bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal Spray Coatings in Printing and Papermaking
Authors: Jungklaus H.
Published: September 2022

The effects of globalization, technology improvement, capacity consolidation, and rising customer demands drive the printing and papermaking business worldwide. Consumption of paper, paperboard, and tissue exceeded 500 million tons in 2007, and it is estimated that one-third to one-half of this production is printed. Paper production in total is not experiencing drastic growth rates due to the increasing market share of digital media; however, market segments such as paperboard and packaging are showing growing demand. In printing, new technologies focus on production speed and quality improvement. For both printing and papermaking, the cost of energy and raw materials requires ongoing improvements in production efficiency. For equipment and machinery manufacturers serving these industries, high-end technology that lowers cost and improves quality drives the market leaders. In both industries, functional roll surfaces generated by thermal spraying help to achieve design and development objectives. The paper gives examples for the role of thermal spray coatings in both industrial areas.
Review of Applications of Thermal Spraying in the Printing Industry in Respect to OEMs
Authors: Döring J.-E. , Hoebener F. , Langer G.
Published: September 2022

Printing machines mirror the art of precise manufacturing and adjusting of fast moving and heavy components with an accuracy of few micrometers. In order to meet the challenge of fast and high quality printing combined with a long lifetime of the machines, the core components transporting the print substrate and the different kinds of ink and other liquids needs to be coated, what is done more and more by applying thermal spray processes. The main requirements cover wear and corrosion resistance as well as suitable wetting and special needs like the ability of laser engraving. Moreover, the coatings are post processed to achieve a sufficiently low surface roughness combined with an appropriate microstructure resulting in a fine structure if laser engraving is considered. This paper will give a review of applications, techniques and materials, which are well-established in printing industry in respect to the specific demands of the case of operation. This covers the surfaces in the printing unit namely the printing and blanket cylinders but also the inking and dampening systems.
Hollow Droplets Micro Explosive Thermal Spraying: Fundamentals
Authors: Solonenko O.P. , Gulyaev I.P. , Smirnov A.V.
Published: September 2022

The peculiarities of plasma treatment of agglomerated YSZ powders as well as mechanically pretreated metal and metal alloy powder with the aim of their spheroidization and subsequent thermal spraying of produced HOSP powders are analyzed. Formation of splats from hollow droplets deserves a special attention for thermal spraying. In this case, immediately prior to particle – substrate collision, we have a droplet that consists of a liquid shell enclosing a gas cavity heated to a temperature close to the particle surface temperature. The paper presented includes the results of computer simulation and model experiments carried out under full control of pre-impact key physical parameters (KPPs): temperature Tp0, velocity up0, external diameter of droplet Dp0, thickness of its shell Δp0 , temperature of substrate Tb0, and its surface state. It was shown that formation of splats from hollow droplets proceeds in a manner more stable compared to the case of “dense” molten particles obtained from fused and crushed compacts, and this provides for a more perfect splat-substrate, splat-splat and coating-substrate interface. Advantages of hollow metal, metal alloy and metal oxide powders over corresponding dense powders for thermal spraying by the example of thermal barrier coatings are discussed. Since the splat formation process involving hollow droplets proceeds, following their high-velocity impact deformation on the base/substrate, in an explosive manner, this type of spraying can be referred as HOSP micro explosive thermal spraying.
Plasma Spraying of Metal Coatings using CO2 Based Gas Mixtures
Authors: Pershin L. , Chen L. , Mostaghimi J.
Published: September 2022

The use of gas mixtures containing hydrocarbons for plasma generation results in higher plasma enthalpy because, molecular gases must dissociate before ionization which requires larger energy input. The torch developed at CACT which operates with CO2+CH4 gas mixtures was used for coating deposition with input power in a range of 30 to 45 kW. This study was focused on the effect of CO2+CH4 mixtures on the particle parameters during spraying of Ni alloy powder. Results of gas composition analysis at various distances from the nozzle exit are presented. The particle in-flight conditions, coating microstructure, and deposition efficiency also were analyzed.
Analysis of the Deposition Mechanism in the Solution Precursor Plasma Spraying using Numerically Predicted Particle Conditions
Authors: Shan Y. , Wang Y. , Coyle T.
Published: September 2022

Solution precursor plasma spraying has been used to deposit ceramic coatings with submicron/nanocrystalline structures. Previous studies revealed that the deposition mechanism in the solution precursor plasma spraying differs from that in the conventional plasma spraying. To increase the understanding of the deposition mechanism in the solution precursor plasma spraying, a numerical model is used to predict the particle conditions on the substrate. Five types of particle conditions, melted particles; small sintered particles; dry agglomerates; wet agglomerates; and wet droplet are assumed based on the computed temperature distribution of the particles. An analysis of the deposition mechanism in the solution precursor plasma spraying is performed. Experiment results s are also collected to verify the numerical prediction and the analysis of the deposition mechanisms.
Deposition Mechanism of Cold Sprayed MCrAlY Coatings Focused on Nanostructure
Authors: Ichikawa Y. , Miyazaki T. , Ogawa K. , Shoji T. , Jeandin M.
Published: September 2022

