Thermal Spray Research Articles

Fluid Velocity Sensors Made by Thermal Spray

Fluid Velocity Sensors Made by Thermal Spray

Rapid Scalable One‐step Production of Catalysts for Low‐Iridium Content Proton Exchange Membrane Water Electrolyzers

AbstractProton exchange membrane water electrolysis (PEMWE) is a promising technology for green hydrogen production, although its widespread development with state‐of‐the‐art loadings is threatened by the scarcity of iridium (Ir). Homogeneous dispersion of Ir in an immiscible electro‐ceramic matrix can enhance catalytic mass activity and structural stability. The study presents IrySn0.9(1−y)Sb0.1(1−y)Ox solid solutions produced by highly scalable flame spray pyrolysis (FSP) process as efficient anode electrocatalysts for PEMWE, containing only 0.2 mg cm−2 of Ir in the catalyst layer (CL). Intense mixing of metal vapor and large thermal gradients in the precursor‐derived high‐temperature flame aids stabilizing sub‐nanoscale entropic mixing within self‐preserved 4–6 nm particles. Detailed investigations confirm that the one‐step prepared solid solution electrocatalysts exhibit up to fourfold higher activity toward the oxygen evolution reaction (OER) compared to Ir black. The anode of a PEMWE utilizing this catalyst exhibits high performance and stability over 2000 h but with tenfold lower Ir loading than the state‐of‐art.

The Study of the Etching Resistance of YOF Coating Deposited by Atmospheric Plasma Spraying in HBr/O2 Plasma

Yttrium oxyfluoride (YOF) coatings with different oxygen content were prepared using atmospheric plasma spraying (APS) technology. The etching resistance of the coatings in HBr/O2 plasma was investigated. Shifts in diffraction peaks of the X-ray diffraction, along with XPS analysis conducted before and after etching, demonstrated that Br ions could replace O and F ions and fill the oxygen vacancies after exposure to HBr/O2 plasma, which is supported by the first-principles calculations. Br ions formed a protective layer on the surface of the YOF coating, slowing down further etching by Br ions. By adjusting the oxygen mass fraction in YOF powder, the oxygen vacancy concentration and Br ion filling were regulated to enhance etching resistance. YOF coatings with 6% oxygen content exhibited improved etching resistance compared to YOF coatings with 3% and 9% oxygen content. This improvement was primarily due to the increased Br ion concentration. These findings provide a new approach for developing coatings with enhanced etching resistance.

Properties of Al0.5CoCrFeNi2Ti High-Entropy Alloy System: From Gas-Atomized Powders to Atmospheric Plasma-Sprayed Coatings

AbstractThe performance of the Al0.5CoCrFeNi2Ti HEA atmospheric plasma-sprayed coating was extended from characterizing the properties of its powder prepared via the gas atomization method. It was observed that the gas-atomized HEA powders possessed a solid solution BCC phase, while a major phase transformation to a FCC-L21 intermetallic phase occurred during the annealing process. The formation of the intermetallic phase resulted in an increase in average hardness from 6.28 to 7.64 GPa after annealing at 900 °C for 1 h. Afterward, HEA powders were applied in the atmospheric plasma spray technology. The phase constitution of Al0.5CoCrFeNi2Ti HEA coatings was investigated by varying powder size and applied current. It was observed that the smaller powder sizes prone to oxidation, whereas higher applied current facilitated the phase transformation from BCC to FCC phase. The nanoindentation test indicated distinct average microhardness values for the interlamellar oxide region, BCC unmelted particle and FCC phase lamellar region, which was measured at 12.35, 8.68 and 5.97 GPa, respectively. As a result, the adjustability of coating hardness was achieved by manipulating the relative phase ratio.

Characterization and Tribology Performance of Refractory Materials Coatings with Blast Furnace Slag (BFS) Fabricated by Thermal Spraying

Characterization and Tribology Performance of Refractory Materials Coatings with Blast Furnace Slag (BFS) Fabricated by Thermal Spraying

Development and Taguchi optimization of HVOF sprayed Al2O3 and ZrO2 blended aluminum coating on 316L SS

