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This paper aims to investigate the hot corrosion behavior of Ni-Cr and Cr3C2-NiCr coatings, deposited on T11, P91 boiler steels by detonation gun spray coating (D-Gun) process to enhance high temperature corrosion resistance.

Hot corrosion studies were conducted in secondary super heater zone of boiler at 900 °C for 10 cycles on bare and D-Gun coated steel specimens. The microhardness and porosity values of as-sprayed coatings were measured before exposing the specimens in the boiler environment. Each cycle consisted 100 h of heating in the boiler environment followed by 20 min of cooling in air. The weight change measurements were performed after each cycle to establish the kinetics of corrosion using thermogravimetric technique. X-ray diffraction, SEM techniques were used to analyze the corroded specimens.

Uncoated boiler steel experienced higher weight loss. The Cr3C2-NiCr coating was found to be more protective than Ni-Cr coating. The phases revealed the formation of oxide scale on coated specimens, mainly consist of nickel and chromium, which are reported to be protective against the hot corrosion.

There is very limited reported literature on hot corrosion behavior of Ni-Cr and Cr3C2-NiCr coatings deposited on the T11 and P91 substrates by detonation gun (D-gun) spray technique. T11 and P91 alloy steels have been chosen for this study because these two alloys are used to manufacture boiler tubes used in Indian thermal power plants.

The original powder commonly used for laser 3D printing is atomized alloy powder. The purpose of this study is to investigate the effect of ball milling (BM) on the structure and performances of the alloy powder and its composite products.

BM powder of Ni-Cr-graphite elements was subjected to laser cladding forming and the effect of BM on the powder structure was studied by X-ray diffraction, metallographic microscopy and scanning electron microscopy. The laser cladding-formed coatings were also tested by reciprocating friction measures and electrochemical corrosion experiment.

The results showed that the grains of laser cladding-formed Cr3C2-NiCr coating of BM powder were more refined compared to the coating of the atomized powder. Moreover, the abrasion resistance and corrosion resistance were slightly improved.

This work offers guidance for new original powder selection for laser 3D printing/powder bed forming/selective laser melting applications.

Due to the harsh underground environment in coal mining, the surface of hydraulic support columns corrodes severely, resulting in significant economic losses. Therefore, a highly corrosion-resistant coatings is needed to extend the service life of the columns.

This study aims to compare the corrosion resistance of ST-Cr₃C₂-NiCr (sealed treatment Cr₃C₂-NiCr) coatings with industrially applied chromium plating. The corrosion failure mechanism of the coatings was investigated.

The results demonstrated that the ST-Cr₃C₂-NiCr coatings exhibited excellent corrosion resistance. After sealing treatment, the corrosion potential of Cr₃C₂-NiCr coatings was −0.215 V, and the corrosion current density of Cr₃C₂-NiCr coatings was lower than that of the plated parts.

ST-Cr₃C₂-NiCr coatings prepared by supersonic atmospheric plasma spraying could provide excellent corrosion resistance in the coal industry.

The low porosity and the presence of the NiCr phase were crucial factors contributing to the preferable corrosion resistance exhibited by the ST-Cr₃C₂-NiCr coatings. The corrosive process of the coatings involved layer-by-layer delamination of surface oxide film, sub-surface pitting, formation and degradation of sub-surface passive film, as well as severe block-like delamination.

In this study, electrochemical deposition method which have cheaper equipment than thermal spraying methods and is available for the production of composite coatings were used.

Composite coatings were electrodeposited from a Watts's bath solution in which the suspended Cr₃C₂-NiCr particles were dispersed in the bath solution during deposition. Potentiodynamic polarization and electrochemical impedance spectroscopy techniques have been used to evaluate the corrosion resistance of the composite coating in the 3.5 Wt.% NaCl solution.

It was found that the submicron Cr₃C₂-NiCr particles distributed uniformly in the coating and depend on the current density of deposition, different amount of particles can be incorporated in the coating. The results showed that the corrosion resistance of the Ni/ Cr₃C₂-NiCr composite coatings is more comparable to the pure nickel coating.

