Diffusion in Ti–54Al–10at%Nb was investigated over a wide temperature range (tables 10 and 11) by using radiotracer techniques. Sectioning was performed by grinding or sputtering in order to measure the tracer diffusivities at high and low temperatures, respectively. Almost-linear Arrhenius dependences were found for Nb and Ti diffusion:

Nb:     D (m2/s) = 1.9 x 10-5 exp[-280(kJ/mol)/RT]

Ti:     D (m2/s) = 4.0 x 10-4 exp[-304(kJ/mol)/RT]

The Nb was a slower diffuser, compared to Ti, in the ternary alloy as well as in the binary α2-Ti3Al and γ-TiAl. Heavily alloying γ-TiAl with 10at%Nb significantly increased both the Ti and the Nb diffusivities. This was attributed to elastic distortion of the L10 structure of TiAl, induced by the over-sized Nb atoms, which decreased the activation barriers for atomic diffusion.

Niobium and Titanium Diffusion in the High Niobium-Containing Ti–54Al–10Nb Alloy. S.Divinski, F.Hisker, C.Klinkenberg, C.Herzig: Intermetallics, 2006, 14[7], 792-9

Table 11

  Diffusivity of Ti in Ti–54Al–10at%Nb