Abstract A significant number of gas turbines, aircraft engines, bearings, and automotive engines operating under a wide temperature range fail frequently due to fatigue and surface oxidation. Thus, a new coating formulation 40Al-35Al2O3-25ZrO2 was deposited on 316L SS substrate through the high velocity oxygen-fuel (HVOF) thermal spray coating method. The number of passes, spray distance and oxygen flow rate were varied by using Taguchi L9 array to achieve an optimized coating with higher hardness, less porosity, and roughness. The coating phase analysis, microstructure, elemental composition, microhardness and nano hardness were examined by X-Ray diffraction (XRD), scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), Vickers microhardness and nano indentation testing. The sample 5 prepared at spray distance of 20 cm and oxygen/acetylene ratio of 2 exhibited optimal hardness (1972 HV1), tensile strength (6.463 GPa), porosity (0.75%) and roughness (6.2 µm) due to α-Al2O3 andt-ZrO2 phases. Oxygen flowrate was the influential parameter contributing 48.71% to microhardness and 42.41% to roughness, while spray distance with contribution 51.62% was influential parameter for porosity.

Journal of Thermal Spray Technology Announces Revised Aims and Scope

Journal of Thermal Spray Technology Announces Revised Aims and Scope

Molten sulphate vanadateinduced hot corrosion behaviour of YSZ-reinforced thermal spray coatings at elevated temperature

Molten sulphate vanadateinduced hot corrosion behaviour of YSZ-reinforced thermal spray coatings at elevated temperature

The Effect of In Situ Laser-Assisted Plasma Spraying on the Plasma Etching Resistance of Yttrium Oxide Coating

In recent years, yttrium oxide coatings prepared by atmospheric plasma spraying (APS) have been employed extensively in semiconductor processing equipment. Meanwhile, defects in yttrium oxide coating, such as unmelted particles and pores, reduce the etching resistance of the coating. In this work, two yttrium oxide coatings were prepared by in situ laser-assisted plasma spraying (LAPS) coupled with a 500 W and 600 W laser for comparison with a coating prepared by APS, and the effects of the laser on the coating properties were investigated. The results show that the surface roughness was reduced by 25.7% (500 W) and 25.3% (600 W) and the porosity was reduced by 52.3% (500 W) and 36.9% (600 W) after laser coupling. After being etched by CF4/CHF3 for a long time, it was observed from SEM, EDS and XPS analyses that the intensity ratios of the Y-F bonds in the coating were 1 (APS):1.3 (LAPS+500W):1.1 (LAPS+600W), which indicated that the LAPS+500W coating had a thicker fluorination layer. It was also observed that the fluorination layer at the defect was first eroded; then, the erosion area gradually spread to the surrounding area, and finally, the fluorination layer was etched. This indicated that the defects had a significant impact on the etching resistance. Consequently, the LAPS+500W coating with fewer defects and a thicker fluorination layer showed the lowest etching rate. Therefore, in situ laser-assisted plasma spraying coupled with an appropriate laser power is an effective method to improve the performance of yttrium oxide coatings.

FeCoNi-based Alloy Coatings as Low Overpotential Electrocatalysts for Alkaline Water Electrolysis.

Developing efficient, stable and low-cost electrocatalysts is a viable approach to solve the current energy crisis. It is found that increasing the surface area of the electrodes can effectively promote the electrocatalytic efficiency. Herein, the atmospheric plasma spraying (APS) technology was used to prepare FeCoNi-Ni3C alloy coating by adding Ni3C powder to FeCoNi powder with an equal molar ratio. The atomic ratios of Ni3C in the powder are 25 %, 50 %, and 75 %, respectively. The results prove that the pores on the surface of the coating have increased after Ni3C doping, which can provide more active sites in the electrocatalytic process to promote the electrocatalytic reaction. By controlling the proportion of Ni3C, the porosity of the coating surface can be effectively regulated. In 1.0 M KOH electrolyte and 10 mA cm-2, the50 at.% Ni3C coatingshows an overpotential of 105 mV and 212 mV for HER and OER, respectively. It is worth noting that the 50 at.% Ni3C coating has a low Tafel slope of 45.78 mV dec-1(HER) and 44 mV dec-1(OER). Furthermore, the 50 %at. Ni3C coating catalyst has a low potential of 1.664 V at 10 mA cm-2in a water-splitting system.

