bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterisation of Inconel 625 Coatings Deposited by Cold Spray
Authors: Pontarollo A. , Vezzù S. , Trentin A. , Rech S. , Guidolin M. , Cafissi A. , Peretti C. , Molinas B.
Published: November 2022

The high strength nickel alloys, and in particular Inconel type alloys, are extensively used in several applications, such as aeronautics and petroleum industry, thanks to the combination of their high mechanical properties and their thermal and chemical resistance. In particular Inconel 625 is already used in oil pipelines and pipelines of large thermal plants, and the possibility to replace high cost bulk Inconel parts with Inconel coated steel parts is of great interest. On this context the first topic to allow the use of coated parts instead of bulk Inconel is the capability to provide high corrosion and thermal resistance. The aim of this study is to investigate the capability of Coldspray in the deposition of high strength materials, such as hard nickel alloys, for corrosion protection, and to compare the corrosion behaviour of Coldspray coatings with commercial HVOF deposited coatings. Inconel 625 coatings were deposited by using CGT Kinetic3000 deposition system with nitrogen as carrier gas on AISI316L flat substrates. The coating thickness ranges between 0.3 and 1.0 mm. Different feedstock materials were used and the effect of powder size distribution on the growth capability, as well on coating microstructure and porosity, were evaluated. The corrosion behaviour of Coldspray coatings were studied by electrochemical potentiondynamic analysis and compared with the behaviour of commercially available coatings deposited by HVOF that could be considered as a high-quality benchmark. In particular, the effects of the different coating microstructures due to the different deposition processes were related with the corrosion resistance. Further development and key features are finally outlined in order to candidate the Coldspray as promising technology for the deposition of high-strength nickel alloys.
Thermal Spraying of Bioactive Polymer Coatings for Orthopaedic Applications
Authors: Chebbi A. , Podporska J. , Stokes J.
Published: November 2022

This research aims at introducing new biodegradable/non-biodegradable materials (biopolymers) to the existing Hydroxyapatite (HA)-titanium combination or as a single coating in order to overcome some of the limitations of HA coatings. Biopolymers can act as drug carriers for a localised drug release following implantation; they can also have a structural role by improving the mechanical performance of implants at the bone –implant interface. The proposed materials consisted of biodegradable and non-biodegradable polymers widely used as drug delivery systems: polymethylmethacrylate and polyhydroxybutyrate 98%/ polyhydroxyvalerate 2%. The method used to apply the polymeric powders was oxygen/acetylene flame spraying, due to its superior mechanical advantages over other techniques. Screening tests were used to determine the suitable range of spraying parameters, followed by optimisation to understand of the effects of spraying parameters on coating characteristics (thickness, roughness, adhesion, wettability), in order to obtain an optimal coating design. The polymers were sprayed onto bare titanium substrates. FTIR results showed that the coatings underwent little chemical degradation. Biocompatibility tests showed that cells proliferated well on flame sprayed polymer coatings, which confirms that the coating technique used did not affect the biological performance of the material.
Polymers in Thermal Spray
Authors: Grimenstein L. F.
Published: November 2022

Over the year’s polymers have been used in thermal spray coatings. The most known usage is as a polymer used to seal porosity in thermal spray materials. The sealers mostly used do not really work because they do not penetrate very far into the coating. Once the coating is machined or ground the sealer is gone and we have a porosity coating due to fail. One major sealer resin system used, is Phenolic as the resin, that resin is older than most of the audience and loaded with flammable acetone. It also is not a high temperature material nor does it last long since it is a rigid material and does not expand or contract. The old sealers mostly had solvent systems in them and were replaced with a water born polymer. However, our industry has not kept up with the technology of resin based systems. Water systems sound good environmentally but it does not penetrate and really does not work well for this application. Later polyester was used with a ceramic filler to produce an abradable coating for the seal area for turbine applications. More recently higher temperature polymers were used to create a high temperature abradable coating. I want to show you some new polymeric materials that have done some new applications and also recommend additional work for the thermal spray industry for improved applications using the technology of tomorrow.
Surface Modification of Austenitic Thermal Spray Coatings by Low-Temperature Carburization
Authors: Wielage B. , Rupprecht C. , Lindner T. , Hunger R.
Published: November 2022

Thermal spray coatings of austenitic materials are mainly used under corrosive conditions. The relatively poor wear resistance strongly limits their use. A selective enrichment of the surface layer region with carbon by means of thermochemical heat treatment improves the residual stresses and increases the wear resistance. The interstitial deposition of carbon causes strong compressive residual stresses and a high surface hardness. The low process temperature of the thermochemical heat treatment avoids the precipitation of chromium carbide, whereas the corrosion resistance is not affected. Increases in the service life of existing applications or new material combinations with face-centred cubic friction partners are possible. In the absence of dimensional change, uniform as well as partial carbon enrichment of the thermal spray coating is possible. In comparative studies between carburized and untreated thermal spray coatings, the influence of the carbon enrichment on the coating properties and the microstructure was investigated. Carburized coatings demonstrate a significant improvement in adhesive wear resistance and an extremely high surface hardness. The cross section micrograph of the carburized coating shows the S-phase formation in the surface layer region. The depth profile of the carbon concentration was determined by GDOS analysis.
Effect of Laser Remelting on the Mechanical Behaviour of Inconel 625 Cold-Sprayed Coatings
Authors: Vezzù S. , Rech S. , Trentin A. , Poza P. , Múnez C. J. , Garrido-Maneiro M. A.
Published: November 2022

