HVOF Technique Research Articles

Artificial Neural Networks in Spray Coatings for Protection of Hydroturbines in Silt Conditions

Background: Artificial intelligence techniques are able to predict the erosion in various coatings. In recent times, the erosion of the coating was successfully predicted using artificial neural networks (ANN). Aim: This patent aims to present the critical findings in the area of spray coatings used for the protection of hydroturbines. This critical review explores the surface erosion of numerous hydroturbine materials and coatings. Moreover, it covers the evolution of coating techniques used in different industries such as hydropower plants and materials handling industry. Objective: The objective of this patent is to present the critical finding in the field of erosion wear in coatings utilizing an artificial neural networks (ANN) technique. Methods: The effect of influencing factors on silt erosion was assessed. However, the evolution of various coating processes was explored comprehensively. Furthermore, the properties of various coatings, namely WC, Cr2C3, and Ni/Co coatings, were reported. A number of comparative analyses were carried out that can help in the selection of coatings on the basis of their mechanical as well as chemical properties. The applications of ANN in the spray industry were explained extensively. Results: The results show that the HVOF coating is the most widely used deposition method. HVOF is an appropriate technique for both ceramics and pure metals. Ceramics, as well as cermet, are deposited to enhance the wear and tear resistance of hydroturbine materials. As a result, the HVOF, laser cladding, D-Gun, and plasma spray technique are optimal in these circumstances. Coatings based on WC have been employed by several researchers to increase stainless steels' resistance to erosion and wear. Conclusion: With the application of appropriate models and ML methods, it is expected that coatings with specific desired properties can be manufactured with fewer experiments. There is no surprise that WC-10Co-4Cr finds widespread usage in a variety of industrial contexts. Ni- and Cobased coatings show promise for use in tribological settings. Stellite is suggested by several researchers for high-erosion duty conditions in hydroturbines. Co-based coatings are more erosion resistant as compared to No-based coatings. Coatings formulated with chromium (Cr) are resistant to erosion and wear in harsh mining environments.

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.

Enhancing comprehensive properties of HVOF thermally sprayed WC-10Co coatings using two grain inhibitors

The industry widely uses WC coatings to protect vital machine parts, including industrial gas turbines, ball valves, and aircraft landing gear shafts. To enhance the comprehensive performance of WC-10Co cemented carbide coatings, this study added VC and Cr3C2 grain inhibitors to refine the WC particles. Two novel powder compositions, S1 (WC-10Co-2Cr3C2-2VC) and S2 (WC-10Co-2VC-2Cr) were developed using the spray granulation method, alongside a commercial WC-10Co-4Cr powder as a control. These coatings were applied to 316 stainless steel substrates using the HVOF technique and subjected to XRD, SEM, hardness, friction, and electrochemical analysis. The microstructures, phase compositions, and various properties of WC-10Co-2Cr3C2-2VC and WC-10Co-2VC-2Cr coatings were systematically investigated. The results indicate a significant reduction in decarburization and porosity in S1 and S2 coatings compared to the commercial WC-10Co-4Cr coatings. VC and Cr3C2 suppressed the Ostwald ripening phenomenon, leading to smaller WC particle sizes in S1 and S2 coatings. In terms of performance, WC-10Co-2Cr3C2-2VC exhibited the highest hardness and superior wear resistance, while the WC-10Co-2VC-2Cr coating displayed the lowest corrosion rate in a 5 wt% H2SO4 solution at 25 °C, all while maintaining excellent mechanical properties. This study opens potential directions for the creation of high-performance WC-based coatings.

Morphological, microstructural, and mechanical study of FGM coatings prepared using the HVOF technique

Morphological, microstructural, and mechanical study of FGM coatings prepared using the HVOF technique

Evaluation of Hot Corrosion Behavior of WC-Co-Cr Coatings Coated by the HVOF Method

Thermal spray coating techniques have wide-ranging applications in various fields, including marine, automotive, biomedical, and aerospace industries. These methods are popularly used because materials coated with thermal spray coatings exhibit excellent resistance to oxidation, erosion, corrosion, and abrasive environments, particularly at high temperatures. The present study utilized the high-speed oxy-fuel (HVOF) technique, a state-of-the-art thermal spray coating method, to apply a hard cermet ceramic coating material consisting of WC-Co-Cr onto a 316L stainless steel substrate. Isothermal hot corrosion tests were also conducted at 750°C in the presence of 45% Na2SO4 and 55% V2O5 hot corrosion salts for 1, 3, and 5 hours. Advanced characterization techniques such as X-Ray Diffractometry (XRD), Energy Dispersive Spectrum (EDS), scanning electron microscopy (SEM), and elemental mapping analysis devices were used to characterize the samples coated with the HVOF technique before and after hot corrosion tests. The findings indicate that WC-Co-Cr hard coatings, which are known for their high resistance to abrasion, sustain severe damage at high temperatures. The coating was damaged after 5 hours in the hot corrosion tests performed in the presence of V2O5 and Na2SO4 molten salt at 750°C.

