PNNL

Abstract

Grain refinement is a well-known phenomenon in metals under severe plastic deformation, which could lead to excellent mechanical properties. However, there is a lack of knowledge about dynamic sub-grain boundary formation process. It has been generally known that formation of sub-grain boundary is the consequences of defects interaction, yet the nature of such defect interaction to form sub-grain boundary during plastic deformation remains obscure. In this work, we use in-situ TEM in combination with finite elemental strain analysis to reveal the sub-grain boundary formation during bending of Cu single crystal. The deformation process is featured by dislocations propagation, formation of stacking faults and deformation twins, and subsequently formation of sub-grain boundary with local lattice rotation. Finite element analysis of strain distribution indicates the stacking faults and deformation twins are all initiated from the region that corresponds to the maximum shear stress. The formation of the sub-grain boundary is through intersection between primary and secondary stacking faults/deformation twins. This work sheds light on plastic deformation induced sub-grain boundary formation and the role of crystal defects in this process.