Crack Propagation Behavior of Gradient Nano-Grained Cocrfemnni High-Entropy Alloy: A Molecular Dynamics Study

Abstract

Gradient nano-grained high-entropy alloys (HEAs) have demonstrated an enhanced synergy between strength and toughness. However, the underlying mechanisms responsible for mechanical performance remain unclear. In this study, molecular dynamics (MD) simulations were employed to investigate the tensile deformation behavior of gradient nano-grained CoCrFeMnNi HEA (G-HEA) containing an initial central or surface crack. The results were compared with homogeneous nano-grained CoCrFeMnNi HEA (H-HEA) and homogeneous nano-grained Ni. The findings suggest that crack propagation in CoCrFeMnNi HEA is characterized by ductile behavior and significant crack tip passivation resulting from the formation of an amorphous layer and dislocation emissions. In contrast, in Ni, the crack propagates rapidly along grain boundaries, exhibiting brittle cleavage. The gradient structure within the plastic zones at the crack tips effectively inhibits central crack propagation while promoting surface crack propagation. This discrepancy arises from the dislocation nucleation capability at the central crack tip of G-HEA compared to that of H-HEA. As the crack propagates, the inherent superior deformation coordination capability of CoCrFeMnNi HEAs dominates, diminishing the advantage of the gradient structure and causing the crack propagation rates of G-HEA and H-HEA to converge. This study provides valuable insights into the impact of gradient nanostructures on the mechanisms of crack propagation in CoCrFeMnNi HEAs.

Keywords: High-entropy alloy, gradient nano-grained, molecular dynamics, crack propagation