Microstructural Features and Oxidation Behaviour of NiCrAlY Coatings Obtained by HVOF Process

NiCrAlY coating system has been widely used for the advanced gas turbines to provide protection against high temperature oxidation and corrosion. Various methods have been used to develop these superalloy coatings. In present investigation, NiCrAlY superalloy coatings have been deposited on the superalloy substrate (Superni76) using commercially available NiCrAlY powder and High Velocity Oxide Fuel (HVOF) process. These coatings have been characterised in terms of their microhardness, porosity, microstructure features and surface roughness. The coatings have been oxidized cyclically (1hour heating and 20minutes cooling) in air at 900οC. The weight change curves have been plotted and the parabolic rate constant has been evaluated. The oxides formed after oxidation has been studied by using various techniques like optical microscopy, FESEM/EDAX and XRD. It has been observed Al¬2O3, NiCr2O4 and Cr2O3 formed upon oxidation of the coatings provide protection to the substrate alloy.