High Velocity Oxygen Fuel Research Articles

Effect of High-Energy Shot Peening on Properties of High-Velocity Oxygen-Fuel Spraying

A Cr3C2-Al2O3-NiCr composite coating was prepared on an INCONEL600 alloy surface through high-velocity oxygen-fuel spraying followed by further processing through high-energy shot peening to create the composite coating. The microhardness and friction properties of the composite coating are analyzed by a microhardness tester and reciprocating friction tester. The microscopic structure and wear trace of the composite coating were analyzed by scanning electron microscope (SEM). The element distribution of the coating was analyzed by energy-dispersive spectroscopy (EDS). The porosity of the coating was detected by industrial CT. The phase and residual stress of the coating were tested by X-ray diffraction (XRD). The electrochemical corrosion and friction wear performance of the samples under different surface states were discussed. The results showed that the compactness of the coating was improved and the porosity was significantly reduced after high-energy shot peening. The high-energy shot peening did not alter the phase composition of the coating but introduced residual compressive stress. The microhardness of theCr3C2-Al2O3-NiCr high-velocity oxygen-fuel coating can reach 2.9 times that of the INCONEL600 substrate, and the hardness of the coating after high-energy shot peening can reach 3.9 times of that of the substrate. After high-energy shot peening, the corrosion resistance of the coating in HCl solution is improved. Compared with the INCONEL600 substrate, the friction coefficient and calculated wear rate of the Cr3C2-Al2O3-NiCr high-velocity oxygen-fuel coating decrease by 62.5% and 79.6%, respectively. After high-energy shot peening, the friction coefficient and calculated wear rate of the coating decrease by 75% and 98.7%, respectively.

Evaluation of tribological characteristics for HVOF deposited Ni based self-lubricating coatings with different h-BN composition

The tribological behaviour of High Velocity Oxygen Fuel (HVOF) thermal spray deposited coatings, namely Ni-Al-Ag-MoS2 (NAMB0), Ni-Al-Ag-MoS2–5 wt. % h-BN (NAMB5), Ni-Al-Ag-MoS2–7.5 wt% h-BN (NAMB7.5) and Ni-Al-Ag-MoS2–10 wt% h-BN (NAMB10), onInconel 718 as substrate material were assessed against an alumina ball as a counterface. The tests were performed using a rotary tribometer under “ball on disc configuration” at various testing loads of 5, 10, 15, 20 N and a fixed sliding speed of 0.5 m/s at room temperature (RT) of 25 °C. The weight percent of MoS2 and Ag as a solid lubricant were kept constant whereas h-BN wt% was varied in the coated samples i.e. 0, 5, 7.5 and 10 wt. According to test results, as the load increases from 5 to 15 N, both coefficient of friction (COF) and wear rate exhibit a decreasing trend in nature, thereafter, by increasing the load up to 20 N, the reverse action is evident. However, the coating having 7.5 wt% h-BN along with MoS2 and Ag has revealed the best tribological behaviour under the investigational parameters. The observed behaviour has been attributed to the synergistic effect of Ag, MoS2 and h-BN and optimum content of h-BN in NAMB7.5 coatings enhances the tribological performance to its apex.

Cavitation-silt erosion behavior and mechanism in simulated sea water slurries of cermet coatings manufactured by HVOF spraying

Understanding the interaction between the sea water slurries and flow-handling components is important for enhancing the cavitation-silt erosion (CSE) resistance of the ocean power generation systems. In this manuscript, two cermet coatings (i.e., Cr3C2-25(NiCr) coating and WC-10(Ni) coating) were manufactured via a high-velocity oxygen fuel (HVOF) spraying method, and influences of sand concentrations (SCs) as well as flow velocities (FVs) on their CSE characteristics in simulated sea water slurries (SSWS) were investigated. Results indicated that the Cr3C2-25(NiCr) coating exhibited larger porosity, lower hardness (H) and elastic modulus (E), stronger ability to resist corrosion in 3.5 wt.% saline solution as well as worse CSE resistance in SSWS, and its CSE resistance was more affected by both the SC and FV by comparison to the WC-10(Ni) coating. Both SC and FV had a positive effect on the CSE damage for the Cr3C2-25(NiCr) and WC-10(Ni) coatings, while SC had more influence on their CSE resistances than FV. The CSE deterioration mechanisms in SSWS under different SCs and FVs of the Cr3C2-25(NiCr) and WC-10(Ni) coatings were also compared and revealed.