Tribological Properties and Corrosion Resistance of Stellite 20 Alloy Coating Prepared by HVOF and HVAF

This study examines the tribological and corrosion properties of Stellite 20 alloy coatings on F310H heat-resistant stainless steel that were prepared using HVOF and HVAF supersonic flame spraying techniques. To investigate the coatings’ microstructure, phase, microhardness, wear, and corrosion resistance, a range of characterization techniques, including SEM, EDS, XRD, microhardness, and friction wear-testers, weas employed. The results indicate that both HVOF and HVAF-prepared coatings exhibit a dense structure with porosity of 0.41% and 0.32%, respectively. The coatings are composed of γ-Co solid solution, ε-Co solid solution, Cr-rich solid solution, Cr7C3, WC, and CoCr2O4 phases. The microhardness of the Stellite 20 coatings prepared by HVOF and HVAF methods was 610 HV0.3 and 690 HV0.3, respectively, which is three times higher than that of the F310H stainless steel substrate. The wear mechanism of the HVAF coating is abrasive wear, while the wear mechanism of the HVOF coating is mainly fatigue wear with slight abrasive wear. The HVAF coating demonstrates superior wear resistance due to its higher flame velocity, denser coating, and higher average microhardness. In contrast, the HVOF coating shows a higher friction coefficient stability due to its lower hardness dispersion. The corrosion potentials of the HVOF and HVAF coatings are −0.532 V and −0.376 V, respectively, with corresponding corrosion current densities of 1.692 × 10−7 A·cm−2 and 6.268 × 10−7 A·cm−2, respectively. Compared to the HVOF coating, the Stellite 20 coating prepared using HVAF technology exhibits better wear and corrosion resistance.

Microstructure Characteristics and Properties of NiCrMoFeCoAl-30%Cr<sub>3</sub>C<sub>2</sub> HVOF Coating on T22 Boiler Tube Steel

In the current investigation, the NiCrMoFeCoAl-30%Cr3C2compositecoating was deposited on T22 baresteel with the HVOF technique. Cr3C2-based coatings offer high hardness, and good corrosion resistance.High-velocity oxy-fuel spray techniquescomprising suspension feedstock have been consideredaparticularly promising substitute for producing more homogeneous and denser Cr3C2coatings with loweras-depositedhigher hardness, surface roughness, and superior quality corrosionresistance.The specimen's microstructure has been characterized by SEM/EDAX and XRD methods. The coating thickness, porosity, microhardness, and coating density have been assessed.

Microstructure Characteristics and Properties of NiCrMoFeCoAl-30%SiO<sub>2</sub> Composite Coating on T22 Boiler Tube Steel

In the present investigation, the NiCrMoFeCoAl-30%SiO2 composite coating was sprayed on T22 bare steel with the HVOF technique. HVOFtechniqueallows the production of dense, excellently structured coatings with smoother surfaces and enhanced mechanical properties of the boiler materials. The produced coatings are characterized for their microstructure, and corrosion resistance by high-temperature corrosion.The specimen microstructure has been characterized by SEM/EDS and XRD methods. The coating thickness, porosity, microhardness, and coating density have been assessed.

Application Of High Velocity Oxy-Fuel Technique To Combat Surface Degradation In Power Generation Industry – A Review

<p>The high temperature corrosion and wear of steels in coal based power plant at elevated temperature is the primary reason behind downtime in power generating plants. The failure of steel components is big hazard to the effectiveness of the power-plant and responsible for the economic loss. To counter the effect of environmental degradation on steels, the chemical composition has been improved and their microstructures are also modified. But these changes have provided limited protection to the steels. The other useful method to control the degradation of steels is to apply coating of the protective material on the surface of target metal with the help of thermal spray technology. In this article, a systematic study of literature has been done to understand the level of protection provided by the HVOF (thermal spray technique) sprayed coatings to the different steels employed in degrading environments in coal based power plant. This article may help to researchers to select the HVOF technique with best coating combination to resist the failure of steels in coal based power plants.</p>

