Early-stage steam oxidation of Inconel 617 and its mechanism for advanced ultra-supercritical coal power plants

Ni-based superalloys are promising candidates for Advanced Ultra-SuperCritical (AUSC) coal-fired power plant components owing to their excellent high-temperature creep strength and oxidation resistance. The present study investigates the initial steam oxidation kinetics and mechanism of IN617, Ni-based solid-solution-strengthened superalloy, exposed to a controlled steam environment at 750 °C, simulating AUSC superheater conditions. The evolution of the protective oxide scale was characterised using X-ray Diffraction (XRD), Laser Raman Spectroscopy (LRS), and Scanning Electron Microscopy - Energy Dispersive X-ray Spectroscopy (SEM-EDS) to identify oxide phases, surface morphology, chemistry, and scale thickness. Weight gain kinetics follow a parabolic rate law (n = 0.466), indicating diffusion-controlled growth. The external scale comprised predominantly Cr 2 O 3 alloyed with Mn and Ti. At the same time, Al 2 O 3 formed beneath the chromia layer and, with exposure time, penetrated deeper into the alloy matrix, forming the internal oxidation product, as depicted by EDS elemental mapping. A mechanistic model is proposed for oxide scale development on IN617 under high-temperature steam conditions, elucidating the transition from initial rapid oxidation to stable protective scale formation. The established rate kinetics help determine the total metal loss due to steam oxidation over the designed plant life and the incorporation of corrosion allowances in the design.