Showing papers in "Journal of Thermal Spray Technology in 1992"

Microstructural evaluation of tungsten carbide-cobalt coatings

Abstract: Tungsten carbide-12 wt.% cobalt coatings were deposited using optimized high-energy plasma (HEP) and high-velocity oxygen fuel (HVOF) thermal spray techniques. The coatings were evaluated using transmission electron microscopy, differential thermal analysis, X-ray diffraction, and subjected to wear tests to relate the coating structure to wear performance. Coatings were evaluated in the assprayed condition, as well as after heat treatments in inert atmosphere. The results indicate that a substantial amount of amorphous matrix material is created during the thermal spray process. Carbon and tungsten, liberated through the dissociation of the WC, combine with cobalt present in the starting powder to form amorphous material on solidification. Differential thermal analysis revealed an exothermic reaction for both the HVOF and HEP coatings at approximately 853 and 860 °C, respectively, which did not occur for the powder. Post-coating heat treatment in an inert atmosphere resulted in the recrystallization of the amorphous material into Co6W6C and Co2W4C, which was dependent on the time and temperature of the heat treatment. Wear testing showed improvement in the wear performance for coatings that were subjected to the heat treatment. This was related to the recrystallization of the amorphous matrix into eta phase carbides.

RF Induction Plasma Spraying: State-of-the-Art Review

Abstract: Radio frequency (RF) induction plasma technology has gained wide acceptance for the preparation of plasma spray coatings and structural free-standing parts of metals, ceramics, and metal-matrix composites. Its principal advantages are the relatively large volume and low velocity of the discharge, which coupled with the ease of axial injection of the powder into the plasma allows for the melting of relatively large particles at high throughput. The absence of electrodes offers the added advantage of ease of operation under a wide range of conditions at atmospheric and low pressure, with an inert, reducing, or oxidizing atmosphere. Highlights of recent advances in induction plasma melting and deposition of materials are presented in this article. The first section deals with advances in induction plasma spraying technology including system and torch design. This is followed by a brief overview of mathematical modeling and diagnostic studies of the induction plasma deposition process. Examples of applications of induction plasma spraying for the preparation of protective coatings and fiber-reinforced metal matrix composites are presented in the final section.

Structure/property relationships in sintered and thermally sprayed WC-Co

Abstract: Thermally sprayed WC-Co is widely used as a wear-resistant coating for a variety of applications. Although it is well established that thermal spray processes significantly affect chemistry, microstructure, and the phase distribution of WC-Co coatings, little is known about how these changes influence wear resistance. In this study, the microstructure and wear behavior of sintered and thermally sprayed WC-Co materials are examined. Powders of WC-12 wt% Co and WC-17 wt% Co were pressed and sintered, as well as thermally sprayed by high-velocity oxy-fuel (HVOF), air plasma spray (APS), and vacuum plasma spray (VPS) techniques. Results indicated considerable differences in the resulting microstructures, mechanical properties, and wear resistance. The thermally sprayed coatings showed anisotropic fracture toughness, whereas the sintered materials did not. It was also shown that a combined mechanical property/microstructure parameter, based on considerations of indentation fracture mechanisms, can be used in most cases to describe abrasive and erosive wear resistance of thermally sprayed WC-Co materials as follows: Wear resistance a % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiFj0de9sqqrpepC0xbbL8F4rrpm0dbba9-u0ddr-df9% qqFn0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-xfr-x% b9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcLbsacqaHXoqyju% aGdaqadaGcbaqcLbsacaWGlbqcfa4aa0baaSqaaGqaaKqzGeGaiaiG% aaab--xsaiacaciaaqW--neaaSqaaKqbaoacaciaaWX-liaameacac% iaaWX-jugibiacaciaaWX-iodaaWqaiaiGaaah-NqzGeGaiaiGaaah% --hoaaaaaaGaamisaKqbaoacaciaaWR-CaaaleqcaciaaWR-bGaGac% aa86Fcfa4aiaiGaaae-VGaaWqaiaiGaaae-NqzGeGaiaiGaaae-Jym% aaadbGaGacaaq8FcLbsacGaGacaaq8-FYaaaaaaaaOGaayjkaiaawM% caaKqbaoaabmaakeaajuaGdaWcaaGcbaqcLbsacGaGacaaKdWGwbqc% fa4aiaiGaaa5a0baaSqaiaiGaaa5aKqzGeGaamOzaaWcbGaGacaaKd% qcLbsacGaGS-3qaiacaY+FVbaaaaGcbaqcLbsacGaG48xmaiacaIZF% TaGaiaiodAfajuaGdGaG40baaSqaiaioieGajugibiacaciaaWO-+z% gaaSqaiaiojugibiacaciaaaX--neacGaGacaaq8-FVbaaaaaaaOGa% ayjkaiaawMcaaaaa!8ABD! $$\alpha \left( {K_{IC}^{{\raise0.7ex\hbox{$3$} \!\mathord{\left/ {\vphantom {3 8}}\right.\kern- ulldelimiterspace}\!\lower0.7ex\hbox{$8$}}} H^{{\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 2}}\right.\kern- ulldelimiterspace}\!\lower0.7ex\hbox{$2$}}} } \right)\left( {\frac{{V_f^{Co} }}{{1 - V_f^{Co} }}} \right)$$ whereK ic is the indentation fracture toughness,H is hardness, andV Co f is the volume fraction of cobalt. This relationship provides a means for assessing wear resistance of WC-Co coatings intended for industrial applications requiring abrasion and/or erosion resistance.

