High-Temperature Erosion-Corrosion Performance of Plasma and High-Velocity Oxy-Fuel Sprayed TiC and TiN Enriched Ni-20Cr Coatings in an Actual Boiler Environment

This study investigates the influence of TiC and TiN additions on the high-temperature corrosion resistance of Ni-20Cr coatings on T22 boiler steel in an actual boiler environment. Plasma and high-velocity oxy-fuel (HVOF) spraying techniques were used to deposit three types of coating: Ni-20Cr, 60%(Ni-20Cr) + 40%(TiC) and 60%(Ni-20Cr) + 40%(TiN). The physical properties of the as-sprayed coated samples, particularly porosity and hardness, as well as their structural and morphological characteristics, were examined using energy-dispersive spectroscopy (EDS), scanning electron microscopy (SEM) and x-ray diffraction (XRD). Further, these coatings were exposed to an actual boiler environment of a superheater zone for 15 cycles at 750 degrees C, where each cycle consists of 100 hours of heat exposure followed by 1 hour of cooling. The corrosion performance of the aforementioned coating was analyzed using weight change measurements. The deposited coatings were found to have enhanced corrosion resistance in terms of weight change in comparison with uncoated steel. The TiC-rich coating deposited by the HVOF and plasma spray process was found to have high microhardness (760 Hv) and low porosity and formation of more protective oxide layers during high-temperature exposure (Cr2O3, NiO, TiO, NiTiO3 and NiCr2O4) leading to the reduction in the corrosion rate of nearly 98.75% and 96.42%, respectively. Hence, based on the above results, 60%(Ni-20Cr) + 40%(TiC) deposited by HVOF showed high corrosion resistance among the coatings and can be implemented in extreme environment applications.