Thermal-sprayed MCrAlY coatings are widely used for land-based gas turbine applications. The cold spray may increase the coating density owing to the high-velocity particle impacts during spraying. Many researchers have considered critical velocity to be the most important factor of the deposition mechanism of cold-sprayed coatings. However, this dominant parameter of critical deposition condition has not been completely understood. In order to understand the mechanism, two approaches were used in this study. One is the transmission electron microscope (TEM) observation of the interface between the coating and the substrate, and the other is the cross-sectional observation of the deposited particle by using the focused ion beam (FIB) cutting technique. From the TEM observations, there are no evidences of melting at the interface, and it is found that the actual bonding occurred at the nascent surfaces. Generally, there is a native oxide on the surface of the particles and substrate. After the plastic deformation of the particles and substrate, the native oxide breaks down; subsequently, a nascent surface can be created and direct contact initiates deposition. From the results of these investigations, it is thought that the dominant factor for deposition is the plastic deformation of the particles and substrates.
Predicting Quenching and Cooling Stresses within HVOF Deposits
Authors: Stokes J.
Published: September 2022

Due to the nature of the HVOF and other thermal spray processes, residual stress build up in thick deposits is a significant and limiting problem. The residual stress-state that evolves in a deposit is largely dependent on the thermal conditions to which the system has been subjected, and is a combination of quenching stresses, which arise during deposition, and cooling stresses, post-deposition. It follows that precise control of these phenomena is essential, if a thick deposit or one with low levels of residual stress are to be thermally sprayed. This paper applies looks at analytical and finite element techniques used to predict quenching and cooling stresses within tungsten carbide-cobalt thermally sprayed deposits. The analysis investigates and predicts the quenching and cooling stresses using improved analytical and FEA techniques by validating the models with experimental results such as X-Ray Diffraction and the Hole Drilling Method. The result of this paper is a thermo-mechanical equation for quenching stress which includes the effects of misfit strain, the Poisson’s effect, variation of coating and substrate thicknesses, thermal expansion and process temperature effects.
Mechanical Properties of W-Re and W-Re-HfC Alloys Made by Vacuum Plasma Spray
Authors: O'Dell J.S. , McKechnie T.N.
Published: September 2022

The mechanical properties of tungsten-rhenium and tungsten-rhenium-hafnium carbide alloys produced by vacuum plasma spray forming have been evaluated. The results of both tensile and three-point bend tests at room temperature and elevated temperatures will be discussed. In addition, the results of a microstructural analysis will be presented.
Microstructure and Wear Behavior of Arc Sprayed WC-12Co/FeB and WC-12Ni/FeB Composite Coatings
Authors: He D. , Fu B. , Jiang J. , Li X.
Published: September 2022

A ceramic composite coating of a FeB alloy reinforced with cobalt-coated tungsten carbide (WC-12Co) particles and nickel-coated tungsten carbide (WC-12Ni) particles was deposited on a mild steel substrate by arc spraying cored wire, respectively. The microstructure and the worn surfaces of the coatings were analyzed by X-ray diffraction (XRD), Scanning electron microscope (SEM). And wear mechanisms of the coatings have been discussed on the basis of the observation. The results showed that adding WC powders can obviously increase the hardness and abrasive wear resistance property of the coating. The average microhardness of the coatings is about 900~1000 HV0.1. In the experimental conditions, the coatings have the excellent abrasive wear resistance which is 7~10 times higher than that of the Q235 mild steel. Plastic microcutting and brittle peeling play the predominant role in abrasion wear of the coating.
Modeling of Oxygen Input Into Particles at Arc Spraying
Authors: Korobov Y. , Boronenkov V.
Published: September 2022

A scheme of an oxygen input by particles at Arc Spraying is offered. Both external and internal diffusion processes are taken into account. The oxygen input was separately examined at arc-burning zone and spraying distance. At first the oxygen is dissolved in liquid metal drop up to a limit of saturation. Then slag formation begins accompanied by metal – slag interaction. Modeling of these processes was performed on a base of oxygen input/output mass balance. It was completed by computation of oxygen diffusion flows into gas and metal through interface surface. Mutual influence of alloying elements was also taken into account at slag formation on particle surface. The modeling results are represented in case of arc sprayed steel (1.1 C, 1.9 Mn, 0.8 Si). Propane - air mixture was used as a transporting gas. Good similarity with experiment data was achieved. As shown by calculations, basic share of oxygen input occurs in the arc-burning zone. The investigation results were used in core wire developing and gun designing as well.
Suspension Plasma-Sprayed Alumina Coating Structures: Operating Parameters vs. coating Architecture
Authors: Tingaud O. , Grimaud A. , Denoirjean A. , Montavon G. , Rat V. , Coudert J.-F. , Fauchais P. , Chartier T.
Published: September 2022

