Self-diffusion along dislocations in ultra-high purity Fe containing 0.5 to 1.2ppm[wt]C, 0.1 to 1.0ppm[wt]N and 1.8 to 4.0ppm[wt]O was studied by using the radioactive tracer method and sputter micro-sectioning. Below 700K, the self-diffusion coefficient along dislocations was deduced directly from the Harrison type-C kinetics whereas, above 800K, it was governed by type-B kinetics; assuming that the effective radius of a dislocation pipe was 5 x 10-10m. The temperature dependence of the self-diffusion coefficient along dislocations did not exhibit a linear Arrhenius relationship (figure 8). Below 900K, the Arrhenius plot had a slight downward curvature. However, above 900K the self-diffusion coefficient along dislocations increased markedly with increasing temperature. The value at 900K was 10-14m2/s, while it was equal to 10-10m2/s at the Curie temperature (1043K). It appeared that a steep increase in the self-diffusion coefficient along dislocations, near to the Curie temperature, was related to the magnetic transformation in ultra-high purity Fe.

Y.Shima, Y.Ishikawa, H.Nitta, Y.Yamazaki, K.Mimura, M.Isshiki, Y.Iijima: Materials Transactions, 2002, 43[2], 173-7

Figure 8

Self-Diffusivity along Dislocations in α-Fe