The diffusion of Ni and Fe was measured by using radiotracers and precision grinding, while Nb concentrations were analyzed via in-depth profiling using secondary ion mass spectrometry. It was found that Ni and Fe exhibited fast-diffusion behavior, in that their diffusivities were 2 and 4 orders of magnitude, respectively, higher than that of Ti. The diffusion data could be described by:

Fe:     D (m2/s) = 1.96 x 10-3 exp[-277.2(kJ/mol)/RT]

Ni:     D (m2/s) = 1.76 x 10-5 exp[-195(kJ/mol)/RT]

The high mobility of these solutes, which had relatively small atomic radii, suggested that some type of interstitial diffusion was occurring. The Nb diffusivity was lower, by about an order of magnitude, than that for self-diffusion. The data could be described by:

Nb:     D (m2/s) = 3.15 x 10-4 exp[-338.7(kJ/mol)/RT]

It was concluded that Nb diffusion occurred substitutionally via thermal vacancies in the Ti sub-lattice.

J.Breuer, T.Wilger, M.Friesel, C.Herzig: Intermetallics, 1999, 7[3-4], 381-8