Suspension plasma spraying (SPS) is a fairly recent technology that is able to process sub-micrometric-sized feedstock particles and permits the deposition of layers thinner (from 5 to 50 µm) than those resulting from conventional atmospheric plasma spraying (APS). SPS consists in mechanically injecting within the plasma flow a liquid suspension of particles of average diameter varying between 0.02 and 1 µm. Upon penetration within the DC plasma jet, two phenomena occur sequentially: droplet fragmentation and evaporation. Particles are then processed by the plasma flow prior their impact, spreading and solidification upon the surface to be covered. Depending upon the selection of operating parameters, among which plasma power parameters (operating mode, enthalpy, spray distance, etc.), suspension properties (particle size distribution, powder mass percentage, viscosity, etc.), and substrate characteristics (topology, temperature, etc.), different coating architectures can be manufactured, from dense to porous layers. Nevertheless, the coupling between the parameters controlling the coating microstructure and properties are not yet fully identified. The aim of this study is to further understand the influence of parameters controlling the manufacturing mechanisms of SPS alumina coatings, in particular the spray patterns influence.
Arc Sprayed Coatings Obtained from Iron Based Cored Wires Under High Temperature Abrasive Wear Conditions
Authors: Pokhmurska H. , Wielage B. , Grund T. , Student M. , Sirak Y.
Published: September 2022

Development of new arc sprayed iron based coatings for protection against gas abrasive wear at room and elevated temperatures are of the great interest because of permanently increasing pressure to reduce production and repair costs of power production facilities. Two cored wires in steel cover with Fe-Cr-B-Al and Fe-Cr-N-Al filling are proposed as an alternative choice for self fluxing and cermet coatings that are considered nowadays for protection of screen tubes of boilers of power stations that are operated under the temperatures 500-600 °C. Oxidation behaviour of arc sprayed coatings is estimated by gravimetric measurements. Abrasive wear resistance at elevated temperatures after 1 hour is investigated by means of laboratory unit that alloys a rotation of coated specimens in heated quartz sand. It is shown that abrasion wear lost of carbon steel increases 1.5 times when test temperature increases from 20 °C to 550 °C. For all investigated coatings the 20-25% decrease of wear lost is observed at higher temperature. Arc sprayed coatings of both investigated systems improve significally the abrasive wear resistance of carbon steel. At room temperature the improvement by factor 1.3-2.2 times and at the temperature 550 °C by factor 2.7-4.6 is observed depending on chemical composition of coatings.
Technology Advances in Compressor and Turbine Abradables
Authors: Wilson S. , Sporer D. , Dorfman M.R.
Published: September 2022

Abradable seals have been used in jet engines since the late 1960's. Today they are seeing applications in low pressure and high pressure sections of compressors as well as the high pressure turbine module of jet engines. Clearance control systems using abradable coatings are also gaining ever more attention in industrial and steam turbine applications. Thermal spraying is a relatively simple and cost effective means to apply abradable seals. Abradable coatings work by minimizing gaps between rotating and stationary components by allowing the rotating parts to cut into the stationary ones. Typically plasma and combustion spray processes are used for applying abradable coatings. The types of coatings employed in the HP turbine are zirconia based abradable material systems with polymer and, in some cases, solid lubricant additions such as hexagonal boron nitride. The coatings are designed to work at service temperatures of up to 1200°C. Types of matrix materials used in the low and high pressure sections of the compressor are aluminum-silicon, nickel and MCrAlY based systems. These compressor type systems typically also contain fugitive phases of polymer and/or solid lubricants such as hexagonal boron nitride or graphite. Operating temperature, depending on the material of choice, can be up to 750°C. Regardless of the specific application, fugitive phases and porosity are needed for abradable coatings. Polymers are used to create and control porosity in plasma sprayed coatings, a critical design requirement in adjusting abradability and erosion properties of thermal spray coatings. Combustion spray coatings generate porosity through the lower deposition velocities and temperatures compared to plasma and typically do not need polymer phases. Solid lubricants are added to help weaken the structure of thermal spray coatings and reduce frictional heating and material transfer to the blade.
Towards Highly Sintering-Resistant Nanostructured ZrO2-7wt% Y2O3 Coatings for TBC Applications by Employing Differential Sintering
Authors: Lima R.S. , Marple B.R.
Published: September 2022

Envisioning the use of nanostructured YSZ coatings at high temperatures cause concerns in the scientific community. Questions have been raised about the possibility of accelerated sintering of these ultra-fine materials and the associated changes in properties that could accompany this sintering. In this work, nanostructured YSZ coatings were engineered to counteract sintering effects by tailoring the coatings to exhibit a bimodal microstructure formed by (i) a matrix of dense YSZ zones (produced from molten YSZ particles) and (ii) large porous nanostructured YSZ zones (produced from semi-molten nanostructured YSZ particles) that were embedded in the coating microstructure during thermal spraying. These coatings were subjected to heat treatment in air at 1400°C for 1, 5 and 20 h. The superior driving force for sintering exhibited by the porous nanozones, when compared to that of the dense zones, caused the nanozones to shrink at much faster rates than those exhibited by the denser matrix zones (i.e., differential sintering), thereby creating a significant network of voids in the coating microstructure. Due to these effects, after 20 h exposure at 1400°C, the thermal conductivity and elastic modulus values of the conventional coatings were approximately two times higher than those of the nanostructured ones.
Application of HVAF for Thermal Spraying of Zn-Al
Authors: Gorlach I.
Published: September 2022