Studies on the thermal spraying of apatite bioceramics

Abstract: Hydroxylapatite (HA) coatings on metal substrates have been investigated for many years. These coatings have proved to be compatible with bone. The degree of crystallinity of HA changed, and sometimes dissociation was observed with respect to the plasma spray process. However, the plasma spray process hardly altered the crystallographic structure, with only line broadening visible. Thein vitro solubility is dependent on the degree of crystallinity of the coating. Tensile strength measurements on the strength of the coating-substrate interface using various adhesives revealed a significant difference between epoxy resin and methacrylate. The failure mode of this tensile test was dependent on the coating thickness and surface texture (polished versus nonpolished). In animal studies, the fixation of hydroxylapatite plasma- spray coated cylinders as well as noncoated Ti- 6A1- 4V cylinders (Ti) in cortical bone was evaluated using pushout tests. It appeared that HA- coated implants showed higher push- out strengths in the first months than the titanium implants, because of the earlier bone formation against the HA coating.

A pragmatic analysis and comparison of HVOF processes

Abstract: A number of high-velocity oxygen-fuel flame (HVOF) systems have evolved during the last 9 years. The most advanced is now challenging the coating qualities produced by the very successful detonation (D-Gun) process. The fundamentals of these various processes are described and compared. A mathematical analysis of an established HVOF gun is profiled. Gas and particle temperatures, velocities, pressures, and Mach numbers are calculated and plotted at various points within the gun and spray stream. Significantly, all measured values were in close agreement with calculated and predicted values. Flow patterns and shock-wave phenomena are also described and compared with actual observations.

Significance of quenching stress in the cohesion and adhesion of thermally sprayed coatings

Abstract: In thermal spraying, molten particles strike a solid surface, where they are flattened and quenched within a very short time. Considerable in-plane tensile stress on the order of 100 MPa can develop within each splat during quenching after solidification because thermal contraction of the particle is constrained by the underlying solid. Ni-20Cr alloy and alumina powders have been plasma sprayed in air onto steel substrates that were maintained at about 473 K. The influence of spraying conditions such as spray distance on the magnitude of the quenching stress have been studied by measuring the curvature of the substrate during spraying. Mechanical properties such as Young’s modulus and bend strength of the deposited coatings have also been measured. A strong correlation was found between the quenching stress and the strength of Ni-20Cr coatings, which suggests that the strength of interlamellar bonding limits the quenching stress at such temperature.