WEAR PROPERTIES AND MICROSTRUCTURE OF WC–10Co–4Cr POWDER COATING APPLIED TO CULTIVATOR BLADES VIA HVOF

Abrasion of cultivator equipment parts working in the soil causes serious losses if necessary precautions are not taken. The cultivator blades used to plow the soil in agricultural production wear out over time. In order to reduce this wear, the hardness and wear resistance of the material should be increased first. In this study, some of the 30MnB5 cultivator blades were heat-treated and some were coated with HVOF technique. The samples were obtained by plowing the soil at 15-cm working depth and 5.4-km[Formula: see text]h[Formula: see text] forward speed in two fields with different soil moisture contents. As a result of the experiments, abrasion losses and surface deformation of the blade material were observed and the effect of soil moisture on wear was also determined. After the treatment of 49.5[Formula: see text]daa (decare) with soil at 9% moisture content, the heat-treated 30MnB5 sample was worn 5.6 g, and the sample coated with WC–10Co–4Cr was worn 3.2[Formula: see text]g. Abrasions at 14% soil moisture were 6.3 g and 3.6[Formula: see text]g, respectively. It was observed that the coated material was less corroded than the heat-treated material. While the results obtained will contribute to the prevention of economic losses, the release of metals into the soil will also be prevented.

Microstructure characteristics and properties of WC-CrC-Ni HVOF coating for boiler tube steel

In the present work, the characterization of HVOF sprayed WC-CrC-Ni coating on three bare alloys of MDN-310, SA213-T22, and Superfer 800H was investigated with the HVOF technique. The microstructure of the specimens were examined using a range of characterization techniques including XRD analysis, SEM, and EDS interfaced to SEM. The as-sprayed coatings are characterized with respect to microstructure and mechanical properties. The porosity, surface roughness, coating thicknesses, density, and bond strength of coatings have been also evaluated.

Fabrication and effect of heat treatment on the microstructure and tribology properties of HVOF-sprayed CoMoCrSi coating

A type of CoMoCrSi coatings were fabricated by using HVOF technique, and the microstructures, mechanical properties and tribological behaviors at room temperature (RT) of the coatings annealed at 800 °C for different time were investigated in detail. Annealed CoMoCrSi coatings exhibited better crystallization and more compact microstructures compared to as-sprayed coatings. The porosity of the annealed coatings reduced to 0.32–0.2%, and adhesive strength increased to 63.8–68.5 MPa, both of that were all reached at an equivalent level with the variation of the annealed time. The surface microhardness could be enhanced from 902.8 HV0.3 for the as-sprayed coating to 1237.6 HV0.3 for the coating annealed for 10 h, which could be attribute to more compact microstructures and hard nano-sized Cr2O3 layer, that resisted indentation effectively. With the increasing of sliding distance at room temperature, the friction coefficients of the annealed coatings reached at 0.39–0.4, and the wear rates decreased to 0.88–1.59 × 10–6 mm3 N−1 m−1, demonstrating enhanced tribological performance of the CoMoCrSi coating after heat treatment. Numerous metallic oxides, i.e., Cr2O3 played a critical role in sustaining and anti-wear, and oxides, i.e., Co3O4, MoO3, and CoMoO4 transferred to the Al2O3 pair surface and formed a continuous transfer film during the friction test at RT, which directly reduced friction and leading to a low friction coefficient and wear rate.

Influence of Adding Nano Coating Layers on the Hardness and Impact strength Properties for Low Carbon Steel

Nanotechnology is one of the great techniques that helping to considerably improve many technologies and industry sectors such as information technology, homeland security, medicine, transportation, energy, food safety, and environmental science. Low carbon steel is widely used in many applications because it is cheap and it has high workability. However, low surface hardness and impact toughness are its main disadvantages. In this work, the nanocoating of tungsten carbide (WC) has been added to the low carbon steel surface with a thickness of 30, 40, and 50μm by using the thermal spray process with the HVOF technique. The present work aims to investigate the coating layer influence on the hardness and impact toughness. The results showed a significant improvement in the hardness, reaching 94.7%, while the impact toughness improved by 36% for a sample coated with a 50μm comparing with uncoated samples. The improvement in the hardness and impact toughness is due to the good adhesion of nano coat with the steel surface and the high hardness of tungsten Carbide as well as the good toughness of tungsten. The thickness of the coating layer is detected by using the scanning electron microscope images for each spray time. The results show that the coating with a layer of a thickness of more than 50μm will cause flaking and removing the coating layers.

