Twin boundaries in ultra-fine grained Cu prepared by powder metallurgy were investigated using high-resolution transmission electron microscopy and geometric phase analysis. Specimens were analyzed both before and after mechanical deformation (compression of 40%) and emphasis placed on the study of TB defects. Twin boundaries in the as-processed specimens were mainly disoriented from the perfect Σ = 3 coincidence. They presented a faceted structure with coherent {111} and incoherent {112} facets. The latter had a 9R structure and the {111}/{112} junctions were associated with sessile dislocations of Frank type: b = a/3<111>. Shockley glissile dislocations with Burgers vector of type were also present. This microstructure was interpreted in terms of the absorption and decomposition at room temperature of lattice dislocations (60° type). After mechanical deformation, an enrichment of twins at dislocations and a decrease of step density and height was observed and quantified by statistical analysis. Deformation mechanisms of ultra-fine grained Cu were explained in terms of these results.

HRTEM Study of Defects in Twin Boundaries of Ultra-Fine Grained Copper. M.Sennour, S.Lartigue-Korinek, Y.Champion, M.J.Hÿtch: Philosophical Magazine, 2007, 87[10], 1465-86