Evolution of the microstructure and mechanical properties of an sigma-hardened high-entropy alloy at different annealing temperatures

In this study, the evolution of the microstructure and mechanical properties of the Co 34.5 Cr 30 Ni 26.5 Al 5.4 W 3.6 (at,%) high-entropy alloy was examined. This study aimed to provide valuable information for the design and modification of the mechanical properties of precipitation-hardened high/medium entropy alloys with partially recrystallized microstructures. With regard to alloy design, Md is a valuable parameter for predicting the formation of σ-phase, and the critical value ranges from 0.902 to 0.908. Alloying elements that strongly interact with principal elements can result in sluggish recrystallization, which facilitates the formation of partially recrystallized microstructures within a wider temperature range. Except for general defects, the σ-phase can also formed on reserved type-{111} slip planes. To regulate the proportion of recrystallized and non-recrystallized grains is the most effective means of controlling strength and ductility. Large σ particles can enhance strength, and a fully recrystallized alloy with large grains has a high work-hardening rate attributable to deformation twinning. • Md criterion was proposed to predict the formation of σ phase. • The reasons for sluggish recrystallization were analyzed in detail. • Some valuable suggestions were proposed for the control of mechanical properties.