查看更多>>摘要：Magnetoelastic couplings in giant magne-tostrictive materials(GMMs)attract significant interests due to their extensive applications in the fields of spin-tronics and energy harvesting devices.Understanding the role of the selection of materials and the response to external fields is essential for attaining desired functional-ity of a GMM.Herein,machine learning(ML)models are conducted to predict saturation magnetostrictions(λs)in RFe2-type(R=rare earth)GMMs with different compo-sitions.According to ML-predicted composition-λs rela-tions,it is discovered that the values of λs higher than 1100 × 10-6 are almost situated in the composition space surrounded by 0.26 ≤ x ≤ 0.60 and 1.90 ≤ y ≤ 2.00 for the ternary compounds of TbxDy1-xFey.Assisted by ML predictions,the compositions are further narrowed down to the space surrounded by 0.26 ≤ x ≤ 0.32 and 1.92 ≤ y≤ 1.97 for the excellent piezomagnetic(PM)performance in the TbxDy1-xFey-based PM device through our devel-oped high-throughput(HTP)micromagnetic simulation(MMS)algorithm.Accordingly,high sensitivities up to 10.22-13.61 mT.MPa-1 are observed in the optimized range within which the available experimental data fall well.This work not only provides valuable insights toward understanding the mechanism of magnetoelastic couplings,but also paves the way for designing and optimizing high-performance magnetostrictive materials and PM sensing devices.
查看更多>>摘要：The development of zero and negative thermal expansion(i.e.,ZTE and NTE)materials is of crucial importance to the control of undesirable thermal expansion for high-precision devices.In the present work,ZTE and NTE were obtained in directionally-solidified MnxFe5-xSi3 alloys with a strong<001>texture,in striking contrast to positive thermal expansion in their isotropic counterparts.Magnetometry and in-situ X-ray diffraction(XRD)mea-surements were performed to uncover the origin of the anomalous thermal expansion.Magnetic measurements indicate a strong easy-plane magnetocrystalline anisotropy in the textured samples,where the magnetic moments are aligned within the ab plane of the hexagonal structure.Temperature-dependent XRD on the x=1 sample reveals a ZTE character in the ab plane that is coupled to a fer-romagnetic transition.As a result,the macroscopic ZTE(～0.22 × 10-6 K-1)in the x=1 sample can be attributed to the microscopic magneto volume effect within the ab plane,which is realized by the introduction of the<001>-textured microstructure.Besides,the competition between antiferromagnetic and ferromagnetic exchange coupling leads to NTE in textured x=1.5 and 2 samples.Addi-tionally,textured x=1 sample displays enhanced magne-tocaloric properties as compared to the conventional counterparts with randomly-oriented grains.Consequently,this work demonstrates a new strategy toward the explo-ration of anomalous thermal expansion properties as well as the enhancement of magnetocaloric properties for materials with a strong magnetocrystalline anisotropy.
查看更多>>摘要：The solid solution and aging treatment for con-ventional manufacturing processes might not be suit-able for laser additive manufactured titanium alloys due to the different lamellar microstructures.In this study,the influence of aging temperatures(600,700 and 800 ℃)on microstructure and mechanical properties of titanium alloy Ti-6Al-2V-1.5Mo-0.5Zr-0.3Si was investigated.The results indicate that after solid solution treatment at 970 ℃ followed by water quenching,the alloy mainly consists of coarsening lamellar α phase in martensite α'matrix.Aging at 600 ℃ will not change the size of primary lamellar αphase but lead to huge amount of secondary α phases(αs)generating with very fine microstructure.By increasing the aging temperature,the number of αs decreases but with coarsened microstructures.When aged at 800 ℃,the width of the αs phase reaches 350 nm,almost 7 times wider than that aged at 600 ℃.The changing size of αs obviously influences the property of the alloy.The fine αs leads to high strength and microhardness but low plasticity,and specimen aged at 700 ℃ with suitable αs size has the best comprehensive properties.
