The interdiffusion coefficients in α and γ Fe-Ni alloys below their Curie temperatures were calculated, based upon the magnetic contribution to the free energy for interdiffusion. The free energy for interdiffusion due to magnetic ordering in body-centred cubic Fe-Ni alloys was positive. The calculated interdiffusion coefficients in body-centred cubic Fe-Ni alloys fitted the experimental data quite well. In face-centered cubic Fe-Ni alloys, the magnetic contribution to interdiffusion depended upon both the temperature and the composition and was abnormal for Ni compositions in the Invar region. The free energy of vacancy formation was positive and the free energy of vacancy migration was negative, due to the effect of magnetic ordering. The interdiffusion coefficient in the ferromagnetic phase was lower than that extrapolated from the paramagnetic phase for Ni compositions of 50at% and greater, and was higher than that extrapolated from the paramagnetic phase for Ni compositions of 40at% and lower.Magnetic Contribution to the Interdiffusion Coefficients in BCC (α) and FCC (γ) Fe-Ni Alloys. J.Yang, J.I.Goldstein: Metallurgical and Materials Transactions A, 2004, 35[6], 1681-90

Figure 2

Diffusivity of Trace Elements in Fe-Ni at 10kbar