Tuning Flame Spray Pyrolysis for Variation of the Crystallite Size in Cu/ZnO/ZrO2 and its Influence on the Performance in CO2‐to‐Methanol Synthesis

CO2 hydrogenation to methanol (MeOH) is a key transformation in the Power‐to‐liquid concept, which aims to store energy in chemical energy carriers and chemicals. Cu/ZnO/ZrO2 (CZZ) shows great promise due to its enhanced stability in the presence of water, a critical by‐product when utilizing CO2‐based feedstocks. The structure‐sensitivity of this reaction, especially for particle sizes below 10 nm and in three‐component systems, remains highly debated. Herein, we systematically prepared a series of CZZ catalysts by flame spray pyrolysis to vary the crystallite size and to study its effect on methanol synthesis in this 3‐component system. FSP enabled us to maintain a fixed Cu/Zn/Zr ratio close to the commercial composition (61/29/10 atomic ratio), while varying the precursor feed rate. This resulted in variation in the crystallinity. The characterization by X‐ray diffraction and electron microscopy revealed an increase in crystallite size with rising feed rate for Cu and t‐ZrO2, whereas ZnO remained mostly unaffected. The testing of the materials in methanol synthesis uncovered an increase in performance, higher space time yield and MeOH selectivity, with decreasing crystallite size for two (Cu, t‐ZrO2) of its three components. The increased selectivity with smaller sizes might be attributed to an increase in interfacial sites.

Anti-Sintering Behavior of GYYSZ, Thermophysical Properties, and Thermal Shock Behavior of Thermal Barrier Coating with YSZ/Composite/GYYSZ System by Atmospheric Plasma Spraying

Anti-Sintering Behavior of GYYSZ, Thermophysical Properties, and Thermal Shock Behavior of Thermal Barrier Coating with YSZ/Composite/GYYSZ System by Atmospheric Plasma Spraying

Failure Evaluation of Thermal Spray Coating Using High-Velocity Oxy-Fuel (HVOF) on Steam Turbine Shaft 940-PT 2 A/B

The repair of worn steel shaft surfaces in power transmission systems is made possible by thermal spray procedures, which have become an essential technology in many sectors. With this novel approach, worn shaft components may be recycled effectively since an API 687-compliant wear-resistant coating designed for specialty rotating equipment repairs is applied. The process's efficacy stems from its capacity to extend the functional life of essential mechanical components, therefore decreasing replacement expenses and downtime. The variety of factors that affect the result highlights the intricacy of thermal spray techniques. Finding the ideal mix of these crucial process variables becomes essential to provide the required degree of wear resistance. The coated shafts perform better as a result of this careful tuning, which also guarantees dependability under challenging working conditions. The coated shafts' surface hardness data in this investigation showed that the initial coating hardness value was below the predetermined goals. Several parts that interact with the shaft were redesigned strategically in response to these discoveries. These adjustments were mainly motivated by economic considerations, to optimize effectiveness while resolving the noted hardness deficiencies. Furthermore, a thorough analysis of failure data showed important correlations between different operational parameters and how they interacted, offering a further understanding of how these factors affected wear resistance. This research allowed for the identification of crucial parameters that required change and emphasized the precise balance essential for optimum thermal spray application. All things considered, this study emphasizes how critical it is to use a methodical approach to improve thermal spray processes, guarantee successful shaft component restoration, and ultimately increase the operational longevity of such components in challenging applications.

Effect of manufacturing route on microstructure and micromechanical properties of AlCoCrFeNi high entropy alloy

The manufacturing route of a particular metallic alloy profoundly affects its microstructure, as well as mechanical properties. In that respect, the present research investigates the microstructure and microstructure-dependent mechanical properties of the AlCoCrFeNi high entropy alloy (HEA), that was manufactured via two different routes: (i) Atmospheric plasma spraying (APS) in the form of coating on a stainless steel subtract and (ii) vacuum arc melting (VAM) in the form of bulk material. AlCoCrFeNi HEA coating microstructure is composed of a solid solution (Ni) as a matrix, which contains different phases, as well as intermetallics and defects, such as splat boundaries. On the contrary, the microstructure of bulk AlCoCrFeNi HEA alloy is free from any secondary phases, and is homogeneous in nature, which consists of only the solid solution of Ni. The experimental results show that the strength of the bulk HEA (963.14 ± 28.58MPa of yield strength and 1005.58 ± 22.08MPa of compressive strength) is better than that of HEA coating (yield strength of 802.33 ± 43.76MPa and compressive strength of 817.73 ± 43.84MPa). The phase, as well as splat boundaries in the microstructure, are the ‘weakest link’ in the HEA coating, that serves as defect initiation site. As the bulk HEA alloy is free from these ‘weakest link’, thus, deformation of the material is guided through plastic flow of materials, in the terms of the barrelling effect.