Traditional metal spraying techniques, which have been used in industry for decades, such as Wire Flame and Twin-Wire Arc are classified as low velocity processes because the sprayed material is conveyed by compressed air having subsonic velocity. In order to improve the bond strength, HVAF was applied for thermal spraying for anticorrosion protection. In this paper, zinc-aluminium (Zn-Al) coatings thermal sprayed using the HVAF method are analysed. The thermal sprayed coatings were characterized by the standard techniques, such as light microscopy, scanning electron microscopy with energy-dispersive spectroscopy, X-ray diffraction, salt spray and bond strength tests. The results show that thermal sprayed coatings have a dense structure, a high bonding strength, low presence of oxides and high resistance to corrosion. This is attributed to high flow/particle velocities and relatively low combustion temperatures of HVAF in comparison with other thermal spraying technologies. High spray rate and good coating quality make the HVAF thermal spray method a viable alternative to the conventional Wire Flame and Twin-Wire Arc methods for thermal spraying of Zn-Al coatings.
Gas-Tight Coatings Produced by Very Low Pressure Plasma Spraying
Authors: Verdy C. , Zhang C. , Sokolov D. , Liao H. , Klein D. , Coddet C.
Published: September 2022

A certain level of porosity is always presented in thermal spray ceramic coatings. LPPS or some specific APS processes can allow to reduce it but it is difficult to obtain coatings with a low thickness (less than 100 m) which are fully gas-tight because of cracks or interconnected pores. This gas-tight property is for example very suitable for the ceramic electrolyte of solid oxide fuel cells (SOFC). Some ZrO2-Y2O3 coatings were obtained by the VLPPS process, a LPPS system operating at a pressure of about 100 Pa. The specific structure of these coatings is a mixture of condensed vapors and splats. The results are very satisfying because ZrO2-Y2O3 coatings with a thickness of about 70 micrometers are tight under a hydrogen pressure of 2x105 Pa. This paper presents some ZrO2-Y2O3 coatings obtained by different processes (APS, LPPS and VLPPS) and their properties.
Study on Gas Permeation Behaviour Through Atmospheric Plasma-Sprayed Yttria Stabilized Zirconia Coating
Authors: Zhang C. , Liao H. , Planche M. , Coddet C. , Li C.-X. , Yang G.-J. , Li C.-J.
Published: September 2022

Gas permeation behaviour through atmospheric plasma-sprayed 8 mol% yttria stabilized zirconia (YSZ) electrolyte coating was studied experimentally. YSZ coatings were fabricated using different powder feedstock. The temperature and velocity of in-flight particles during spraying were measured with a diagnostic system. The results showed that particle temperature and velocity were significantly influenced by the size of powders. The gas permeability of these coatings was estimated by a specific instrument with pure O2, N2 and H2. It was found that the gas permeability was reduced by decreasing the size of powder. Gas permeation behaviour through plasma-sprayed YSZ coating was studied. Transition flow was compatible to gas permeation behaviour for all three plasma-sprayed YSZ coatings. The relationship between gas permeation behaviour and coating microstructure is discussed in this article.
Detailed Analysis of the Plasma Jet of F4 and Delta Torches by Means of Tomography
Authors: Dschung F. , Forster G. , Zierhut J. , Marqués J.-L. , Schein J. , Haberbosch R. , Guide B.
Published: September 2022

One important aspect concerning the coating of surfaces using thermal spray is the improvement of the injection of material particles into the gas jet and thus the deposition efficiency. Therefore a better knowledge of the temperature distribution within the jet is relevant in order to optimize spraying conditions. Particularly interesting is the existence of a well-defined threefold finger structure in the plasma jet produced by triple electrode torches, which allows an efficient injection of coating material due to the existence of zones with higher and lower viscosity. The jet structure, however, lacks rotational symmetry and can therefore not be analyzed by systems relying on the validity of the Abel inversion, thus new systems have to be developed. In this work an innovative tomography device is described that has been designed for this purpose. By circling half around the plasma jet and taking simultaneously intensity images under different view orientations, a three-dimensional intensity distribution of the jet is generated, which can be used to determine the temperature distribution.
Thermoelectric Properties of Plasma Sprayed (Sr, Y)TiOx Thick Film
Authors: Sodeoka S. , Suzuki M. , Inoue T. , Obara H.
Published: September 2022

SrTiOx is an expected oxide thermoelectric material, which performance can be improved by doping Y3+ in place of Sr2+. However, the maximum content of Y3+ is limited to about 10% because of the phase transformation in the equilibrium sintered material. By contrast, plasma sprayed (Sr, Y)TiOx, which was essentially rapidly quenched, could solve Y up to 20% of Sr-site without the second phase, and produce the increase in the electric conductivity and the decrease in the thermal conductivity. But the absolute value of Seebeck coefficient decreased with an increase of Y content. As the result, the ZT value, which showed the performance for thermoelectric power generation, was reached only 0.1 in the Y content range 10% to 25% of Sr site.
Plasma Sprayed Coatings of High Purity Ceramics for Semiconductor and Flat-Panel Display Production Equipment
Authors: Kitamura J. , Ibe H. , Mizuno H. , Aoki I.
Published: September 2022

