The fundamental concepts of grain boundary engineering were reviewed. It was concluded that there were many processing routes to the production of a grain boundary engineering microstructure having improved properties. The role of twinning was indirect and twins had several functions, at various stages of grain boundary engineering, which were necessary for the development of microstructures and properties. Firstly, they retained strain, then they generated non-coherent Σ = 3 and other special boundaries, and finally they broke up the random boundary network. The connectivity of boundary types was more important than the absolute fraction of special boundaries. The so-called strain recrystallization description of grain boundary engineering was therefore really a recovery process. Thus, strain-recrystallization and strain-annealing grain boundary engineering did not involve separate mechanisms. It was noted that the CSL model exhibited ambiguities with regard to the recognition of special boundaries.

Twinning-Related Grain Boundary Engineering. V.Randle: Acta Materialia, 2004, 52[14], 4067-81