Revealing effects of creep damage on high-temperature fatigue behavior for HfNbTiZr refractory high-entropy alloys: Experimental investigation and crystal-plasticity modelling

Refractory high-entropy alloys (RHEAs) are promising for high-temperature applications due to their exceptional mechanical properties at high temperatures. However, limited studies on their high-temperature fatigue behavior hinder further development. This study systematically investigates the low-cycle fatigue (LCF) behavior of HfNbTiZr RHEA at room temperature (25 °C) and elevated temperatures (350, 450, and 600 °C) through a combination of experimental analyses and dislocation-based damage-coupled crystal plasticity finite element (CPFE) simulations, to unveil the effects of creep damage on LCF behavior at varying temperatures. The results indicate that the LCF life dramatically decreases at an increased temperature, shifting from transgranular fatigue damage at lower temperatures (25–350 °C) to a dual damage mechanism involving both intergranular fatigue and creep damage at higher temperatures (450–600 °C). At 600 °C, creep damage notably contributes to the accumulation of geometrically necessary dislocations (GNDs), crack initiation, and propagation at grain boundaries, and thus accelerates LCF failure. Comparative CPFE simulations reveal that creep damage significantly contributes to cyclic softening and reduction in elastic modulus, which also amplifies the strain localization under the LCF loading. The contribution of creep damage to the total stored energy density (SED) representing the overall damage increases with temperatures, accounting for 11 % at 600 °C. Additionally, CPFE simulations indicate that the creep damage notably influences the magnitude of GND density localized at grain boundaries. This study provides critical insights into the fatigue damage mechanisms of RHEAs, offering valuable guidance for their application in high temperatures.