The tracer diffusion of 44Ti and 63Ni in single crystals, at 1133 to 1307K and 1053 to 1278K respectively, was studied by means of ion-beam sputter sectioning. The diffusivities were measured parallel to, and perpendicular to, the [001] axis. The data (tables 294 and 295, figure 49) could be described by:

63Ni[001]:     D (m2/s) = 5.07 x 10-5 exp[-2.87(eV)/kT]

63Ni||[001]:     D (m2/s) = 4.34 x 10-7 exp[-2.32(eV)/kT]

44Ti[001]:     D (m2/s) = 7.66 x 10-4 exp[-3.22(eV)/kT]

44Ti||[001]:     D (m2/s) = 2.38 x 10-7 exp[-3.85(eV)/kT]

It was found that the diffusivity of 44Ti in the direction perpendicular to [001] was about an order of magnitude higher than that parallel to [001]. This anisotropy was attributed to the defect structure and the correlation factor. The anisotropy was less marked in the case of 63Ni. It was suggested that Ni atoms diffused more randomly in both sub-lattices.

T.Ikeda, H.Kadowaki, H.Nakajima: Acta Materialia, 2001, 49[17], 3475-85

Table 294

Diffusivity of 63Ni in TiAl