Ni base overlay coatings are being used to protect metallic engineering components in extreme conditions and actually traditional thermal spray deposition technologies such as Air Plasma Spraying (APS) and High Velocity Oxy-Fuel (HVOF) are mainly used to deposit these materials. However, Coldspray is receiving increased attention during the last years because of the lower spraying temperature required to deposit metallic coatings avoiding oxidation and reducing the coating porosity and the amount of residual stresses. The adhesion to the substrate and the growth mechanism of coldspray deposits are based on plastic deformation of impinging particles, so, in the case of high strength materials such as for example Ni alloys, it could be a lack in plastic deformation leading to insufficient compactness of the coating, barrier properties and high temperature resistance. Further improvements in the coatings performances could be attained by post-deposition thermal treatments to enhance coating adhesion and barrier properties. In this sense, the aim of this study is to explore a two-step way to produce high performances Inconel 625 alloy coatings by coldspray deposition followed by a laser glazing treatment. Coldspray Inconel 625 alloy coatings has been deposited onto AISI304 steel substrates. Laser glazing is performed using high power diode laser (HPDL) ROFIN-SINAR 13DS; the local thermal treatment on the coating surface induce microstructural changes which could modify and improve the coating compactness and performances. Coating morphology and microstructure has been evaluated and reported both before and after laser consolidation as a function of different laser conditions.
Laser Treatment of Thermal Sprayed NiCrBSi Coating: Modelling, Study and Characterization
Authors: Buza G. , Molnar A. , Felde I. , Balogh A.
Published: November 2022

Thermal sprayed NiCrBSi wear resistant coating is widely used in industry life increasing of worn parts for protective coating of the metallic surfaces. The coating is based on the mechanical anchoring of the splats onto the substrate surface and thermal integration among the splats in the coating is not possible during the spraying process due to the operation temperature, which is lower than the melting temperature of the coating material. This, in turn, results in the formation of non-homogeneous structures and voids in the coating. One of the techniques to avoid such situations is to integrate the splats through the controlled melting. This can be achieved through the laser melting process. In the present study, laser melting of thermal sprayed coating is modeled to determine the melt layer thickness. A lump parameter analysis is introduced in the model study and simulations are carried out in relation to the actual laser melting conditions. The melt layer predicted is compared with the experimental measurements. The micro structural analyses prior and post laser melting process are carried out using SEM and XRD, and the mechanical properties such as hardness, were also investigated. It is found that the predictions of the melt layer are in good agreement with experimental results.
Pt Thermal Sprayed Coating on Refractory-Bricks for Glass Melting
Authors: Ishikawa Y. , Hamashima K.
Published: November 2022

The dense refractory is applied for the high-temperature glass melting equipment. Furthermore, platinum or its alloy-clad refractory bricks are utilized to melt high quality glass in fields of optical and display glasses. From the viewpoint of the resource saving of rare metal, the decreasing of Pt-consumption is very serious problem for glass manufacturing. The platinum thermal spray coating is effective alternative technology to solve this problem for platinum cladding. A Pt-spray coated ceramics is difficult to get reliability due to the large difference of thermal expansion between the ceramic and the metal. In this study, we have investigated the bond strength of the platinum coat on the dense refractories which was textured by the mechanical process. As a result, the bond strength between the ceramic and the metal is 3-5 MPa. It is almost the same as the thermal spray ceramics coating on the metal. Furthermore, in case of the ceramics substrate that contains the glass phase, the bond strength between the ceramic and the metal increased to 14-17 MPa after 1773 K heat treatment.
Cold Spraying of Titanium using Enhanced Conditions and Optimized Nozzles
Authors: Binder K. , Gärtner F. , Klassen T.
Published: November 2022

In the past years a number of publications reported about Titanium coatings cold sprayed with a nominal power input between 17 to 47 KW (e. g Kinetiks 4000) reaching gas temperatures of maximum 850 °C and gas pressure of maximum 4 MPa. In a recent study at Helmut-Schmidt University (HSU), a Kinetiks 8000 prototype was used to spray titanium, employing a nominal power of about 92 KW to increase the gas temperature up to 1000°C at a pressure of 4 MPa. Under these parameters, a high tensile strength of over 480 MPa and a deposition efficiency (DE) close to 100% were achieved. The present study focuses on further enhanced gas and particle velocities by optimized nozzle designs. The increased particle velocities in comparison to that obtained by using commercial nozzles (types 24, 51) result in better coating performance and allow deviations from ideal (90°) impact angle without significantly reducing coating strength. The influences of process conditions are evaluated and discussed on the basis of coating strengths by Micro Flat Tensile and Tubular Coating Tensile tests, as well as electrical conductivities, nitrogen and oxygen contents.
The Effect of Fracture-Induced Ceramic Free Surfaces for Vacuum Kinetic Spray Bonding
Authors: Yong W. , Bae G. , Kang K. , Lee C.
Published: November 2022

