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

Tracer diffusion of boron in pure α-Ti and γ-TiAl (54 at.% Al) was measured by secondary ion mass spectroscopy using the stable 11B isotope. The diffusion coefficients follow Arrhenius temperature dependencies with the frequency factors D0 = 4.2 × 10−6 and 2.48 × 10−5 m2 s−1 and the activation enthalpies Q = 113 and 200 kJ mol−1 for B diffusion in polycrystalline α-Ti and γ-TiAl, respectively. Boron is a fast diffuser in both Ti and TiAl. The ratio of boron and titanium diffusivities is as large as 106-107 in α-Ti and amounts to 103-104 in γ-TiAl. These results indicate a diffusion mechanism involving interstitial jumps. The relatively high activation enthalpy of B diffusion in γ-TiAl is explained by the structure of the octahedral sites in the intermetallic compound.