Determination of specific wear rate of steel coated with tungsten carbide using Taguchi technique for textile applications

Textile industry is one of the promising industries in India. Textile machineries have a huge number of components that are subject to wear and tear. Replacement of the components is very expensive and may not produce break even in many cases. Coatings have been widely used on the mechanical components that are being used in the textile machinery. In this work, the wear characteristics of tungsten carbide coated steel specimens have been studied for probable application in the textile industry. For the purpose of coating, different coating techniques have been studied, among that HVOF technique and plasma coating technique have been extensively studied. In this work, plasma coating technique was used to coat the EN 8 steel specimens with tungsten carbide. The coatings were of varying thickness and different stand-off distance of the plasma torch was considered for the coating to see which would be the best coating thickness and the best stand-off distance. Using the pin on disc experimental set up, the specific wear rate was calculated and the friction coefficient was calculated. It was observed that the frictional force and the Co-efficient were the least in the case of the first experiment that is, at 4 in. stand-off distance and 100 µm coating thickness. SEM analysis and XRD analysis were done on the specimens for mechanical characterization and to ensure that the coatings are uniform and also to determine the composition of the coating.

High temperature friction and wear performance of TiB2-50Ni composite coating sprayed by HVOF technique

The work aims to study the effect of temperature on friction and wear properties of TiB2-50 mass%Ni coatings. TiB2-50Ni ceramics-metal composite coatings were fabricated on 304 stainless steel substrate by high velocity oxygen flame spraying (HVOF) with “shell and core type” Ni coated TiB2 powder. Microstructure, element map distribution and phase structure of HVOF coatings were characterized by SEM, EDS and XRD, respectively. High temperature friction and wear properties of TiB2-50Ni composite coatings and 304 stainless steel substrates were systematically investigated. Porosity, thickness, average surface roughness, micro-hardness and bond strength of HVOF TiB2-50Ni coating are 2.3%, 300.8 μm, 2.3 μm, 766.1 HV and 22.6 MPa, respectively. Values of nano-indentation hardness (H), Young's modulus (Er), ratio of hardness to elastic modulus (H/Er), yield strength (H3/Er2) and elastic recovery (η) of HVOF coatings are all higher than those of 304 stainless steel matrix. The friction coefficient of 304 stainless steel substrate fluctuates greatly with wear rate being increased sharply during high temperature wear test. However, the friction coefficient of HVOF TiB2-50Ni coating without significant fluctuation from room temperature to 600 °C. The wear rate of HVOF coating at 600 °C is (2.73 ± 0.01) × 10−5 mm3/N·m, which is about a quarter of the wear rate of 304 stainless steel substrate of (11.07 ± 0.01) × 10−5 mm3/N·m. As friction temperatures increasing from room temperature to 150 °C, 300 °C, 450 °C and 600 °C, oxygen contents of worn surfaces of TiB2-50Ni coatings increased from 5.10 mass% to 10.88 mass%, 20.40 mass%, 31.21 mass% and 38.78 mass%, respectively. Abrasive wear, adhesion wear and oxidation wear are the main wear mechanisms of HVOF TiB2-50Ni coatings during high temperature friction test. Comparing to 304 stainless steel matrix, TiB2-50Ni composite coating has more superior high temperature friction and wear properties.

Carbide dissolution in WC-17Co thermal spray coatings: Part 1-project concept and as-sprayed coatings

Tungsten carbide-cobalt (WC-Co) thermal spray coatings are widely used for ambient temperature wear applications and are typically deposited using agglomerated feedstock consisting of 1–5 μm sized carbide particles. There are technical challenges to reduce the carbide particle grain size to the desirable <1 μm because of carbide dissolution and carbon loss in-flight’; i.e., in transit from the torch to the substrate. This work explores a novel processing route for the WC-Co system that has been conceptualised previously for the chromium carbide-nickel chromium (Cr3C2-NiCr) system. The approach is based on the tendency for carbides to dissolve in-flight and for precipitation of submicron carbide particles on subsequent heat treatment. Part 1 of this two-part series reviews the equilibrium Co-W-C system to assess this concept for the WC-17 wt%Co composition. WC-17 wt%Co thermal spray coatings, targeting varying degrees of carbide dissolution/decomposition and carbon loss, were sprayed using HVOF, plasma Ar-He and plasma Ar-H2 techniques. The deposits were characterised by XRD pattern fitting, cross-sectional SEM and LECO carbon combustion analysis. The mechanisms of phase formation and carbon loss are discussed.

