Twinning/detwinning-mediated grain growth and mechanical properties of free-standing nanotwinned Ni foils: Grain size and strain rate effects

Both twinning and its reversible process, i.e., detwinning, play important roles in crystalline plasticity, especially for nanostructured metals and alloys. Contrary to the popular belief that the nanotwinned (NT) microstructure is quite stable, in this work, we reported the twinning/detwinning-mediated grain growth (GG) and dislocation nucleation-controlled strength softening in the high stacking fault energy (SFE) NT-Ni foils with different grain sizes but nearly identical twin lamellar thickness during tension at room temperature. We further proposed two possible dislocation-boundary interaction mechanisms that cause GG via twinning/detwinning processes, and elucidated strain rate effect on the double-inverse grain size dependence of twinning/detwinning in nanostructured Ni samples. Our findings provide in-depth insights into the manipulation of internal features of metals and alloys with high SFE to achieve optimum robust performance for practical applications and fundamental understanding of the twinning/detwinning behavior of NT-materials to predict their stability and evolution of microstructures.