Interface-mediated plasticity and fracture in nanoscale Cu/Nb multilayers as revealed by in situ clamped microbeam bending

Abstract

Properties of metal-metal nanolaminates have been studied for the past decade to meet the ever-increasing demand for strong and tough structural materials. Interface engineering is typically employed to prolong the material lifecycle by hindering crack propagation across the layers of nanolaminates. Various studies have been performed to understand the role of interfaces during plastic deformation in such nanolaminates. Nevertheless, detailed studies with direct observation capability on the mechanisms of deformation leading to failure are still scarce, especially in bending mode (which is the more realistic loading condition of structural materials in service). Therefore, in this study, in situ beam bending tests (inside a Scanning Electron Microscope) were performed on accumulative roll bonded (ARB) pre-notched Cu/Nb clamped beams. A large extent of notch widening (which was used as a measure for the extent of the capacity of the materials for interfacial sliding/shearing) during cross-layer fracture was observed for Cu/Nb (16 nm) ARB beams (i.e., with 16 nm individual layer thickness in both Cu and Nb layers) which were fabricated along the transverse direction (TD) of the ARB process. This may be attributed to an increase in layer strength (due to the small sizes) and interface-based localized plastic mechanisms (sliding/shearing, rotation, etc.). Upon comparison with our previous work (Cu/Nb ARB samples with large individual layer thickness, or fabricated along different directions in the ARB process), the extent of the interfacial sliding was found to be significantly large, indicating possible size effects and/or different/additional mechanisms of localized shearing/plasticity on the interfaces. These mechanisms can be further exploited for the design and development of a novel class of metallic flexible materials or conductor technologies.