Structural and oxidation behavior of atmospheric heat treated plasma sprayed WC–Co coatings

In this study, structural and oxidation behavior of WC–Co coatings was analyzed during atmospheric heat treatment process between 150 °C and 1100 °C. Two types of WC–12%Co coatings with different particle size and morphology were deposited on steel substrates using Air Plasma Spraying. The coated samples were heat treated in atmosphere in different temperatures between 500 and 1100 °C. Microstructural evaluation, X-ray diffraction analysis and microhardness testing were performed before and after heat treatment. In this case, the results showed that, regarding increase hardness of coating samples based on increasing applied temperature, coatings kept their properties up to 500 °C. In addition, by increasing heat treatment temperature up to 1100 °C, oxidation process in coated layer accelerated and caused coating detachment from the coating-substrate interface.

► WC–Co coating using finer powder size has lower structural porosity and higher hardness.
► WC–Co coating becomes oxidize to WO3 and CoWO4 phases at high temperatures.
► Carbide phases subsequently decarburize to η-carbides during controlled heat treatment.
► By increasing oxidation temperature up to 900 °C, coating detachment occurred.