Production of Ni-base composite coating from an electrolytic bath containing Cr₃C₂-NiCr particles is possible via electrodeposition.

The purpose of this paper is to investigate the tribological performance of Cr₃C₂–NiCr–Mo–BaF₂ composite sliding against a Si₃N₄ ball at high temperatures.

A Cr₃C₂–NiCr composite and a Cr₃C₂–NiCr–Mo–BaF₂ composite were prepared using spark plasma sintering. Tribological properties of the composites were investigated using a ball-on-disk type tribotester. The relationships among the microstructure, wear mechanism and tribological performance were determined by analyzing the wear track morphologies and the glaze layer’s phase composition.

The wear rate of the Cr₃C₂–NiCr–Mo–BaF₂ composite was approximately one order of magnitude lower than that of the Cr₃C₂–NiCr composite from 700°C to 900°C when sliding against a Si₃N₄ ball. The favorable tribological performance of the Cr₃C₂–NiCr–Mo–BaF₂ composite at high temperatures results from the synergistic lubrication of MoOx, BaF₂ and BaMoO₄.

This paper reports a new Cr₃C₂–NiCr matrix self-lubricating composite with better tribological properties than Cr₃C₂–NiCr composite at temperatures up to 900°C through Mo and BaF₂ addition.

Molten sulphate-vanadate induced hot corrosion is the main reason of failure of boiler tubes used at high temperatures in thermal power plants. The hot corrosion can be encountered by applying thermal spray coatings on the alloy steels. In this perspective, this paper aims to attempt to investigate the effect of carbon nanotubes reinforcement on Cr₂O₃ composite coatings on hot corrosion behaviour of ASTM-SA213-T22 steel in a corrosive environment of Na₂SO₄ – 60%V₂O₅ at 900^°C for 50 cycles.

The coatings have been deposited with high velocity oxy fuel process. The samples were exposed to hot corrosion in a Silicon tube furnace at 900^°C for 50 cycles. The kinetics of corrosion behaviour were analysed by the weight gain measurements after each cycle. Corrosion products were analysed with X-ray diffraction, scanning electron microscopy, energy dispersive and cross-sectional analysis techniques.

During investigations, the carbon nanotubes (CNT) reinforced Cr₂O₃ composite coatings on T22 steel were found to provide better corrosion resistance in the molten salt environment at 900^°C. The coatings showed lower weight gain along with formation of protective oxide scales during the experiment. Improvement in protection against hot corrosion was observed with increase in CNT content in the coating matrix.

The addition of CNT has resulted in reduction in porosity by filling the voids in chromium oxide coating, with interlocking of particle and has blocked the penetration of corroding species to enhance the corrosion resistance of the composite coatings. The corrosion rate was found to be decreasing with increase in CNT content in coating matrix.

It must be mentioned here that high temperature corrosion behaviour of thermally sprayed CNT-Cr₂O₃ composite coatings has never been studied, and it is not available in the literature. Hence, present investigation can provide valuable information for application of CNT-reinforced coatings in high temperature fuel combustion environments.

In this work, Cr₃C₂-25NiCr coatings were deposited on 410 stainless steel substrate by using the atmospheric plasma spray technique, at varying spaying parameters. The porosity and microhardness, adhesion strength and corrosion behaviour of coatings were examined in relation to these spraying parameters.

The microstructure of prepared coatings was examined by using scanning electron microscopy. The coating compositional analysis was performed by using X-ray diffraction (XRD) technique. The corrosion resistance of coated steel was investigated by potentiodynamic polarization. Results indicate that optimal factors for minimalizing the porosity were as follows: 10 g/min feed rate, 600 A plasma current and 100 mm spraying distance. The spraying factors influencing corrosion resistance of coating were also evaluated.

Under this optimal condition, the porosity of coating reached its minimal value of 3.1 per cent. The microhardness and adhesion of coatings also reached their maximum values of 64.8 Rockwell Hardness scale C and 60 MPa, respectively. XRD results indicated the transformation of Cr₃C₂ originating from Cr₃C₂-25NiCr source powder into Cr₇C₃ and Cr₂₃C₆ crystalline phases, due to the high temperature during spraying process. The undetectable Cr₃C₂ peaks indicating that this phase was remained in coating at very low concentrations. The potentiodynamic polarization and salt spray tests confirmed the highest corrosion resistance for the coating prepared by optimal spraying parameters.

