Abstract
Self-diffusion of Co60 in the bcc (α) and fcc (γ) phases of iron-cobalt alloys has been measured between 630° and 1310°C by the residual activity technique. Interesting changes in the diffusivity result from the α-γ phase change, the magnetic transitions in the α and γ phases, and the order-disorder transformation in the α phase. In both the phases, the activation energy for diffusion in the ferromagnetic state is larger than in the paramagnetic state. The diffusivity decreases discontinuously due to the α-γ transformation, and the order-disorder transformation causes a nonlinear relationship between logD and 1⁄T in the α phase.
The activation energies and frequency factors for the bcc and fcc phases vary with composition, showing minima at 25 and 75 at% Co and a maximum at about 50 at%. The effect of ferromagnetism is explained in terms of the changes in elastic properties.
