High Velocity Oxy-fuel Spray Process Research Articles

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.

Room and elevated temperature sliding wear of high velocity oxy-fuel sprayed Diamalloy3001 coatings

CoMoCrSi alloys exhibit high hardness and excellent wear resistance due to the presence of intermetallic Laves phases in a metallic Co-matrix. In this study, we deposited Diamalloy3001 coatings using high velocity oxy-fuel (HVOF) spraying process and evaluated their tribology at temperatures 25ᵒC, 200ᵒC and 350ᵒC. At room temperature, formation of tribolayers composed of oxides of Co, Cr, and Mo resisted localized shear deformation and resulted in low wear rates. At elevated temperatures, detachment of the tribolayers, and formation of cavities during reciprocating sliding resulted in high wear rates. Electron channel contrast imaging (ECCI) of the worn subsurface showed that at elevated temperatures, oxidation of splat boundaries led to interparticle debonding during wear and decreased the stability of the tribolayers.

High temperature erosion behaviour of high-velocity oxy-fuel sprayed CNT/NiCr-Cr3C2 composite coatings

In the present work, the effect of different weight percentages of carbon nanotubes on the high-temperature erosion behaviour of NiCr-Cr3C2 composite coatings is demonstrated. The high-velocity oxy-fuel (HVOF) spraying process was employed for the deposition of coatings on ferritic low-alloy steel (SA-213 T12). The solid particle erosion test of the coating with and without carbon nanotubes was conducted at a temperature of 600 °C with 30, 45, 60, and 90° impact angles using Al2O3 erodent particles. This work exhibited high erosion resistance for composite coatings with the highest CNT content of 7 %. However, as the impact angle was increased from 30° to 90°, the erosion rate of all coatings, irrespective of CNT content, increased. An Optical 3-Dimensional Profilometer was used to estimate lower crater depths for lower impact angles and deeper crater depths for higher impact angles observed through surface topography. The effect of the addition of CNTs in NiCr-Cr3C2 coatings resulted in a reduction in weight loss and erosion rate at different angles of impingement working under high temperatures. The outstanding mechanical properties of CNTs impart improved erosion resistance.

An Influence of Oxygen Flow Rate and Spray Distance on the Porosity of HVOF Coating and Its Effects on Corrosion—A Review

Thermal spray coating, exceptionally high-velocity oxyfuel (HVOF), improves the corrosion resistance and wear of metal. Coating parameters play a vital role in the properties of the coating. The quality of coating can be increased by selecting appropriate coating parameters. In the case of HVOF, the oxygen flow rate and spray distance are the most significant parameters that directly influence the porosity and corrosion resistance of the coating. Porosity is essential in thermal barrier coatings for low thermal conductivity, but there is a limit of porosity beyond which it can cause failure. Hence, understanding the effects of these parameters is essential to evaluate and further minimize the porosity in order to improve the corrosion resistance and durability of the thermal barrier coating. This article reviews hot corrosion in thermal barrier coatings, the stages of corrosion, the importance of spray parameters, and the effect of the oxygen flow rate and spray distance on the corrosion resistance of HVOF-sprayed coatings. Afterwards, the coating materials, the substrate, the flow rate of oxygen, the spray distance, and the fuel used during the HVOF spraying process from recent articles are summarized. In summary, this review compares the flow rate of oxygen and the spray distance with the corrosion capacity of the coating under different corrosive environments and materials to optimize these parameters for high-quality coating, which would sustain under high temperatures for future applications.

Effect of nano yttria-stabilized zirconia on properties of Ni-20Cr composite coatings

In the present work, 5 wt.% and 10 wt.% yttria-stabilized zirconia (YSZ) nanoparticles were reinforced in Ni-20Cr powder and deposited on boiler tube steel using a high-velocity oxy-fuel spraying process. The effect of YSZ reinforcement on microhardness, surface roughness and porosity was investigated. The hardness was the highest for nanocomposite coating reinforced with 10 wt.% YSZ and hardness was found to increase with a decrease in porosity. The coating microstructure and elements were characterized using field emission scanning electron microscopy (FE-SEM) with an energy dispersive spectroscope (EDS). The constituents of the coating were identified using X-ray diffractometer. It was found that the composite coating with 10 wt.% YSZ reinforced nanocomposite coating has the highest microhardness, in the range of 1008-1055 hv. During the coating process, nano YSZ particles were dispersed in the gaps between the micrometric Ni-20Cr particles, providing a better coating matrix than conventional Ni-20Cr. The Ni-20Cr with 10 wt.% of YSZ nanoparticles showed better results in terms of mechanical and microstructural properties during the investigation.

