Thermal Spray Research Articles

High-Temperature Wear Behavior and Mechanisms of Self-Healing NiCrAlY-Cr3C2-Ti2SnC Coating Prepared by Atmospheric Plasma Spraying

High-Temperature Wear Behavior and Mechanisms of Self-Healing NiCrAlY-Cr3C2-Ti2SnC Coating Prepared by Atmospheric Plasma Spraying

Microstructure and Mechanical Properties of Nanocrystalline CoCrCuFeNi High-Entropy Alloy Coating Manufactured by Atmospheric Plasma Spraying

Microstructure and Mechanical Properties of Nanocrystalline CoCrCuFeNi High-Entropy Alloy Coating Manufactured by Atmospheric Plasma Spraying

Influence of Reinforcing nano-Al<sub>2</sub>O<sub>3</sub> Particles on Microstructure and Hardness Properties of HVOF Sprayed 80Ni20Cr Coatings

80Ni20Cr coatings produced by high-velocity oxygen fuel (HVOF) thermal spray technique are novel and widely used to improve the corrosion and wear resistance of metal and steel components in many applications, especially in coal-fired power plants. The present study investigated the effects of nano-Al2O3 at 0.5 wt.% on the microstructure of HVOF-sprayed 80Ni20Cr coating deposited on AISI 304L steels corresponding to its coating hardness. The coating was successfully sprayed with a thickness of 150 – 180 µm. The microstructure and phase formed by the coating were analyzed by a field emission electron microscope (FE-SEM) and an X-ray diffractometer (XRD). Synchrotron X-ray fluorescence spectroscopy (SRXRF) was used to confirm the Cr solid solution in the Ni-based coating. The presence of the nano-Al2O3 phase in the 80Ni20Cr coating was characterized by electron backscattered diffraction (EBSD). The nano-Al2O3 particles were homogenously distributed in the coating layers. The incorporation of nano-Al2O3 into 80Ni20Cr enhanced coating characteristics by decreasing surface roughness by 23% and increasing coating hardness by around 4%.

Quantification of the hetero-contact formation process for a CuO/CeO2 hetero-aggregate model system prepared by double flame spray pyrolysis

In hetero-aggregates, different materials form sintered hetero-contacts, which lead to new material properties. In this study, the influence of process parameters on the formation of hetero-contacts in Double Flame Spray Pyrolysis (DFSP) was quantified. The mixing of jets was monitored by Particle Image Velocimetry (PIV) measurements as well as by thermocouples and compared to the single flame setting. Overlap of the jets was evaluated using tracers to visualize the mixing zone. Ten CuO/CeO2 model material samples were prepared with different flame inclination angles, nozzle distances and different particle volume fractions. Mixing on hetero-aggregate level was quantified using Convolutional Neural Network (CNN) evaluations of STEM images, Temperature-Programmed Reduction (TPR) and Differential Centrifugal Sedimentation (DCS) disk centrifugation to determine cluster sizes and hetero-coordination numbers as mixing quantifiers. Here, good correlations between the differently measured quantifiers were observed.

Study on Initial Corrosion Behavior of Arc-thermally Spray Zn, Zn–Al, and Al–Mg Coatings Exposed in Atmospheric Environment for One-Year

AbstractThis paper presents the results of a study comparing the initial corrosion characteristics of thermal spray coatings on Zn, Zn-Al, and Al–Mg thermal spray coatings after one year atmospheric exposure tests at two atmospheric environment sites. The thermal spray coatings were obtained by electroric arc spraying of various metals onto a carbon steel substrate. Atmospheric exposure tests were also conducted for outdoor accelerated exposure tests in which test specimens were applied with artificial seawater. The corrosion properties of these spray coatings were evaluated by surface analysis, film thickness measurements, cross-sectional analysis and anodic/cathodic polarization measurement. After one year of atmospheric exposure testing, white, granular corrosion products were observed on the surface of the Zn and Zn-Al thermal spray coatings, while no significant changes were observed in the Al–Mg thermal spray coating. Similar results were obtained for the surfaces of test specimens in atmospheric exposure tests with artificial seawater. The thickness of the thermal spray coating increased for the Zn thermal spray coating, while no significant change was observed for the other thermal spray coatings. Thus, differences in corrosion behavior were observed due to the composition of the thermal spray coatings. The initial corrosion behavior of the thermal spray coatings was also investigated based on the results of coating morphology and cross-sectional elemental distribution of the coatings.

