Flame Spray Technique Research Articles

Preparation and characterization of cermet MSZ/Ni-Al coating deposited by flame spraying technique

Preparation and characterization of cermet MSZ/Ni-Al coating deposited by flame spraying technique

Highly bioactive hydroxyapatite coating made by flame spray technique

This research involves fabrication and characterization of flame sprayed hydroxyapatite (HA) coatings on 316 stainless steel substrates where the desirable structure with high porosity can be obtained. Nano-sized HA powder was synthesized and calcined at 600 °C. The subsequent powder was used as feedstock powder for flame spray technique (FS). In-flight particles of HA were spherical with the range of particle size between 3–37 µm. The average coating thickness was 128 µm and the crystalline phases were a mixture of HA and tricalcium phosphate (TCP). Simulated body fluid (SBF) test showed that HA layer was formed after 7 days. Highly bioactive properties were due to high surface area from rough coating and porous structure, which would be beneficial from the flame spray technique. The coating is promising for applications in biomedical field.

Effects of Laser Remelting on Frictional Properties of Supersonic Flame-Sprayed Coatings

In this study, Cr3C2-Al2O3-NiCr coatings were prepared on INCONEL 600 alloy surfaces using the supersonic flame spraying technique, followed by a laser remelting treatment. In this way, this study further explored what impacts laser remelting has on coating performance. To this end, optical microscopy (OM), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD) were employed to carry out microstructural characterization. Energy-dispersive X-ray spectroscopy (EDS) was applied to conduct an analysis of the coatings’ elemental distribution while X-ray diffraction (XRD) was used to determine the coating phases. To measure the microhardness of the coatings, a microhardness tester was applied. In addition, the study investigated the samples’ electrochemical corrosion resistance and friction-wear performance under different surface conditions. According to the results, laser remelting enhanced the coating density, improved metallurgical bonding with the substrate, and optimized the carbide distribution, thereby enhancing corrosion and wear resistance in both air and corrosive media. However, excessive laser power hinders Cr3C2 nucleation, leading to diminished coating hardness and wear resistance in Cr7C3 formation.

Effects of Gas Layer Thickness on Capillary Interactions at Superhydrophobic Surfaces.

Strongly attractive forces act between superhydrophobic surfaces across water due to the formation of a bridging gas capillary. Upon separation, the attraction can range up to tens of micrometers as the gas capillary grows, while gas molecules accumulate in the capillary. We argue that most of these molecules come from the pre-existing gaseous layer found at and within the superhydrophobic coating. In this study, we investigate how the capillary size and the resulting capillary forces are affected by the thickness of the gaseous layer. To this end, we prepared superhydrophobic coatings with different thicknesses by utilizing different numbers of coating cycles of a liquid flame spraying technique. Laser scanning confocal microscopy confirmed an increase in gas layer thickness with an increasing number of coating cycles. Force measurements between such coatings and a hydrophobic colloidal probe revealed attractive forces caused by bridging gas capillaries, and both the capillary size and the range of attraction increased with increasing thickness of the pre-existing gas layer. Hence, our data suggest that the amount of available gas at and in the superhydrophobic coating determines the force range and capillary growth.

Structure and mechanical properties of cermet Ni-Al/MSZ thick coating prepared by flame spraying technique

Structure and mechanical properties of cermet Ni-Al/MSZ thick coating prepared by flame spraying technique

Improvement in tribological and hydrophobic properties of thrust plate of gear pump through oxyacetylene flame spraying in diverse cooling Medium

In the present research, a flame spraying technique with diverse cooling mediums has been used to enhance the surface properties of the thrust plate of a gear pump made of aluminium alloy. The influence of flame spraying on the surface of the thrust plate with reference to the coefficient of friction, wear volume, micro-hardness, change in microstructure, surface roughness, and formation of hard phases have been highlighted in this research. The field emission scanning electron microscopy micrograph indicates the formation of fine-grain microstructure in the flame-hardened surfaces due to the formation of the hard phases. Dry sliding wear test results indicate the improvement in friction coefficient in the hardened sample with olive oil cooling as compared to the parent surface. Optical profile analysis of the wear track shows the lower wear volume for the hardened samples with oil cooling as compared to the parent material. Micro-hardness of the flame-hardened surface increased from 80 HV0.5 (parent surface) to a maximum value of 132 HV0.5 (flame-hardened with oil-cooled). A significant improvement in water contact angle (from 740 to 970) also has been observed, indicating the enhancement in the hydrophobic nature of flame-hardened surfaces.

