Glide transfer across structural twin plates in TiAl involving faults and deformation nanotwins

Abstract

A lamellar TiAl-Ti₃Al alloy has been plastically deformed by compression at 600°C (5%, rate 10⁻⁴s⁻¹). From high resolution electron microscope images of a TiAl lamella (crystal 1) containing two consecutive parallel structural twin plates denoted S1 and S2, it is shown that the front end of a plastic zone propagates in crystal 1 with the generation of deformation nanotwins and faults. These defects meet the twin plates, which produces strong local elastic fields. Simulations have been used to determine, at the atomic scale, the residual elastic interactions associated with the head terminations of two defects A and B limited by the twin plate S2, identified as an extrinsic stacking fault (B) and a deformation nanotwin (A).They show that the corresponding Burgers vector contents are, respectively, 1/6[110]₁ and 1/6[33 2]₁. The glide transfer at the entrance boundary of either twin plate (crystal 2) is consistent with a 1/2[110]₂/(001)₂, slip system. By contrast on the exit boundary of the twin plate S1, the glide transfer is consistent with a 1/6[11 2]₁/(111)₁ slip system, and the emission of 1/6[112]₂, de-twinning dislocations. The strong local stress field at the exit boundary of S1 is probably at the origin of the observed 60° superpartial dislocation limiting an antiphase boundary linked to the extrinsic stacking fault.