Studies on the surface chemistry of oxide films formed on IN-738LC superalloy at elevated temperatures in dry air

Abstract

The oxidation behavior of IN-738LC was studied to develop high-temperature materials for low cost and highly efficient turbine systems. The present study was undertaken to investigate the kinetics and the surface chemistry of the oxide films formed during isothermal oxidation of IN-738LC superalloy in the temperature range 1123–1223 K in dry air. The oxidation kinetics followed the parabolic law. The activation energy of oxidation was 264 kJ mol−1. The scaling process is controlled mainly by the diffusion of chromium ions through the intermediate chromia layer in the scale. The surface morphology and the oxide phases of the scale were characterized by SEM, XRD, and EDS studies. XRD analysis revealed the presence of NiO, NiAl2O4, NiCr2O4 spinel, Al2O3, and Cr2O3 on the top-scale surface. The scale surface and cross section were further characterized using X-ray photoelectron spectroscopy (XPS), which revealed the presence of NiO, Ni2O3, NiAl2O4, Al2O3, and TiO2 on the top-oxide surface. The chromia layer was found to be underneath the top scale. The chromia layer also contains NiCr2O4 and NiAl2O4 spinels along with Al2O3. Application of XPS was found to be successful to understand the oxide-scale chemistry in terms of the oxide-growth mechanism of IN-738LC at elevated temperatures.