High Velocity Oxy-fuel Spraying Research Articles

Influence of spray distance on mechanical and tribological properties of HVOF sprayed WC-Co-Cr coatings

Abstract In this work, the tungsten carbide reinforcement in cobalt matrix (WC-Co-Cr) coatings was studied. The deposition process was carried out by high-velocity oxy-fuel spraying (HVOF). The study aimed to investigate the influence of one of the key process parameters, namely spray distance, on the coatings’ microstructure and phase composition, as well as their mechanical and tribological properties. The manufactured coatings were analysed by scanning electron microscopy, X-ray diffraction (XRD), instrumented indentation test, pull-off adhesion test and ball-on-disc method. The results revealed that selection of proper spray distance caused a high index of carbide retention (ICR) amounting to 0.95, which promoted higher hardness and better wear resistance. Instrumental microhardness was in the range of 14.2–14.8 GPa, whereas the Young modulus exhibited values from 336 GPa up to 342 GPa. The bond strength of deposited coatings was in the range of 55–65 MPa. Wear factor values were in the range of 73–81 × 10−7 mm3/(N · m) and the friction coefficient was about 0.4. The dominant wear mechanism is abrasion and adhesive mode supported by the fatigue-induced material delamination.

Effect of addition of Al2O3 on the high-temperature solid particle erosion behaviour of HVOF sprayed Inconel-718 coatings

In the present study, three different coatings Inconel718 + 10 wt%Al2O3, Inconel718 + 20 wt%Al2O3 and Inconel718 + 30 wt%Al2O3, were deposited by using a high-velocity oxy-fuel (HVOF) spray process. The effect of adding Al2O3 content in the Inconel-718 matrix was analyzed for the mechanical and microstructural properties. Using an 800 °C high-temperature air-jet erosion test apparatus, the erosion behaviour of the bare and coated specimens was examined at various impact angles. The XRD (x-ray diffraction) technique for determining the phases prevalent in the powders and coatings. Scanning electron microscopy (SEM) and energy dispersive spectroscopy were used to examine the surface morphology and elemental analysis of coatings (EDS). The composite coatings with maximum alumina content (30 wt%) exhibited maximum erosion resistance with a maximum microhardness of about 801 ± 40 HV0.2. However, the coating with 20 wt% alumina showed the highest fracture toughness. The inclusion of alumina reinforcement has improved the coating’s mechanical properties as well as their erosive wear resistance.The removal of splats and micro-cracking wereidentified as theprimary material removal mechanisms at a 90° impact angle. The ploughing and micro-cutting were identified as the dominant material removal mechanisms at 30° impact angle.

Effect of carbon nanotubes on microhardness and adhesion strength of high-velocity oxy-fuel sprayed NiCr–Cr3C2 coatings

NiCr–Cr3C2 coatings are widely used for high temperature and tribological applications due to their high hardness, oxidation, and wear resistance properties. In the present investigation, an attempt is made to further enhance the hardness and adhesion strength of NiCr–Cr3C2 coatings by reinforcing them with multi-walled carbon nanotubes. The carbon nanotubes (3–7 wt%) with varying weight percentages were mixed with NiCr–Cr3C2 using a planetary ball rolling mill and sprayed on SA213 T12 (T12 alloy steel tube) using a high-velocity oxy-fuel spraying process. The microstructures of mixed powder, coating cross-section, and fractured coating surface were characterized using a scanning electron microscope while X-ray diffraction was used for phase identification in the fractured coating surface. The coated samples were subjected to microhardness and adhesion strength tests according to ASTM E384 and ASTM D4541-09 standards. Out of all coatings, NiCr–Cr3C2/7% carbon nanotube composite coating showed the lowest porosity of 1.17%, highest microhardness, and adhesion strength of 563.8 HV and 55.8 MPa, respectively. A fracture analysis after a pull-off adhesion test revealed adhesion failure for NiCr–Cr3C2 coating and combined adhesion/cohesion failure for NiCr–Cr3C2/7% carbon nanotube composite coating.

