Mechanical twinning has long been recognized as an important deformation mechanism in many intermetallics including γ(TiAl)-based alloys. The generation of a twin could be triggered by dislocations at grain boundaries. The reduction of the stored strain energy in relation to a configuration without any twins could be shown by applying an established transformation criterion, considering twinning as a transformation shearing process. In addition, the application of a thermodynamic extremal principle permitted the prediction a distinct twin nucleus in good agreement with experimental observations. The concept was rather general and could be adapted to any initial eigenstress field produced by dislocations present at misfitting interfaces.

A Thermodynamic Model for the Nucleation of Mechanical Twins in TiAl. F.D.Fischer, F.Appel, H.Clemens: Acta Materialia, 2003, 51[5], 1249-60