High Velocity Oxy-fuel Spraying Research Articles

Review of Functionally Graded Thermal Sprayed Coatings

The paper briefly describes major thermal spray techniques used to spray functionally graded coatings such as atmospheric plasma spraying, high velocity oxy-fuel spraying, suspension and solution precursor plasma spraying, and finally low and high pressure cold gas spray method. The examples of combined spray processes as well as some examples of post spray treatment including laser and high temperature treatments or mechanical one, are described. Then, the solid and liquid feedstocks used to spray and their properties are shortly discussed. The reviewed properties of functional coatings include: (i) mechanical (adhesion, toughness, hardness); (ii) physical (porosity, thermal conductivity and diffusivity, thermal expansion, photo-catalytic activity), and; (iii) bioactivity and simulated body fluid (SBF) corrosion. These properties are useful in present applications of functionally graded coatings as thermal barriers, the bioactive coatings in prostheses, photo-catalytic coatings in water treatment, coatings used in printing industry (anilox and corona rolls). Finally, some of the future possible fields of functional thermal sprayed coatings applications are discussed, e.g., to coat polymer substrates or to use the cheap technology of low pressure cold gas spray method instead of expensive technology of vacuum plasma spraying to obtain bond coatings.

Effects of Heat Treatment on the Structures and Wear Behaviors of HVOF-Sprayed Ni–MoS<sub>2</sub> Coatings

Numerous studies have addressed the augmentation of the hardness and tribological properties of material surfaces with the aim of diminishing the wear. However, there is significant scope for further enhancing the performance of self-fluxing nickel alloys utilized as abrasion-resistant coatings. In this work, Ni–MoS2 powders were prepared by electroless plating, and high-velocity oxy-fuel (HVOF) spraying was used to prepare low-coefficient-of-friction coatings with these powders. The coatings were then subjected to heat treatment. Various surface analysis techniques including hardness testing, scanning electron microscopy, and X-ray fluorescence were subsequently used to characterize the compositions and mechanical properties of the composite HVOF coatings. In addition, ball-on-disc tests were performed under dry abrasive conditions on specimens that were heat treated at different temperatures according to the ASTM G99 standard. The wear of each specimen was evaluated, and the measurements were used to provide a comprehensive assessment of the coating’s wear resistance. When the Ni–MoS2 composite coating was heat treated at 500°C, the growth of MoO2 crystals evaporates from the surface, and condenses on the protruding oxide crystals, which led to an increase in porosity and structural looseness. Consequently, the hardness and structural strength of the coating decreased significantly, dramatically increasing its wear loss. The HVOF Ni–MoS2 composite coatings are suitable for high-temperature abrasion environments with temperatures below 500°C, and an operating temperature of 500°C or higher should be avoided to maintain its hardness, structural strength, and wear resistance.

Sliding and erosion wear behaviour of thermal sprayed WC-Cr3C2-Ni coatings

The present work investigates comprehensively the tribological behaviour of WC-Cr3C2-Ni coatings prepared by atmospheric plasma spray (APS) and high-velocity oxy-fuel (HVOF) spray methods. The dry sliding wear at room and elevated temperature (up to 800 °C), wet (oil-based fracturing fluid) sliding wear at room temperature were studied against an alumina ball using the ball-on-disc tribometer according to the ASTM G99 standard. The erosion wear was studied using air-jet erosion tester (ASTM G76) at the impact angles 30° and 90° and temperatures 500 °C and 650 °C. The HVOF coating showed higher hardness, dense morphological structure and a lower degree of decarburisation as compared to APS coating. The HVOF coating offers better wear resistance over the APS coating under both dry and wet sliding conditions. Significant improvement in the wear resistance, especially above 500 °C is attributed to the uniform formation of lubricious WO3. The solid particle erosion resistance of both coatings is observed to be the same up to 650 °C under 30° and 90° impact angles.

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.

