Point defect processes during incubation period of void growth in austenitic stainless steels, Ti-modified 316SS

The defect structures in neutron-irradiated austenitic stainless steel, Ti-modified 316SS, were studied by using positron annihilation spectroscopy and transmission electron microscopy. By low dose irradiation of the order of 10-3 dpa, mono-vacancies and small microvoids were detected below 423 K by positron annihilation lifetime measurement. With increasing irradiation temperature, the positron lifetime was found to decrease, indicating no microvoid formation. Irradiation at doses above 4.2 dpa and temperatures above 673 K led to the formation of microvoids. These results indicated that microvoid formation below 423 K occurs even at low dose without incubation. Above 673 K, during the incubation period, irradiation damage changes the microstructure leading to vacancy clustering to form voids.