Twinning-Induced Plasticity (TWIP) steels have received great attention due to their excellent mechanical properties as a result of austenite twinning during straining. In this paper, the effects of stress state on the strain hardening behaviors of Fe-20Mn-1.2C TWIP steel were studied. A twinning model considering stress state was presented based on the shear-band framework, and a strain hardening model was proposed by taking dislocation mixture evolution into account. The models were verified by the experimental results of uniaxial tension, simple shear and rolling processes. The strain hardening behaviors of TWIP steel under different stress states were predicted. The results show that the stress state can improve the austenite twining and benefit the strain hardening of TWIP steel.

Description: To obtain medical implants with better performance, it is necessary to conduct studies on the quality and other performances of the selective laser melting (SLM) manufacturing parts. Interior defects in CoCrMo parts manufactured by SLM were detected using x-ray radiographic inspection, and the manufactured parts compared with three-dimensional models to assess manufacturing quality. Impact tests were employed to establish the mechanical properties of the manufactured parts. With the aim of studying the mechanism of fracture of the parts, we utilized a metalloscope and SEM to observe the surface and fractal theory was used to analyze the appearance of fractures. The results show that part defects manifested in an increase in transmittance caused by the non-uniform distribution of density, resulting in variation in the residual stresses of the parts. The density of the parts was more uniform following heat treatment. Internal residual stress of the manufactured parts enhanced their impact toughness. There was a ductile-brittle transition temperature between the two annealing temperatures. We determined that the fracture mechanism was brittle fracture. Fractures exhibited significant fractal behavior. The impact energy and fractal dimension were positively correlated, which provided good support for using selective laser melting manufacturing of CoCrMo alloy in medical implants.

Description: Texture and tempered condition combined effects on fatigue behavior in an Al-Cu-Li alloy have been investigated using tensile testing, cyclic loading testing, scanning electron microscope (SEM), transmission electron microscopy (TEM) and texture analysis. Results showed that in near-threshold region, T4-tempered samples possessed the lowest fatigue crack propagation (FCP) rate. In Paris regime, T4-tempered sample had similar FCP rate with T6-tempered sample. T83-tempered sample exhibited the greatest FCP rate among the three tempered conditions. 3% pre-stretching in T83-tempered sample resulted in a reducing intensity of Goss texture and facilitated T 1 precipitation. SEM results showed that less crack deflection was observed in T83-tempered sample, as compared to other two tempered samples. It was the combined effects of a lower intensity of Goss texture and T 1 precipitates retarding the reversible dislocation slipping in the plastic zone ahead the crack tip.

Description: Non-collinear nonlinear ultrasonic (NCNLU) wave mixing technique has been established to study the localized plastic deformation at the crack tip during fatigue. A pair of ultrasonic shear wave was mixed non-collinearly to obtain a longitudinal wave of frequency equal to the sum of the two shear wave frequencies under a resonant condition. Experiments were carried out on notched 9Cr-1Mo 3-point bend specimen during high-cycle fatigue. The variation of the NCNLU parameter with the stress accumulation at the crack tip during the fatigue crack initiation and propagation and mapping of the deformation zone around the crack tip are described in this paper.

Description: In this study, a fine-grained structure was obtained in high-Mn austenitic steel through martensite treatment. The corrosion response of fine-grained and coarse-grained steels was studied and compared in 3.5 wt.% NaCl solution. Electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, and Mott-Schottky analysis were performed to understand the effect of grain refinement on the electrochemical behavior of this steel. Microstructural evaluation showed that by reduction in grain size, the amount of low energy grain boundaries was increased, which led to better electrochemical behavior. In addition, the corrosion resistance of fine-grained steel did not deteriorate in comparison with coarse-grained steel. Both specimens showed a charge-transfer resistance of about 4-5 kΩ cm 2 in NaCl. Besides, a protective film related to fine-grained sample was detected by EIS and Mott-Schottky analysis, which could be a sign of higher grain boundaries in this steel.

Description: The mechanical properties of dual-phase (DP) steels were correlated with the amount of martensite and its carbon content. The application of rule of mixtures for predicting the mechanical properties was critically discussed. Subsequently, a modified rule of mixtures was developed to estimate the mechanical properties of DP steels, which accounts for the variation of carbon content in martensite as a function of its volume fraction. The proposed model was able to predict the observed trends and values of hardness, yield stress, and tensile strength in a DP steel with ~0.1 wt.% C. Then, its applicability was also verified for a DP steel with ~0.2 wt.% C to cover the usual range of carbon content in DP steels. As a result, this simple and effective approach is anticipated to find application in estimating the properties of DP steels.

Description: In this study, the effect of friction layer thickness and subsurface nano-hardness of wear track on tribological behavior of γ-TiAl matrix composites is investigated. The results of dry sliding tribolocial tests of γ-TiAl matrix composites with 0-2.25 wt.% multilayer graphene (MLG) (0.25 wt.% in tolerance) under different applied loads are reported. The testing results show that the optimized addition amount of MLG is 1.75 wt.% at 12 N (friction layer thickness 3.23 µm, subsurface nano-hardness of wear track 9.03 GPa). It can be found that a continuous and thick friction layer is formed in γ-TiAl-1.75 wt.% MLG at 12 N, resulting in a lower friction coefficient of 0.31 and wear rate of 2.09 × 10 −5  mm 3  N −1  m −1 . During dry sliding process, the high subsurface nano-hardness of wear track leads to the increase in resisting plastic deformation capacity and reduces the material loss. Meanwhile, the thick friction layer contains MLG with high tensile strength which is easily sheared off. Hence, γ-TiAl matrix composites show excellent tribological performance of a friction-reducing and an increase in wear resistance. The investigation shows that γ-TiAl-1.75 wt.% MLG, due to its excellent tribological behavior at 12 N, can be chosen as a promising structural material for minimizing friction- and wear-related mechanical failures in sliding mechanical components.

