Competition between shear localization and tensile detwinning in twinned nanowires

Abstract

Recently, a transition of deformation mechanism from localized dislocation slip to delocalized plasticity via an anomalous tensile detwinning mechanism has been discovered in bitwinned metallic nanowires (NWs) with a single twin boundary (TB) running parallel to the NW length. However, experiments showed that the anomalous tensile detwinning in most of bitwinned NWs does not propagate through the whole NW, which limits the NWs failure strain when compared to the twinning-induced superplasticity in single-crystalline NWs. An elusive but fundamentally important question is that what factors might affect the propagation of tensile detwinning in such bitwinned NWs. In addition, can this tensile detwinning mechanism be applied to other types of twinned NWs? Here, based on in situ transmission electron microscopy testing and molecular dynamics simulations, a competition between shear localization and tensile detwinning is identified. By dividing the tensile detwinning mechanism into two steps and investigating each step separately, it is found that the quality of a single-crystalline embryo formed during step one determines the succeeding detwinning propagation (step two) and the final plastic strain. Furthermore, this anomalous tensile detwinning mechanism is extended to other metallic NWs with multiple TBs running parallel to the length direction, such as asymmetric pentatwinned NWs and NWs with multiple parallel TBs. This work highlights the important role of detwinning in large plasticity in metallic NWs with different twin structures.