Tracer diffusion behavior of Ga as an Al-substituting element in Ti3Al and TiAl intermetallic compounds

Tracer diffusion of Ga-69 was measured in pure alpha-Ti, alpha(2)-Ti3Al (33 at% Al), and gamma-TiAl (54 at% Al) over wide temperature intervals up to the upper limits of stability of the corresponding phases. The concentration profiles were determined by secondary ion mass spectroscopy (SIMS). The diffusion coefficients revealed a good Arrhenius behavior with the frequency factors D-0 = (2.1(-0.5)(+0.7)) x 10(-3). (6.3(-3.8)(+9.7)) x 10(-5); and (4.4(-1.3)(+1.9)) x 10(-5) m(2) s(-1) and the activation enthalpies Q = 295.5 +/- 2.3; 315 +/- 10; and 293 +/- 4 kJ mol(-1) for the Ga solute diffusion in alpha-Ti, Ti3Al and TiAl, respectively. The systematics of Ga diffusion behavior in these materials is discussed in dependence on the topology of the Ti sublattice in the compounds. The experimental data of Ga diffusion suggest that Ga behaves as an Al-substituting element in titanium aluminides. The mechanisms of diffusion of Al-substituting solutes in ordered titanium aluminides are considered. It is shown that Ga diffuses in Ti3Al most likely as anti-structure-like defects via the Ti sublattice by nearest neighbor jumps. The experimental data for the Ga diffusion in TiAl can be explained by a predominant contribution of anti-structure bridge jumps. (C) 1999 Elsevier Science Ltd. All rights reserved.