Multi-layered heterostructured CoCrFeMnNi high-entropy alloy processed using direct energy deposition and ultrasonic nanocrystalline surface modification

The advantages of heterostructured materials as structural materials include superior mechanical properties and the ability to tailor the strength-ductility combination via microstructure customization. To maximize heterostructure effects, this study combined direct energy deposition and ultrasonic nanocrystalline surface modification processes to create a CoCrFeMnNi equiatomic high-entropy alloy with multi-layered microstructures. The fabricated CoCrFeMnNi high-entropy alloy has a novel microstructure composed of multiple layers of repetitive microstructures with heterogeneity and demonstrates a remarkable synergetic strengthening effect in comparison to conventional heterogeneous materials. The outstanding mechanical properties derived from various hard and soft layer interfaces, as well as the effects of each layer and interface, were quantitatively analyzed using grain-scale digital image correlation technology. By combining the direct energy deposition and ultrasonic nanocrystalline surface modification processes, this study presents a method for fabricating a new class of heterostructured materials with multi-layered microstructure that exhibit deformation heterogeneity and grain size heterogeneity. The multi-layered microstructure with multiple heterogeneous boundaries breaks the conventional wisdom regarding heterostructured materials having only one or two heterogeneous interfaces.