Precipitates in Incoloy 800H under proton and proton + helium irradiation at 700°C

The precipitation behavior in Incoloy 800H subjected to proton irradiation and helium implantation was investigated using transmission electron microscopy (TEM) along with energy-dispersive X-ray spectroscopy (EDS). Long, needle-like TiC precipitates were observed in both the reference and irradiated samples, with their size decreasing in high dose regions. Proton irradiation led to the formation of core-shell structured TiC-Ni₃Al precipitates, where Ni and Al enrichment occurred at TiC-matrix interfaces. Subsequent helium implantation seems to further promote this phenomenon. Two types of γ' (Ni₃(Al,Ti,Si)) precipitates were identified in the proton irradiated and helium implanted sample: (i) large, irregular precipitates associated with helium bubbles and dislocations, and (ii) smaller, spherical γ' precipitates (∼6.5 nm in diameter) homogeneously present in the matrix. Dislocations and TiC-matrix interfaces, where helium bubbles preferentially nucleated at, served as primary nucleation sites for γ'. The observed phase stability suggests a balance between radiation-induced dissolution and irradiation-enhanced diffusion, with high interfacial energy sites playing a key role in promoting precipitation. These findings provide valuable insights into the microstructural evolution of Fe-Ni-Cr based alloys under irradiation.