Hot-corrosion behaviour of CNT reinforced Cr3C2-NiCr coatings working under high-temperature sprayed by HVOF method

Abstract

The thermal power plant boiler tubes experience degradation of their surfaces due to oxidation and molten salt corrosion while working at elevated temperatures. The formation of protective coating layers can overcome such surface degradation. In the current research, protective coated layers composed of Cr3C2-25% NiCr/Carbon nanotube coatings are deposited on the ASTM SA-213T12 boiler tube substrate by the High-Velocity Oxy-Fuel (HVOF) thermal method. The coating powder Cr3C2-25%NiCr is reinforced with 3, 5 and 7 wt% of Multi-Wall Carbon Nano-Tube (MWCNT) prior to deposition. The uncoated and coated specimens are evaluated for hot corrosion behaviour in the molten salt environment (Na2SO4 + 60%V2O5) for 50 cycles, constituting 1 h of heating at 600 °C. Thermogravimetric analysis is used to investigate the kinetics of hot corrosion behaviour in both coated and uncoated samples. Coatings are characterized with the help of X-ray diffraction and Scanning Electron Microscope/Energy Dispersive Spectroscopy (SEM/EDS) techniques. Microstructural investigations with the help of SEM/EDS and X-ray diffraction of coated and uncoated samples revealed that 7 wt% of CNT coated samples minimized the voids and pores of the coatings, leading to better interlocking with the substrate surface. Furthermore, it is observed in the studies that the appreciable corrosion resistance of 7 wt% of CNT composite coatings is higher than 3 and 5 wt% of CNT-coated and uncoated samples.