It was noted that computer models, for the prediction of solute segregation in alloys under irradiation, required expressions for the diffusion coefficients that appeared in the generalized Fick’s equations which were used in such models. These expressions were obtained by analyzing the atomic transport that was caused by the movement of vacancies and interstitials which were generated by irradiation. Expressions for the required 10 diffusion coefficients were determined in terms of the properties of atomic models which were appropriate for body-centered cubic transition metals such as -Fe. The results which were obtained here for body-centered cubic alloys exhibited both similarities and differences with respect to data on face-centered cubic alloys. Thus, in face-centered cubic alloys, vacancies caused solute atoms to drift up or down the gradient of vacancy concentration; depending upon the detailed local effect of the solute atoms upon the vacancy jumps. In the case of body-centered cubic alloys, the present model predicted that solute atoms always drifted up the vacancy concentration gradient. Interstitials caused the solute atoms to drift down the gradient of interstitial concentration. However, in the body-centered cubic lattice there was no analogy to the so-called caging effect which could arise in face-centered cubic lattices. Strong caging effects in face-centered cubic lattices could reduce the overall flow of interstitials to sinks, and could lead to effects such as enhanced interstitial clustering. These effects appeared to be absent from body-centered cubic lattices.

A.Barbu, A.B.Lidiard: Philosophical Magazine A, 1996, 74[3], 709-22