bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Directional Re-Solidification on Thermal Plasma Spray Silicon Depositions
Authors: Jackson D. D. , Sereda M. , Gansert R.
Published: November 2022

Thermal plasma spray of silicon has large potential for economic impact in the semiconductor and solar power industries. By post processing a thermally sprayed silicon deposition using directional re-solidification, impurities in the substrate can be controlled. We used a Thermach gun and powder feeder (SG100 and AT-1200, respectively, Appleton, WI), to deposit silicon onto steel samples. These samples were optically heat treated up to their melting point in order to increase crystal grain sizes. The depth and microstructure of the melted region was analyzed through imaging of the cross-sectioned samples. Directional re-solidification also had an effect on the impurity concentration along the depth sample. Control of impurities is demonstrated through this heat treatment and analyzed using SIMS and Laser Ablated ICP-MS. Understanding and controlling the impurity concentration has important implications in producing coatings in the solar industry as well as wafer processing equipment in the semiconductor industry.
Solar Selective Coatings for Concentrating Solar Power Central Receivers
Authors: Hall A. , Every K. V. , Knight M. , Mccloskey J. , Urrea D. , Ambrosini A. , Lambert T. , Siegel N. , Mahoney A. , Ho C.
Published: November 2022

Concentrating solar power (CSP) systems represent a zero emission method for conversion of sunlight to electricity. CSP systems use an array of mirrors to concentrate sunlight on the surface of a heat exchanger and heat a working fluid. These heat exchanger surfaces must have high absorptivity and low emissivity in the solar spectrum. In addition, they must be capable of extended operation at temperatures in excess of 600°C. Initial development of solar selective coatings using the air plasma spray process will be discussed. Eight different coating materials were deposited onto 304L stainless steel substrates. Solar absorptance and emittance were measured from each coating in three conditions: as-deposited, after heat treatment at 600°C for six hours, and after polishing to a 1 µm finish. A figure of merit based upon solar power tower (SPT) operation was calculated from these data and compared to the industry standard solar selective coating for SPT receivers, Pyromark Series 2500 high temperature paint. This comparison shows that Ni-5Al, 80WC-20Co, and CeO plasma-sprayed coatings all have potential as solar selective surfaces for SPT receivers.
Cold Gas Spraying of Ceramics Using the Example of Titanium Dioxide
Authors: Gutzmann H. , Freese S. , Gärtner F. , Klassen T.
Published: November 2022

Functional titanium dioxide coatings have a high potential for photocatalytic applications. However, the high process temperatures of conventional thermal spray methods lead to undesirable phase transformations. Cold gas spraying seems to be beneficial, since for ceramic coatings no phase transformations have been observed so far. In this study, bonding of cold-sprayed ceramic particles on metal substrates is elucidated by investigating single impacts obtained from wipe tests. Different feedstock powders were used, consisting of agglomerated titanium dioxide nanoparticles. The single particle impacts were investigated by scanning electron microscopy and confocal microscopy. The results demonstrate that bonding of particles is influenced by the substrate material, substrate temperature, powder properties and spray conditions. In addition, powder characteristics seem to be of particular importance. The results allow for conclusions regarding favorable conditions for cold spraying of ceramics.
Influence of the Suspension Characteristics and Spraying Parameters on the Properties of Dense Suspension-HVOF Sprayed Al2O3 Coatings
Authors: Toma F.-L. , Langner S. , Barbosa M. M. , Berger L.-M. , Rödel C. , Potthoff A.
Published: November 2022

In this work suspension-HVOF spraying (S-HVOF) was used to prepare dense and mechanical stable Al2O3 sprayed coatings with high contents of α-Al2O3 phase. Aqueous suspensions with various contents of powder (from 25 wt.% up to 50 wt.%) have been developed starting from two commercial α-Al2O3 powders, characterized by different purity and particle sizes. The suspensions have been internally injected in a modified combustion chamber of a HVOF TopGun-torch. Coating microstructures, phase compositions and mechanical properties resulting from the interaction between suspension characteristics and spray parameters are presented. Use of suspensions with high solid contents allowed the production of thick, dense and mechanically stable coatings. The α-Al2O3 was the main phase in the coatings produced through the injection of suspensions containing powders with very high purity.
Important and More In-Demand than Ever: Training and Qualification of Thermal Spray Personnel
Authors: Huber R. , Ohliger-Volmer A.
Published: November 2022