Interfacial characteristic and microstructure of Fe-based amorphous coating on magnesium alloy

Due to the susceptibility to corrosive environment, it is necessary for the surface protection of magnesium alloy. Fe-based amorphous coatings are deposited on the surface of WE43 magnesium alloy with a Ni60 interlayer which is fabricated by the high velocity oxy-fuel (HVOF) spraying. The interfacial characteristic, microstructure and properties as bonding strength, wearing and corrosion resistance of the amorphous coating are investigated. The results indicate that the Fe-based amorphous coating with high amorphous content and low porosity is attained on WE43 magnesium alloy, and a metallurgical bonding between the lamellar structures is identified by transmission electron microscopy (TEM). The bonding strength between amorphous coating and magnesium substrate exceeds 56 MPa. Comprehensive corrosion resistance of coatings is superior than stainless steel in 0.1 mol/L HCl solution. The coefficient of friction is only half of that WE43 magnesium alloy. Therefore, the Fe-based amorphous coating shows a potential application for surface protection of magnesium alloy in chloride environment.

Thermally sprayed coatings for protection of integrated sensor systems on tribological loaded surfaces

Piezo-element integration in WC-NiCr and Cr3C2-NiCr thermally sprayed coatings resulted in electric voltage curves, which can provide information about the wear and friction condition in the tribological contact zone. The coatings were produced by high-velocity oxy fuel (HVOF) spraying with a thickness of 350 μm. The thermal sprayed coatings provided good wear protection of the embedded piezo-elements. The electrical energy outcome was slightly higher for the more wear resistant WC-NiCr coatings under dry sliding with a WC-12Co ball. The Cr3C2-NiCr coatings are known to give a better wear resistance at higher temperatures, but exhibit an inferior behaviour in comparison to WC-NiCr coatings at room temperature. This tendency was observed and is very well mirrored by the shape of electric voltage and the electric signal output at room temperature. Piezo-element integration was carried out after HVOF spraying embedding the 200 μm thick piezo-elements into cross-sectional slit which was produced by wire erosion.

High-Temperature Corrosion of APS- and HVOF-Coated Nickel-Based Super Alloy under Air Oxidation and Melted Salt Domains.

Various thermal spraying approaches, such as air/atmospheric plasma spraying (APS) and high-velocity oxy-fuel (HVOF) spraying, are widely employed by plants owing to their flexibility, low costs and the high surface quality of the manufactured product. This study focuses on the corrosion behavior of a Ni superalloy coated with powder Cr3C2-25NiCr through APS and HVOF at 950 °C under air oxidation and Na2SO4 + 0.6V2O5 molten salt environments (MSE). The results show that HVOF-deposited Ni superalloys have higher hardness and bond strength than the respective APS coating. The thermo-gravimetric probe reveals that the Ni superalloys exposed to an oxidizing air environment has a minor mass gain compared to those under the MSE domain for both non-coated and coated samples, in line with the parabola curvature rate oxidizing law. The Ni superalloys show good corrosion resistance but poor oxidation resistance in APS-deposited Ni superalloys under the MSE. HVOF-coated Ni superalloys in both environments exhibit better corrosion resistance and lower mass gain than APS-coated superalloys. The excellent coating characteristics of HVOF-coated Ni superalloys lead to their better high-temperature corrosion performance than APS.

Wear Behavior Analysis of Al2O3 Coatings Manufactured by APS and HVOF Spraying Processes Using Powder and Suspension Feedstocks

Thermally sprayed ceramic coatings are applied for the protection of surfaces that are exposed mainly to wear, high temperatures, and corrosion. In recent years, great interest has been garnered by spray processes with submicrometric and nanometric feedstock materials, due to the refinement of the structure and improved coating properties. This paper compares the microstructure and tribological properties of alumina coatings sprayed using conventional atmospheric plasma spraying (APS), and various methods that use finely grained suspension feedstocks, namely, suspension plasma spraying (SPS) and suspension high-velocity oxy-fuel spraying (S-HVOF). Furthermore, the suspension plasma-sprayed Al2O3 coatings have been deposited with radial (SPS) and axial (A-SPS) feedstock injection. The results showed that all suspension-based coatings demonstrated much better wear resistance than the powder-sprayed ones. S-HVOF and axial suspension plasma spraying (A-SPS) allowed for the deposition of the most dense and homogeneous coatings. Dense-structured coatings with low porosity (4 vol.%) and good cohesion to the metallic substrate, containing a high content of α–Al2O3 phase (56 vol.%) and a very low wear rate (0.2 ± 0.04 mm3 × 10−6/(N∙m)), were produced with the S-HVOF method. The wear mechanism of ceramic coatings included the adhesive wear mode supported by the fatigue-induced material delamination. Moreover, the presence of wear debris and tribofilm was confirmed. Finally, the coefficient of friction for the coatings was in the range between 0.44 and 0.68, with the highest values being recorded for APS sprayed coatings.

