High Velocity Oxy-fuel Spraying Research Articles

Microstructural characterization and electrochemical behaviour of HVOF sprayed WC-Co-Cr coatings on 316L boiler steel stainless steel

Corrosion is the gradual erosion of metal, primarily because of electrochemical attacks especially under gaseous and alkaline conditions owing to the presence of sulphur and Alkali metals may cause rapid material degradation called Hot corrosion and result in untimely failure of components. To improve surface qualities for corrosion applications, the austenitic 316L stainless steel (SS) in this study was coated with Wc-10%Co–4%Cr utilizing the High-velocity oxy-fuel (HVOF) spray method. After the coated sample was heated to 800 °C for an hour, XRD was used to confirm the coating powder's composition. Using the FESEM technique, the microstructure features were examined, and XRD analysis was performed to ascertain the phase and composition of the substrate. Investigations were also conducted on the electrochemical corrosion characteristics that were impacted by the heat treatment after coating. SEM and EDAX technologies were used to characterize the sample and study its microstructure.

A Study on the Corrosion Behavior of RGO/Cu/Fe-Based Amorphous Composite Coatings in High-Temperature Seawater

In this paper, based on an Fe-based amorphous alloy, four kinds of RGO/Cu/Fe-based amorphous composite coatings with mass ratios of 5%, 10%, 15%, and 20% of RGO/Cu were prepared on the surface of 45# steel by using high-velocity oxy-fuel (HVOF) spraying. The coatings were immersed in simulated seawater at room temperature and at 90 °C for different lengths of time, and their corrosion resistance was tested using electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and X-ray diffraction (XRD), and the surface morphology and phase distribution of the samples were observed. The results showed that with the increase in the introduction ratio of RGO/Cu, when the addition ratio reached 15%, the composite coating had the best corrosion resistance. After soaking in simulated seawater at 90 °C for 18 days, the surface of the coating showed slight peeling and crack propagation, but no obvious pitting phenomenon occurred. The corrosion mechanism of the RGO/Cu/Fe coating in high-temperature seawater is mainly that high temperature causes the cracking of the coating, which opens up a transport channel for corrosion media. However, due to the addition of RGO, the corrosion has a certain self-limitation effect, which is mainly due to the toughening effect of RGO on the coating and its effect on extending the corrosion channel.

Tribological performance of c-BN/TiC-enhanced NiCrBSi coatings prepared by high-velocity oxy-fuel spraying tested from room temperature to 1000 °C

The c-BN/TiC-enhanced NiCrBSi composite powder and coatings were prepared by spray-drying and high-velocity oxygen-fuel (HVOF) spraying, respectively. The phases, microstructures and tribological performance were studied from room temperature to 1000 °C, and the wear mechanisms of coatings were analyzed and discussed. The results showed that TiC and c-BN distributed evenly in NiCrBSi phase, but with the increase of temperature, c-BN showed a certain degree of aggregation, while TiC particles grew significantly. Therefore, the coating shows good wear resistance at room temperature. As the temperature increased, the wear rate of the coating increased, and the wear resistance decreased, so the maximum wear rate was obtained at 800 °C. However, when the temperature was increased to 1000 °C, a composite enamel layer of oxide and hard phase was generated on the surface of the abrasion marks, which improved the wear resistance of the coating, significantly reducing the wear rate.

Steel Boiler Tube with HVOF Coating: Peculiarity and Interfacial

In this research, a NiCrMoFeCoAl-30%Cr3C2 composite finish was deposited using an HVOF technique on the T22 bare steel. Cr3C2 coatings provide excellent durability and corrosion resistance. When manufacturing homogenous and dense Cr3C2 layers with decreased as-deposited greater hardness, surface roughness, and enhanced quality corrosion resistance, high-velocity oxy-fuel spraying with suspension feedstock has been a viable choice. Scanning electron microscopy with energy dispersive spectroscopy and X-ray diffraction have been used to examine the specimen's microstructure. Coating properties such as thickness, microhardness, and porosity were measured.

