It was noted that strain annealing could increase the twinning ( = 3) levels in commercially pure material. The use of an O-rich atmosphere, when followed by cooling and further heat treatment, significantly increased both the total number of  = 3 boundaries and the proportion of those which were coherent twins. Differences were identified between the surface and bulk recovery mechanisms. Thus, twinning was more prevalent in surface regions, whereas grain rotation dominated energy minimization in the bulk. The use of lower strain rates resulted in increased proportions of low-angle boundaries. A correlation between low-angle boundaries and incoherent twins was observed. Limited grain growth did not reduce the degree of twinning, and could even result in a higher proportion of near-coherent twins.

C.B.Thomson, V.Randle: Scripta Materialia, 1996, 35[3], 385-90