Particle deposition on the convergent nozzle walls of thermal-spray guns

The present study investigates particle depositions on convergent nozzle walls of (HVOF) spray guns, a process that reduces nozzle lifetime and degrades operation stability and reliability. We perform three-dimensional, two-way coupled simulations of reactive particle-laden compressible flow through a typical thermal spray gun nozzle. We determine critical radial particle velocities at which particles deposit on the wall. We characterize critical velocities concerning particle trajectories, particle diameter, and downstream location of particles deviating from the nozzle center. The critical velocity decreases with particle diameter and increases with the downstream location at which particles deviate from the nozzle center. We exclude the possibility that single particle–particle collision events create sufficient radial particle momentum for deposition. We use the gained insights to propose mitigating measures against particle depositions.

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.

Progressive technologies of laser surfacing and gas‑thermal spraying

The article notes the experience of Yantai Huaheng Energy Conservation Technology Co., Ltd in applying protective anti‑corrosion polymer coatings and discusses the most promising modern recovery and strengthening technologies of thermal spraying (PAPS, AS, HVAF, HVOF) and laser cladding (LASC). Examples of installations that the company has and typical restored machine parts with protective wearand corrosion‑resistant coatings and the microstructure of coatings are given. The main stages of a typical technological process for applying coatings are noted. Using the example of the company, the feasibility and effectiveness of the development of this area in China is noted.

Effect of controlling residual moisture in atmospheric plasma spray-Y2O3 coatings on random defect generation by halogen-based plasma

The fluorine-based plasma resistance properties of atmospheric plasma spray (APS)-Y2O3 coatings were investigated based on residual moisture control levels. APS-Y2O3 coatings at different moisture levels are exposed to F-poor (Ar, NF3, and O2) and F-rich (NF3 and O2) plasma. Outgassing varies with the residual moisture control level. When the plasma supplies sufficient energy, internal moisture reacts with the coating surface to form Y-OH, accelerating the coating degradation. This confirms the decreasing random defect occurrence in the moisture-controlled coatings. The F radical preferentially binds to Y-OH bonds, which have a lower strength than Y-O bonds in F-poor plasma, and reacts with Y-OH and Y-O bonds to form YOxFy in F-rich plasma. YOxFy formed by Y-OH bonds is vulnerable to plasma owing to its low binding strength, which accelerates the formation of random defects. This study highlights the importance of reducing random defects by effective moisture control.

Особенности тонкой структуры Ni-Al покрытий, полученных методом HV-APS

Introduction. Development of Ni-Al intermetallic compounds is one of the priority directions of modern machine building. Due to such characteristics as high heat resistance, high temperature strength, and low density, nickel aluminides are used as functional coatings in the aerospace industry. The main methods of Ni-Al coating surfacing are High-Velocity Oxygen-Fuel and High-Velocity Air-Fuel spraying (HVOF and HVAF), atmospheric plasma spraying (APS) and its modification such as High-Velocity Atmospheric Plasma spraying (HV-APS) which provides non-equilibrium cooling conditions. Since there are eight different intermetallic compounds, as well as martensite transformation, Ni-Al coatings is quite interesting to study. The work purpose is to study the features of the martensitic structure in HV-APS coatings, and also to establish the effect of heating temperature on its decomposition. Materials and methods. Ni-Al coatings were surfaced onto a low-carbon steel substrate using the HV-APS method. Studies of the fine structure of the coatings were carried out using transmission electron microscopy (TEM). In addition, the influence heating temperature on structural transformations of the coatings was analyzed. Results and discussion. Two types of particles are formed in HV-APS coatings: with a dendritic and granular structure. The most part of HV-APS coatings consists of particles with a two-phase grain structure (NiхAl1-х and γ'-Ni3Al grains). Only NiхAl1-x grains undergo martensitic transformation at cooling. Martensite in large grains (sizes greater than 500 nm) has a lamellar structure, while small grains are completely transformed into one martensite plate. In addition, the coatings contain grains in which martensite plates (NiхAl1-х) and β-phases alternated. It is shown the behavior of martensitic plates at colliding with each other, as well as with the γ′-Ni3Al grain. Heating up to 400 °C contribute the begins of martensite decomposition in individual grains with the release of a secondary phase; after heating up to 600 °C all martensite dissolves.

Regulation of Ir Dopant in Mo Oxides by Flame Spray Pyrolysis for Efficient CO2 Hydrogenation.