An HVOF-Sprayed (Cr3C2-NiCr+Co) Composite Coating on Ductile Cast Iron: Microstructure, Mechanical Properties, and Scratch Resistance.

High-velocity oxy-fuel (HVOF) thermally sprayed Cr3C2-NiCr coatings have been shown to be effective in shielding important machinery and equipment components from wear in harsh, high-temperature conditions. In this investigation, the HVOF thermal spray coating technique was used to deposit Cr3C2-NiCr powder with 10% Co particles onto ductile cast iron. The effect of the Co particles on the mechanical, tribological, and microstructure characteristics of a Cr3C2-NiCr/ductile cast iron system was investigated. The microstructure analysis employed various techniques, including light microscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDS). Scratch tests were applied to analyze the coating quality and adhesion. The coatings created using the HVOF spray method with Cr3C2-NiCr powders mixed with Co particles exhibited a dense structure containing large Co particles, partially melted, and very fine Cr3C2 particles embedded into the NiCr alloy matrix. Additionally, they possessed high hardness and excellent adhesion to the substrate. The results of bending strength tests were also presented, together with information on the coating's microhardness and fracture toughness. These included an analysis of the cracks and delamination in the Cr3C2-NiCr/ductile cast iron system. It was observed that the addition of Co particles significantly increased the resistance to cracking and wear behavior in the studied system.

Development of fine WC-NiCr powder coatings by optimising HVOF spray parameters

Thermal spray processing parameters need to be optimised to mitigate decarburisation and oxidation of carbide-based coatings that causes unacceptable brittleness. In the present work, a theoretical model was developed to optimise kerosene fuelled high-velocity oxy-fuel (HVOF) flame characteristics and spray parameters for producing high-quality WC-NiCr coatings using finer feedstock of particle size distribution of – 30 + 5 μm. The model suggested an oxygen-to-kerosene ratio of 3.3 and a shorter torch barrel to avoid decarburisation in coatings. In total four parameter sets suggested by the theoretical model were selected to spray the fine-cut powder using a 100 mm long torch barrel. The developed theoretical framework was successful to provide optimised set of HVOF spray parameters to deposit high-quality fine carbide coatings with less decarburisation. Also, the coatings deposited using the optimised set of parameters exhibited the best performance in terms of low porosity, inter-splat cracks, brittleness, as-spray surface roughness, and corrosion resistance. Hence, the optimised parameters can be used to produce a finer as-sprayed finish, thereby demonstrating the potential in reducing grinding efforts.

Microstructure, residual stress and mechanical properties of double carbides cermet coatings manufactured on AZ31 substrate by high velocity oxy-fuel spraying

Microstructure, residual stress and mechanical properties of double carbides cermet coatings manufactured on AZ31 substrate by high velocity oxy-fuel spraying

Addressing challenges in high-temperature oxidation of ultra-supercritical boiler tubes via FeCoNiCrMo high-entropy alloy coatings

The engineering realm confronts formidable challenges in combating the persistent issue of high-temperature oxidation in ultra-supercritical coal-fired boiler tubes. This study is dedicated to tackling these challenges by employing high-velocity oxy-fuel spraying (HVOF) and high-frequency induction remelting techniques. Our primary objective is to establish a metallurgical bond between self-fusing FeCoNiCrMo high-entropy alloy (HEA) powder and the conventional 15CrMo boiler steel tube surfaces, all within ambient atmospheric conditions. Our investigation reveals two distinct stages of oxidation for the HEA coating when exposed to a 900 °C air environment. Initially, there is a rapid oxidation stage driven by interfacial reactions, followed by a steady-state slow oxidation stage influenced by ion diffusion. The presence of a dense Cr2O3 layer plays a pivotal role in reducing the oxidation rate significantly, thereby imparting exceptional high-temperature oxidation resistance to the FeCoNiCrMo HEA coating. Notably, during the steady-state stage, the oxidation rate is two orders of magnitude lower than observed in Ni-based superalloys. Minimal phase transformations or transitional layers at the interface underscore superb interface bonding at 900 °C. These findings provide a promising avenue for the cost-effective fabrication of highly oxidation-resistant ultra-supercritical boiler tubes. This advancement contributes significantly to the progress of engineering applications.