Fabrication of metal-ceramic matrix composite multilayer coatings with diamond protective layer for heating elements in the vacuum systems

We report a novel methodical approach to the design of multilayer composite coatings with a final diamond protective layer for vacuum applications, specifically for controlled heating in vacuum apparatus, cryogenic systems, and for space applications. Diamond is a promising option to add unique properties to such multilayers while maintaining fast and uniform heat distribution. The multilayer composite systems were based on the insulating layer - Al2O3, a Cu-based interconnect layer and a TiO2-based heating element. The study demonstrated the compactness and high temperature resistance of the developed composite system, which are necessary for real-world applications. To enhance the functional properties of the deposited multilayer coatings, diamond films were deposited on them using microwave plasma enhanced chemical vapor deposition (MPCVD). The diamond film was deposited as the last layer of the metal-ceramic multilayer coating prepared from various powders using high velocity oxygen fuel (HVOF) and atmospheric plasma spraying (APS) deposition techniques.

Fretting wear behavior of aluminum coatings

The aluminum bronze coating is a type of soft solid lubricant film with excellent performance. In this work, to improve the wear resistance and tribological behavior of the aluminum alloy, the aluminum bronze coatings were prepared on aluminum alloy substrates using the High- Velocity Oxygen Fuel (HVOF) system. Fretting wear tests were performed on the coatings at 200 °C with different frequencies to analyze the wear behavior. The worn surface was characterized by scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). The results showed that as the frequency increased from 5 Hz to 15 Hz, the coefficient of friction increased from 0.653 to 0.929. It then decreased to 0.890 at 20 Hz. There was an overall trend of the coefficient of friction increasing and then decreasing. The worn surface’s morphology changed from pits to bulges. At a low frequency, the wear mechanism was abrasive wear with delamination. As the frequency increased, adhesive wear was observed and gradually became the dominant wear form. Oxidation occurred on the surface of the worn tracks caused by the high temperature and thermal effect of high-frequency micromotion. Due to the intensification of the oxidation phenomenon, oxidation films formed on the worn surface. The wear rate of the coating was significantly reduced. The oxide was identified as mainly CuO and Cu2O. The presented results confirmed that the aluminum bronze coating fabricated via HVOF exhibited a great resistance performance even at a high frequency.

Study on Microstructure and Properties of Thermal Barrier Coating for Gas Turbine

Thermal barrier coating (TBC), which can protect the metallic components from hot gas, is one of the core technologies to achieve the development goal of higher thermal efficiency and lower emission for gas turbine. A double-coat TBC was prepared on the Mar M247 substrate of turbine blade for gas turbine which consisted of a CoNiCrAlY bond coat(BC) was prepared by high velocity oxygen fuel(HVOF) and a ZrO2-8Y2O3(8YSZ) top coat(TC) was prepared by atmospheric plasma spraying (APS).The microstructure of the TBC was analyzed by optical microscope(OM) and scanning electron microscope(SEM), and the thermal insulation and thermal shock resistance of the TBC were investigated. The results show that the homogeneous and fine microstructure in TBC is obtained,the interfacial bonding between the top coat and the bond coat, between the bond coat and the substrate is well. The thermal insulation temperature can reach 156°C,under the condition of test temperature of 1150°C and cooling air flow of 4 m3/h. And the thermal shock resistance is greater than 100 cycles at the test condition of 1050 °C.

Long-term oxidation behavior for Ni-5Al coating in air-H2O at 650 ℃

The oxidation behavior of the Ni-5Al coating produced by high-velocity oxygen-fuel on the Fe-Cr alloy was investigated at 650 ℃ in air containing 20% water vapor. The oxidation kinetics of the Ni-5Al coating were establish by classical oxidation theory for 8000 h. According to the oxidation kinetic data, we calculated the time of breakaway oxidation occurred and compared between experimental measurement and model calculation of internal oxidation. And then the correlation between oxidation depth and oxidation time was plotted according to the measurement and model calculation.

