Size-dependent stability of stacking fault tetrahedron in coherent twin boundary bicrystal: Comparisons among Al, Ni, Cu and Ag

Abstract

Both stacking fault tetrahedron (SFT) and nanoscale twins have been found to significantly affect the plasticity of metals. In this study, molecular dynamics simulations are performed to investigate the size-dependent stability of SFT in four face-centered cubic (FCC) metal (i.e., Al, Ni, Cu, and Ag) coherent twin boundary (CTB) bicrystals under shear. It is found that different size-dependent SFT stability stems from the competition between CTB migration and SFT dissociation at the incipient plasticity of CTB bicrystal. For SFT of any sizes in Al and smaller size SFT in Ni, SFT always keeps stable so that CTB migrates at the incipient plasticity. For SFT of any sizes in Cu and Ag, and larger size SFT in Ni, initial CTB always keeps still and SFT dissociates instead. SFT size effect transforms the deformation mechanism at the incipient plasticity from CTB migration to SFT dissociation in Ni. In Cu and Ag, it reduces a lot of the critical stress corresponding to the incipient plasticity of CTB bicrystal. Whether CTB migration or SFT dissociation occurs first will cause completely different final configurations of SFT and CTB. This study may not only shed light on revealing the SFT-CTB interaction mechanism but also provide new insight into the plasticity of irradiated FCC nanotwinned metals.