Improvement of the durability of thermal barrier coating by pre-oxidation

To suppress thermally grown oxides (TGO) in thermal barrier coatings (TBCs), the effect of pre-oxidation treatment was investigated for different thermal spray processes, such as high-velocity oxy-fuel spraying (HVOF) and low-pressure plasma spray (LPPS). A pre-oxidation treatment was applied before or after the top coat processing. When the pre-oxidation treatment was applied before top coat processing, TGO growth was suppressed during isothermal oxidation compared to when pre-oxidation was applied after the top coat process. Thermal spray processing did not affect the TGO growth behavior.

Elevated temperature tribological performance of non-equiatomic CoCrNiTiWx high entropy alloy coatings developed by mechanical alloying and high-velocity oxy-fuel spray

High entropy alloys (HEA) have applications in multiple fields owing to their exceptional mechanical and physical properties. In the current study, mechanical alloyed CoCrNiTiWx (x; a molar fraction, x = 0.5 and 1.5) HEA feedstock powders were deposited on maraging steel substrate using high-velocity oxy-fuel spray (HVOF). The phase evolution and the microstructure of the milled powders and as-sprayed coatings were analysed by X-ray diffraction (XRD) and scanning electron microscope (SEM). The tribological behaviour of CoCrNiTiW0.5 and CoCrNiTiW1.5 HEA coatings at elevated temperatures was studied extensively using a Pin-on-Disc tribometer. The CoCrNiTiW0.5 and CoCrNiTiW1.5 HEA coatings retained the BCC solid solution phases formed during the milling stage. However, additional oxide and intermetallic phases were formed owing to the in-flight oxidation and high temperatures experienced during the HVOF deposition. The deposited coatings exhibited a lamellar structure and good mechanical bonding with the substrate. The porosities of CoCrNiTiW0.5 and CoCrNiTiW1.5 HEA coatings were found to be 1.69 ± 0.32 % and 1.51 ± 0.37 % respectively.Consequently, the CoCrNiTiW0.5 and CoCrNiTiW1.5 HEA coatings displayed average microhardness values of 863 ± 52 HV0.3 and 1025 ± 39 HV0.3, respectively. Further, the wear rates of coatings exhibited a significant reduction at elevated temperatures, owing to the formation of TiO2, NiCr2O4 oxide tribofilms for CoCrNiTiW0.5, and CoCr2O4, NiWO4, WO3 oxides for CoCrNiTiW1.5. The specific wear rate of CoCrNiTiW0.5 HEA coating dropped by 73.6 % from 22.7 ± 2.6 × 10−6 mm3/N-m to 5.99 ± 1.9 × 10−6 mm3/N-m, while CoCrNiTiW1.5 dropped by 78.8 % from 11.86 ± 3.5 × 10−6 mm3/N-m to 2.51 ± 1.5 × 10−6 mm3/N-m, with a rise in the temperature from RT to 600 °C. Likewise, The frictional coefficients of CoCrNiTiW0.5 HEA dropped from 0.504 ± 0.015 to 0.397 ± 0.005, while CoCrNiTiW1.5 HEA dropped from 0.578 ± 0.025 to 0.471 ± 0.004, with a rise in temperature from RT to 600 °C. At room temperature, the wear mechanisms of the as-sprayed CoCrNiTiWx coatings were dominated by adhesive wear. However, at elevated temperatures, a shift towards oxidative wear was observed.

