An unified viscoplastic micro-damage constitutive model for NiAlCrFeMo high-entropy alloys at elevated temperatures considering triaxiality stress

Understanding high-temperature deformation in complex refractory alloys is critical for advanced structural applications, yet a fundamental linkage between microstructural evolution and mechanical response remains elusive. In this study, tensile deformation and damage behavior of NiAlCrFeMo, a refractory high-entropy alloy (HEAs), were examined across temperatures of 1000–1100℃, strain rates of 0.001–0.1 s⁻¹ and stress triaxialities of 0.333–0.595. Combined scanning electron microscope (SEM) and electron backscattered diffraction (EBSD) and EBSD-based quantitative dislocation-density mapping demonstrate that elevated temperatures promote AlNi₃ precipitation and dynamic recrystallization, while higher strain rates increase dislocation density from 0.2 × 10¹⁴–0.5 × 10¹⁴ m⁻², jointly dictating hardening and damage initiation. A unified viscoplastic-damage constitutive model incorporating a temperature-dependent Zener-Hollomon parameter was formulated and calibrated via genetic algorithm, accurately reproducing flow-stress curves and ductile damage evolution under all tested conditions. These mechanistic insights elucidate the origins of high-temperature plasticity in complex alloys and establish a predictive framework for designing refractory HEAs with tailored performance.