Tribological Behavior of Carbon Nanotubes Reinforced High Velocity Oxy-Fuel Sprayed WC-20 wt.% Co Coatings

Tribological Behavior of Carbon Nanotubes Reinforced High Velocity Oxy-Fuel Sprayed WC-20 wt.% Co Coatings

Characterization of Thermally Sprayed Coated GT Components Made of 3D Printing Based Selective Laser Melting Processed Inconel Alloy 718

Functional requirements like higher strength, resistance, and shielding from chemical reactions, degradation, etc., of the base metal are achieved by modifying their exposed surfaces using TBC (thermal barrier coating). Modified outer surface of components in the GT (gas turbine) improves the performance by the increase of inlet temperature, enhancing longer life and providing many interrelated surfaces to withstand severe working conditions. This work is based on characteristic (mechanical, thermal, and tribology) evaluation of TBC-coated GT components made of Inconel 718 manufactured from traditional and 3-D printing-based selective laser melting (SLM) process and compared. TBCs comprising bond coat and top ceramic oxide coat were deposited by High-Velocity Oxy-Fuel and Atmospheric Plasma Spraying techniques, respectively. Characteristics evaluated by varying coating thickness, standoff distance, substrate preheating, Input torch power, etc., revealed that characteristics of substrates manufactured from SLM methods improved significantly except porosity and average surface roughness. These improvements are essential for embedding sensors, thin films, etc., in TBCs for continuous monitoring of outputs.

Residual, Corrosion & Tribological Behavior of HVOF Sprayed Sustainable Temperature-Dependent Carbon-Based Hybrid Composite Coating

At present, cost-effective coatings that cause less pollution are in great demand; to decrease frictional losses, carbon-based hybrid composite coatings have been developed using a high-velocity oxy-fuel (HVOF) spray process. The microstructural, tribological, corrosion, and mechanical properties of these coatings have been evaluated using high-resolution X-ray diffraction (HRXRD), field emission scanning electron microscopy-Energy dispersive X-ray Spectroscopy (FESEM-EDS), Raman spectrum, Vickers micro-hardness tester, µ-360 cos(α) residual stress analyser, corrosion tester, and high temperature tribometer. The residual stress, corrosion and tribological behaviour at high temperatures were investigated using a pin-on-disc high-temperature tribometer. The tribological performance was evaluated using a high-temperature tribometer, and the experimental result shows that a coefficient of friction (COF) varies from 0.12 to 0.52, while wear results were in the range of 45 µm to 120 µm, as the test condition of temperature ranging from 50 °C to 350 °C, load from 60 N to 90 N and sliding velocity from 0.1 m/s to 0.4 m/s respectively. The experimental results of corrosion testing show that the mass loss decreases from 0.10 g to 0.04 g, when samples were dipped for 1 h; when the samples were dipped for 8 h, the mass loss of hybrid composite coating varied from 0.12 g to 0.045 g. The tribological test showed a 78.9 % increase in micro-hardness, a 78 % decrease in residual stress, and 60 % and 62.5 % decreases in mass loss due to corrosion at 1 h and 8 h, respectively, a 76.9 % decrease in COF and 62.5 % reduction in the wear at test condition of 350 ºC temperature, a sliding velocity of 0.4 m/s and 90 N load.