Advances in Corrosion Mitigation for Waste-to-Energy Systems: Evaluating Coatings and Application Techniques

Waste-to-Energy (WTE) systems, utilizing post-recycled municipal solid waste (MSW) and other biomass materials, are proven alternatives to landfilling for sustainable waste management. These processes offer benefits such as reduced landfill space, decreased methane emissions, and minimized waste volume. However, operational challenges, specifically high-temperature corrosion (HTC) of superheater tubes, hinder their efficiency due to the presence of chlorine, alkaline salts, and sulfates. To address this issue, a range of coating techniques have been developed, with thermal spray techniques, particularly high velocity oxy-fuel (HVOF) spray, proving the most effective for protecting superheater tubes. A comparative analysis of experimental data from multiple studies indicates that coatings with Alloy 625, Alloy C-276, Colmonoy 88, FeCr, IN625, NiCr, NiCrTi, and A625 offer high corrosion resistance at relatively low material costs, with corrosion rates below 1 mm/year. High chromium, nickel, and molybdenum content coatings perform exceptionally well under high-temperature and high-chlorine conditions. Notably, T92 and P91, due to their low cost and high corrosion resistance, are strong candidates for superheater tubes operating at 550°C. While A625 demonstrates excellent corrosion resistance, its high cost limits its practicality. Ultimately, the selection of suitable coatings depends on the specific WTE plant design and operating experience. The additional cost of applying these coatings is a minor fraction of the overall financial gains, as it extends the superheater tubes' lifetime and reduces plant downtime for tube repair or replacement.

Effect of interlayer interfaces enriched with multi-walled carbon nanotubes network on microstructure and mechanical properties of carbide-based composite coatings

In this paper, a WC-20Cr3C2-7Ni/multi-walled carbon nanotubes (MWCNTs)-Ni composite powder with a core-shell structure was prepared by surface modification and electroless nickel plating. After high-velocity oxy-fuel (HVOF) spraying, MWCNTs enriched in the shell and reinforced the interlayer interface of the composite coating. The addition of 0.2 wt% MWCNTs increased the reduced modulus and energy dissipation capacity of the composite coating by 12.6 % and 25.0%, respectively. The HRTEM results showed that MWCNTs formed a network structure at the interface. During the deformation process, stress was effectively transferred to network MWCNTs due to the strong metallurgical bond between MWCNTs and the binder phase. It allowed MWCNTs to absorb more energy and promoted stress to be transferred to the interior along the interlayer interface. The influence of MWCNTs on the elastic deformation process of the coatings was analyzed by numerical simulation.

Effect of Cobalt and Chromium Content on Microstructure and Properties of WC-Co-Cr Coatings Prepared by High-Velocity Oxy-Fuel Spraying.

To explore the Co/Cr ratio impact on the high-velocity oxygen fuel (HVOF)-sprayed WC-Co-Cr coatings microstructure and performances, three kinds of WC-Co-Cr coatings, namely WC-4Co-10Cr, WC-7Co-7Cr, and WC-10Co-4Cr, were prepared by using a high-velocity oxygen fuel (HVOF) spraying process. The three coatings' phase composition, microstructure, basic mechanical properties, abrasive wear, and corrosion resistance were investigated. The results show that all three WC-Co-Cr coatings comprise the main phase WC, minor W2C, and amorphous W-Co-Cr phase, besides the WC-4Co-10Cr coating containing a small amount of CrxCy phase. In addition, WC-7Co-7Cr coating exhibited the highest hardness and abrasive wear resistance, followed by WC-10Co-4Cr and WC-4Co-10Cr coatings. The corrosion resistance as a hierarchy was found to be WC-10Co-4Cr > WC-7Co-7Cr > WC-4Co-10Cr.

Enhancement in wear-resistance of 30MNCRB5 boron steel-substrate using HVOF thermal sprayed WC–10%Co–4%Cr coatings: a comprehensive research on microstructural, tribological, and morphological analysis