High purity oxide ceramic powders of alumina (Al2O3) and yttria (Y2O3) for plasma spraying have been developed to apply to semiconductor and flat-panel-display (FPD) production equipments. The ceramic coatings onto inside chamber wall of the equipments are required to have highly erosion resistance against CF containing plasma, widely used in dry etching process for micro-fabrications of the devices. Yttria is increasingly used in this application due to the high resistance compared to alumina. It is found that the yttria coating formed from agglomerated-and- sintered powder consisting of large primary particle has smoother eroded surface. Considering that particle deposition onto the devices, this coating will be effective to decrease generation of large sized particle, which is easily deposit onto the devices. Electric insulating properties of the coatings are also investigated to apply to electrostatic chuck. Electric breakdown voltage of yttria coatings is almost comparable to that of alumina coatings. However, yttria is difficult to apply due to its lower mechanical strength. Using smaller powder as feedstock is effective to improve the electric properties and influence of coating purity is lower than the powder size.
Parameters Controlling Properties of Coatings Sprayed by Suspension Plasma Spraying
Authors: Etchart-Salas R. , Rat V. , Coudert J.F. , Fauchais P.
Published: September 2022

Recent works have been devoted to achieve dense and thin (<15 µm) zirconia coatings using a relatively new process, Suspension Plasma Spraying (SPS). Nevertheless, the parameters controlling the microstructure of the deposit are not yet clearly identified, particularly for the injection of suspension. Hence, the liquid penetration into the plasma has been observed with a fast shutter (10-5 s) camera coupled with a laser flash and triggered by a defined instantaneous voltage level of the plasma torch. This paper is focused on the treatment of the suspension jet or drops according to the suspension properties (with the viscosity, particles load, injection velocity…) and depending on the different spray parameters such as the plasma forming gas mixture composition and the plasma torch design (either PTF4 or home made torch). These works have permitted the obtention of zirconia coatings with low thicknesses (~10 µm) and dense structure (~4% of porosity).
Liquid Precursor Plasma Spraying: Observation of Liquid Feedstock Break-Up
Authors: Marchand C. , Chazelas C. , Mariaux G. , Vardelle A.
Published: September 2022

The use of liquid precursors in plasma spraying makes it possible to produce coatings with more refined microstructures than in conventional plasma spraying. Depending on the injection device, the liquid feedstock is injected into the plasma jet in the form of liquid jet or droplets. The instabilities on the liquid-gas interface cause the mechanical break-up of liquids into drops that are subjected to further break-up until the droplets reach a stable state or evaporate. The process break-up may strongly influence the size, trajectories and, therefore, treatment of the droplets in the plasma medium. This study deals with the experimental observation of liquid break-up under plasma spray conditions when using a conventional DC plasma torch with radial injection by means of a pneumatic injection system that can deliver either liquid stream or blobs.
Tribological Comparison between FeCrSiMnB and FeCrSiMnC+WSC Arc Sprayed Coatings
Authors: Tillmann W. , Vogli E. , Ferreira da Cunha A.
Published: September 2022

Thermal spraying technologies take part in the current worldwide scene as serviceable and profitable technologies for a wide range of intents. The growing adoption of those techniques has driven companies to progressive investments in efforts to reach innovative designs and market needs. Wear resistance is among the desired features which certain components must be able to provide while performing. In this context tribology has an outstanding importance, where the adoption of suitable materials and operational parameters jointly contribute for a longer lifetime of parts. This contribution presents a comparison of AISI 1045 (DIN C45) steel surfaces coated by means of arc spray process, employing cored wires as feedstock. Corresponding light microscopy, SEM-EDX, 3Dprofilometry, hardness and ball-on-disk analyses were conducted to understand the tribological behaviour of two unlubricated iron-based layers with and without carbides reinforcement. The results point out equivalent thickness, porosity and as-sprayed roughness for both coatings. Higher hardness and lower friction coefficients for the carbide free coating as well as a downward trend considering the coefficients of friction for coated and uncoated surfaces under heavier loads.
Numerical Simulation of an Electromagnetically Controlled Plasma Jet During Atmospheric Plasma Spraying
Authors: Brußies E. , Stiller J. , Grundmann R.
Published: September 2022

We present the results of an investigation of the effects of a travelling magnetic field (TMF) on the plasma flow using a commercial program package. The argon plasma generation in the electric arc and the Lorentz force induced by the TMF are simulated with specific equations, which are derived from the magnetofluiddynamic equations using appropriate simplifications. First calculations confirm the predicted effects.
Preparation and Mechanical Properties of Cold Sprayed Nanocrystalline Aluminum
Authors: Hall A. , Yang P. , Brewer L. , Buchheit T. , Roemer T.
Published: September 2022

Nanostructured materials are of widespread interest because of the unique properties they offer. We have demonstrated that nanocrystalline 6061 and 5083 aluminum powders, prepared using liquid nitrogen (LN2) ball milling, can be consolidated using the cold spray process. TEM analysis of the cold spray coatings reveals that the cold spray process caused significant grain refinement. Gas atomized 6061 and 5083 aluminum powders were ball milled in liquid nitrogen resulting in a powder microstructure containing 250-400 nm grains. Cold spray coatings prepared using these feed stock materials exhibited homogenous microstructures with grain sizes of 30-50 nm. TEM analysis of the as-received powders, ball milled powders, and coatings are shown. Mechanical property measurements made using nano-indentation techniques show that the hardness of the coatings prepared using the LN2 ball milled 6061 is approximately double the hardness of the coatings prepared using the same powder in its as-received condition.
Comparison between APS, HVOF and High-Velocity Suspension Flame Spraying (HVSFS)-Deposited Al2O3 Coatings
Authors: Bolelli G. , Cannillo V. , Lusvarghi L. , Rauch J. , Killinger A. , Gadow R.
Published: September 2022