Diagnostics of thermal spraying plasma jets

Abstract: Direct current thermal plasma jets are strongly affected on the one hand by the arc root fluctuations at the anode, resulting in a type of pulsed flow and enhanced turbulence, and on the other hand by the entrainment of surrounding cold gas in the plasma jet. These phenomena and the resulting temperature distributions have been studied using a wide range of diagnostic techniques, including fast cameras, laser doppler anemometry (LDA), coherent anti-Stokes Raman spectroscopy (CARS), Rayleigh scattering, emission spectroscopy, Schlieren photography, enthalpy probes, and sampling probes. The information obtained by these techniques is evaluated and compared. The effect of the arc fluctuations on the spectroscopic measurements is emphasized, and the possibility of using these fluctuations to determine information on the arc behavior and the axial velocity of the jet is presented. Optimization of plasma processing of solid particles requires information about their size and surface temperature, as well as number flux, and velocity distributions at various locations in the flow field. The different statistical techniques of inflight measurements are discussed together with their limitations. A method to determine the temperature and species density of the vapor cloud or comet traveling with each particle in flight is then presented. However, such statistical measurements present ambiguities in their interpretation, which can be addressed only by additional measurements to determine the velocity, diameter, and surface temperature of a single particle in flight. Moreover, information on single particles is required to understand the coating properties, which depend strongly on the way the particles flatten and solidify upon impact. A method to obtain data related to a single particle in flight and to follow the temperature evolution of the corresponding splat upon cooling is presented. The article concludes with the description of the experimental techniques to follow the temperature evolution of the successive layers and passes. This is important because temperature distribution within the coating and substrate controls the adhesion and cohesion of coatings as well as their residual stress.

Flattening and solidification of thermally sprayed particles

Abstract: In this article, molybdenum particles were plasma sprayed on copper, zirconia, and glass substrates. The impact of the molten particles was monitored using a fast two-color optical fiber pyrometer focused on a small spot on the substrate surface. The apparent duration of the flattening process and the cooling speed, both determined from the pyrometer signals, were found to depend on the substrate conditions and to vary with coating thickness. The substrate material and its roughness were also found to influence the texture in the sprayed coatings. Furthermore, a transient thermal flow numerical model was used to compute reliable thermal histories of the impinging particles and the underlying lamellae, the interfacial thermal resistance being determined by comparison of experimental thermograms with computed ones.

Thermal spray shape deposition

Abstract: This paper describes a new spray-forming process based on thermal spray shape deposition. Shape deposition processes build three-dimensional shapes by incremental material buildup of thin, planar crosssectional layers. These processes do not require preformed mandrels and can directly build three-dimensional structures of arbitrary geometric complexity. The basis for the thermal spray approach is to spray each layer using a disposable mask that has the shape of the current cross section. Masks can be produced from paper rolls, for example, with a CO2 laser. In addition to applications for rapid prototyping, this approach makes possible the fabrication of composite structures and integrated electronic/mechanical assemblies that are not feasible with conventional manufacturing technologies.

Current Problems in Plasma Spray Processing

Abstract: This article summarizes eight contributions from a thermal spray conference that was held in late 1991 at Brookhaven National Laboratory, Upton, Long Island, New York. Plasma spray processing is discussed in terms of plasma-particle interactions, deposit formation dynamics, thermal properties of thermal barrier coatings, mechanical properties of coatings, feedstock materials, porosity, manufacture of intermetallic coatings, and synchrotron X-ray microtomographic methods for thermal spray materials. Each section is intended to present a concise statement of a specific practical and/or scientific problem. It then describes current work that is being performed to investigate this area, and finally suggests areas of research that may be fertile for future activity.

Reactive plasma spraying of wear-resistant coatings

Abstract: A method for producing wear-resistant, carbide-reinforced coatings has been investigated. A conventional low-pressure plasma gun has been modified with a downstream reactor into which carbon-containing gases are mixed, heated, and disassociated. The disassociated gas ions—H* and C* —are subsequently brought into contact with heated, molten metal matrix powders. Experiments with NiCr/Ti blends and W powders have shown that uniformly dispersed carbides such as, TiC, Cr^Cy, WC, and W2C were formed in situ on the metal precursor powders during deposition. The in situ formed particles, being formed directly from the matrices, show excellent matrix cohesion and lead to high and uniform deposit microhardnesses. The process is described and several evaluations of materials, reactive gases, and spray conditions are reported. Microanalysis of the coatings are presented, microhardness values are reported, and XRD identifies the in situ formed phases.

Hypervelocity impact fusion—a technical note

Abstract: A very simple outline of the engineering theory for the implementation of hypervelocity oxygen fuel (HVOF) and hypervelocity air fuel (HVAF) processes is presented. Several calculations show that a condition can be reached where the impact energy of these processes can be optimized to produce a new class of coatings termed “hypervelocity impact fusion” coatings. The microstructures of these coatings exhibit minimum oxidation and very good bonding to the substrate.