The application of Cr₃C₂-NiCr cermet carbit coating for protection of steel from corrosion-erosion is very promising.

The purpose of this paper is to study the effect of slurry erosion at different parameters on plasma sprayed Cr₃C₂ coated 13Cr4Ni turbine steel and compare the results of coated steel with bare steel.

Cr₃C₂ + 25NiCr coating was successfully developed on 13Cr4Ni turbine steel using plasma spraying method. The slurry erosion test was performed using a simulated erosion testing rig. The commercially available silica sand was used as abrasive media and the effect of concentration (ppm), average particle sizes and rotational speed on the slurry erosion behavior were studied at 300 and 900 impact angles. Developed coatings were characterized by scanning electron microscope, XRD, EDS and micro hardness tests and study of erosion wear.

Results revealed that three times higher hardness of coatings was obtained because of the hard phases of chromium carbide and nickel carbide, which restricted the abrasive wear in comparison to uncoated steel. Lower abrasive wear was observed at 900 impact angle coupled with lower levels of slurry concentration and rotational speed. Further, it was observed that initially cumulative mass loss rate was high which gets stabilized after the surface become smooth and on exposing for higher periods. Overall results indicated that erosive wear was reduced significantly by the application of developed coating.

The developed plasma sprayed coating is very useful to enhance the service life of turbine steel by lowering the effect of slurry erosion.

The purpose of this paper is to investigate the erosion performance of high velocity oxy fuel- (HVOF) sprayed Al₂O₃–Cr₂O₃ composite coatings under silt slurry conditions.

The requisite HVOF composite coatings has been deposited on the stainless steel substrate (SS-304). The slurry erosion pot tester of make Ducom was used for conducting the silt slurry erosion tests on the required substrates. The comprehensive experiments were conducted at different particle size of silt in the range 212–250, 150–212, 53–106 µm, and the concentration of the silt ranged from 10%–40% by weight. The rotational speed of the pot tester has been varied between 500 and 1,500 revolutions per minute, and the test duration has been kept to 4 h.

The erosion wear resistance of the uncoated SS-304 has been greatly enhanced by the application of HVOF-sprayed Al₂O₃–Cr₂O₃ composite coatings. The addition of CeO₂ has a significant impact in reducing the erosive wear caused by silt slurry. The composite coating powder composition of 65%Cr₂O₃ + 34.5%Al₂O₃ + 0.5%CeO₂ has shown the highest erosion resistance.

The developed coatings have the potential to be used for hydro turbines as subjected to silt slurry conditions.

The erosion wear experiments are conducted comprehensively for coated and uncoated samples and the scanning electron micrographs supports the findings.

The purpose of this paper is to investigate the combined erosion and corrosion behavior of WC-Ni vacuum brazed coating.

Al₂O₃ particles and 10 wt% NaCl solution are used to evaluate erosion and corrosion resistance of WC-Ni vacuum brazed coating. Combined test of erosion and corrosion is also conducted. The microstructure of each specimen is characterized by the scanning electron microscopy. The chemical composition was determined by energy-dispersive X-ray spectroscopy.

WC-Ni vacuum brazed coating layer is effective protective coating under combined erosion and corrosion environment. The weight loss of coating layer is more reduced as the cumulative test time.

WC-Ni vacuum brazed coatings are investigated to check characteristic of the combined erosion and corrosion environment. WC-Ni vacuum brazed coatings are kind of diffusion coating that attract attention because of the resistance of superb impact and corrosion in comparison with other coatings. Some previous researches reported the properties of vacuum brazed WC material. Erosion and corrosion behaviors of WC-Ni vacuum brazed coatings were studied in our previous research, respectively. Hence, in this research, the principal objective is to examine the combined erosion and corrosion behavior of WC-Ni vacuum brazed coating.