Description: A microspring is an important actuating component used widely in micro-electromechanical systems. It is important to develop microforming techniques for high-fatigue life microsprings manufactured. In this work, a micro-extrusion die was designed and manufactured for a plane microspring, and a CuAl7 copper alloy plane microspring was fabricated by cold extrusion. Effects of pre-annealing treatment, extrusion velocity, and lubrication conditions on the extrusion loading, surface crack and fatigue life of the spring were studied. The spring microstructure was characterized by equiaxed grains on the spring ends, and elongated grains exhibited the spring interior. Both internal and surface cracks were present in the springs. A good lubrication condition, an appropriate pre-annealing treatment, and a suitable extrusion velocity would reduce surface cracks. The fatigue life of the spring extruded at higher velocity was larger than that extruded at lower velocity under the same surface crack density. The fatigue life decreased with increasing annealing treatment temperature and holding time. A good lubrication condition during the extrusion process would improve the fatigue life of the spring. The maximum fatigue life of these extruded microsprings was 19,260 cycles when the cycle force was 10 N.

Description: The effect of H 2 S/HS − , which simulates the main metabolites of sulfate-reducing bacteria (SRB), on the electrochemical and stress corrosion cracking (SCC) behaviors of X100 steel was investigated in a near-neutral solution. The results showed that different H 2 S/HS − contents mainly affected the cathodic process of X100 electrochemical corrosion. As the concentration of H 2 S/HS − increased, the corrosion potential was shifted negatively, the corrosion current density was considerably increased, and the corrosion rate was linearly increased. Different rust layers with shifting structures were formed under different conditions and had different effects on electrochemical behaviors. However, sulfide mainly promoted local corrosion processes. With the synergistic effects of stress and H 2 S/HS − , SCC susceptibility was considerably enhanced. The accelerated process of hydrogen evolution by sulfide was crucial in enhancing SCC processes. In brief, the trace H 2 S/HS − generated by SRB metabolites played a positive role in promoting SCC.

Description: Acrylonitrile-Butadiene-Styrene (ABS), also known as a thermoplastic polymer, is extensively utilized for manufacturing home appliances products as it possess impressive mechanical properties, such as, resistance and toughness. However, the aforementioned properties are affected by operating temperature and atmosphere humidity due to the viscoelasticity property of an ABS polymer material. Moreover, the prediction of optimum working conditions are the little challenging task as it influences the final properties of product. This present study aims to develop the finite element (FE) models for predicting the creep behavior of an ABS polymeric material. In addition, the material constants, which represent the creep properties of an ABS polymer material, were predicted with the help of an interpolation function. Furthermore, a comparative study has been made with experiment and simulation results to verify the accuracy of developed FE model. The results showed that the predicted value from FE model could agree well with experimental data as well it can replicate the actual creep behavior flawlessly.

Description: In this paper, the sources of variability and lower values in toughness measurements of a high-strength low alloy weld metal are investigated by detailed observations of fracture surfaces and the microstructures at crack initiation. The results reveal that the variability of the notch Charpy toughness is related to the location of the cleavage initiation origins. The three factors jointly contribute to give rise to variability and lower value of toughness. That is, (1) the location that the notch is sampled at deposited weld metal or reheated weld metal, (2) the location that a large grain region is appeared on the path ahead of the notch root, (3) the distributed location of the defect or the brittle second-phase particle. When three factors were simultaneously satisfied, the lower value of the Charpy toughness is appeared. The notch is sampled at the largest grain region at deposited weld metal, and the defect or the brittle second-phase particle is close to the notch root and sampled by its high stress field, the lowest Charpy toughness is obtained.

Description: The ever more pressing and concurrent requirements of light design, increased performances and reliability, energy savings together with acceptable costs, is always pushing researchers and engineers toward the definition and application of new materials and treatments, able to guarantee superior properties and adequate repeatability and reliability. This means that one step beyond the definition of a potentially successful solution, a complete characterization of the new materials is needed, in order to get the right data and use them in the design process. A promising severe plastic deformation surface treatment to improve the fatigue properties of materials and metal parts is considered in this paper. The used treatment is called the severe shot peening, and it is derived from the conventional shot peening but with use of unusually high peening parameters. It was proven that it is able to generate a nanostructured surface layer of material, which results in superior fatigue properties when applied to many structural materials. The severe shot peening is applied to an AW 7075 Al alloy, widely used in mechanical and aeronautic constructions and the effects of such a treatment on this material are investigated in this paper, with particular emphasis on the ultra-high-cycle fatigue behavior. The results address the choice of the correct treatment parameters for getting an evaluable advantage of this treatment and are critically discussed for a complete understanding of the mechanisms leading to the modified fatigue behavior, in view of the future developments and research in the field.

Description: In situ tensile tests at room temperature have been conducted on a duplex stainless steel (DSS) thermally aged at 400 °C for 10,000 h to investigate both the plastic deformation mechanisms and the effect of long-term thermal aging on crack initiation. After thermal aging, the ultimate tensile strength of the DSS increases and the plasticity significantly decreases. The fracture morphology changes from ductile fracture with shallow dimples to a mixture of cleavages in ferrite and tearing in austenite. Electron backscattered diffraction (EBSD) technique has been used to determine the crystallographic orientations of austenite and ferrite grains on three areas deformed differently. The EBSD analysis results indicate that high strain occurs near grain boundaries and phase boundaries. The localized strain incompatibility is considered to be responsible for high stress concentration and crack initiation. The long-term thermal aging affect on the crack initiation and the cleavage cracks are found to be initiated in aged ferrite grains.

Description: Composites are one of the fastest developing materials. Research is particularly intensive in case of light metal alloys due to i.a. economic and environmental aspects. One of the innovative solutions is production of the metal matrix composites (MMC) by adding the cordierite ceramics obtained from fly ashes to magnesium alloys. In addition to obtaining new-generation materials with improved mechanical properties, also the waste is utilized which has a significant environmental and economic importance. In order to select the suitable operating conditions for such alloys, their corrosion resistance must be determined. This paper presents the results of corrosion resistance tests of AM60 magnesium alloy matrix composites reinforced with cordierite ceramics. The following issues were examined: (1) impact of the volume fraction of cordierite ceramics, 2 or 4 wt.%; (2) impact of surface roughness (two variants of surface treatment); and (3) impact of heat treatment on corrosion resistance of obtained composites. The results were compared with data recorded for the base AM60 alloy (which surface treatment was identical as of the composites). Moreover, the XRD and microanalysis of the chemical compositions by EDS method were applied to determine phases occurring in the investigated composites. Furthermore, the XRD was also performed in order to identify the corrosion products on the surface of the material. The test results indicate that the alloy reinforced with 2 wt.% addition of cordierite ceramics had the best corrosion resistance. It was also presented that surface and heat treatment affect the obtained results.

