Refining grains into nanoscale can significantly strengthen and harden metallic materials;however,nanograined metals generally exhibit low thermal stability,hindering their practical applications.In this work,we explo...Refining grains into nanoscale can significantly strengthen and harden metallic materials;however,nanograined metals generally exhibit low thermal stability,hindering their practical applications.In this work,we exploit the superposition of the contribution of nanotwins,low-angle grain boundaries,and microalloying to tailor superior combinations of high hardness and good thermal stability in Ni and Ni alloys.For the nanotwinned Ni having a twin thickness of∼2.9 nm and grain size of 28 nm,it exhibits a hardness over 8.0 GPa and an onset coarsening temperature of 623 K,both of which are well above those of nanograined Ni.Re/Mo microalloying can further improve the onset coarsening temperature to 773 K without comprising hardness.Our analyses reveal that high hardness is achieved via strengthen-ing offered by extremely fine nanotwins.Meanwhile,the superior thermal stability is mainly ascribed to the low driving force for grain growth induced by the low-angle columnar boundary architecture and to the additional pinning effect on the migration of twin/columnar boundaries provided by minor Re/Mo solutes.The present work not only reveals a family of nanotwinned metals possessing the combination of ultra-high hardness and high thermal stability but also provides a strategy for tailoring properties of metallic materials by pairing low-angle grain boundaries and twin boundaries.展开更多
Rejuvenation,bringing metallic glasses(MGs)to the younger and higher energy states,provides an alternative avenue to explore the interplay between the property and microstructures of MGs.In this study,the creep behavi...Rejuvenation,bringing metallic glasses(MGs)to the younger and higher energy states,provides an alternative avenue to explore the interplay between the property and microstructures of MGs.In this study,the creep behavior of the Zr_(69.5)Cu_(12)Ni_(11)Al_(7.5)MGs was experimentally examined by controlling the energy state in terms of structural rejuvenation and thermal annealing.It is found that compared to the as-cast counterpart,the annealed MG at a lower energy state exhibits a higher hardness,a smaller displacement,and a lower creep rate due to the decreased free volume and the inhibited activation of the shear transformation zone.Conversely,the rejuvenated MG at a high energy state displays lower hardness and increased free volume content,yet it demonstrates superior creep resistance compared to its as-cast counterpart,which deviates from conventional understanding.This unexpected phenomenon occurs as the initial high-content free volume annihilates during creep,and strain hardening takes precedence over strain softening as the prevailing process during creep deformation,leading to a superior creep performance in extremely rejuvenated MGs.展开更多
基金This work was supported by the National Natural Science Foundation of China(Nos.52022100,52001075,and 52101162)the Shenyang National Laboratory for Materials Science(No.E01SL102)+6 种基金J.Pan is also grateful for support from the Youth In-novation Promotion Association of the Chinese Academy of Sci-ences(No.2020194)Y.Li acknowledges financial support from the Shenyang National Laboratory for Materials Science.J.Lu gratefully acknowledges the support of the National Key R&D Program of China(No.2017YFA0204403)the Major Program of the National Natural Science Foundation of China(NSFC,No.51590892)the Hong Kong Collaborative Research Fund(CRF)Scheme(C4026-17W)Theme-Based Research Scheme(Ref.T13-402/17-N)Gen-eral Research Fund(GRF)Scheme(CityU 11247516,CityU 11209918,CityU 11216219)Shenzhen-Hong Kong Science and Technology Innovation Cooperation Zone Shenzhen Park Project(No.HZQB-KCZYB-2020030).Atom probe tomography research was conducted at the Inter-University 3D Atom Probe Tomography Unit of the City University of Hong Kong,which is supported by the CityU grant 9360161.
文摘Refining grains into nanoscale can significantly strengthen and harden metallic materials;however,nanograined metals generally exhibit low thermal stability,hindering their practical applications.In this work,we exploit the superposition of the contribution of nanotwins,low-angle grain boundaries,and microalloying to tailor superior combinations of high hardness and good thermal stability in Ni and Ni alloys.For the nanotwinned Ni having a twin thickness of∼2.9 nm and grain size of 28 nm,it exhibits a hardness over 8.0 GPa and an onset coarsening temperature of 623 K,both of which are well above those of nanograined Ni.Re/Mo microalloying can further improve the onset coarsening temperature to 773 K without comprising hardness.Our analyses reveal that high hardness is achieved via strengthen-ing offered by extremely fine nanotwins.Meanwhile,the superior thermal stability is mainly ascribed to the low driving force for grain growth induced by the low-angle columnar boundary architecture and to the additional pinning effect on the migration of twin/columnar boundaries provided by minor Re/Mo solutes.The present work not only reveals a family of nanotwinned metals possessing the combination of ultra-high hardness and high thermal stability but also provides a strategy for tailoring properties of metallic materials by pairing low-angle grain boundaries and twin boundaries.
基金the National Natural Science Foundation of China(Nos.52022100,51871217,52001075,and 51971097)J.P.is also grateful for support from the Youth Innovation Promotion Association of the Chinese Academy of Sciences(No.2020194)Y.Lin thanks the China Postdoctoral Science Foundation(No.2021M701290).
文摘Rejuvenation,bringing metallic glasses(MGs)to the younger and higher energy states,provides an alternative avenue to explore the interplay between the property and microstructures of MGs.In this study,the creep behavior of the Zr_(69.5)Cu_(12)Ni_(11)Al_(7.5)MGs was experimentally examined by controlling the energy state in terms of structural rejuvenation and thermal annealing.It is found that compared to the as-cast counterpart,the annealed MG at a lower energy state exhibits a higher hardness,a smaller displacement,and a lower creep rate due to the decreased free volume and the inhibited activation of the shear transformation zone.Conversely,the rejuvenated MG at a high energy state displays lower hardness and increased free volume content,yet it demonstrates superior creep resistance compared to its as-cast counterpart,which deviates from conventional understanding.This unexpected phenomenon occurs as the initial high-content free volume annihilates during creep,and strain hardening takes precedence over strain softening as the prevailing process during creep deformation,leading to a superior creep performance in extremely rejuvenated MGs.