Extreme learning machine and support vector regression wear loss predictions for magnesium alloys coated using various spray coating methods

Magnesium alloys are popular in the aerospace and automotive industries due to their light weights and high specific strengths. The major disadvantages of magnesium alloys are their weak wear and corrosion resistances. Surface coating is one of the most efficient methods of making material surfaces resistant to wear. Experimental determination of wear loss is expensive and time-consuming. These disadvantages can be eliminated by using machine learning algorithms to predict wear loss. This study used experimentally obtained wear loss data for AZ91D magnesium alloy samples coated via two different spray coating methods (plasma and high velocity oxy-fuel spraying) using various parameters. Support vector regression (SVR) and extreme learning machine (ELM) methods were used to predict wear loss quantities. In models tested using 10-k cross-validation, R2 was calculated as 0.9601 and 0.9901 when the SVR and ELM methods were applied, respectively. The ELM method was more successful than SVR. Thus, the ELM method has excellent potential to support the production of wear-resistant parts for various applications via spray coating.

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.

An investigation on oxidation behaviour of high velocity oxy-fuel sprayed Inconel718-Al2O3 composite coatings

The grey cast iron (GCI) components such as exhaust manifolds, turbocharger housings, and furnace parts are subjected to high temperature oxidation. GCI alone cannot retain its mechanical strength at elevated temperatures due to this high temperature oxidation. The composite coatings can effectively be used to counter the high temperature oxidation induced degradation of the GCI components. In the present work, Inconel718-Al2O3 (INAL) based composite coatings were deposited on GCI substrate by using high velocity oxy-fuel (HVOF) spray process. The effects of varying Al2O3 contents (10, 20, and 30 wt%) on the microstructure, porosity, micro-hardness, and oxidation resistance of Inconel718 (IN718) coating were studied. High temperature cyclic oxidation testing was conducted on these coatings and bare GCI substrate in a laboratory tube furnace at 900 °C in air. The kinetics of oxidation were determined by using weight change measurements of the bare GCI and coated specimens at regular intervals for a duration of 50 h. The important phases present in the feedstock powders, deposited coatings, and the oxidised specimens were identified by using X-ray diffraction (XRD). The surface morphology and chemical compositions of the coated and tested specimens were determined by using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The microhardness of IN718 coating was found to be improved with an increase in alumina contents and a maximum average hardness of about 801 ± 40 HV0.2 was observed in case of IN718-30 wt% Al2O3 composite coating. The increase in alumina contents resulted in an increase in porosity and proportion of un-melted feedstock powder particles in the IN718 coating. The coating with 30 wt% alumina contents showed the maximum resistance to oxidation with a minimum weight gain of 1.29 mg/cm2 as compared to the other coatings. The improved oxidation of composite coatings can be attributed to the formation of protective phases such as Al2O3, NiCr2O4 and Cr2O3 on its exposed surface during the hot corrosion condition.

Wear and Corrosion Properties of Stellite-6 Coating Fabricated by HVOF on Nickel–Aluminium Bronze Substrate

Ni–Al bronze (NAB) was coated with Stellite-6 through gas-fueled high-velocity oxyfuel spraying. Scanning electron microscopy observations revealed the accumulation of Tungsten-rich particles at the substrate-coating interface. These areas played an important role in the enhancement of the mechanical properties of the coating. The coating hardness increased 5 times with respect to the substrate one. The tribological analysis of the coating was done via pin on disk method. Results showed that abrasive wear is the dominant mechanism for the substrate; on the contrary, delamination is the dominant wear mechanism in the coating. The corrosion performance of bare and coated alloy was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy. The corrosion potential of coated sample increases in comparison with bare alloy, corrosion current density decreases from 3.91 to 1.82 µA/cm2 and the capacitive resistance is much larger.

Elevated-Temperature Wear Study of HVOF spray Cr3C2–NiCr-Coated Die Steels

Abstract Wear and surface damage of tools (die materials) in the hot metal forming industry is a critical problem observed and is producing an adverse effect on the process economy. The problem occurs when tool and workpiece interact at higher temperatures. However, the research related to the wear and friction of dies is still lacking. In the present investigation, tribological (wear and friction) studies were conducted with an aim to explore the potential of Cr3C2–NiCr surface coating. The high-velocity oxy-fuel (HVOF) spray technique was used to formulate the coatings. The microhardness, surface roughness, bond strength, and porosity of the coated specimens were found and analyzed. Subsequently, elevated-temperature wear and friction study of the uncoated and coated specimens were done in the laboratory. The study was conducted at 25 N and 50 N loads. The coated specimens showed an increase in wear resistance at all test parameters. The lowest value of coefficient of friction (COF) and the specific wear-rate for the coated specimens were observed at 400 °C. Wear mechanisms were studied by the scanning electron microscopy (SEM) technique. The wear mechanisms were observed to be adhesive in nature at room temperatures and the combination of abrasive/oxidative/adhesive in nature at higher temperatures for the Cr3C2–NiCr-coated specimens.

