  Avalanche behaviors, characterized by power-law statistics and structural
relaxation that induces shear localization in amorphous plasticity, play an
essential role in deciding the mechanical properties of amorphous metallic
solids (i.e., metallic glasses). However, their interdependence is still not
fully understood. To investigate the influence of structural relaxation on
elementary avalanche behavior, we perform molecular-dynamics simulations for
the shear deformation test of metallic glasses using two typical metallic-glass
models comprising a less-relaxed (as-quenched) glass and a well-relaxed
(well-aged) glass exhibiting a relatively homogeneous deformation and a
shear-band-like heterogeneous deformation, respectively. The data on elementary
avalanches obtained from both glass models follow the same power-law statistics
with different maximum event sizes, and the well-relaxed glass shows shear
localization. Evaluating the spatial correlation functions of the nonaffine
squared displacements of atoms during each elementary avalanche event, we
observe that the shapes of the elementary avalanche regions in the well-relaxed
glasses tend to be anisotropic, whereas those in the less-relaxed glasses are
relatively isotropic. Furthermore, we demonstrate that a temporal clustering in
the direction of the avalanche propagation emerges, and a considerable
correlation between the anisotropy and avalanche size exists in the
well-relaxed glass model.
