Abstract
The nickel-based Hastelloy N alloy samples were implanted with helium ions at room temperature and then annealed at 600°C (sample S2), 800°C (sample S3) and 900°C (sample S4) for 1 hour, respectively. The effects of post-irradiation isochronous annealing on defects evolution and hardening in the alloy were investigated by transmission electron microscopy (TEM) and nanoindenter. TEM characterization shows that the mean diameter and number density of helium bubbles in sample S2 keep unchanged. It is found that the increments of helium bubbles size in samples S3 and S4 are mainly caused by migration and coalescence (MC) and Ostwald ripening (OR) mechanisms, respectively. Additionally, the MC mechanism can promote the formation of dislocation loops due to matrix atoms diffusion. In sample S4, the recovery effects of defects are striking, resulting in a significant reduction in the number density of dislocation loops. The values of Vac. / He. at different regions have been calculated to explain the size variation of helium bubbles in all the samples. Moreover, nanohardness increments calculated by dispersed barrier hardening (DBH) model agree with those measured by nanoindentation.
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