High Velocity Oxy-fuel Research Articles

Synergism of h-BN and La2O3 in improving the tribological performance of Al2O3 coatings

Wear is a significant cause of material loss, contributing to surface degradation of crucial components, notably within engineering sectors. This article is dedicated to enhancing tribological properties through the implementation of Al2O3-based ceramic coatings, specifically targeting situations where reciprocating sliding wear predominates. This study introduces lanthanum oxide (La2O3), a rare earth oxide, as a reinforcing material in Al2O3 coatings in varying weight percentages of 1.2%, 1.6%, and 1.8% respectively along with 3% hexagonal boron nitride (h-BN). The coatings were developed by the high-velocity oxy-fuel (HVOF) surface modification technique, with SS304 serving as the substrate. The porosity, hardness, and chemical composition of the developed coatings were examined. Additionally, reciprocating tribological testing of the coatings was conducted at two loads (5 N and 15 N) under dry sliding conditions. Results indicated that coating containing 95.4% Al2O3–3% h-BN–1.6% La2O3 reduced the porosity up to 50% and improved hardness by 46% compared to the 97% Al2O3–3% h-BN coating. The formation of the α-Al2O3 phase leads to an increase in coating hardness and a reduction in porosity. Notably, the coating comprising 97% Al2O3–3% h-BN exhibited the lowest coefficient of friction among all developed coatings under both loads. Furthermore, an increase in load led to a decrease in the coefficient of friction for all developed coatings. Furthermore, the addition of La2O3 (1.6 wt%) to the coating with 3 wt% h-BN exhibited the lowest wear at both loads. The findings also revealed increased wear at high loads for all developed coatings. SEM, EDS, and XRD analysis of the worn surfaces revealed the contribution of h-BN and La2O3 in enhancing friction behavior through the formation of oxides such as α-Al2O3, B2O3, Al8B2O15, and Al11La0.497O17, along with alterations in wear mechanism and the size of wear debris. The composite coatings developed in this study shall be helpful in advanced engineering applications.

Corrosion resistance analysis of Al2O3-TiO2 composite ceramic coatings on carbon steel pipe surfaces

This study investigates the corrosion resistance of Al2O3-TiO2 composite coatings reinforced with multi-walled carbon nanotubes (MWCNTs) on carbon steel pipe surfaces. Coatings were deposited using atmospheric plasma spraying (APS) and high velocity oxy-fuel (HVOF) techniques. Microstructural analysis revealed that HVOF-sprayed coatings exhibited denser and more homogeneous structures compared to APS-sprayed coatings. Electrochemical tests in 3.5 wt% NaCl solution showed that the HVOF-sprayed Al2O3-13 wt% TiO2-1.5 wt% MWCNT coating demonstrated the lowest corrosion current density of 7.6 × 10−9 A/cm2 and the most positive corrosion potential. Hot corrosion tests in a simulated boiler environment (500°C, 1000 h) revealed that this coating also exhibited minimal weight gain (0.9 mg/cm2) and thickness loss (2 μm). The corrosion rate of the optimal coating was 0.05 mm/year, significantly lower than the bare carbon steel (2.45 mm/year). XRD analysis of corroded samples showed that HVOF-sprayed coatings maintained their original phase composition without detectable substrate corrosion products. The superior corrosion resistance of the HVOF-sprayed Al2O3-13 wt% TiO2-1.5 wt% MWCNT coating is attributed to its optimized composition, dense microstructure, and the reinforcing effect of MWCNTs. These findings provide valuable insights for developing advanced coating solutions to mitigate corrosion-related challenges in the oil and gas industry and other harsh industrial environments.

