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17 pages, 5118 KiB

Open AccessArticle

Numerical Analysis of the Interactions between Plasma Jet and Powder Particles in PS-PVD Conditions

by Tao Zhang, Gilles Mariaux, Armelle Vardelle and Chang-Jiu Li

Coatings 2021, 11(10), 1154; https://doi.org/10.3390/coatings11101154 - 24 Sep 2021

Viewed by 2044

Plasma spray-physical vapor deposition (PS-PVD) refers to a very low-pressure (~100 Pa) deposition process in which a powder is injected in a high-enthalpy plasma jet, and mostly vaporized and recondensed onto a substrate to form a coating with a specific microstructure (e.g., columnar). [...] Read more.

Plasma spray-physical vapor deposition (PS-PVD) refers to a very low-pressure (~100 Pa) deposition process in which a powder is injected in a high-enthalpy plasma jet, and mostly vaporized and recondensed onto a substrate to form a coating with a specific microstructure (e.g., columnar). A key issue is the selection of the powder particle size that could be evaporated under specific spray conditions. Powder evaporation takes place, first, in the plasma torch between the injection location and nozzle exit and, then, in the deposition chamber from the nozzle exit to the substrate location. This work aims to calculate the size of the particles that can be evaporated in both stages of the process. It deals with an yttria-stabilized zirconia powder and two commercial plasma torches operated at different arc powers with gas mixtures of argon and helium or argon and hydrogen. First, it used computational fluid dynamics simulations to calculate the velocity and temperature fields of the plasma jets under very low-pressure plasma conditions. Then, it estimated the evaporation of the particles injected in both plasma jets assuming an isothermal evaporation process coupled with momentum and heat transfer plasma-particle models in a rarefied plasma. The calculations showed that, for different powers of the Ar–H₂ and the Ar–He operating conditions of this study, the heat flux from the plasma jet to particles inside the torch is much higher than that transferred in the deposition chamber while the specific enthalpy transferred to particles is comparable. The argon-helium mixture is more efficient than the argon-hydrogen mixture to evaporate the particles. Particles less than 2 μm in diameter could be fully evaporated in the Ar–He plasma jet while they should be less than 1 µm in diameter in the Ar–H₂ plasma jet. Full article

(This article belongs to the Special Issue Plasma Sprayed Coatings)

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14 pages, 6698 KiB

Open AccessFeature PaperArticle

Plasma Spraying of a Microwave Absorber Coating for an RF Dummy Load

by Andreas Killinger, Gerd Gantenbein, Stefan Illy, Tobias Ruess, Jörg Weggen and Venancio Martinez-Garcia

Coatings 2021, 11(7), 801; https://doi.org/10.3390/coatings11070801 - 02 Jul 2021

Cited by 5 | Viewed by 3132

Abstract

The European fusion reactor research facility, called International Thermonuclear Experimental Reactor (ITER), is one of the most challenging projects that involves design and testing of hundreds of separately designed reactor elements and peripheric modules. One of the core elements involved in plasma heating [...] Read more.

The European fusion reactor research facility, called International Thermonuclear Experimental Reactor (ITER), is one of the most challenging projects that involves design and testing of hundreds of separately designed reactor elements and peripheric modules. One of the core elements involved in plasma heating are gyrotrons. They are used as a microwave source in electron–cyclotron resonance heating systems (ECRH) for variable injection of RF power into the plasma ring. In this work, the development and application of an alumina-titania 60/40 mixed oxide ceramic absorber coating on a copper cylinder is described. The cylinder is part of a dummy load used in gyrotron testing and its purpose is to absorb microwave radiation generated by gyrotrons during testing phase. The coating is applied by means of atmospheric plasma spraying (APS). The absorber coating is deposited on the inner diameter of a one-meter cylindrical tube. To ensure homogeneous radiation absorption when the incoming microwave beam is repeatedly scattered along the inner tube surface, the coating shows a varying thickness as a function of the tube length. By this it is ensured that the thermal power is distributed homogeneously on the entire inner tube surface. This paper describes a modeling approach of the coating thickness distribution, the manufacturing concept for the internal plasma spray coating and the coating characterization with regard to coating microstructure and microwave absorption characteristics. Full article