The High-Velocity Suspension Flame Spraying (HVSFS) technique, a recently-developed modification to the standard HVOF process enabling the use of suspension feedstock, was employed in order to deposit Al2O3 coatings from a nanopowder suspension. These coatings were compared to conventional APS and HVOF-sprayed ones. HVSFS coatings possess lower overall porosity and lower pore interconnectivity degree. Indeed, most of the nanoparticles were fully melted by the gas jet, thus forming very thin, well-flattened lamellae, having smaller columnar crystals than conventional coatings. Accordingly, HVSFS coatings possess higher hardness and elastic modulus, as determined from nanoindentation tests. Ball-on-disk tribological tests also indicate that HVSFS coatings possess much better sliding wear resistance than conventional ones, because they are capable of forming denser and more protective surface tribofilms during dry sliding.
Plasma Spraying of Tungsten Carbide-Cobalt Coatings by the Water-Stabilized System (WSP)
Authors: Ctibor P. , Kasparova M. , Bellin J. , Le Guen E.
Published: September 2022

Tungsten carbide – cobalt powders (WC-17wt.%Co) were plasma sprayed by a water-stabilized system WSP. A matrix of experiments with variable feeding distances and spray distances was carried out. Thinner coatings were carried out on carbon steel substrates and thicker coatings on stainless steel substrates to compare fast cooling conditions – the former with slower cooling conditions. Basic characterization of coatings was done by XRD, SEM and light microscopy plus image analysis. Microhardness was measured on polished cross sections. The main focus of investigation was on resistances against wear in dry as well as wet conditions. The appropriate tests were performed with set-ups based on ASTM G65 and G75, respectively. The influence of spray parameters onto coating wear performance was observed. The results of mechanical tests are discussed in connection with changes of phase composition and with the character of the coating’s microstructure. The results show that for obtaining of the best possible WC-17Co coating with WSP process, from the viewpoint of wear resistance, the desired parameters combination is long feeding distance combined with short spray distance.
Evaluation of Shear Test Results for Determination of Shear Load Resistance of Thermally Sprayed Coatings
Authors: Hartmann S. , Deuerler F. , Winkler R.
Published: September 2022

The shear test in accordance with EN 15340 is a new test method for testing the bond between substrate and thermally sprayed coatings. It has been developed in order to enable a test method without the disadvantages of the method currently in use, the adhesion test. In the adhesion test the adhesives influence the test results; therefore in the shear test no adhesives are used. The adhesives are among others the reason for a large deviation of the test results using the pull-off test. Using the shear test the mode of the test results depend on the ratio between adhesion and cohesion; this ratio causes three different fracture modes. In order to investigate the deviation depending on the fracture mode samples have been coated by wire flame spraying, arc, plasma and HVOF spraying. Different ceramics, carbides and metals have been used as thermal spraying materials. For each material-process combination between 30 and 120 samples have been coated. This report describes the interpretation of the results of the shear test depending on the fracture mode and the coating materials applied by different thermal spraying processes. The deviation of the results depending on the fracture mode has been investigated using a shear test device by which the shear force is recorded over the displacement of the coating. The knowledge of the deviation and the distribution of the results is necessary to decide on the required number of samples to reach a result with a defined reliability.
Microstructures and Oxidation Behavior of Cr39Ni7C Cermet Coatings Oeposited by Diamond Jet Spray Process
Authors: Ye F.-X. , Wu S.-H. , Ohmori A.
Published: September 2022

For the promising erosion and oxidation resistance of carbide cermet coating, Cr39Ni7C cermet coatings were deposited by Diamond Jet spray process using a commercial Sulzer Metco 5241 powder in this study. The microstructure, phase composition and high temperature oxidation behavior of the deposited coatings were investigated. The speed and temperature of in-flight particles were measured by DPV-2000. The results revealed that the speed of in-flight particles decreased from 229 m/s to 150 m/s with the increasing of spraying distance from 100 mm to 300 mm, whereas the average temperature of in-flight particles increased from 1926 to 2245 K. The decarburization of Cr3C2 increased with the increasing of fuel gas flow from 30 FMR to 40 FMR for higher heat enthalpy of flame. Due to the formation of Cr2O3 on/in the coatings at high temperature, the sprayed coatings had good oxidation resistance at 1073 K in air atmosphere. For the lower porosity of the coating deposited under the spraying distance of 150 mm, its oxidation resistance was better than that sprayed under the spraying distance of 200 mm.
Effect of the Blasting Time on the Amount of the Residual Grit on a Blasted Steel Substrate
Authors: Maruyama T. , Miyazaki T. , Kobayashi T.
Published: September 2022

