bluuebunny/crossref_metadata_2025_split huggingface dataset:
Microstructure and Abrasion Resistance of Plasma Sprayed Cermet Coatings
Authors: Khan M.S.A. , Clyne T.W. 
Published: May 2021

Abstract
Cermet (WC-Co) coatings have been produced on steel substrates by plasma spraying in vacuum and in air. These have been examined microstructurally and characterised in terms of porosity content, stiffness, microhardness and abrasion resistance. Particular attention has been paid to the phase constitution, as revealed by X-ray diffraction and scanning electron microscopy. High precision densitometry has been used to study porosity levels. Coatings with three different metal contents (9, 12 and 17wt.%Co) have been examined. There is a strong tendency for chemical reactions to occur within the plasma plume, particularly for spraying in air. These reactions can result in the formation of various carbides and even of metallic tungsten. Thermodynamic and kinetic aspects of the reactions involved are briefly examined. Such reactions are strongly promoted by the presence of oxygen, and are much less marked during vacuum plasma spraying. Plasma power and substrate temperature have secondary effects on the degree of reaction which occurs. A marked correlation was observed between degree of reaction and resistance to abrasive wear. This is consistent with the reaction products being brittle and causing poor interfacial cohesion. It was also found that wear resistance was greater for the coatings with lower metal contents. This behaviour can be attributed to the wear occurring predominantly by ploughing of the metallic phase and consequent release of ceramic particles. This occurred more readily when the metal content was higher. In coatings which had undergone pronounced chemical reaction, however, metal had been replaced by reaction products which conferred poor cohesive strength, leading to poor wear resistance.
Chromium Carbide Coatings for High Temperature Erosion Resistance
Authors: Sielski D.R. , Sahoo P. 
Published: May 2021

Abstract
Escalating operation and maintenance costs and increasing intervals between outages place a heavy burden upon electric power producing components. To meet this demand, component life cycles must be extended with either material upgrades or utilization of surface protection products. This paper will discuss the experiences of the Tennessee Valley Authority in the application of thermal spray coatings and try to relate some of these experiences to component performance in fossil power plants' steam turbine components. The development of high velocity thermal spray processes has given coatings an advantage over the use of high priced material upgrades. Chromium carbide coatings have proven the most economical of the surface protection products for use in high temperature applications where solid particle erosion occurs. These coatings have received extensive laboratory testing where limited field results are now just becoming available. Various thermal spray coatings will be described. The development of newer coatings and laboratory test data will be discussed. Optical microscopy and wear studies will be included in the discussion. Where appropriate and available, comparisons to standard plasma sprayed coatings and uncoated substrata are made.
Production of Heat and Corrosion-Resistant Plastic Coatings
Authors: Kawase R. , Nakano A. 
Published: May 2021

Abstract
Thermal sprayed coatings of polypenylene-sulphide (PPS) and polyphenyletherether-ketone (PEEK) have been produced by HVAF spray system. The properties of these coatings have been investigated by corrosion test and FT-IR analysis. The main results of this study are summarized as follows; (1) In case of PPS coatings, PPS powder is oxidized during thermal spraying. However, PPS coatings have a good corrosion resistance. However, PEEK coatings have high porosity so that corrosion of the substrate occurs. (2) In case of PEEK coatings, the molecular structure of PEEK powder is not changed during thermal spraying.
Analysis of Zirconia Powder for Thermal Spray: Reference Material for Particle Size Distribution Measurement
Authors: Pei P. , Kelly J. , Malghan S. , Dapkunas S. 
Published: May 2021

Abstract
The thermal spray industry identified the need for repeatable and reproducible feedstock powder characterization methods, especially particle size distribution (PSD), for cost effective manufacturing of thermal barrier coatings. The PSD measurement by a laser light scattering method was identified as the technique most widely used in the industry. This technique offers high resolution, rapid measurements and ease of use. A round robin study by nine laboratories using different models of a commercial light scattering instrument has been completed as the first step towards the development of a Standard Reference Material (SRM) for the calibration of light scattering instrument. Other measurement techniques were also employed for additional comparison. The PSD measurements employing light scattering techniques evidenced some method dependence, despite the use of identical sample preparation procedures. The round robin results will serve as reference values for the development of the SRM.
Thermal and Mechanical Properties of Plasma Sprayed ZrO2-CeO2-Y2O3 Coatings
Authors: Sodeoka S. , Suzuki M. , Inoue T. , Ueno K. , Oki S. , Kamisono N. 
Published: May 2021