Influence of solid lubricants addition on the tribological properties of HVOF sprayed NiMoAl coating from 30 °C to 400 °C

The present study focuses on the influence of solid lubricants (MoS2, h-BN, Cr2AlC, and Cr2AlCAg) addition on the tribological properties of NiMoAl alloy in the range of 30 °C (Room Temperature, RT) to 400 °C. For this, NiMoAl and NiMoAl with 20 wt% of different solid lubricant powders were prepared and coated on a stainless steel substrate by High-Velocity Oxy-Fuel (HVOF) spraying. The coefficient of friction (COF) of NiMoAl coating at RT and 400 °C is 0.72 ± 0.05 and 0.47 ± 0.03, respectively. The addition of 20 wt% MoS2, h-BN, Cr2AlC, and Cr2AlCAg in NiMoAl reduces the COF by (50% & 30%), (47% & 45%), (37% & 49%) and (64% & 66%), respectively at RT & 400 °C. Characterization of the worn-out surfaces shows that the tribo-chemical by-products such as Ni3S2, Cr7C3, and Ag2MoO4 act as a friction modifier and reduces the COF. NiMoAl-20 wt% Cr2AlC coating shows a large decrease in COF with an increase in temperature.

The effect of impingement angle on erosion wear characteristics of HVOF sprayed WC-Ni and WC-Cr3C2-Ni cermet composite coatings

The present study investigated the erosion wear behavior of WC-Ni and WC-Cr3C2-Ni cermet coatings deposited by high velocity oxy-fuel (HVOF) spray process on the substrate of 1Cr18Ni9Ti stainless steel. Microstructures and morphologies of the coatings were examined using SEM images, and x-ray diffractometer was used to analyze the phase composition of the powder and the coatings. The erosion test was carried out using home-made jet rig. In order to better fit the research background of this study, the erodent used for erosion was taken from the Yellow River, China. The coating is well combined with the substrate; and WC-Cr3C2-Ni coating consists of WC, Cr3C2 and Ni phases, WC-Ni coating consists of WC, W2C and Ni phases. Some mechanical properties of the two coatings were compared, WC-Cr3C2-Ni coatings have higher hardness to be compared with WC-Ni ones due to a lower binder content; and the elasticity modulus and nano-hardness values of the WC-Cr3C2-Ni coating are higher than that of the WC-Ni coating. The relationship between the wear performance of the coatings and impingement angle was obtained; and the erosion resistance of the coatings was analyzed. It was observed that WC-Cr3C2-Ni cermet coating exhibits higher erosion resistance under all testing conditions as compared with the WC-Ni cermet coating and 1Cr18Ni9Ti stainless steel. The results show that the erosion mechanism at low angle is mainly cutting, while erosion pits dominate at high angle for the coatings, moreover, plastic deformation could be observed in the case of the binder depletion and cracking found place. and the erosion mechanisms of the 1Cr18Ni9Ti stainless steel are mainly cutting and plastic deformation at low angle and high angle, respectively.