The substrate surface roughening and cleaning are very important process for pre-treatment of a substrate for thermal spraying. There are some methods for the pre-treatment. Especially, the grit blasting process is the most general process. However, some grits embed into the blasted substrate, and the embedded grits remain on it. The girt embedment is affected by various conditions of the blasting process. It is important to make known the effect of the blasting time on the residual grit amount. A carbon steel substrate was blasted by white alumina grit. The blasting time was changed. The surface roughness of the blasted substrate increased monotonically with increasing blasting time. During very short time at the starting of blasting, the residual grit amount increased with increasing blasting time. Then the amount of the residual grit decreased with increasing blasting time. The penetration depth of the residual grit on the blasted substrate denoted the same tendency of the residual grit amount. There may be a critical time that the residual girt amount becomes the local minimum value.
Effects of Surface Chemistry on Splat Formation during Plasma Spraying
Authors: Tran A. , Hyland M.M. , Qiu T. , Withy B. , James B.J.
Published: September 2022

In this study, aluminium 5005 and stainless steel 304L substrate surfaces were modified by thermal and hydrothermal treatments. Ni-Cr single splats were deposited onto these substrates at room temperature using plasma spraying. The collected splats were characterised qualitatively and quantitatively by Scanning Electron Microscopy (SEM) and ImageJ software. A splat classification scheme was developed based around splash and disk-type splats. The proportions of the different splat types were found to vary significantly as a function of substrate pretreatment, especially when the pretreatment involved heating. The effect of surface roughness to splat formation and splat shape was investigated. It was observed that surface roughness was not a critical factor in splat morphology. The above substrate surfaces were also characterised by X-ray photoelectron spectroscopy (XPS) using in-situ heating in vacuum to determine the effect of thermal pretreatment on substrate surface chemistry and the oxide thickness. It was found that heat treatment promoted a change in the chemical structure of the oxide surface layer which was consistent with the dehydration of oxyhydroxide to oxide. Dehydration of the substrate surface layer improved the physical contact between the splat and substrate which enhanced the formation of disk-splats, decreased the number of pores evident in the splats and increased number of splats and their diameter.
New LN2 Cryogenic Process to Strip Parts Thermal Spray Coated
Authors: Ducos M.D. , Richard F. , Matile O. , Warnecke R. , Hume H. , Debionne T.
Published: September 2022

Thermal spray coatings applied for aircraft gas turbine maintenance often needs to be stripped and removed. Various methods are used, such as chemicals or a very high pressure water jet. None of them are environmentally friendly and they must be applied with care to prevent substrate damage. Also, these methods can produce a great deal of waste that has to be managed. As regulation gets tougher, a new technology using very high pressure liquid nitrogen could be the future for such treatments. As the worldwide exclusive licensee, over several years Nitrocision LLC has developed and commercialized this technology, which initially was conceived in the late 90s by the Idaho National Laboratory. The NITROJET 6000 can pressurize Liquid Nitrogen up to 4000 bars and to temperatures as low as - 170°C. Various sets of tools can provide single or multiple nozzles on a fixed, or alternatively, a rotary head that provides greater coverage and efficiency. This publication presents case studies of the technology applied to coating removal on aeronautical parts in gas turbines and landing gears.
Improving Wear and Corrosion of Magnesium Alloys through a Combination of Thermal Spraying and Laser Cladding
Authors: Biermann T. , Weisheit A. , Bobzin K. , Zwick J. , Ernst F. , Richardt K.
Published: September 2022

Saving energy is a major concern in every aspect of the economy, especially in the automotive and aerospace industry. The use of lightweight materials is one way to reduce weight of moving parts and thus energy consumption. Research activities to improve the porosity on the one hand, and the coating properties like wear and corrosion resistance on the other hand, show the potential of a hybrid coating process. The creation of thermal-sprayed coatings and a laser post-treatment enable a minimization of porosity and an improvement of wear properties. Different coating materials (e.g. Al-Si alloy) have been investigated regarding microstructure, hardness, wear- and corrosion protection.
Improvement in Deposition Efficiency of Copper Particles onto Metallic Substrate in Cold Spray Process
Authors: Fukumoto M. , Terada H. , Satoh K. , Mashiko M. , Yamada M. , Yamaguchi E.
Published: September 2022

To improve the deposition efficiency of copper particles, especially fine particle, in cold spray process onto metallic substrate, optimization of nozzle shape and dimension was performed by numerical simulation. Maximum velocity of the particle reached up to 685 m/s under the optimum conditions by using self-designed nozzle based on the simulation results. In the spraying of copper particle onto steel substrate, lamellar-like unique micro-structure was observed near the interface region of the steel substrate. Correspondingly, hardness increase in this region of steel substrate was recognized. Work hardening was induced in the steel substrate due to the higher velocity of copper particles. Furthermore, to reduce the bow shock effect on the substrate surface region in cold spray process, special shaped nozzle was newly developed. While nominal particle velocity decreased in the special nozzle, deposition efficiency, Vickers hardness and adhesion strength increased significantly especially in the case of fine particle and higher pressure levels of the working gas. Numerical simulation showed that pressure level on the substrate surface decreased effectively in the special nozzle. In the observation of a cold sprayed individual particle onto mirror polished substrate, extended metal jet was recognized at particle’s periphery when the particle was sprayed by the special nozzle. The results indicate that the decrease of particles velocity by bow shock was suppressed effectively in the special nozzle as compared with conventional nozzle.
TGO Growth and Crack Propagation in a Thermal Barrier Coating
Authors: Chen W.R. , Archer R. , Huang X. , Marple B.R.
Published: September 2022

