Evaluation of corrosion mechanism for tungsten carbide coating exposed in actual boiler environment

Abstract The metals and alloys are prone to high-temperature oxidation and hot corrosion under severe environmental conditions. The degradation phenomenon is likely to occur by various mechanisms of deterioration such as creep damage, microstructural degradation, high-temperature fatigue, embrittlement, carburization, hydrogen damage, graphitization, thermal shock etc. In order to combat the degradation, thermal sprayed coatings can be deposited on the surface of the metal which can alter the surface properties of the metal. In the present study, WC-12%Co D-gun sprayed coating is investigated to know the corrosion phenomenon in actual coal fired boiler environment. The investigation consists of hot corrosion cyclic study at 1100 °C under cyclic conditions. The exposed samples were examined using scanning electron microscopy (SEM) along with energy dispersive spectroscopy (EDS), X-ray diffractometer (XRD), cross-sectional analysis by X-ray mapping. It was found that the deposition of tungsten carbide-cobalt (WC-12%Co) coating has increased the oxidation resistance, however, the coating was partially consumed after 875 h of corrosion. The corrosion rate for WC-12%Co coated SS 304 and SS 316 was calculated in terms of MPY (mils per year) and found to be 99.41 and 47.72 respectively for 875 h.