Microstructural analysis of steam oxidation of IN617 for use in ultra-supercritical steam plants

The microstructural evolution of IN617 subjected to oxidising atmospheres of 100% steam, 50% steam/argon and air in the temperature range 700-750 degrees C for exposures times up to 4000 h at atmospheric pressure has been investigated using a range of analytical electron microscopy techniques. It has been found that for this alloy the presence of steam in the atmosphere has an effect on the oxidation kinetics, and influences the nature of the scale. It has also been shown that there are differences in the volume and nature of voids formed, and that the voids are often associated with an internal structure of alumina. Significant internal oxidation was observed, particularly in the presence of steam, and a 3D reconstruction of the microstructure using FIBSEM techniques showed that this comprised interconnected alumina plates that followed the grain boundaries into the substrate.