Enhancing the fatigue resistance of high and medium entropy alloys by manufacturing-driven microstructural developments

Excellent fatigue performance is essential for broader applications of structural materials. In the present work, we report a microstructural design that improves fatigue resistance for high and medium-entropy alloys fabricated by direct energy deposition and hot-rolling processes. Specifically, we discover that the concurrent evolution of microstructures with fine-structure, including stacking faults, nano-twins and hexagonal-close-packed (HCP) structures, leads to zig-zag fracture that hinders crack propagation under cyclic loadings. These multiple characteristic microstructures improve fatigue resistance, which are attributed to the combination of low effective stacking fault energy and a high capacity for strain energy density. Anisotropic microstructural evolution is driven by the correlation between partial dislocations and the resolved shear stresses depending on the crystallographic orientation relationship. Consequently, stacking faults and nano-twins form prominently in the {111} grains under tension and in the {200} grains under compression. The current work provides an effective method to design advanced alloys for high fatigue resistance through microstructural tuning that controls the stacking fault energy combined by manufacturing processes.