Study of phase changes in plasma sprayed deposits

Abstract: The formation of a plasma-sprayed coating that exhibits predictable properties requires the control of many process variables The phase changes that take place during plasma spraying are significant material variables that should be controlled Several different materials were deposited in air with a water-stabilized plasma torch (model PAL 160) Usually, air was used as a carrier gas for the powder; however, argon was also used for some coatings The injected powders (NiAl, Ni, ZrSiO4-based, Al2O3-based, etc) as well as the coatings were studied for, among other properties, their structure, particle size, microhardness, and chemical and phase composition Phase changes induced by the different cooling rates of molten particles after their impact on a substrate are illustrated for ZrSiO4 It has also been found that the oxidizing power of the water-stabilized torch is less than previously believed For example, coatings produced with nickel powder injected with argon as the carrier gas exhibited almost no oxides Significant element redistribution during plasma spraying was demonstrated with a two-phase NiAl feedstock powder The coating exhibited almost all the phases that are present in the binary NiAl alloy as well as envelopes of oxides and traces of amorphous phase

Synthesis and high-temperature stability of titanium aluminide matrixin situ composites

Abstract: A premixture of elemental powders of titanium and aluminum was supplied as a spray material for the direct fabrication of titanium aluminide matrixin situ composites by means of reactive low-pressure plasma spraying with a nitrogen and hydrogen mixed plasma gas. The aluminum content varied from 10 to 63 wt.% in the premixtures. The matrix of sprayed layers consisted of three kinds of titanium aluminides—Ti3A1, TiAl, and TiAl3—which begin to form on a low-carbon steel substrate immediately after deposition. The formation of nitrides, which act as a reinforcement, occurs both during the flight of liquid droplets and on the substrate. The nitrogen content is approximately 4 to 5 wt.% in the sprayed intermetallic matrix composites, regardless of the aluminum content of the premixtures. The kinds of titanium aluminides andin situ nitrides developed depend on the aluminum content of the premixtures. The homogeneity of the distribution of aluminum and titanium in sprayed intermetallic matrix composites has been improved by vacuum annealing. The predominant TiAl phase that formed in the sprayed intermetallic matrix composites with a Ti-36 wt.% AI premixture increases in quantity through annealing. Although some minor nitrides disappear through annealing, the principal reinforcement, Ti2AlN, does not decompose, but increases in quantity. The hardness of sprayed intermetallic matrix composites varies with aluminum content of the premixtures, but is always greater than that of sprayed titanium aluminides containing no nitrides. Annealing does not reduce the hardness of sprayed intermetallic matrix composites. Sprayed and annealed intermetallic matrix composites with a Ti-36 wt.% Al premixture maintain their hardness of approximately 500 HV up to 800 K. Hence, reactive low-pressure plasma spraying offers a promising fabrication method for titanium aluminide matrixin situ composites, which are expected to excel in wear resistance applications at elevated temperatures.

Response surface methodology for optimization of plasma spraying

Abstract: Response surface methodology was used to describe empirical relationships among three principal independent variables that control the plasma spraying process. The torch-substrate distance, the amount of hydrogen in the primary gas (argon), and the powder feed rate were studied. A number of dependent variables (responses) were determined, including the deposited layer roughness, density, hardness, chemical composition, and erosion rate. The technique facilitates mapping of the responses within a limited experimental region without much prior knowledge of the process mechanisms. The maps allow process optimization and selection of operating conditions to achieve the desired specifications of the plasma sprayed coating. To illustrate the approach, a simple system of WC-12%Co was deposited on a mild steel substrate. The resulting response surfaces were used to define optimum, or “robust,” deposition parameters.

Industrial guide—markets, materials, and applications for thermal-sprayed coatings

Abstract: This article is presented in two parts. First, some select industrial sectors are analyzed, and the activities most likely to sustain or promote growth are highlighted. The second part profiles current activity by showing, for each of these industrial sectors, which equipment and processes are operating, which coating functions are required, and which types of material are currently consumed.

Status of thermal spray technology in japan

Abstract: This article summarizes the present status and prospects for future progress of the thermal spraying business and technology in Japan. Organizations that have supported thermal spraying business and technology consist of coating contract shops, producers and suppliers of spray equipment and consumables, and large companies that have been using thermal spray technology in their production lines. Moreover, out-side, noncommercial organizations such as universities, government, or local industrial institutes and academic societies for thermal spraying are reviewed. In terms of thermal spraying equipment, in particiular, the installation of atmosphere-controlled plasma spray and high-velocity oxygen/fuel spray (HVOF) are investigated. Typical examples include industrial applications that are performed mainly by coating contract shops and large companies. In emerging spraying process technologies, synthesis of new materials using atmospheric plasma spray and atmosphere-controlled plasma spray, laser-assisted spraying, and new plasma torches are presented.

