Low cycle fatigue behaviors and damage mechanisms of Mo-alloyed CrCoNi medium entropy alloy

This study investigated the deformation and damage behaviors of Mo-alloyed CrCoNi medium-entropy alloys (MEAs) with fine-grained (FG) and coarse-grained (CG) microstructures under cyclic loading. At low strain amplitudes (Δε t /2 < 0.5%), the FG alloy exhibited superior fatigue properties as high-density grain boundaries inhibited localized dislocation slip and delayed crack initiation. At high strain amplitudes (Δε t /2 ≥ 0.5%), the CG alloy showed longer fatigue lives as the larger grain size facilitated deformation twinning to dissipate plastic work and retard fatigue crack growth. Based on a hysteresis energy-based fatigue life model, FG alloys excelled at low strain amplitudes due to high damage tolerance, whereas CG alloys outperformed at high amplitudes because twinning enhanced damage dispersion. The contradictory trend between damage tolerance and accumulation rate explains the performance crossover, providing a guideline for designing fatigue-resistant MEA.