The effect of carbon on void formation in neutron-irradiated nickel

The effect of carbon on void formation in neutron-irradiated high purity nickel was investigated using transmission electron microscopy. After irradiation to fluences ranging from 4.0 x 1018 to 2.0 x 1020n/cm2 (E > 0.1 MeV) at 500 and 7100C, voids were found in specimens containing up to 84 wppm carbon, whereas void formation was not observed in specimens with 600 wppm carbon. The present results have thus revealed a pronounced suppressing effect of interstitial carbon atoms on void formation. The quantitative analysis on void size and density indicates that the effect of carbon is mainly on void nucleation, not on void growth. A trapping mechanism, based on a relatively large divacancy-carbon atom complex binding energy of 0.86 eV, is proposed in which the dissolved carbon atoms are assumed to effectively trap at least two vacancies per carbon atom. This trapping mechanism is dynamic in nature because 'free' interstitial carbon atoms are quite mobile in the nickel lattice at and above 5000C. (author)