The effect of post heat treatment and TiO2 addition on tribological and electrochemical performances of thermally sprayed alumina

ABSTRACT The heat treatment of alumina ceramics is a fundamental process for controlling the physical, mechanical and thermal properties of these components during industrial operations. The problem statement in this case is about the effects of TiO2 addition and post heat-treatment on the expansion behaviour of alumina coating. For that alumina (Al-99) and alumina-titania coatings 5% wt. TiO2 (AT-5) and 15% wt. TiO2 (AT-15) were formed onto E335 substrate steel via the flame spraying technique. The samples were heat-treated (1000°C for 2 h in Air) and their wear and electrochemical behaviour was compared with the as-sprayed samples. The X-ray diffraction (XRD) patterns reveal a change in the phase composition of the heat-treated coatings compared to the as-sprayed coatings, as alpha alumina matrix but with different ratio. The heat-treated coatings exhibit higher values to as-sprayed coating. At the same time, the addition of TiO2 present hardness twice than pure alumina coating (Al-99). The tribological properties show that the deposits after heat treatment have low wear values compared to the as-sprayed coatings, the lowest specific wear rate was obtained for the heat-treated AT-5 composite coatings. The heat treatment had a positive effect on the corrosion resistance.

Modeling Temperature of Contact Generated in Coatings of Pure Alumina Ceramic onto Low Carbon Steel Type 1.0060 Obtained by the Thermal Spraying Process

In previous research problem statement occur in hardness to reach the thermal flux between surfaces during movement. The aim of the present investigation has been conducted to study the thermal behavior of ceramic Al2O3 (AL-99) coated on a low carbon steel type 1.0060 by using a thermal flame spray technique. The key methods used is microstructural characterization and comparing between experimental data record and numerical program.SEM showed that the Al2O3 coatings have a dense microstructure, lamellar morphology and complex of several phases. The XRD analysis of the coating after the spray showed a majority phase of α -Al2O3 rhombohedral structure and secondary phase of γ-Al2O3 orthorhombic structure. The experimental data recorded From wear indicate two step, first one corresponds to the phase of accommodation between surfaces (samples/ disc), the contact temperature gradually increases to a value Of 75 °C for both pairs, the second step , we could remark from experimental and numerical simulation, it reach 95°C for experimental test and 85 for numerical model.The important findings in tribological results showed that the temperature at the contact is related to the shear stress that will result from the increase of the heat flux. From these results it can be said that the measured temperature increases with the increase of the charge and converges with the contact time. The gap of temperature between experimental and numerical results is probably due to the parameter of microstructure, where in experimental porosities improve convection in the area, in contrast the numerical materials don't add this phenomena.

Tribological Properties and Corrosion Resistance of Stellite 20 Alloy Coating Prepared by HVOF and HVAF

This study examines the tribological and corrosion properties of Stellite 20 alloy coatings on F310H heat-resistant stainless steel that were prepared using HVOF and HVAF supersonic flame spraying techniques. To investigate the coatings’ microstructure, phase, microhardness, wear, and corrosion resistance, a range of characterization techniques, including SEM, EDS, XRD, microhardness, and friction wear-testers, weas employed. The results indicate that both HVOF and HVAF-prepared coatings exhibit a dense structure with porosity of 0.41% and 0.32%, respectively. The coatings are composed of γ-Co solid solution, ε-Co solid solution, Cr-rich solid solution, Cr7C3, WC, and CoCr2O4 phases. The microhardness of the Stellite 20 coatings prepared by HVOF and HVAF methods was 610 HV0.3 and 690 HV0.3, respectively, which is three times higher than that of the F310H stainless steel substrate. The wear mechanism of the HVAF coating is abrasive wear, while the wear mechanism of the HVOF coating is mainly fatigue wear with slight abrasive wear. The HVAF coating demonstrates superior wear resistance due to its higher flame velocity, denser coating, and higher average microhardness. In contrast, the HVOF coating shows a higher friction coefficient stability due to its lower hardness dispersion. The corrosion potentials of the HVOF and HVAF coatings are −0.532 V and −0.376 V, respectively, with corresponding corrosion current densities of 1.692 × 10−7 A·cm−2 and 6.268 × 10−7 A·cm−2, respectively. Compared to the HVOF coating, the Stellite 20 coating prepared using HVAF technology exhibits better wear and corrosion resistance.