The new kinetic spray coating technique, vacuum kinetic spray (aerosol deposition), utilizes the pressure gap between powder hopper and coating chamber which is vacuumed. In this study, to investigate the deposition mechanisms present in the vacuum kinetic spray coatings, α-Al2O3 and glass were chosen as the powder and substrate materials, respectively, and these were considered as the reference materials to examine the effect of free surfaces after particle fractures. Based on the finite-element modeling (using an AUTODYN-2D 12.1), single particle impacts were simulated, and the results elucidated the material shape, temperature variation and mass change of particle due to its fracture during impact. The plots of total mass change as a function of particle impact velocity demonstrate the deposition-optimized velocity zone (DOVZ) for successful deposition. Compared to as-received powders, from the transmission electron microscope (TEM) images, the defects such as dislocations of the ball-milled powders might increase the tendency of the powder particles to fracture upon impact. The cross-section images of the coating showed that the particle sizes of the coating were drastically decreased compared to those of initial powders. During coating, fractured particles enlarged the thermodynamically unstable free surface area and have a tendency of formation of bonding.
Applications of Cold Gas Spraying Compared to Manual Laser Welding in Connection with a Repair Contract in the Aerospace Field
Authors: Lutz P.
Published: November 2022

The attachment hooks of training missile wings are worn out. A technology must be found to repair the hooks. The hooks cannot be replaced. They are made of annealed steel of approx. 50 HRC hardness. A similar hardness should be achieved by the repair procedure without changing the basic material in its hardness and strength characteristics through heating. Additional annealing of the assembly is not possible due to its size. To find a solution to this problem, the cold gas spraying procedure was tested first. Cold gas spraying is a highly kinetic coating procedure in which powdery metal particles are strongly accelerated using inert gases at pressures of up to 40 bars and gas velocities far beyond 1000m/sec. When the particles hit the component surface, they form compact, strongly adherent layers of very low oxide content without preceding melting. As a second procedure, manual laser welding was tested using an Nd:YAG laser under a microscope with filling material. In this procedure, a weld pool can be generated within a few milliseconds. Due to the high velocity with which the energy is applied to the material and absorbed by it, a physical reaction is almost ruled out due to its thermal conductivity. Both procedures have the following advantages: function-related composition of the material applied is possible; the characteristics of the base material are not changed due to the low heating levels; and repeated treatment is possible. This paper compares the results of the procedures and discusses the limits of the technology for this specific application.
Development of Porous Ceramic Coating for High-Efficiency Cooling System
Authors: Arai M. , Suidzu T.
Published: November 2022

A transpiration cooling system for gas turbine applications has significant benefit for reducing the amount of cooling air and increasing cooling efficiency. In this paper, the porous ceramic coating using a plasma-spraying process, which can infiltrate a cooling gas and control the loss of coolant gas pressure, and the properties of the porous coating material fabricated in this study, such as permeability of the cooling gas, thermal conductivity and adhesion strength, are shown. The mixture of 8wt% yttria stabilized zirconia and polyester powders was employed as the coating, in order to deposit the porous ceramic coating onto the Ni-based super alloy substrate. The ceramic coating deposited with such mixed powder showed superior permeability for cooling gas and thereby to lead to considerable reduction of the substrate temperature based on the transpiration cooling mechanism. The adhesion strength of the porous ceramic coating was almost the same level as that of the ceramic coating utilized in current gas turbine components. The high-temperature exposure test revealed that the permeability of cooling gas did not change though a rigorous experience for a long period of up to 1000hours. It was also confirmed that the coating peeling damage did not occur after the thermal cycling test. It is concluded consequently that the transpiration cooling system proposed here for gas turbine could be achieved using the porous ceramic coating.
Deposition of Ceramic Oxides in Atmosphere and at Room Temperature Using the Powder Jet Deposition Technique
Authors: Ogawa K. , Arata H. , Takegoshi M. , Ono F. , Saito T.
Published: November 2022

Ceramic coating is a very important technique used to develop structures that resist wear, corrosion, or oxidation. In this study, the Powder Jet Deposition (PJD) technique is used to form ceramic coatings on structures. The PJD technique is similar to the cold spray technique, but it can be used to coat ceramic layers under room temperature and atmospheric conditions. Therefore, PJD was used for the creation and on-site repair of ceramic coatings on large, complicated structures. The aim of this study is to optimize the spray conditions for an aluminum titanate (TiAl2O5) coating on various substrates using the PJD technique and to evaluate the mechanism of ceramic deposition. In the case of the cold spray technique, a high particle velocity is essential to cause the large-scale plastic deformation of particles that is necessary for deposition. However, while using PJD on ceramic oxides, lower particle velocity proved to be a better deposition condition. The optimized spraying pressure, resulting in the thickest coating, was approximately 0.05 MPa. The particle velocity as measured using a high-speed camera was approximately 90m/s. Therefore with PJD, it is optimal to use a low velocity within a narrow range to form a ceramic coating.
Synthesis of Al2O3 Coatings by Plasma Transferred Arc
Authors: Drozda F. O. , Pianaro S. A. , d´Oliveira A. S. C. M.
Published: November 2022