Description: In an effort to better understand the impact of material degradation on the fatigue life of mining wheels made of a high-strength low alloy carbon steel (Q345), this study seeks to evaluate the effect of surface corrosion on the high-cycle fatigue behavior of the Q345 alloy. The fatigue behavior of the polished and corroded alloy was investigated. Following exposure to a 3.5 wt.% NaCl saltwater solution, polished and corroded fatigue specimens were tested using an R.R. Moore rotating-bending fatigue apparatus. Microstructural analyses via both optical microscopy and scanning electron microscopy (SEM) revealed that one major phase, α -iron phase, ferrite, and one minor phase, colony pearlite, existed in the extracted Q345 alloy. The results of the fatigue testing showed that the polished and corroded specimens had an endurance strength of approximately 295 and 222 MPa, respectively, at 5,000,000 cycles. The corroded surface condition resulted in a decrease in the fatigue strength of the Q345 alloy by 24.6%. Scanning electron microscope fractography indicated that failure modes for polished and corroded fatigue specimens were consistent in the high-cycle low loading fatigue regime. Conversely, SEM fractography of low-cycle high-loading fatigue specimens found considerable differences in fracture surfaces between the corroded and polished fatigue specimens.

Description: In this paper, the Mg-9%Al alloy reinforced by 5 wt.% SiC nanoparticles was fabricated by hot pressing of powder with ultrasonic vibration under a semi-solid state. The influence of hot-pressing temperature on the microstructure and mechanical properties of the n-SiCp/Mg-9%Al composite was investigated. The results indicated that the density of the composite was increased significantly and the agglomeration of SiC nanoparticles was evidently reduced with the increase in the hot-pressing temperature from 450 to 510 °C. Additionally, the elevated hot-pressing temperature resulted in remarkable grain refinement. However, as the hot-pressing temperature increased to 530 °C, the density decreased and the average grain size increased, which caused a decline in the mechanical properties. The study of the interface between the n-SiCp and the matrix in the nanocomposite suggested that n-SiCp bonded well with the matrix without interfacial activity. The ultimate tensile strength, yield strength and elongation to fracture of the nanocomposites were simultaneously enhanced compared with that of the Mg-9%Al alloy. This improvement could be attributed to obvious grain refinement and the Orowan strengthening mechanism.

Description: In the present work, high-energy ball milling was employed to synthesize Al-(5-10 wt.%)B 4 C nanocomposite. To do this, two sizes of particles of 50 nm as nanoparticles (NPs) and 50 μm as coarse particles (CPs) were used. The morphology and microstructure of the milled powders were characterized using particle size analyzer, SEM, TEM and EDX techniques. It was found that milling time, B 4 C particles size and their content strongly affect the characteristics of powders during milling process. The breaking and cold welding of powders was recognized as two main competitive actions during the milling process that influence the microstructural evolutions. It was found that the presence of CPs led to the formation of microcracks which promote the fracture process of Al powders. The dominated mechanisms during the fabrication of composites and nanocomposites were discussed. Also, the theoretical issues regarding the changes in morphology and distribution of B 4 C particles in CPs and NPs are clarified.

Description: A microalloying of the low-carbon and low-alloy cast steel was conducted with Zr, Ti, and Al that were added to the steel in four combinations. After heat treatment, the samples were tested for impact toughness at room temperature using the Charpy method. The highest values of impact toughness were obtained in the group treated with Zr, while Zr-Ti and Zr-Ti-Al groups showed moderate toughness values; the lowest values were observed in the Zr-Al group. Difference among the treatment groups was observed in the fracture mechanisms, morphology, and area distribution of the inclusions. High toughness values achieved in the trials treated with zirconium corresponded with smooth ductile fracture. The metal treated with a combination of zirconium and titanium had a relatively small area occupied by inclusions, but its toughness was also moderate. Lowest impact toughness values corresponded with the larger area occupied by the inclusions in the trials treated with aluminum. Also, a connection between the solubility product [Al][N] and impact toughness was established. The study also provides a qualitative description and quantitative analysis of the nonmetallic inclusions formation as a result of microalloying treatment. The precipitation sequence of the inclusions was described based on the thermochemical calculations for the nonmetallic compounds discovered in the experimental steel. A description of the size distribution, morphology, and composition was conducted for the oxides, nitrides, sulfides, and multiphase particles.

Description: In this paper, the wear mechanism of punches made of M3:2 and M2 steel sheet which are used in blanking process of the rotor part of the low-power asynchronous motor was presented. The influence of additional TiN coating on the punch flank surface degradation intensity was described. The punch wear influence on the hardness changes close the material intersection surface was determined. The research results indicate that the tool durability ensures the quality of parts blanked from electrotechnical steel. The results will allow for selection of new tools materials for this type of tools which are used in difficult tribological conditions.

Description: A gamma prime ( γ ′) precipitation (~35% in volume)-hardened powder metallurgy (P/M) superalloy FGH96 was welded using inertia friction welding (IFW). The microstructure and γ ′ distributions in the joints in two conditions, hot isostatic pressed state and solution-treated and aged state, were characterized. The recrystallization of grains, the dissolution and re-precipitation of γ ′ in the joints were discussed in terms of the temperature evolutions which were calculated by finite element model analysis. Regardless of the initial states, fully recrystallized fine grain structure formed at welded zone. Meanwhile, very fine γ ′ precipitations were re-precipitated at the welded zone. These recrystallized grain structure and fine re-precipitated γ ′ resulted in increasing hardness of IFW joint while making the hardness dependent on the microstructure and γ ′ precipitation.

Description: Knowledge of the cyclic properties of metallic materials is often critical to correctly design structural components. However, cyclic data are not easily available in the literature, while tensile test data are easier to find in specialized sites or vendor catalogs. In this study, the cyclic strength coefficient and the cyclic strain hardening exponent of the Ramberg–Osgood law were evaluated using exclusively data obtained through monotonic tensile tests. The analyses were carried out on a large set of materials. The database used is composed of 338 alloys, mainly iron alloys, but also titanium and aluminum alloys. New subdivisions of the materials were introduced. Several original relations were suggested to correlate static and cyclic strength parameters. The evaluated values of both cyclic strength coefficient and cyclic strain hardening exponent were compared with experimental values coming from cyclic test, obtaining a satisfactory agreement and a higher accuracy if compared with similar relations found in the literature.