Cyclic Oxidation Resistance of MoSi2 Added FeCrAlTiY Coatings on ST41 Steel at 700oC Prepared by a Flame Spraying Technique

Advanced power generation will be operated at higher temperatures and pressure to achieve higher efficiency and reduce CO2 emission. This may significantly impact the use of carbon steel that previously has been used in boiler fabrication. In thi

Sliding wear behavior of high entropy alloy coatings deposited through cold spraying and flame spraying: A comparative assessment

High entropy alloys (HEAs) are a promising class of advanced materials composed of multi-component elements that possess outstanding mechanical and corrosion properties, which enable their use in many industrial applications. However, limited studies have focused on the tribological behavior of HEAs fabricated by means of thermal spray technologies. In this study, AlCoCrFeMo equimolar HEAs were fabricated successfully using flame spraying and cold spraying techniques to determine the phase compositions, microstructures, properties, and sliding wear resistance. The results show the existence of oxides in the flame-sprayed HEA coatings due to in-flight oxidation and body-centered cubic (BCC) phases. Oxide evolutions improve the hardness of flame-sprayed HEA coatings compared to that of cold-sprayed coatings. The sliding performance was investigated at room temperature by varying the normal loads (i.e., 5 N, 10 N) and with constant sliding speed (i.e., 3.1 cm/s) using Al2O3 counterface. The cold-sprayed coatings showed overall lower coefficient of friction (i.e., ∼0.5) with numerous fluctuations compared to the flame-sprayed coatings. However, the flame-sprayed coatings showed improved wear resistance when compared to HEA deposited by means of cold spray. This correlated well with the observations of ex situ analysis, which showed greater material transfer and increased formation of debris on the cold-sprayed coatings compared to the flame-sprayed coatings. The results obtained in this study suggest that flame-sprayed HEA materials are promising candidates for next-generation tribological interfaces under specific conditions, pointing to new materials designed with improved microstructural features and enhanced mechanical properties.

Corrosion Behavior of Flame Sprayed Cr2O3 Coatings on Carbon Steel in Chloride Solutions

Cr2O3 coatings were deposited on carbon steel through the flame spraying technique using two types of flames (neutral and oxidizing). The protective and morphological characteristics of the coatings were determined. The coatings had layer thickness values of 114 and 214µm for oxidizing and neutral samples, respectively. Porosity percentages of 4.5 % and 2.5 % were determined, where the neutral sample presented the greatest porosity due to the insufficient fusion of the oxide particles during the process, resulting in the formation of a heterogeneous and less compact layer. Microcracks and pores were found on the surface and cross-section of the coatings, due to the thermal expansion generated during the solidification process. The coating protective capacity was evaluated by electrochemical techniques over 672 hours in a 3.5 %wt NaCl saline solution. The results evidenced that the coatings manufactured with the oxidizing flame presented more corrosion resistance compared to those prepared with the neutral flame. The corrosion products were more evident in the neutral flame coatings, because of the diffusion mechanisms from the substrate to the surface coating through the interconnected pores. Finally, the wettability of the sodium chloride solution in the Cr2O3 coatings was measured by the contact angle technique, finding that the oxidizing flame coatings exhibited a higher angle contact value (64.8°) in contrast to the neutral flame coatings (35°).

Structural characteristics and high-temperature oxidation behaviour of nano-HfO2-doped thermal barrier coatings

The uneven growth of thermally grown oxides (TGOs) in thermal barrier coating systems is an important cause of cracking failure at the coating interface in high-temperature environments. The doping of rare earth elements in the bonding layer can effectively inhibit the formation of spinel oxides in the TGO and improve the high-temperature oxidation resistance of the coating. However, a single rare earth element has a limited effect on inhibiting TGO failure. In this study, a NiCoCrAlYHf coating was prepared using a supersonic flame spraying (HVOF) technique. The effects of HfO 2 doping on the high-temperature oxidation behaviour of the coatings and diffusion behaviour of metallic elements in the coatings were investigated at 1100 °C. The results showed that the nano-sized HfO 2 filled the pores between the powder particles and improved the hardness of the coating. During the high-temperature oxidation process, the oxides formed by Hf and Y had a large size and low solubility, which effectively blocked the diffusion of Al. This slowed the generation of spinel oxides, effectively inhibited the growth of the TGO, it inhibits the initiation and propagation of cracks within the coating, reduces damage to the coating from tensile and compressive stresses at the interface, and improved the high-temperature oxidation resistance of the coating.

