Flame Spray Technology Research Articles

Performance-tunable thermal barrier coating for carbon fiber-reinforced plastic composites via flame spraying

Thermal barrier coatings (TBCs) are essential for improving the heat resistance of materials operating in high-temperature environments. This paper proposes a new method for manufacturing double-layered TBC with graded porosity for carbon fiber-reinforced plastic (CFRP) composites. The TBC was created by a flame spraying process, consisting of relatively dense and porous layers: (1) a dense layer was produced by spraying yttria-stabilized zirconia (YSZ) particles directly onto neat carbon fabric substrate and (2) a porous layer was prepared by co-spraying YSZ particles with sacrificial polyetheretherketone (PEEK) particles. The porosity of the porous layer was controlled by varying a PEEK injection distance (D) and a PEEK feed rate (R). The correlation between porosity and thermal conductivity of the TBC layer was investigated to assess its thermal barrier performance. The TBC fabricated with the D = 5 cm and the R = 1.0 g/min offered the optimal porosity and conductivity. The 640μm-thick TBC with 34% porosity and 0.27 W/m·K thermal conductivity protected the CFRP substrate remarkably under the subjected torch at 500°C, as the TBC layer reduced the surface temperature of CFRP to 230°C. Thermomechanical analysis, following thermal shock tests, revealed that the double-layered TBC/CFRP composite retained 87% and 75% of its pristine flexural strength and modulus, respectively, while the neat CFRP composite was completely burnt out. This study explored the application of flame spray technology to develop highly effective double-layered TBCs with tunable porosity to maximize their thermal barrier performances. All results from the current study provide new insights into the design and development of TBC and CFRP composites, which will benefit a wide range of lightweight high-temperature applications.

Microstructure and properties of Ni20Cr–MoS2 composite coating by subsonic flame spraying

In this study, a Ni20Cr–MoS2 composite coating was fabricated using subsonic flame-spraying technology, and the effects of adding MoS2 on the microstructure, mechanical properties, and tribological properties of the coating were studied. The microstructure analysis of the coatings revealed that the Ni20Cr and Ni20Cr-MoS2 coatings prepared by subsonic flame spraying had fewer microscopic defects and significant particle flattening. After the addition of MoS2, the porosity of the coating decreased, whereas its microhardness increased. The cohesive strength of the coating was measured using the scratch method, and it was found to be enhanced after the addition of MoS2. Moreover, in the dry friction state, compared with the Ni20Cr coating, the Ni20Cr–MoS2 coating performs better. At a load of 20 N, the friction and wear performances of the Ni20Cr–MoS2 coating were the best, and the friction coefficient decreased by 11.63 %. Based on this, the relationships between the cohesive strength and tribological properties and between the wear mechanism and scratch mechanism of the coating are discussed.

Research on Thermocouple Integration Method of Hollow Thin-Walled Turbine Rotor Blade Surface

The hollow thin-walled structure is increasingly used in advanced aero-engine turbine rotor blades, and the traditional surface temperature measurement method based on groove buried couple is no longer applicable. In this paper, a new thermocouple integration method is proposed. The laser additive manufacturing process is used to generate thermocouple embedding channels on the surface of turbine blades. After the thermocouple is embedded, it is pre-fixed, and the thermocouple protection is realized by supersonic flame spraying technology. The strength of the thermocouple integrated structure of the turbine blade is verified by finite element analysis. Based on CFD analysis, the influence of thermocouple integration on the efficiency, pressure ratio and temperature distribution of the turbine blade is studied. The high-speed rotation test shows that the thermocouple integrated structure has high strength and reliability and meets the measurement requirements. This method can provide technical support for the surface temperature measurement of hollow thin-walled turbine rotor blades.

Impact of thermal shock on the R-curve and subcritical damage behaviour of flame-sprayed alumina compounds

An alumina rich Al2O3–ZrO2–TiO2 compound was used for the preparation of self-supporting parts via the rod flame spraying technology. The as-sprayed material was compared to self-supporting parts, fabricated from commercially available alumina rods. For both materials, the flexural strength, the fracture resistance, and the behaviour under subcritical loading was evaluated and compared, either before as well as after cold thermal shock. While the flexural strength and the subcritical damaging of both materials were basically affected through thermal shock in a similar manner, the Al2O3–ZrO2–TiO2 compound showed an outstanding behaviour in terms of its fracture resistance, which was only barely reduced after thermal shock quenching.