The Effect of Spray Distance on the Hot Corrosion Behavior of HVOF‐Sprayed NiCrAlY Coatings in a Simulated Gas Turbine Environment

ABSTRACTTo utilize the unique properties of coatings produced using the high‐velocity oxy‐fuel (HVOF) method, this study examined the effect of spray distance on the hot corrosion behavior of NiCrAlY coatings deposited on a steel substrate. The coating samples were obtained at spray distances of 20, 25, and 30 cm. The flow rates of oxygen and propane were maintained constant at 300 and 60 lit/min, respectively. Additionally, the powder feeding rate was 32 g/min. The samples were then subjected to the hot corrosion test in a salt mixture of Na2SO4−60% V2O5 at 900°C in an ambient atmosphere. The surface and the cross section of the samples were observed using a scanning electron microscope (SEM) and the chemical composition of different sections was determined by energy‐dispersive spectroscopy (EDS). The phases were also characterized using X‐ray diffraction analysis (XRD). The best corrosion resistance was found in the sample coating formed at a spraying distance of 20 cm, as the results showed that increasing the spraying distance led to a reduction in the thermal and kinetic energy of the flame, resulting in increased porosity in the coating. This behavior can be attributed to the low oxide content of the coating, the higher aluminum content, and the richer NiAl phase, which serves as a reservoir for aluminum.

Improving hot corrosion behaviour of Cr3C2-25NiCr coatings by reinforcing nano yttria stabilized zirconia at 850 °C

Yttria-Stabilized Zirconia (YSZ)-enhanced Cr3C2-25NiCr coatings were applied to T22 boiler tube steel using the High Velocity Oxy Fuel (HVOF) method. Conventional Ni-20Cr, 5 wt.% YSZ- Cr3C2-25NiCr, and 10 wt.% YSZ- Cr3C2-25NiCr composite coatings were prepared. High-temperature corrosion tests were conducted on both uncoated and coated samples in a Na2SO4-60%V2O5 environment at 850°C under fluctuating thermal conditions. These experiments were carried out in a silicon tube furnace at high temperatures, with each sample subjected to 50 cycles of exposure. Each cycle consisted of 1 hour in the corrosive environment followed by 20 minutes of cooling at room temperature. Corrosion products were analyzed using energy-dispersive x-ray analysis (EDS) and scanning electron microscopy (SEM). The addition of YSZ to the Cr3C2-25NiCr coatings significantly improved corrosion resistance, with the Ni-20Cr, 5 wt.% YSZ-Ni-20Cr, and 10 wt.% Cr3C2-25NiCr coatings reducing overall weight gain by 73.08%, 84.70%, and 89.96%, respectively, compared to uncoated T22 steel.

Investigation of the Influence of the Oxygen Flow Rate on the Mechanical, Structural and Operational Properties of 86WC-10Co-4Cr Coatings, as Determined Using the High-Velocity Oxyfuel Spraying Method

The structural-phase composition and tribological and performance properties of coatings based on an 86WC-10Co-4Cr composition obtained by the HVOF method at varying (150 L/min, 170 L/min, 190 L/min) oxygen flow rates were studied. The results showed that the coefficient of friction of coatings in gear oil remained almost unchanged with the variation in oxygen flow rate. However, microhardness increased significantly with an increasing oxygen flow rate, reaching a maximum at 190 L/min. An increasing oxygen flow rate was also accompanied by an increase in roughness and coating thickness, with a decrease in porosity, particularly notable at 190 L/min. Adhesion strength reached the maximum values for the A2 and A3 coatings under high loads. The phase composition of the coatings included WC, W2C and CoO phases irrespective of the oxygen flow rate, and their microstructure was characterized by a more homogeneous and dense structure. Thus, this study confirmed that the optimal oxygen flow rate for achieving an improved performance and tribological characteristics of 86WC-10Co-4Cr coatings is 190 L/min.

Physical and microstructural properties of YSZ + Cr2O3 thermal barrier coatings developed using HVOF technique

A composite coating material of Yttria-Stabilized Zirconia (YSZ) and Chromium Oxide (Cr2O3) was developed on the surface of Al-6061 substrates. The coating consisting of equal measures of the composite material of YSZ and Cr2O3 was successfully obtained using the High-Velocity Oxy Fuel (HVOF) technique. The surface roughness and coating thickness of the composite coatings are evaluated. The surface roughness (Ra) was evaluated showing an average of 6.0848 µm using the Surface Roughness Tester (SRT). The coating thickness was evaluated showing an average of 220.8 µm using the Coating Thickness Tester (CTT). The surface roughness and the coating thickness obtained are comparable to typical physical properties of Thermal Barrier Coatings (TBC’s). The microstructural evaluation of the coated specimens was performed through the Scanning Electron Microscope (SEM), showing the clear unification of materials The determination of the elemental composition of surface coatings was performed through the EDAX tests, which clearly established the elements in the coatings. This article is indicative of the achievement of TBC’s consisting of composite materials though HVOF technique as an alternative to TBC’s obtained through surface coats and bond coats.