APPLICATION OF HVOF TECHNOLOGY FOR WC-BASED WEAR-RESISTANT COATINGS – AN OVERVIEW

The article presents the main problems of wear and service life of slide gate valves for trunk pipeline transport of oil and gas industry. One of the possible ways to solve these problems is the application of a thin layer of wear-resistant and corrosion-resistant coatings. Due to the ever-increasing cost of materials, as well as the increased requirements for materials, coating methods have recently become increasingly important. Among the gas-thermal coating methods, the High Velocity Oxygen-Fuel Spray (HVOF) technology is a new and rapidly developing technology that produces high density coatings with porosity less than 1%, with improved hardness and adhesion as well as improved erosion, corrosion and wear resistance properties. This overview article provides a comparative review of the characteristics of carbide coatings produced using different spraying technologies.

One-step gas phase sulfided NiFe coating as self-supporting electrode for high efficiency oxygen evolution reaction

The development of cost-effective oxygen evolution reaction (OER) electrocatalytic electrodes is one of the essential means of applying green hydrogen energy. Due to the complex steps in the anodic OER, the high overpotential hinders the kinetics of water splitting. In this paper, the sulfided NiFe coating was innovatively designed as a self-supporting OER electrode by high-velocity oxygen fuel (HVOF) spraying coupled with one-step gas phase sulfuration. The thickness of the NiFe coating is approximately 20 μm. After the sulfuration treatment, the surface of the NiFe coating is remolded into a uniform rock sugar-like structure, and simultaneously forms new NiS and Ni3S4 phases. The sulfided NiFe coating electrode shows relatively low overpotentials of 220 mV and 253 mV at the current density of 10 mA cm−2 and 100 mA cm−2, respectively, and the Tafel slope is as low as 28.6 mV dec−1. The excellent electrocatalytic activity is mainly attributed to the synergistic effect of sulfides, the adsorption of OH− by the Ni3+ in alkaline electrolyte, and the acceleration of O2 separation by the S2− through promoting the cleavage of O–O bonds. In addition, the sulfided NiFe coating electrode also has a small charge transfer resistance, and the potential stability is as high as 98.1% in the 70 h stability test. Therefore, the development of sulfided transition metal coating electrodes can provide a new idea for the large-scale industrialization of water splitting.

Numerical and Experimental Investigations of CoNiCrAlY Particle Suspension Dynamics in Kerosene-Oxygen High Velocity Oxygen Fuel Spraying

Three-dimensional computational fluid dynamics (CFD) modelling is employed to simulate a typical high velocity oxygen fuel process (HVOF) under laboratory operating conditions. Two different modelling approaches, viz., the continuum and discrete models, are engaged to model the liquid fuel kerosene, and their influence on the resulting primary gas dynamics is investigated. Numerical results of the primary gas dynamics are validated against the available measurements and found to be in good agreement. It is observed that the fuel droplets less than 5 μm react completely inside the combustion chamber, whereas the larger droplets do not. With increasing fuel droplet size, the chemical reaction gets extended to the downstream of the combustion chamber, resulting in decreased flame temperature. Thus, it is inferred that a fuel droplet size of up to 5 μm yields better combustion characteristics. Discrete solid CoNiCrAlY particles are then injected into the high velocity primary gas stream, and their inflight dynamics are simulated. Results reveal that a maximum mean particle velocity of 700 m/s and a maximum particle temperature of 1350 K may be achieved under the given operating conditions. Particle deposit shape and size are determined both numerically and experimentally and found to be in good agreement. The influence of substrate stand-off distance on the particle deposit characteristics is investigated and reported in detail.

