Crack and its interaction with defects in Al coated with Cu₅₀Zr₅₀ metallic glass thin film: an MD simulation study

Molecular dynamics (MD) simulation studies are carried out to investigate the crack propagation behavior and crack-void interactions in Al coated with Cu₅₀Zr₅₀ metallic glass (MG) thin film model. The model thin film is subjected to mode I and mode II loading conditions at a temperature of 300 K and a strain rate of 10¹⁰ s^-1. The simulations are carried out in the framework of EAM (embedded atom method) potential based on the CZM (cohesive zone model). The model size is 435 Å (x-axis) × 174 Å (y-axis) × 17 Å (z-axis). Nine models are investigated containing an edge crack (length, L = 43 Å, and 118 Å) located at the interface and voids (diameter, ϕ = 10-36 Å) located in the Al region and at the interface. The results show that crack propagation occurs by dislocation emission and blunts the crack tip. The presence of void ahead of the crack tip restricts the crack propagation due to the stress field resulting in bowing out of the crack and is effective with an increase in the void size which grows normal and parallel to the loading direction. The estimated crack speeds in mode I and mode II are 366 m/s and 370 m/s during stable crack growth. Separation of the interface occurs by fracture of the ligaments between the voids. Shockley partial dislocations are found nucleating from the void surfaces; twinned regions are found between the voids. The work of separation is found to be 11.56 J/m² for mode I and 3.7 J/m² in mode II, indicating that failure occurs in mode II. Graphical abstract.