In the current work,the BCC-AlCoCrFeNi bulk nanocrystalline high-entropy alloy(nc-HEA)with ultra-high hardness was formed by nanoscale diffusion-induced phase transition in a nanocomposite.First,a dual-phase Al/CoCrFeNi nanocrystalline high-entropy alloy composite(nc-HEAC)was prepared by a laser source inert gas condensation equipment(laser-IGC).The as-prepared nc-HEAC is composed of well-mixed FCC-Al and FCC-CoCrFeNi nanocrystals.Then,the heat treatment was used to trigger the interdiffusion between Al and CoCrFeNi nanocrystals and form an FCC-AlCoCrFeNi phase.With the in-crease of the annealing temperature,element diffusion intensifies,and the AlCoCrFeNi phase undergoes a phase transition from FCC to BCC structure.Finally,the BCC-AlCoCrFeNi bulk nc-HEA with high Al con-tent(up to 50 at.％)was obtained for the first time.Excitingly,the nc-HEAC(Al-40％)sample exhibits an unprecedented ultra-high hardness of 1124 HV after annealing at 500℃for 1 h.We present a systematic investigation of the relationship between the microstructure evolution and mechanical properties dur-ing annealing,and the corresponding micro-mechanisms in different annealing stages are revealed.The enhanced nanoscale thermal diffusion-induced phase transition process dominates the mechanical per-formance evolution of the nc-HEACs,which opens a new pathway for the design of high-performance nanocrystalline alloy materials.

Herbert Gleiter Institute of Nanoscience,School of Material Science and Engineering,Nanjing University of Science and Technology,Nanjing 210094,China;Institute of Nanotechnology,Karlsruhe Institute of Technology,Karlsruhe 76021,Germany;Department of Physics,City University of Hong Kong,Hong Kong,China;Center for Neutron Scattering,Shenzhen Research Institute,City University of Hong Kong,Shenzhen 518057,China

[1]Junjie Wang;Zongde Kou;Shu Fu;Shangshu Wu;Sinan Liu;Mengyang Yan;Zhiqiang Ren;Di Wang;Zesheng You;Si Lan;Horst Hahn;Xun-Li Wang;Tao Feng-.Ultrahard BCC-AlCoCrFeNi bulk nanocrystalline high-entropy alloy formed by nanoscale diffusion-induced phase transition)[J].材料科学技术（英文版）,2022(20):29-39

Ultrahard,HEACs

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