Real-time imaging for thermal spray process development and control

Abstract: Thermal spray and other high-temperature industrial processes are quite difficult to monitor with the human eye, because the luminous volume of the plasma or flame obscures the behavior of the solid or molten material in the heat-affected area. When a photographic or video camera is used, viewing is further degraded by the extreme contrast variation across the image area, making it impossible to achieve proper exposure throughout the image—except possibly for small areas of comparable brightness. Optical filtering with neutral density filters, such as those used in a welder’s helmet, are of no practical benefit. With thermal spray processes, the injection and flow of particles within the plasma flame is almost totally concealed by the extreme brightness of the plasma, flame, or arc. In addition, the particles quickly accelerate to very high speeds, making their detection even more difficult. This article discusses the development of integrated thermal spray process monitoring and analysis techniques based on two principles. The first is a unique vision sensing system that suppresses the flame, plasma, arc, or other high-luminosity phenomena in the video image. A further improvement is the use of dedicated image and analysis processing to enhance the sensor images and extract features of interest or dimensional measurements. These experimental techniques can be used as feedback for automated process monitoring and control.

Evaluation of thermally sprayed coatings under reciprocating lubricated wear conditions

Abstract: To find an alternate coating to hard electroplated chrome in internal combustion engines, wear tests and metallurgical characterization have been performed on plasma-sprayed chromium oxide, metal-arc-sprayed martensitic stainless steel, and electroplated chromium coatings applied to steel base material. A wear test rig was fabricated that simulated the reciprocating sliding wear under lubrication encountered in internal combustion engines. The chromium oxide coating was found to perform equally well compared to the hard chrome coating that is conventionally used.

Structure and properties of plasma-sprayed sialon coatings

Abstract: â’-Sialon(Si6_zAlzOzN8-z, where z = 1,2,3, or 4) was plasma sprayed in air, and the structure and properties of the coating were evaluated. Coatings of the Sialon could be produced when z = 3 or 4, whereas coatings were hardly formed for Sialon with z = 1 and 2. The relative density and the Vickers hardness of the Sialon coatings (z = 3 and 4) increased with an increase in plasma power. Elemental analysis and X-ray diffractometry revealed that Sialon partially decomposed during thermal spraying. Nitrogen gas addition to the secondary plasma gas was effective in suppressing this decomposition.

Thermal spraying of reactive materials to form wear-resistant composite coatings

Abstract: The dispersion of more than 20 vol.% submicrometer ceramic particles within a metallic matrix and the deposition of such a cermet to form a thick and tough coating presents problems. Most of the coating techniques have failed in attempting to homogeneously disperse very fine and hard particles in large amounts while avoiding their decomposition or reaction with the metal matrix during the deposition process. A simple and efficient method has been developed for producing ceramic-containing composite coatings. It consists in synthesizing cermet-based materials and in depositing them by a rapid solidification process such as thermal spraying. Boride- and carbide-based materials have been successfully obtained by plasma spraying reactive powders comprising the basic reagents. These materials, with a microstructure of submicrometer ceramic particles dispersed in a metallic matrix, exhibit good wear-resistant properties (abrasion and sliding wear). Finally, reactive core wire arc spraying is suggested as a flexible way to produce coatings containing up to 25 vol.% TiB2.

Mechanofused powders for thermal spray

Abstract: Mechanofusion is a novel powder processing technique, in which raw powdered materials are fed into the apparatus, and through mechanical-thermal interactions, the powder characteristics are changed, e.g., shape, size, and composition distribution. Mechanofusion has been used in this study to produce intermetallic nickel aluminide compounds and composite powders as feedstock for vacuum plasma spraying. Significant effects of the mechanofusion production route on the powder characteristics and spray deposition features have been observed.