A comparison of cold spray, atmospheric plasma spray and high velocity oxy fuel processes for WC-Co coatings deposition through LCA and LCCA

In this study, an environmental and economic assessment of WC-Co coatings deposited by Cold Gas Spray (CGS), Atmospheric Plasma Spray (APS) and High Velocity Oxy Fuel (HVOF) spray technologies is carried out. Using SimaPro LCA software, several environmental impact categories are analyzed to compare their environmental performance. The economic analysis includes capital and operating expenditures. The results have highlighted that all three processes exhibit low environmental impact in terms of CO2 emissions but the performance of the CGS process is heavily influenced by the low deformability of WC-Co, while the APS process is affected by high electricity consumption. In terms of economic analysis, the HVOF process exhibits the best performance, while the CGS process requires most time to deposit the coating, and consequently, it is the process where the workforce component is most significant. These results depend on the fact that CGS might not be the most suitable deposition technique for fabricating WC-Co coatings.

Effect of HVOF method spraying parameters on phase composition and mechanical and tribological properties of 86WC-10Co-4Cr coating

Valve components used in the petroleum industry are subjected to intense wear during operation, which leads to a sharp decrease in their durability. Usually, the often subjected to the wear process surface of the valves is treated by tungsten carbide cladding to improve its durability. Because of the difficulty in applying tungsten carbide using conventional surfacing techniques, high velocity oxyfuel (HVOF) spraying technology is rec- ommended. In this work, the mechanical, tribological properties and phase composition of 86WC-10Co-4Cr composition coatings obtained by HVOF Termika-3 high-velocity gas-fuel spraying were investigated. Vary- ing the technological parameters of spraying was carried out by changing the spraying distance, which led to differences in the thickness of the coatings. The phase composition, microstructure and distribution of ele- ments were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM) methods. The hardness of the samples was measured on a microhardness tester using the Vickers method, the friction coef- ficient and the wear rate were investigated using a friction and wear tester. It was determined that the surface of the coatings had developed character and high roughness. The results of X-ray phase analysis showed the predominance of hexagonal WC as the major phase, with a small amount of hexagonal tungsten carbide W2C as the minor phase, and the minor presence of cobalt oxide CoO. It was found that the increased wear re- sistance and low friction coefficient of 86WC-10Co-4Cr coatings are explained by the high volume fraction of hard and stable WC grains with high resistance to wear.

Preparation of in-situ synthesized TiC/AlSi30Cu5 coating by high velocity oxy-fuel (HVOF) spraying: Microstructure evolution, mechanical properties, and tribological behavior

To enhance the wear resistance of AlSi30Cu5 coating even further, TiC-reinforced AlSi30Cu5 (TiC/AlSi30Cu5) coatings were prepared using TiH2-C-AlSi30Cu5 agglomerates by HVOF. The results confirmed that the phases composition of TiC/AlSi30Cu5 coating included α-Al, β-Si, θ-Al2Cu, β-Ti, TiC, rutile TiO2 (R-TiO2), and anatase TiO2 (A-TiO2). The mechanical properties of TiC/AlSi30Cu5 coating, microhardness and fracture toughness, were greatly improved by 37.8 % and 5.5 times. The combination of high hardness, high fracture toughness and residual graphite significantly strengthened the wear resistance of TiC/AlSi30Cu5 coatings by 91.1 % and 54.1 % over the substrate and AlSi30Cu5 coating. Analysis of the worn morphologies and abrasive debris revealed that the wear mechanisms of TiC/AlSi30Cu5 coating were primarily abrasive wear, with contributions from oxidative wear and fatigue wear.