In thermal barrier coating (TBC) systems, a continuous alumina layer developed at the ceramic topcoat/bond coat interface helps to protect the metallic bond coat from further oxidation and improve the durability of the TBC system under service conditions. However, other oxides such as spinel and nickel oxide, formed in the oxidizing environment, are believed to be detrimental to TBC durability during service at high temperatures. It was shown that in an air-plasma-sprayed (APS) TBC system, post-spraying heat treatments in low-pressure oxygen environments could suppress the formation of the detrimental oxides by promoting the formation of an alumina layer at the ceramic topcoat/bond coat interface, leading to an improved TBC durability. This work presents the influence of post-spraying heat treatments in low-pressure oxygen environments on the oxidation behaviour and durability of a thermally sprayed TBC system with high-velocity oxy-fuel (HVOF)-produced Co-32Ni-21Cr-8Al-0.5Y (wt.%) bond coat. Oxidation behaviour of the TBCs is evaluated by examining their microstructural evolution, growth kinetics of the thermally grown oxide (TGO) layers, as well as crack propagation during low frequency thermal cycling at 1050°C. The relationship between the TGO growth and crack propagation will also be discussed.
Development and Investigation on New Composite and Ceramic Coatings as Possible Abradable Seals
Authors: Bardi U. , Giolli C. , Scrivani A. , Rizzi G. , Borgioli F. , Fossati A. , Partes K. , Seefeld T. , Sporer D. , Refke A.
Published: September 2022

In order to improve gas turbine performance it is possible to decrease back flow gases in the high temperature combustion region of the turbo machine reducing shroud/rotor gap. Thick and porous TBC systems and composite CoNiCrAlY/Al2O3 coatings made by Air Plasma Spray (APS) and composite NiCrAlY/graphite coatings made by Laser Cladding were studied as possible high temperature abradable seal on shroud. Oxidation and thermal fatigue resistance of the coatings were assessed by means of isothermal and cyclic oxidation tests. Tested CoNiCrAlY/Al2O3 and NiCrAlY/graphite coatings after 1000 hours at 1100°C do not show noticeable microstructural modification. The oxidation resistance of new composite coatings satisfied Original Equipment Manufacturer (OEM) specification. Thick and porous TBC systems passed the thermal fatigue test according to the considered OEM procedures. According to the OEM specification for abradable coatings the hardness evaluation suggests that these kinds of coatings must be used with abrasive tipped blades. Thick and porous TBC coating has shown good abradability using tipped blades.
Development of HVOF-Sprayed Nanostructured TiO2 Coatings for High Temperature Applications
Authors: Lima R.S. , Moreau C. , Garcia E. , Miranzo P. , Osendi M.I.
Published: September 2022

Titania (TiO2) coatings are candidates for high-temperature applications in the fields of wear, corrosion, and environmental barrier coatings (EBCs); however, at temperatures at or above 540 °C, titania coatings are not pursued due to the usual presence of the anatase phase in the as-sprayed TiO2 coatings. This phase tends to impede the applications of these materials at high temperatures due to the stresses provided by the critical anatase-to-rutile phase transformation at temperatures higher than 540 °C; such stresses tend to generate cracks in the coating microstructure, leading to premature coating failure. It has been hypothesized that this barrier could be overcome by the use of nanostructured TiO2 coatings, due to their known high toughness and resilience levels. Nanostructured TiO2 powders were HVOF-sprayed. The high velocity levels of the HVOF-sprayed particles generated a gas-tight microstructure (i.e., no through-thickness porosity). SEM pictures of the as-sprayed and heat-treated (800 °C for 1 h) coatings did not show any significant signs of crack network formation, which may have been prevented by the high toughness and resilience of these coatings. These coatings were also HVOF-sprayed on SiC substrates and did not exhibit macroscopic signs of delamination after a 1400 °C exposure for 1 h in air.
A Comparison of Sintering Behavior and Phase Transformation Characteristics Between Plasma Sprayed Commercial CSZ and Conventional YSZ Based TBCs
Authors: Altuncu E. , Ustel F.
Published: September 2022

Plasma-sprayed thermal barrier coating (TBC) systems are widely used in gas turbines blades in order to increase turbine entry temperature (TET) with better efficiency. Yttria stabilized zirconia (YSZ) has been usually chosen as the top thermal barrier coating material because of its low thermal conductivity, high thermal expansion coefficient and good corrosion resistance. However as a new candidate commercial TBC material, ceria stabilized zirconia (CSZ) currently looks to be promising. Ceria and ceria based ceramics show an outstanding potential for use at temperatures exceeding 1200 °C. CSZ coatings do not only have high temperature stability, good corrosion resistance and high fracture toughness but also lower thermal conductivity and higher thermal expansion coefficient than YSZ coatings. The sintering and phase transformation characteristics of both ceramic thermal barrier coatings under high temperature conditions are complex phenomena. In this paper, microstructural differences, sintering behaviours (1200 oC, 10h, 25h and 50h) and phase transformations of the plasma sprayed ceria stabilized zirconia (CSZ: ZrO2–2.5 wt.%Y2O3– 25 wt.%CeO2) and conventional yttria stabilized zirconia (YSZ; ZrO2–8 wt.%Y2O3) coatings and their powder materials have been investigated and compared using thermal analysis techniques, XRD and scanning electron microscope.