Atom Probe Tomography has been performed on as-irradiated and post-irradiation annealed surveillance weld samples from Ringhals Unit 3. The weld contains low Cu (0.07 at.%) and high Ni (1.5 at.%). A high number density (∼4 × 1023 m−3) of Ni–Mn–Si-enriched clusters was observed in the as-irradiated material. The onset of recovery was observed during the annealing for 30 min at 450 °C. Much more significant dissolution of clusters occurred during the 10 min 500 °C anneal, resulting in a reduction in mean cluster size and a halving of their volume fraction. Detailed analyses of the changes in microstructure demonstrate that the dissolution process is driven by migration of Mn atoms from the clusters. This may indicate a strong correlation between Mn and point defects. Dissolution of the clusters is shown to correlate with recovery of mechanical properties in this material.
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Styman, P. D., Hyde, J. M., Parfitt, D., Wilford, K., Burke, M. G., English, C. A., & Efsing, P. (2015). Post-irradiation annealing of Ni–Mn–Si-enriched clusters in a neutron-irradiated RPV steel weld using Atom Probe Tomography. Journal of Nuclear Materials, 459, 127-134. https://doi.org/10.1016/j.jnucmat.2015.01.027