Cavity-mediated cooperative shear transformation in metallic glasses

Molecular dynamic simulation was performed to study the correlation between atomic packing and shear transformation under compressive deformation in apparent elastic regime in CuZr metallic glass. The packing feature of atomic structures was characterized in terms of cavities in metallic glass. It is found that while atoms surrounded by larger cavity volumes, i.e., loosely packed regions, show very small nonaffine displacements, some atoms surrounded by very small cavities, i.e., densely packed regions, undergo very large nonaffine displacement and form cooperative shear transformations with large scale in space. The size of shear transformation zones monotonically increases with decreasing cavity volume. However, shear transformations rarely occur in either densely packed or loosely packed regions with very small probability. In addition, metallic glasses are revealed to possess characteristic cavity volumes around which atoms have more probability to undergo relatively larger nonaffine displacements. It is found that more neighboring atoms together with these central atoms experience cooperative shear transformations. These findings are general in different metallic glasses and provide a general underlying structural basis for different sizes of shear transformation zones observed in previous studies.