Description: To study the effect of Sc and Sr additions on modifying eutectic silicon particles and mechanical properties for Al-Si-Mg casting alloy, they were added with different amounts in F357 alloy without beryllium addition in the present work. It was found that (0.4 wt.% Sc and 0.04 wt.% Sr)-modified F357 alloy presented the optimal tensile properties when compared with the individual addition of Sc or Sr. This was mainly attributed to the synergic modification of eutectic Si in F357 alloys due to the combined additions of Sc and Sr. The silicon modification mechanisms via Sc and Sr were emphasized to be examined in this paper, and the fracture mechanism of the obtained alloys was also discussed.

Description: In this research, the effect of rapid tempering on the microstructure, mechanical properties and corrosion resistance of AISI 420 martensitic stainless steel has been investigated. At first, all test specimens were austenitized at 1050 °C for 1 h and tempered at 200 °C for 1 h. Then, the samples were rapidly reheated by a salt bath furnace in a temperature range from 300 to 1050 °C for 2 min and cooled in air. The tensile tests, impact, hardness and electrochemical corrosion were carried out on the reheated samples. Scanning electron microscopy was used to study the microstructure and fracture surface. To investigate carbides, transmission electron microscopy and also scanning electron microscopy were used. X-ray diffraction was used for determination of the retained austenite. The results showed that the minimum properties such as the tensile strength, impact energy, hardness and corrosion resistance were obtained at reheating temperature of 700 °C. Semi-continuous carbides in the grain boundaries were seen in this temperature. Secondary hardening phenomenon was occurred at reheating temperature of 500 °C.

Description: In this study, in effort to improve the sliding wear resistance of gray cast iron under wet lubrication conditions, specimens with different bionic units were manufactured and modified according to bionic theory. Inspired by the structure and appearance of biological wear-resistant skin, two kinds of bionic units were processed by laser on the specimen surfaces. We investigated the wear resistance properties of the samples via indentation method and then observed the wear surface morphology of specimens and the stress distributions. The results indicated that coupling the bionic units enhanced the wear resistance of the cast iron considerably compared to the other samples. We also determined the mechanism of wear resistance improvement according to the results.

Description: The effects of thermo-mechanical treatment on selected properties related to the structure of Fe-0.85Mo-0.65i-1.4C powder metallurgy (PM) steel are reported. Three kinds of initial microstructure of specimens, i.e., pearlite + ferrite + cementite, martensite + retained austenite and α  + spheroidized cementite were examined. Processing was carried out on a plastometer-dilatometer Bähr machine by compression cylindrical specimens at 775 °C at a strain rate of 0.001 s −1 . X-ray diffraction was carried out with symmetrical Bragg-Brentano and grazing incident angle methods on a D8-Advance diffractometer with filtered radiation of cobalt CoK α . The following features were determined: texture, density of dislocations, density of vacancies, lattice parameter of Fe α and mean size of crystallites. Significant differences in structure were observed, especially in quenched specimen, as a result of the thermo-mechanical treatment. Regardless of initial state of the specimens, the determined properties were on a similar level. Crystallite size was in the range 97-106 nm, crystallite texture ( I {200}/ I {110}) × 10 = 1.15-1.62 and density of vacancies I {110}/ I {220} = 7.06-7.52.

Description: The benefits of ultrasonic vibration auxiliary metal forming have been shown by many studies. In this study, a series of experiments were carried out to investigate the deformation behavior of Ti foils under ultrasonic vibration in tension, and the tensile properties of Ti foils with/without the application of ultrasonic vibration were investigated. Then, the microstructure of different tensile samples was analyzed by transmission electron microscopy (TEM). The results of the tensile experiments showed that the tensile strength of tensile samples was reduced when ultrasonic vibration was applied, while the elongation of these samples increased. The flow stress increased with increasing strain without applying ultrasonic vibration, while it decreased steeply when the ultrasonic vibration was applied, and this reduction of flow stress demonstrated the effect of acoustic softening on the properties of the material. Additionally, the range of flow stress reduction was inversely proportional to the time for which ultrasonic vibration was applied. The TEM images showed that there were remarkable differences in dislocation distribution and tangles with/without ultrasonic vibration. The dislocation distribution was inhomogeneous, and copious dislocation tangles were discovered without ultrasonic vibration. When it was applied, the parallel re-arrangement of dislocations could be observed and the mass of dislocation tangles was mostly absent.

Description: Electrochemical properties of coarse and nano-grained pure copper can be modified and improved effectively through applying cyclic potentiodynamic passivation (CPP) treatment. It is found that the success of this method depends up to a large extent on grain size. Eight passes of accumulative roll bonding processing are successfully used at room temperature to produce nano-grained pure copper. Transmission electron microscopy image and selected area diffraction pattern both attest to the occurrence of intense grain refinement under the influence of aforementioned process, in which an average grain size 〈100 nm is attainable. Using several electrochemical characterization methods reveals that CPP treatment fully exploits potentials of nano-grained samples to form a dense and thick protective passive film. It is speculated that high-quality passive layers relate to the presence of high-density structural defects on the surface of nano-grained samples.

Description: Nanostructured Al/SiC composite was fabricated by accumulative roll bonding (ARB). The effect of Gr, as the soft and second reinforcing particle, on the microstructure and deformation behavior of Al/SiC composite was examined. After eight ARB cycles, a homogeneous ultra-fine grained structure with the average grain size of about 710 nm was obtained in the Al/SiC composite. Results showed that Gr could not affect the particle distribution. However, the bonding quality between the layers reduced and the mechanical properties of the composite deteriorated considerably with increasing the Gr content. Compared with the Gr-free composite, the Al/SiC-Gr hybrid composite with the highest Gr content exhibited the lowest bonding quality and the lowest tensile strength. Tensile fracture surface of the composites showed that the number of delaminated layers was increased by increasing the Gr content. The best wear resistance was obtained in the composite whose powder mixture contained 80 SiC and 20 Gr (in wt.%).

Description: Brush plating provides an effective method for creating a coating on substrates of various shapes. A corroded zirconium-based conversion coating was removed from the surface of a magnesium alloy and then replaced with new coatings prepared via brush plating. The structure and composition of the remanufactured coating were determined via x-ray photoelectron spectroscopy, x-ray diffraction, and Fourier transform infrared spectroscopy. The results revealed that the coatings consist of oxide, fluoride, and tannin-related organics. The composition of the coatings varied with the voltage. Furthermore, as revealed via potentiodynamic polarization spectroscopy, these coatings yielded a significant increase in the corrosion resistance of the magnesium alloy. The friction coefficient remained constant for almost 300s during wear resistance measurements performed under a 1-N load and dry sliding conditions, indicating that the remanufactured coatings provide effective inhibition to corrosion.

