Post-irradiation annealing of dislocation microstructure and radiation-induced segreation in proton-irradiated stainless steels

摘要

Both microstructural effects (radiation hardening) and microcompositional effects (radiation-induced segregation (RIS)) have been identified as potential contributors to irradiation-assisted stress corrosion cracking (IASCC).However,the importance of each in IASCC is unclear .In an effort to isolate their roles,post-irradiation annealing of proton-irradiated 304 L stainless steel samples has bene studied.Model simulations of post-irradiation annealing at intermediate temperatures (400-650 deg C) indicate that microstructural features such as dislocation loops are removed faster than RIS.Simulations also predict that there exist time-termperature combinations that will significantly reduce the dislocation loop population while leaving the grain boundary segregation essentially unaffected.Ultra-high purity (UHP) 304L stainless steel samples have been irradiated with 3.2 MeV protons at 360 deg C to 1.0 dpa and then annealed in-situ as thinned TEM disks in the temperature range of 500 deg C- 625 deg C for times between 20 and 60 minutes.RiS and dislocation loops were characterized before and after annealing in the same areas of each specimen.Post-irradiation anneals at 500 deg C for 45 minutes or 60 minutes resulted in no appreciable change in dislocation loop population or RIS>Annealing at 600 deg C for 20 minutes.,or 40 minutes and at 625 deg C for 40 minutes,resulted in decreasing disolocation loop densities and increasing loop size with increasing annealing time or temperature,while the amount of RIS did not change significantly fromthe pre-annealed condition.