Abstract
Impurity diffusivities of Mo in pure Fe in the temperature range of 710 to 1300°C and the self-diffusivities of Fe and Mo in Fe-Mo alloys in the temperature range of 1000 to 1300°C have been determined by the residual activity method using the radioisotopes, Fe59 and Mo99.
Effects of both the α-γ phase transformation and the magnetic transformation on the temperature dependence of the diffusivity of Mo in pure Fe have been observed. The results on the self-diffusion of both Fe and Mo in Fe-Mo alloys show a minimum diffusion coefficient and corresponding to this, a maximum activation energy and a frequency factor in the ε phase.
Concentration dependence of the self-diffusivities in the α solid solution and in the two-phase (α+ε) alloys were quantitatively discussed. Further, through investigating the data on the impurity diffusion of various elements in α-Fe and γ-Fe including the present result, an empirical equation was proposed to correlate the activation energy for diffusion with the atomic volume of diffusing atom and excess valence of impurity.