The rotavator blade, a part of an agricultural equipment rotavator, is used for the soil bed preparation. These blades have direct interaction with soil in agricultural land. Bad, rocky, gravel, sandy, and high rough-hard texture of soil are the main factor to damage the surface of the rotavator blade and a high wear rate is observed. This causes to decrease in the overall life of a rotavator blade. It also changes the geometry of the rotavator blade after a few operations, and that all effects the performance capability of this blade. Hence HVOF (High-velocity oxy-fuel) is used to modify the surface that improved wear resistance of the rotavator blade's surface. Feedstock powder used for the coating is WC–10%Co–4%Cr with Ni–20%Cr as a bond coat on 30MNCRB5 steel substrate (Rotavator blade's material). Six samples are prepared to test it on the Pin-On-Disc wear testing apparatus to determine the wear rate, weight loss, cumulative volume loss and linear wear rate, three bare 30MNCRB5 steel and three WC–10%Co–4%Cr coated samples are prepared with 8 mm diameter and 30 mm length in a cylindrical pin shape. Coated samples are characterized using the XRD (X-ray diffraction), SEM (Scanning electron microscope) with EDAX (Energy-dispersive spectroscopy), and X-ray mapping techniques. Worn out surfaces of bare 30MNCRB5 steel and WC–10%Co–4%Cr coated samples are investigated using the SEM (Scanning electron microscope) to study the microstructure of worn surface that helped out to identify the wear behavior. The HVOF (High-velocity oxy-fuel) spray coating drastically improved the surface to defend it from wear, and very less weight loss was seen in the WC–10%Co–4%Cr coated samples as compared to bare 30MNCRB5 steel material. Weight loss determined by the bare (30MNCRB5) material at 40N, 50N, 60N loads are 2.996 × 10−3 Kgm, 3.003 × 10−3 Kgm, 3.123 × 10−3 Kgm, and coated (WC–10%Co–4%Cr) sample at 40N, 50N, 60N loads are 0.006 × 10−3 Kgm, 0.030 × 10−3 Kgm, 0.038 × 10−3 Kgm respectively.

The Potential of High-Velocity Air-Fuel Spraying (HVAF) to Manufacture Bond Coats for Thermal Barrier Coating Systems

Driven by the search for an optimum combination of particle velocity and process temperature to achieve dense hard metal coatings at high deposition efficiencies and powder feed rates, the high-velocity air-fuel spraying process (HVAF) was developed. In terms of achievable particle velocities and temperatures, this process can be classified between high-velocity oxy-fuel spraying (HVOF) and cold gas spraying (CGS). The particular advantages of HVAF regarding moderate process temperatures, high particle velocities as well as high productivity and efficiency suggest that the application of HVAF should be also investigated for the manufacture of MCrAlY (M = Co and/or Ni) bond coats (BCs) in thermal barrier coating (TBC) systems. In this work, corresponding HVAF spray parameters were developed based on detailed process analyses. Different diagnostics were carried out to characterize the working gas jet and the particles in flight. The coatings were investigated with respect to their microstructure, surface roughness and oxygen content. The spray process was assessed for its effectiveness. Process diagnostics as well as calculations of the gas flow in the jet and the particle acceleration and heating were applied to explain the governing mechanisms on the coating characteristics. The results show that HVAF is a promising alternative manufacturing process.

Enhanced erosion resistance of HVOF-deposited laser-textured TiC coating with PTFE

ABSTRACT This research explores the enhanced slurry erosion behaviour of a composite coating comprising Titanium Carbide (TiC) deposited via High Velocity Oxy-Fuel (HVOF) spraying process. The study integrates laser texturing and Polytetrafluoroethylene (PTFE) spraying techniques to improve the coating's performance. TiC coating is applied to SS316 substrates using HVOF, followed by laser surface texturing to create micro-scale circular patterns. A thin layer of PTFE is then sprayed onto the textured surface, enhancing static contact angle and anti-adhesive properties. Slurry erosion tests reveal significant improvements in the coating's resistance. The findings offer promising applications in slurry erosion-prone industries. Further investigations aim to study the erosive mechanism of the different samples and evaluate their long-term performance.