查看更多>>摘要：In this work,the underlying mechanism responsible for the near-linear elastic deformation behavior of a dual-phase Ti-Nb alloy consisting of β and α"phase with large recoverable strain was systematically elucidated.Based on in situ synchrotron X-ray diffraction(SXRD)analyses,it was found that besides intrinsic elastic defor-mation,a slight reversible β ↔ α"stress-induced marten-sitic(SIM)transformation,which proceeded in a consecutive mode under the retarding effect of micro-de-fects,took place during the near-linear elastic deformation.After unloading,a small amount of residual macroscopic strain remained in the specimen due to the incomplete reverse α"→ β transformation on unloading.The high near-linear elastic deformability of the cold drawing(CD)Ti-Nb alloy has been revealed to be attributed to the cou-pling actions of intrinsic elasticity as well as the consecu-tive and reversible β ↔α"SIM transformation.Our research may contribute to a new avenue for the design and development of novel dual-phase Ti-based alloys with desirable elastic deformability.
查看更多>>摘要：The volume fractions and morphology of pre-cipitates in precipitation-strengthened Cu-Ti alloys,which precipitate mainly as continuous and discontinuous pre-cipitates,are important for the application of the alloy.This study employed hardness and electrical conductivity tests,transmission electron microscopy(TEM),atom probe tomography(APT),and first-principles calculations to demonstrate that the addition of Mg is effective for accelerating nanosized continuous β'-Cu4Ti precipitation as well as for suppressing the precipitation of coarse lamellar discontinuous β-Cu4Ti precipitates along the grain boundaries,resulting in Cu-Ti alloys with high yield strength and good electrical conductivity.The results showed that the continuous precipitation of β'-Cu4Ti was accelerated by the Mg additions,which reduced the supersaturation of the matrix,thereby reducing the chem-ical driving force for the discontinuous precipitates.On the other hand,Mg additions increased the mismatch between the discontinuous β-Cu4Ti precipitates and matrix,decreased the nucleation rate of the discontinuous precip-itates,and increased the spacing of the discontinuous pre-cipitation layer,resulting in a lower growth rate of the discontinuous precipitates.Therefore,the addition of Mg to Cu-Ti alloys enhances the strength and improves the resistance to over-ageing.
查看更多>>摘要：High-cost pre-alloyed powder is the bottleneck problem that limits the widespread application of additive-manufactured shape memory alloys.In this work,the low-cost ternary NiTiFe shape memory alloy is fabricated by laser powder bed fusion(LPBF)technique via mechani-cally mixed pre-alloy NiTi powder and varying contents pure Fe powder(1,2,3 wt％).All NiTiFe alloys show a relative density of up to 99.8％by optimizing the LPBF processing parameters.Owing to the heterogeneous nucleation effect of micron-sized Fe particles,both grain refinement and texture weakening are generated in the NiTiFe alloys,accompanied by the reduction of dislocation density.For the room-temperature mechanical properties,the NiTi-3Fe alloy shows the highest microhardness of HV 370,but the fracture strength and elongation reduce to 1701 MPa and 23％simultaneously.The evolution of mechanical properties is attributed to the high internal defects,low dislocation density and the incoherent oxide.Moreover,the NiTi-3Fe alloy shows the quasi-linear superelasticity behavior;the superelastic recoverable strain of NiTi-1Fe and NiTi-2Fe decreased with the increase in Fe content.This study provided a new-fangled insight for the development of multi-component NiTi-based shape memory alloys by additive manufacturing.
查看更多>>摘要：Serrated flow phenomenon has been widely observed among different metals due to the potential influence on their applications.Uniaxial tensile tests of nickel-based superalloy GH536 were carried out at loading rates of 0.06,0.60,3.60,and 36.00 mm·min-1 at room temperature,respectively.The tensile stress-strain curves demonstrate repetitive and discontinuous yielding behav-ior,namely serrated flow.It is observed that the stress-strain curves were dominated by type B serration,and original annealing twin boundaries(TBs)were distorted to various degrees under comparatively different lower tensile rates.In contrast,the TBs almost disappear,and the type B serrations become smoother and regular under the higher loading rates.This phenomenon can be attributed to the interactions between TBs and dislocations during tensile deformation.Coupled effects of the mobile and immobile dislocations illustrate the unsteady amplitude of serrations observed in stress-strain curves.Transmission electron microscope images of tested pieces reveal the interaction of dislocation and TB,with dislocation tangling around the TBs.
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