Description: The effect of welding speed on the microstructural evolution, mechanical properties and strain-hardening behavior of friction stir welded (FSWed) high-strength AA7075-T651 was investigated. Large intermetallic particles and grains, whose sizes increased at lower welding speeds, were present in the heat-affected zone. FSWed joints fabricated at the higher welding speed or lower strain rates exhibited higher strength, joint efficiency and ductility than those fabricated at lower welding speeds or higher strain rates. A maximum joint efficiency of 97.5% and an elongation to failure of 15.9% were obtained using a welding speed of 400 mm/min at a strain rate of 10 −5  s −1 . The hardening capacity, strain-hardening exponent and strain-hardening rate of the FSWed joints were significantly higher than those of the base material, but materials exhibited stage III and stage IV hardening characteristics. The results morphology of the fracture surfaces is consistent with the above results.

Description: In the present work, the influence of surface mechanical attrition treatment (SMAT) parameters on the microstructural and mechanical properties of an aluminum-magnesium-silicon alloy AA 6061 was studied using design of experiment technique. Balls of three different diameters were used, and SMAT was done for three different durations. The microstructural features of the surface layer fabricated by SMAT were characterized by cross-sectional scanning electron microscopic observations, x-ray diffraction technique and transmission electron microscopy. The microindentation hardness, nanoindentation hardness and surface roughness were determined. Due to SMAT, nanocrystallites formed on the surface and near-surface regions, and hardness and surface roughness increased. The ball diameter was the most influencing SMAT parameter compared to the treatment duration. However, interaction between ball diameter and treatment duration could not be ignored. Regression equations were developed relating the process parameters to the surface properties. The ball diameter and treatment duration could thus be properly selected as per the required values of roughness and/or the hardness.

Description: Crystal plastic finite element method (CPFEM) is used to simulate microstructural evolution, texture evolution and macroscopic stress-strain response of polycrystalline NiTiFe shape memory alloy (SMA) with B2 austenite phase during compression deformation. A novel two-dimensional polycrystalline finite element model based on electron back-scattered diffraction (EBSD) experiment data is developed to represent virtual grain structures of polycrystalline NiTiFe SMA. In the present study, CPFEM plays a significant role in predicting texture evolution and macroscopic stress-strain response of NiTiFe SMA during compression deformation. The simulated results are in good agreement with the experimental ones. It can be concluded that intragranular and intergranular strain heterogeneities are of great importance in guaranteeing plastic deformation compatibility of NiTiFe SMA. CPFEM is able to capture the evolution of grain boundaries with various misorientation angles for NiTiFe SMA subjected to the various compression deformation degrees. During uniaxial compression of NiTiFe SMA, the microstructure evolves into high-energy substructure and consequently the well-defined subgrains are formed. Furthermore, the grain boundaries and the subgrain boundaries are approximately aligned with the direction in which metal flows.

Description: In this work, we investigated the influence of galvanizing immersion time and cooling modes environments on the electrochemical corrosion behavior of hot-dip galvanized steel, in 1 M sulfuric acid electrolyte at room temperature using potentiodynamic polarization technique. In addition, the evolution of thickness, structure and microstructure of zinc coatings for different immersion times and two cooling modes (air and water) is characterized, respectively, by using of Elcometer scan probe, x-ray diffraction and metallography analysis. The analysis of the behavior of steel and galvanized steel, vis-a-vis corrosion, by means of corrosion characteristic parameters as anodic ( β a ) and cathodic ( β c ) Tafel slopes, corrosion potential ( E corr ), corrosion current density ( i corr ), corrosion rate (CR) and polarization resistance ( R p ), reveals that the galvanized steel has anticorrosion properties much better than that of steel. More the immersion time increases, more the zinc coatings thickness increases, and more these properties become better. The comparison between the two cooling modes shows that the coatings of zinc produced by hot-dip galvanization and air-cooled provides a much better protection to steel against corrosion than those cooled by quenching in water which exhibit a brittle corrosive behavior due to the presence of cracks.

Description: Spark plasma sintering (SPS) has been recognized, in the recent past, as a very useful method to produce metal matrix composites with enhanced mechanical and wear properties. Obviously, the materials’ properties are strongly related to the reinforcement types and percentages as well as to the processing parameters employed during synthesis. The present paper examines the effect of 2 wt.% of Al 2 O 3 nanoparticles on mechanical and microstructural behaviors of Al-based metal matrix composites produced via SPS. The composite mechanical properties were evaluated through micro-, nanoindentation and tensile tests. The microstructural evolution was studied through scanning electron microscopy observations. It was found that the addition of nanoparticles produces the reduction of materials porosity and the improvement of mechanical properties in SPSed materials.

Description: According to specification standards, the basic chemical composition of steel 17-4PH for special and critical applications is 15-17% Cr, 3.0-5.0% Ni, 3.0-5.0% Cu, 0.07% C (max) and 0.15-0.45% (Nb + Ta) (wt.%). The maximum sulfur content is 0.030%. However, as it will be shown in this work, this maximum limit for sulfur is too high for services where high corrosion resistance is necessary. Two samples of 17-4PH steel with similar base compositions, but quite different sulfur contents (0.027% and 0.001%S), were compared with respect to pitting corrosion and sensitization. Both materials were heat treated according to commercial treatments A, H900, H1100, H1150 and H1150D (ASTM A-1082). Two corrosion tests were applied to compare the steels. The first one was the double-loop electrochemical potentiodynamic reactivation (DL-EPR) test in 0.25 M H 2 SO 4  + 0.01 KSCN solution, which is used to measure the degree of sensitization. The second test was the anodic polarization in 3.5%NaCl solution, commonly used to evaluate the pitting corrosion resistance. Detailed microstructural characterization by magnetic measurements, light optical and scanning electron microscopy was performed. As main conclusion, despite that both steels have chemical compositions in accordance with the standards, the steel with higher sulfur was much more susceptible to pitting and sensitization.

