Dislocation processes during the plastic deformation of gamma-TiAl

In situ straining experiments in a high-voltage electron microscope have be en performed on coarse-grained gamma-Ti-52 at.% Al at room temperature and elevated temperatures, in addition to macroscopic compression tests. At all temperatures examined, ordinary dislocations, superdislocations of [101] B urgers vectors and microtwins carry the deformation, with ordinary dislocat ions dominating. The processes controlling the deformation differ greatly f or the temperature ranges below and above about 850 K. At low temperatures, ordinary dislocations as well as superdislocations move jerkily between po sitions where they are locally pinned, which can best be described by a pre cipitation-hardening mechanism. At high temperatures, the [101] superdisloc ations show a shape typical of the locking-unlocking mechanisms. The ordina ry dislocations are created and move in a very instantaneous event. Later, they are smoothly curved and move in a viscous way. The nonplanar arrangeme nt of these dislocations indicates the importance of diffusion processes. T he dynamic behaviour and the results of macroscopic deformation tests are e xplained by the formation of intrinsic atmospheres around the dislocations.