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annealing hardening effect aroused by solute segregation in gradient ultrafine-grained Mg-Gd-Zr alloy

Journal of Materials Science & Technology 2023年第13期144卷 70-80页

作者： Chunquan Liu Xianhua Chen Domonkos Tolnai Yaobo Hu Wei Zhang Yusheng Zhang Fusheng Pan College of Materials Science and Engineering Chongqing UniversityChongqing 400045China National Engineering Research Centre for Magnesium Alloys Chongqing UniversityChongqing 400045China Institute of Metallic Biomaterials Helmholtz-Zentrum HereonMax-Planck Street 1Geesthacht 21502Germany Northwest Institute for Nonferrous Metal Research Xi’an 710016China

In this study,a remarkable annealing hardening effect was detected in gradient ultrafine-grained(UFG)Mg-0.32Gd-0.11Zr(at.%)alloy sheet fabricated by sliding friction treatment(SFT).Under the precipitation-free condition,the annealed UFG structure shows an obvious hardness increment from 1.40 GPa to 1.89 GPa after 200℃ heating for 12 h,which exhibits a much higher hardening response than the annealed coarse-grained(CG)*** high-angle annular dark-field scanning transmission elec-tron microscopy(HAADF-STEM)and elemental mapping reveal prominent segregation of solute Gd atoms along grain boundaries,which endows the UFG structure with excellent grain boundary ***-over,Gd segregation is also found around the extrinsic stacking fault(E-SFs)and the low-angle grain boundaries composed of edge *** large-scale solute partitioning provides a significant seg-regation hardening effect,which completely resists the softening effect aroused by the grain coarsening and dislocation *** work realizes a good combination of surface mechanical processing for fabricating UFGs and subsequent heat treatment,which earns desirable segregation hardening effects.

关键词： Ultrafine grains Segregation annealing hardening

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Investigations of annealing hardening in Au micropillar based on a modified discrete-continuous model

Investigations of annealing hardening in Au micropillar base...

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北京力学会第二十三届学术年会

作者： Fengxian Liu Zhan-li Liu Peng Lin Zhuo Zhuang Applied Mechanics Lab. School of Aerospace Engineering Tsinghua University

In contrast to the typical behavior at macro level, recent studies at sub-micro scale have shown that metals may harden rather than soften during high temperature annealing. In the present work, a modified three-dimensional discrete-continuous mode(DCM) is proposed to address the limitations of the local model, in which the vacancy diffusion equation is solved by the FEM. Based on this DCM model, the intrinsic mechanism of annealing hardening at sub micro scale and detailed evolution of defects during the annealing are investigated. Numerical simulation results shows that the hardening is caused by the decrease of dislocation density, which can be ascribed to two main aspects:(i) The climb of dislocation during the high temperature annealing promotes the annihilation of the dislocations, leading to a decrease in dislocation density.(ii) The jogs, nucleated during annealing due to the high temperature climb, have very weak mobility and act as obstacles to the dislocation glide motion, leading to mobile dislocation starvation and resulting in a higher flow strength level.

关键词： annealing hardening dislocation climb discrete-continuous model jogs

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Detwinning and Anneal-hardening Behaviors of Pre-Twinned AZ31 Alloys under Cryogenic Loading

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Acta Metallurgica Sinica(English Letters) 2024年第9期37卷 1551-1563页

作者： Lingyu Zhao Wei Zhu Chao Zhang Yunchang Xin Changjian Yan Yao Cheng Zhaoyang Jin School of Mechanical Engineering Yangzhou UniversityYangzhou225127China Key Laboratory for Light-Weight Materials Nanjing Tech UniversityNanjing210009China Institute of Corrosion Science and Technology Guangzhou510070GuangdongChina Jiangsu Key Laboratory of Advanced Structural Materials and Application Technology Nanjing Institute of TechnologyNanjing211167China

Detwinning behavior of a pre-twinned magnesium alloy AZ31 at cryogenic temperature was investigated,also with a focus on the annealing hardening behavior of samples with different fractions of ***-compression along the transverse direction with strains of 1.7%,3.0%,and 6.0% was applied to generated[1012]*** behavior,microstructure,and texture evolution during subsequent tension were *** results show that low temperature did not change the fact that detwinning still pre-dominated in the pre-twinned samples under reverse ***,a relatively harder migration of twin boundaries was found at cryogenic *** annealing hardening of 27-40 MPa was observed in the pre-twinned samples,and such a hardening effect shows a close relation with the fraction of pre-twins or the level of *** annealing hardening effect disappeared if the matrix was consumed by twins along with the increased pre-compression *** corresponding reasons for the annealing hardening behavior were discussed.

