The diffusion of 95Nb in α-Fe was determined between 823 and 1163K by using a serial sputter-microsectioning technique. The diffusion coefficient of Nb was about 2 times as large as the self-diffusion coefficient in α-Fe. The temperature dependence of the diffusion coefficient (table 3) within the whole temperature range spanning the Curie temperature (1043K) could be described by:

D (m2/s) = 1.40 x 10-1 exp[-299.7{1+0.061s2}(kJ/mol)/RT]

where s was the ratio of the spontaneous magnetization at TK to that at 0K. The factor, 0.061, was smaller than the 0.156 value for self-diffusion; showing that the magnetic effect upon the diffusion of Nb in α-Fe was smaller than that upon self-diffusion. The activation energy of 299.7kJ/mol for Nb diffusion in paramagnetic Fe was much higher than the 250.6kJ/mol value for self-diffusion.

Diffusion of Niobium in α-Iron. N.Oono, H.Nitta, Y.Iijima: Materials Transactions, 2003, 44[10], 2078-83

Table 3

Diffusivity of 95Nb in α-Fe