The effect of alloying elements on the vacancy defect evolution in electron-irradiated austenitic Fe–Ni alloys studied by positron annihilation

The vacancy defect evolution under electron irradiation in austenitic Fe–34.2 wt% Ni alloys containing oversized (aluminum) and undersized (silicon) alloying elements was investigated by positron annihilation spectroscopy at temperatures between 300 and 573 K. It is found that the accumulation of vacancy defects is considerably suppressed in the silicon-doped alloy. This effect is observed at all the irradiation temperatures. The obtained results provide evidence that the silicon-doped alloy forms stable low-mobility clusters involving several Si and interstitial atoms, which are centers of the enhanced recombination of migrating vacancies. The clusters of Si-interstitial atoms also modify the annealing of vacancy defects in the Fe–Ni–Si alloy. The interaction between small vacancy agglomerates and solute Al atoms is observed in the Fe–Ni–Al alloy under irradiation at 300–423 K.