Exploring Nanoscale Precursor Reactions in Alloy 600 in H2/N2–H2O Vapor Using In Situ Analytical Transmission Electron Microscopy
Oxidation studies were performed on Alloy 600 in situ in high-temperature H2/N2 + H2O vapor mixture at 400 °C. The initial stages of preferential intergranular oxidation (PIO), shown to be an important precursor phenomenon for primary water stress corrosion cracking, have been successfully identified using the in situ approach. The behaviour of Alloy 600 was observed in real time using the Protochips environmental cell and analysed via analytical electron microscopy (AEM). Post in situ AEM analyses were compared with previous ex situ post-exposure characterization results obtained from bulk specimens, demonstrating good agreement. The in situ results confirmed the grain boundary migration and intergranular oxide formation in solution-annealed Alloy 600. The excellent agreement between the in situ and previous studies demonstrates that this approach can be used to investigate the initial stages of PIO relevant to nuclear power systems.
KeywordsAlloy 600 Stress corrosion cracking Preferential intergranular oxidation Diffusion-induced grain boundary migration Analytical electron microscopy In situ analytical transmission electron microscopy Energy dispersive X-ray spectroscopy
MGB, GB and FS acknowledge the support of AREVA and the Engineering and Physical Sciences Research Council (EPSRC) EP/JO21172/1. SJH and EP acknowledge support of the Defence Threat Reduction Agency (HDTRA1-12-1-0013) and the EPSRC (EP/M022498/1 and EP/K016946/1). The authors acknowledge the UK Research Partnership Investment Funding that established the in situ analytical TEM capabilities, and the support from HM Government (UK) for the provision of the funds for the FEI Titan G2 80-200 200S/TEM.
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