Atomistic deformation mechanism of CoCrFeNi high-entropy alloy with the grain-size gradient microstructure induced by shaped charge acceleration

The microstructural evolution of high-entropy alloys (HEAs) during the collapse process is crucial for evaluating their suitability as shaped charge liners. Here, an experimental apparatus was developed to recover liner material at collapse stage for microstructural characterization. Result reveals a pronounced gradient grain-size in the CoCrFeNi HEA liner during collapse deformation, and this feature is expected to participate in the subsequent collapse and jet formation process. Molecular dynamics (MD) planar impact simulations were further conducted to clarify the mechanical response and microstructural evolution under different gradient configurations. Simulation results under ideal nanocrystalline conditions indicate that the gradient grain-size structure exhibits a certain tendency toward shear-stress localization. Grain refinement weakens dislocation-mediated plastic deformation in this high-entropy alloy. For the gradient nanograin-size structure, increasing the proportion of the fine-grained region and introducing pre-existing twins suppress the formation of dislocation-related defect structures to some extent, thereby weakening dislocation activity. In contrast, strengthening the grain-size gradient feature significantly enhances grain-boundary activity. Grain refinement helps promote deformation homogenization in this high-entropy alloy. For the gradient nanograin-size structure, increasing the proportion of the fine-grained region and introducing pre-existing twins reduce shear-strain fluctuations in the coarse-grained region, thereby enhancing the deformation homogenization