Time-varying evolutionary mechanism analysis of the multiphase flow during high-velocity oxygen-fuel (HVOF) thermal spraying WC-12Co particle

HVOF thermal spraying with the fuel of aviation kerosene has unique advantages for spraying WC-12Co ceramic particles. The time-varying evolution mechanism of the multiphase flow formed by the particles wrapping with the combustion flame flow is quantitatively revealed, which is essential for preparing of high-quality coatings. In this study, the breakup and gasification process of kerosene droplet was considered. The fuel droplet, flame flow and spraying particles were directly coupled. Based on the computational fluid dynamics (CFD) method, a transient evolution model of HVOF thermal spraying multiphase flow with JP5000 spray gun was established. The Euler-Lagrange method of bidirectional coupling was used to track the continuous and discrete phases. The spraying combustion flame characteristics were expressed by the realizable k-ε turbulence model and eddy dissipation model (EDM). The results show that the multiphase coupling transient evolution model quantitatively captures the nonlinear changes of the breaking and gasification for the kerosene droplet, combustion reaction, particle flight behavior and others during spraying. The kerosene droplets in the combustion chamber aggregate with each other to form large droplets, which are rapidly broken and gasified in the peripheral areas. Due to the violent combustion, a gas-phase circulation was formed by the heat and cold air. As the combustion progresses, the flame flow becomes stable and orderly. When particles with a size of 20 to 30 μm impact the substrate, the particle temperature is close to the solid phase temperature, and the velocity is fast. The particle temperature and velocity decrease with the increase of the particle size.

Wear and corrosion behaviour of the cryogenically treated tungsten carbide coatings

ABSTRACT The WC–12Co coatings were deposited on SS 410 substrates using a high-velocity oxygen fuel (HVOF) process and the coatings were heat-treated at 750°C for 1 h in argon environment. Further, the coatings were subjected to cryogenic treatment for 1, 2, 8 and 24 h, and its influence on the reciprocating sliding wear and corrosion characteristics was studied. The structural changes in the coatings after post-treatment were assessed by X-ray diffraction analysis and Raman spectroscopy. Microhardness was improved for cryogenically treated coatings due to the α-Co transformation into ϵ-Co. Cryogenic treatment duration was not having a significant effect on the microhardness values. However, the specific wear rate was influenced by the cryogenic treatment duration. Also, corrosion resistance was increased with the increased cryogenic treatment duration. The protective layers consisting of WO3 and Co3O4 phases formed during the cryogenic treatment are attributed to the improved corrosion resistance of the coatings.

Effects of Cr contents on tribological and corrosion behavior of HVOF sprayed Ni-based alloy coating

High-velocity oxygen fuel (HVOF) spray process was employed to fabricate nickel-based alloy coatings composed of different chromium contents (NC-A, 7.15 wt%; NC-B, 16.98 wt%). Based on the results of the tribocorrosion test, a mechanical plowing effect can be observed on the coatings at low applied potential (< +100 mVSCE), and the wear behavior of coatings was aggravated by intensified corrosion effect when a higher potential (>+300 mVSCE) was applied. Through the quantitative analyses, we have concluded that the total weight loss (Wtotal) of the coatings increased significantly as a function of the growing potential loading, and the synergic effects between corrosion and wear played a vital role in the overall weight loss.

Plasma nitrided CoCrFeNiMn high entropy alloy coating as a self-supporting electrode for oxygen evolution reaction

Noble metal electrocatalytic electrodes used in water electrolysis for hydrogen production are expensive and non-noble metal nanoparticle catalysts are not conducive to large-scale production. In this paper, the CoCrFeNiMn high entropy alloy (HEA) coating was prepared by high-velocity oxygen fuel (HVOF) spraying on the surface of stainless steel as a self-supporting oxygen evolution electrode, and the electrocatalytic activity of the electrode was further improved by plasma nitriding. The results show that the CoCrFeNiMn coating is mainly composed of FCC solid solution phase and MnCr2O4 spinel phase, and the thickness of the coating is approximately 100 μm. After nitriding, the surface of the coating is reshaped from the original semi-molten morphology to cauliflower-like structure, and the N atoms are mainly enriched in the MnCr2O4 phase. In addition, the binding energies of Co, Cr, and Ni to O in the nitrided coating decrease by 0.7 eV, while the binding energies of Fe and Mn to O are not significantly affected. The overpotential of the nitrided CoCrFeNiMn coating decreases from 363 mV to 309 mV at the current density of 10 mA cm−2, and it has a smaller Tafel slope and charge transfer resistance, and larger double-layer capacitance compared to the CoCrFeNiMn coating. Both the CoCrFeNiMn coated electrodes with and without nitriding show good long-term stability during the 60 h stability test. The high entropy alloy coating coupled with plasma nitriding technique provides a new research idea for the eletrocatalytic field of the water splitting.

