Formation of Zigzag Deformation Twins in Aluminum Nanowires

Abstract

A theoretical model is proposed that describes the formation micromechanism of a zigzag-shaped deformation twinning structure in aluminum nanowires covered with an amorphous aluminum oxide layer. Within the framework of a two-dimensional model, this structure is formed by successive nucleation of twins in the aluminum nanolayer between the interfaces with the amorphous oxide films. In this case, the primary twin is formed at a stress concentrator near one of these interfaces, secondary twins nucleate in the stress concentration sites at the ends of the primary twin, and then this process repeats cyclically, i.e., new twins nucleate at the ends of the previous ones. Contour plots of von Mises shear stresses and elastic energy density of the primary twin are generated. Using these plots, the nucleation sites and growth directions of secondary twins are determined. According to the results of the model, the successive nucleation of deformation twins should lead to the formation of a zigzag twinning structure. It is concluded that the main reason for the formation of such a structure in aluminum nanowire is the presence of an oxide amorphous layer on its surface, which prevents the escape of the twins to the free surface of the nanowire, and as a result new stress concentration sites emerge in their locking points.