Molecular dynamics study on the nanovoid collapse and local deformation in shocked Cu₅₀Zr₅₀ metallic glasses

The nanovoid evolution is an important part of understanding the physical and mechanical properties of metallic glasses (MGs). Here, the void-included Cu₅₀Zr₅₀ MGs under different shock intensities are investigated by the molecular dynamics simulations, focusing on the characteristics of void collapse, the evolution and correlation of clusters in the collapsed region. The results show that there are two typical mechanisms for the void collapse along the shock direction: the vertical collapse mechanism and the horizontal collapse mechanism. The vertical collapse mechanism is dominated by the hoop stress under the weak shock intensity, while the horizontal collapse mechanism is led by the principal stress along the shock direction under the strong shock intensity. In terms of shock-induced void collapse in the MGs, the plastic deformation mainly concentrates around the void and forms local shear transformation zones. There is very weak activity of the Zr-centered clusters in the shear transformation zones under the weak shock intensity, whereas the Cu-centered clusters appear a strong spatial correlation, and several of them tend to strongly aggregate. When the shock velocity exceeds 1.0 km/s, the Zr-centered clusters also begin to correlate intensely in the shear transformation zones, which corresponds to the horizontal collapse of the void. The results also show that the void defects in the Cu₅₀Zr₅₀ MGs can be almost fixed by long-term shock compression.