Temperature-Dependent Oxidation Behavior of Inconel 718 under Cyclic Conditions

Abstract

This study investigates the temperature-dependent cyclic oxidation behavior of Inconel 718 superalloy by combining experimental characterization with Thermo-Calc-based thermodynamic predictions. The samples were exposed to 25 oxidation cycles at 550 degrees C, 650 degrees C, and 750 degrees C, with each cycle consisting of 1 h exposure followed by cooling to room temperature. The oxidation kinetics showed a rapid initial mass gain followed by a slower quasi-steady regime, and the total mass gain increased with temperature, reaching its highest value at 750 degrees C. XRD, SEM-EDS, and XPS analyses revealed the formation of protective oxide scales mainly consisting of NiO, Cr-containing oxides, and possible Ni-Cr spinel-type oxides, with more developed multilayer oxide features at 750 degrees C. Thermodynamic predictions supported the experimentally observed phase stability and oxide formation tendencies. The combined results indicate that oxidation resistance IN-718 is governed by the temperaturedependent evolution of diffusion-controlled oxide layers and elemental redistribution across the oxide/metal interface. The novelty of this study lies in correlating cyclic oxidation kinetics with microstructural, chemicalstate, and thermodynamic evidence to clarify protective oxide scale evolution IN-718 under repeated thermal exposure.