Oxygen Fuel Spraying Process Research Articles

Optimization of High-Velocity Oxygen Fuel Spray Process Parameters to Achieve Maximum Thickness and Minimum Porosity in Vanadium Carbide Coating

Optimization of High-Velocity Oxygen Fuel Spray Process Parameters to Achieve Maximum Thickness and Minimum Porosity in Vanadium Carbide Coating

Microstructure and wear resistance of HVOF sprayed WC-10Co-4Cr coating on Ti-6Al-4V

ABSTRACT WC-10Co-4Cr coating was deposited on Ti-6Al-4V by the high velocity oxygen fuel spray process to improve the surface hardness and wear resistance. The results show that the porosity of the coating is 2.0%, the microhardness is 1300 HV0.2, the surface roughness Ra is about 6.0 μm, and the bonding strength is 70 MPa. SEM and XRD analyses show that the coating is composed of WC, W2C, and Co phases. Under the condition of dry sliding with a load of 20 N and frequency of 10 Hz, the volume wear rate of the WC-10Co-4Cr coating is 9.2 × 10−6 mm3/N·m, while the wear rate of the Ti-6Al-4V is 4.6 x10−4 mm3/N·m, which means that the coating significantly improves the wear resistance of Ti-6Al-4V. With the load increased from 20 N to 50 N, the wear rate of the coating changes little. The analysis of the worn coating surface shows that the dominant wear mechanism of WC-10Co-4Cr coating was abrasive wear.

Obtaining and characterizing of WC-Co coatings obtained from thermal spray by flame

Tungsten carbide is used in the production of cutting tools for steel and as protection against wear due to its extremely high hardness. High speed oxygen fuel spraying process has been widely used to deposit WC-Co coatings. However, the decomposition and oxidation of WC-Co has been reported during the process, where carbon and tungsten are released, resulting in the formation of an amorphous matrix with the cobalt of the compound. This is attributed to the high heating and cooling rates suffered by the raw material. An alternative method is the thermal spray by flame, which allows controlling the working temperature and the residence time of the particles in the hot flame, avoiding the decomposition of tungsten carbide, on the other hand, it is a versatile and a low cost method. In this study projection parameters of a WC-18Co coating sprayed with a thermal flame spraying process from a commercial feedstock powder were determined to decide the conditions under which compact coatings are obtained with low porosity, avoiding dissociation of the tungsten carbide. The composition of the powders and substrates was determined by X-ray fluorescence microscopy and optical emission, respectively, X-ray diffraction studies were performed to characterize compositions and microstructures the coatings sprayed; the morphology was by scanning electron microscope. It was found that the best condition for this type of coatings is a neutral flame at a projection distance of 12 cm.

Taguchi approach to erosion wear optimization of WC-10Co-4Cr sprayed austenitic steel subjected to equisized slurry

PurposeThis paper aims to optimize the erosion wear analysis of slurry impeller material. Stainless steel (SS-410) was used as the pump impeller material. This erosion test was established to influence the rotational speed, solid concentration, time period and particle size. Fly ash was used as the erodent material.Design/methodology/approachThe erosion wear experiments were performed at different particle size, rotational speed, time duration and solid concentration (by weight). These tests were performed at four different speeds of 750, 1,000, 1,250 and 1,500 rpm, and the time durations of these experiments are 75, 120,165 and 210 min. For protective coating, high-velocity oxygen-fuel spray process was used for depositing WC-10Co-4Cr coating on stainless steel. To investigate the influence of controlled process parameters on slurry erosion wear of pump impeller material, Taguchi method was used.FindingsResults show that significant improvement in erosion wear resistance has been observed by using WC-10Co-4Cr coating. The process parameters affecting the erosion wear loss were in following order: time > rpm > concentration > particle size. The means of signal-to-noise ratio of stainless steel SS410 with and without coating vary from 93.56 to 54.02 and from 86.02 to 48.18, respectively.Originality/valueFor the erosion wear rate of both uncoated and coated stainless steel, the most powerful influencing factor was identified as time. The erosion test reveals that the coating exhibits ductile erosion mechanism and shows better erosion wear resistance (approximately two times) compared to uncoated stainless steel.

