The grain-boundary self-diffusion coefficient, Dgb, in high-purity Fe was measured by using a serial sectioning method, and the radioactive tracer 59Fe at 523 to 703K, using type-C kinetics (table 5). Furthermore, the grain-boundary self-diffusivity, δDgb, was measured between 873 and 1173K by using type-B kinetics (table 6). Upon inserting the width of the grain boundary, δ = 0.5nm, into the Dgb obtained using type-C kinetics, the temperature dependence of δDgb linked smoothly with that obtained by using type-B kinetics over the entire temperature range across the Curie temperature. The grain-boundary self-diffusivity in Fe, obtained here, was much higher than that found previously. The activation energy (55.7kJ/mol) for grain-boundary self-diffusion in paramagnetic α-Fe was only 22% of the activation energy for volume diffusion. A factor of 1.28 in the above equation was about 8 times that of volume diffusion; showing that the influence of the magnetic transformation upon grain-boundary diffusion was much greater than that upon volume diffusion.

Grain Boundary Self-Diffusion in High Purity Iron. A.Inoue, H.Nitta, Y.Iijima: Acta Materialia, 2007, 55[17], 5910-6

Table 5

Grain-Boundary Diffusivity of 59Fe in Fe

(type-C kinetics)