THERMALLY ACTIVATED DEFORMATION MECHANISMS IN MICRO-ALLOYED 2-PHASE TITANIUM ALUMINIDE ALLOYS

The processes controlling the dislocation mobility in micro-alloyed tw o-phase gamma-titanium aluminides have been investigated over a wide t emperature range by determining activation parameters of plastic defor mation and TEM observations. The deformation behavior of the materials is characterized by a relatively high athermal stress component due t o dislocation interactions with grain boundaries and lamellar interfac es. The glide resistance of the dislocations is controlled by several processes. At room temperature, the mobility of ordinary dislocations is determined by a combination of localized pinning and lattice fricti on. Additional glide resistance arises from nonconservative processes at jogs in screw dislocations and leads to a thermal contribution to w ork hardening. Dislocation climb processes start above 900 K and seem to initiate the transition from brittle to ductile material behavior. (C) 1997 Elsevier Science S.A.