Multi-scale mechanical properties of Fe-based amorphous/nanocrystalline composite coating synthesized by HVOF spraying

Fe-based (Fe–Cr–B–P–C) amorphous/nanocrystalline composite coatings were synthesized by high velocity oxy-fuel (HVOF) thermal spray method with varying powder feed rates and the multi-scale wear behaviour of the coatings’ is reported here. Microstructural characterization of the composite coating envisaged the presence of embedded nanocrystalline phases in the amorphous matrix. The porosity content decreased, whereas the amorphicity of the coating increased gradually with increment in the feed rate. The combined effect of (i) splat morphology and (ii) extent of devitrification on the mechanical and tribological properties of the various coatings was investigated. Increasing the powder feed rate resulted in higher hardness of the coating, which was attributed to better inter-splat bonding and reduction in α-Fe content in the amorphous matrix of the coating due to lower extent of devitrification. Nanotribology test on a single-splat revealed increment in wear resistance at elevated feed rate due to the reduction in volume fraction of softer nanocrystalline α-Fe phases. Besides, dry sliding wear investigated the coatings’ wear behaviour on a global basis and revealed decreasing trends for both wear rate and coefficient of friction with increasing feed rate. Most importantly, the Fe-based composite coatings exhibited low wear volume during nanotribology and lower friction coefficient, low wear rate of dry sliding wear study, compared to an SS316L coating, prepared using industrially optimized parameters. The enhanced wear resistance of the composite coating compared to that of the stainless steel coating makes it an effective method of surface protection for metallic substrates.

Effect of vacuum heat treatment on the oxidation kinetics of freestanding nanostructured NiCoCrAlY coatings deposited by high-velocity oxy-fuel spraying

In this study, the nanostructured NiCoCrAlY powder feedstock was coated on the substrate via the high-velocity oxy-fuel spraying process. Freestanding nanostructured NiCoCrAlY coatings were then vacuum heat-treated at 1100 °C for 1, 2, and 5 h under a pressure of 10−3 Pa. The microstructure examinations of the nanostructured NiCoCrAlY coatings before and after vacuum heat treatment were investigated using x-ray diffraction and the field-emission scanning electron microscope equipped with electron dispersed spectroscopy analysis. In order to measure the high-temperature oxidation resistance, the freestanding coatings were evaluated using the isothermal oxidation test at 1000 and 1100 °C, respectively, under the air atmosphere. The obtained results showed that homogeneous and adherent α-Al2O3 was successfully formed on the surface of the heat-treated coating during isothermal oxidation. Results also indicated that the heat-treated NiCoCrAlY coating had a higher isothermal and cyclic oxidation resistance. As a consequence, a lower oxide growth rate was achieved by controlling diffusion due to the finer and denser structure of Al2O3 on the heat-treated nanostructured coating for 2 h after the oxidation test.

Creep behavior of polycrystalline and single crystal Ni-based superalloys coated with Ta-containing NiCoCrAlY by high-velocity oxy-fuel spraying

Creep behavior of coated superalloys is important since critical metallic parts operating at high temperature are functionalized to resist oxidation, corrosion, etc. Unfortunately, there is a lack of information about creep data of coated superalloys. Polycrystalline and single crystal Ni-based superalloys coated with Ta-containing NiCoCrAlY by high-velocity oxy-fuel spraying were creep tested at 980 °C under 150 MPa constant load in air to address the influence of substrate thickness on their creep strength behavior. The contribution of the coating to both superalloys creep resistance was found to be negligible. However, a superalloy thickness debit effect was observed and is discussed.

Investigation of tribological behavior of 20NiCrBSi-WC12Co coated brake disc by HVOF method

In braking systems, which consist of dry sliding lining against a pearlitic cast-iron disc, disc wear has a significant impact on the overall wear rate. In this work, dynamometer tests were conducted to find out the friction and wear behaviour of 20NiCrBSi-WC12Co cermet coating accumulated on the cast-iron disc by High velocity oxy-fuel spraying (HVOF) and the findings were compared with those of the uncoated disc. Braking tests of the coated and uncoated discs were performed on a full-scale brake dynamometer, which was designed in line with the SAE-J2430 Brake Effectiveness Procedure. Microhardness values, surface properties, scanning electron microscopy (SEM) analysis, energy dispersive x-ray (EDX) and x-ray diffraction (XRD) analysis of the discs were evaluated. As a result of these analyses, it was found out that cermet coating had a much higher microhardness and abrasion resistance with the combination of hard WC phase and mild Ni matrix compared to the conventional disc. The coated disc exhibited stable braking effectiveness with lower surface contact temperature. At the same time, this coating results in longer service life by reducing abrasive wear on the brake disc surface and a lower lining wear rate, reducing particle matter emissions to the environment.

