Dislocation processes during the plastic deformation of γ-TiAl

Abstract

In situ straining experiments in a high-voltage electron microscope have been performed on coarse-grained γ-Ti-52at.% Al at room temperature and elevated temperatures, in addition to macroscopic compression tests. At all temperatures examined, ordinary dislocations, superdislocations of ⟨101] Burgers vectors and microtwins carry the deformation, with ordinary dislocations dominating. The processes controlling the deformation differ greatly for the temperature ranges below and above about 850 K. At low temperatures, ordinary dislocations as well as superdislocations move jerkily between positions where they are locally pinned, which can best be described by a precipitation-hardening mechanism. At high temperatures, the ⟨101] superdislocations show a shape typical of the locking-unlocking mechanisms. The ordinary dislocations are created and move in a very instantaneous event. Later, they are smoothly curved and move in a viscous way. The nonplanar arrangement of these dislocations indicates the importance of diffusion processes. The dynamic behaviour and the results of macroscopic deformation tests are explained by the formation of intrinsic atmospheres around the dislocations.