(This article belongs to the Special Issue Plasma Sprayed Coatings)

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15 pages, 6237 KiB

Open AccessArticle

Numerical Simulation of Plasma Jet Characteristics under Very Low-Pressure Plasma Spray Conditions

by Tao Zhang, Gilles Mariaux, Armelle Vardelle and Chang-Jiu Li

Coatings 2021, 11(6), 726; https://doi.org/10.3390/coatings11060726 - 17 Jun 2021

Cited by 8 | Viewed by 3264

Abstract

Plasma spray-physical vapor deposition (PS-PVD) is an emerging technology for the deposition of uniform and large area coatings. As the characteristics of plasma jet are difficult to measure in the whole chamber, computational fluid dynamics (CFD) simulations could predict the plasma jet temperature, [...] Read more.

Plasma spray-physical vapor deposition (PS-PVD) is an emerging technology for the deposition of uniform and large area coatings. As the characteristics of plasma jet are difficult to measure in the whole chamber, computational fluid dynamics (CFD) simulations could predict the plasma jet temperature, velocity and pressure fields. However, as PS-PVD is generally operated at pressures below 500 Pa, a question rises about the validity of the CFD predictions that are based on the continuum assumption. This study dealt with CFD simulations for a PS-PVD system operated either with an argon-hydrogen plasma jet at low-power (<50 kW) or with an argon-helium plasma jet at high-power (≥50 kW). The effect of the net arc power and chamber pressure on the plasma jet characteristics and local gradient Knudsen number (Kn) was systematically investigated. The Kn was found to be lower than 0.2, except in the region corresponding to the first expansion shock wave. The peak value in this region decreased rapidly with an increase in the arc net power and the width of this region decreased with an increase in the deposition chamber pressure. Based on the results of the study, the local Knudsen number was introduced for detecting conditions where the continuum approach is valid under PS-PVD conditions for the first time and the CFD simulations could be reasonably used to determine a process parameter window under the conditions of this study. Full article

(This article belongs to the Special Issue Plasma Sprayed Coatings)

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14 pages, 10121 KiB

Open AccessArticle

The Microstructure and Conductivity Evolution of Plasma-Sprayed (Mn, Co)₃O₄ Spinel Coatings during Conductivity Measurements at Elevated Temperature

by Jianbo Zou, Chen Song, Kui Wen, Taikai Liu, Chunming Deng, Min Liu and Chenghao Yang

Coatings 2021, 11(5), 533; https://doi.org/10.3390/coatings11050533 - 30 Apr 2021

Cited by 5 | Viewed by 1824

Abstract

(Mn, Co)₃O₄ spinel is widely used to protect the metallic interconnect of solid oxide fuel cells while it suffers deoxidization during the preparation by plasma spray. This work was proposed to study the effect of spray parameters on the microstructure [...] Read more.

(Mn, Co)₃O₄ spinel is widely used to protect the metallic interconnect of solid oxide fuel cells while it suffers deoxidization during the preparation by plasma spray. This work was proposed to study the effect of spray parameters on the microstructure and conductivity of spinel coatings. In this work, spinel coatings were prepared by the atmospheric plasma spray. The prepared coatings were heated up to 700 °C and held on for 15 h to allow the conductivity evolution. The microstructure and composition of coatings were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectrum (XPS). The results show that all coatings were evidently densified in two hours of heating while the measured conductivities were continuously evolved. The phase composition was found contributed more to the conductivity evolutions than the densification. The conversion of CoO to MnCo₂O₄ was observed and thus endowed the coatings a conductivity of 40 S/cm. A high fraction of Co³⁺ diffraction peaks, a high amount of Mn²⁺ and a low content of Co²⁺ jointly showed that more Co³⁺ occupied the B site of AB₂O₄ phase and more Mn²⁺ stood at the A site, indicating a stoichiometric composition of MnCo₂O₄. Annealing twins were detected by TEM and EBSD for the heated coatings but only a limited contribution to the evolution of the conductivity was considered. Finally, we suggest a high flowrate of plasma gas and a high input energy to prepare spinel coatings with designed conductivity. Full article

