Self-diffusion in unidirectionally solidified Fe-50 at.% Co alloys at 833-1123 K

The self-diffusion coefficients D_Fe and D_Co of radioactive tracers ⁵⁹Fe and ⁵⁷Co, respectively, in a binary Fe-50 at.% Co alloy were experimentally determined for the disordered (α) phase with the body-centered cubic (bcc) structure and the ordered (α′) phase with the B2 structure using specimens solidified unidirectionally at solidification rates of 32, 60 and 12,000 mm/h. These specimens were electroplated with the tracers and then heat treated at a temperature range between 883 and 1123 K for various times of 1.5 × 10³-1.204 × 10⁶ s. Penetration profiles of the tracers in the heat treated specimen were measured by a serial sputter-microsectioning technique. The measurement implies that the penetration of each tracer is controlled by the volume diffusion. As to the α phase, the values of D_Fe and D _Co coincide well with those obtained by lijima and Lee using well annealed polycrystalline specimens of a binary Fe-50 at.% Co alloy. On the other hand, D _Fe and D _Co in the α′ phase are greater for the unidirectionally solidified specimen than for the well-annealed polycrystalline specimen. Such greater values of D _Fe and D _Co are attributed to the contribution of the dislocation diffusion.