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Purpose 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. Design/methodology/approach 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). Findings 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. Originality/value The probable mechanism of attack for the plasma-sprayed Ni3Al coating in the given boiler environment is presented.

Al 2 O 3-40% TiO 2 coating is deposited on Superni 601 and Superco 605 superalloys by low-velocity oxy-fuel (LVOF) process. LVOF sprayed coating is characterized for surface roughness, microhardness, scanning electron microscopy and X-ray diffraction analysis. Hot corrosion of the coated and uncoated superalloys have been evaluated in an aggressive environment of Na 2 SO 4-82% Fe 2 (SO 4) 3 under cyclic conditions at temperatures of 800 and 900 • C. The microhardness and surface roughness values of the as-sprayed coatings are found to be in the range of 742-946 Hv and 14.40-14.80 μm, respectively. Al 2 O 3-40% TiO 2 coating on both the superalloys has indicated protective behaviour during hot corrosion studies. Keywords. Superalloy; Al 2 O 3-40% TiO 2 coating; LVOF; microhardness; hot corrosion.