Enhanced strength-ductility synergy in a Ta-doped CoCrNi medium-entropy alloy with a dual heterogeneous structure

Abstract

The CoCrNi medium-entropy alloy (MEA) has attracted much attention owing to its promising comprehensive properties. However, the low yield strength of the CoCrNi alloy at room temperature is a major hurdle in its engineering application. In this pursuit, the present study proposed a strategy for strengthening the CoCrNi MEA by tailoring the heterogeneous grains resulting from heterogeneous precipitates regulated by thermo-mechanical processing. Specifically, a Ta-doped CoCrNi MEA ((CoCrNi)98Ta2) with a dual heterogeneous structure was designed and developed. The resulting (CoCrNi)98Ta2 alloy exhibited a high yield stress of ∼1200 MPa, an ultimate tensile stress of ∼1500 MPa, and possessed a high fracture elongation of ∼33%. The excellent mechanical properties of the (CoCrNi)98Ta2 alloy were attributed to the hetero-deformation induced (HDI) hardening, which played an important role during the deformation. The microstructural origin of the enhanced HDI stress was a result of the dynamically reinforced heterogeneous grain structure through numerous deformation twins.