Erosion–corrosion performance of NiCrAlY coating produced by plasma spray process in a coal-fired thermal power plant

Abstract

Degradation of materials due to erosion–corrosion is encountered in a large variety of engineering industries including thermal power plants. In such environments, superalloys are used due to their excellent mechanical properties at high temperature. They often lack resistance to erosion–corrosion and to increase their life, protective coatings play an important role. In the present paper, the erosion–corrosion performance of plasma sprayed Ni–22Cr–10Al–1Y coating on four different superalloys (namely Superni 75, Superni 600, Superni 718 and Superfer 800H) have been evaluated in actual industrial environment. The nickel and iron based superalloys and NiCrAlY coating on these superalloys have been investigated by exposing them to the low temperature primary superheater zone of the coal-fired thermal power plant at the temperature zone of 540°C for 10cycles of 100h duration. Scanning electron microscope (SEM) attached with energy dispersive X-ray analyser (EDAX), X-Ray Diffraction (XRD) and electron probe micro analysis (EPMA) were used to analyse the exposed products along the surface and cross-section. The erosion–corrosion resistance of the plasma sprayed coating on four different superalloys has been investigated. The probable mechanism of attack for this coating in the given boiler environment is discussed. Main phases identified in all the NiCrAlY coated superalloys after 1000h of exposure to the coal fired boiler environment are Al2O3 and Cr2O3. Oxides of aluminium, chromium and yttrium are recognized as protective oxides for boiler environment.