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

Solute diffusion of Nb, Zr. Fe, Cr, and Ni was measured in the phase gamma -TiAl within a wide temperature interval. Both the SIMS method (Nb-93, Fe-5 8, and Cr-52 isotopes) and the radiotracer technique (Nb-95, Zr-95, and Fe- 59 isotopes) were applied. Linear Arrhenius dependencies were found for Nb, Zr, and Cr diffusion, whereas Fe diffusion in TiAl revealed a substantiall y curved Arrhenius dependence similarly to Ti self-diffusion in this compou nd. The observed solute diffusion behavior is interpreted in terms of the p referential 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 alpha (2)-Ti3Al, neither Fe diffusion nor Ni diffusion is extremely fast in gamma -TiAl. This feature is explained by the different m odes of forming solid solutions (substitutional or interstitial) in both co mpounds, which seems to be related to the different Ti atom arrangements ar ound the interstitial octahedral sites in both compounds. (C) 2001 Elsevier Science Ltd. All rights reserved.