Effect of HVOF spraying parameters on fracture, erosion and thermal properties of Fe alloy-based coating materials

Fe-based coating (Fe50Mo5C15Si10Cr10Ti10) was deposited on 316L stainless steel substrate by high-velocity oxy-fuel spraying coating process. High-velocity oxy-fuel spraying process parameters such as oxygen flow rate and spray distance were varied to investigate their effect on mechanical, wear and thermal properties. The prepared coatings were characterized in terms of mechanical properties such as micro-hardness and fracture toughness, thermal properties and erosion wear properties. X-ray diffraction analysis showed presence of hardened phase Fe2Ti and Fe-Cr. Results of this study indicated that increase in oxygen flow rate from 200 to 250 slpm improved the fracture toughness and micro-hardness by 33% and 6.7%, respectively. On the other hand, increase in spray distance decreased the fracture toughness and micro-hardness by 27.2% and 6.7%, respectively. The wear rate was increased with the increase in oxygen flow rate and decreased with the increase in spray distance. The erosion wear rate was more dependent on fracture toughness as compared to micro-hardness.

Characterization and Corrosion Behavior Evaluation of Nanostructured TiO2 and Al2O3-13 wt.%TiO2 Coatings on Aluminum Alloy Prepared via High-Velocity Oxy-Fuel Spray

In this study, nanostructured titania (TiO2; n-TO) and nanostructured alumina-titania (Al2O3-13 wt.%TiO2; n-ATO) coatings were successfully deposited on the 6061 aluminum alloy by applying the high-velocity oxy-fuel process. The n-TO coating showed limited pores or microcracks accompanied by both partially and fully melted areas within splats. The n-TO coating exhibited about 25% higher microhardness compared with the n-ATO coating. The agglomerated non-molten nanostructured TiO2 particles that are randomly dispersed and embedded within the n-TO coating microstructure act as arresters of cracks through either branching or blunting crack tips, resulting in about 17% higher bonding strength, as compared to the n-ATO coating with a looser microstructure. The n-TO coating demonstrated superior hardness, higher wear resistance, and smoother wear scar than the n-ATO and uncoated Al substrate. The electrochemical test indicated that the n-ATO coating had about a 50% higher corrosion rate than the n-TO coating because of its looser structure. The immersion test revealed that the n-ATO coating had been severely attacked by blistering and deep cracks corrosions, whereas limited attacks could be distinguished using the n-TO coating in the substrate interface. Based on the results, the n-TO coating can effectively protect the Al alloy substrate against 3.5 wt.% NaCl solution.

Different Coating Methods of Titanium Dioxide on Metal Substrates for Orthopedic and Dental Applications: A Review

The outstanding physico-chemical characteristics to assist bone regeneration and cell development, titanium dioxide (TiO2) based materials have showed significant promise for applications in implants. Due to its excellent performance in a wide variety of applications, chemical stability, and inexpensive cost, this metal oxide has received the more attention. Coating techniques for creating surfaces made of this substance have been thoroughly investigated. The aim of this review article is to look at the current status of TiO2 technology for orthopedic and dental implants. Over the years, researchers have investigated several TiO2 coating deposition techniques on metal implants, with the goal of improving adhesion strength and long-term dependability. This review examines a variety of TiO2 deposition techniques on metal substrates in depth. Anodization, sol-gel method, plasma spray coating, cold spray coating, high velocity oxy-fuel spray, high velocity suspension flame spraying, pulsed laser deposition (PLD), ion beam deposition (IBD), magnetron sputtering deposition, electrophoretic deposition (EPD), electrochemical deposition and biomimetic deposition are among the methods examined.

The Formation and Frictional Behavior of Ni and Cu Aluminide Coatings on Copper

The microstructure and frictional behavior of candidate protective coatings for steel continuous casting copper molds were studied. A number of conventional coatings, consisting of the hard chromium deposited by electroplating, nickel-phosphorus deposited by electroless plating, and WC-17Co deposited by high-velocity oxy-fuel spraying, were compared with copper aluminide and nickel aluminide coatings. The copper aluminide coating was formed via pack cementation diffusion and aluminized in the Al-AlCl3-Al2O3 powder mixture at 500 °C. The nickel aluminide coating was obtained using the same aluminizing treatment, yet after depositing an electroless nickel-phosphorus interlayer. The microstructure of the coated specimens was characterized by scanning electron microscopy, energy-dispersive x-ray spectroscopy and x-ray diffraction phase analysis. Cu9Al4 was identified as the main phase of the copper aluminide coating, whereas Ni2Al3 and NiAl phases were identified in the nickel aluminide coating. The evaluation of the coatings frictional behavior through a pin-on-disk machine applying a 12 N loading showed that the copper aluminide coating is worn away and that the nickel aluminide coating remains intact up to the end of the test. The reference coatings revealed negligible wear with the material transfer from the pin to their surface. The copper aluminide coating demonstrated the least friction coefficient among the entire evaluated coatings.

