Abstract
The incipient plasticity and dislocation behavior in a nanocrystalline(NC)CrCoNi medium-entropy alloy were systematically investigated in terms of pop-in events during instrumental nano-indentation tests.Quantitative statistical analysis and molecular dynamic simulations were performed to reveal the effects of grain boundaries(GBs)on initial st(a)ges of plastic deformation.Multiple pop-in events appeared dur-ing loading on the NC CrCoNi.The first pop-in that represents the initial yielding was identified to be controlled by dislocation nucleation,which is in sharp contrast to the continuous elastic-plastic transi-tion mediated by GB mechanisms in NC pure metals.This can be attributed to the sluggish kinetics of the chemically complex GBs(CCGBs)in the NC CrCoNi that hinders diffusive GB activities but facilitates dislocation nucleation.Subsequent pop-ins were also found to be closely related to the extra dragging effects imposed by the CCGBs on dislocation propagation in the NC alloy.Moreover,the extremely small grain sizes and the consequent high-volume fraction of GBs in the NC alloy severely restrict the lengths of dislocation source and the radii of dislocation loop,giving rise to a higher critical stress,smaller ac-tivation volume and lower pop-in width as compared with its coarse-grained counterpart.These results provide new insights into the onset of nano-plasticity in concentrated multi-principal element alloys.
基金项目
国家自然科学基金(51601067)
国家自然科学基金(51801184)
Zhejiang Public Welfare Technology Research Program(LGC21E010001)
吉林省科技发展计划(20160520007JH)
Program for Jilin University Science and Technology Innovative Research Team(JLUSTIRT)
Program for Jilin University Science and Technology Innovative Research Team(2017TD-09)
NETL
NSTL
维普
万方数据