Grain boundary self-diffusion was investigated as a function of temperature and composition. The grain-boundary diffusion of 44Ti diffusion in high purity α-Ti was studied at 840 to 1120K. The results could be explained in terms of so-called normal vacancy-mediated grain-boundary diffusion, with a ratio of grain-boundary to volume diffusion activation enthalpy of 0.62. The bulk self-diffusion of Ti was essentially independent of composition in the case of Ti3Al. The grain-boundary self-diffusion of Ti exhibited a distinct compositional dependence. With increasing Al content, on the Al-rich side of α2-Ti3Al, the grain-boundary diffusivity systematically decreased. The grain-boundary diffusion data for γ-TiAl revealed essentially no compositional dependence. A comparison of the absolute values showed that the grain-boundary diffusivity of Ti in γ-TiAl was about an order of magnitude larger than in α2-Ti3Al of stoichiometric composition. It was 2 orders of magnitude larger than that in α2-Ti68Al32 at similar temperatures. The interphase boundary diffusion of 44Ti was studied in 2-phase Ti48Al52 alloy, using samples with a unidirectional lamellar α2/γ structure. The absolute values of the α2/γ interphase diffusivity were found to be very similar to the grain-boundary diffusion data for the most Al-rich α2-Ti3Al alloy. This was explained in terms of the specific atomistic structure of the α2/γ interphase boundary.

Titanium Tracer Diffusion in Grain Boundaries of α-Ti, α2-Ti3Al and γ-TiAl and in α2/γ Interphase Boundaries. C.Herzig, T.Wilger, T.Przeorski, F.Hisker, S.Divinski: Intermetallics, 2001, 9[5], 431-42