Formation of single and multiple deformation twins in nanocrystalline fcc metals

Deformation twins are often observed to meet each other to form multi-fold twins in nanostructured face-centered cubic (fcc) metals. Here we propose two types of mechanism for the nucleation and growth of four different single and multiple twins. These mechanisms provide continuous generation of twinning partials for the growth of the twins after nucleation. A relatively high stress or high strain rate is needed to activate these mechanisms, making them more prevalent in nanocrystalline materials than in their coarse-grained counterparts. Experimental observations that support the proposed mechanisms are presented.