(This article belongs to the Special Issue Plasma Sprayed Coatings)

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21 pages, 9922 KiB

Open AccessArticle

Synthesis of Cubic Aluminum Nitride (AlN) Coatings through Suspension Plasma Spray (SPS) Technology

by Faranak Barandehfard, James Aluha and François Gitzhofer

Coatings 2021, 11(5), 500; https://doi.org/10.3390/coatings11050500 - 23 Apr 2021

Cited by 6 | Viewed by 5337

Abstract

Thermal spraying of aluminum nitride (AlN) is a challenging issue because it decomposes at a high temperature. In this work, the use of suspension plasma spray (SPS) technology is proposed for the in situ synthesis and deposition of cubic-structured AlN coatings on metallic [...] Read more.

Thermal spraying of aluminum nitride (AlN) is a challenging issue because it decomposes at a high temperature. In this work, the use of suspension plasma spray (SPS) technology is proposed for the in situ synthesis and deposition of cubic-structured AlN coatings on metallic substrates. The effects of the nitriding agent, the suspension liquid carrier, the substrate materials and the standoff distance during deposition by SPS were investigated. The plasma-synthesized coatings were analyzed by X-ray diffraction (XRD), optical microscopy (OM) and scanning electron microscopy (SEM). The results show higher AlN content in the coatings deposited on a carbon steel substrate (~82%) when compared to titanium substrate (~30%) or molybdenum (~15%). Melamine mixed with pure aluminum powder produced AlN-richer coatings of up to 82% when compared to urea mixed with the Al (~25% AlN). Hexadecane was a relatively better liquid carrier than the oxygen-rich liquid carriers such as ethanol or ethylene glycol. When the materials were exposed to a molten aluminum–magnesium alloy at 850 °C for 2 h, the corrosion resistance of the AlN-coated carbon steel substrate showed improved performance in comparison to the uncoated substrate. Full article

(This article belongs to the Special Issue Plasma Sprayed Coatings)

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11 pages, 5121 KiB

Open AccessArticle

Influence of Substrate Removal Method on the Properties of Free-Standing YSZ Coatings

by Robert Vaßen, Emine Bakan and Sigrid Schwartz-Lückge

Coatings 2021, 11(4), 449; https://doi.org/10.3390/coatings11040449 - 13 Apr 2021

Cited by 3 | Viewed by 1905

Abstract

Thermally sprayed ceramic coatings are often tested as free-standing layers to investigate different properties such as thermal expansion coefficient, thermal conductivity, sintering, mechanical behavior, corrosion resistance, gas tightness, or electrical properties. In this paper, four different substrate removal methods were used to obtain [...] Read more.

Thermally sprayed ceramic coatings are often tested as free-standing layers to investigate different properties such as thermal expansion coefficient, thermal conductivity, sintering, mechanical behavior, corrosion resistance, gas tightness, or electrical properties. In this paper, four different substrate removal methods were used to obtain free-standing YSZ coatings. At first, spraying on a steel substrate and subsequent dissolution of the substrate-coating interface by hydrochloric acid (HCl) was used. Second, the steel substrate was removed by applying an electrical field via electrochemical corrosion of the surface of the substrate. In a third method, the coating was sprayed on a salt (NaCI) interlayer, which was removed later by dissolution in water. At last, the coating was sprayed on a graphite substrate and the substrate was removed by heat treatment. After the preparation of free-standing coatings, these were characterized using scanning electron microscopy, mercury porosimetry, indentation tests, and room temperature three-point bending tests, which allowed the determination of Young’s modulus and viscosity. The results revealed measurable differences in coating properties as a result of the substrate removal methods, i.e., HCl method led to higher porosity and lower modulus in the YSZ coating. Full article

