Scott X. Mao¹, Jiangwei Wang¹; ¹University of Pittsburgh

Twinning is a fundamental deformation mode that competes against dislocation slip in crystalline solids. In metallic nanostructures, plastic deformation requires higher stresses than those needed in their bulk counterparts, resulting in the “smaller is stronger” phenomenon. Such high stresses are thought to favour twinning over dislocation slip. Deformation twinning has been well documented in face-centred cubic (FCC) nanoscale crystals. However, it remains unexplored in body-centred cubic (BCC) nanoscale crystals, especially twinning nucleation. Here, by using in situ high-resolution transmission electron microscopy, we show that how twinning is nucleated at bi-crystals grain boundary in BCC tungsten. Such deformation twinning and its nucleation is found to be pseudoelastic, manifested through reversible detwinning during unloading. Our work provides direct observations of deformation twinning and nucleation process as well as new insights into the deformation mechanism in BCC nanostructures.