The diffusivity of 44Ti in the -phase was determined by using serial sectioning methods at temperatures ranging from 948 to 1174K. In the paramagnetic  phase, the Ti diffusion obeyed a linear Arrhenius relationship at temperatures ranging from the - transformation, to about 30K above the Curie temperature of 1043K. At temperatures below 1076K, the temperature dependence of the diffusion coefficient deviated from the linear Arrhenius relationship, due to magnetic spin ordering. The temperature dependence of the diffusion coefficient over the entire temperature range of the  phase could be described by:

D(m2/s) = 0.21 exp[-293.2(kJ/mol)/RT(1+0.079M2)]

where M was the magnetic long-range order parameter. The frequency factor and activation enthalpy indicated the operation of a normal vacancy diffusion mechanism. The diffusion of Ti was some 5 times more rapid than that of Fe self-diffusion. This was attributed to vacancy-solute binding, due to the larger atomic radius of Ti. A comparison with the diffusion behaviors of other transition elements in -Fe confirmed the existence of a correlation between diffusion rate and solute atomic radius.

P.Klugkist, C.Herzig: Physica Status Solidi A, 1995, 148[2], 413-21