  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.