Microstructural evolution and high temperature hot corrosion behaviour of AlCoCrFeNiTi high-entropy alloy coatings

The fuels used contain undesirable impurities such as Na, V, K, S, and Mg in gas turbine engines. These impurities react with hot components under service conditions, leading to the deterioration of the thermal barrier coatings (TBCs) structure and the formation of hot corrosion damage. In this study, metallic powders containing CoNiCrAlY were deposited as bond coat on Inconel 718 superalloy material using high velocity oxygen fuel (HVOF) coating technique. High entropy alloy (HEA) powder containing AlCoCrFeNiTi was synthesized as coating material using mechanical alloying (MA) method. AlCoCrFeNiTi powders were produced using atmospheric plasma spray (APS) coating technique. The produced coating system was subjected to hot corrosion tests at 700 °C and 800 °C temperatures for different time periods in corrosive environment conditions containing Na2SO4 (sodium sulfate) and V2O5 (vanadium pentoxide). Hot corrosion behavior of the coating system was determined, damage formations and degradation processes were investigated in detail. As a result of the determination and synthesis of HEA powder materials, production of coatings, experimental studies and hot corrosion test studies under service conditions, it was seen that the Ti-containing AlCoCrFeNi HEA coating system has usable qualities without any damage such as cracking, buckling or spalling.

Water vapor corrosion behaviours of nanostructured Yb2O3-Yb2SiO5/mullite/Si environmental barrier coatings

In this work, the nanostructured Yb2O3-Yb2SiO5/mullite/Si environmental barrier coatings (EBCs) were designed and prepared by atmospheric plasma spraying. The water vapor corrosion behavior of coatings was investigated at a temperature of 1350 °C for durations ranging from 100 to 500 hours, and the influence of phase compositions, microstructure on this behavior was systematically investigated. The results indicate that phase transformation occurs during the water vapor corrosion process, and severe corrosion takes place at the Yb2O3-Yb2SiO5 top coating and the mullite intermediate layer. Obvious diffusion reaction between Yb2O3-Yb2SiO5 and mullite layers occurred without water vapor, while the diffusion reaction cannot be observed under water vapor. The water vapor corrosion mechanism of EBCs is mainly attributed to residual thermal mismatch stresses, phase transformation resulting from sintering of Yb2O3-Yb2SiO5, as well as the formation of TGO by oxidation.

Comparison of microstructural evolution and high temperature oxidation behavior of AlCoCrFeNiTi and AlCoCrFeNiZr high-entropy alloy coatings

In this study, the isothermal oxidation behaviors of HEA coating systems with AlCoCrFeNiTi and AlCoCrFeNiZr contents were evaluated by comparing microstructurally and investigated in terms of potential applications of thermal barrier coatings (TBCs). For this reason, their oxidation resistance under isothermal conditions, as well as diffusion phenomena occurring at the bond and top coating interface, were investigated. CoNiCrAlY bond coating was applied to the surface of a Nickel-based superalloy substrate by high velocity oxygen-fuel (HVOF) spraying. HEA coating materials were produced by using the mechanical alloying (MA) process. The mechanical activated synthesized HEAs were sprayed on a CoNiCrAlY bond coating by Atmospheric Plasma Spraying (APS). The microstructural changes at the coating interface of CoNiCrAlY, AlCoCrFeNiTi and AlCoCrFeNiZr (HEAs) coatings resulting from oxidation processes at 1200 °C for 5, 25, 50 and 100 h, and the formation and growth behaviors of the thermally grown oxide (TGO) layer were investigated. The present results demonstrate a potential of HEAs in TBC applications. After oxidation tests, crystal lattice transformations took place in both coating systems. In the AlCoCrFeNiZr-HEA TBC system, an increase in diffusion rate, oxygen permeability, and consequently TGO layer thickness was observed by the transformation from the cubic lattice structure to a monoclinic lattice structure with a larger volume. In the AlCoCrFeNiTi-HEA TBC system, the transformation of a narrow rhombohedral lattice with tight planes was maintained. Therefore, the TBC system with AlCoCrFeNiTi-HEA has a lower TGO layer thickness compared to the TBC system with AlCoCrFeNiZr-HEA and has a longer service life against oxidation failure at high operating temperatures. As a result of the production, experimental studies and high temperature oxidation test studies under service conditions, it was seen that AlCoCrFeNiTi and AlCoCrFeNiZr-HEA coatings can be used in the structure of TBC systems.

