Defect structure development in electron-irradiated Cu-based Si, Ge and Sn binary alloys

Systematic experiments of 1 MeV electron irradiation were made on Cu-based binary alloys above 300 K using a high-voltage electron microscope in order to study the effects of solute atoms on defect structure development. The solute elements examined were Si (+5.08%), Ge (+27.77%) and Sn (+83.40%), the volume size factors of which are given in parentheses; the amounts of these were 0.05, 0.3 and 2 at.% respectively. Interstitial-type dislocation loops and stacking-fault tetrahedra (SFTs) were formed in pure Cu and all the alloys. In pure Cu, the temperature dependence of the loop number density had a ‘down peak’ (i.e. loops hardly formed) around 373 K; below this temperature the majority of the loops shrank and disappeared during irradiation, while all the loops grew larger above it; and SFTs were unstable and repeated the formation and disappearance. In the alloys, the loop number density decreased monotonically with increasing temperature (no down peak was observed); loop formation was greatly enhanced except for complete suppression above certain temperatures in Cu-Ge and Cu-Sn alloys; and stable SFTs formed up to higher temperatures. The mechanisms for these effects were proposed, taking into account the trapping of point defects by solute atoms, the radiation-induced segregation of solute elements, and the bias effect on point-defect absorption at defect clusters owing to the segregated solute elements.