Si promotes nano-clusters and alpha phase separation in early-stage neutron irradiated low activation ferritic/martensitic steel

Two types of 9Cr-2W steels with one by an addition of 0.1 wt. % Si were neutron irradiated at 290 degrees C to 0.1 dpa, and studied by positron annihilation spectroscopy. The addition of Si brought about the formation of Si -containing nanoclusters and an alpha phase separation under irradiation. Isochronal annealing indicates that the nano-clusters can survive and be promoted up to 450 degrees C and recovered at 500 degrees C. Our results suggest that even a trace Si can significantly influence the microstructural evolution under irradiation. The nano-clusters/ precipitates are irradiation enhanced by the generation of interstitial clusters in the cascade process.