Transition of low and high-angle grain boundaries during strain rate-induced dislocation storage and annihilation

Abstract

This work explores the characteristics of dislocation storage and annihilation behavior in heterogeneous metal welded joints under different strain rates. It forms the micro-strain gradient alternating between the strain and strain-free zones due to the annihilation of dislocations and transition of substructure in welded joints. This gradient structure keeps the strain values at a lower level by limiting the slip of geometrically necessary dislocations (GNDs) in the fine-grained region, while most of the plastic strain is accommodated in the coarse-grained region, thus promoting the storage of GNDs and low-angle grain boundaries (LAGBs). The strain rate enhances the degree of transition among GNDs, LAGBs, and high-angle grain boundaries (HAGBs) by promoting the transition from LAGBs to HAGBs in the fine-grained region, which accelerates the annihilation of GNDs. More importantly, the formation of micro-strain gradient improves the strength and strain hardening ability of welded joints. This work will provide a better understanding of the substructure transition behaviors of heterogeneous metals under different strain rates.