Structure, Mechanical and Tribological Properties of HVOF Sprayed (WC-Co+Al) Composite Coating on Ductile Cast Iron

The paper presents the results of examinations of WC-Co coating sprayed on ductile cast iron by high velocity oxygen fuel spray process (HVOF) with powder containing Al particles in an amount of 10%. The impact of Al particles added to the tungsten carbide coating on the structure, mechanical and tribological properties in the system of (WC-C)/ductile cast iron was examined. The microstructure of the thermal sprayed WC-Co+Al coating was characterized by light, scanning electron (SEM) and transmission electron (TEM) microscopes as well as the analysis of chemical and phase composition in micro areas (EDS, XRD). It was found that by supersonic thermal spraying with WC-Co powders with the addition of Al particles, the coatings of low porosity, high hardness, a very good adhesion to the substrate, compact structure with molten Al particles and finely fragmented WC particles embedded in a cobalt matrix, reaching the nanocrystalline sizes were obtained. Moreover, the results were discussed in reference to examination of bending strength considering cracking and delamination in the system of (WC-Co+Al)/ductile cast iron as well as hardness and wear resistance of the coating. It was found that the addition of Al particles was significantly increase resistance to cracking and wear behaviour in the studied system

Two-Body Dry Abrasive Wear Performance of High Velocity Oxygen Fuel Spray Process and Electrodeposited Cermet Coatings

In order to protect parts against wear, the carbon steel used are commonly coated by cermet coatings to increase the wear resistance. In this paper, the coatings consist of tungsten carbide 17wt% cobalt (WC-17Co), tungsten carbide 9wt% nickel (WC-9Ni), electrodeposited nickel (electro Ni) and electrodeposited nickel-silicon carbide (electro Ni-SiC) coatings. All coatings are deposited onto AISI 1018 carbon steel by using two different methods which are high velocity oxygen fuel (HVOF) and co-electrodeposition method. Abrasive wear test were observed under two‑body dry abrasion conditions with pin-on-disc test arrangement. Based on the volume loss after the wear test, the wear rates were calculated by using Archard’s law. The wear tracks of the coatings were investigated by using scanning electron microscope (SEM) and atomic force microscopy (AFM). The hardness of each coating was measured by using Vickers microhardness. The results showed that HVOF coatings have lower wear rate compared to the electrodeposited coatings. WC-9Ni has the lowest wear rate which is 4.06×10-3 mm3/Nm much lower compared to electro Ni-SiC of 16.36×10-3 mm3/Nm. This result was expected as the hardness of WC-9Ni is 1625.37 HV higher than electrodeposited coatings which approximately 380.51 HV. In conclusion, the methods of coating deposited affect the wear resistance as well as the hardness of the coatings.

Microstructure and Properties of Cu Coating Fabricated onto Diamond-Cu Substrate by Low-Temperature HVOF Process

Diamond-Cu composites have been considered to be the next generation of electronic packing materials. One of the key stumbles for such an application is the joining problem between diamond-Cu composites and other materials due to the poor wettability of the diamond particles in the composites. In order to overcome this hurdle, pure Cu powder was thermally sprayed onto diamond-Cu substrate by low-temperature high-velocity oxygen fuel spraying process. Microstructure and some fundamental properties of the coating obtained were systematically investigated, and morphologies of the single splat deposited on the diamond-Cu substrate were also observed. The splats obtained have good adhesion with the substrate as fine particles flattened sufficiently, while the coarse particles were significantly deformed. The coating was quite dense with porosity lower than 1%, oxygen content under 0.5% and thermal conductivity about 266 Wm−1 K−1 and still remained on the diamond-Cu substrate after 50 thermal shock cycles between 300 °C and water bath at room temperature. Meanwhile, the solderability of the coating was significantly improved. Therefore, Cu coating deposited on diamond-Cu substrate by low-temperature high-velocity oxygen fuel spraying process can be beneficial in electronic industry assisting with soldering and improved wettability for joining of other materials.

