Shear band relaxation in a deformed bulk metallic glass

TL;DR

This study investigates shear band relaxation in a deformed bulk metallic glass using radiotracer diffusion and MD simulations, revealing non-monotonous diffusion behavior and persistent heterogeneity post-deformation.

Contribution

It provides the first measurement of effective activation enthalpy of diffusion along shear bands and links microscopic heterogeneity to macroscopic relaxation phenomena.

Findings

Shear bands relax during annealing below Tg.

Diffusion along shear bands shows non-monotonous behavior.

Residual stresses persist in localized regions after shear is stopped.

Abstract

Relaxation of shear bands in a Pd40Ni40P20 bulk metallic glass was investigated by a combination of radiotracer diffusion and molecular dynamics (MD) simulations, allowing to determine for the first time the effective activation enthalpy of diffusion along shear bands in a deformed glass. The shear bands relax during annealing below the glass transition temperature and the diffusion enhancement reveals unexpectedly a non-monotonous behavior. The development of shear bands and the subsequent relaxation of stresses after switching off the shearing are characterized on microscopic to mesoscopic length scales by MD simulation subjecting the model glass to a constant strain rate. Mean-squared displacements as well as strain maps indicate that the heterogeneity, as manifested by shear bands in the systems under shear, persist after the shear is switched off. We observe a further relaxation of residual stresses that remain localized in regions where the shear band has been present before, although the system is - different from the macroscopic experiment - homogeneous with respect to the local density. These results indicate that even on a local scale one may expect strong dynamic heterogeneity in deformed glassy solids due to shear banding. The results thus suggest that plastically deformed metallic glasses present poly-amorphous systems that necessitate descriptions that are analogous to multiphase materials including the presence of heterophase interfaces.