查看更多>>摘要：? 2022In this paper, we explore the synthesis of new antimonide compounds based upon concepts of high entropy alloys (HEA). HEAs are usually multi-element (?5) alloys with near the equiatomic composition. They have been given very large attention due to their vast potential within many fields. We investigated the thermoelectric transport properties of antimony-based high entropy alloys. The observed electrical conductivity, Seebeck coefficient, and thermal conductivity were comparable to those of cutting-edge half-Heusler thermoelectric alloys. Alloys with different valence electron counts (VEC) were synthesized and correlated with measured electrical properties.
查看更多>>摘要：? 2022 Elsevier LtdIn this study, the correlations between structural characteristics, shear transformation zone (STZ) size and shear-band mediated plasticity were systematically investigated in crystalline-layer confined amorphous (CLCA) NiW alloy films. In these films, the structural states with or without distributed structural defects – the so-called nano shear bands (NSBs) – could be regulated by thermal treatment. It was found that NSBs positively impacted the STZ size obtained by strain rate sensitivity (SRS) method (known as engineering STZ size), which actually reflected the combined size of the connected STZs and was proportional to the plasticity of amorphous alloys. Whilst, NSBs were unprevailing in case of the statistically determined STZ size. This was owing to the fact that such a size was closer to the real STZ size that was independent of the structural state and plasticity of amorphous alloys. The findings of the present work enabled one to elucidate the underlying mechanism of the discrepancy of STZ size, as well as to establish its relationship with structural characteristics and plasticity of amorphous alloys.
查看更多>>摘要：? 2022 Elsevier LtdCu–9Ni–6Sn specimens with different Nb contents ranging from 0 to 0.22 wt% were prepared by a vacuum induction furnace, and needle-like NbNi3 particles were found at the grain boundaries and interior after solution treatment. The results indicated that these NbNi3 particles suppressed the discontinuous precipitation (DP) growth during aging treatment. By using Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation and Arrhenius equation, the kinetics of DP is also figured out and the activation energy (Q) of the DP in Cu–9Ni–6Sn-xNb (x = 0, 0.05, 0.22 wt%) alloys are 75.8 kJ/mol, 80.9 kJ/mol and 88.5 kJ/mol, respectively, indicating that the atom diffusion for producing DP is more difficult in Nb-bearing alloys, and the formation of DP is inhibited correspondingly. What's more, the lamellar spacing (S) of DP increased and the growth rate of DP decreased in the with the Nb-bearing Cu–9Ni–6Sn alloy.
查看更多>>摘要：? 2022 Elsevier LtdIn this work, two Nb(Ta)TiZr medium-entropy alloy (MEA) coatings were fabricated successfully on a commercially pure Zr sheet by pulsed laser cladding. Their phase constitutions, microstructural characteristics, chemical compositions and grain orientations were well characterized and analyzed by using X-ray diffraction (XRD), electron channeling contrast (ECC) imaging, energy dispersive spectrometry (EDS) and electron backscatter diffraction (EBSD) techniques, with hardness and wear resistance measured and correlated with the microstructural characteristics as well. Results show that irregular-shaped bulk grains (BCC solid-solution phase) are formed in the two Nb(Ta)TiZr MEA coatings (cladding zones), both of which have a thickness of ～800 μm with good metallurgical bonding to the substrate. After adding Ta, grains in the MEA coating are slightly refined. The phase constitutions in both the coatings agree with calculations based on several theoretical parameters. Hardness tests show that the NbTiZr and the NbTaTiZr coatings have hardnesses of 360 ± 18 HV and 430 ± 28 HV, respectively, ～1.8 times and ～2.2 times that of the substrate (196 ± 4 HV). This can be ascribed to combined effects of grain refinement strengthening, solid solution strengthening with denser low angle boundaries in the MEA coatings. Specific wear rates of the NbTiZr and the NbTaTiZr coatings are only ～17% and ～6% of that of the substrate, respectively, indicating markedly improved wear resistance. This is demonstrated to be closely related to complete oxide films easily formed on the coatings with oxidation and abrasive wear mechanisms.
