Fatigue crack growth behavior of a high entropy alloy

Compact-tension (CT) specimens of the equiatomic Co–Cr–Fe–Mn–Ni high-entropy (Cantor) alloy were cycled to failure and the fracture surfaces examined by scanning electron microscopy. The surface separates into a fatigue-propagation region and a final overload zone. The fatigue region is predominantly transgranular and exhibits a tortuous, step-rich morphology with short secondary cracks—features consistent with heterogeneous slip in a low-stacking-fault-energy FCC alloy and with roughness-induced deflection. Localized parallel markings compatible with striation-like features appear in select high-magnification areas, although continuous periodic striations are not uniformly resolved. Final fracture proceeds by ductile microvoid coalescence, producing a dimpled morphology with occasional particle imprints at dimple bases. No pervasive intergranular decohesion is observed. Taken together, these observations indicate that fatigue-crack advance reflects a synergy of intrinsic crack-tip plasticity and extrinsic shielding that promotes crack-path tortuosity. Crack-closure was not quantified; interpretations are strictly fractography-based.