Outside-in disintegration of medium-range order in nano metallic glasses during torsion deformation revealed by molecular dynamics simulations

Medium-range order (MRO) is a substantial structure unit in understanding the structural characteristics, properties, and yield mechanism of amorphous solids. In this work, the evolution of MRO structures in nano metallic glasses under torsion deformation was studied by using molecular dynamics simulations. Upon torsion deformation, an interesting outside-in disintegration of MROs was detected, with most of the reduced icosahedral clusters in MRO structures transforming into other types of clusters while few of them become disconnected and turn into isolated icosahedral clusters. In addition, the proportion of face or volume-sharing icosahedra decreases, while the proportion of vertex or edge-sharing icosahedra increases. Specially, the average number of nearest neighboring icosahedra of <0,0,12,0> clusters also decreases. It was revealed that the significantly heterogeneous distribution of local shear stress was responsible for the outside-in disintegration of MROs, with a stress threshold for degradation of about 1.9 GPa.