Dynamic response mechanism and cumulative damage effect of Al_0.3CoCrFeNi high-entropy alloy under repeated impact loading

To investigate the evolution of phase structure, dislocation distribution, energy absorption capacity, and impact accumulation effect of high-entropy alloys (HEA) under shock loading, molecular dynamics simulations were employed to systematically analyze the dynamic response behavior of Al_0.3CoCrFeNi HEA plate subjected to single and secondary impact load. The results show that under the first impact, the phase structure evolution and energy absorption mode of the plastic region of Al_0.3CoCrFeNi HEA plate exhibits significant velocity dependence. As the velocity increases, the proportion of face-centered cubic structure shows a three-stage downward trend, while the disordered structure increases accordingly. Under low velocity impact (0.5－1.0 km/s), energy is mainly absorbed by dislocation network; at medium velocity impact (1.0－2.0 km/s), both dislocations and disordered atoms contribute; under high velocity impact (2.0－3.0 km/s), disordered atoms dominate energy absorption. Within the velocity range of 0.5－0.8 km/s of the rigid sphere, the dislocation line length increases linearly with the impact velocity. However, at higher impact velocities, the dislocation line length decreases due to the limitation of the plate thickness. The stress analysis shows that when the impact velocity increases, both the maximum stress and the boundary stress of the plastic zone exhibit nonlinear variations characterized by a quadratic relationship. Under the secondary impact, the Al_0.3CoCrFeNi HEA plate forms a damage zone resembling a trapezoidal shape after impact. The radius of the pit within this damage zone exhibits a quadratic relationship with the impact velocity. Additionally, the minimum affected area resulting from the secondary impact also demonstrates a quadratic relationship with the impact velocity. Regarding impact resistance, as the initial impact velocity increases, the residual velocity following the secondary impact also rises, indicating a reduction in the resistance capability of HEA. At a distance of 10 nm from the impact center, the ballistic limit velocity decreases nonlinearly with increasing initial impact velocity. However, an increase in the secondary impact velocity mitigates the effects induced by the initial impact.