Straining experiments in a high-voltage electron microscope were performed in situ on coarse-grained γ-phase Ti-52at%Al, at ambient or high temperatures, together with macroscopic compression tests. At all temperatures, ordinary dislocations, super-dislocations with a <101] Burgers vector and micro-twins produced the deformation; with ordinary dislocations predominating. The processes which controlled deformation differed greatly at temperatures below and above about 850K. At low temperatures, ordinary dislocations as well as super-dislocations moved jerkily between positions where they were locally pinned. This could best be described by a precipitation-hardening mechanism. At high temperatures, the <101] super-dislocations exhibited a shape which was typical of locking/unlocking mechanisms. Ordinary dislocations were created, and moved as an instantaneous event. They were smoothly curved later, and moved in a viscous manner. The non-planar arrangement of these dislocations indicated the importance of diffusion processes. The dynamic behavior and the results of macroscopic deformation tests were explained by the formation of intrinsic atmospheres around the dislocations.

Dislocation Processes during the Plastic Deformation of γ-TiAl. D.Häussler, M.Bartsch, M.Aindow, I.P.Jones, U.Messerschmidt: Philosophical Magazine A, 1999, 79[5], 1045-71