Microstructure and high temperature ciclyc oxidation in atmospheres with variable oxygen contents of plasma and HVOF NiCrBSiFe sprayed coatings

Abstract

The influence of thermal spraying procedure (plasma and HVOF) on the microstructure, high temperature oxidation resistance and adherence of NiCrBSiFe coatings has been examined. Two different series of oxidation tests have been carried out, in air (21% oxygen) at 800 and 1,000°C (1,073 y 1,273 K) and in a simulated gas turbine environment (10% oxygen) representative of a combined-cycle power generation plant, at the same temperatures. Coating microstructure, porosity, oxide content and microhardness are highly dependent on the spraying procedure and coating hardness also significantly decreases after long maintenances at high temperature (1,000°C). Finally, the oxidation weight gain and the adherence of NiCrBSiFe coatings are also dependent on the morphology of the coating but, nevertheless, the oxidation behaviour of these coatings was very good as protective chromium and silicon oxides were always formed.