The effect of elevated air pressure on the oxidation properties of the nickel-based superalloy, RR1000, at 650°C with different surface modifications

Abstract

Samples of RR1000 with differing grain size and surface finish have been exposed to air at different pressures. Specimens were exposed for 4000 h at 650°C with some exposed to atmospheric pressure air and some exposed to air at 40 bar pressure. Samples exposed to elevated pressure formed a surface layer of NiCr₂O₄ whereas that formed on samples tested at 1 bar pressure was chromia. The surface layer formed at 40 bar pressure was thinner than that a 1 bar pressure. At 1 bar pressure, some samples exhibited regions of convoluted buckled oxides but no spallation. In adjacent regions of planar oxides, spallation did occur. For the latter case, an estimate of 6 Jm⁻² for the interfacial fracture energy has been made. None of the specimens tested at 40 bar pressure exhibited oxide spallation.

Keywords:

• Oxidation
• pressure
• chromia former
• superalloy
• spinel
• XRD

Acknowledgements

The authors thank the Centre for Electron Microscopy at the University of Birmingham for their technical expertise, Peter Deem of Amec FW for completing the elevated pressure test and David Walker and the University of Warwick where XRD analysis was conducted. This project has been jointly funded by the Engineering and Physical Sciences Research Council and Rolls-Royce plc. Their financial support is most appreciated as well as the provision of material by Rolls-Royce.