Atomic study on the deformation behavior of nanotwinned CoCrCuFeNi high entropy alloy during nanoscratching

Abstract

Nanotwinned high entropy alloys (HEA) offer promising applications in engineering due to their remarkable mechanical properties. However, the influence of twin boundaries (TB) on the deformation behavior and surface/subsurface damage of nanotwinned HEAs during friction and nanocutting processes is still unclear. To address this issue, molecular dynamics simulations were conducted to investigate the TB effect on the nanoscratching response of nanotwinned CoCrCuFeNi HEA (nt-HEA). The results show that the TB leads to lateral atomic movement in the upper twinning layer during nanoindentation, which hinders the slip of dislocations to the lower twinning layer. During nanoscratching, downward TB migration and upward TB migration are observed due to the lateral atomic movement in TB or in upper atomic layer of TB at different positions of the sample. In addition, the propagation of dislocations in the lower twinning layer is observed, leading to the release of shear stress in the upper twinning layer. The nt-HEA also exhibits strong anisotropy during nanoscratching, with more sessile dislocations generated for backward (along [1¯1¯2] orientation) scratching. The sessile dislocations contribute to the strengthening and dislocation hardening in the subsurface of nt-HEA. The stacking faults in the lower twinning layer are more stable for backward scratching due to the formation of stair-rod dislocations. These findings provide new insights into the TB effects on the deformation behavior of CoCrCuFeNi HEA during nanoscratching, and are of great significance for the industrial application of nanotwinned HEA.