The protection of metallic components against severe operating conditions has motivated the development of coatings for a wide range of applications. In particular, ceramic coatings can be used to protect components that operate under high temperatures and corrosive environments aiming to extend their service life. Several Thermal Spray processes can be used to process ceramic coatings on the metals, taking advantage of the mechanical bond typical of these processes. The exception is the Plasma Transferred Arc (PTA) process which results in a metallurgical bond between the coating and the substrate metal. This study analyzed the potential of PTA to process ceramic coatings on a steel substrate. Powder mixtures of aluminum (Al) and silicon oxide (SiO2) were deposited using three deposition currents aiming to synthetize alumina coatings “in situ” as the reaction between Silicon Oxide and Aluminum powders occurred. X-Ray diffraction, Scanning electron microscopy, Semi-quantitative chemical analysis by EDS and microhardness were used to analyze the processed surfaces. Coatings characterization confirmed that the synthesis of alumina occurred but it was not completed and a two layer coating was formed. A layer near the fusion line composed of Fe-Al matrix with Fe3Al precipitates and an external layer of Al, Si, and Al2O3. An increased in the iron content in the coating due to the higher interaction of the plasma arc with the substrate reduced the amount of Alumina formed.
Finite Element Simulation of Impacting Behavior of Particles in Cold Spraying by Eulerian Approach
Authors: Li W.-Y. , Yu M. , Liao H. L.
Published: November 2022

Numerical simulations focused on the impacting behavior of cold-sprayed particles are usually conducted with the Lagrangian method. However, the calculated output is much dependent on the mesh size due to the mesh distortion and/or the element-averaged variables in simulations. While the Eulerian method is attractive to overcome the mesh distortion. In this study, an investigation on the impacting behavior of cold-sprayed particles using the Eulerian formulation available in ABAQUS/Explicit was conducted with typical copper material. The results show that a jet can not be formed at the impacting velocities of 200-300m/s, but a continuous and smooth jet composed of the particle and substrate materials can be formed as the impacting velocity is in the extent of about 300-400 m/s which could be a theoretical value of the critical velocity for a successful bonding. At this velocity extent, the maximum PEEQ almost keeps unchanged accompanying with a temperature fluctuation. In addition, the jet presents discontinuous and the splashing causes the loss of material as the impacting velocity exceeds this velocity extent. Therefore, this model could be also used to predict the critical velocity of other materials besides the copper.
Influence of Gas Temperature, Particle Size and Substrate Material on the Deposition Behaviour of Cold Sprayed Magnesium Coatings
Authors: Suo X. K. , Guo X. P. , Li W. Y. , Planche M. P. , Bolot R. , Liao H. L. , Coddet C.
Published: November 2022

Magnesium coatings were deposited upon aluminum and stainless steel substrates by cold spraying. Three Mg powders with different particle size distributions were used as feedstock. The microstructures of as-sprayed coatings were evaluated by optical microscopy, and scanning electron microscopy. The coating observations show that a main gas temperature has an important effect on the deposition behaviour of particles. Changing the gas temperature from 350°C to 630°C involves an increase of the deposition efficiency from 1.57% to 19.57%. The effects of the particle size distribution and substrate material on the deposition efficiency of particles were also investigated. The results show that the particle size distribution has a significant effect on the deposition efficiency of particles which increases from 19.57% to 59% when the mean particle size decreases from 63 µm to 38 µm under gas temperature of 630°C. However, the deposition efficiency of particles was slightly influenced by the substrate material. In addition to these experimental results, the in-flight particle velocities were simulated by FLUENT software to point out the effects of the gas temperature and particle size distribution.
Influence of Annealing Treatment on the Microstructure and Microhardness of Cold Sprayed Nanostructured FeAl Coating
Authors: Wang H.-T. , Li C.-J. , Ji G.-C. , Yang G.-J.
Published: November 2022

In the present study, a nanostructured FeAl coating was prepared by cold spraying of ball milled powder. Annealing treatment was applied to the coating to investigate its effect on the phase structure, grain size and microhardness of the cold-sprayed nanostructured FeAl coating. The results showed that the FeAl phase was kept unchangeable when the coating annealed at the temperature above 500°C. Annealing temperature significantly influenced the microstructure and microhardness of cold-sprayed FeAl coating. With raising annealing temperature, the lamellar structure in the as-sprayed coating disappeared and a dense coating microstructure with fully bonding of deposited particles at their interfaces was achieved after annealing at 950°C. Nanograin growth of the FeAl phase occurred at an annealing temperature higher than 800°C. The microhardness of cold-sprayed FeAl coating remained about 400 Hv0.1 at the annealing temperature below 800°C and decreased to 300 Hv0.1 at 1100°C.
Study of the Influence of Particle Velocity on Adhesion Strength of Cold Spray Deposits
Authors: Huang R. , Fukanuma H.
Published: November 2022

