Abstract
Irradiations with 4 MeV Ni ions and 200–400 keV He ions were carried out on two alloys, Fe-15Cr-15Ni and Fe-15Cr-35Ni, at 675°C and doses up to 84dpa. Both dual-ion irradiation experiments and sequenced He injection-anneal-Ni irradiations were used. The dual-ion experiment showed that the two alloys exhibited large differences in microstructural development, with the low nickel alloy having significantly greater swelling. The injection-anneal-irradiation experiment was designed to test the hypothesis, suggested by our earlier work, that the lower swelling of the high nickel alloy may result from a larger critical radius/critical number of gas atoms required to achieve bias driven swelling. This experiment provided a direct measurement of these critical quantities by the induction of a bimodal cavity size distribution. The measurement gave minimum critical radii of about 5nm for the high nickel alloy and < 0·5nm for the low nickel alloy, values consistent with the hypothesized mechanism. The basis of this difference in critical quantities was further investigated. Evidence suggests that interstitial absorption at interstitial type dislocation loops is significantly more difficult in the high nickel alloy.
