The influence of oversized solute additions on radiation-induced changes and post-irradiation intergranular stress corrosion cracking behavior in high-purity 316 stainless steels

Abstract

The influence of oversized solute additions on the radiation-induced microstructure, radiation-induced segregation (RIS) at grain boundaries and post-irradiation intergranular stress corrosion cracking (IGSCC) behavior of model, high-purity 316 stainless alloys, doped with either 0.3 at.% platinum or 0.3 at.% hafnium, and proton-irradiated to 2.5 and 5 dpa at 400 °C was examined. Radiation-induced microstructure was characterized using both bright and dark field imaging techniques in transmission electron microscopy. Platinum addition was found to promote void nucleation and to increase both the loop density and the mean loop diameter relative to the base alloy at 2.5 dpa. Addition of hafnium was effective in reducing swelling at 2.5 and 5 dpa. Hafnium addition also significantly decreased the mean loop diameter relative to the base alloy. Both platinum and hafnium additions also resulted in significant suppression of RIS at grain boundaries at 2.5 dpa. At 5 dpa, the influence of hafnium addition on RIS was still beneficial but much less pronounced. Comparative constant elongation rate tensile tests performed in a simulated boiling water reactor environment at 288 °C demonstrated a beneficial effect of hafnium addition and to a lesser extent platinum addition on the post-irradiation IGSCC behavior of 316 stainless steel alloys. The 316SS alloy doped with platinum exhibited a slightly lower susceptibility to post-irradiation IGSCC than the 316SS base alloy at both 2.5 and 5 dpa. Most spectacularly, the 316SS alloy doped with hafnium was found to be not susceptible to post-irradiation IGSCC at both 2.5 and 5 dpa. The mechanisms by which oversized solute additions impact point defect behavior as well as the links between radiation-induced changes and irradiation-assisted stress corrosion cracking are discussed.