The diffusivity of 51Cr in α-Fe was determined by using radio-frequency sputtering and serial-sectioning techniques at 885 to 1174K (table 4). For α-Fe, in the paramagnetic state between the Curie temperature and the α-γ transformation temperature, the Cr diffusion coefficient exhibited a linear Arrhenius relationship; with a negligible effect of short-range magnetic spin ordering. Below the Curie temperature, the temperature dependence of the diffusion coefficient deviated from the linear Arrhenius relationship; due to magnetic spin ordering. Upon taking account of the effect of the magnetic transformation, the temperature dependence of the diffusion coefficient over the entire temperature range across the Curie temperature could be expressed by:

D (m2/s) = 0.00373 exp[-267.4(kJ/mol)(1 + 0.133s2)/RT]

where s was the ratio of the spontaneous magnetization at a given temperature to that at 0K. The factor of 0.133 was smaller than the factor (0.156) for self-diffusion in α-Fe. It was concluded that the effect of the magnetic transformation upon the diffusion of Cr in α-Fe was smaller than that upon self-diffusion. This was attributed to the negative magnetic moment of the Cr atom in the lattice of ferromagnetic Fe.

C.G.Lee, Y.Iijima, T.Hiratani, K.Hirano: Materials Transactions, 1990, 31[4], 255-61

Table 4

Diffusion of 51Cr in α-Fe

Table 5

Diffusion of Cu in Fe