Mechanical and microstructural properties of carbon nanotubes reinforced chromium oxide coated boiler steel

Abstract

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 different Cr3C2–NiCr coatings on boiler tube steel at elevated temperature

“…The high corrosion is shown in macrograph of the uncoated substrate and weight change continuously with the very first cycle and went increasing after every cycle. Kamal et al (2017) had suggested that Na 2 SO 4 on reacts with V 2 O 5 form NaVO 3 , (Goyal et al, 2018a(Goyal et al, , 2018b(Goyal et al, , 2018c(Goyal et al, , 2019cRani et al, 2017;Zhou et al, 2017). In case of 20 per cent Cr 3 C 2 -80 per cent (NiCr) coating, the macrograph shows better surface of the substrate.…”

“…One of the protecting ways to counteract the problem of high-temperature degradation is to coat the bottom part with the protective layer using different surface coating techniques (Goyal et al, 2016). The necessary mechanical strength was provided by the composite system of a base material with a protective surface layer different in structure and chemical composition is supplied by a surface treatment can be the best choice in combining material properties (Goyal et al, 2019c(Goyal et al, , 2018b(Goyal et al, , 2018cMehta et al, 2017;Onuoha et al, 2017). Corrosion is controlled by using inhibitors, the addition of an organic inhibitor is sufficient to reduce corrosion of metals in many corrosive media.…”

“…To overcome the problem of corrosion in boiler tubes a composite system of base material has been used, which provide a good mechanical strength and increased the limits of the use of material by enhancing the properties of the substrate material by providing thermal insulation, anti-wear and anti-oxidation to protect the surface of steel from the degradation of materials (Singh Sidhu et al, 2017). The coating must be dense enough to increase the life of substrate until the protective oxides present within the coating (Anderson, 2017;Bose, 2017;Dudziak et al, 2017;Goyal et al, 2018b). The need of protective coating is increased in gas turbines and other heat engines.…”

Hot corrosion behaviour of CNT-reinforced ZrO2-Y2O3 composite coatings on boiler tube steel at 900°C

“…A hot corrosion cycle composed of heating the test specimen for 1-h exposure in the furnace followed by 20 min of cooling to room temperature. The cyclic tests were performed to simulate an actual boiler environment (Goyal, 2018b; Goyal et al , 2017; Rani et al , 2017; Goyal and Goyal, 2020). The weight of each specimen along with the alumina boat was measured carefully on digital weighing machine after every cycle.…”

Microstructural and mechanical properties of CNT-reinforced ZrO2-Y2O3 coated boiler tube steel T-91

“…Compositions of coating powders were prepared by blending conventional zirconium yttrium, ZrO2-Y2O3 and 1 wt.% CNT, and ZrO2-Y2O3 and 4 wt.% CNT in a laboratory ball mill, using a low-energy ball milling method. Mixing of coating powders was done in a ball mill for 4 hours at 200 rpm [26]. Powder particles were asymmetric in shape and size 45 ± 10 µm.…”