Cyclic oxidation behaviour and characterization of HVOF deposited inconel 718 coatings at 700°C

Abstract

In the current investigation, oxidation behaviour of HVOF sprayed Inconel 718 coating deposited on T22 boiler steel has been evaluated under cyclic settings for fifty cycles at 700°C. Oxidation of both with or without coating samples were examined using thermogravimetric technique. Microstructure and coating thickness was investigated across the cross section. Characterization of the coating was done before and after the oxidation using XRD, FE/SEM and EDS techniques. Microstructure revealed that the coatings were dense, uniform and adhered to the substrate steel. Both coated and uncoated steel obeyed parabolic rate law of oxidation. Uncoated steel resulted in heavy mass gain in comparison to coated steel due to formation of unprotective Fe2O3 scale which resulted in massive spallation. The results showed that the IN 718 coated boiler steel exhibited good oxidation resistance due to the presence of protective oxides i.e. NiO, Cr2O3 and NiCr2O4.