The characteristics of deformation twinning in single crystals of this D019 compound, with an off-stoichiometric composition (36.5at%Al), were studied via trace analysis and transmission electron microscopy. Deformation twinning operated only above 1000C, when the compression axis was parallel to, and close to, the hexagonal c-axis. All of the observed deformation twins were of type-II, and the twinning elements were found to be: K1 = {¯2 12▪3}, K2 = {¯20▪1}, η1 - <¯51▪6>, η2 - <13▪2> and s = 0.346. The critical resolved shear stress for the {¯2 12▪3} twin was estimated to be about 50MPa at 1000C, and gradually decreased with increasing temperature. The possible atom movements during deformation twinning were described, and the reasons why twinning of this type occurred only under special conditions (off-stoichiometric composition, high temperature, compression axis close to c-axis) were considered in terms of the atom movements produced by deformation twinning.

Deformation Twinning in Single Crystals of a D019 Compound with an Off-Stoichiometric Composition (Ti–36.5at%Al). K.Kishida, Y.Takahama, H.Inui: Acta Materialia, 2004, 52[16], 4941-52