Effects of Core-Shell Heterogeneous Grain Structure Topology on Tensile Strength of CoCrFeMnNi High-Entropy Alloy...

Heterogeneous grain structured design has emerged as an effective strategy to overcome the limitations of mechanical properties in structural materials. Core-shell heterogeneous grain structured materials exhibit a good strength-ductility synergy owing to their continuously networked grain topology. However, controlling the grain size and fraction in core-shell structures through mechanical milling and powder metallurgy remains challenging. Therefore, the effects of grain structure topology on mechanical behavior remain unclear. This study establishes a crystal plastic finite element (CPFE) model of a core-shell structure and discusses the effects of core-shell topological characteristics, i.e., core-shell fraction (S_f = 15% to 65%), the core-shell interface gradient (θ = 63° to 90°), and the coarse grain/ultrafine grain size ratio (CG/UFG = 8/2 to 8/1), on tensile strength and hetero-deformation induced (HDI) hardening. The results indicate that the tensile strength is strongly correlated with the core-shell fraction and CG/UFG size ratio. The tensile strength is enhanced with increasing core-shell fraction and CG/UFG size ratio, which can be attributed to the increased fraction of ultrafine grains and their reduced grain size. The tensile strength increases by approximately 30% when the core-shell fraction increases from 15% to 65%, and increases by approximately 12% when the CG/UFG size ratio changes from 8/2 to 8/1. However, these two parameters exhibit a negligible influence on HDI hardening. In contrast, compared to θ = 63°, the HDI hardening at θ = 90° increases by approximately 20%, thus it indicates the sharp core-shell interface gradient markedly promotes HDI hardening, thereby improving the tensile strength through an increased hardening rate. Collectively, this study provides useful information for the microstructure design of core-shell heterogeneous grain structured materials.