The adhesion mechanism of deposits/substrate interface prepared by cold spray method has not been fully understood up to now. It seems that the adhesion strength is mainly determined by the mechanical (including the plastic deformation of particle and substrate) and thermal interaction between the particle and substrate when the particles impact onto the substrate with a high velocity. In order to understand the adhesion mechanism, the influences of particle impact velocity on the adhesion strength were investigated in this study. The particle velocity was obtained with DPV-2000 measurement and CFD simulation. The relationships between the adhesion strength of deposits/substrate interface and particle velocity were discussed. The results show that greater adhesion strength can be obtained with the increase of particle velocity. There are two available ways to improve the adhesion strength. One is to increase the temperature of working gas, and another is to employ helium gas as the working gas instead of nitrogen gas.
Thermal Stability of Microstructure and Hardness of Cold-Sprayed cBNp/NiCrAl Nanocomposite Coating
Authors: Luo X.-T. , Li C.-J.
Published: November 2022

cBN/NiCrAl nanocomposite coating was deposited by cold spraying using mechanically alloyed composite powders. To examine the thermal stability of coating microstructure, the nanocomposite coating was annealed at different temperatures from 750 to 1000°C. The microstructure of composite coatings was characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results showed that the nanostructure was retained in the coating when the annealing temperature was lower than 825°C which is 0.7 times of the melting point of NiCrAl matrix. The dislocation density significantly reduced when annealing temperature was higher than 750°C. The cBN particle growth became significant when the annealing temperature was higher than 825°C. The effects of crystal grain refinement and work-hardening strengthening mechanisms were quantitatively estimated as the function of annealing temperature. The effect of annealing temperature on the contribution of different strengthening mechanisms to coating hardness was discussed.
Influence of Metal Binder of WC Cermet Powder for Cold Spray and HVOF
Authors: Sato K. , Furukawa H. , Kitamura J. , Seo D. , Ogawa K.
Published: November 2022

From the appearance of high velocity oxygen fuel (HVOF) thermal spray system on 1980s, WC cermet coatings have been used as an anti-wear coating in many industrial manufacturing. Recently, WC cermet spray materials were applied to new thermal spray methods such as warm spray and cold spray under research phase. In HVOF spraying, WC-Co or WC-Ni series powder are used as standard contents. Ni and Co are binder metals for WC because of good wettability and suitable melting point. On the other hand, warm spray and cold spray are lower temperature process than HVOF. It is considered that any other factors of metal material such as hardness, toughness and crystal phase should be investigated in warm spray and cold spray. In this study, WC with Co or Fe alloy powders were sprayed by cold spray and HVOF to investigate the influence of binder metal for spray efficiency and coating property. It is cleared that Ni and Fe were superior to Co in spray efficiency and coating property in cold spray. The detail of above reason was under investigation, however, plastic deformability of binder metal is expected to be an important factor for WC cermet cold spraying.
Influence of Chromia Alloying on the Characteristics of APS and HVOF Sprayed Alumina Coatings
Authors: Niemi K. , Hakalahti J. , Hyvärinen L. , Laurila J. , Vuoristo P. , Berger L.-M. , Toma F.-L. , Shakhverdova I.
Published: November 2022

In order to improve both corrosion and wear resistance of standard plasma sprayed alumina coatings chromia alloyed feedstock powders and high velocity oxygen fuel (HVOF) spraying as an alternative process were used in this work. Alumina and alumina-chromia powders with different chromia contents (27% and 50%-mass., but with different amount of (Al,Cr)2O3 solid solution formed) were deposited by TopGun HVOF spraying and atmospheric plasma spraying (APS). The coatings were evaluated by optical microscopy, microhardness measurements, XRD and SEM. Abrasion wear resistance of the coatings was tested with the rubber-wheel abrasion test. Corrosion characteristics of the coatings were evaluated by exposure tests at 85 °C for 310 hours at low and high pH conditions. The amount of dissolved elements in solution, as analysed by ICP, was found to be a direct indication of the corrosion resistance of the coatings. Coatings deposited by TopGun HVOF spraying resulted in a denser microstructure, higher microhardness and significantly improved abrasion wear resistance as compared to corresponding coatings deposited by APS. For the tested conditions, corrosion resistance of both APS and HVOF-sprayed alumina coatings was low but significantly improved by chromia addition for both spray processes. However, the content of chromia addition alone does not allow to draw conclusions on the effectiveness of this measure.
Effect of Accelerating Gas Flow on Pore Structure and Mass Transport Property of Vacuum Cold Sprayed TiO2 Coatings Using Strengthened Nanostructured Powder
Authors: Yang G.-J. , Liao K.-X. , Li C.-J. , Fan S.-Q. , Li C.-X. , Li S.
Published: November 2022

The pore structure in nano-porous TiO2 coating influences the ion diffusion property and photovoltaic performance of dye-sensitized solar cells (DSC). In this paper, TiO2 coatings were deposited by vacuum cold spray (VCS) using a strengthened nanostructured powder. The pore structure, ion diffusion and dye infiltration properties were examined to understand the deposition mechanism of the coating and the suitability of cold sprayed TiO2 coating for DSC. It was interestingly found that the pores in the VCS TiO2 coating presented a bimodal size distribution with two peaks at ~15 nm and ~50 nm, which contributed to a much higher ion diffusion coefficient comparing to that of the conventional unimodal-sized nano-porous coating. The dye infiltration and loading are beneficial from the bimodal size distribution of the pores. Based on the impact behavior of the spray powder, a deposition model was proposed to explain the deposition mechanism of the strengthened nanostructured powder during vacuum cold spray.
Relationship between Particle and Plasma Properties and Coating Characteristics of Samaria-Doped Ceria Prepared by Atmospheric Plasma Spraying for Use in Solid Oxide Fuel Cells
Authors: Cuglietta M. J. , Kesler O.
Published: November 2022