Production of spherical apatite powders—the first step for optimized thermal-sprayed apatite coatings

Abstract: Regardless of the thermal spraying system, a coating can only be as good as the quality of the input powders. Powder quality in turn is dependent on the manufacturing process and conditions. Thus, it is possible to alter characteristics such as morphology, porosity, phase composition, and the mechanical strength of the individual particles. This article looks at powder agglomerations using the spray drying technique. Two different spray drying configurations were used to produce spherical apatite powders. Apatite powders could be produced with variable densities. Rotary-atomized powders possessed internal porosity as well as open porosity. More applicable for thermal spraying are the nozzle-atomized powders, which are more dense. The particle size range produced is dependent on the many parameters in the spray drying process. Hydroxyapatite is more sensitive than fluorapatite to alterations in process conditions. The powders produced were clean, free of other phases, and possessed good flowability for thermal spraying purposes.

Preparation of cross sections of thermal spray coatings for TEM investigation

Abstract: A technique for the preparation of cross sections for transmission electron microscopy (TEM) of thermal spray coatings has been developed. The procedure is designed to minimize specimen damage during mechanical thinning and to reduce the effect of differential thinning during ion milling. Specimens were made by two different coating systems— WC- Co coating produced by the FARE Gun process on a mild steel substrate and Tribaloy T- 800 sprayed by the HVOF process on a nickel- base superalloy. These specimens have large areas that are electron transparent on either side of the interface, and the results have shown the atomic scale microstructure of the interface between the thermal spray coating and the substrate.

A Study of Ni-5wt.% Al coatings produced from different feedstock powder

Abstract: Ten different Ni-5wt.%Al powders—three clad, done sintered, three water atomized, and three gas atomized—have been evaluated and plasma sprayed. The study focused on how manufacturing method, chemical composition, and particle size distribution of the powders affect the quality of the coating. Properties such as microstructure and mechanical behavior, as well as oxidation and corrosion resistance, are discussed. In conclusion, recommendations concerning the selection of powders for different applications are presented.

Optimization of spraying process and laser treatment of CoNiCrAlY

Abstract: This article describes the investigation of a new generation of vacuum plasma sprayed CoNiCrAlY coatings on NiCr20Ti in the sprayed as well as the laser-treated condition. The aim of the study was the improvement of MCrAlY coating properties by modifying the microstructure through laser remelting with 5-kW Co2: lasers. Parameter analysis and optimization was carried out for the vacuum plasma spraying process, as well as for the laser remelting technique. The effect of the laser treatment on microstructure, quality of the coatings, and oxidation as well as hot gas corrosion behavior are reported.

Ceramic-coated components for the combustion zone of natural gas engines

Abstract: The use of ceramic coatings on the combustion zone surfaces of large,natural gas-fueled,internal com-bustion engines is discussed. Unique handling and quality control systems are required for plasma spray-ing thin (0.25 mm,0.0010) in.coatings on up to 48.25(cm19)-in.diameter piston crowns and cylinder heads weighing up to(1200 lb).The in-service performance characteristics of two types of natural gas-fu-eled combustion engines powering natural gas compressors that had thin zirconia ceramic coatings ap-plied to their combustion zone surfaces are presented. Their performance was measured in the field be-fore and after coating. It was determined that the durability,power output,fuel consumption,exhaust emissions,and other operating characteristics all improved due to ceramic coating of the flame side sur-faces of cylinder heads,power pistons,and valves.

Laboratory report—thermal spraying at the shanghai institute of ceramics

Abstract: Plasma spraying has received considerable attention as a process for obtaining protective coatings. In this article, experiments and results obtained at the Shanghai Institute of Ceramics pertaining to the developments and application of plasma-sprayed coating materials such as thermal barrier, wear resistance, infrared radiation, electrode materials, biomedical materials, and diamond films are presented. The physical, mechanical, and thermal properties of the coatings were measured. The microstructural features of the coatings were also examined. Examples of applications of plasma-sprayed coatings in various industries are illustrated. In addition, the manufacture of some oxide powders and their characteristics are discussed.

Underwater plasma processing of stabilized zirconia for thermal barrier coatings

Abstract: The influence of powder technology on the spraying process is growing. The use of powders of different morphologies results in a variety of coating properties. Plasma processing of ceramic composite powders underwater produces dense and spherical powders with excellent morphologies. Coatings of improved quality are produced by spraying these powders. This paper describes the concept of producing zirconia powders by a plasma process that is performed underwater. The most important parameters and standards are highlighted. Moreover, the influence of powder characteristics on coating properties will be described and some results presented.