Constructing a heterogeneous microstructure in the CoCrFeNi-based high entropy alloy to obtain a superior strength-ductility synergy

In the present work, the CoCrFeNi-based alloy was prepared, and a heterogeneous microstructure was constructed via thermo-mechanical processing. The heterogeneous microstructure consists of fine recrystallized grains and deformed matrix, containing high-density dislocations (HDDs), stacking faults (SFs), deformation/annealing twins (DTs/ATs) and precipitates of the γ′-L12, σ and (Ti, Nb, Mo)-rich phases. The precipitation particles are very effective in strengthening the alloy. In addition, dislocation strengthening and grain boundary strengthening play important roles. In tensile deformation, planar slip of the Shockley partial dislocations is active, generating Lomer-Cottrell locks which could promote twinning or HCP martensite transforming. The tensile yield strength of the alloy can reach as high as ∼2.2 GPa with a promising uniform elongation of ∼11.0%.