HVOF Thermally Sprayed Ni50Cr Coatings Onto Power Plant Steels: Microstructure, Porosity and Oxidation Performance

The increasing energy demand has put significant pressure on the power generation industry to produce electricity more efficiently and to reduce the CO₂ emissions. To meet this target, the industry is increasingly moving towards higher steam temperatures (and pressures). There is a growing interest in using NiCr coatings for high temperature protection in the power plants. In this study, a commercial Ni50Cr powder was sprayed onto two boiler steels (P22 & P92) using a MetJetIV HVOF spraying gun. The effect of various oxygen/fuel ratios on the resulting coating microstructure was investigated using a SEM/ EDX. The pore volume and the distribution were measured using mercury intrusion porosimetry and gas pycnometry. Oxidation tests were carried out on the debonded coatings at 700-800°C (temperatures anticipated in the ultra supercritical power plants) using the thermogravimetric analysis. The coatings were further investigated in long-term air oxidation and in atmospheric pressure recirculating steam for 1000h.