Microstructural, phase and microhardness characterization of nano-reinforced Cr 3 C 2 –20NiCr coatings deposited on T91 boiler steel by HVOF spraying

This study examines the microstructural characteristics, phase composition, and microhardness of nano-reinforced Cr3C2–20NiCr coatings deposited on ASME SA213-T91 boiler steel. Coatings containing 5 wt.% Y2O3 + 5 wt.% SiC, 10 wt.% Y2O3 and 10 wt.% SiC reinforcements were deposited using the high-velocity oxy-fuel (HVOF) spraying process. SEM, EDS, XRD and microhardness were assessed. Porosity decreased from 1.91% in the unreinforced coating to 1.36% in the hybrid-reinforced coating. The coating containing 10 wt.% SiC achieved the highest microhardness, ranging from 1150 to 1180 HV. Coating thicknesses ranged from 250 to 255 µm. The XRD analysis revealed Cr3C2 as the dominant phase, along with weaker reflections assigned to the added Y2O3 and SiC. These results indicate that reinforcement composition influences the measured microstructural and mechanical properties of the coatings. Corrosion, wear, oxidation, and adhesion performance were not evaluated; further testing is therefore required to establish suitability for high-temperature boiler service.