Mo carbide is recognized as one of the most promising catalyst for CO2 utilization via reverse water-gas shift (RWGS). However, it always suffered from low processing capacity, undesired products and deactivation. Herein, an Ir modified MoO3 synthesized by the flame spray pyrolysis (FSP) method exhibits higher reaction rate (63.0 gCO2·gcat-1·h-1) compared to the one made by traditional impregnation method (45.8 gCO2·gcat-1·h-1) over the RWGS reaction at 600°C. The distinguishing feature between the two catalysts lies in the chemical state and space distribution of Ir species. Ir species predominated in the bulk phase of MoO3 during the quenching process of the FSP method and were mainly in the metallic states, which revealed by X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectroscopy (ToF-SIMS) characterizations. In contrast, the Ir introduced via impregnation method were mainly on the surface of MoO3 and in oxidized state. The regulation of Ir dopant in MoO3 catalyst by different methods determines the carbonization process to Mo carbides, and thus affects the catalytic performance. This work sheds light on the superiority of the FSP method in synthesizing Mo oxides with heteroatoms and further creating an efficient Mo-based catalyst for CO2 conversion.

Thermal Spray Nanostructured Coatings Integrated with Artificial Intelligence: A Sustainable Approach in Industry for Corrosion Applications

Coatings are the most common method for protecting metals from corrosion. The use of nano-sized coating materials can enhance the strength and decrease the porosity level of the developed coatings. The nano-coatings have shown improved mechanical properties, corrosion resistance, and wear resistance in recent studies. As a result, the use of nano-sized coatings can provide the benefit to the Industrial machinery components for longer operational periods. This review article covers the corrosion behavior of nano-structured coatings in the initial section followed by the role of artificial intelligence in predicting the corrosion rate of nanostructured coatings.

A case study: anti-corrosion performances of plasma sprayed AT13 coatings on CrZrCu thin wall cylinder with adjusted parameters for controlling deformation

PurposeThis paper aims to control the deformation of a thin wall CrZrCu cylinder components (wall thickness 5 mm, diameter 400 mm) during thermal spray alumina-titania (AT13) coating by adjusting the spray parameters without deteriorating its quality evidently.Design/methodology/approachThe deformation was controlled by lowering the temperature of the component in the way of adjusting the spray parameters. The main parameters adjust included extending the spraying distance, from normally 120 mm to 140 mm, decreasing plasma power from 50to 42 kW. An alumina-titanium (AT13) ceramic coating was chosen for protecting the substrate from corrosion. Microscopic morphology and phase analysis, insulation resistance testing, neutral salt test and electrochemical method were used to analyze the anti-corrosion and insulation performances of the coating.FindingsThe results indicate that, after adjusting the spraying parameters, the coating has a relatively high porosity, with an average value of 8.96 ± 0.77%. The bonding strength of the coating is relatively low, with an average value of 17.69 ± 0.85 MPa. However, after sealing, the polarization resistance of the coating in seawater can be maintained above 6.25 × 106 Ω.cm2 for an extended period. The coating has a high resistance (=1.1 M Ω), and there is no apparent galvanic corrosion when contacted with TC4 alloy. Additionally, analysis of corrosion products on the sample surface reveals that the samples with sprayed alumina-titanium ceramic show no copper corrosion products on the surface, and the coating remains intact, effectively isolating the corrosive medium.Originality/valueBy adjusting the spraying parameters, the deformation of the cylinder thin-walled component can be effectively controlled, making the φ 400 × 392 mm (thickness 5 mm) CrZrCu cylinder com-ponent with a maximum diameter deformation of only 0.14 mm. The satisfactory corrosion performances can be achieved under adjusting spraying parameters, which can guarantee the application of ceramic coating for weapon launching system of naval ships.

Rare earth-doped ceramic coatings: Analysis of microstructure, mechanical properties, and slurry Erosion resistance using high pressure-high velocity oxy-liquid fuel deposition

The high pressure-high velocity oxy liquid fuel (HP-HVOLF) is a current industry-adopted thermal spraying technique for developing high melting point powder coating over surfaces. In the current manuscript, the rare earth (La2O3/CeO2/Er2O3–0.3 wt%. each) doped and without rare earth doped carbide (WC-10Co-4Cr) coatings have been deployed on stainless steel (SS410) via HP-HVOLF process. The comparison among the properties of the substrate, without rare earth coating and rare earth oxides doped coatings have been characterized by conducting mechanical, microstructural, and slurry jet erosion analysis. The results show that the hardness, modulus of elasticity, and flexural strength of the cermet coating are considerably higher for rare earth-doped coatings than those without rare earth-doped coatings and substrates (SS410). The EDX (energy dispersive X-ray spectroscopy) has recognized the occurrence of different elements on the surface together with rare earth. Moreover, its compounds such as Co3W3C and W2C were inveterate using X-ray diffraction (XRD) measurements. The porosity level of the rare earth doped, and un-doped coatings are obtained to be less than 1 % and≥1 to ≤2 % respectively. Moreover, the rare earth-doped cermet coated surface shows hydrophobic behavior with a maximum water contact angle (WCA) of ≈129.4°. Furthermore, the slurry jet behavior of rare earth doped coating shows high wear resistance as compared to without RE doped coatings, indicating its potential for robust performance under erosive conditions.

