Atomic resolution analyses on defects in nanocrystalline Cu-based alloys generated by severe plastic deformation

Abstract

Bulk nanocrystalline (NC) materials possess high volume fraction (up to 50%) of grain boundaries (GBs), which contributes significantly to their mechanical and physical properties. Nevertheless, high density of dislocations at GBs and the associated strain fields complicate the analyses on the fine GBs structures of NC materials. Here, taking NC Cu-based alloys as model systems, the atomic-scale configurations of dislocations and typical GBs triggered by severe plastic deformation are well investigated using aberration-corrected high-resolution transmission electron microscopy and geometric phase analysis. A periodic array of extended dislocations with a spacing of 2.2 nm is found to form low-angle GBs (LAGBs) in NC Cu-based alloys. The interaction between dislocations and twins play a crucial role in forming the GBs of NC. Twin boundaries (TBs) in NC Cu-based alloys can serve as barriers for trapping dislocations, which in turn tune the TBs directly evolving into LAGBs or high-angle GBs. In addition, a symmetric 6° [001] tilt LAGB is also analyzed to be composed of a/2〈100〉 edge dislocations, which are activated by the a/2〈110〉 full dislocation dissociation or simple shear deformation of {100} planes. Our study offers insights into the atomic resolution structures of dislocations and GBs in NC materials.