Intelligent temperature measuring thermal spray multilayer thermal barrier coatings based on embedded thin film thermocouples

Thermal barrier coatings (TBCs) have garnered significant attention as crucial protective components for turbine blades. However, the current use of TBCs is limited by their singular functionality and the inability to accurately obtain the temperature gradient distribution within the coatings. Addressing the aforementioned issues, this paper proposes an intelligent thermal barrier coating embedded with thin-film thermocouples. This method not only provides effective thermal protection but also facilitates the precise measurement of the internal temperature gradient within the coating. To mitigate the thermal mismatch in TBCs under high-temperature environments, which can compromise their lifespan, this study employs multi-objective optimization of structural parameters to design an optimal coating thickness. This strategy ensures both superior thermal protection and extended service life. The intelligent temperature-sensing TBCs were fabricated using atmospheric plasma spraying and magnetron sputtering, followed by comprehensive characterization. To validate the performance of the intelligent temperature-sensing TBCs, static tests were conducted in a muffle furnace. The results demonstrated that the sensors exhibit excellent repeatability and high-temperature durability. Furthermore, a test platform replicating the thermal shock conditions of an engine environment was developed. This platform confirmed that the intelligent temperature-sensing TBCs are capable of accurately measuring the internal temperature gradient within the coating under engine-like conditions, offering a novel methodology for engine monitoring and diagnostics.

Influence of FeSiAl Content on the Morphological Evolution and Electromagnetic Properties of FeSiAl/CaO–B2O3–SiO2 Microwave-Absorbing Coatings

CaO–B2O3–SiO2 (CBS) is a promising lightweight, low-dielectric matrix material for high-temperature microwave-absorbing coatings. However, the comprehensive study of absorbent morphology evolution within such coatings and its influence on electromagnetic (EM) performance has not been conducted. In this work, a series of FeSiAl (FSA)/CBS composite coatings with various FSA contents were fabricated using atmospheric plasma spraying. The morphological evolution of the FSA phase and the resulting EM properties of the coatings were systematically analyzed. Experimental findings show that during the spraying process, when the size of FSA clusters in the composite powder exceeds the thickness of CBS splats, FSA clusters form a rigid contact with the underlying solidified coating, leading to the development of a lamellar structure. This lamellar FSA phase creates local conductive networks, which significantly increase the complex permittivity of the coating. These results provide valuable guidance for controlling absorbent morphology and optimizing the EM properties of CBS-based coatings.

Enhancing high-temperature wear resistance of plasma-sprayed NiCrBSi coatings with nanodiamond reinforcement

High-temperature wear causes industrial components to degrade quickly, leading to reduced efficiency, frequent breakdowns, and costly repairs. Thermal spraying is a surface modification technique employed to address these wear issues by shielding the component using protective coatings. In this study, the high-temperature wear behavior of plasma-sprayed NiCrBSi coatings reinforced with Nanodiamond (ND) particles was systematically evaluated. The coatings were reinforced with 1 wt% and 2 wt% ND, and their tribological performance was assessed under varying thermal conditions. Tribological tests were conducted using a ball-on-disk setup at elevated temperatures of 473 K, 673 K, and 873 K for 60 min. The experimental results demonstrated a significant improvement in the wear response and frictional characteristics of the NiCrBSi coatings with the incorporation of ND particles. Specifically, the NiCrBSi coating reinforced with 2 wt% ND exhibited a significantly lower wear volume loss and a reduced coefficient of friction when compared to the pure NiCrBSi coating. At 873 K, the NiCrBSi-2ND coating demonstrated a 64 % reduction in wear volume loss and 85 % decrease in the coefficient of friction, compared to the pure NiCrBSi coating. The incorporation of NDs greatly enhanced the lubrication and hardness of the NiCrBSi-2ND coating as well as improved the adhesion of wear debris to the newly exposed wear track. The high thermal conductivity of NDs enhanced heat transfer to the coatings, facilitating the formation of a protective tribo layer at elevated temperatures, which improved the wear resistance of the NiCrBSi-2ND coating. These findings underscore the potential of ND as a reinforcing agent to significantly enhance the durability and efficiency of NiCrBSi coatings in extreme thermal environments.