Grain boundary dislocation structures in symmetric [001] tilt boundaries in aluminum

Abstract

Grain boundary dislocation (GBD) structures in symmetric [001] tilt boundaries in Al bicrystals of controlled geometry have been studied using transmission electron microscopy. The intrinsic GBD structure of near-Σ1, Σ5 and Σ13 boundaries consisted of families of straight edge GBDs with Burgers vectors b=〈100〉 or ¹/₂〈110〉, ¹/₁₀〈310〉 and ¹/₂₆〈510〉, respectively. In each case the system chose GBDs with the smallest perfect Burgers vector perpendicular to the boundary, in agreement with previous computer simulations using the method of molecular statics and a pairwise pseudo-potential model. In addition, the b = 〈100〉 GBDs were straight and not serrated by dissociations into partial GBDs and patches of stacking fault as, according to earlier work, they are in gold. This result is attributed to the higher stacking fault energy of Al. Observations were also made of extrinsic GBD structures produced by the superposition of lattice dislocations on the intrinsic GBD arrays. The results were consistent with structures which could be obtained through a sequence of reactions in which each lattice dislocation dissociated into GBDs, possessing Burgers vectors corresponding to the boundary DSC lattice, which then interacted in various ways with the intrinsic array.