Effects of interface shear strength during failure of semicoherent Metal-Metal nanolaminates: An example of accumulative roll-bonded Cu/Nb

Plastic deformation mechanisms in metal metal nanolayer composites (nanolaminates) have been studied extensively during the last decade. It has been observed that, for the case of metal metal nanolaminates with a semicoherent interface, such as Cu/Nb, low interface shear strength increases the interface barrier to dislocation crossing, which improves nanolaminate plasticity. In this study, we use Cu (63 nm)/Nb(63 nm) accumulative roll-bonded nanolaminates, which have a large anisotropy of the interface shear strength between rolling and transverse directions (RD and TD, respectively), to study the effect of interface shear strength on the failure in metal metal nanolaminates with a semicoherent interface during in situ clamped beam bending. Further, finite element analysis is used to understand the observed behavior. The results show a substantial difference between the fracture behaviors along the RD and TD owing to differences in the interface shear strength and grain size. For the RD beams, the slip bands originate from the Nb layers at the notch/crack tip followed by crack propagation along these bands. For the TD beams, the crack propagation is inhibited by interface shear. We suggest that shear bands form subsequently through the beam and lead to the final beam failure. However, under the assumption of the presence of the grain boundaries near the stress concentration zone, the interface shear in the TD beams could be inhibited. In this case, the crack growth can be attributed to the formation of microcracks at grain boundaries beside the main crack. (C) 2018 Published by Elsevier Ltd on behalf of Acta Materialia Inc.