Alloy 600 GB observed in situ TEM after 3 h at 320 °C in ~1 bar pure N2
Image courtesy of Ultramicroscopy

Abstract

In situ analytical transmission electron microscopy (TEM) can provide a unique perspective on dynamic reactions in a variety of environments, including liquids and gases. In this study, in situ analytical TEM techniques have been applied to examine the localised oxidation reactions that occur in a Ni-Cr-Fe alloy, Alloy 600, using a gas environmental cell at elevated temperatures. The initial stages of preferential intergranular oxidation, shown to be an important precursor phenomenon for intergranular stress corrosion cracking in pressurized water reactors (PWRs), have been successfully identified using the in situ approach. Furthermore, the detailed observations correspond to the ex situ results obtained from bulk specimens tested in hydrogenated steam and in high temperature PWR primary water. The excellent agreement between the in situ and ex situ oxidation studies demonstrates that this approach can be used to investigate the initial stages of preferential intergranular oxidation relevant to nuclear power systems.

Impact Statement

Electropolished sample was exposed to H2-H2O vapor for replicate nuclear power systems corrosion environments. Combination of images, EDS and ex-situ verifications revealed the degradation mechanism and effect of grain boundary.