Oxidation behaviour of functionally gradient coatings including different composition of cermets

Functionally gradient coatings are coating systems which are used to increase performances of high temperature components in the hot gas turbine section of gas turbine engines, diesel engines, in aerospace and aircraft applications. These coatings consist of a transition from the metallic bond layer to cermet and from cermet to the ceramic layer. In this study, oxidation behaviour of functional gradient coatings produced by plasma-spray on AISI 304 L stainless steel substrates was investigated. The plasma spray process was employed to deposit metallic, cermet and ceramic powders such as NiCrAl, NiCrAl+MgZrO3 and MgZrO3 on the substrate. A certain cermet composition for each sample was selected. Oxidation tests were carried out at temperatures of 800 and 1000°C. The coatings and oxidised coatings were examined by means of an optical microscope, SEM and X-ray diffractometry. The results showed that the oxide film thickness and oxidation rate at 1000°C are considerably higher than at 800°C.