Effect of HVOF parameter on titanium oxide (TiO2) coating characteristics on AZ81 magnesium alloy

High-velocity oxy-fuel (HVOF) coating to enhance the erosion, wear, and corrosion-resistant properties crucial for orthopedic applications. HVOF is distinguished for its capability to provide surfaces with a dense and superior finish. Porosity and hardness serve as vital process variables in assessing performance. This current study aims to optimize HVOF process parameters to minimize porosity values in titanium oxide (TiO2) coatings applied on AZ81 magnesium substrate. Oxygen flow, liquefied petroleum gas (LPG) flow, coating material feed rate, and spray distance were selected due to their significant impact on the coating quality. Statistical techniques such as response surface methodology (RSM), analysis of variations, and design of experiments (DoE) were employed to obtain the necessary results. The findings indicate that LPG flow has the most significant influence on coating quality, followed by standoff distance, oxygen flow rate, and feed rate. The coating obtained using optimal spray parameters exhibits a lower surface porosity of 0.86 vol.% and achieves a greater hardness of 922 HV. This has been confirmed through validation via the response graph. Consequently, the optimized parameters for TiO2 deposit entail an oxygen flow rate of 266 lpm, an LPG flow rate of 68 lpm, a powder feed rate of 35 g/min, and a spray distance of 236 mm. KEY WORDS: High-velocity oxy-fuel, Response surface methodology, Porosity, Hardness, AZ81 Magnesium alloy, Titanium oxide Bull. Chem. Soc. Ethiop. 2024, 38(6), 1869-1886. DOI: https://dx.doi.org/10.4314/bcse.v38i6.28

Microstructure evolution mechanism of WB-doped Fe-based amorphous composite coating under proton beam irradiation

Fe-based amorphous coatings exhibit exceptional irradiation resistance attributed to their distinct topologically disordered structure, rendering them highly attractive for advanced nuclear energy applications. The incorporation of WB secondary phase doping can notably alter the coating to enhance its operational safety. In this investigation, three different Fe-based composite coatings, with varying WB doping levels of 5 %, 10 %, and 15 % were fabricated through the High-Velocity Oxy-Fuel (HVOF) spraying technique. Irradiation tests were conducted at room temperature utilizing a proton beam with an energy of 1.52 MeV to simulate neutron irradiation environment in a nuclear reactor. The microstructure evolution before and after irradiation was systematically investigated with XRD, SEM, and TEM techniques. The results demonstrated that proton irradiation induced free volume, crystallization and H bubbles evolution. The doping of WB diminished the proton implantation dose threshold for segregation in irradiation plateaus while enhancing the growth of precipitates around the damage zone by inducing the production of M23C6 carbides and, at the same time, increasing the probability of H bubble nucleation and growth. These findings provide insights for iterative updates in Fe-based amorphous materials, informing their further development and application.

Comparison on erosion performance of HVOF sprayed NiCrSiBCFe-WC-Co and NiCrSiBCFe-Cr3C2NiCr coatings

Hard coatings are used to improve the wear resistance of various engineering materials while maintaining the mechanical properties of the base material. In this work, the high-velocity oxy-fuel (HVOF) thermal spray process was used to deposit NiCrSiBCFe(65)-WC-Co(35) and NiCrSiBCFe(65)-Cr3C2-NiCr(35) coatings on SA213-T17 boiler steel to improve the erosion wear resistance of the base material. The erosion wear behaviours of the specimens were investigated using an air jet erosion tester at 30 and 90° impact angles and 400 ± 25 °C temperature. The surface morphologies of the as-deposited and eroded samples were examined using the Scanning electron microscope. The NiCrSiBCFe-WC-Co ceramic coating deposited on SA213-T17 boiler steel exhibited superior erosion resistance compared to NiCrSiBCFe-Cr3C2-NiCr coating and boiler steel under all the tested conditions. This enhanced performance can primarily be attributed to the higher hardness of the NiCrSiBCFe-WC-Co coating due to the presence of harder phases such as WC, W2C and NiCo2O4.