Samaria-doped ceria (SDC) has become a promising material for the fabrication of intermediate-temperature, metal-supported solid oxide fuel cells (SOFCs). While typical SOFC materials, such as yttria-stabilized zirconia (YSZ), require high temperatures (> 700°C) to exhibit suitable ionic conductivity for high cell performance, SDC displays similar ionic conductivities at lower temperatures (600°C – 650°C). The atmospheric plasma spray (APS) process is a promising technique for manufacturing metal-supported SOFCs. In this study, the in-flight characteristics, such as particle velocity and surface temperature, of spray-dried SDC agglomerates were analyzed at various plasma spray conditions using the DPV-2000 in-flight particle sensor manufactured by Tecnar Automation. Coatings of SDC were applied on stainless steel substrates using a range of spray conditions, and their resulting microstructures and deposition efficiencies were analyzed. It was found that particle temperature could be related to the specific plasma energy, and that coating porosity was related closely to the measured average particle temperature.
The Solution Precursor Plasma Spray Process for Making Zirconia based Electrolytes
Authors: Christenn C. , Ansar A. , Haug A. , Wolf S. , Arnold J.
Published: November 2022

Ceramic layers, such as yttria-stabilized zirconia or scandia-stabilized zirconia, used for functional layers of solid oxide fuel cells, i.e. the gas tight oxygen ion conductive electrolyte or as ceramic component in the porous cermet anode, were obtained by the Solution Precursor Plasma Spray (SPPS) process. The influence of different solvent types on microstructure was analyzed by comparison of coatings sprayed with water-based solution to ethanol-based one. Use of solvent with low surface tension and low boiling point enhances splat formation, coating microstructure and crystalline structure. Parameter adjustment to receive coatings from nitrate solutions with ethanol as solvent was carried out. Results of Raman spectroscopy indicate that an intermediate of both nitrates (zirconyl and scandium nitrate hydrate) was deposited.
Anisotropic Electrical Conductivity of Copper Coatings Deposited by HVOF
Authors: Aghaee M. , Salehi M. , Salimijazi H. R.
Published: November 2022

Copper coatings were deposited on ferrous substrates by utilizing high-velocity oxy-fuel spraying (HVOF). Three different coating process parameters have been used in order to optimise the required electrical characteristics. Microstructure and phase formation in the coatings were analyzed by scanning electron microscope (SEM), X-ray diffraction (XRD), and oxygen analyzer (ELTRA). Electrical resistivity of coatings was measured in-plane and through-thickness using the four-contact method. Results shown that dense coatings with high purity and low level of porosity are required to achieve high electrical conductivity. The coatings exhibited an anisotropic electrical resistivity due to the nature of the thermal spray coating microstructure. Microstructural evaluation shown that individual splats morphology and splats interfaces play important roles in the electrical conductivity.
Densification of Low Temperature HVOF Ti Coating
Authors: Liu M. , Deng C. M. , Deng G. C. , Chen J. Q. , Zhou K. S.
Published: November 2022

Fundamental properties of Titanium coating prepared by low temperature HVOF process aided by injection of water had been published by our research group. The results showed that low temperature HVOF process provided as a good means for the deposition of comparatively dense Ti coating, however the interconnected pores observed in Ti coating degraded corrosion resistance of Ti coating, therefore it was necessary to manufacture denser Ti coating. Two processes were respectively applied for the densification of Ti coating. One process was to perform post heat treatment for as-sprayed Ti coating with conventional Ti powder as feedstock. The other process was to modify thermal spray powder. Ti powder mixing with spherical glass powder was used to deposit denser Ti coating as a result of shot peening effect of hard glass powder. Finally the corrosion resistance for densified Ti coatings was evaluated by electrochemical characterization.
Failure in APS Porous Thick YSZ Coatings Caused by Thermal Stress
Authors: Chen Z-Y. , Feng J. , Gao Y.
Published: November 2022

NiCrAl/ZrO2-8Y2O3 coatings deposited on SUS304 stainless steel and 45 carbon steel substrates were prepared by APS at different preheating temperatures, of which thickness exceeded 1mm. This study analyzed the coatings’ separation from different preheated substrates in the cooling process after spraying due to residual thermal stress. The Young’s modulus of the porous YSZ coatings was calculated and also measured by Knoop indentation methods for comparison purposes. The result indicated that the failure of porous thick YSZ coatings is mainly caused by the cracks nucleation, propagation and coalescence, which is related to the thermal-expansion coefficient difference between substrate and coatings, preheating temperature, porosity of coatings and so on. Due to their increased porosity, the porous and thick YSZ coatings had much lower calculated and measured Young’s modulus values than the sintered YSZ coatings.
A Novel Plasma-Sprayed Durable Thermal Barrier Coating with the Well-Bonded YSZ Interlayer between Porous YSZ and Bond Coat
Authors: Li C.-J. , Li Y. , Yang G.-J. , Li C.-X.
Published: November 2022