Mechanical and Tribological Properties of HVOF-Sprayed (Cr3C2-NiCr+Ni) Composite Coating on Ductile Cast Iron

The aim of the investigations was to compare the microstructure, mechanical, and wear properties of Cr3C2-NiCr+Ni and Cr3C2-NiCr coatings deposited by HVOF technique (the high-velocity oxygen fuel spray process) on ductile cast iron. The effect of nickel particles added to the chromium carbide coating on mechanical and wear behavior in the system of Cr 3 C 2 -NiCr+Ni/ductile cast iron was analyzed in order to improve the lifetime of coated materials. The structure with particular emphasis of characteristic of the interface in the system of composite coating (Cr 3 C 2 -NiCr+Ni)/ductile cast iron was studied using the optical, scanning, and transmission electron microscopes, as well as the analysis of chemical and phase composition in microareas. Experimental results show that HVOF-sprayed Cr3C2-NiCr+Ni composite coating exhibits low porosity, high hardness, dense structure with large, partially molten Ni particles and very fine Cr3C2 and Cr7C3 particles embedded in NiCr alloy matrix, coming to the size of nanocrystalline. The results were discussed in reference to examination of bending strength considering cracking and delamination in the system of composite coating (Cr 3 C 2 -NiCr+Ni)/ductile cast iron as well as hardness and wear resistance of the coating. The composite structure of the coating provides the relatively good plasticity of the coating, which in turn has a positive effect on the adhesion of coating to the substrate and cohesion of the composite coating (Cr3C2-NiCr+Ni) in wear conditions.

Influence of heat treatment on the abrasive wear resistance of a Cr3C2NiCr coating deposited by an ethene-fuelled HVOF spray process

Abstract This work reveals the influence of heat treatments on the microstructure, mechanical properties and abrasive wear behaviour of a Cr 3 C 2 NiCr coating deposited by an ethene-fuelled high-velocity oxygen-fuel spray process using an agglomerated-and-sintered feedstock powder. The wear resistance of an as-sprayed and heat treated (8 h at 800 °C) coating was evaluated in low- and high-stress abrasion regimes, the latter in a temperature range up to 800 °C. Precipitation of secondary carbides from the supersaturated as-sprayed binder matrix is at the core of the observed changes in the coatings wear resistance upon heat treating. This aging process renders the binder matrix softer and more ductile, as was probed by means of nanoindentation, and thereby improves its resistance against micro-cracking which is identified as an important wear mechanism in high-stress abrasion conditions.

Numerical analysis of particle impacting and bonding processes during high velocity oxygen fuel spraying process

In this paper, the dynamic impact behavior of a particle and a substrate under different particle temperatures and velocities as well as using different materials for the particle and substrate were systematically studied. We found that the highest temperature occurred at the side edge of the particle after the collision, which is consistent with the distribution of equivalent plastic strain. The deformation of the particle and substrate was very severe at the first 40ns, slowed down after 40ns and remained almost unchanged after 80ns. With the increase in the particle velocity, the effective combination area became larger, the equivalent plastic strain of the substrate is increased, and the equivalent plastic strain of the particle is decreased. As the initial temperature of particles increased, the effective combination area between the particle and substrate increased, and higher temperature and larger equivalent plastic strain of the particle could be obtained. With the increase in the substrate strength, the temperature and the equivalent plastic strain of the particle is increased, whereas the plastic deformation of the substrate is decreased.

Modeling of Two-Phase Flow and Heat Transfer in Low-Temperature Oxygen-Fuel Spray Process

The low-temperature oxygen-fuel (LTOF) spray is a modification of high velocity oxygen fuel spray. In this process, the high-temperature gas is accelerated to supersonic speed through a Laval nozzle followed by a straight barrel. By injecting room temperature gas into the mixing chamber, the temperature of the gas can be controlled in a range of about 1000-2500 K, so that some oxygen and temperature-sensitive materials, such as titanium and copper, can avoid oxidation or decomposition during the spraying process. The purpose of this paper is to establish a 2-D mathematical model to simulate the supersonic gas dynamics and particles behavior in LTOF process. The temperature and velocity of the flow fields, and the trajectory and heating of in-flight particles are predicted for different operating parameters. The model is validated by experimental data in the literature. Effects of the mixing gas flow rates, particle sizes, and injection conditions on this process were investigated as well.

