CONTRIBUTION OF INTERSTITIAL MIGRATION TO SEGREGATION IN CONCENTRATED ALLOYS

This paper describes a theory for the migration of dumb-bell interstitials in a concentrated alloy with an fcc lattice. For simplicity, the influence of correlations between successive jumps of the interstitials is neglected, but there is no restriction on the number of constituents in the alloy. It is found that the frequency of rotation of the interstitial dumb-bells is very important in determining the diffusion behaviour. The results of calculations show that the diffusion rate of interstitials in alloys can be significantly less than that in a pure metal, particularly when the frequency of rotation of the interstitial dumb-bells is considerably less than the frequency for migration jumps. Simple calculations of segregation to grain boundaries are also presented, and it is shown that the migration of interstitials can explain some of the experimental results in this field which were previously poorly understood.