Stacking Faults and Interfaces Dominated Mechanical Behaviors of Cobalt and Copper/Cobalt Multilayers

Metallic materials with nanotwins have been extensively studied for the past twenty years due to their excellent mechanical properties including high strength, great ductility and good thermal stability. Twin boundaries (TBs) can inhibit dislocation migration to increase strength and renucleate new dislocations to accommodate plasticity. However, the roles of stacking faults (SFs), another important planar defect, on the deformation mechanisms in face-centered cubic (FCC) and hexagonal close-packed (HCP) metals are less well understood. The focus of this research is to identify the effect of SFs on deformation mechanisms in FCC and HCP Co thin films and investigate the collaborated strengthening effect between SFs, TBs and layer interfaces in Cu/Co multilayer systems. We utilized in situ micropillar compression tests to investigate the mechanical behaviors of FCC Co with inclined SFs, HCP Co with parallel SFs and Cu/Co multilayers with defect networks, which consisting of SFs, TBs and layer interfaces. Post deformation transmission electron microscopy analyses and molecular dynamic simulations revealed that SFs can strengthen the materials by impeding partial dislocation migration and accommodate plastic deformation by defaulting process and/or intriguing phase transformation. Furthermore, the interplay between TBs, SFs and layer interfaces provides high strength and good deformability in Cu/Co nanolaminates. This research shows an in-depth investigation on deformation mechanisms of nanostructured metals with high-density SFs and provides a new perspective for the design of metallic materials with high strength and great ductility.