Atomic-scale dissecting the formation mechanism of gradient nanostructured layer on Mg alloy processed by a novel high-speed machining technique  

作　　者：Hui Fu Xiaoye Zhou Bo Wu Lei Qian Xu-Sheng Yang 

机构地区：[1]State Key Laboratory of Ultra-precision Machining Technology,Advanced Manufacturing Technology Research Centre,Department of Industrial and Systems Engineering,The Hong Kong Polytechnic University,Hung Hom,Kowloon,Hong Kong,China [2]Hong Kong Polytechnic University Shenzhen Research Institute,Shenzhen,China [3]Guangdong Province Key Laboratory of Durability for Marine Civil Engineering,School of Civil Engineering,Shenzhen University,Shenzhen 518060,China

出　　处：《Journal of Materials Science & Technology》2021年第23期227-238,共12页材料科学技术（英文版）

基　　金：financially supported by the National Natural Science Foundation of China(Nos.51701171 and 51971187);the Partner State Key Laboratories in Hong Kong from the Innovation and Technology Commission(ITC)of the Government of the Hong Kong Special Administration Region(HKASR),China;financial support from the PolyU Research Office(Project Code:1-BBXA)。

摘　　要：Severe plastic deformation(SPD)-induced gradient nanostructured(GNS)metallic materials exhibit superior mechanical performance,especially the high strength and good ductility.In this study,a novel high-speed machining SPD technique,namely single point diamond turning(SPDT),was developed to produce effectively the GNS layer on the hexagonal close-packed(HCP)structural Mg alloy.The high-resolution transmission electron microscopy observations and atomistic molecular dynamics simulations were mainly performed to atomic-scale dissect the grain refinement process and corresponding plastic deformation mechanisms of the GNS layer.It was found that the grain refinement process for the formation of the GNS Mg alloy layer consists of elongated coarse grains,lamellar fine grains with deformation-induced-tension twins and contraction twins,ultrafine grains,and nanograins with the grain size of~70 nm along the direction from the inner matrix to surface.Specifically,experiment results and atomistic simulations reveal that these deformation twins are formed by gliding twinning partial dislocations that are dissociated from the lattice dislocations piled up at grain boundaries.The corresponding deformation mechanisms were evidenced to transit from the deformation twinning to dislocation slip when the grain size was below 2.45μm.Moreover,the Hall-Petch relationship plot and the surface equivalent stress along the gradient direction estimated by finite element analysis for the SPDT process were incorporated to quantitatively elucidate the transition of defo rmation mechanisms during the grain refinement process.Our findings have implications for the development of the facile SPD technique to construct high strength-ductility heterogeneous GNS metals,especially for the HCP metals.

关 键 词：Gradient nanostructured Mg alloy High-speed machining Deformation twinning High-resolution transition electron microscopy Hall-Petch relationship 

分 类 号：TG146.22[一般工业技术—材料科学与工程]