Wetting Behavior of Wear-Resistant WC-Co-Cr Cermet Coatings Produced by HVOF: The Role of Chemical Composition and Surface Roughness

Despite the existence of several methods for production of superhydrophobic coatings from various materials, their application in harsh environments is still a great challenge. In this work, WC-Co-Cr cermet coatings were prepared by means of high velocity oxy-fuel (HVOF) spraying. WC particles dispersed in Co-Cr metallic matrix allowed to form the multi-scale surface roughness and thus to achieve hydrophobicity of the coatings in the as-sprayed state. The additional surface treatment by the silicone oil rendered the coatings superhydrophobic. The WC-Co-Cr coatings were fabricated from three different powder feedstocks: coarse powder with coarse WC particles, coarse powder with ultrafine WC particles, and fine powder with ultrafine WC particles. The investigation of microstructure, phase composition, and surface topography of produced coatings was conducted to study the influence of these factors on the water contact angle and surface free energy, which were obtained by the sessile droplet method. Theoretical models were used to explain the wetting behavior of all the coatings. Finally, preliminary results of the slurry abrasion response test revealed very good robustness of hydrophobicity of the coatings and also pointed to a need for further research on surface modifications for sacrificial applications.

Process characteristics, particle behavior and coating properties during HVOF spraying of conventional, fine and nanostructured WC-12Co powders

In recent years, great effort has been taken in science and industry to find novel material-related solutions, which provide improved properties for future technological applications. One of these approaches is the use of fine structured and nanostructured materials. Within the field of wear protection, the use of fine or nanostructured WC-Co powder feedstock in the thermal spray process enables the application of highly wear resistant, thin near net-shape coatings on parts with complex geometries. In this study, the processing of WC-12Co powders by means of High Velocity Oxy-Fuel (HVOF) flame spraying is fundamentally investigated and the results are compared to those obtained with conventional powders. The influence of process parameter and scaling effects on the spray process and the thermo-kinetic particle behavior in the flame, the heating of the substrate as well as on the coating properties, the microstructure, the behavior of elements and phases and the residual stress is discussed comprehensively. The investigations of this work have shown that HVOF spraying of fine and nanostructured WC-12Co powders instead of conventional ones leads to a significant alteration of the thermo-kinetic spray conditions. Under optimized spray conditions, achieved by the use of special spray equipment and statistical design of experiments (DoE), improvements in terms of the economy of the spray process (higher deposition efficiencies) and the mechanical properties (higher microhardness and fracture toughness, lower porosity and roughness) can be achieved.

INFLUENCE OF CARBON NANOTUBES REINFORCEMENT ON CHARACTERISTICS OF THERMALLY SPRAYED CERAMIC COATINGS

The influence of reinforcement of carbon nanotubes (CNTs) on microstructural features and mechanical properties of thermally sprayed Al2O3–3[Formula: see text]wt.%TiO2and WC–20[Formula: see text]wt.%Co coatings was investigated. Alumina–Titania coatings were deposited by Air Plasma Spraying (APS) and Tungsten Carbide–Cobalt coatings were deposited by High-Velocity Oxy-Fuel (HVOF) spraying process. The coatings obtained with reinforcement of CNTs were characterized to interpret the microstructural changes and also to evaluate the variation in their mechanical properties. The percentage composition of CNTs in both APS and HVOF coatings systems were varied in the order of 2, 4, and 6[Formula: see text]wt.%. It has been found that homogenous dispersion of carbon nanotubes in the coating systems results in increased microhardness and reduced surface roughness. Also, the microstructural features of the coating systems clearly showed that the coatings are denser with fewer pores due to the presence of CNTs.

