Plastic deformation of SUS304 under in situ and post-irradiation fatigue loadings

Side-notched subsize specimens of SUS304 were fatigued in the unirradiated condition, during in situ irradiation with 17 MeV protons at 300 °C and post-irradiation conditions. Nano-indentation tests were conducted on the specimens fatigued for 6, 24, 100 and 200 h in the unirradiated condition, for 24 h in the in situ irradiation condition and for 200 h in the post-irradiation condition. When comparing the distribution maps of nano-hardness for the specimens fatigued for 24 h during in situ irradiation and unirradiated conditions, less significant change of hardness was detected at the notch tip for the in situ irradiation specimen. As for the post-irradiation specimen fatigued for 200 h, the area of higher nano-hardness at the notch tip was smaller than that of the unirradiated specimen fatigued for 200 h. The mechanism of the irradiation effect on fatigue behavior is discussed in terms of the plastic deformation under in situ and post-irradiation fatigue loadings.