Atmospheric plasma-sprayed YSZ thermal barrier coatings (TBCs) are widely used in industrial gas turbine engines to prevent the superalloy blades from failure. The failure of TBCs in service occurs by the spalling of YSZ coating. Crack propagation leading to the failure of plasma-sprayed thermal barrier coatings usually occurs within YSZ coating near the YSZ/Bond coat interface. In the present study, a novel durable TBCs consisting of a YSZ interlayer of the well-bonded interlamellae between the bond coat and conventional YSZ top porous coat was introduced. The YSZ interlayer was deposited at different coating surface temperatures, which resulted in the formation of YSZ with significantly improved interlamellar bonding. The result shows that thermal cyclic lifetime of the novel TBCs with the 20-30 µm thick YSZ interlayer increased by factor of 4 compared with that of the conventional one. The improved thermal cyclic lifetime was attributed to the controlled transition of cracking path from the near YSZ/bond coat interface to YSZ top layer. The effect of thickness of the YSZ interlayer on the lifetime of TBCs was also investigated.
Characterisation of Plasma Sprayed HAp Coatings on Ti Alloys
Authors: Altuncu E. , Erdogan G. , Ozturk S. , Ustel F.
Published: November 2022

Biocompatibility of hydroxyapatite (HAp) coatings have led to its use in a wide range of applications in both dentistry and orthopaedics. The plasma spraying method is the most commonly used method for the production of Hap (Ca5(PO4)3OH) coatings on Ti alloys. When HAp is injected into the plasma jet, several phases can coexist under the effect of a temperature gradient occurring in the bulk of the particle. The amounts of residual compounds, amorphous and recrystallized phases are related to the conditions of spraying such as gas flow rates, feed rate, spray distance, plasma current and cooling effect. Plasma-sprayed HAp coatings were analyzed by X-ray diffraction and electron microscopy.
A 3D Finite-Difference Model for the Effective Thermal Conductivity of Thermal Barrier Coatings
Authors: Qiao J. H. , Bolot R. , Liao H. L. , Bertrand P. , Coddet C.
Published: November 2022

Effective properties of TBCs may be quantified thanks to different measurement techniques. Image-based analysis represents an alternative method for predicting these effective properties. During the last 10 years, 2D modelling was intensively applied to estimate the thermal conductivity from coating cross-sectional images. However, real coatings present a complex 3D architecture so that the use of 2D computations based on cross-sections has to be validated. In the recent decade, 3D imaging approaches were applied for capturing 3D images of thermal spray coatings with relatively high resolution (up to 1 micrometer). Nevertheless, high resolution brings very large computational systems for which finite-element (FE) methods seem to be unsuitable due to high requirements in terms of computer memory (RAM) capacity. In the present study, a three-dimensional finite-difference-based heat transfer model was developed for analyzing the heat transfer mechanisms through a porous structure by saving RAM usage. An artificial 3D coating image, containing 300×300×300 voxels, was generated from microstructural information measured for a real coating cross-sectional image. In particular, this 3D artificial pore network was generated so that calculations performed on its cross-sections present similar results in comparison with those concerning SEM images of real coating cross-sections. Then, the results computed for the 3D image were compared with those obtained from 2D computations performed on cross-sections of the same 3D image, revealing the differences between 2D and 3D image-based analyses. Finally, the results were then compared with those computed by FE packages (OOF2 and ANSYS).
Simulation of Arc Root Fluctuation in a DC Non-Transferred Plasma Torch with Three Dimensional Modeling
Authors: Huang R. , Fukanuma H. , Uesugi Y. , Tanaka Y.
Published: November 2022

It has been well known that the coating quality of plasma spraying is strongly influenced by instability of jets in plasma spray due to the arc root fluctuation. A three dimensional (3D) unsteady modeling was employed in the research to analyze the arc root fluctuation in a DC non-transferred plasma torch. Numerical calculations on the distribution of gas temperature and velocity in plasma torch were carried out using argon as plasma gas. The electrical current density and potential were also discussed. The results indicate that the fluctuation of arc inside the plasma torch is mainly induced by the movement of the arc root on the anode surface. The arc root moves downstream with the flow of gas, and the arc will warp from the electromagnetic force simultaneous to the movement. While the arc warps close to the anode boundary, a new arc root is formed somewhere upstream of the original attachment. This article represents nature of fluctuation of arc root, also in this paper we will present that the voltage-drop calculated is larger than that measured experimentally based on the hypothesis of local thermodynamic equilibrium.
Properties of Nanostructured Composite Titanium Coating on Aluminium Surface
Authors: Tyurin Yu. N. , Kolisnichenko O. V. , Ivanov O. N. , Kovaleva M. G. , Maradudina O. N. , Trusova Y. V.
Published: November 2022

Composite coatings of titanium powder were deposited on aluminium samples by using the cumulative-detonation equipment. Consumption of fuel mixture components (propane-oxygen-air) was up to 4.3 m3 per kilo of a coating. The coatings were examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM) with diffraction, X-ray phase analysis, hardness measurements, as well as plasticity and adhesion/cohesion resistance scratch tests. It is shown that the coatings are characterised by the presence of nanodispersed ceramic formations, and feature high values of plasticity, hardness and adhesion strength.
Deposition and Characteristics of Submicrometer-Structured Ceramic Coatings by Suspension Thermal Spraying
Authors: Guignard A. , Mauer G. , Vaßen R. , Stöver D.
Published: November 2022