Thermal Ablation Experiments of Carbon Phenolic and SiC-Coated Carbon Composite Materials Using a High-Velocity Oxygen-Fuel Torch

For future spacecraft TPS (heat shield) applications, ablation experiments of carbon phenolic material specimens with two lamination angles (0° and 30°) and two specially designed SiC-coated carbon-carbon composite specimens (with either cork or graphite base) were conducted using an HVOF material ablation test facility. The heat flux test conditions ranged from 3.25 to 11.5 MW/m2, corresponding to an interplanetary sample return re-entry heat flux trajectory. A two-color pyrometer, an IR camera, and thermocouples (at three internal locations) were used to measure the specimen temperature responses. At the 11.5 MW/m2 heat flux test condition, the 30° carbon phenolic specimen's maximum surface temperature value is approximately 2327 K, which is approximately 250 K higher than the corresponding value of the SiC-coated specimen with a graphite base. The 30° carbon phenolic specimen's recession value is approximately 44-fold greater, and the internal temperature values are approximately 1.5-fold lower than the corresponding values of the SiC-coated specimen with a graphite base. This indicates that increased surface ablation and a higher surface temperature relatively reduced heat transfer to the 30° carbon phenolic specimen's interior, leading to lower internal temperature values compared to those of the SiC-coated specimen with a graphite base. During the tests, a phenomenon of periodic explosions occurred on the 0° carbon phenolic specimen surfaces. The 30° carbon phenolic material is considered more suitable for TPS applications due to its lower internal temperatures, as well as the absence of abnormal material behavior as observed in the 0° carbon phenolic material.

Crack Evolution and Computational Model Based Thermal Stress Evaluation of Laser Cladding Based on HVOF Sprayed WC/Co Deposits

A comprehensive experimental study on the high-velocity oxygen-fuel (HVOF) sprayed tungsten carbide/cobalt (WC/Co) deposits using laser cladding was conducted. A response surface methodology based on a central composite design was used to analyze, predict and optimize the WC/Co deposits of the laser-based HVOF sprayed coatings. The morphologies and microstructures of the laser clads were characterized using optical microscope, scanning electron microscope and X-ray diffraction techniques. The crack behavior and residual stress-based fractures were explored. In addition, the relationships between the residual stress of the laser clad and three factors: laser power, scanning speed and stand-off distance were examined. Further, optimization of the control factors: laser power, scanning speed and stand-off distance to minimize the residual stress was attained using a response surface methodology. The resulting lower residual stress has decreased the fracture crack activities and did not easily induce delamination in the laser clads. Findings from this study would greatly contribute to optimizing the experiments and achieve an enhanced structural evolution in the protective coating of traditional handicraft products by laser cladding.

Development of rGO doped alumina-based wear and corrosion resistant ceramic coatings on steel using HVOF thermal spray

This study deals with the development of hard, wear-resistant ceramic-based coatings containing Alumina (Al2O3) doped with 0.8% Ceria (CeO2) and reduced graphene oxide (rGO, 0–0.2%) on 17-4 PH steel using High-Velocity Oxygen Fuel (HVOF) thermal spray process. The tribological response of the coatings were recorded using Universal Tribo Tester. The corrosion response of the coatings was studied using potentiostat galvanostat corrosion setup. The introduction of rGO to the Al2O3–CeO2 helps in reducing the coefficient of friction and better corrosion response in the coatings. The elastic modulus and nano hardness of Al2O3–CeO2-rGO coating are ≈101% and ≈ 87% higher than that of Al2O3–CeO2 coating, respectively. The specific wear rate of Al2O3–CeO2-rGO coating is reduced by ten times compared to that of 17-4 PH steel. The improved properties can be attributed to the dense microstructure of the coatings with the introduction of rGO and participation of rGO in the tribological process.

