Degradation of nickel-based alloys for precise casting in high-temperature gas environment

The corrosion resistance of the alloys designed for precise casting Inconel 713LC and Inconel 738 in high temperature gas environment were tested. The environments during tests simulated helium coolant of advanced gas cooled reactors and high temperature carbon capture storage environment (CO2). The specimens were exposed in helium containing 500 vppm CO, 100 vppm CH4, 100 vppm H2 a 10 vppm H2O at 900 °C for 1000 hours and in CO2 at 900 °C during 200 hours. After exposure weight changes were investigated, the corrosion damage was observed by optical and electron microscope, the samples exposed in CO2 were investigated by XPS (X-ray Photoelectron Spectroscopy), GD-OES (Glow Discharge Optical Emission Spectrometry). After exposure in helium, 2 types of scales with different composition were observed on the sample surface. The depth corrosion damage was up to 20 μm, on the alloy Inconel 738 was deep corrosion damage only local, on the alloy Inconel 713LCcontinuous. After exposure in CO2 the surface corrosion layer was compact and almost uniform, corrosion interfered up to 30 μm under the surface layer. In high temperature helium, the alloy Inconel 738 could be said to bo more corrosion resistant than Inconel 713LC. In high temperature CO2 both tested alloys performed almost the same corrosion resistance.