Abstract
Plasma sprayed ZrO2-CeO2 and ZrO2-CeO2-Y2O3 coatings were investigated to develop advanced thermal barrier coating (TBC) with improved thermal and mechanical properties. The addition of a large amount of CeO2 to ZrO2 decreased the thermal conductivity, but it also reduced the mechanical property like hardness. Addition of Y2O3 to ZrO2-CeO2 was effective to improve the hardness. Double layered coating composed of a low thermal conductive top layer, such as ZrO2-CeO2-Y2O3 and a high strength base layer like yttria stabilized zirconia was fabricated. It exhibited an excellent thermal shock resistance and high thermal barrier capability.
Investigation of the Silicon Loss in APS MoSi2 under Typical Spray Conditions
Authors: Hollis K.J. , Bartlett A. , Castro R.G. , Neiser R.A. 
Published: May 2021

Abstract
MoSi2 provides good high temperature oxidation and corrosion resistance. However, the lower silicides such as MosSis do not provide such resistance. In this study, atmosphereic plasma sprayed (APS) MoSi2 particle temperatures and velocities were measured under various torch conditions chosen to span the majority of typically utilized spray parameters. Empirical models of particle temperature and velocity were computed from the data. Three spray conditions were chosen to produce high, medium and low particle temperatures and velocities. Coatings produced under these spray conditions were characterized by profile tracing, quantitative x-ray diffraction, and SEM analysis. The Mo5Si3 level in the coatings ranged from 5% to 8% while the Mo5Si3 level in the starting powder was 0.6%. Particle size, particle trajectory, and torch parameters were found to be important factors in the Si loss process when APS depositing MoSi2.
Oxygen Partial Pressure Measurement in the Plasma Gun Jet
Authors: Korpiola K. , Jalkanen H. , Kinos T. , Siitonten P. , Vuoristo P. 
Published: May 2021

Abstract
An important aspect of the APS plasma spray process is the turbulent mixing of the spray jet with the surrounding air. The air mixing into the jet causes undesirable oxidation of the sprayed coating. In this work the air mixing in the plasma jet was determined by direct measurement of the oxygen content. The measuring method is based on electrochemical determination of the oxygen potential using a solid electrolyte cell. The partial pressure of oxygen along the centreline of the plasma jet was measured with the hydrogen/argon and helium/argon ratio, the gas flow rate and the stand-off distance as experimental parameters. The oxygen content of the plasma tail flame was found to vary between 13.6 to 19.3 % depending on the hydrogen to argon ratio and the stand-off distance. Such high oxygen contents are far too high to avoid serious oxidation of metal coatings. The plasma spraying tests were carried out with WC-Co 17 coating powder. The plasma gases were Ar/H2 and Ar/He. The respective oxygen contents by air mixing were measured to be 18.9 and 17.3 %. The WC-Co was observed to be decarburised more in the Ar/H2 mixture than in the Ar/He mixture, which was attributed to the higher oxygen concentration, higher particle temperature and longer flight time in the plasma jet. Solid electrolyte cell technique was applied to this type of measurements and it proved to be a convenient way to determine the oxygen mixing in the plasma jet.
Surface Modification of Thermal Sprayed Coatings
Authors: John G. , Troczynski T. 
Published: May 2021