Optimisation of HVOF Spray Process Parameters to Achieve Minimum Porosity and Maximum Hardness in WC-10Ni-5Cr Coatings

High-velocity oxy-fuel (HVOF) spray coating plays a major role in many surface treatment methods, which tend to improve erosion and corrosion resistance properties. HVOF is well known for its dense and high-quality coating ability. This is due to the less in-flight exposure time, which tends to have less oxide content because of its high-velocity properties. Among the number of process parameters, porosity and hardness are predominant factors while considering wear rate and corrosion behaviour analysis. The current study aims to optimise HVOF process parameters to obtain low levels of porosity and high hardness values in the WC-10Ni-5Cr coating sprayed on 35 Mo Cr steel. The flow rates of oxygen, LPG, coating powder feed rate and spray distance are selected in this study as these have a superior influence on the final condition of the coating. Statistical tools such as the design of experiments (DoE), analysis of variants and response surface methodology (RSM) were used to achieve the desired results. As per the result analysis, the oxygen flow rate has a higher effect on the porosity value and microhardness value of the coating.

Cavitation erosion behavior of high velocity oxy fuel (HVOF) sprayed (VC + CuNi-Cr) based novel coatings on SS316 steel

A well-known hard material (VC) has not been explored as potential candidate for surface modifications to overcome the problem of cavitation erosion (CE) in hydro machinery components. Therefore, in this course of work, VC has been blended with a malleable and soft binder material (CuNi-Cr) in three different proportions (VC, VC + 50%CuNi-Cr, and CuNi-Cr) and coated over SS316 steel with the help of HVOF spraying system. It has been observed that with the increase in VC content in the candidate coatings, the hardness, porosity, and thickness increased. CE tests were carried out with the help of an in-house fabricated cavitation erosion apparatus as per ASTM G134 Standard. The CE resistance of SS316 steel was found to be enhanced with the application of HVOF sprayed VC and CuNi-Cr based coatings. HVOF coating prepared with 100% VC content have showed excellent wear resistive properties owing to its maximum hardness (1023 HV 9.81N ) and better rebounding properties due to maximum thickness and porosity. CE parameters consisting of highest velocity of jet, intermediate stand-off distance (SOD) and normal impedance were found to be dominating to produce maximum cavitation erosion. Moreover, SS316 steel have showed ductile mode of failure with signatures of material removal as overlapped CE pits and plastic deformation sites. However, the mode of failure for coatings have been changed from ductile to brittle with the increase in VC content in the coating matrix with signatures changes from plastic deformation to cracks and pores in case of CuNi-Cr and VC coatings, respectively. • VC and CuNi-Cr composite coatings have been efficaciously prepared using HVOF spray process. • Microhardness of coatings was reported to be increased with increase in VC content. • Erosion resistance of SS316 steel was found to be significantly improved after deposition of coatings. • Mode of failure for coatings have been changed from ductile to brittle with the increase in VC content.

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.

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.

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.

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.

Bond Strength, Hardness, and Microstructure Analysis of Stellite Coating Applied on 410 Steel Surface Using Flame Spray, Plasma Spray, and High-Velocity Oxyfuel Spray Process

Three thermal spray methods often used in industry are flame spray, plasma spray, and high-velocity oxyfuel (HVOF) spray. This research is intended to compare the properties of those methods in depositing Stellite coating on 410 martensitic stainless steel. The results showed that both plasma spray and HVOF coating show an even deposition, which could not be achieved by a flame spray method. Those three coatings meet manufacture minimum bond strength requirements. The highest bond strength and hardness were provided by the HVOF process with a value of 33.1 MPa and 719 HV, respectively. According to bond strength and standard hardness deviation, the HVOF process gives the most homogeneous coating. Substrate hardness just below the coating interface after flame spray, plasma spray, and HVOF process are raised by 236%, 56%, and 65% each from the specification. HVOF coating has the best cross section compared to others. Smallest porosity percentage, porosity size, and average interface unbonding is got by the HVOF process, with a value of 0.2%, 7.2 um, and 31%, respectively. Coating microstructure after etching shows phases related to heat input during application. The dendritic structure is observed on flame spray and plasma spray coating after etching but not on HVOF coating. Oxides and carbides of both cobalt and chrome are formed in the coating.

Microstructural investigation of bonding and melting-induced rebound of HVOF sprayed Ni particles on an aluminum substrate

In this study, nickel powder was sprayed on a polished aluminum substrate using the high-velocity oxy-fuel spraying process. Detailed microstructural characterization was conducted to analyse the mechanims of splat formation, with particular attention to the changes occurring at the splat-substrate interface and the subsequent bonding behaviour due to the impact of high thermal and kinetic energy particles with a soft, low melting point substrate. Characterization was performed using scanning electron microscopy, focused ion beam microscopy, transmission electron microscopy, together with the scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy. It was observed that a large number of particles had rebounded upon impact, which was correlated with the degree of substrate melting and the associated time for re-solidification. The remnant splats that adhered to the substrate surface were found to exhibit both mechanical and metallurgical bonding with the substrate. The experimental results were supported by transient finite element based thermal simulation.

