Enhancing fatigue resistance of high-entropy alloy by designing a hierarchically heterogeneous microstructure

Fatigue property is an important index for novel high-entropy alloys (HEAs) before their engineering applications. Here we engineer a Al_0·3CoCrFeNi HEA with hierarchically heterogeneous microstructure by cold rolling and annealing treatment, which includes heterogeneous grains, annealing and deformation twins, residual dislocations and B2 precipitates with different morphologies, sizes and distributions. Stress-life (S–N) tests and characterization techniques including scanning electron microscope (SEM) and transmission electron microscope (TEM) were carried out to investigate fatigue properties as well as corresponding mechanisms. It is found that this HEA possesses good strength-ductility combination (i.e., yield strength of ∼870 MPa, ultimate tensile strength of ∼1060 MPa and ductility of ∼26 %) and fatigue resistance with fatigue ratio of ∼0.46 under stress ratio of −1. This fatigue ratio exceeds those of most reported HEAs. High strength renders the fatigue deformation mainly occurs in deformation twin regions decorated with B2 precipitates. Surface damage morphologies indicate that fatigue cracks initiate from persistent slip band-like shear bands. In addition, microstructural hierarchy results in the deflected fatigue crack propagation path, which is beneficial for the enhancement of fatigue resistance. Present results offer the guidance on future design for high fatigue-resistant HEAs by manipulating heterogeneous microstructure.