Abstract
Thermal sprayed coatings are frequently used in corrosive environments, even when their major purpose is to provide wear or thermal resistance, rather than corrosion resistance. This includes Thermal Barrier Coatings (TBC), where high porosity is a desired feature to give good thermal protection. However, as this proves to be a limiting factor in the corrosion protection, a trade off is involved. This is because the interconnected porosity in TBCs allows the corrosive media to reach the coating-substrate interface, which eventually leads to delamination of the coatings. This work addresses the problem of permeability of TBCs which can lead to premature delamination due to interfacial corrosion. The coatings studied were yttria-stabilized zirconia TBCs. A simple infiltration technique has been proposed using sol-gel ceramic precursors. The precursors studied include aluminum isopropoxide or pre-hydrolyzed ethyl silicate, which decomposed to alumina and silica respectively, at surface heat treatment temperatures as low as 550°C. In addition to sealing the surface, it is believed that some level of compressive stress is generated on the surface of TBCs on cooling from the processing temperature. Electrochemical tests in 3.0% NaCl have been carried out to study the effectiveness of the sealant. These potentiodynamic tests as well as permeability tests show a considerable decrease in interconnected porosity with sol-gel modifications of the coatings.
Particle Velocity and Temperature influences on the Microstructure of Plasma Sprayed Nickel
Authors: Wright R.N. , Fincke J.R. , Swank W.D. , Haggard D.C. 
Published: May 2021

Abstract
The variation in microstructure of high power plasma sprayed nickel coatings deposited with particle velocities ranging from 150 to 425 m/s and nominal particle temperatures of 1650 or 2050°C has been characterized. The relative density of coatings produced at the higher temperature is above 99.5% of theoretical regardless of the particle velocity; at the lower particle temperature the relative density is found to increase with increasing particle velocity. The fraction of unmelted particles is also found to increase with increasing velocity at the lower temperature. The relative deposition efficiency is approximately twice as high for the lower temperature particles compared to the high temperature, and for both temperatures the deposition efficiency decreases substantially with increasing velocity. Changes in the morphology of individual splats with changes in particle characteristics are also described.
Plasma Sprayed Zirconia: Relationships among Particle Parameters, Splat Formation, and Deposit Generation - Part II: Microstructure and Properties
Authors: Sampath S. , Matejicek J. , Berndt C.C. , Herman H. , Léger A.C. , Vardelle M. , Vardelle A. , Fauchais P. 
Published: May 2021

Abstract
This is the second paper of a two part series based on an interdisciplinary research investigation between the University of Limoges, France, and the State University of New York, Stony Brook, USA, aimed at fundamental understanding of the plasma-particle interaction, deposit formation dynamics and microstructure development. In this paper, the microstructure development during plasma spraying of zirconia is investigated from the point of view of deposition parameters and splat formation (part I). Splats and deposits have been produced at Limoges and Stony Brook under controlled conditions of particle parameters and substrate temperatures. The zirconia splat microstructures thus obtained are examined for their shape factors, grain size, crystallographic texture and defects. Further the deposits were analyzed for phases, porosity and mechanical properties in an effort to develop a process-microstructure property relationship. The results suggest a strong role played by the deposition temperature on the microstructure and properties of the deposit.
Phase Transformations on Flame Sprayed Alumina
Authors: Lima R.S. , Bergmann C.P. 
Published: May 2021

Abstract
Flame-sprayed coatings of alumina were produced by an oxyacetylene flame spray system in order to study the phase transformations that occurs on alumina during the spraying. The X-ray diffraction pattern of the alumina powder to be sprayed, showed the main presence of the stable phase alpha alumina and an impurity probably resulting from the process of purification of alumina. For as-sprayed coatings, phase changes occur. The X-ray diffraction pattern shows the presence of the stable form alpha alumina, but also the metastable form gamma alumina and amorphous alumina. True density measurements were done using a helium pycnometer, as an aid to observe the phase transformations. The density of the powder to be sprayed was 3.98 g/cm3 and the density of the as-sprayed coatings was 3.62 g/cm3. This change of density is linked to the phase transformation during spraying. Scanning electron microscopy (SEM) of the incident particles was made after 1 second of deposition onto glass substrates in order to observe the degree of melting of the incident particles, by analyzing their profiles (degree of flattening).
Training in Coating Evaluation Techniques - A Unique Approach for Discussion
Authors: Sauer J.P. 
Published: May 2021