Scratch Resistance of High Velocity Oxy-Fuel Sprayed WC-20% Co Coatings Reinforced with Carbon Nanotubes

Tungsten Carbide-20 weight % Cobalt (WC-20 wt% Co) coatings were extensively used material to achieve a combination of extreme hardness and excellent strength. Hence, an effort has been made to improve the toughening properties of WC-Co coatings through reinforcement of Carbon Nano-Tubes (CNTs) using High-Velocity Oxy-Fuel (HVOF) spraying process. In this work, 2 wt%, 4 wt%, and 6 wt% of CNTs were blended by the ball milling process with WC-Co powders. These composed powders were deposited by HVOF process on to the plain mild steel substrates. The scratch test analysis on as-sprayed coatings showed that due to the addition of CNTs on WC-Co coatings, the resistance to penetrate the coating surface increased. Also, by varying the percentage of CNTs in the coating system, the pores were reduced. This phenomenon is attributed to the toughening mechanism by forming a CNT bridge which avoids the formation of internal cracks.

Milling of Complex Surfaces of EN 10060 Steel after HVOF Sprayed NiCrBSi Coatings

The high-velocity oxy-fuel spraying process was used to investigate and improve the surface properties of a workpiece. The research was focused on the spherical surface of a workpiece made of high-strength steel, a ball and socket assembly. After spraying with a nickel alloy, the surface was machined by milling. The coating was carried out as a process in which a very thin layer of coating of the required thickness and the required specific properties, i.e., high Vickers hardness, adhesion to the surface, wear resistance and other important characteristics, which must be respected in other machining methods, was applied to the already finished, heat-prepared metal substrate. This article deals with the milling of complex surfaces of steel substrate EN 10060 after spraying with NiCrBSi alloy. After spraying, a total of 15 milling experiments were performed in order to determine precisely the optimal cutting parameters of milling and surface adhesion, based on newly acquired prediction relations. The main presented results are new relations for the determination of optimal technological milling conditions based on the identification of adhesive sections using derived equations. The new relations were verified and also compared with the current literature in the field.

Erosive wear behaviour of HVOF-sprayed Ni-20Cr2O3 coating on pipeline materials

The present work describes the application of High-Velocity oxy-fuel spray process with Ni-20Cr2O3 powder deposition on the various pipeline steels namely SS 202, SS 304, and mild steel. The slurry erosion wear tests were performed on coated and uncoated steels by considering slurry concentration, impact velocity, and erosion time as input parameters. It was concluded that for all materials, rpm (impact velocity of erodent's) influences on erosion wear the most. It was also noticed that the erosion resistance has been improved with SS 202 steel followed by to SS 304 and mild steel. Further, Ni-20Cr2O3 coatings showed maximum enhancement in slurry wear resistance of mild steel, followed by SS 304 steel and SS 202 steel.

Preparation, characterization and oxidation behavior of CeO2-gradient NiCrAlY coatings applied by HVOF thermal spraying process

Conventional and CeO2-gradient NiCrAlY coatings (0.5–2.0 wt% of nano-CeO2 from the inner layer to layers adjacent to the outer surface) were produced by the high-velocity oxy-fuel spraying (HVOF) process. Microstructural characteristics, phases analysis and high-temperature oxidation behavior of the functionally graded (FG) NiCrAlY/nano-CeO2 coatings were investigated and compared with those monolayer (ML) NiCrAlY coatings with without CeO2 nanoparticles. The microstructure of the ML- and FG-coatings, as well as processed powders, were characterized using a transmission electron microscope (TEM), field emission scanning electron microscope (FESEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction analysis (XRD), microhardness testing and Raman spectroscopy. On account of the calculation of oxidation behavior of the coating, the ML- and FG-coatings were exposed to laboratory's air at 1000 °C up to 100 h (short-term exposure) and 5000 h (long-term exposure) and moreover, the weight gain versus oxidation time and oxide growth rate were subsequently examined. Obtained results indicated that FG-NiCrAlY/nano-CeO2 coating had a better oxidation resistance as well as a lower oxide growth rate compared to the rest of the ML-coatings. In addition, increasing oxidation resistance of FG-NiCrAlY/nano-CeO2 coating can be attributed by controlling Al and O diffusion due to the formation of relatively thin, dense, and sticky Al2O3 oxide scale. Besides, all cases of the oxidized ML- and FG-coatings had a parabolic rate behavior owing to their diffusion-controlled oxidation under short- and long-term oxidation tests.

Characterization and Sliding Wear Behavior of Iron-Based Metallic Coating Deposited by HVOF Process on Low-Carbon Steel Substrate

The main aim of this work is to improve the sliding wear resistance of boiler steel material. The iron-based or Metco 41C metallic feedstock was deposited over the ASTM-SA213-T11 steel substrate using high-velocity oxy-fuel spraying process. The resultant deposits were subsequently characterized for microstructure, density, hardness, porosity and surface roughness. These characterizations were carried out with the help of XRD, SEM and Vickers’s microhardness tester. The sliding wear performance of the substrate and coatings were investigated by varying normal loads of 10 N and 20 N at temperatures of 200 °C, 300 °C as well as room conditions by employing pin-on-disk tribometer. The friction coefficient, volume of wear loss and wear rate were being found out. The wear results were compared among the substrate and coating. The formation of additional carbide phases such as Fe2C and SiC in Metco 41C coating led to higher hardness results in better wear resistance compared with the substrate.