The manufacture of submicrometer-structured coatings by thermal spraying is subjected nowadays to increasing research efforts in order to obtain unique and often enhanced properties compared to conventional coatings. Injecting suspensions of submicron ceramic particles into the plasma jet or the flame enables to deposit finely-structured coatings. Such fine microstructures can be advantageous for applications in the field of thermal barrier coatings (TBCs) for gas turbines. Often, suspension plasma sprayed (SPS) TBCs show unique mechanical, thermal and optical properties compared to conventional atmospheric plasma sprayed (APS) TBCs. They have thus the potential of providing increased TBC performances under severe thermo-mechanical loading. Experimental results show the capability of SPS to obtain yttria-stabilized zirconia (YSZ) coatings with high density of vertical segmentation cracks, yielding high strain tolerance and low Young’s modulus, while the porosity is still large compared to APS segmented coatings. Besides, sintering behavior of complete TBC systems under a thermal gradient exposure is of high importance. The evolution of the coating microstructure during thermal cycling test at very high temperature (1400°C) in our burner rigs as well as under isothermal annealing and its effects on the coating properties such as Young’s modulus were investigated.
Comparison of the Electrical Properties of Al2O3 Sprayed Coatings from Feedstock Powders and Aqueous Suspensions
Authors: Toma F.-L. , Scheitz S. , Langner S. , Berger L.-M. , Sauchuk V. , Kusnezoff M.
Published: November 2022

In this paper the characteristics (microstructure, phase compositions) and electrical insulating properties of thermally sprayed alumina coatings produced by suspension-HVOF (S-HVOF) process and conventional HVOF spray method are compared. The electrical resistance (electrical resistivity) and dielectric strength were investigated using DC-electrical resistance measurements, electrochemical impedance spectroscopy (EIS) and dielectric breakdown test. The electrical resistance was determined at room temperature at different relative air humidity (RH) levels, from 6% RH up to 97% RH. Differences in the electrical insulating properties due to the different coating characteristics are discussed. The suspension-sprayed Al2O3 coatings showed better electrical resistance stability at high humidity levels (> 75% RH), which could be explained by a specific microstructure and retention of a higher content of α-Al2O3. Nonetheless, the values of dielectric breakdown voltage and dielectric strength recorded for suspension sprayed coatings were lower than those of HVOF coatings.
Properties of Coating by Plasma Spraying Ultrafine Cr3C2-25%NiCr Powders
Authors: Li Z. , Yu Y. , Zeng K. , Xianjing R. , Jianghong M.
Published: November 2022

Agglomerated and sintered Cr3C2-25%NiCr powders possess excellent flow ability and appearance that have been extensively applied to resist abrase and erosion in high temperature applications such as power boiler and turbine blade. Microstructure of Cr3C2-25%NiCr coatings were observed through scanning electronic microscope (SEM), and bond strength and microhardness of coatings were measured by tensile shearing test and Vickers hardness test. It is indicated that ultrafine Cr3C2-25%NiCr coatings have some outstanding properties to traditional Cr3C2- 25%NiCr coatings by plasma sprayed.
Three Anodes Compared to Three Cathodes: Evaluation of Gun Concepts for High Performance Plasma Spraying Operation
Authors: Erne M. , Kolar D. , Möhwald K. , Bach Fr.-W.
Published: November 2022

When plasma spraying operations require high throughput, three-cathode guns may be specified due to their stationary plasma jet and elevated power characteristics, higher feeding rates, and adequate deposition efficiencies compared to one-cathode guns. A new three-anode gun system has been introduced to the market that offers a combination of high power inputs into the plasma as well as stable process conditions. These new guns feature a narrower nozzle outlet diameter compared to multi-cathode designs and they can be used with hydrogen as secondary plasma gas. Both of these characteristics result in higher plasma velocities and net powers. The conceptional designs for two such guns are discussed as well as their suitability for suspension and shrouded plasma spraying.
Theory and Experiment on Hollow Spherical Powders Production
Authors: Solonenko O. P. , Gulyaev I. P. , Smirnov A. V.
Published: November 2022

Hollow spherical (HOSP) powders of metals, metal alloys and oxide ceramics are of great interest for thermal spraying, powder metallurgy and material science. For the last decade due to constant rise of interest in HOSP powders and expansion of areas of their application, the efforts of researchers, including authors of present paper, are focused on developing methods of producing the hollow microspheres, based on processing of agglomerated powders in thermal plasma. Exists a range of methods of producing the agglomerated powders with size of dozens of microns, which particles consist of several uniformly mixed nano- submicron- and micron sized powder components: 1) spray drying, 2) processing of atomized suspensions; 3) mechanical treatment of powder mixtures in high-energy planetary mills, etc. A brief overview the results of R&D directed to production of various HOSP oxide and metallic powders (α-alumina, zirconia stabilized by yttria, quartz, nickel allow) by the use of DC torches with interelectrode inserts (cascade torches) and twin torch is presented. In particular, the theoretical approach providing the requirements to plasma flow in criterion view have been developed. A physical and mathematical model of hollow particle behavior in plasma flow is developed and discussed.