Achieving strength and ductility synergy in (CoCrFeNi)₉₄Ti₂Al₄ high entropy alloy with multi-scale heterogeneous microstructure

The CoCrFeNi-series high entropy alloys (HEAs) with face-centered cubic (FCC) structure generally exhibit exceptional tensile ductility and fracture toughness, but the insufficient strength limits their practical engineering application. In this study, the (CoCrFeNi)₉₄Ti₂Al₄ (at. %) HEA was prepared by the liquid-nitrogen rolling, followed by partial recrystallization and aging heat treatments to obtain the multi-scale heterogeneous microstructure consisting of heterogeneous grain size, precipitates, and grain defects. By constructing the heterogeneous microstructure, (CoCrFeNi)₉₄Ti₂Al₄ HEA exhibits the yield and ultimate tensile strength of ∼1 and 1.2 GPa, respectively, accompanied by a uniform elongation of ∼21 %. The exceptional strength and ductility synergy can be attributed to the hetero-deformation induced (HDI) strengthening and hardening effects, as evidenced by the microstructural observation and load-unload-reload (LUR) tensile tests.