Microstructure and cavitation-silt erosion behavior of two HVOF-sprayed hardfacing coatings for hydro-turbine applications

The cavitation-silt erosion (CSE) has caused severe technical challenges and economic losses to the hydro-turbine operated in silt-laden river. In this manuscript, two hardfacing (i.e., WC-20(Cr3C2)-7Ni and Cr3C2-25(NiCr)) coatings were manufactured via a high-velocity oxygen fuel (HVOF) spraying method, and effects of flow velocities (FVs) and sand concentrations (SCs) on their CSE behaviors with the help of a rotating disk rig facility were investigated. Results indicated that the WC-20(Cr3C2)-7Ni coating exhibited lower porosity, higher KIC, H/E and H3/E2 as well as superior CSE resistance, and its CSE resistance was less affected by FV as well as SC compared with the Cr3C2-25(NiCr) coating. Both FV and SC had a positive effect on the CSE degradation of the two hardfacing coatings, while SC had a greater effect on their CSE resistances than FV. With increasing FV and SC, the WC-20(Cr3C2)-7Ni coating experienced the CSE damage of the few micro-cracks, scattered cavitation pinholes, fracturing of carbide particles, pronounced scour marks, isolation and peeling off of carbide particles, and crater formation, while the CSE process of the Cr3C2-25(NiCr) coating primarily included the micro-cracks and scattered cavitation pinholes, peeling off of chromium carbide particles, long and deep scour marks, and coating spalling and crater formation.

Hot Corrosion Behavior of TWAS and HVOF NiCr-Based Coatings in Molten Salt.

In order to extend the life of boilers by applying an anti-corrosion coating without the need to dismantle them, it is advisable to find coatings that can be applied using cheaper and portable techniques, such as Twin Wire Arc Spray technology (TWAS). In this study, we compare selected NiCr-based coatings and two uncoated steel substrates (steel 1.7715 and 1.4903). Two coatings, Cr3C2 - 25% NiCr and Hastelloy C-276 are deposited using High velocity oxygen-fuel technology (HVOF) and three coatings, NiCrTi, NiCrMo, and Inconel 625, are deposited using TWAS. In addition to the corrosion weight gain during 50 cycles of loading in an 18% Na2SO4 and 82% Fe2(SO4)3 salt environment at 690 °C evaluated using the gravimetric method, the microstructure and phase composition of the coatings were analyzed on the samples after the exposure in order to compare the properties and gain a deeper understanding of the corrosion kinetics. Coating cross-sections and free-surfaces were observed with a scanning electron microscope (SEM) with an energy-dispersive (EDX) system. The phase composition was investigated using X-ray diffraction (XRD) and Raman spectroscopy. No significant differences were observed between the TWAS and HVOF coating methods for the coatings compared. Due to the similar corrosion products found on all coatings, a very effective corrosion protective layer was formed on the surface, forming a barrier between the corrosive environment and the coating regardless of the used deposition technology. Therefore, for industrial use on the inner surface of coal-fired boilers we recommend NiCrTi, NiCrMo, or Inconel coatings prepared with the more cost-effective and portable TWAS technology.

Effects of frequency on the fretting wear behavior of aluminum bronze coatings

The aluminum bronze coating is a type of soft solid lubricant film with excellent performance. In this work, to improve the wear resistance and tribological behavior of the aluminum alloy, the aluminum bronze coatings were prepared on aluminum alloy substrates using the High-Velocity Oxygen Fuel (HVOF) system. Fretting wear tests were performed on the coatings at 200 °C with different frequencies to analyze the wear behavior. The worn surface was characterized by scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). The results showed that as the frequency increased from 5 Hz to 15 Hz, the coefficient of friction increased from 0.653 to 0.929. It then decreased to 0.890 at 20 Hz. There was an overall trend of the coefficient of friction increasing and then decreasing. The worn surface's morphology changed from pits to bulges. At a low frequency, the wear mechanism was abrasive wear with delamination. As the frequency increased, adhesive wear was observed and gradually became the dominant wear form. Oxidation occurred on the surface of the worn tracks caused by the high temperature and thermal effect of high-frequency micromotion. Due to the intensification of the oxidation phenomenon, oxidation films formed on the worn surface. The wear rate of the coating was significantly reduced. The oxide was identified as mainly CuO and Cu2O. The presented results confirmed that the aluminum bronze coating fabricated via HVOF exhibited a great resistance performance even at a high frequency.