A lamellar TiAl-Ti3Al alloy was plastically deformed (5%, 0.0001/s) by compression at 600C. On the basis of high-resolution electron microscopic images of a TiAl lamella which contained 2 consecutive parallel structural twin plates, S1 and S2, it was deduced that the front of a plastic zone propagated with the generation of deformation nano-twins and faults. These defects met the twin plates, and produced strong local elastic fields. Simulations were used to determine, at the atomic scale, the residual elastic interactions that were associated with the head terminations of 2 defects, A and B, that were limited by the twin plate S2. These defects were identified as being an extrinsic stacking fault (B) and a deformation nano-twin (A). The corresponding Burgers vectors were 1/6[110] and 1/6[332], respectively. The glide transfer at the entrance boundary of either twin plate in another crystal was consistent with a ½[110]/(001) slip system. At the exit boundary of the twin plate S1, the glide transfer was consistent with a 1/6[112]/(111) slip system and with the emission of 1/6[112] de-twinning dislocations. It was suggested that a high local stress field at the exit boundary of S1 was probably the cause of an observed 60 super- partial dislocation which limited an antiphase boundary that was linked to the extrinsic stacking fault.

M.Loubradou, R.Bonnet, J.M.Pénisson: Philosophical Magazine A, 1995, 72[5], 1381-95