Overcoming intermediate temperature brittleness in L12-strengthened NiCoCr-based high-entropy alloys via phase engineering strategy

Abstract

High-entropy alloys (HEAs) have garnered significant attention due to their exceptional high-temperature mechanical properties. However, L1₂-strengthened HEAs commonly suffer from intermediate temperature brittleness (ITB) at 700~800 ℃, severely limiting their engineering applications. This study proposes an innovative phase engineering strategy that successfully eliminates ITB by regulating the morphology and distribution of topologically close-packed (TCP) phases through thermomechanical processing. The designed processing route enables chain-like precipitation of nanoscale TCP phases that pin grain boundaries while preserving nano-sized L1₂ precipitates for matrix strengthening. Compared to the as-cast HEA, the thermomechanically processed (RAA) HEA demonstrates significantly enhanced mechanical properties at 750 ℃, with YS increasing from 716 MPa to 863 MPa and elongation improving from 2.8% to 13.1%. Notably, the elongation of RAA HEA increases from 5% to 23.7% with negligible strength loss at 800 ℃. Microstructural analysis reveals that chain-like TCP phases effectively suppress intergranular crack propagation, while dynamic recrystallization mitigates stress concentration, synergistically enhancing intermediate-temperature ductility. Additionally, deformation mechanism analysis reveals that low stacking fault energy promotes the formation of stacking faults, Lomer-Cottrell locks, and deformation twins, which maintain high-temperature strength via the dynamic Hall-Petch effect. This study proposes a counterintuitive approach that utilizes traditionally detrimental TCP phases to improve the ITB of HEAs, offering a different perspective for solving ITB through interface phase engineering strategies.