Effect of cerium on the microstructure and anti-corrosion performance of Al-Zn coatings

With the increasing application scope of aluminum alloys in the marine field, exploring the surface anti-corrosion technologies of aluminum alloys is becoming more and more important. In current industries, thermal spraying is generally used to prepare AlZn coatings for surface protection. In this paper, AlZn coating and Al-Zn-Ce coating were prepared by flame spraying technology, and the effects of adding rare earth element Ce on the microstructure and corrosion resistance of AlZn coating were systematically studied by using OM, SEM, XPS, LCSM and electrochemical corrosion tests. The results show that the addition of Ce is conducive to promoting the mobility and solidification shrinkage of AlZn alloy melt, thereby increasing the density of the coating while decreasing porosity and roughness. Moreover, adding Ce improves the hardness and wear resistance of the AlZn coating. During immersion, adding a trace of Ce to the AlZn coating will affect the passivation process and the formation of the passivation film, endowing the coating with a strong passivation ability and thus improving the corrosion resistance of the coating.

Flame-sprayed alumina molten metal filters for dead-mould casting application

Ceramic foam filters are applied to remove non-metallic inclusions during steel melt filtration. The flame-spray technology can contribute to improving such filters by increasing the deposition capability of inclusions and decreasing the impairment of the filter substrate by the steel melt. This makes them suitable for application to the continuous steel casting process and foundry casting. The ball-on-three-balls test was utilized at elevated temperatures to determine the high-temperature behaviour of thermally sprayed alumina. Additionally, the flame-spray technology was used to produce carbon-free filters composed of flame-sprayed alumina by coating and burning out the Al2O3–C filter substrate during a sintering step. The B3B revealed a ductile behaviour with increasing temperature and a bending strength of 23.28 MPa at 1400 °C. After sintering at 1400 °C, the filters showed a sufficient CCS of 0.16 MPa, which allows the performance of casting tests (immersion and pouring) with molten steel at 1580 °C.

Effect of tungsten and vanadium additions on the dry abrasive wear and solid particle erosion of flame-sprayed AlCoCrFeMo high entropy alloy coatings

Equiatomic AlCoCrFeMoW and AlCoCrFeMoV HEA compositions were fabricated using a cost-effective flame spraying technology. The microstructure, phases, average microhardness, and nano hardness of the fabricated HEA coatings were systematically investigated, in order to assess their resistance to dry abrasive wear (ASTM G65 Standard) and solid-particle erosion (ASTM G76 Standard). Furthermore, linear regression analysis was performed to assess the relationship between the variables based on microhardness, hardness to elastic modulus (H/E) ratio, and strain hardening coefficient (α) in order to describe the coating's performance under abrasive wear and solid particle erosion. The results showed the formation of BCC1 and BCC2 phases coupled with mixed oxide inclusions for the AlCoCrFeMoW HEA coatings, whilst FCC and spinel-type oxides were observed in the AlCoCrFeMoV HEA coatings. Owing to differences in phase formations, the average microhardness as well as the average nanohardness were 18% and 46% higher, respectively, for the AlCoCrFeMoV HEA coatings than those of the AlCoCrFeMoW HEA coatings. Performance assessment under dry abrasive wear indicated that lower wear rates (210 × 10−6 mm3/Nm) were achieved for the AlCoCrFeMoV HEA coatings, which showed moderate to strong correlation with microhardness and strain hardening coefficient. In terms of solid particle erosion, lower erosion rates (i.e., 0.51 mm3/g for 300 and 0.65 mm3/g for 900) were achieved for the AlCoCrFeMo HEA coatings, followed by AlCoCrFeMoW and AlCoCrFeMoV HEA coatings, which are in good agreement with the H/E values. These results indicate the efficacy of flame-sprayed HEA coatings under demanding environments, which can be potentially transformative for addressing different tribological features for industrial component protection.

Research on the technology of flame spraying aluminum coating for composite material

Aluminum coating was prepared on composite material surface by using oxygen-acetylene flame spraying technology. The H01-103H sealants were used to seal the thermal sprayed aluminum coatings. The characteristics of the aluminum coatings with and without H01-103H sealant, including surface morphologies, phase composition, and bonding strength, were investigated by means of SEM, EDS, and mechanical testing machine. Thermal shock experiment and low temperature cooling test were also used to examine the thermal shock resistance and frost resistance of the Al coatings. Electrical conductivity and electromagnetic shielding properties were then tested according to four-probe measurement principle and GJB 5239-2004, respectively. The results showed that the bond strength was 7.36 MPa and the surface porosity was about 5.21% for Al coating without H01-103H sealant, in addition, the H01-103H sealants could fill into the pores, reducing the porosity and increasing the bond strength of the coating. Furthermore, the main component of the coating was Al, the oxygen content was only 1.43%. Flame sprayed aluminum coating, with surface electrical resistance 0.89 mΩ and 5–18 GHz electromagnetic shielding effectiveness above 35 dB, was an ideal candidate for electromagnetic shielding utilization. The Al coating remained intact, compact, no cracks, peeling, layering under 50–200°C and −30°C, which showed good thermal shock resistance and frost resistance.