Immersion corrosion behavior, electrochemical performance and corrosion mechanism of subsonic flame sprayed FeCoCrMoSi amorphous coating in 3.5% NaCl solution

A FeCoCrMoSi amorphous coating (AC) was fabricated on Ti6Al4V alloy (TA) by subsonic flame spraying (SFS) technique, which was used to improve its corrosion resistance. The morphology, element distribution and chemical composition of obtained coating were analyzed using a scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X–ray Fluorescence (XRF), respectively, and its amorphous structure was confirmed by X–ray diffraction (XRD). The immersion corrosion behavior and electrochemical performance of FeCoCrMoSi AC immersed in 3.5% NaCl solution for the different days were systematically investigated, and the corrosion mechanism of amorphous structure was also discussed by the model of passive film. The results show that the FeCoCrMoSi AC exhibits the dense amorphous structure, which is beneficial to improving the anti–corrosion performance of TA. The potentiodynamic polarization curve (PPC) and electrochemical impedance spectroscopy (EIS) indicate that the FeCoCrMoSi AC with the lowest icorr of 1.479 × 10−6 A·cm−2 immersed for 60 days has the largest capacitor loop diameter of 7.53 × 105 and charge transfer resistance Rct of 4.31 × 104 Ω, showing the highest comprehensive corrosion resistance. The mechanism of corrosion resistance is contributed to the Cr–rich passive film, which is further stabilized by the addition of Mo.

Tribological performance of thermally sprayed NiWCrBSi alloy coating by two different oxyacetylene flame stoichiometries

ABSTRACT In the present work, the effects of oxidising and standard flame spray techniques on microstructure and wear performance of Low Velocity Oxygen Fuel NiWCrBSi coatings produced onto mild steel substrate were studied. Results showed that coating microstructure was dependent on the stoichiometry of the reacting gas mixture. Coatings produced in oxidising flame conditions showed higher amounts of semi-molten particles and high quantity of WC phases. Those coatings showed a good behaviour in dry sliding wear test, due to their higher hardness and the formation of compact and adherent oxide tribofilms. The wear behaviour of non-molten particles against friction forces is discussed, with the aim of establishing relationships between the tribological response of the material and its process-induced microstructure defects.

Evaluation of Ti/Al alloy coated with biogenic hydroxyapatite as an implant device in dogs\u2019 femur bones

The main target of the present research was a full assessment of the toxicity effects and biocompatibility of a Ti/Al-alloy device coated with biogenic hydroxyapatite (bHA) when implanted in dogs in comparison with those of an uncoated Ti/Al-alloy device. The coating of the alloy was carried out using controlled high-velocity suspension flame spray (HVSFS) technique. Both coated and uncoated devices were implanted in dogs’ femur bones for different time periods (45 days and 90 days). Bone-formation ability and healing were followed up, and blood analysis was performed, at Time zero (immediately post surgery), and then at 3 days, 45 days, and 90 days post surgery. Bone mineral density checks, radiological scans of the femur bone, and histological analysis were also conducted. The in-vivo study results proved that implantation of a device made from bHA-coated Ti/Al alloy in dogs’ femur bones is completely safe. This is due to the high osteoconductivity of the coated alloy, which enables the formation of new bone and a full connection between new and original bone material. At 90 days post surgery, the coated alloy had been completely digested within the original bone; thus, it appeared as a part of the femur bone and not as a foreign body. Both the scanning electron microscopy with energy-dispersive X-ray and histology analysis findings affirmed the results. Furthermore, the blood tests indicated no toxicity effects during the 90 days of implantation.

Gas pressure and coating distance for nanohydroxyapatite deposition on stainless steel 316L using flame spray technique

Metal implant coating engineering is needed to improve the surface biocompatibility properties of metals. For this, coating metal surfaces with bioactive and biocompatible biomaterials will be an option. Having high biocompatibility as well as similarity in chemical properties, nanohydroxyapatite may be a candidate as biomaterials for coating the metal implant. The key to the success of metal implant plating is the formation of pores which increase the bioactivity and biocompatibility properties of the implant. In this study, nanohydroxyapatite was used to be coated on stainless steel type 316L (SS316L). To ensure that the coating works properly on the surface, an appropriate measure of gas and distance is required. The purpose of this study was to determine the possible firing distance and gas pressure of the flame spray coating technique. The X-ray diffractometer (XRD), scanning electron microscope - energy dispersive X-ray spectroscopy (SEM-EDS), and optical microscopy (OM) characterizations were carried out to determine the phase, morphology, and presence of pores. After coated product, hydroxyapatite dehydroxylation occurred which led to the tetracalcium phosphate (TTCP) and β-tricalcium phosphate (β-TCP) phases. The thickness decreases with the addition of gas pressure and the farther the firing distance the layer thickness decreases. Nanohydroxyapatite coating on a bone implant substrate can increase the porosity of the layer.

