The effects of lamellar boundaries upon deformation in 2-phase TiAl(γ)-Ti3Al(α2) alloys were examined. Polysynthetically twinned crystals were fatigued, at 420MPa, with the loading axis parallel to the lamellar boundaries and to the <11¯2> of γ domains. The lamellar boundaries could be classified into 13 groups, which consisted of three γ/γ true-twin, three γ/γ pseudotwin, three γ/γ 120° rotation boundaries and four γ/α2 interfaces. These could be further sub-divided into 2 groups with continuous and discontinuous geometry. Transmission electron microscopy showed that deformation modes which were unexpected, on the basis of Schmid-factor considerations, were activated in some γ domains in order to maintain the macroscopic strain continuity through the lamellar boundary. The boundary acted as an effective barrier to the transfer of deformation.

Classification of γ-γ and γ-Α2 Lamellar Boundaries on the Basis of Continuity of Strains and Slip-Twinning Planes in Fatigued TiAl Polysynthetically Twinned Crystals. T.Nakano, H.Biermann, M.Riemer, H.Mughrabi, Y.Nakai, Y.Umakoshi: Philosophical Magazine A, 2001, 81[6], 1447-71