Erosion wear performance of HVOF sprayed WC-10Co-4Cr + 2% TiO2 coating on SS-409 using slurry jet erosion tester

Erosion is a phenomenon and is the primary cause of failure in numerous slurry transportation equipment such as pump impellers, pipeline fittings, etc. It reduces the working life of the equipment and is thus an essential factor in the design, choice, and operation of any system. Pipeline materials used to convey slurry often experience severe wear from erosive forces. Researchers are interested in minimizing erosion wear using different coatings to increase equipment life. The High-Velocity Oxy-Fuel (HVOF) spray technique was employed to deposit WC-10Co-4cr + 2% TiO2 coating on the SS409. The erosion wear was evaluated using a slurry jet erosion tester of uncoated and coated materials with sand as the erodent. The impact of impingement angle, velocity, time, and other parameters was studied. On the erosion wear of uncoated and coated materials, it was found that the influence of jet velocity was greater than the impact of other parameters. The deteriorated surfaces were analyzed using a scanning electron microscope (SEM). The erosion wear resistance of SS 409 was significantly improved by the WC-10Co-4cr + 2% TiO2 coating. The coating demonstrated a brittle mechanism of erosion wear. Furthermore, image processing software investigated the mechanism of erosion wear.

Experimental and computational investigation of FGM coated cylinder liners prepared using HVOF technique

In the present work, to improve the wear resistance of the cylinder liner, without affecting the heat dissipation, cast steel cylinder liners are coated with five-layer Functionally Graded Material (FGM) coatings prepared using High-velocity oxy-fuel (HVOF) technique. The powders were designated as C1 (WC-10Co-4Cr) which is Tungsten Carbide with 10% Cobalt and 4% Chromium, C2 (WC-12Co) which is Tungsten Carbide with 12% Cobalt and C3 (Ni-25Cr) which is Nickel with 25% Chromium. The results revealed that the FGM coating designated as Functionally Graded Coated Sample-1 (FGCS-1) wears less compared to Functionally Graded Coated Sample-2 (FGCS-2) and Functionally Graded Coated Sample-3 (FGCS-3), due to the presence of wear resistive elements in the composition and uniform material homogeneity. Numerical analysis of FGCS-2, conducted using Ansys Fluent software, revealed a negligible temperature gradient across the coating thickness. This is due to the highly conductive coating material and the extremely thin coating layers, making it suitable for engine cylinder liner applications where less wear and high heat transfer rate is desirable.

Elevated temperature wear and friction performance of WC-CoCr/Mo and WC-Co/NiCr/Mo coated Ti-6Al-4V alloy

The effect of adding Mo to WC-based coatings on the microstructure and dry sliding wear performance at elevated temperatures is investigated. The WC-based coatings are deposited using a high-velocity oxy-fuel process on the titanium-31 substrate. The coating was characterized by microstructure, microhardness, porosity, surface roughness, density, and bond strength. The wear and friction behavior of coatings was evaluated using a ball-on disc tribometer at temperatures of 200, 400, 600, and 800 °C and loads of 20 and 30 N. SEM-EDS and an optical profilometer were utilized to evaluate the wear rate and mechanism. The microhardness and bond strength of WC-CoCr/10%Mo coating is more than that of WC-Co/20%NiCr/10%Mo coatings. The WC-CoCr, WC-CoCr/10%Mo, and WC-Co/20%NiCr/10%Mo coatings exhibited decreasing wear rates up to 600 °C, transitioning to an increase at 800 °C. The oxide phases of CoWO4, WO3, MoO3, CoMoO4, and NiMoO4, formed at 600 °C, aid in reducing the rate of wear and friction coefficient. However, the wear rate slightly increased at 800 °C due to vigorous oxidation and softness of coatings. The friction coefficient of WC-CoCr, WC-CoCr/10%Mo, and WC-Co/20%NiCr/10%Mo coating decreases with increasing temperatures due to the lubricating properties of oxide phases on the worn surface. The WC-CoCr/10%Mo coating demonstrates a lower friction and wear rate than the WC-CoCr and WC-Co/20%NiCr/10%Mo coating. At 200 °C, the predominant wear mechanisms were abrasive and fatigue wear, while at 800 °C, oxidative wear, abrasive wear, and adhesive wear were observed.