Description: The potentiodynamic polarization test and slow strain rate tensile test were carried out in 3.5 wt.% Na 2 SO 4 solution with different pH values (2, 7, and 12). It was found that the SCC susceptibility of AZ31 magnesium alloy in 3.5 wt.% Na 2 SO 4 solution was deteriorated significantly with the decreasing pH. This was consistent with the electrochemical properties. There were filiform corrosion forms on the specimen surface after slow strain rate tensile test in 3.5 wt.% Na 2 SO 4 solution, which indicated the characteristics of general corrosion. Moreover, there were multiple stress corrosion crack initiation sources. The SCC fracture of AZ31 magnesium alloy in air was a mix type, while it was cleavage fracture in 3.5 wt.% Na 2 SO 4 solution.

Description: In the present study, 5052 Al alloy was processed through different rolling methods to obtain ultrafine grains and its high-cycle fatigue behavior were investigated. The solution-treated Al-Mg alloys (AA 5052) were deformed through different methods such as cryorolling (CR), cryo groove rolling (CGR) and cryo groove rolling followed by warm rolling (CGW), up to 75% thickness reduction. The deformed samples were subjected to mechanical testing such as hardness, tensile and high-cycle fatigue (HCF) test at stress control mode. The CGW samples exhibit better HCF strength when compared to other conditions. The microstructure of the tested samples was characterized by optical microscopy, SEM fractography and TEM to understand the deformation behavior of deformed Al alloy. The improvement in fatigue life of CR and CGR samples is due to effective grain refinement, subgrain formations, and high dislocation density observed in the heavily deformed samples at cryogenic condition as observed from SEM and TEM analysis. However, in case of CGW samples, formation of nanoshear bands accommodates the applied strain during cyclic loading, thereby facilitating dislocation accumulation along with subgrain formations, leading to the high fatigue life. The deformed or broken impurity phase particles found in the deformed samples along with the precipitates that were formed during warm rolling also play a prominent role in enhancing the fatigue strength. These tiny particles hindered the dislocation movement by effectively pinning it at grain boundaries, thereby improving the resistance of crack propagation under cyclic load.

Description: BCC alloys commonly tend to develop strong fibre textures and often represent as isointensity diagrams in φ 1 sections or by fibre diagrams. Alpha fibre in bcc steels is generally characterised by 〈110〉 crystallographic axis parallel to the rolling direction. The objective of present research is to correlate carbon content, carbide dispersion, rolling reduction, Euler angles ( ϕ ) (when φ 1  = 0° and φ 2  = 45° along alpha fibre) and the resulting alpha fibre texture orientation intensity. In the present research, Bayesian neural computation has been employed to correlate these and compare with the existing feed-forward neural network model comprehensively. Excellent match to the measured texture data within the bounding box of texture training data set has been already predicted through the feed-forward neural network model by other researchers. Feed-forward neural network prediction outside the bounds of training texture data showed deviations from the expected values. Currently, Bayesian computation has been similarly applied to confirm that the predictions are reasonable in the context of basic metallurgical principles, and matched better outside the bounds of training texture data set than the reported feed-forward neural network. Bayesian computation puts error bars on predicted values and allows significance of each individual parameters to be estimated. Additionally, it is also possible by Bayesian computation to estimate the isolated influence of particular variable such as carbon concentration, which exactly cannot in practice be varied independently. This shows the ability of the Bayesian neural network to examine the new phenomenon in situations where the data cannot be accessed through experiments.

Description: Ternary Al-Ag-Ga system at 200 °C was experimentally and thermodynamically assessed. Isothermal section was extrapolated using optimized thermodynamic parameters for constitutive binary systems. Microstructure and phase composition of the selected alloy samples were analyzed using light microscopy, scanning electron microscopy combined with energy-dispersive spectrometry and x-ray powder diffraction technique. The obtained experimental results were found to be in a close agreement with the predicted phase equilibria. Hardness and electrical conductivity of the alloy samples from four vertical sections Al-Ag 80 Ga 20 , Al-Ag 60 Ga 40 , Ag-Al 80 Ga 20 and Ag-Al 60 Ga 40 of the ternary Al-Ag-Ga system at 200 °C were experimentally determined using Brinell method and eddy current measurements. Additionally, hardness of the individual phases present in the microstructure of the studied alloy samples was determined using Vickers microhardness test. Based on experimentally obtained results, isolines of Brinell hardness and electrical conductivity were calculated for the alloys from isothermal section of the ternary Al-Ag-Ga system at 200 °C.

Description: The scratching process of particle is a complex material removal process involving cutting, plowing, and rubbing. In this study, scratch experiments under different loads are performed on a multifunctional tester for material surface. Natural diamond and Fe-Cr-Ni stainless steel are chosen as indenter and workpiece material, respectively. The cutting depth and side flow height of scratch are measured using a white light interferometer. The finite element model is developed, and the numerical simulation of scratching is conducted using AdvantEdge TM . The simulated forces and side flow height under different cutting depths correspond well with experimental results, validating the accuracy of the scratching simulation. The mises stress distribution of the particle is presented, with the maximum stress occurring inside the particle rather than on the surface. The pressure distribution of the particle is also given, and results show that the maximum pressure occurs on the contact surface of particle and workpiece. The material flow contour is presented, and material flow direction and velocity magnitude are analyzed.

Description: The room-temperature reactive ball milling (RBM) approach was employed to synthesize nanostructured fcc-titanium nitride (TiN) powders, starting from milling hcp-titanium (Ti) powders under 10 bar of a nitrogen gas atmosphere, using a roller mill. During the first and intermediate stage of milling, the agglomerated Ti powders were continuously disintegrated into smaller particles with fresh surfaces. Increasing the RBM time led to an increase in the active-fresh surfaces of Ti, resulting increasing of the mole fraction of TiN against unreacted hcp-Ti. Toward the end of the RBM time (20 h), ultrafine spherical powder (with particles ~0.5 μm in diameter) of the fcc-TiN phase was obtained, composed of nanocrystalline grains with an average diameter of 8 nm. The samples obtained after different stages of RBM time were consolidated under vacuum at 1600 °C into cylindrical bulk compacts of 20 mm diameter, using spark plasma sintering technique. These compacts that maintained their nanocrystalline characteristics with an average grain size of 56 nm in diameter, possessed high relative density (above 99% of the theoretical density). The Vickers hardness of the as-consolidated TiN was measured and found to be 22.9 GPa. The modulus of elasticity and shear modulus of bulk TiN were measured by a nondestructive test and found to be 384 and 189 GPa, respectively. In addition, the coefficient of friction of the end-product TiN bulk sample was measured and found to be 0.35.

