Interstitial migration in dilute FeSi and FeAu alloys

Dilute FeSi and FeAu alloys containing 50-400 at. PPM of solute have been electron-irradiated together with pure Fe, first at low temperatures ( approximately 30K) where the induced Frenkel defects are frozen, and then at higher temperatures ( approximately 150K) where the Fe self interstitials migrate freely. The recovery spectra of the radiation-induced resistivity show that both Si and Au impurities do trap migrating Fe interstitials. A rough estimate of the corresponding trapping radii is given. In the case of silicon (a slightly undersized impurity in iron), a mixed interstitial is formed which becomes mobile around 175K before dissociating. In the case of gold (an oversized impurity), detrapping takes place at 160 K, not very far above the self-interstitial free migration. The possible mechanisms for interstitial migration in iron are reviewed and discussed.