Grain boundary dislocations in aluminium bicrystals after high-temperature deformation

Abstract

Aluminium bicrystals containing a symmetrical [011] tilt grain boundary have been examined by thin-foil electron microscopy after high-temperature shear deformation. In all tests abundant crystal shear deformation had accompanied grain boundary shear. Grain boundary dislocations were observed and their Burgers vector was always [011]. They originated from lattice dislocations which entered the boundary and dissociated. It is deduced that the reactions: occurred. The component (R) was not visible in the electron microscope and is presumed to consist of several Bollmann dislocations with small Burgers vectors. Movement of the a/4[011] grain boundary dislocations along the boundary plane was observed. It is suggested that this took place by a process of glide and climb, and represented the mechanism of grain boundary shear. Multiplication of the grain boundary dislocations on the boundary plane and slide hardening processes are also discussed. Fine grain boundary lines were sometimes observed in both tested and untested specimens. Their presence can be related to a form of interaction, or matching of the (022) planes across the grain boundary and it is significant that this same plane matching is necessary for the existence of the a/4[011] grain boundary dislocation.