Description: To elucidate the effect of Mn content on the microstructure and mechanical properties of weld metal, flux-cored wires with three different Mn contents were prepared to conduct high heat input welding experiments. Complex inclusions and Mn-depleted zones were observed in the weld metal with heat input of 85 kJ/cm. The study indicated that complex inclusions enabled nucleation of acicular ferrite with interlocking structure, leading to enhanced impact toughness. With decrease in Mn content, the number of complex inclusions with Mn-depleted zone and the volume fraction of acicular ferrite were both decreased. Additionally, the impact toughness of weld metal was significantly degraded with lower Mn content present in martensite-austenite (M-A) constituent and bainite.

Description: Aluminum and its alloys are widely used in different industries due to such attractive properties as adequate strength, ductility, and low density. It is desirable to characterize welds of aluminum alloys obtained using “friction stir welding” at high temperatures. Al-to-Al (both 6061-T6) butt joints are produced by friction stir welding at tool rotation speed of 1600 rpm and four levels of tool advancing speeds: 250, 500, 750, and 1000 mm/min. Microstructural properties of the different welds are investigated. Observed are noticeable differences in microstructure characteristics between the various weld zones. Mechanical properties of these welded joints are characterized under tensile tests at temperatures of 25, 100, 200, and 300 °C, at a constant strain rate of 10 −3 /s. The optimum microstructural and mechanical properties were obtained for the samples FS welded with 1600 rpm tool rotation speed at 1000 mm/min tool advancing speed. The studied welds exhibited yield strength, ultimate tensile strength, and strain to failure with values inferior of those of the base material. Observations of postmortem samples revealed that in the temperature range of 25-200 °C the locus of failure originates at the region between the thermo-mechanically affected zone and the heat-affected zones. However, at higher temperatures (300 °C), the failure occurs in the stir zone. A change in the crack initiation mechanism with temperature is suggested to explain this observation.

Description: Tribological behaviors of TiAl-multilayer graphene-microsphere composites (TMMC) are investigated at different loads in this paper. The tribological results show that TMMC exhibit excellent wear and friction performances from 4 to 20 N for the formation of the intact and smooth tribo-films containing multilayer graphene (MLG) and WS 2 -SiO 2 microsphere (WSM) on the worn surfaces. During the sliding process, MLG and WSM are ground out of TMMC to form the tribo-films on the worn surfaces, which is beneficial to the decreasing in friction coefficients and wear rates. MLG is easy to be sheared for the weak interlayer binding force, which can reduce the friction coefficients and wear rates. WSM can repair the tribo-film by filling its worn pits, resulting in the smooth worn surface and excellent tribological performance of TMMC. Moreover, the hardness of TMMC is increased for the addition of MLG and WSM, which makes contributions to the improvement of tribological behaviors of TMMC.

Description: Controlling the amount of retained austenite is a concern in austempered ductile iron formation. Retained austenite has a strong influence on austempered ductile iron properties, such as hardness and wear resistance. In this research, the characteristics of the transformation of retained austenite were investigated as a function of the number of tempering cycles. The hardness of the austempered ductile iron samples was measured, and the specific amount of retained austenite was analyzed by x-ray diffraction (XRD). Wear tests were conducted on a ball-on-flat sliding fixture. The tempering process was found to have no effect on the hardness of the austempered ductile iron samples. This may be due to retained austenite being partially converted into brittle quenched martensite during the tempering process. However, tougher tempered martensite was also formed from existing martensite. The two effects seemed to offset each other, and no significant differences occurred in overall hardness. XRD analysis showed that under the same austempering temperature and holding time, the amount of retained austenite decreased with additional tempering cycles. Also, with the same holding time and tempering cycles, less retained austenite was contained in the matrix at higher austempering temperatures. This was due to more high carbon content austenite and needle-like ferrite being present in the austempered ductile iron matrix. In addition, tempered austempered ductile iron exhibited significantly higher wear resistance as compared to traditionally treated ductile iron.

Description: A WC-reinforced composite coating was fabricated on the surface of 45 steel samples by plasma, cladding process with WC powder added to the molten pool synchronously or in the tail of the molten pool. The microstructure, phase composition, and element distribution in the coating were analyzed. The results show that the undissolved WC particles and crystallized carbide (WC, W 2 C) were distributed uniformly in the sub-eutectic matrix in both cases. Fewer of the WC particles are dissolved in the matrix when they are injected into the tail of the molten pool. There are fewer needle-like tungsten carbide formations seen in the composite coating fabricated by back-feeding process than in that formed by synchronous feeding. The former results in a finer microstructure and a higher concentration gradient of elements near the interface between the WC particles and the coating matrix.

Description: In this study, electrical discharge machining (EDM) is used to directly drill normal effusion cooling holes in thermal-barrier-coated nickel-based superalloys (TBCs) via the assisting electrode method. The formation of the conductive layer was studied using scanning electron microscopy and energy-dispersive spectroscopy. The effects of the EDM process parameters including peak current, pulse duration, and duty cycle on delamination and recast layer characteristics were investigated. The analysis results indicate that the conductive layer possesses a feature of bilayer structure for the EDM of TBCs. The bottom layer is generated first due to the deposition of carbon-based products and molten brass debris, and its composition primarily contains C, Cu, Zr, and Zn; the surface layer is the result of the overlying of subsequently molten superalloy debris and carbon-based products, and its composition primarily consists of Ni, C, Cr, Nb, Co, Al, Fe, Cu, and Zr. The microcracks of the superalloy substrate only reside in the recast layer during the EDM of TBCs. The thickness of recast layer sharply increases with increasing peak current, pulse duration, and duty cycle, respectively. The delamination occurs at the ceramic coating/bond coating interface for the EDM of drilling normal holes in TBCs, and it can be eliminated by the selection of low discharge energy and appropriate duty cycle. Additionally, the length of delamination increases with increasing peak current, pulse duration, and duty cycle, respectively. The spalling of ceramic coating appears at the entrance of the hole due to the thermal-shock brittle fracture if excessive peak current, pulse duration, or duty cycle is selected.

