EFFECT OF SPRAY VELOCITY ON THE SURFACE PROPERTIES AND HIGH-TEMPERATURE OXIDATION BEHAVIOR OF WIRE ARC-SPRAYED Ni–Cr AND Ni–Al COATINGS ON BOILER STEELS

High-temperature oxidation, erosion, and corrosion severely damage materials in thermal power plant boilers, turbines, and incinerators, causing downtime. This results in huge economic losses. To mitigate these losses, various thermal spray coating techniques — including High-velocity Oxy-fuel (HVOF) Spray, Cold Spray, Detonation Gun (D-Gun) Spray, Electric Arc Spray (Wire Arc Spray), Flame Spray (Combustion Spray), and Plasma Spray — are commonly employed. Among these coating techniques, coatings of boiler steels by using electric arc spray (wire arc spray) are effective due to their lower cost than other thermal spray techniques and their suitability for on-site applications. Also, Ni–Cr and Ni–Al-based coatings are attractive, especially for superheater and reheater tubes in coal-fired boilers, owing to their strong resistance to high-temperature corrosion. Moreover, the effectiveness of coatings in terms of microstructure, corrosion resistance, and mechanical properties depends upon the processing parameters. Hence, this paper aims to investigate the surface roughness, porosity, microhardness and high-temperature oxidation behavior of the Ni-20Cr and Ni-5Al coatings deposited on SA516 boiler steel using high-velocity and low-velocity wire arc spray techniques. The coatings were characterized through Scanning Electron Microscopy (SEM), Energy-dispersive Spectroscopy (EDS), and optical microscopy. Further, the high-temperature oxidation behavior of deposited coatings was examined in air environment at [Formula: see text]C for 50 cycles. However, the kinetics of oxidation was established using weight change study (thermogravimetric technique). The results indicate that among all coatings, high-velocity wire arc-sprayed Ni-20Cr coatings on SA516 exhibit lower surface roughness (2 [Formula: see text]m), lower porosity (0.75%), along with higher hardness (425[Formula: see text]Hv) as compared with other coatings. This may be due to the improved kinetic energy and temperature of the particles during deposition. However, during the oxidation study the bare steel experienced higher weight gain than the coated samples, which may be due to the development of unprotective oxide phase (Fe 2 O[Formula: see text]. The high-velocity arc-sprayed Ni-20Cr coated SA516 steel was observed to be more protective than other deposited coatings.