The effect of oxidation on tribology behavior of nickel-graphite coated stainless steel SS420

The main solution to the challenge of maintaining maximum sealing in the compressor section of each gas turbine is the use of abradable coatings. These coatings have a double duty, including (a) maintaining the lagging and (b) protecting the tips of the rotor blades. Choosing the type of abradable coating primarily depends on the service temperature of the coating. Nickel-graphite (Ni-G) coating is a good choice for use up to 480 °C and, or steel/sub-alloy rotor blades. In this research, the Ni-G coating was applied by the flame spraying method of Ni-G powder with a thickness of about 250 μm on an SS420 stainless steel substrate. The effect of the composition of the bonding layer was also investigated using two compositions, Ni-5Al and NiCrAlY. Obtaining the knowledge of applying Ni-G coating by flame spraying, identifying the structural and compositional characteristics of the coating (through optical and electron metallography), and the effect that oxidation can have on the tribological behavior of the coating were among the goals of this project. The best conditions for spraying the Ni-G coating were achieved an oxygen gas pressure of 6 bar, oxygen flow rate of 18 L min−1, acetylene pressure of 1.5 bar, acetylene flow rate of 24 L min−1, and the distance between the gun head and the sample surface was 22 cm. The results showed that placing the coating in oxidizing conditions increases its coefficient of friction. The increase in the coefficient of friction was attributed to the formation of oxide shells on the surface of the coating after 500 h of exposure to oxidation conditions. Corresponding to the higher coefficient of friction, the oxidized coating showed a decrease in wear resistance as a result of oxidation. This result can show the decrease in abradable of this coating with increasing service time.

Wear behavior of electron beam remelting modified Ni/WC thermal spray coatings

Ni/WC composite coatings were prepared by combining thermal spraying and electron beam remelting. Characterization methods such as SEM, EBSD and XRD were used. The effect of electron beam remelting beam current on the corrosion and wear resistance of Ni/WC composite coatings was investigated. The microstructure showed that hard carbides and borides such as W2C, Cr23C6, and M3B were generated within the remelted coating. Compared to the thermal spray specimens, the hardness of the 16 mA specimen was increased by a factor of 1.47, and the hardness of the 22 mA specimen was also increased by a factor of 1.14. The results of the corrosion experiments showed that the 16 mA specimen had the lowest corrosion current density and the highest corrosion potential, which showed the best corrosion resistance. Wear experiments were carried out by using SiC balls as the counterbodies. The results showed that the wear resistance of both 16 mA and 22 mA specimens under dry friction with 3.5 % NaCl solution conditions was improved compared to the thermal spray coating. The 22 mA specimens showed more obvious subsurface damage. The wear mechanism of thermal spray coatings is mainly abrasive, and the wear mechanism of remelted coatings is mainly abrasive and adhesive.

Thermal cycling property of the novel Hf6Ta2O17/YSZ TBCs prepared by atmospheric plasma spraying technology

Hf6Ta2O17, with low thermal conductivity, high thermal expansion coefficient, and excellent fracture toughness, was a promising candidate ceramic top coat material of thermal barrier coating (TBC). A novel Hf6Ta2O17/YSZ double ceramic top coat prepared by atmospheric plasma spraying (APS) was applied to study the role of the microstructure and mechanical property on the thermal cycling property at 1200 °C. Results show that the rapid decomposition of Hf6Ta2O17 occurred during the spraying process. As the increased spraying power, more HfO2 phases were observed in the Hf6Ta2O17/YSZ TBCs. Besides, the porosity of the Hf6Ta2O17 ceramic top coat decreased with the increased spraying power, resulting in the elastic modulus of the Hf6Ta2O17 ceramic top coat enhancement. The highest cycles at 1200 °C were obtained for the Hf6Ta2O17/YSZ TBCs with the lowest elastic modulus and least HfO2 phases, and were twice as long as the cycles of the single YSZ TBCs. The chemical reaction between HfO2 and Hf6Ta2O17 might have contributed to the cracking of the Hf6Ta2O17/YSZ TBCs. This work provides a new option for the preparation and development of the ternary oxides by APS.