Thermal spraying is a constantly expanding technology within the surface technology sector, established long time in a wide range of hi-tech applications. Whether in jet engines, in power plants or the printing industry, endless coating requirements can be fulfilled with thermal spraying. However in order to master the “special process” – a term used in international standards and rules – calibrated and monitored systems and parameters are needed. Also, experienced, trained and certified personnel plays an important role to rule such a special process, whose results can only be tested by non-destructive methods to a certain restricted extent. Training and examination of spray personnel is aligned with the respective European training and qualification guidelines of the EWF (European Federation of Welding, Joining and Cutting). Passing the examination, especially for the thermal sprayers confirms their technical proficiency and skills. Additionally, it clearly influences the worker´s labour input and his quality awareness in the workplace. Compliance with standards like ISO 9001 or GTS-QM-Guidelines, means for companies to have their staff trained, qualified and further educated. Experiences have shown that - contrary to expectations - the complete EWF training is in high demand. Sectors such as aerospace, railway and power plant engineering are also increasingly demanding the qualifications for ETS – European Thermal Sprayer and ETSS – European Thermal Spraying Specialist.
Modelling Ceramic Droplet Impingement
Authors: Tabbara H. , Kamnis S. , Gu S.
Published: November 2022

Ceramic powders such as zirconia and titania are especially useful in their application as thermal barrier coatings, but are also useful in the production of more advanced coatings such as the dye-sensitized solar cell and functionally gradient prosthetic coatings. Due to their low thermal conductivity large temperature gradients through the powder particles are experienced during plasma spray deposition. As a result the particles often impinge at the substrate in a semi-molten form, which in turn substantially affects the final performance characteristics of the coating. This paper firstly summarizes some simulations and key results for completely solid and completely liquid particles. The modelling of semi-molten droplet impingement is then outlined, which is applicable to ceramic powders. The study examines the semi-solid impingement process during impact, spreading and solidification, and contributes to the growing insight being provided by numerical simulations on the topic of particle impingement in thermal spraying.
Detonation Spraying of TiO2-Ag Powders Under a Controllable Atmosphere
Authors: Dudina D. V. , Zlobin S. B. , Yu V. , Ulianitsky N. , Bulina V. , Bychkov A. L. , Lomovsky O. I.
Published: November 2022

In the present work, TiO2(rutile)-2.5vol.%Ag composite powders produced by mechanical milling were detonation sprayed under different atmospheres using acytelene as a fuel. The atmosphere of spraying was set to be reducing or oxidizing by changing the O2/C2H2 mole ratio. Reduction of TiO2 to Ti3O5 occurred in the coatings deposited under a reducing atmosphere (O2/C2H2 =1.05) when particles were heated to reach a molten or a semi-molten state. In the coatings sprayed using a stoichiometric O2/C2H2 =2.5 mixture, the major phase was rutile. The composition of the atmosphere does not only determine the chemical environment for the sprayed powders, but also influences the temperature conditions. Increasing oxygen content in the explosive mixture led to much higher temperatures of the sprayed particles as was calculated using a previously elaborated model. When titanium dioxide did not reach melting, the coatings were porous with a spongy surface. Coatings formed by fully or partially molten particles possessed a denser structure. Silver particles experienced melting during spraying but remained uniformly distributed in the coatings. This study demonstrated that careful selection of the composition of the spraying atmosphere offers potential of controlling the phase composition and microstructure of the detonation sprayed coatings.
Characterization of Novel Bioactive Hydroxyapatite-TiO2 Coatings Obtained by High Velocity Oxy-Fuel
Authors: Melero H. , Fernández J. , Dosta S. , Guilemany J. M.
Published: November 2022