Comprehensive study on the effect of HVOF processing parameters and particle size on high-temperature properties of NiCoCrAlYTa coatings

This paper investigates the microstructural and high-temperature properties of NiCoCrAlYTa coating deposited by High-Velocity Oxy-Fuel spraying (HVOF) by focusing on the optimization of process parameters and particle size effect. Since the NiCoCrAlYTa powder has a high amount of fine particles (5–38 μm), spraying of these fine particles due to the high surface-to-volume ratio is associated with an increase in particle surface energy, which can lead to in-flight oxidation of particles. To evaluate the oxidation behavior of these particles, the oxygen/fuel ratio, spray distance, powder size, and spraying under shrouded condition was considered as influencing factors. The formation of unmelted particles and in-flight oxidation can strongly be influenced by the oxygen and fuel flows, which determine the velocity of sprayed particles, and the temperature of the jet, respectively. Among the applied coatings, at a constant spraying distance of 300 mm, the sample with an oxygen flow rate of 900 SLPM and a fuel flow rate of 400 ml/min obtained a lower oxide content equal to 11.7 %. Different spraying distances can also play a significant role in the final microstructure evolution of the coating. Under constant flow rates of oxygen and fuel, the spraying distance was changed from 300 mm to 250 mm and 350 mm, which resulted in oxide content change from 11.7 % to 14.3 % and 7.8 %, respectively. Under the same spraying condition, increasing the sprayed particle sizes from 5–38 μm to 25–38 μm, the oxide content decreased from 7.8 % to 1.8 %. It is because smaller particles can expose to higher temperatures and cause them to heat up faster, resulting in more intense in-flight oxidation of the particles. The present study aims to provide a comprehensive understanding of the influence of spraying conditions and particle size distribution on the performance and durability of the NiCoCrAlYTa coating by evaluating the isothermal oxidation, thermal shock behavior, and high-temperature erosion.

Long-term salt spray corrosion behaviors of HVOF-sprayed WC-Cr3C2-Ni coatings before and after vacuum sealing with silicone resin

The application of thermal sprayed WC based cermet coatings is restricted by their structure defects including pores and cracks during thermal spraying. This article fabricated a corrosion-resistant WC-Cr3C2-Ni coating by high velocity oxy-fuel (HVOF) spraying and vacuum sealing with silicone resin. Experiment outcomes show that silicone resin fills into the defects of the WC-Cr3C2-Ni coating. Benefiting from the block of silicone resin in pores and cracks, the sealed coating shows less corrosion pits than the unsealed coating after long-term salt spray corrosion. The sealed coating shows surface without grooves, corrosion pits with smaller size and cracks with decreased amount in comparison with the as-sprayed coating. The vacuum sealing with silicone resin is a strategy with high potential for expanding the application range of thermal sprayed coatings.

Response surface methodology (RSM) based analysis on slurry erosion behavior of laser textured and PTFE sprayed VC+TiC coating deposited via HVOF

This research article focuses on investigating the slurry erosion behavior of vanadium carbide (VC) + titanium carbide (TiC) coating deposited via high-velocity oxy-fuel (HVOF) spraying. The study also focuses on examining the potential effects of laser texturing and polytetrafluoroethylene (PTFE) spraying on enhancing the resistance of the deposited coating against slurry erosion. Moreover, the study employs response surface methodology (RSM) to precisely model and optimize erosion behavior across various slurry conditions, while considering key process parameters such as velocity of jet, angle of impact, and concentration of slurry. By utilizing a central composite face-centered design (CCFD) matrix, an empirical correlation between these parameters and resulting mass loss is established. The failure mechanism was also examined using SEM images.

Effect of cermet interlayer on the electrochemical behavior of Cr3C2-NiCr/DLC duplex coating

Duplex coating consisting of a Cr3C2-NiCr interlayer and a top DLC film was prepared using the high-velocity oxyfuel (HVOF) spraying and a closed field unbalanced magnetron sputtering (CFUBMS). The electrochemical behaviors of the Cr3C2-NiCr/DLC duplex coatings in 3.5 wt% NaCl solution was investigated by comparing it with a single DLC film and a single Cr3C2-NiCr coating. Then the role of cermet interlayer on the anticorrosion mechanism of the duplex coatings was explored. Results showed that introducing the cermet interlayer increased the surface roughness of DLC films without changing its microstructure. In the dynamic potential polarization test, duplex coatings maintained high surface integrity even after corrosion, and corrosion only occurs in localized areas. The inclusion of an interlayer avoided substrate corrosion caused by penetrating cracks and therefore provided excellent corrosion resistance.