Analysis of Thermal Barrier Coating’s Behaviors on Alloys – A Review

Thermal barrier coatings (TBC) are made from alloys such as super alloys, titanium alloys and advanced steel materials. These alloys are widely used to make parts of aircraft, and these parts are used for in corrosive environments and high temperature operations. TBCs are therefore miserably needed to improve fatigue life, creep strength and corrosion resistance of these alloys. Thermal barrier coating consists of a bond coat and a top coat. The behaviour of the coating, such as oxidation resistance, hardness, microstructure and thermal oxide formation, depends on the coating technique and the bond and top coating materials. Therefore, an attempt has been made in this paper to review recent research on the Thermal Barrier Coating Behavior. Most researchers used NiCoCrAlY as a bond coat and YSZ as a top coat. HVOF and plasma spray techniques were found to be effective than other techniques such as Electron beam physical vapor deposition in this review.

Comparison of microstructure and oxidation behavior of CoNiCrAlY coatings produced by APS, SSAPS, D-gun, HVOF and CGDS techniques

MCrAlY coatings are widely preferred in materials used at high temperature applications exposed to oxidation and hot corrosion. The coating process used in the production of thermal spray coatings directly affects the microstructure and lifetime of the coating. In this study, a CoNiCrAlY metallic bond coat was deposited on Inconel 718 superalloy substrate material using APS, SSAPS, D-gun, HVOF and CGDS spraying techniques. The produced coatings were subjected to isothermal oxidation tests at 1000 °C for different exposure times. Porosity, surface roughness, XRD, SEM, EDX-elemental mapping analysis were used to investigate and determine the microstructures and the changes in the dimensions of thermally grown oxide (TGO) layer as a function of time and temperature. The obtained data were compared before and after the oxidation tests, and the findings were evaluated considering other related studies within the literature. The results show that CGDS CoNiCrAlY coatings exhibited better oxidation resistance than the coatings produced by the other techniques.

Energy dissipation in WC-Co coated A356.2/RHA composites

Energy dissipation, usually, mechanical damping and storage modulus of WC-Co coated A356.2 and their composites dispersed with silica rich rice husk ash (RHA) particulates have been studied in this work. All the specimens are coated using HVOF technique with an optimum coating thickness of 100 µm as obtained by MATLAB. The damping and storage moduli have been measured using dynamic mechanical analyzer at three distinct frequencies (0.1, 1 and 10 Hz) over a temperature range of 35 °C to 150 °C. Introspection of these results reveals that the mechanical damping and storage modulus has been improved with the incorporation of RHA and further increases with the increase in the RHA content. Furthermore, coated WC-Co samples demonstrate higher mechanical damping than the base alloy and its composites, however, a loss in the storage modulus has been noticed which is due to the presence of W2C phase. Porosity, hardness and the residual stresses are the mechanisms responsible for the increase in mechanical damping of WC-Co coated Al/RHA composites.

HVOF Sprayed Mullite Coatings for Use In Extreme Environments

Products used in industry and marine applications are exposed to extreme environments like high heat, humidity, acidic or alkaline or hyper saline environment, UV and IR radiation. Metals with good corrosion and oxidation resistance may be used but are restricted to Ni and Cr alloys, titanium and super alloys etc., which are costly and have their limitations. Hence ceramic coatings on low cost metals may be an answer to this problem. Ceramics are inherently chemically inert, high temperature resistant, corrosion and oxidation resistant. Flame spraying of ceramics is a good and reliable method for applying ceramic coatings on metallic substrates with good bond strength (&gt; 80 MPa) and 1% porosity. In this work, HVOF technique is applied to obtain 100 microns thick mullite coatings on MS substrates with a NiCr bond coat. Mullite has a high oxidation and corrosion resistance. It is chemically inert. It has high temperature resistance even at 2000 C. These properties are ideal for industrial components exposed to salty environments. Characterization studies like XRD, SEM/EDS, Corrosion tests using polarization technique, coating thickness and surface roughness have been studied and reported. A corrosion rate of 1.55 mm/ year has been achieved in a sea water environment.