The purpose of this study is to investigate the application of Ni3Al coating for boilers and other power plant equipment, which suffer severe erosion-corrosion problems resulting in substantial losses. Currently, superalloys are being used to increase the service life of the boilers. Although the superalloys have adequate mechanical strength at elevated temperature, they often lack resistance to erosion-corrosion environments.
In this paper, the erosion-corrosion performance of plasma-sprayed nickel aluminide (Ni3Al) coating on nickel- and iron-based superalloys have been evaluated 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 ten cycles of 100 h duration. The exposed products were analysed along the surface and cross-section using scanning electron microscopy (SEM), X-ray diffraction (XRD) and electron micro probe analysis (EPMA).
The XRD, SEM and EPMA analyses have shown the formation of mainly NiO, NiAl2O4 and indicated the presence of Ni3Al, Ni and Al2O3. In the boiler environment, Ni3Al coating partially oxidizes and acts as a perfect barrier against erosion-corrosion of superalloys. The partially oxidised Ni3Al coating remains intact even after 1,000 h cycle exposure.
The probable mechanism of attack for the plasma-sprayed Ni3Al coating in the given boiler environment is presented.