Исследование структуры и свойств износостойкого газотермического покрытия с содержанием вольфрама

The paper presents the results of reverse engineering including metallographic, mechanical, and engineering-technical studies of used rods of a compressor produced by the Dresser-Rand company (Siemens, Germany). The study established that the original product is made of AISI 4140 steel with a working coating based on tungsten carbide applied to a depth of 0.2 mm by the HVOF method. The paper contains the results of the development of an import-substituting technological process for producing a wear-resistant powder coating of the Ni–Cr–B–WC system applied by cold gas flame spraying on the surface of a critical unit of compressor equipment in the oil and gas industry. Microanalysis identified that the sprayed spherical WC particles are evenly distributed in the nickel bond without the formation of free cavities at the lamella boundary, retain the size identical to the original powder composition upon the high-speed collision with the substrate, and minimize the level of residual mechanical stresses in the surface layer. The study shows that the sprayed coating has a high microhardness (the bases – 700 HV0.1, WC – up to 2000 HV0.1), which ensures high wear resistance during operation of the rod in a friction pair. A comparative analysis of the tribological properties of the coatings showed that when changing the shape, particle size distribution, and percentage ratio of tungsten carbide from 20 to 70 % in the nickel matrix, the overall wear resistance of the coating equivalently increases. The authors concluded on the possibility of manufacturing an import-substituting product using the gas flame spraying technology with metallurgical powder compositions containing tungsten. The authors developed an industrial technology for applying a wear-resistant coating on the working surface of a rod made of AISI 4140 steel. The paper presents the results of the analysis of the stress state of a material with a coating produced using the developed technology in comparison with the original product. In the product obtained by the experimental technology, in the process of applying the coating and its subsequent mechanical processing, uniform residual mechanical stresses are formed that do not exceed the value of the difference in the principal mechanical stresses. The paper presents the results of the study obtained both on standard samples and on a pilot part.

Three-Body Abrasive Wear Behavior of WC-10Cr3C2-12Ni Coating for Ball Mill Liner Application.

Carbide coatings are frequently used to improve the wear resistance of industrial components in various wear environments. In this research, aiming at the service characteristics of easy wear and short service life of ball mill liners, WC–10Cr3C2–12Ni coatings were prepared by supersonic flame spraying technology (HVOF). The reciprocating sliding tests were conducted under four different WC particle size conditions, and the differences in the tribological behavior of the coatings and three–body abrasive wear mechanism were obtained. The findings reveal that the average nanohardness of the WC–Cr3C2–Ni coating is nearly five times greater than that of the steel substance. The COF of tribo-pairs decreases and then increases as the particle size increases. In the case of no particles, the surface of the coating is slightly worn, with fatigue and oxidative wear being the primary wear mechanisms. Small particles (1.5 μm and 4 μm) are crushed and coated on the coating surface, in which the extremely fine particles are plasticized to form friction layers that have a protective effect on the coatings. The protective effect of the particles disappears as the particle size increases and is replaced by a powerful chiseling effect on the coatings, resulting in serious material loss. The particle size has a direct relationship with coating wear.

The effect of mechanical and thermal stresses on the performance of lubricated icephobic coatings during cyclic icing/deicing tests

Evaluating the performance of icephobic coatings interests various industries, such as aviation, maritime, energy, and transportation. Recent developments on icephobic coatings have consistently highlighted the need for durable icephobic surfaces in cold conditions. This study investigates the icing performance and durability of lubricated polymer coatings under cyclic icing/deicing tests. Coatings were made of polyethylene and a solid lubricant and manufactured using flame spray technology. Icing was performed by accreting ice in an icing wind tunnel. Deicing was conducted by removing ice with a centrifugal ice adhesion tester. Surface properties, such as surface morphology, roughness, wettability and chemical composition, were measured before and after the cyclic tests. The results showed stable icephobic behaviour for some coatings, while the performance of others decreased over the cycles. The cyclic tests caused mechanical damage to the surfaces, producing erosion, scratches and, for some coatings, surface cracks. These defects resulted in increased surface roughness and reduced hydrophobicity. However, no chemical changes were revealed for any of the surfaces. Moreover, the causes of cracks were attributed to the difference in thermal expansion behaviour of substrate and coating materials. This result highlights the importance of materials and process parameters selection in flame sprayed coatings designed for cold applications.

