Effects of Ti addition and annealing on microstructure and mechanical properties of CoCrFeMnNi high-entropy alloy

High-entropy alloys (HEAs) with a face-centered cubic (FCC) structure have recently received significant attention due to their outstanding ductility and fracture toughness. In this study, the effects of Ti addition and annealing on the microstructures and mechanical properties of CoCrFeMnNi HEAs were investigated. Two CoCrFeMnNiTix (x = 0 and 0.2, named Ti-0 and Ti-0.2) HEAs were prepared by arc melting, followed by homogenization, cold rolling and annealing at 800 degrees C and 900 degrees C, respectively, for 1 h. The microstructure evolution, crystallographic texture and mechanical properties were studied. It was found that the Ti-0 alloy exhibited a single-phase FCC solid solution, while Cr-rich sigma phase and (Ni, Co)3Ti eta phase precipitated in the Ti-0.2 alloy after annealing. With the precipitation of the hard yet brittle sigma and eta phases, the yield strength and hardness of Ti-0.2 alloy increased significantly but with the sacrifice in the tensile elongation. The contributions of intrinsic strength, solid solution, grain size and precipitation strengthenings to the tensile yield strength were calculated and compared with measurements. Both grain boundary strengthening and precipitation strengthening were the main strengthening mechanisms for the Ti-doped CoCrFeMnNi HEAs.