Revealing the impact of sink strength, injected interstitial and grain growth on the temperature-dependent depth distribution of voids in nanocrystalline Ni

Abstract

The application of electrodeposited (ED) Ni coating on structural materials of molten salt reactors has emerged as an attractive option for improving the corrosion resistance of the base alloy. However, the radiation response of the Ni coating, especially the void swelling, is an important aspect to be considered for potential in-pile applications. The study investigates depth-dependent void swelling behavior in 20 nm grain-sized ED nanocrystalline (NC) Ni, irradiated with 1.4 MeV Ni+ ion irradiation at 350–550°C to a peak displacement damage of 18.5 dpa. The injected interstitial effect is absent at 350°C; however, it becomes prominent at 450°C and less at 550°C. This is atypical of ion irradiations in coarse-grained Ni, where the effect becomes more pronounced at lower temperatures. The occurrence of voids at all temperatures goes deeper than TRIM predictions; this effect is more significant at 350°C, surpassing any previous findings in coarse-grain systems. Depending on the irradiation temperature, various types of void distributions about grain boundaries are observed: grain boundaries with no void denudations or one-sided and double-sided denudations. Here, we demonstrate that the instability of NC grains due to the combined influence of temperature and irradiation and the high fractions of internal sinks in NC Ni are responsible for void distributions that may be unique to NC systems.