A study to analysis of corrosion rate of uncoated and coated WC- Co- Cr naval brass materials

In this work, use of high velocity oxy-fuel (HVOF) spraying technique was explored as a way of producing coatings with a resistance to corrosion and erosion. Response surface methodology (RSM) was employed to develop the empirical relationships to predict corrosion rate of uncoated and coated WC-Co-Cr naval brass materials. Dissolution of naval brass and formation of naval hydroxide are the key factors for immersion corrosion. Atomic microscope analysis shows that the corroded surface of uncoated naval brass shows higher Ra value is owing to the surface damage. Coated naval brass show less undulations on the analyzed region.

Tribo-performance of 80%WC + 20%TIO2 HVOF thermal spray coating on SS-404

Erosion wear occurs when solid particles impact on a metal surface with high velocity. In this work, the erosion wear of SS-404 is analyzed by utilizing slurry erosion pot tester. The test has been carried out with coated (WC-TiO2) and uncoated stainless steel (SS-404). The impact of different parameters such as rotational speed, particle concentration, and the time period and particle size on erosion wear of SS 404 has been examined. While performing experiments four distinct speeds such as 700, 950, 1200 and 1450 rpm with a time duration of 45, 90, 135 and 180 min have been considered. To protect SS 404 material from erosion the process named High-velocity oxy-fuel (HVOF) spray has been applied. At the end of the experiment, the impact of the above-defined parameters on slurry erosion wear of pipeline material using the Taguchi mechanism has been conducted. Signal to Noise Ratio (SNR) of the proposed work based on the smaller are better properties with coated and without coated material has been examined. The signal to noise ratio examined with and without a coating of SS 404 varies from 37.19 dB to 47.75 dB, 37.18 to 47.74, 37.16 to 47.72, and 37.20 to 47.76. Particle size was identified as the most influencing parameter for erosion wear in SS 404.

Better wear resistance of HVOF coating CrC-NiCrFeSiBCoC(35%–65%) and CrC-NiCrFeSiBCoC(80%–20%)on SS316 steels

High Velocity Oxy-Fuel (HVOF) technique was used to deposit an CrC-NiCrFeSiBCoC(35%–65%) and CrC-NiCrFeSiBCoC(80%–20%) coating on 316 stainless steel substrate to improve its wear performance at high temperature. The two ratios of same coating is chosen to predict better wear resistant in it on SS316 base metal by using HVOF spray coating parameters. The ratio 35%–65% is used commonly in all the R & D but 80%–20% is used in industrial labs to test which ratio will give better performance. In the both ratios CrC is the base powder of 35% and 80%, remaining composition of 65% and 20% blend sprayed on the substrate metal about the thickness of 270microns. Usually wear can be occurred in high temperature applications like turbine blades, water profilers and other thermal power applications. The sliding wear test conducted by using Pin-on-Disc test rig on these coatings to find out better wear resistance. Scanning Electro meter analysis gives the exact prediction that, CrC-NiCrFeSiBCoC(35%–65%) coating is the better wear resistance than CrC-NiCrFeSiBCoC(80%–20%) and substrate, because it will gives the protection to base metal. The line graphs and bar chart will shows the variation occurs at varying load with constant speed and varying speed with constant load.

Thermal Spray Techniques for Developing a Carbide Coating

In the industries, different components of different materials are being used in a different service environment, in the view of this requirement day by day specific surface properties are demanding by industries to enhance the product life cycle. A range of surface protection techniques are accessible for various apps with a common goal of protecting a part or object that is subjected to a chemical environment. This process leads to decreases manufacturing cost as no need to fabricate a new part. Commercially Coating materials include strong and rigid metal alloys, ceramics and polymers, composites material are available for durable protection. There are different methods of thermal spray such as flame spray, D-gun spray, high-velocity oxy-fuel Spray, Plasma Spray, and cold spray process have been introduced and investigated. Even though each method has distinct values and procedures that limit their applications. However, there are many things to understand that are used to overcome the lack of thermal spray coating methods by combining process parameters. In this article, we have discussed the various coating materials have been used commercially, and further categorized and compared various thermal spray processes.