Oxidation Behaviour of HVAF-Sprayed NiCr Coating in Moisture-Laden Environment

Reducing CO₂ emissions from power generation plants is intimately related to enhancing their thermal efficiency, which can be achieved by increasing the temperature/pressure of steam. However, any increase in steam temperature is inevitably accompanied by accelerated oxidation of boiler components. The use of renewable fuels such as biomass increases the problem by introducing a number of corrosive compounds into the boiler environment, resulting in more rapid degradation of components. Although thermal sprayed coatings are technocommercially attractive solutions for augmenting the durability of degradation-prone boiler components and are already used, further improvements in their performance are continuously sought. High-velocity air fuel (HVAF) coatings are promising in this context. In the present work, isothermal oxidation behavior of a candidate HVAF-sprayed Ni21Cr was studied in N₂ + 5% O₂ + 20% H₂O at 600°C for 168h. The oxide scale growth mechanisms were studied by BIB/SEM/EDX to evaluate the effectiveness of the coatings. It was found that the water vapor effect is insignificant due to the Cr reservoir in the Ni21Cr coating, which yielded enhanced oxidation protection by forming nano-scale Cr₂O₃.