Abstract

Gradient nano-grained (GNG) materials have shown synergetic high strength and ductility due to their unique gradient microstructure, where the grain size changes from tens of nanometers in the surface region to tens of micrometers in the core. This work develops a deformation mechanisms based constitutive model to describe the deformation behavior of GNG materials and to offer a guidance for the design of their microstructures. The established constructive model employs a modified Hall-Petch relation to describe the initial yielding. The different strain hardening behaviors of nano-grained and ultra-fine grained/coarse-grained regions in GNG materials are correlated with the different mechanisms of dislocation microstructure evolution. In addition, the mechanically driven grain growth observed in experiment is also taken into account to capture the effect of grain size evolution on strength and ductility. It is found that grain growth helps to reduce the heterogeneity of the internal stress and plastic strain fields, and thus delays failure of GNG materials. The model successfully predicts the tensile response of a GNG copper bar and captures the distinctive, inverse linear relation between strength and ductility typical of GNG materials. The model can serve as a potential tool for microstructure design of GNG materials by manipulation and optimization of the grain microstructure.

Link

https://www.nstl.gov.cn/paper_detail.html?id=91fe5b2617e72f6bf5b19c35be490a95