查看更多>>摘要：? 2022 Elsevier LtdHigh strength ultrafine grained CoCrFeNiMn high entropy alloys (HEAs) containing TiO(C) nanoparticles were fabricated by thermomechanical consolidation of a mechanically milled powder at 950 and 1000 °C, respectively. The sample consolidated at 950 °C with an average grain size of 417 nm had a high yield strength (YS) of 1457 MPa, but exhibited necking immediately after yield drop, leading to a limited elongation to fracture of 1.3%. In contrast, the sample consolidated at 1000 °C with an average grain size of 489 nm had a clearly lower YS of 1236 MPa, but exhibited yield drop, Lüders deformation, work hardening and then necking, with a significant elongation to fracture of 10.0%. Our work shows that by introducing intragranular Ni–Ti nanoparticles in the coarser grained sample through quenching to liquid nitrogen and aging, the YS of the sample was brought back to 1449 MPa, and still kept a substantial elongation to fracture of 4.2%. The transition of the plastic deformation behavior with grain refinement is analyzed based on dislocation dynamics theory. Based on this analysis, it is proposed that to maintain the uniform deformation, the grain sizes should be larger than a critical value, above which maximum flow stress of the material is higher than the upper yield stress. Introducing intragranular Ni–Ti nanoparticles is an effective strategy to further enhance yield strength without losing work hardening ability due to the synergistic effect with intragranular TiO(C) nanoparticles to inhibiting dislocation annihilation at grain boundaries.
查看更多>>摘要：? 2022ZrTi0.1V2-x (x = 0, 0.2, 0.4) alloys are designed to investigate the effect of hypo-stoichiometry on hydrogenation properties of Laves phase dominated multiphase alloys. The samples are synthetized by arc melting and homogenizing annealing treatment. Phase abundances and lattice parameters are studied by XRD and Rietveld refinement. The morphology of each phase is confirmed by SEM and EDS, hydrogenation kinetics, pressure-composition-temperature characteristics and hydrides have been studied. Annealing increases the content of Laves phase and Zr3V3O, while decreases that of V-BCC and α-Zr. The decrease in atomic ratio B/A, i.e. V/(Zr + Ti), results in the increase of Zr3V3O, the decrease of Laves and V-BCC, and the lattice expansion for each phase. Alloys show easy activation and fast hydrogenation kinetics, which is controlled by a different process. Hydrogen absorption capacity and formation enthalpy increase while equilibrium pressure decreases with the decrease in B/A ratio, which could be related to the decrease of V-BCC phase and lattice expansion for each phase. Zr8V16H36.29 is the dominated hydride after saturated hydrogenation, the proportion of hydrides and their hydrogen mass fraction accord with the hydrogen absorption behavior. Among the samples, ZrTi0.1V1.6 shows the best overall properties for rapid and massive hydrogen absorption at low pressure.
查看更多>>摘要：? 2022 Elsevier LtdThe influence of iron on the formation of Al–Mn–Fe intermetallic compounds (IMCs) has been investigated in the solidification of Mg–9Al-0.7Zn-0.2Mn (wt.%, AZ91) with iron contents ranging from ～0.001 to > 0.01 wt.% Fe. Four Al–Mn–Fe IMCs formed depending on the Fe-content and location in the crucible: B2–Al(Fe,Mn), Al8Mn5, Al11Mn4 and, at the bottom of crucibles, Al5Fe2. The four IMCs nucleated and grew on one another, producing multiphase particles. These usually contained numerous orientations that were all interrelated through simple orientation relationships that are discussed in terms of the similarities between the IMC crystal structures. The iron content affected the IMC phase fractions and the multiphase particle morphology. At low iron content, the Fe-rich B2 phase was encapsulated by a low-Fe Al8Mn5 shell. With increasing iron content, the Fe-rich phases (B2 and Al5Fe2) gradually became in direct contact with the α-Mg. The threshold Fe:Mn content for adequate corrosion performance is found to correlate approximately to where B2–Al(Fe,Mn) first becomes exposed to the α-Mg matrix.
查看更多>>摘要：? 2022 Elsevier LtdIntermittent high-frequency vibration loading is introduced into the Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk amorphous alloy as an ultrashort time, easy-to-obtain, nondestructive physical method to adjust its atomic arrangement and shear deformation behavior. It is found that the method of intermittent high-frequency vibration loading can make the ductility and strength of the bulk amorphous alloys increase quickly within 4 s, increasing to 5.3% and 2240 MPa, respectively. And there is a mechanical power threshold of approximately 0.43 kJ/mol. Apart from the as-cast sample, when it is less than this threshold, with the increase of amplitude and pre-pressure, the relaxation enthalpy of IHF-treated samples increases, the ductility increases, but the compressive yield strength is basically unchanged, and there is basically no precipitation of nanocrystals at the same time. When it is greater than the threshold, as the amplitude and pre-pressure increase, the relaxation enthalpy decreases, nanocrystals precipitate, the ductility and the compressive yield strength begin to decrease. Both the increase in free volume content and the appearance of nanocrystals will lead to an increase in the critical stress of the first ejection event, thereby simultaneously increasing the ductility and yield strength. It is also found that the increase in free volume content is the main factor for the increase in ductility and strength, and the appearance of nanocrystals is a secondary factor. Our findings provide a new ultrashort time method for overcoming the strength-ductility trade-off dilemma.
查看更多>>摘要：? 2022In this study, a novel Ti–Zr–Cu–Ni amorphous filler metal was fabricated and applied to vacuum brazing of TiAl alloy and Ni-based superalloy (GH536). The effects of brazing temperature on the interfacial microstructure and mechanical properties of the joints were analyzed. Three different regions, the isothermal solidification layer Ⅰ, continuous reaction layer Ⅱ and continuous diffusion layer Ⅲ, were formed in the joints after brazing. The SEM and EDS results show that brazing temperature plays an important role in element diffusion, microstructure evolution and metallurgical quality of brazed joints, while the thickness of layer Ⅱ and Ⅲ was basically not affected by brazing temperature. The obtained joints showed excellent shear strength both at room temperature and elevated temperature. With the increase of brazing temperature, the shear strength of joints at room temperature firstly increased and then decreased. The optimal shear strength of 279 MPa was obtained after brazing at 1100 °C for 10 min. With the increase of test temperature, the shear strength of joints obtained at 1110 °C/10 min firstly decreased, then increased, and decreased again, with the maximum value of 156 MPa at 600 °C. The shear fracture mainly occurred in the thinnest layer Ⅱ and the fracture morphology exhibited typical cleavage fracture characteristics.
NSTL
Elsevier