Tracer solute diffusion of Nb, Zr, Cr, Fe, and Ni in γ-TiAl: effect of preferential site occupation

Solute diffusion of Nb, Zr, Fe, Cr, and Ni was measured in the phase γ-TiAl within a wide temperature interval. Both the SIMS method (93Nb, 58Fe, and 52Cr isotopes) and the radiotracer technique (95Nb, 95Zr, and 59Fe isotopes) were applied. Linear Arrhenius dependencies were found for Nb, Zr, and Cr diffusion, whereas Fe diffusion in TiAl revealed a substantially curved Arrhenius dependence similarly to Ti self-diffusion in this compound. The observed solute diffusion behavior is interpreted in terms of the preferential site occupation in the compound and by the interplay of the Ti sublattice diffusion mechanism and the intersublattice jumps of the solute atoms. Unlike in α2-Ti3Al, neither Fe diffusion nor Ni diffusion is extremely fast in γ-TiAl. This feature is explained by the different modes of forming solid solutions (substitutional or interstitial) in both compounds, which seems to be related to the different Ti atom arrangements around the interstitial octahedral sites in both compounds.