HIGH-TEMPERATURE OXIDATION PERFORMANCE OF HVOF AND PLASMA-SPRAYED Ni-20Cr, Ni-20Cr+TiC, AND Ni-20Cr+TiN COATINGS ON T22 BOILER STEELS

Thermal-sprayed coatings utilizing Ni-20Cr tend to be employed to safeguard boiler steels from corrosion, erosion, and oxidation at higher temperatures. However, carbide and nitride are well known for having unique characteristics under challenging conditions, owing to higher thermal stability, wear resistance, high melting point, and high hardness. In the current study, T22 steel was coated with Ni-20Cr, 60% (Ni-20Cr)+40% (TiC), and 60% (Ni-20Cr)+40% (TiN) utilizing plasma spray (PS) and high-velocity oxy fuel (HVOF) for prevention in an extreme boiler environment. The microstructure of the deposited coatings and their oxidation behavior at extreme temperatures were analyzed. It was observed that the deposited coatings were uniformly thick and that they were well-intact to the substrate. Furthermore, a weight change study was carried out for 50 cycles at 900 degrees C in a controlled environment to determine the high-temperature oxidation behavior of the as-sprayed coatings. X-ray diffraction (XRD), scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS), and X-ray mapping analysis were used to examine the bare, coated, and oxidized substrates. The air oxidation study observations indicate that the development of an unprotected phase (Fe2O3) caused severe spalling and surface cracking of oxide scale deposited on bare steel. HVOF-sprayed Ni-20Cr+TiC coating on T22 steel reduced the maximum weight gain by 99.85% compared to bare steel. Higher microhardness, less porosity, and the development of protective oxide scale (Cr2O3, TiO2, NiTiO4, and NiO) are responsible for the enhanced resistance of HVOF-sprayed Ni-20Cr+TiC-coated T22 steel against oxidation.