Abstract
The Central Coatings Laboratory (CCL) is a program that deals with training in coating evaluation techniques. The approach uses a combination of both theoretical and hands-on instruction to teach various concepts. The system is educational based, incorporating a philosophy of making the students problem solvers in lieu of following "cookbook" evaluation procedures. Examples of teaching techniques will be discussed and suggested course material reviewed to highlight this training philosophy.
Effect of Gas Velocity and Particle Velocity on Coating Adhesion in Wire Arc Spraying
Authors: Wang X. , Heberlein J. , Pfender E. , Gerberich W. 
Published: May 2021

Abstract
In wire arc spraying, atomizing gas velocity and particle velocity are important factors influencing coating quality. A nozzle with secondary gas injection has been developed to increase the gas velocity and to improve coating quality. In this study, wire arc spraying of stainless steel on aluminum substrates has been investigated with the objective of establishing correlations between atomizing gas velocities, particle velocities, particle sizes and coating bond strength. Cold gas velocity is measured with a Pitot tube. Particle velocities are determined from high speed images of particle streaks taken with a Kodak high speed vision system and evaluated using image analysis. Bond strength is measured with pull-off tensile test. Secondary gas atomization clearly leads to improved adhesion due to additional metallurgical bonding between the coating and the substrate achieved through higher particle temperatures at the moment of impact.
Residual Stress Analysis in Thermal Spray Coated Rolling Elements
Authors: Ahmed R. , Hadfield M. , Tobe S. 
Published: May 2021

Abstract
The full potential of rolling element bearings operating in specialised conditions such as high speed and corrosive environments are realised using surface coatings. Tungsten Carbide coating by thermal spray HVOF and D-Gim processes are considered for these applications. An experimental approach using a modified four-ball machine simulates the tribological conditions within a rolling element bearing. The fatigue failure modes of the tungsten carbide coating in rolling contact with steel and silicon nitride are examined using conventional surface analysis techniques. The stress fields within the coating are examined using traditional contact theory and residual stress measurement by X-ray diffraction. The residual stress measurements of the pre-test coating, the contacting surface and the fatigue failures are described. Results of residual stress relating to orientation, failure depth, coating thickness are discussed along with the fatigue failure mode.
Reactive Plasma Spraying of Wear Resistant Coatings of Ti Composites
Authors: Lugscheider E. , Remer P. , Zhao L. 
Published: May 2021

Abstract
In this investigation reactive plasma spraying was used to produce wear resistant coatings of Ti-carbides/titanium or Ti-nitrides/titanium composites. Ti-powders with different powder size distributions were used as raw materials. Methane and nitrogen were used as reactive gases to form carbides and nitrides. A reactor was adapted to the plasma gun F4 of a Sulzer Metco vacuum plasma spraying equipment to increase the degree of the expected reactions. Phase analysis and micrography of the coatings reveal that the Ti-hardphases were synthesized during spraying and embedded in the titanium matrix. The in situ synthesized hardphases show different forms and sizes. Most of them are non-stoichiometry. Compared to the titanium coating the coatings produced by reactive plasma spraying are much harder and more resistant against both sliding and abrasive wear.
Plasma Spraying of Solid Oxide Fuel Cell Components
Authors: Schiller G. , Müller M. , Ruckdäschel R. , Henne R. , Lang M. 
Published: May 2021

