Dislocation Mechanisms of Deformation Band Formation in Aluminum Alloy Studied Via in Situ Micropillar Compression

Abstract

This work systematically investigated the formation mechanisms of deformation band in precipitation strengthened aluminum alloy from the perspective of orientation evolution and dislocation structures. Direct evidence was provided for the orientation evolution and grain boundary development during the formation and growth of deformation band. An experimental approach utilizing in situ micropillar compression tests was performed. Through the analysis of slip system activation, lattice orientation evolution and dislocation structures, it has been found that local bend-gliding region characterized by orientation change forms as the precursor and evolves into deformation band, both of which are perpendicular to the primary slip direction. Lattice rotation occurs inside the deformation band around the [112] axis under the activation of the primary slip system and the geometric constraint. The deformation band and the matrix are observed to be separated by a deformation induced grain boundary consisting of edge dislocation arrays, caused by the annihilation of the screw component inside the dislocation wall. The formation of the deformation band is observed to be pillar size dependent, where it was absent for pillars with diameters smaller than 1 μm. This can be attributed to the escape of dislocation from the free surface, leading to insufficient dislocation storage, which further demonstrates that the stress field caused by primary dislocation pile-up is necessary for the formation of deformation band.

Keywords: deformation band, dislocation structure, strain accommodation, size dependence, Aluminum alloy