Molecular dynamics simulation of spallation of metallic glasses under ultra-high strain rates

Metallic glass (MG) is often used in extreme operating conditions such as high-speed shock because of its excellent physical and mechanical properties. Spallation is a typical form of dynamic failure of materials under shock load. However, the mechanism and law of spallation in metallic glass have not been fully revealed. In this paper, the impact loading of Cu₅₀Zr₅₀ MG at different velocities was carried out by using molecular dynamics (MD) and the piston method. The simulation results of the spall process of metallic glass at an ultra-high strain rate of ∼10¹⁰ s⁻¹ were obtained. We found that a higher loading velocity will lead to a higher material strain rate, and the material will reach a higher temperature in the process of wave transmission, thus reducing the spall strength. Through the analysis of the atomic model, we can directly observe the process of nucleation, growth and coalescence of the voids and the formation of the fracture surface. We found that icosahedral clusters are greatly reduced in spallation through Voronoi analysis. We also found that a higher strain rate leads to more voids and a larger spall region, and the characteristics of the fracture surface also change from classical spall to micro-spall. The insights gained in this study can contribute to a better understanding of the spall mechanism and characteristics of MGs under an ultra-high strain rate loading.