Abstract
The central components for solid oxide fuel cells (SOFC) are the electrodes-electrolyte multilayer arrangement (PEN) and the separating bipolar plates. The PEN (Positive electrode- Electrolyte-Negative electrode) assembly consists of a dense gastight yttria-stabilized zirconia (YSZ) electrolyte and porous electrodes for which usually Ni-YSZ cermet anode and Sr-doped LaMnO3 cathode layers are used. The various PEN units are connected in a cell stack by bipolar plates which are either metallic or ceramic ones. Furthermore, a protective layer on the metallic bipolar plates consisting of a chromium alloy is required to prevent chromium evaporation leading to a rapid and strong degradation of the SOFC performance. At the DLR Stuttgart both the DC and the RF vacuum plasma spraying technique have been further developed and adapted to meet the requirements for the manufacture of the different SOFC components. The DCVPS process using specially developed Laval-like nozzles is especially appropriate to the production of thin and dense coatings as required for the electrolyte and the protective layers. However, applying special spray parameters and nozzles it is also possible to deposit porous electrode layers. The production of the entire PEN arrangement in one consecutive DC-VPS process is the objective of the actual development. On the other hand, the RF plasma spray technique is suitable for the near net-shape production of bulk components such as the metallic bipolar plate. The development of the deposition processes for the production of SOFC components using DC and RF plasma spray methods and the results obtained concerning PEN fabrication, deposition of protective layers and the near net-shape production of metallic bipolar plates are presented in the paper.
Processing and Thermal Cycling Effects on the Erosion Behavior of Thermal Barrier Coatings
Authors: Gutleber J. , Sampath S. , Usmani S. 
Published: May 2021

Abstract
The erosion behavior of yttria stabilized zirconia thermal barrier coatings is investigated with respect to powder particle size. Solid particle erosion experiments were conducted at room temperature to determine the mechanism of erosion for ceramic thermal spray coatings. Testing was carried out on as-sprayed as well as thermally cycled specimens. Porosity and bend testing measurements indicate that a decrease in porosity and an increase in inter-lamellar strength leads to an increase in the erosion resistance of ceramic thermal spray coatings.
The Effect of Substrate Temperature on the Adhesion of Plasma-Sprayed Borosilicate Glass Coatings
Authors: Gawne D.T. , Bao Y. , Zhang T. 
Published: May 2021

Abstract
Experimental work has been undertaken to investigate the importance of the temperature of the substrate during deposition on the coating-adhesion of plasma sprayed borosilicate glass coatings. The work shows that the measured adhesion increases markedly with substrate temperature up to 400°C above which no further major increase takes place. Heat transfer and fluid mechanics calculations predict that the effect of substrate temperature is due to its influence through the cooling rate on the viscosity and flow of the molten glass particles as they impact on the substrate surface. The theoretical calculations also predict large temperature gradients through the thickness of the splats and glass coatings, and the consequent non-uniform thermal stress distributions are expected to contribute to the reduced splat retention rate and coating-adhesion at low substrate temperatures. The predictions were confirmed by an electron microscopy examination of the morphology of isolated splats, the deposits and the coating-substrate interface.
High Energy Beam Surface and Interface Modification of Thermally Sprayed Coatings
Authors: Wilden J. , Brune M. , Kruzhanov Y. , Steffens H.-D. 
Published: May 2021

Abstract
The application of thermally sprayed coatings is often limited by their porosity as well as their low adhesion. A new approach for high energy beam surface treatment of thermally sprayed coatings is presented using simultanously a lower power level for continuous remelting and pulses of higher power in order to get coatings with good corrosion behaviour and improved adhesion. This technology is applied to titanium as well as to NiCr-coatings on steel substrates. The investigations prove that remelted thermally sprayed coatings with a smooth and dense surface layer, followed by a heat treated section of the coating and a reaction zone at the substrate/coating interface can be obtained. Therefore, a change in chemical composition of the coating is avoided, while at the same time the bond strength of the remelted coatings can be influenced by metallurgical reactions at the interface zone.
Impression Creep Behavior of Atmospheric Plasma-Sprayed and Hot Pressed MoSi2/Si3N4
Authors: Hollis K.J. , Butt D.P. , Castro R.G. 
Published: May 2021

Abstract
The use of MoSi2 as a high temperature oxidation resistant structural material is hindered by its poor elevated temperature creep resistance. The addition of second phase Si3N4 holds promise for improving the creep properties of MoSi2 without decreasing oxidation resistance. The high temperature impression creep behavior of atmospheric plasma sprayed (APS) and hot pressed (HP) MoSi2/Si3N4 composites was investigated. Values for steady state creep rates, creep activation energies, and creep stress exponents were measured. Grain boundary sliding and splat sliding were found to be the dominant creep mechanisms for the APS samples while grain boundary sliding and plastic deformation were found to be the dominant creep mechanisms for the HP samples.