The self-diffusion of Fe was investigated by using the radiotracer technique and the isotope, 59Fe. Most of the measurements were performed in the B2-structure regions of the phase diagram, plus some in the A2-structure region and a few in the D03-structure region. There were 2 ordering transitions in Fe3Al; between A2 and B2, and between B2 and D03. Both of them led to an increase in the activation enthalpy for diffusion in the phase having the higher degree of order. With increasing Al content, the activation enthalpy for diffusion increased, even though the melting point decreased significantly. The data (table 40, figure 12) could be described by:

59Fe in Fe74.5Al25.5 (A2):     D (m2/s) = 8.1 x 10-5 exp[-2.26(eV)/kT]

59Fe in Fe74.5Al25.5 (B2):     D (m2/s) = 3.8 x 10-4 exp[-2.40(eV)/kT]

59Fe in Fe74.5Al25.5 (D03):     D (m2/s) = 3.3 x 10-3 exp[-2.88(eV)/kT]

The results were explained in terms of information on the defect structures, as well as on the basis of theoretical results arising from ab initio calculations of defect properties.

M.Eggersmann, H.Mehrer: Philosophical Magazine A, 2000, 80[5], 1219-44

Table 37

Diffusivity of 114mIn in Fe2Al

Figure 10

Diffusivity of 114mIn in Fe67Al33