Defects analysis in low displacement damage neutron-irradiated austenitic stainless steels

Abstract

Analysis of neutron irradiation-induced defects is carried out using Transmission Electron Microscope (TEM) on three variants of austenitic stainless steels, SS 304 L(N), SS 316 L(N), and SS 316 grid plate material irradiated in the Indian Fast Breeder Test Reactor at Kalpakkam to low displacement damage levels of 1.76–6.75 dpa at an irradiation temperature of 380 °C-400 °C and dpa rate in the order of 10−7dpa/s. There is a significant variation in the faulted dislocation loop size distribution and number density as a function of irradiation dose among these stainless steels due to their different stacking fault energies which is evident from the quantified defects data presented. At ∼5.08 dpa, SS 304 L(N), SS 316 L(N) and SS 316 exhibited faulted dislocation loop number densities of 2.3 × 1022/m3, 4.8 × 1021/m3, and 1.2 × 1022/m3 with mean loop sizes of 15.5 ± 6.3 nm, 35.4 ± 13.7 nm, and 16.1 ± 5.6 nm respectively. Thus, at an identical dpa level, SS 304 L(N) and SS 316 L(N) have the highest and the lowest faulted loop number densities respectively. The general size-distribution behaviour, the increment in the loop size with enhanced size distribution as a function of dpa is observed only for SS 316 L(N). The dislocation density data previously determined using X-ray diffraction analysis is correlated to the number density of dislocation loops along with their size distribution determined using TEM analysis. Finally, the change in the yield strength due to the increment in the faulted dislocation loop number density is determined.