(This article belongs to the Special Issue Plasma Sprayed Coatings)

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16 pages, 8552 KiB

Open AccessArticle

Control of the Pore Structure of Plasma-Sprayed Thermal Barrier Coatings through the Addition of Unmelted Porous YSZ Particles

by Yuanjun Li, Jibo Huang, Weize Wang, Dongdong Ye, Huanjie Fang, Dong Gao, Shantung Tu, Xueping Guo and Zexin Yu

Coatings 2021, 11(3), 360; https://doi.org/10.3390/coatings11030360 - 21 Mar 2021

Cited by 5 | Viewed by 2443

Abstract

In this study, a new pore structure control method for plasma-sprayed thermal barrier coatings (TBCs) through the addition of unmelted, porous yttria-stabilized zirconia (YSZ) particles was investigated. Through a unique way of feeding powder, two powder feeders were used simultaneously at different positions [...] Read more.

In this study, a new pore structure control method for plasma-sprayed thermal barrier coatings (TBCs) through the addition of unmelted, porous yttria-stabilized zirconia (YSZ) particles was investigated. Through a unique way of feeding powder, two powder feeders were used simultaneously at different positions of the plasma flame to deposit a composite structure coating in which a conventional plasma-sprayed coating was used as a matrix and unmelted micro-agglomerated YSZ particles were dispersed in the dense conventional coating matrix as second-phase particles. The effects of the distribution and content of second-phase particles on the microstructure, mechanical properties, and lifetime were explored in a furnace cyclic test (24 h) of the composite coating. The mechanical properties and lifetime of the composite coating depend on the content and morphology of the particles embedded in the coating. The lifetime of the composite structure coatings is significantly higher than that of the conventional coatings. By adjusting the spraying parameters, the lifetime of the composite coating prepared under the optimum process is up to 145 days, which is about three times that of the conventional coating. The results of this study provide guidance for the preparation of high-performance composite structure TBCs. Full article

(This article belongs to the Special Issue Plasma Sprayed Coatings)

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12 pages, 3721 KiB

Open AccessArticle

Comparative Analysis on the Structure and Properties of Iron-Based Amorphous Coating Sprayed with the Thermal Spraying Techniques

by Amjad Iqbal, Sumera Siddique, Moazam Maqsood, Muhammad Atiq Ur Rehman and Muhammad Yasir

Coatings 2020, 10(10), 1006; https://doi.org/10.3390/coatings10101006 - 21 Oct 2020

Cited by 15 | Viewed by 3417

Abstract

Iron-based amorphous coatings are getting attention owing to their attractive mechanical, chemical, and thermal properties. In this study, the comparative analysis between high-velocity oxy-fuel (HVOF) and atmospheric plasma (APS) spraying processes has been done. The detailed structural analysis of deposited coatings were studied [...] Read more.

Iron-based amorphous coatings are getting attention owing to their attractive mechanical, chemical, and thermal properties. In this study, the comparative analysis between high-velocity oxy-fuel (HVOF) and atmospheric plasma (APS) spraying processes has been done. The detailed structural analysis of deposited coatings were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Mechanical and electrochemical properties were investigated by using micro-Vickers hardness testing, pin-on-disc tribometry and potentiodynamic analysis. The microstructure comparison revealed that HVOF-coated samples had better density than that of APS. The porosity in APS-coated samples was 2 times higher than that of HVOF-coated samples. The comparison of tribological properties showed that HVOF-coated samples had 3.9% better hardness than that of coatings obtained via APS. The wear test showed that HVOF-coated samples had better wear resistance in comparison to APS coatings. Furthermore, the potentiodynamic polarization and electrochemical impedance spectroscopy showed that the HVOF-coated samples had better corrosion resistance in comparison to APS-coated samples. Full article

(This article belongs to the Special Issue Plasma Sprayed Coatings)

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