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 1). 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
Table 7
Self-Diffusion and Isotope Effect in Fe
Temperature (C) | D (cm2/s) | 1-[D59/D52] |
1460 | 1.18 x 10-7 | 0.0204 |
1433 | 8.8 x 10-8 | 0.0207 |
1412 | 5.87 x 10-8 | 0.0206 |
1410 | 5.93 x 10-8 | 0.0208 |
1368 | 4.49 x 10-10 | 0.0325 |
896 | 3.32 x 10-11 | 0.0258 |
895 | 2.76 x 10-11 | 0.0286 |
Table 8
Self-Diffusion in Fe as a Function of Co Content
Temperature (C) | Co (at%) | D (cm2/s) |
1428 | 0 | 7.29 x 10-8 |
1428 | 0.77 | 7.43 x 10-8 |
1428 | 1.50 | 7.38 x 10-8 |
1428 | 2.21 | 7.30 x 10-8 |
1428 | 2.95 | 7.18 x 10-8 |
1368 | 0 | 5.24 x 10-10 |
1368 | 0.77 | 5.27 x 10-10 |
1368 | 1.50 | 5.16 x 10-10 |
895 | 0 | 3.11 x 10-11 |
895 | 0.77 | 3.06 x 10-11 |
895 | 1.50 | 3.45 x 10-11 |
895 | 2.21 | 3.10 x 10-11 |
895 | 2.95 | 2.97 x 10-11 |
Figure 1
Self-Diffusivity along Dislocations in α-Fe