Interpreting room temperature deformation of Zr67Cu33 metallic glass through Voronoi cluster dynamics

The plastic deformation in metallic glasses is manifested as shear bands when subjected to room temperature loading. The amazing variation in short range order of these materials in terms of topology and chemistry, pose serious challenge to interpret the atomistic mechanisms behind nucleation and propagation of shear bands. In this work, bond energy modeling is performed on certain potential Voronoi clusters pertaining to Zr-Cu binary glass ranging from coordination number 10 to 15. AMBER force field has been chosen to optimize Voronoi cluster geometry and infer about its stability in terms of its bond energy. The modeling results corroborate that the degree of fivefold symmetry of a cluster is indeed a remarkable parameter for its stability. It was further demonstrated how the cluster chemistry complicates the bond energy landscape and why Cu centered <0 0 12 0> is the exceptionally stable cluster in this binary system. We also noted that lower coordination clusters prefer Cu as the central atom whereas higher coordination clusters prefer Zr as central atom to minimize the bond energy. This transition happens at coordination 13 cluster and is in line with the earlier reported results. In light of these results, a schematic cluster energy hierarchy map is constructed from coordination number 10 to 15 clusters. The micro indented deformation response of Zr67Cu33 metallic glass ribbon is discussed under the purview of cluster energy hierarchy diagram. The origin of cracking along the shear band contours in the micro indented ribbon is ascribed to void formation, and is hypothesized to be due to the generation of tensile and compressive stresses at atomic scale in shear band. The cluster bond energy basis for void formation has been discussed.