Description: In order to analyze the effects of friction layer thickness on the tribological performance of Ni 3 Al matrix self-lubricating composites containing Ag and MoO 3 tabular crystals (Ni 3 Al-Ag-MoO 3 ), the dry sliding tribological tests of Ni 3 Al-Ag-MoO 3 against Si 3 N 4 ball are undertaken under 4-16 N and 20-800 °C at 0.2 m/s. The results show that the friction layer thickness of Ni 3 Al-Ag-MoO 3 is obviously affected by the applied loads and ambient temperatures. At 12 N-400 °C-0.2 m/s, Ni 3 Al-Ag-MoO 3 exhibits excellent tribological performance, and the friction layer thickness obtained the maximum value of about 5 µm. Moreover, the simulation results, which based on the building of finite element models with different thickness of the friction layer, indicate that the decreased degree of the maximum equivalent stress in the substrate of Ni 3 Al-Ag-MoO 3 with maximum thickness of friction layer is the larger one (about 39%), if compared to other thickness. It could avoid the generation of cracks and the spalling of subsurface materials during the dry sliding process, resulting in the excellent tribological performance. The results could be used to guide the selection of suitable working conditions and study the self-lubricating mechanisms of Ni 3 Al-Ag-MoO 3 for having stable friction layer structure and excellent antifriction and antiwear performance.

Description: The hot deformation behavior of AZ61 magnesium alloy was studied by hot compression testing in the temperature range from 250 to 400 °C with strain rates from 10 −3 to 1 s −1 . Typical flow stress/true strain curves with the features of dynamic recrystallization (DRX) have been obtained. According to the flow stress curves, the processing maps were constructed via the dynamic material model (DMM). The maps exhibit a domain of DRX at temperatures between 330 and 370 °C and strain rates ranging from 10 −3 to 10 −2  s −1 . The corresponding extrusion deformation was carried out in this DRX region. Gleeble 3500, optical microscopy (OM) and transmission electron microscopy (TEM) were used to characterize the microstructure evolution. The microstructure detection of this DRX region shows that the average grain size decreases with decreasing extrusion temperature. TEM observation further indicated that there are irregularly shaped subgrains with a high dislocation density, a dislocation network, the feature of dislocation pileup and an appearance of twin formation in the alloy hot-extruded using the parameters determined by our constructed processing maps.

Description: The sintering behavior of Mo-Si-B alloys with iron as a sintering additive was investigated. The addition of small amounts of Fe effectively enhanced the densification of Mo-Si-B at temperatures below 1900 °C. The addition of 5 at.% Fe resulted in nearly full densification (97.0% of theoretical density) when sintered at 1750 °C for 2 h, while the unmodified Mo-Si-B alloy could be densified to only 66.8% of its theoretical density under these conditions. Addition of 0.5 at.% Fe and 2 at.% Fe increased the degree of densification of Mo-Si-B by 15.4 and 17.0%, respectively, and led to nearly full densification at 1900 and 1850 °C, respectively. Fe-Si-B eutectic liquid was formed at low temperatures and disappeared at high temperatures. We propose that the addition of Fe led to the formation of a transient liquid, facilitating liquid-phase sintering of the powder compacts.

Description: Isothermal uniaxial compression tests were conducted on aluminum alloy AA2219 to study the evolution of microstructure over a wide range of temperatures (300-500 °C) and strain rates (0.001-100 s −1 ) with a view to study the flow behavior and concurrent microstructural evolution. True stress-true strain curves showed only a gradual flow softening at all temperatures except at 300 °C where strain hardening was followed by severe flow softening. Processing map delineating the stable ‘safe’ and unstable ‘unsafe’ regions during hot working is developed and validated by comparing the microstructures observed in the deformed compression specimens. Optimum processing parameters (temperature 450 °C and strain rate 0.001 s −1 ) for hot deformation of AA2219 were proposed based on contour maps of efficiency of power dissipation and strain rate sensitivity parameter. The activation energy value ( Q avg ) of AA2219 for hot working was computed to be 169 kJ/mol. Finally, a constitutive equation for hot working of AA2219 was established as: \(\dot{\varepsilon } = 4.99 \times 10^{9} \cdot \exp (0.06149\sigma ) \cdot \exp \left( { - 168.958/RT} \right)\) .

Description: The corrosion behaviors of copper, 6063 aluminum alloy, and Q235 steel were investigated by open-circuit potential (OCP), anodic polarization curve analysis, and electrochemical impedance spectroscopy (EIS). Scanning electron microscopy revealed that a small number of translucent rod-shaped bacterial colonies on the copper surface of copper, whereas plenty of rod-shaped microbes colony were detected on the surface of 6063 aluminum material. Moreover, rod-shaped bacteria and mold colonies attached to the surface of Q235 steel. The decrease in the OCP of copper, 6063 aluminum alloy, and Q235 steel led to higher corrosion tendency. EIS analysis showed that bacteria can reduce the value of AC impedance of copper, the polarization resistance, and the surface resistance, thereby accelerating corrosion. Moreover, the polarization resistance of aluminum alloy in bacterial seawater is lower than that in non-bacterial seawater, indicating the existence of bacteria accelerated the corrosion of 6063 aluminum alloy. The adherence of microbes on Q235 steel surface accelerated the dissolution of the surface layer, and then the passive film is replaced by incompact biofilm layer. Q235 steel corrodes faster under the influence of bacteria because the polarization resistance in bacterial seawater is much lower than that in non-bacterial seawater.

Description: Spot continual induction hardening (SCIH) is a surface heat treatment process, which can strengthen more than one small area or relative large area on complicated component surface. In order to investigate the microstructure and mechanical properties of gray cast iron with curved surface after SCIH, the microstructure, microhardness and residual stresses were analyzed under different process conditions. The results showed that the martensite grain in hardened region of concave surface was larger than that of convex surface. The domain sizes of concave and convex surfaces were smaller than that of matrix region due to the high heating rate in SCIH process. The phase transformation depth increased with the increasing of convex surface radius but decreased with the increasing of concave surface radius. The maximum values of residual tensile and compressive stresses increased with the increasing of feed velocity for convex and concave surfaces, respectively. The appearance positions of maximum tensile and compressive stresses were closer to center for convex and concave surfaces, respectively, when feed velocity increased from 1 to 5 mm/s. The achieved results indicated that the SCIH with relatively low feed velocity was more suitable for improving the mechanical properties of gray cast iron. Compared with convex surface, the concave surface of workpiece can obtain better mechanical properties under the same feed velocity of inductor.