Effects of systematic modification with oversized elements on void formation in 316L austenitic stainless steel under electron irradiation

Solution annealed type 316L austenitic stainless steels modified with IV or V group elements were electron irradiated up to a dose of 10.8 dpa at temperature of 623 to 843 K in an HVEM. X-ray diffraction analysis was also performed to determine the quantitative size factors of the additional elements in the 316L steel. All the additives are shown to be oversized atoms with the size factors in the order Hf>Zr>Ta>Nb>Ti>V. Each addition retards void swelling through a prolongation of the incubation period for void nucleation and a suppression of the void growth, and decreases the peak swelling and shifts it to lower temperature. The larger the size factor is, the more emphasized those tendencies are. The size, number density and resultant swelling of voids clearly shows a systematic dependence on the size factor. The increase in the apparent vacancy migration energy of the steel due to the presence of the additives and the interaction of vacancies with them are confirmed in terms of the interstitial loop growth. The above findings indicate that the enhancement of the vacancy-interstitial recombination and reduction of the vacancy mobility are attained through vacancy trapping at the oversized additional atoms, and furthermore, the atoms act as nucleation sites for voids. (author) 81 refs