Revealing crack resistance in gradient nano-grained CoCrFeMnNi high-entropy alloys: A molecular dynamics study

Gradient nano-grained high-entropy alloys (HEAs) offer a promising route to concurrently enhance strength and toughness, yet the atomistic mechanisms governing their fracture resistance remain elusive. In this study, molecular dynamics (MD) simulations were employed to unravel the crack propagation behavior of gradient nano-grained CoCrFeMnNi HEA (G-HEA) containing either a central or surface crack. Compared with its homogeneous counterpart and pure Ni, G-HEA exhibits pronounced crack-tip passivation and ductile crack propagation, driven by dislocation nucleation and amorphous layer formation at the crack front. Notably, the gradient structure suppress central crack propagation while promoting surface crack advancement through regulation of bilateral dislocation activity. As deformation proceeds, strain-localized shear bands gradually erode the gradient structure’s toughening benefit, leading to convergence in crack growth rates between G-HEA and H-HEA. These findings demonstrate the significant role of gradient nanostructures in modulating fracture behavior and provide atomic-scale insights for toughening design in high-entropy alloys.