Effect of residual and injected oxygen on swelling in irradiated Fe-Ni-Cr alloys

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Abstract
Mechanisms by which oxygen affects swelling during Fe-ion irradiation are investigated in a series of Fe-15Ni-13Cr-base alloys containing minor additions of titanium, silicon and carbon. The irradiations are carried out at 948 and 1000 K to doses up to 100 dpa. Effects of both residual oxygen content and accelerator-injected oxygen are studied. It is found that pre-injected oxygen promotes cavity swelling and, in some cases, leads to a fine distribution of stable bubbles for oxygen injection levels as high as 1000 at.p.p.m. The results are interpreted in terms of the chemical activity of oxygen in forming precipitates with alloying elements, and in terms of radiation dissolution of oxygen leading to oxygen-pressurized bubbles. Accounting for the interaction with alloying elements, we conclude that oxygen exhibits a direct cavity-pressurization effect on swelling similar to that previously reported for helium. The results are analyzed in terms of the theory of the critical radius and critical number of gas atoms, together with Gibbs free energies or precipitate formation.