查看更多>>摘要：? 2021 Elsevier LtdTo determine the effect of mixing entropy on multicomponent alloys and to find the mixing entropy threshold for entropy-tailored materials, including high-entropy alloys and medium-entropy alloys, the microstructure and mechanical properties of 23 Ti–Zr–Nb–V alloys were investigated. The Laves phase content of Ti–Zr–Nb–V alloys was obtained using image recognition technology. According to the component threshold for Laves phases and HCP phase disappearance, V(Nb)–Zr(Ti) pseudo-binary phase diagrams, which can predict the phases of ternary Ti–Zr–V and Zr–Nb–V alloys, were established. By comparing the Laves phase content in Ti–Zr–Nb–V alloys obtained from experimental statistics, pseudo-binary phase diagrams and thermodynamic calculations, the ΔSmix threshold for entropy-tailored materials was 1.10–1.21R. The dependence of the yield strength and fracture strain of the Ti–Zr–Nb–V alloys further reveals that the mechanical properties of entropy-tailored alloys are essentially controlled by ΔSmix.
查看更多>>摘要：? 2021 Elsevier LtdThis study investigates the microstructure, mechanical, and tribological properties of the AA2024-Al3NiCu composite coating fabricated by the friction surfacing process on the AA2024 substrate. The findings indicated that increasing the mechtrode's nickel concentration from 0 to 3 wt% reduced the coating's thickness from 1.43 ± 0.05 to 1.21 ± 0.02 mm and its width from 22.3 ± 0.90 to 19.5 ± 0.95 mm. There was no noticeable difference in the grains, precipitates, and intermetallic particles size at different parts of the coating. The size and fraction of the S-Al2CuMg precipitates decreased by increasing the nickel content in the mechtrod from 0 to 3 wt%. Adding 4.5 wt% nickel to the mechtrod formed T-Al6CuMg4 precipitates instead of S-Al2CuMg precipitates. The modulus strengthening mechanism was the main factor in strengthening AA2024-Al3NiCu composite coating when the nickel content was less than 3 wt%; however, the precipitation strengthening mechanism was dominant at higher percentages of nickel. Relative to the AA2024 substrate, enhancing the nickel concentration up to 3 wt% resulted in a 37% reduction in the wear rate.
查看更多>>摘要：? 2021 The AuthorsOne of the major challenges in welding of aluminium (Al) alloys and steels is the growth of brittle intermetallic phases, which depends on the thermomechanical processing history and the alloying elements. This work focuses on the intermetallic phase layers formed in roll bonded composites of Al alloy 6082 and stainless steel 316L after interdiffusion at temperatures in the range of 400 – 550 °C. Scanning and transmission electron microscopy characterisation showed that during interdiffusion, an αc-Al15(Fe,Cr,Mn)3Si2 phase layer formed first, before a discontinuous layer of τ1-FeNiAl9 formed at the Al-αc interface. Subsequently, a layer of θ-Fe4Al13 and τ11-Al5Fe2Si formed at the αc-steel interface, followed by a layer of η-Fe2Al5 with precipitates rich in Cr and Si or Ni. Nanoindentation and density functional theory calculations were performed to assess the mechanical properties of the formed phases. Miniature tensile testing confirmed that the bond strength decreased as the thicknesses of brittle phase layers increased. Further, it was found that the growth rate of the total intermetallic phase layer was significantly reduced for the high alloyed 6082-316L composites compared to unalloyed reference composites of 1080-S355. Altogether, this work provides insight into the combined effects of the alloying elements Si, Mn, Cr and Ni on the formation, growth and mechanical properties of the interfacial intermetallic phases in Al-steel joints.
