The tracer diffusion of B in pure α-Ti and γ-TiAl (54at%Al) was measured via secondary ion mass spectroscopy, using the stable 11B isotope (tables 14 and 15). The diffusion coefficients obeyed an Arrhenius temperature dependence with frequency factors of D0 = 4.2 x 10−6 and 2.48 x 10−5m2/s and activation enthalpies of Q = 113 and 200kJ/mol for B diffusion in polycrystalline α-Ti and γ-TiAl, respectively. The B was a fast diffuser in both Ti and TiAl. The ratio of the B and Ti diffusivities could be as large as 106 to 107 in α-Ti, and amounted to 103 to 104 in γ-TiAl. The results indicated a diffusion mechanism involving interstitial jumps. The relatively high activation enthalpy for B diffusion in γ-TiAl was explained by the structure of the octahedral sites in the intermetallic compound.

Tracer Diffusion of Boron in α-Ti and γ-TiAl. S.V.Divinski, F.Hisker, T.Wilger, M.Friesel, C.Herzig: Intermetallics, 2008, 16[2], 148-55

Table 15

Diffusivity of B in γ-TiAl