Research on Anti-cavitation Coating Performance of Shipping Fluid Machinery

In this paper, micro-nano-structure and nano-structure WC-based coatings were prepared by supersonic flame spraying technology for the cavitation of fluid mechanical parts. We used SEM and XRD to analyze the coating structure, mechanical properties and electrochemical properties. We also studied the cavitation’s mechanism of the coating in 3.5% NaCl simulated seawater medium. The results show that the micro-nano structure WC-10Cr-4Cr coating prepared by supersonic flame spraying has a micro-nano structure and added 4% Cr element, while the nanostructure WC-12Co coating is prone to have decarburization during the preparation process, resulting in generating a certain amount of W to reduce the hardness of the coating. Therefore, the micro-nano structure WC-10Cr-4Cr coating has better porosity, micro hardness and crack toughness properties. In the simulated seawater cavitation environment, the coating has more excellent anti-cavitation performance.

Icephobic Behaviour and Thermal Stability of Flame-Sprayed Polyethylene Coating: The Effect of Process Parameters

The present work investigates the effect of different process parameters on the production of low-density polyethylene (LDPE) coatings by flame spray technology. Previously, flame spraying of polymers has been successfully performed to obtain durable icephobic coatings, providing an interesting solution for applications facing icing problems, e.g. in marine, aviation, energy, and transportation industry. However, the fine tailoring of the process parameters represents a necessary strategy for optimising the coating production due to the unique thermal properties of each polymer. For this purpose, we vary the heat input of the process during flame spraying of the coating, by changing the transverse speed and the spraying distance. The results show that the variation in the process parameters strongly influenced the quality of the polymer coating, including its areal roughness, thickness, chemical composition, thermal stability, and degree of crystallinity. Furthermore, we demonstrate that these properties significantly affect the icephobic behaviour of the surface within the spray window of the chosen parameters. In conclusion, the relationship between the thermal degradation of the polymer and the icephobicity of the surface was defined. This highlights the importance of process parameter optimisation in order to achieve the desired icephobic performance of the LPDE coatings.

Influence of LBE Temperatures on the Microstructure and Properties of Crystalline and Amorphous Multiphase Ceramic Coatings

An Al2O3–TiO2 amorphous composite coating with a thickness of 100–120 μm was fabricated on China low activation martensitic steel (CLAM steel) by oxygen acetylene flame spraying technology and the laser in-situ reaction method. We investigated the microstructures and mechanical properties of the coating after liquid lead-bismuth eutectic (LBE) alloy corrosion under different temperatures for 300 h and found that the corrosion temperature of the LBE had no observable effect on the microstructure and chemical phase of the Al2O3–TiO2 amorphous composite coatings. However, the mechanical properties (micro-hardness and shear strength) of the Al2O3–TiO2 multiphase coating deteriorated slightly with the increase in the immersion temperature of the LBE. As a result of oxygen acetylene flame spraying and laser in-situ reaction technology, it was found that the Al2O3–TiO2 amorphous composite coating exhibits an excellent LBE corrosion resistance, which is a candidate structural material for the accelerator-driven subcritical system (ADS) to handle nuclear waste under extreme conditions.

Comparison of Solid Particle Erosive Wear Rate At Room Temperature of Flexicord Flame Sprayed Different Oxide Coatings

Flame spray technology is basic member of the thermal spray coating family. Higher cost-effective coatings can be produced at higher speeds with new flame spray equipments which developed in recent years. The Flexicord flame spray method developed in this direction offers many advantages. A wide variety of ceramic coatings can be deposited on metallic surfaces with this spray methods in the face of wear-induced problems. In this study, solid particle erosion rates and wear behaviors of different oxide (Al2O3, MgO-Zr2O3, Al2O3-MgO based coatings have been studied comparatively with respect to ASTM G76 standard. Spinel based coatings between the oxide based coatings exhibited superior wear resistance and significantly lower mass loss than the others. Due to the fragile nature of the ceramic coatings, the erosive wear rate is increased by crack growth formation related with the porosity of coating. Due to the accelerated solid particle impacting at high impact angles, wear rate is highest.

