Enhanced fatigue resistance of a face-centered-cubic single-phase Al0.3CoCrFeNi high-entropy alloy through planar deformation characteristic

Abstract

High-entropy alloys (HEAs) represent a new class of materials with excellent mechanical properties. However, more studies on the fatigue behavior of HEAs are urgently required before they can be used in engineering applications. Here, we report the four-point-bending fatigue properties of a face-centered-cubic (fcc) single-phase Al0.3CoCrFeNi HEA under a stress ratio of 0.1 and testing frequency of 40 Hz, as well as the corresponding fatigue mechanisms based on scanning electron microscopy and transmission electron microscopy images. This HEA exhibited a fatigue endurance limit of ∼248 MPa and fatigue ratio of ∼0.3, exceeding those of other fcc single-phase HEAs when compared using an identical stress ratio of −1. Good fatigue properties are attributed to the formation of planar dislocations, stacking faults, and deformation twins. Fatigue cracks were found to form at the slip bands, grain boundaries, and twin boundaries simultaneously under high stress levels; however, twin-boundary cracks vanished under low stress levels. The interaction of planar dislocations with grain boundaries and twin boundaries is the reason for the occurrence of their cracking behaviors based on microstructural observation. In addition, fatigue cracks propagated in a deflected manner, even forming a zig-zag path locally, which is beneficial for fatigue resistance. The present findings offer a viable path for the design of HEAs with improved fatigue properties through the enhancement of their planar deformation characteristics.