Topology of icosahedral network responsible for yielding in CuZr metallic glasses

Abstract

Metallic glasses exhibit yielding behavior under mechanical deformation. However, the underlying atomic structural basis is still elusive. Here we investigated atomic structural evolution in both average fraction of atomic clusters and their spatial distribution for CuZr metallic glasses during deformation via molecular dynamic simulation. It is found that while the icosahedral clusters in the initial structures of CuZr glassy samples exhibit unique mechanical response to deformation, compared to other types of atomic clusters, its fraction is not key to the yielding of metallic glasses. We further explored the spatial distribution of icosahedral clusters, i.e., icosahedral medium-range order by analyzing the network formed via their interpenetrating connections. It is found that the topology of the icosahedral network plays the essential roles in the yielding of CuZr metallic glasses. Within the icosahedral networks, nodes with degree k > 1 mainly determine the yield strain, which is general in CuZr metallic glasses and independent of the fraction of icosahedral clusters. Moreover, it is also found that the larger the node degree of the interpenetrated icosahedral network is, the higher the yield strain is. Therefore, the disruption of the icosahedral network corresponds to the yielding of metallic glasses. The roles of nodes with degree k = 0 and 1 in the yielding were also elucidated. In addition, the newly formed icosahedral clusters during deformation are found to have almost no impact on the yielding of metallic glasses. Our findings establish a quantitative relation between atomic structures and yielding in CuZr metallic glasses based on the perspective of structural topology, and may shed light on the deformation mechanism of amorphous solids.