查看更多>>摘要：? 2021High-entropy alloys (HEAs) are a new type of multi-principal metal materials that exhibit excellent mechanical properties, good thermal stability, and high corrosion resistance, with versatile potential applications. In this paper, we have investigated CoCrFeNi(Al0.3Ti0.2)x HEA with different Ti and Al contents using XRD, tensile testing, and molecular dynamics simulations. The effects of Ti and Al contents and temperature on the mechanical properties were also explored. The experimental results showed that the CoCrFeNi(Al0.3Ti0.2)x HEAs were mainly composed of the FCC matrix phase and γ′ phase (Ni3(Al, Ti)) after rolling and annealing. The addition of Ti and Al induced the formation of high-temperature strengthening phases in the CoCrFeNi HEA, which significantly improved the mechanical properties. The molecular dynamics simulations also indicates that the elastic modulus and tensile strength of CoCrFeNi(Al0.3Ti0.2)x HEA are steadily improved with the Ti and Al addition. The tensile strength increases with the dislocation density. Besides, we have performed a high-temperature mechanical characterization of the CoCrFeNiAl0.225Ti0.15 HEA. The experimental data have revealed that the material's strength continuously declines with stretching temperature, opposed to that of toughness. The high-temperature tensile modulus of elasticity decreases with the temperature. Temperature also diminishes the tensile strength due to the average reduction of the dislocation density.
查看更多>>摘要：? 2021 The Author(s)The effect of the degree of severe plastic deformation (SPD) on the thermal stability of a nanocrystalline CoCrFeNi multi-principal element alloy was studied. The SPD method of high-pressure torsion (HPT) was utilized to achieve the nanocrystalline microstructure. The structural stability was investigated near the centers and edges of the HPT-processed disks deformed for ?, 1, 5 and 10 turns. For almost all studied samples, two exothermic peaks in the temperature ranges of 600–750 and 750–950 K were observed by differential scanning calorimetry (DSC) between room temperature and 1000 K. The saturation released heat value for the first DSC peak was about 4 J/g that was achieved at the shear strain of ～200. For the second exothermic peak, the released heat saturated at the shear strain of about 20 with the value of about 6–7 J/g. It was revealed that the first DSC peak is related to the annihilation of dislocations for low degree of deformation. At the same time, for edge parts of the disks processed by one or higher numbers of turns the vacancy annihilation has also a major contribution to the first exothermic peak. The annihilated vacancy concentration estimated from the released heat was between (0.6–0.9) × 10?3. The second DSC peak was related to the disappearance of grain boundaries due to recrystallization and annihilation of the remaining dislocations. The HPT-processed CoCrFeNi MPEA samples exhibited very high hardness values between 4000 and 5100 MPa, depending on the number of turns and the location along the disk radius. The hardness decreased only during the second exothermic peak when recrystallization occurred.
查看更多>>摘要：? 2021 Elsevier LtdHarsh service environment especially in sulfur-containing atmosphere and complex structures of dominant γ' + γ dendrite, interdendritic region and interface region have significant effect on service life of polycrystalline Ni3Al-based superalloys. In this work, hot corrosion behavior of polycrystalline Ni3Al-based superalloy in sulfur-containing atmosphere was studied at 900 °C. Growth behaviors of corrosion products were analyzed by X-ray Photoelectron Spectroscopy, Raman spectrometer, Scanning Electron Microscope and Transmission Electron Microscope. The results showed that the growth behaviors of corrosion products were different in different regions. Corrosion products in interdendritic regions were Ni3S2 and Al2O3. While, as for dominant γ' + γ dendrite and interface regions, corrosion products were mainly composed of Ni3S2, Cr3S4 and mixed oxides. However, though the corrosion products are similar in composition, they have different growth mechanism. Spatial structure and precipitates were observed to analyze and explain the reasons for difference of corrosion behaviors in different regions.
查看更多>>摘要：? 2021The influence of V addition on the microstructure and high-temperature tensile performance of Ti46Al7Nb0.4W0.6Cr alloy, fabricated by using the cold crucible directional solidification method, is comprehensively investigated. The results show that V addition can refine the columnar grain width and promote the brittle-to-ductile transition (BDT) of the TiAl alloy. After the addition of 2 at.% V, the ultimate tensile strength and elongation increased at 973–1173 K. The fracture mode change from interlamellar to translamellar; this is attributed to the decrease in the angle between the lamellar alignment and growth direction. The BDT behaviour of V-containing TiAl alloy at 1073 K results from the transition from dislocation-dominated to twin-dominated deformation as indicated by transmission electron microscopic investigations.
