SELF-DIFFUSION IN ALPHA-IRON - THE INFLUENCE OF DISLOCATIONS AND THE EFFECT OF THE MAGNETIC PHASE-TRANSITION

Self-diffusion in dislocated α-iron single crystals has been studied with the radioactive tracer 59Fe in the temperature range 754-1163 K. Serial sectioning was performed either by microtome cutting or by sputtering. Based on systematic studies of diffusion along dislocations in the same material by the present authors [in DIMETA 88-Diffusion in Metals and Alloys (edited by F. J. Kedves and D. L. Beke). Defect and Diffusion Forum 66-69, 591 (1989)] lattice diffusion coefficients have been selected by considering the influence of dislocations on the apparent diffusivities measured in dislocated crystals. The temperature dependence of the lattice self-diffusion coefficient shows a deviation from the Arrhenius behaviour due to the magnetic order-disorder transition. The general relations and several semi-empirical models which describe this magnetic diffusion anomaly are discussed. From fits of the respective models to a set of lattice diffusion coefficients activation parameters for self-diffusion in the ferromagnetic state (Df0 and Qf) and in the completely disordered paramagnetic state (Dp0 and Qp) are obtained: Df0 = 6.8-27.7 · 10-4 m2 s-1, Qf = 2.95-3.10 eV, Dp0 = 6.8-12.3 · 10-4 m2 s-1, and Qp = 2.57-2.68 eV. Independent of the details of these models the parameters fall within fairly narrow limits. © 1990.