Tracer diffusion of boron in α-Ti and γ-TiAl

Tracer diffusion of boron in pure alpha-Ti and gamma-TiAl (54 at.% A]) was measured by secondary ion mass spectroscopy using the stable B-11 isotope. The diffusion coefficients follow Arrhenius temperature dependencies with the frequency factors D-0 = 4.2 x 10(-6) and 2.48 x 10(-5) m(2) s(-1) and the activation enthalpies Q = 113 and 200 kJ mol(-1) for B diffusion in polycrystalline alpha-Ti and gamma-TiAl, respectively. Boron is a fast diffuser in both Ti and TiAl. The ratio of boron and titanium diffusivities is as large as 10(6)-10(7) in alpha-Ti and amounts to 10(3)-10(4) in gamma-TiAl. These results indicate a diffusion mechanism involving interstitial jumps. The relatively high activation enthalpy of B diffusion in gamma-TiAl is explained by the structure of the octahedral sites in the intermetallic compound. (C) 2007 Elsevier Ltd. All rights reserved.