Effect of NaNO3 foaming agent on barium ferrite hollow microspheres prepared by self-reactive quenching technology

Al+Fe2O3+BaO2 and NaNO3 as the reactive system and the foaming agent, respectively, are used to prepare barium ferrite hollow microspheres (BFHMs) by self-reactive quenching technology based on flame spraying technology, self-propagating high-temperature synthesis (SHS) technology and quick chilling technology. Effects of NaNO3 on the particle size, morphology, phase structure and microwave absorption properties of BFHMs are investigated through SEM, XRD, particle size analyzer, high-speed camera and vector network analyzer. The results show that, after adding 10wt.% NaNO3, the average particle size of BFHMs decreases initially from 28μm to 6μm, as well as the particle distribution gets narrower. Micro-nano lamellar crystals appear on the surface of BFHMs, with the dimension ranging from 500nm to 2μm. BaFe2O4 and Fe3O4, which have spinel structures, can be seen in XRD, and they are beneficial for microwave absorption properties. The real part (ɛ′), imaginary part (ɛ″) of permittivity, and the imaginary part of permeability (μ″) increases in 0.5–18GHz. The real part (μ′) of permeability increases in 0.5–10.3GHz, while decreases in 10.3–18GHz. The microwave absorption properties are improved greatly, and the minimum reflectivity decreases from −3.1dB to −9.8dB. The reasons for improvement of microwave absorption properties after adding NaNO3 foaming agent may be the decreasing of the particle size of BFHMs, the appearance of ferrites (BaFe2O4 and Fe3O4) with spinel structure and special micro-nano tabular crystals. Magnetoplumbite-type barium ferrites (BaFe12O19) hollow microspheres are obtained after heat-treatment and the microwave absorption properties are further improved.

Study on Preparing Coating for the Anti-Erosion Property of Artillery

To enhance anti-erosion property of artillery barrel and prolong the using period of the artillery, some new technologies are summarized and discussed in this paper, which including electric explosion spraying technology, hypersonic flame spraying technology and plasma surfacing. The experimental results show that the electric explosion spraying technology is a feasible method to prepare coating for the anti-erosion property of 100mm diameter artillery barrel.

Orthogonal Analysis on Hardness of Nickel/Graphite Sealing Coating

Ni/Graphite seal coating was fabricated by flame spraying technology and the effect of oxygen pressure, the powder feeding rate and spraying distance on the coating hardness was investigated base on the orthogonal regression experimental design method. Analysis of orthogonal calculation results suggest that powder feeding rate is the key spraying influential factor valuing 140.884 which affects coating hardness; both oxygen pressure and spraying distance can be considered as secondary factors; the analysis of cross-sectional microstructure shows that the coating hardness value increases with the increase of graphite content; during coating deposition process, the content of graphite in the coating will change when adjusting the flame spraying parameters, which furthermore leads to that the coating hardness changes with variation of flame spraying parameters

Investigation of Surface Coating Preparation of High-Aluminum Bronze Alloy by Induction Remelting Process

With the oxygen-acetylene flame spray technology, the high aluminum copper alloy coating (Cu-14Al-X) was precasted in surface of steel 45#. Then, the coating was remelted by using the high frequency induction heating technology. Using the optical microscope, EPMA,the coating organization, interface combination and interface element diffusion was analysised. The results showed that the high frequency induction remelting process can prepare metallurgicalbonding interface, get good rid of the oxide residue of coating, and get compact structure coating. From this investigation, The conclusion can get that high frequency induction remelting process has the ability of the preparation of non-self-fluxing coating of copper-based alloy, and there was a good interface combination attribute the success to interdiffusion of the coating elements and substrate elements.

Forming and Transforming of by-Product Phases in Reactive Flame Sprayed Al<sub>2</sub>O<sub>3</sub>-Based Coatings

The multiphase coatings with major phases Al2O3-AlxCuy were prepared by the reactive flame spray technology. The melting and reactive behavior of the Al-CuO agglomerated particles and the forming process of the coatings were studied by means of water-quenching experiments and the methods of XRD and SEM. It was shown that during the spray distance between 60 and 150 millimeters, CuO in the agglomerated particles was heated to decompose into Cu2O, Cu and O2. During the flying course, a little of Al reacted with Cu2O and produced Al2O3 and Cu. The reduced Cu mutually dissolved with Al and formed liquid Al-Cu alloy. After the spray particles bumped into the substrate, Cu2O reacted with Al richly, then lots of Al2O3 was produced and Cu was reduced at the same time. These products were wallowed up by the liquid Al-Cu alloy soon. When the temperature of the system dropped quickly, the structure transforming process began. The intermetallics of Cu9Al4 and Al2Cu3 were deposited from the liquid Al-Cu alloy via complicated eutectic reaction and eutectoid reaction.