How the toughness in metallic glasses depends on topological and chemical heterogeneity

To gain insight into the large toughness variability observed between metallic glasses (MGs), we examine the origin of fracture toughness through bending experiments and molecular dynamics (MD) simulations for two binary MGs: Pd₈₂ Si₁₈ and Cu₄₆ Zr₅₄ . The bending experiments show that Pd₈₂ Si₁₈ is considerably tougher than Cu₄₆ Zr₅₄ ,and the higher toughness of Pd₈₂ Si₁₈ is attributed to an ability to deform plastically in the absence of crack nucleation through cavitation. The MD simulations study the initial stages of cavitation in both materials and extract the critical factors controlling cavitation. We find that for the tougher Pd₈₂ Si₁₈ , cavitation is governed by chemical inhomogeneity in addition to topological structures. In contrast, no such chemical correlations are observed in the more brittle Cu₄₆ Zr₅₄ , where topological low coordination number polyhedra are still observed around the critical cavity. As such, chemical inhomogeneity leads to more difficult cavitation initiation in Pd₈₂ Si₁₈ than in Cu₄₆ Zr₅₄ , leading to a higher toughness. The absence of chemical separation during cavitation initiation in Cu₄₆ Zr₅₄ decreases the energy barrier for a cavitation event, leading to lower toughness.