关键词： Mg alloys Detwinning annealing hardening Cryogenic temperature Mechanical property

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Unveiling anneal hardening in dilute Al-doped Al_(x)CoCrFeMnNi(x = 0,0.1) high-entropy alloys

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Journal of Materials Science & Technology 2021年第32期91卷 270-277页

作者： Q.Cheng X.D.Xu P.Xie L.L.Han J.Y.He X.Q.Li J.Zhang Z.T.Li Y.P.Li B.Liu T.G.Nieh M.W.Chen J.H.Chen Centre for High Resolution Electron Microscopy College of Materials Science and EngineeringHunan UniversityChangsha 410082China State Key Laboratory of Powder Metallurgy Central South UniversityChangsha 410083China Applied Materials Physics Department of Materials Science and EngineeringKTH-Royal Institute of TechnologyStockholm SE10044Sweden Department of Materials Science and Engineering University of TennesseeKnoxvilleTN37996United States Department of Materials Science and Engineering Johns Hopkins UniversityBaltimoreMD 21214USA

Anneal hardening has been one of the approaches to improve mechanical properties of solid solution alloys with the face-centered cubic(FCC) structure,whereby a considerable strengthening can be attained by annealing of cold-worked alloys below the recrystallization temperature(T_(rx)).Microscopically,this hardening effect has been ascribed to several mechanisms,*** segregation to defects(dislocation and stacking fault) and short-range chemical ordering,***,none of these mechanisms can well explain the anneal hardening recently observed in phase-pure and coarse-grained FCC-structured high-entropy alloys(HEAs).Here we report the observations,using high-resolution electron channeling contrast imaging and transmission electron microscopy,of profuse and stable dislocation substructures in a cold-rolled CoCrFeMnNi HEA subject to an annealing below T_(rx).The dislocation substructures are observed to be thermally stable up to T_(rx),which could arise from the chemical complexity of the high-entropy system where certain elemental diffusion retardation *** microstructure feature is markedly different from that of conventional dilute solid solution alloys,in which dislocation substructures gradually vanish by recovery during annealing,leading to a strength ***,dilute addition of 2 at.% Al leads to a reduction in both microhardness and yield strength of the cold-rolled and subsequently annealed(≤500℃) *** Al induced softening effect,could be associated with the anisotropic formation of dislocation substructure,resulting from enhanced dislocation planar slip due to glide plane softening *** findings suggest that the strength of HEAs can be tailored through the anneal hardening effect from dislocation substructure strengthening.

关键词： annealing hardening Dislocation substructure strengthening High-entropy alloy Solid solution structure

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Influence of pre-strain and heat treatment on subsequent deformation behavior of extruded AZ31 Mg alloy

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Transactions of Nonferrous Metals Society of China 2015年第11期25卷 3604-3610页

作者：陈红兵刘天模卢立伟何杰军翟彦博重庆大学材料科学与工程学院重庆400044 西南大学工程技术学院重庆400716 湖南科技大学机电工程学院湘潭411201 中南大学材料科学与工程学院长沙410083 贵州理工学院材料与冶金工程学院贵阳550003

Pre-compression and heat treatment were performed on an extruded AZ31 Mg alloy,and their effects on subsequent deformation behavior were *** results show that at low temperature annealing(170 ℃ for 4 h),the extruded samples with and without annealing exhibit a nearly equivalent yield stress(~148 MPa) because their microstructures are nearly ***,under the same annealing condition,the yield stress of sample with pre-twinning and subsequent annealing(~225 MPa) is higher than that of the pre-twinned one(~200 MPa).The former sample presents a hardening effect because the solute atoms segregated on twin boundaries lead to a strengthening *** pre-twinned sample annealed at 400 ℃ for 1 h shows a higher ultimate elongation(~28%) than the pre-twinned one(~15%),but its yield stress(~125 MPa) is much lower than that of the pre-twinned one(~200 MPa).

关键词： AZ31 Mg alloys twinning annealing hardening pre-compression heat treatment deformation

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