Reaction-induced unsaturated Mo oxycarbides afford highly active CO2 conversion catalysts.

Sustainable CO2 conversion is crucial in curbing excess emissions. Molybdenum carbide catalysts have demonstrated excellent performances for catalytic CO2 conversion, but harsh carburization syntheses and poor stabilities make studies challenging. Here an unsaturated Mo oxide (Mo17O47) shows a high activity for the reverse water-gas shift reaction, without carburization pretreatments, and remains stable for 2,000 h at 600 °C. Flame spray pyrolysis synthesis and Ir promoter facilitate the formation of Mo17O47 and its in situ carburization during reaction. The reaction-induced cubic α-MoC with unsaturated Mo oxycarbide (MoOxCy) on the surface serves as the active sites that are crucial for catalysis. Mechanistic studies indicate that the C atom in CO2 inserts itself in the vacancy between two Mo atoms, and releases CO by taking another C atom from the oxycarbide to regenerate the vacancy, following a carbon cycle pathway. The design of Mo catalysts with unsaturated oxycarbide active sites affords new territory for high-temperature applications and provides alternative pathways for CO2 conversion.

Thermal cycle behaviour of plasma sprayed thermal barrier coatings on cast iron substrate for the application of liner of internal combustion engine

In the present scenario, research on Thermal Barrier Coatings (TBCs) is attracting significant attention in high-temperature applications due to the rising demand in industrial applications, such as gas turbine blades and internal combustion engine components. To meet these demands, it is essential to enhance the mechanical and oxidation properties of thermal barrier coatings. The atmospheric plasma spray methodology for producing these coatings has become a central focus in recent times. In this work, TBCs were prepared by blending pure alumina and Yttria-Stabilized Zirconia (YSZ) in equal proportions. Extensive study of TBCs carried out under high-temperature conditions through thermal cycle tests at elevated temperatures, around 850 °C. A total of 350 thermal cycles were conducted, and microstructures of the coating surface were examined at 150, 250, and 350 cycles. High-temperature stress, generated due to the sintering of the coating, also influences the life of the coatings. Specimen with a topcoat thickness of 300 μm, exhibited good thermal shock resistance compared to the specimens with topcoats of thickness of 100 μm and 200 μm. The effects of process parameters, porosity, and thermal shock resistance are presented in detail. The topcoat with a thickness of 300 μm demonstrated excellent thermal shock resistance and reduced formation of thermally grown oxide (TGO). The porosity of the coating, found to be between 2% and 3%, contributed to its dense nature, effectively reducing oxidation rates and enhancing the coating's lifespan under cyclic high-temperature conditions.

Enhanced cyclic oxidation resistance of Metcoloy II coated ASTM A53 Grade B steel by electric arc thermal spray

This study evaluates the enhanced cyclic oxidation resistance of Metcoloy II coatings applied to ASTM A53 Grade B steel substrates using electric arc thermal spray, across temperatures ranging from 500 °C to 700 °C. The research identifies distinct performance differences between coated and uncoated samples under cyclic oxidation conditions. Initially, both sample types exhibited mass increases due to oxide formation. However, uncoated samples developed non-protective iron oxides, while Metcoloy II coatings formed a protective layer of chromium and nickel oxides. During 500 oxidation cycles at 500 °C, uncoated samples showed a rapid mass increase, indicative of accelerated oxidation, whereas Metcoloy II coatings experienced a controlled mass gain, reflecting effective protection by chromium and aluminum oxides. At 700 °C, the mass variation trends were similar for both types initially; however, uncoated samples suffered significant mass loss due to iron oxide volatilization, emphasizing their susceptibility. Conversely, Metcoloy II coatings exhibited a reduced but steady mass increase, indicating their resilience under high-temperature conditions. Microstructural analysis confirmed the presence of a protective oxide layer in the coated samples, which is essential for reducing substrate oxidation. Although challenges such as coating detachment and thinning were observed, particularly at higher temperatures, Metcoloy II coatings maintained their protective role. This study highlights the coating's effectiveness in extending the lifespan of steel substrates subjected to cyclic oxidation, providing valuable insights for optimizing protective coatings in demanding industrial applications and advancing material science strategies for enhanced durability.