Erosion–corrosion behaviour of Ni–20Cr plasma coating in actual boiler environment

Abstract

Erosion–corrosion is encountered in a large variety of engineering industries. In such environments, protective coatings are used. In this investigation, erosion–corrosion of the Ni–20Cr coating on nickel and iron based superalloys has been investigated by subjecting them to the boiler of coal fired thermal power plant at the temperature zone of 540°C for 1000 h duration. The erosion–corrosion kinetics of the plasma sprayed Ni–20Cr coating on different superalloys has been investigated. XRD, SEM with EDS and EPMA have been used to analyse the eroded–corroded products along the surface and cross-section. Main phases identified in all the Ni–20Cr coated superalloys after exposure are NiO, Cr₂O₃, Al₂O₃ and SiO₂. Aluminium has penetrated from the bond coat to the top coat along the splat boundaries. Oxides of chromium, nickel and aluminium are recognized as protective oxides for boiler environment. The probable mechanism of attack for Ni–20Cr coating in the given boiler environment is discussed.