Grain-size effect on dislocation source-limited hardening and ductilization in bulk pure Ni  

作　　者：Kai Hu Jun Yi Bo Huang Gang Wang 

机构地区：[1]Institute of Materials, School of Materials Science and Engineering, Shanghai University, Shanghai 200444, China

出　　处：《Journal of Materials Science & Technology》2023年第23期9-21,共13页材料科学技术（英文版）

基　　金：financially supported by the National Natural Science Foundation of China(Nos.51827801 and 52171160);the National Key Research Development Program of China(No.2016YFB0700203).

摘　　要：Dislocation source-limited hardening and ductilization is an effective strategy to obtain superior strength-ductility synergy in some engineering structural metals. Recent works demonstrated that the synergy could be enhanced by grain-size reduction. However, the mechanism of grain-size dependence is still a mystery. In this work, bulk pure Ni produced by electrodeposition and subsequent annealing, with grain sizes ranging from ∼20 nm to ∼20 µm, were methodically investigated to unravel the mechanism of the grain-size effect on dislocation source-limited hardening and ductilization. The high-density nano-twinning in the as-electrodeposited nanograined specimens exhibited better thermodynamic stability than the peers with random high-angle grain boundaries, leading to fine recrystallized grains with low-density dislocations. The low dislocation density enabled extra hardening beyond grain boundary strengthening via yield-point behavior with grain sizes ranging from ∼110 nm to ∼10 µm and extra ductilization over ∼500 nm. This work demonstrated that the prerequisite for dislocation source-limited hardening was that the dislocation density of the specimen should be lower than the size-dependent critical value of ((1.1 × 107 /d ) m^(–2), d is the grain size in unit of the meter) where a transition from forest-dominated hardening to dislocation source-limited hardening could occur. On the other hand, dislocation source-limited ductilization only worked when the grain size was comparable to/larger than the theoretical dislocation mean slip distance. Dislocation source-limited ductilization resulted from more room in grains for accumulation of dislocations and deformation nano-stacking faults enabling the higher work hardening rate. This work offered an altogether new avenue to obtain stronger and more ductile metallic materials through utilizing grain-size dependent dislocation source-limited hardening and ductilization.

关 键 词：Dislocation source-limited hardening Dislocation source-limited ductilization Grain size Yield point Hall-Petch slope 

分 类 号：TG146.22[一般工业技术—材料科学与工程]