MICROPLASTIC DEFORMATION OF CoCrFeMnNi HIGH-ENTROPY ALLOY UNDER LASER SHOCK: A MOLECULAR DYNAMICS SIMULATION

Laser shock processing (LSP) can effectively improve the fatigue life of materials, which is widely used in the aerospace field. CoCrFeMnNi high-entropy alloy is a classic high-entropy alloy system, so the studies on microstructure evolutions and shock wave responses after LSP play an important role in the application of this material in the aerospace field. The molecular dynamics method is used to simulate the shock of CoCrFeMnNi high-entropy alloy, and it is obtained that the elastoplastic two-wave separation phenomenon is related to the shock direction, showing obvious orientation-dependence. It is found that there is no two-wave separation structure when shocking along the 100 direction, and an intermediate phase will be produced in the process of plastic deformation. But, when shocking along the 110 and 111 directions, a two-wave separation structure is produced, and there are a large number of stacking faults and disordered structures in the impacted area, the high dislocation density is an important reason for the disordered structure. The phenomenon of two-wave separation is related to the number of active slip systems, the Hugoniot elastic limit and the critical impact velocity for plastic deformation when impacted along different orientations are related to the Schmid factor of the active slip systems. In addition, a gradient dislocation density structure is induced due to the shocking loading, the dislocation density first increases and then decreases along with the shock depth, and a greater dislocation density is produced when shocked in the close-packed direction. After the shock, there is residual compressive stress at the both ends of the model, the residual tensile stress is at the core of the model, and the magnitude of residual stress has obvious orientation dependence. Finally, compared with pure Ni with the same size and orientation, it is found that there are more disordered structures in CoCrFeMnNi high-entropy alloy than pure Ni during the impact process due to the lattice distortion effect.