A MODEL FOR RADIATION-INDUCED SEGREGATION IN FCC BINARY-ALLOYS

A model is presented for radiation-induced segregation (RIS) in a face -centered cubic (fee) binary alloy containing A- and B-atoms. Assuming that the interstitial in an fee crystal takes the configuration of th e [100] dumbbell, three types of interstitial dumbbells, AA-, BB- and AB-type, are considered. The present model includes the diffusion and conversion of the three types of interstitial dumbbells via an interst itialcy migration, their recombination with a vacancy, and vacancy dif fusion by position exchange with a lattice atom. The fraction of AA-, BB- and AB-type dumbbells is determined through the conversions, and t he AB-type mixed dumbbell plays an important role in the determination of the segregation direction. When a large number of mixed dumbbells moves toward the sinks, enrichment of the lower concentration element occurs, because the AB-dumbbell includes the same number of A- and B-a toms. When mixed dumbbell migration is rare, on the other hand, the lo wer concentration element can be depleted, even if the self-interstiti al dumbbell composed of that element moves more quickly. Consequently, the direction of RIS depends on the mobility of point defects as well as alloy compositions. When the RIS kinetics of a Cu-Au alloy is calc ulated with the model, good agreement is obtained with experimental re sults.