Deposition behavior and microstructural development of TiNi powder particles in low temperature-HVOF spraying process

TiNi alloy particles were deposited at high velocity on Q235 steel substrate in thermally softened solid state by the modified high-velocity oxygen fuel spraying process (so called low temperature HVOF). Microstructural developments and deposition behaviors of a deposited single particle were observed by high resolution scanning electron microscopy and transmission electron microscopy. A single TiNi particle sprayed onto the substrate was severely deformed and the jetting-out phenomenon occurred in the margin of the splat. Extremely fine grains were observed along the interfacial boundary of the deposited particles where the most severe deformation had taken place. The grain refinement at the high deformed region of a splat was arisen from dynamic recrystallization of heavily deformed grain during deformation.

Influence of HVOF process parameters on microstructure and bond strength of NiCrAlY coatings

In the present study, NiCrAlY coatings were applied on steel substrate using high velocity oxygen fuel spraying process. The spray parameters were varied in order to study their influence on the coating properties. Powder and coating microstructures were investigated by a combination of X-ray diffraction, optical and scanning electron microscopy as well as energy dispersive spectroscopy analysis. Bond strength and microhardness tests were also performed on the coatings. It was found that the propane flowrate, the oxygen flowrate, the spray distance and powder feedrate have a significant effect on the coating characteristics. Finally, with the aim of minimising oxygen content and maximising bond strength, the optimum parameters were selected as the preferred spray parameters.

Development of Photocatalytic Active TiO2 Surfaces by Thermal Spraying of Nanopowders

Titanium dioxide is a very useful photocatalyst for the decomposition and diminution of environmental water and air pollutants. In such applications, it can be used as slurry or as immobilized coating obtained by different deposition methods. The studies performed in the last years showed that thermal spraying could be employed to elaborate TiO2 coatings with high performance for the decomposition of organic compounds. This manuscript presents a comparative study on the microstructure and photocatalytic performance of titania coatings obtained by different thermal spray techniques: atmospheric plasma spraying (APS), suspension plasma spraying (SPS) and high‐velocity oxygen fuel spray process (HVOF). Different titania powders and suspensions were used to study the influence of the feedstock materials on the coating characteristics. The deposits were mainly characterised by SEM and X‐ray diffraction. The photocatalytic performance was evaluated from the removal of nitrogen oxides. The experimental results showed that a drastic reduction of the pollutant concentration was obtained in presence of coatings elaborated by suspension plasma spraying. TiO2 coatings resulting from the spraying of agglomerated powder presentd less efficiency. That was mainly explained by the significant phase transformation from anatase to rutile that occurred in the enthalpic source during the spray processes.

Durability of Sprayed WC/Co Coatings in Al-added Zinc Bath.

In order to develop protective coatings for sink rolls used in continuous hot-dip galvanizing, the sprayed WC/Co cermet coating was formed on a mild steel by the High Vilocity Oxygen Fuel Spraying process and its durability in the molten zinc bath (753 K) containing 0-3 mass%Al has been investigated on the basis of the constitutional change measured by SEM and EDS. The following results were obtained. (1) During immersion periods, Al was enriched in the Zn-Al solution close to the sprayed coating surface and Al-rich phase was deposited on the sprayed coating surface. (2) Under the sprayed coating surface, the diffusion layer, where Zn was rich and Co was poor, was built up. As Al concentration in the molten zinc bath was increased, the thickness of the diffusion layer was decreased and the durability of the sprayed coating could be kept for longer times. (3) It is presumably a reason for such improvement of the durability that the Al-rich phase acts as a diffusion barrier against Zn and Co at the interface of molten zinc/sprayed coating and consequently suppresses the growth of the diffusion layer.