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Purpose The purpose of this study was to fabricate carbon nanotubes (CNT)-reinforced chromium oxide coatings and investigate mechanical and microstructural properties of these newly developed coatings on the boiler tube steel. Design/methodology/approach 1 and 4 Wt.% CNT-reinforced Cr2O3 composite coatings were prepared and successfully deposited on ASTM-SA213-T22 (T22) boiler tube steel substrates using high-velocity oxy fuel (HVOF) thermal spraying method. Microhardness, porosity, metallography, X-ray diffraction (XRD), scanning electron microscopy (SEM)/energy-dispersive X-ray spectroscopy, cross-sectional elemental analysis and X-ray mapping analysis have been used to examine the coated specimens. Findings The porosity of the CNT-Cr2O3 composite coatings was found to be decreasing with the increases in CNT content, and hardness has been found to be increasing with increase in percentage of CNT in the composite coatings. The CNT were able to increase hardness by approximately 17 per cent. It was found that the CNT were uniformly distributed throughout Cr2O3 matrix. The CNT were found to be chemically inert during the spraying process. Originality/value It must be mentioned here that studies related to fabrication of HVOF sprayed CNT reinforced Cr2O3 composite coatings on T22 boiler tube steel are not available in the literature. Hence, present investigation can provide valuable information related to fabrication and properties of CNT reinforced coatings on boiler steel.

Hot corrosion behaviour of Carbon Nanotubes (CNT) reinforced Cr 2 O 3 composite coatings have been investigated in actual boiler environment of a thermal power plant at 900°C under cyclic thermal loading conditions. The CNT content was varied from 1 to 8 wt-% and the coatings were deposited with the high-velocity oxy-fuel method. The comparative effects of variation in CNT content (from 1 to 8 wt-%) on hot corrosion behaviour were studied by weight change analysis and corrosion products were analysed with X-ray diffraction, scanning electron microscopy, energy dispersive and cross-sectional analysis techniques. The results confirmed that variation in CNT content enhanced the corrosion resistance of surface coatings in actual boiler environment at elevated temperature. The coatings showed lower weight gain along with the formation of protective oxide scales during the experiment. Reduction in corrosion rates during hot corrosion was observed with an increase in CNT content in the coating matrix.