A stochastic study of the deformation and failure strain of Au bi-crystalline nanowires with a longitudinal twin boundary

Abstract

Molecular dynamics (MD) simulations have been performed to understand the deformation mechanisms and ductility (failure strain) dependence on nanowire cross-sectional size for Au bi-crystalline nanowires with a longitudinal twin boundary (LTB). Different cross-sectional aspect ratios and volume ratios of grain sizes have been constructed in the MD simulations and tensile loaded. The simulation results indicate that all nanowires exhibit a similar elastic regime till peak yield stress and yielding occurs through nucleation of 1/6<112> Shockley partial dislocations from nanowire edges. Once interacting with the LTB, there are different paths of plasticity, mainly leading to two types of mechanisms: detwinning of the LTB with reorientation of the crystal and dislocation slip. For a given shape of nanowire, we found that the competition between these two operating mechanisms is stochastic and results in a distribution of detwinned volume fractions and strain to failures. Based on the simulation results we found that the average extent of detwinning is in correlation with the volume ratio of the grains. Also, it is in a linear correlation with the average strain to failure, which suggests that the LTB affects the ductility of the nanowire. We concluded from the results that the more symmetric are the grains that composes the nanowires, the smaller is the ductility.