Micro-mechanisms of plastic deformation of two-phase TiAl-base alloy at room temperature

The room-temperature deformation modes and the activities of various deformation systems in two-phase TiAl-base alloys have been studied by means of TEM diffraction-contrast examination on compressively deformed structures and in-situ tensile observations. The resolts show that ordinary dislocation slipping and deformation twinning are very active in y- matrix, while the critical resolved shear stress for superdislocation slip systems is at least 3.8-4.2 times as large as that of ordinary dislocation ones. The <011] shear strain in γ-lamella can be realized by the combination of deformation twinning and ordinary dislocation slipping. Besides, a detailed analysis on deformation compatibility shows that the necessary condition for compatible deformation among polycrystalline grains cannot be satisfied only by ordinary dislocation slipping and deformation twinning. Based on the above consideration, the relationship between room-temperature ductility and grain size has been established:εf =a/(d+b)