Metals and Materials International最新文献

High Entropy Alloys (HEA) are new class of materials exhibiting remarkable properties owing to multiple alloying elements to form solid solution phase and high configurational entropy. The properties of HEA are greatly influenced by the composition of each metallic element. Therefore, the focus of present study is to evaluate the effect of aluminum (Al) molar ratio ‘x’ on the structural, electronic, mechanical, and thermal properties of Al_xCoCrFeNi (x = 0.0, 0.1, 0.3, 0.5, 0.9, 1.0, 1.5 and 2.0) HEA using Density Functional Theory (DFT). Based on the reported literature, Face Centered Cubic (FCC) crystal form of Al_xCoCrFeNi was chosen for x = 0.0, 0.1, 0.3, 0.5,1.0 and Body Centered Cubic (BCC) form was chosen for x = 0.9, 1.0, 1.5, 2.0. The Special Quasi Random Structure (SQS) models of Al_xCoCrFeNi were used for the property evaluation. The phase stability of Al_xCoCrFeNi HEA for all molar ratios of Al was confirmed based on thermodynamic stability criteria and atomic size difference parameter. The thermodynamic stability of Al_xCoCrFeNi increased with Al molar ratio. Mechanical properties were computed for a microscopic level strain rate of ± 0.7% and were evaluated based on elastic moduli, Vickers hardness, fracture toughness, Debye temperature and acoustic wave velocity. The properties computed based on phase change from FCC to BCC at x > 1.3 of Al_xCoCrFeNi match well with available experimental and theoretical literature values. Positive Cauchy pressure, B/G > 1.75 and ν > 0.26 indicate that as Al concentration increases, ductility of the alloy increases. Further, the elastic moduli, hardness, and fracture toughness decrease with increase in Al concentration. The lattice thermal conductivity of the HEAs studied using DFT match well with molecular simulation-based literature values and suggest that Al_1.5CoCrFeNi has lowest thermal conductivity.

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The microcrack formation mechanisms and mitigation strategies were thoroughly investigated and explained in Hastelloy X samples fabricated via Laser Powder Bed Fusion (LPBF) with varying printing parameters and geometries. The microstructure evolution regarding microcrack formation is comprehensively examined in conjunction with thermal residual stresses affected by process parameters (e.g., laser power, scan velocity determining volumetric energy density, VED), proximity to build/substrate interface, and print section aspect ratio. Results indicated for microcracks to form in Hastelloy X, the VED must exceed the critical value of ~ 114 J/mm3, below which the lack-of-fusion porosity persists, thereby highlighting a trade-off with densification. Similar trends were also observed for a Cantor high-entropy alloy. Higher residual stresses near the print/substrate interface increase susceptibility to hot-cracking, leading to a higher density of microcracks at lower build heights along the Z-axis. A higher aspect ratio of the print section can further intensify the residual stresses, thus contributing to a higher density of microcracks as well as warpage in the bar sample. Finally, SEM observations and quantitative EBSD analysis establish a strong correlation between microcrack susceptibility, grain coarsening, and a Z-aligned grain/crystallographic texture, especially at higher VEDs or closer to the substrate. These findings provide insights for mitigating microcrack evolution and refining LPBF processes.

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Zinc (Zn)-based biodegradable alloys have been at the forefront of absorbable biomaterial research in recent years due to their high biocompatibility and corrosion rates. The arc melting process was used to produce the Zn–1Cu–1Ag biodegradable alloy. The influence of different plastic deformation rates on the microstructure of the material was examined after the cold rolling at deformation rates of 47% and 61%. The undeformed and deformed alloys have been hydroxyapatite-coated using the electrophoretic deposition process to improve its surface, corrosion, and bioactivity properties. Optical, XRD, SEM, and EDS examinations were used to analyze the samples’ uncoated, coated, and rolled-unrolled forms. The nucleation of the (Ag, Cu)Zn4 secondary phase was formed during the rolling process. Hardness and compression tests were used to determine the mechanical properties of cast and rolled alloys, and in vitro corrosion tests were carried out in simulated body fluid. Antimicrobial and cell viability tests are executed to demonstrate the biocompatibility of the deformed and HA-coated Zn–1Cu–1Ag alloy. The mechanical properties were improved after the rolling process, with the highest results found in 47% of the rolled samples exhibiting a compressive strength of 412.65 ± 0.5 MPa and 61% of the rolled samples exhibiting a hardness value of 88.1 ± 0.5 HV. The samples that were rolled (61%) and coated with hydroxyapatite (HA) exhibited the highest level of corrosion resistance. The antimicrobial tests revealed that the rolled and HA coated Zn1Cu1Ag groups exhibited greater inhibition rates (47 and 61%) compared to the other groups when tested against E. coli. The HA-coated groups exhibited good cell viability ratios, with the maximum viability seen in the rolled and HA-coated group at 47%.

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Two ASTM A295 52100 bearing steels with different concentrations of Al (0.02 and 1.90 wt%) were nitrided by three processes: pure nitriding (gas), oxy-nitrocarburizing (gas) and salt bath nitriding. To assess their electrical performance, the area-specific resistance (ASR) of the surface was measured by the four-point probe method. The microstructure of the surface layer was investigated by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that the ASR of the non-nitrided sample was only approximately 0.005 Ω cm², but it became larger after all nitriding processes. Among the 0.02 wt% Al-added samples, the greatest ASR was approximately 30 Ω cm² for the sample nitrided in a salt bath, which can be ascribed to the large amount of oxides (Fe₃O₄) in the compound layer that exhibits higher electrical resistivity than other nitrides (ε-Fe₃N and γ′-Fe₄N) observed in the pure or oxy-nitrocarburized samples. Additionally, the addition of Al significantly increased the ASR in the salt bath nitrided sample, which indicated that the Al₂O₃ formed along the pores in the compound layer played an important role in improving the electrical resistance.