High-temperature erosion behavior of Al2O3 reinforced Inconel625 high velocity oxy-fuel sprayed and direct-aged composite coatings

In this study, Inconel625+30%Al2O3 (IN30AL) blended powders were sprayed on a commercially used boiler steel ASTM SA210 GrA1 using high-velocity oxy-fuel approach (HVOF). The microstructure, mechanical properties and elevated temperature erosion behavior of post-processed coatings and as-sprayed IN30ALcoatings were investigated. The elevated temperature erosion studies on IN30AL coatings both as-sprayed and post-processed were investigated at 900 °C temperature at two impact angles 30° and 90° using standard high temperature erosion test rig. Phase composition, interface of substrate/coating, and morphologies of eroded coatings were examined using x-ray diffraction, x-ray maps, scanning electron microscope, & energy dispersive spectrometer techniques. Compared with the as-sprayed IN30AL coatings, the heat-treated coatings have refined microstructure, better mechanical properties which improve the elevated temperature erosion resistance of IN30ALcoatings.

Effect of High-Velocity Oxy-Fuel (HVOF) Tungsten Carbide Nickel (WC-Ni) Coating on the Fatigue Properties of Carbon Steel with Different Spraying Distances

Effect of High-Velocity Oxy-Fuel (HVOF) Tungsten Carbide Nickel (WC-Ni) Coating on the Fatigue Properties of Carbon Steel with Different Spraying Distances

Effect of Heat Treatment on Mechanical Properties and Corrosion Response of HVOF Sprayed High Entropy Alloy Coatings

Surface and sub-surface related degradation of steels can be minimized using suitable surface coatings. High entropy alloys (HEA) are prominent and emerging materials among many coating materials. The current study investigates the effect of heat treatment of HEA coating on mechanical, metallurgical, and corrosion properties. The HEA coatings on SS304 steel were deposited using a High-Velocity Oxy-Fuel (HVOF) thermal spray process. The developed coatings were furnace heat treated at 700 °C, 900 °C, and 1100 °C, respectively, and their performance was benchmarked with the as-sprayed coatings. The metallurgical, mechanical, and microstructural analyses were performed using X-ray diffraction (XRD), Nanoindentation, Scratch test, and Field Emission Scanning Electron Microscope (FESEM) techniques. The corrosion response of the as sprayed and heat-treated coatings were recorded using a Potentiostat. The results indicated that as-sprayed coatings consisted of a single-phase BCC solid solution; however, the single-phase changed to a dual dual-phase system after heat treatment (BCC+FCC). The 900 °C heat-treated HEA coating exhibited superior mechanical and corrosion properties. But those characteristics started diminishing when the heat treatment temperature exceeded 900 °C. The introduction of the new FCC phase softened the coating, thereby leading to the evolution of microcracks in the coating. These micro-cracks acted as channels for electrolyte diffusion and further corroded the coatings. The current study surmised that HVOF-sprayed HEA coating should not be heat treated at above 900 °C.

Artificial neural network model for wear characteristic analysis of WC-10Co4Cr and Stellite 6 thermal spray coatings

In this paper, wear characteristic analysis of the thermal spray powders namely WC-10Co4Cr and Stellite 6 high velocity oxy-fuel (HVOF) coated on SS 316 L steel were studied. Artificial neural network (ANN) model predicts the accuracy by the coefficient of R= 0.99 and R2 = 0.98. The R2 of present ANN model was far better as compared to regression models Enbt (0.85), Coarse Tree (0.04), linear regression i.e. LR (0.37), and Enbag (0.19). Results show that uncoated SS 316 L steel was severely eroded, and wear occurred on the bare SS 316 L was about 7.5 ± 2.5 times higher as compared to WC-10Co4Cr coating, and 3.5 ± 1.5 times than Stellite 6 coating.

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

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