Spallation in homogeneous and gradient nano-grained high-entropy alloys

The strength and hardness can be improved by adjusting grain size in nano-grained structures. However, their behavior under extreme shock loading remains largely unexplored. This study investigates the shock wave response and spallation characteristics of homogeneous and gradient nano-grained CoCrFeMnNi high-entropy alloys (H-HEA and G-HEA) by molecular dynamics simulation. The results demonstrate that both H-HEA and G-HEA exhibit an elastic-plastic two-wave separation phenomenon, which diminishes with decreasing grain size. Notably, the spall strength of H-HEAs initially decreases and then increases as the grain size decreases, while G-HEA consistently shows superior spall strength compared to H-HEA. The findings suggest that GNG structures inherently possess better shock resistance. The spall strength is closely related to the nucleation ability of voids, which is dominated by the content of disordered structure. In nano-grained structures, voids mainly nucleate at grain boundaries, and the subsequent growth and coalescence lead to intergranular fracture. Additionally, shock loading induces various plastic mechanisms such as stacking faults, deformation twinning, and phase transformations. These findings underscore the critical role of microstructural design, especially GNG structure, in enhancing the shock mechanical properties of HEAs and contribute to the application of HEA in extreme shock environments.