查看更多>>摘要：? 2021 Elsevier LtdForged β-solidifying TiAl alloys can exhibit nine independent elastic constants in accordance with the orthorhombic symmetry of forging texture. In this study, we measured the elastic constants and high-frequency internal friction of two forged Ti–43Al–5V–4Nb (in at.%) alloys with nearly lamellar and triplex microstructures using resonant ultrasound spectroscopy at temperatures between room temperature and 760 °C. We demonstrated that a two-step heat treatment after the forging process produces nearly isotropic elasticity in the TiAl alloys, and the elastic anisotropy is virtually constant with temperature. The Young's modulus of the TiAl alloy with a triplex microstructure was comparable to that of the alloy with a nearly lamellar microstructure. In addition, the triplex-microstructure TiAl alloy showed a significant energy loss for shear vibration modes compared with the nearly lamellar alloy. These findings are supported by the effect of the hexagonal ω-phase present in the βo-phase on mechanical stiffness and loss. Internal friction measurements at high frequencies exhibited an internal-friction peak at approximately 200 °C, which may be related to the isothermal ω-phase. This research may contribute to the development of sophisticated forged TiAl components.
查看更多>>摘要：? 2021 Elsevier LtdTitanium alloys (Ti–6Al–4V) are attractive in many industries due to their weight ratio, high thermal stability and corrosion resistance. However, their poor tribological properties limit their usage in many applications. In this work, Fe, Co, Cr, Ni and Al powders are mechanically mixed by ball milling and preplaced on the Ti–6Al–4V substrate. Plasma Transferred Arc (PTA) alloying process is performed to fuse the preplaced powder into the substrate surface. X-ray diffraction (XRD), microstructure and microhardness testing is performed to assess the presence of phases, formation of structure and hardness improvement, respectively. Then, the dry sliding pin-on-disc wear testing is conducted on the substrate and PTA alloyed samples. The various wear mechanism and their corresponding roughness were analysed and discussed. XRD result reveals that the ball milled powder and PTA samples possess BCC and FCC phases. However, BCC phases are formed higher than FCC phases due to rapid cooling and controlled heat input. Moreover, broadened BCC phases are observed in the PTA sample at 27°, 36°, 42°, 54° and 70° than that of the ball milled powder. Microstructure of the PTA sample contains both (Ni, Co) rich inter-dendrite and (Al, Fe, Cr) rich needle like dendrite. The microhardness of PTA region has improved with 2.39 times higher than substrate. The wear resistance of the PTA sample has improved by two times compared to substrate. Abrasive, adhesive and plastic deformation were observed on the worn out substrate while PTA sample showed with mild abrasive wear with reduced roughness. The overall results reveal that the various elements are properly alloyed on the Ti–6Al–4V surface through the PTA process and significantly improved the wear resistance. As a result, the PTA process can be used for alloying of other elements to improve the wear resistance of Ti–6Al–4V substrate.
查看更多>>摘要：? 2021 Elsevier LtdTi-based bulk metallic glass composites (BMGCs) with the microstructure consisting of micro-scale β-Ti dendrites and nano-scale interdendritic glassy matrix were prepared via suction casting. Effects of minor Sn addition on mechanical behavior of the BMGCs were investigated. It was found that the Sn addition presented “dual effects” on mechanical properties of the dendrites in the BMGCs, i.e., solid solution strengthening and increase of Young's modulus. As a result, remarkably enhanced strength without reducing plasticity could be achieved for the BMGCs. The BMGCs exhibited a unique plastic deformation mode, which was attributed to the presence of the glassy matrix in nano-scale. The results might give some hints for improving the mechanical properties of dendrite-reinforced Ti-based BMGCs by tuning the microstructure.
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