Microstructural and Tribological Resistance of Flame-Sprayed CoMoCrSi/WC-CrC-Ni and CoMoCrSi/WC-12Co Composite Coatings Remelted by Microwave Energy

The hard facing composite coatings such as CoMoCrSi/30%WC-CrC-Ni and CoMoCrSi/30%WC-12Co are coated on grade-2 titanium substrate through Flame spray technique. Prior to deposition of coatings CoMoCrSi feedstock were processed using high energy ball milling to obtain intermetallic laves phases. The sprayed coatings are subjected to post-heat treatment through microwave energy to homogenize coating structure which reduces surface defects and to achieve metallurgical bonding. The as-sprayed and microwave treated coatings are examined for metallography analysis by using XRD, SEM–EDS and mechanical properties are estimated by using microhardness, universal tensile equipment. The high-temperature sliding wear tests are performed against alumina counterpart under dry conditions. The sliding wear test is conducted with normal loads of 10 N and 20 N at a sliding velocity of 1.5 m/s with a constant sliding distance of 3000 m. Microwave treated coatings obtained homogeneous structure and metallurgical bonding with improved hardness. Fused coatings revealed better wear resistance due to formation of oxides and fatigue spalling mechanism.

Microstructure and mechanical property of high velocity oxy-fuel sprayed WC-Cr3C2-Ni coatings

WC-Cr3C2-12Ni coatings, with Cr3C2 weight content of 10% and 30%, were fabricated on steel substrate by high velocity oxy-fuel (HVOF) flame spraying technique, and microstructure, phase composition and mechanical properties of WC-Cr3C2-12Ni coatings prepared by different oxygen flows were investigated. The results reveal that phase compositions of WC-Cr3C2-12Ni coatings were mainly influenced by the Cr3C2 content rather than the oxygen flow. WC-Cr3C2-12Ni coatings demonstrated low decarburization and decomposition of WC due to coarse WC gains and high in-flight particle velocities during HVOF. WC-Cr3C2-12Ni coatings exhibited low porosities and typical microstructures, where a mixture of fine and coarse WC grains was uniformly embedded in the Ni/Cr3C2 matrix. The microhardness, indentation fracture toughness and elastic modulus of WC-Cr3C2-12Ni coatings were improved by coarse WC grains, Cr3C2 addition and dense microstructure, which resulted in high wear resistances of WC-Cr3C2-12Ni coatings. The abrasive wear features with groove, peel-off and exposed/fractured WC grains were observed in WC-Cr3C2-12Ni coatings after dry-sliding wear. The relationship between microstructure and mechanical property of WC-Cr3C2-12Ni coatings was discussed from the viewpoints of powder properties and process parameters.

Flame-sprayed strontium- and magnesium-doped hydroxyapatite on titanium implants for osseointegration enhancement

Strontium (Sr) and magnesium (Mg) have been reported to promote osteoblastic cell proliferation and to accelerate bone formation. However, the biofunctional effect on osseointegration caused by coating dental implants with hydroxyapatite (HA) incorporating both of these elements has not been investigated to date. The aim of this study was to examine bone formation and osseointegration in Sr- and Mg-doped HA-coated titanium implants. In this study, the flame-spraying technique was used to deposit Sr- and Mg-doped HA onto titanium discs and implants. The biocompatibility and alkaline phosphatase (ALP) activity of human embryonic palatal mesenchymal pre-osteoblasts on titanium discs was evaluated. In addition, the expression of the osteogenesis gene and the protein expression of Runt-related transcription factor 2 (RUNX2), osteopontin (OPN), and osteocalcin (OCN) on titanium discs were determined by using real-time polymerase chain reaction assays, Western blot analysis, and enzyme-linked immunosorbent assays. Ultimately, the effects of Sr- and Mg-doped HA on the osseointegration of implants were examined in beagle dogs. The results showed that of the groups tested, the 5Sr5Mg-HA group exhibited the highest biocompatibility, ALP activity, and mRNA and protein expression of RUNX2, OPN, and OCN. Prominent new bone ingrowth with osteoblasts and osteoid tissue was found in the 5Sr5Mg-HA group at 4 weeks and 8 weeks. In addition, the highest bone-to-implant contact ratio was found in the 5Sr5Mg-HA group compared to other groups at 8 weeks in beagle dogs. The results show the potential of using 5Sr5Mg-HA coating on dental implants for enhanced osseointegration. Statement of SignificanceOsseointegration is assessed according to the extent of bone-to-implant contact and is an indication of implant success. This study is the first to report that flame-sprayed Sr- and Mg-doped HA coatings on titanium surfaces enhance osseointegration and new bone apposition in a beagle dog model. Therefore, the use of titanium implants incorporating Sr and Mg might be advantageous for patients with a low bone density.