查看更多>>摘要：? 2022We have prepared 2.5% Cu-doped Nb3Al wire by the Rapid-Heating Quenching and Transformation (RHQT) method with optimized annealing. XRD results show that A15 and supersaturated bcc phase are formed after high current RHQ process, and the supersaturated bcc phase is transformed into A15 phase after conventional annealing (800 °C\10 h). We observed the microstructures at different annealing time by field-emission scanning electronic microscope (FESEM) and found that σ phase is generated from the decomposition of the metastable A15 phase after prolonged annealing due to its lower free energy at 800 °C, and gradually accumulates Cu to form the Cu-rich σ phase after 20 h. The low-field superconducting properties were also given through magnetic measurement. Both Tc and Bc2 decreased slightly along with the increase of σ phase volume when the annealing is prolonged, while Jc reached its peak after 20 h\800 °C annealing, which were 1836 A/mm2 at 4.2 K and 5 T and 822 A/mm2 at 8 K and 5 T for 800 °C\20 h annealing, about 34% and 36% higher than that of the conventional transformed sample, respectively. The calculated Fpmax of the samples with optimized annealing condition also increased accordingly. The fitting analysis of fp using the Dew-Hughes model showed that the pinning mechanism was surface pinning. The additional diffusion channels for Cu provided by newly generated interfaces of σ and Nb(Al) particles enhance the Cu segregation on the A15 boundaries and may be the source of the pinning force improvement.
查看更多>>摘要：? 2022 Elsevier LtdPhase equilibria in the Sm–Co, Sm–Fe and Co–Fe-Sm systems were investigated in detail using DTA, X-ray diffraction, SEM and EPMA. Based on the experimental data from the present work, the liquidus and solidus projections, the isothermal section at 1000 °C and the Scheil reaction scheme for the Co–Fe-Sm system over the whole concentration range were constructed. The phase diagram of the Sm–Co system was revised. The Sm-rich region of the Sm–Fe system was studied for the first time. The stability domains of the intermetallic phases (binary phases and their extension inside ternary) were defined. Three continuous solid solutions Sm2(Co,Fe)17, Sm(Co,Fe)3 and Sm(Co,Fe)2 were found in the Co–Fe-Sm system at the solidus temperatures. In contrast to a previous analysis of the phase diagram for the system, wide homogeneity regions were revealed for the SmCo5 and Sm2Co7 phases and alternative invariant four-phase equilibria. The magnetic properties of samples containing Sm2(Co,Fe)17 phase were measured. The values of the Curie temperature and the magnetic moment of these samples were quite close to those earlier presented in the literature.
查看更多>>摘要：? 2022 Elsevier LtdThe recently emerged CoCrNi-based medium-entropy alloys (MEAs)/high-entropy alloys (HEAs) have a good combination of high strength and ductility. However, there are still challenges for further increasing their mechanical properties by finding optimal composition with simple processing. In this investigation, we revisited the commercial superalloys MP35N and MP159 with similar composition and entropy to CoCrNi-based MEAs/HEAs to find inspirations for designing CoCrNi-based MEAs. After a simple thermomechanical process, MP35N/MP159 can achieve a high tensile strength over 2.2 GPa at ambient temperature, better than a majority of present CoCrNi-based MEAs/HEAs. At intermediate temperature tensile tests, the aged MP159 also has a considerable tensile strength (1.8 GPa) and tensile elongation (12.5%). The underlying strengthening factors of aged MP35N/MP159 were investigated by transmission electron microscope. It indicated that precipitation strengthening, solid solution strengthening, and work-hardening could be introduced in CoCrNi-based MEAs through alloying, and simple thermomechanical treatments to significantly improve the performance. The present findings and perspectives provide useful enlightenment for developing ultra-strong CoCrNi-based MEAs/HEAs.
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