Electrochemical Corrosion Behavior and Microstructural Characterization of HVOF Sprayed Inconel-718 Coating on Gray Cast Iron

In the present work, Inconel-718 (IN718) coating was developed on a gray cast iron (C.I) substrate by utilizing a high-velocity oxy-fuel spray technique. The microstructural analysis was performed to know the topological characteristics of the deposited IN718 coating. Corrosion testing of bare and coated samples was carried out at an ambient temperature in a NaCl solution (3.5 wt.%) using potentiodynamic polarization technique. The kinetics of corrosion and surface characteristics of the as-sprayed and corroded coatings were studied by scanning electron microscopy/energy-dispersive spectroscopy techniques. The different phases in the feedstock powder and as-sprayed coating were determined through X-ray diffraction analysis. The reported average microhardness value of the developed IN718 coating was 563 ± 15 HV0.2. The increased hardness of the IN718 coating is credited to the existence of Mo and Ti elements in the IN718 coatings. Corrosion testing showed that the IN718 coating exhibited the maximum corrosion resistance compared to a C.I. substrate due to a stable passive layer in the IN718 specimen.

Comparative high temperature oxidation studies of HVOF IN 625 coating on T22 boiler steel at 900 °C and 700 °C

Abstract IN 625 coating was deposited on T22 boiler tube steel by high velocity oxy fuel (HVOF) process to increase high-temperature corrosion resistance. High-temperature oxidation behavior of steel with and without coating has been examined at 700 °C and 900 °C under cyclic conditions. Each cycle consisted 1 h of heating in the silicon carbide tube furnace followed by 20 min of cooling in air. The cyclic oxidation conditions have been chosen as these conditions resembles actual industrial environment conditions where occurrence of shutdown is very frequent. Cyclic studies give the more severe conditions for testing and may be similar to the actual industrial environment of frequent breakdown/shutdown occurrence. Thermo gravimetric technique was implemented to study the kinetics of corrosion by observing weight change after each cycle. The bare steel experienced higher weight gain, which may be credited to the development of un-protective Fe2O3 dominated oxide scales. Evaluation of corrosive products was done using X-ray diffraction (XRD), scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDAX) and X-ray mapping techniques. It was observed that the uncoated steel suffered corrosion in the form of spalling and peeling up of its oxide scale. On the converse, the IN 625 coating provided significant resistance to the corrosion. The IN 625 coating was found to be more protective at 700 °C than at 900 °C. The better air oxidation resistance in the coatings may be attributed to the phases discovered in the oxide scale of the coated specimens which mainly consisted of oxides and spinals of nickel and chromium. The information gathering from the investigation will be useful to explore the possibility of the use of the HVOF spray coatings on the boiler tubes working in the range of 700–900 °C.

Tribological Study of HVOF Sprayed Tungsten Carbide Coated Stainless Steel

Corrosion and Wear, or a combination of both, are the main causes of degradation of metals used in the various industrial sectors. Degradation of the metals can be slowed down by adding a layer of resistant coating on the metal surface. This coating separates the base metal from a corrosive environment, reduces wear, and improves the appearance of the metal. The workpiece after coating becomes a composite that has properties far better than the substrate alone. There are various coating techniques, HVOF is one of the most important and widely used processes to protect the metals from wear, corrosion by providing hard and dense coatings. WC coating done by the high-velocity oxy-fuel (HVOF) spray method is the widely used method for providing a layer of corrosive resistance to a wide range of materials that are used in many different industries. In this study, Tungsten carbide (WC-12CO) Coating, HVOF Spray method was studied in great detail. Tungsten Carbide coating was done on a SUS400 Stainless steel substrate using HVOF Spray Process. An, Experiment was done to analyze the various effect of different parameters namely, oxygen rate, propane (fuel) rate, powder rate, spray distance on hardness, and surface roughness of a SUS 400 Stainless Steel substrate. Process optimization was done by using Taguchi and ANOVA methods. It was found that achieving maximum hardness was greatly dependent on propane (fuel) rate followed by powder rate, spray distance, and oxygen rate. The hardness decreases with the increasing fuel rate. And, achieving minimum surface roughness was greatly dependent on spray distance followed by oxygen rate, propane (fuel) rate, powder rate. Surface Roughness increases with increasing spray distance.