The tracer diffusion of 44Ti was investigated in monocrystalline samples, at 1133 to 1307K, by using ion-beam sputtering techniques. The tracer diffusion coefficient of 44Ti was measured parallel to, and perpendicular to, the [001] axis and was found to be anisotropic. That is, the diffusivity in the direction parallel to [001] was an order of magnitude lower than that perpendicular to [001]. The diffusion data could be described by:

D (m2/s) = 7.66 x 10-4 exp[-311(kJ/mol)/RT]

for the direction perpendicular to [001], and by:

D (m2/s) = 2.38 x 10-2 exp[-370(kJ/mol)/RT]

for the direction parallel to [001]. The anisotropy of the diffusion coefficient was explained in terms of the defect structure, and the degree of correlation of the jump-vectors of successive vacancy jumps.

T.Ikeda, H.Kadowaki, H.Nakajima, H.Inui, M.Yamaguchi, M.Koiwa: Materials Science and Engineering A, 2001, 312[1-2], 155–9