Structure and failure of Fcc/Bcc heterophase boundaries in metals

The atomistic structure, thin-film stability, and mechanical failure processes at fcc/bcc heterophase boundaries are studied in the Cu-Ta model system by ab initio density functional theory (DFT) calculations and molecular dynamics (MD) simulations. For thin films, Cu is found to dewet from Ta, leaving a single stable semi-coherent monolayer of Cu on Ta. For bulk systems, the first Cu layer at the interface is found to exhibit a distinct, mixed fcc-bcc structure from the rest of the fcc Cu. This layer facilitates the transition from the bcc to the fcc crystal structures across the interface. Mechanical failure under tensile stress is found to occur above this first Cu interface layer.