Hydroxyapatite (HAp: Ca10(PO4)6OH2) is a biocompatible and bioactive ceramic material widely used as a coating on metal surfaces (dental implants, hip replacements ...), but the low adhesion between HAp and the substrate due to the differences in thermal expansion coefficients of both, and the degradation of HAp, is being improved through the addition of TiO2 to reach a good combination of mechanical properties. Therefore, the objective of this project is to produce 80%HAp-20%TiO2 (by weight) coatings on Ti6Al4V by High-Velocity Oxy Fuel (HVOF). The microstructure study has been carried out using scanning electron microscopy, and the characterization of the present phases, hydroxyapatite and rutile mainly, using X-ray diffraction and Raman spectroscopy (the last one to find out which are the minority phases, such as anatase and tricalcium phosphates). Also Rietveld method has been used to quantify the amount of amorphous phase, lower than in the case of plasma-sprayed coatings. The coatings adhesion has been measured by tensile tests according to ASTM C633-01(2008), finding an improvement over the adhesion of plasma sprayed coatings, and also of hydroxyapatite coatings; also their bioactivity has been evaluated through its immersion in simulated body fluid (SBF), and through in vitro tests to study osteoblast behaviour on the coatings surfaces, with positive results. To conclude, a discussion about the results is made to analyze the industrial viability of these kinds of coatings.
Life Cycle Assessment of Surface Preparation Processes Implemented before Thermal Spray
Authors: Serres N. , Costil S. , Lamraoui A. , Langlade C. , Coddet C.
Published: November 2022

The aim of this paper is to propose a LCA comparison of different surface preparation processes (degreasing + sandblasting, laser ablation and laser texturing) which tend to be used before thermal spray. The SimaPro software was used and the needs of materials, the energy and the corresponding emissions of each process, were converted to impact scores on human health, ecosystems, and resource conservation (fossil and mineral resources) by mean of the Eco-Indicator-99 method. Laser pretreatments processes present a very good environmental behaviour in comparison with degreasing + sandblasting.
Review on the Art of Anilox-Manufacturing – from the Coated Cylinder up to the Gravure
Authors: Döring J.-E. , de Schoulepnikoff L.
Published: November 2022

Anilox rolls are used as metering rolls in the flexographic printing process, delivering a precise quantity of ink to the plate roll (which contains the image to be printed). Anilox rolls are high precision parts with respect to their dimensional tolerances as well as to the engraved structures. The latter can nowadays be either very coarse in conjunction with a high volume of ink to be transferred or rather fine showing cell diameter of 20 µm, cell walls below 3 µm in thickness and cell depth of only 6 µm and below. Moreover, the market needs for high quality printing will lead more and more to the outer limits of these ranges, which can be matched only by tailoring the coating properties, as well as the interaction of the laser radiation with the sprayed surface. Besides the needs for extreme screen counts in conjunction with requirements of certain volumes of liquid to be transferred, new types of surfaces are needed to meet these requirements and providing a wear resistant coating and concurrent an easy to clean surface. Therefore this paper will give a review of the interaction of the laser with a thermally sprayed surface focussing on the main laser parameters, different coating materials, the application of sealants as well as the type of engravings with respect to the achievable screen counts and transferrable ink volumes.
Novel Thermal Barrier Coatings Produced by Axial Suspension Plasma Spray
Authors: Tang Z. , Kim H. , Yaroslavski I. , Masindo G. , Celler Z. , Ellsworth D.
Published: November 2022

Ceramic Thermal Barrier Coatings (TBCs) on superalloy components are being used successfully in land-based gas turbine and aircraft engines. These coatings are generally made by either air plasma spraying (APS) or electron beam physical vapour deposition (EB-PVD). In general, EB-PVD TBCs have superior durability due to the columnar structure, but they are very expensive compared to APS TBCs. EB-PVD TBCs are used primarily in the most severe applications such as turbine blades and vanes in aircraft engines. This paper presents an economical process to make durable TBCs, called Axial Suspension Plasma Spray (ASPS). This technology combines Mettech’s axial injection plasma process and automatic suspension feed system. The resulting TBCs exhibit columnar structures with vertical cracks, similar to EB-PVD coatings. Such structures allow the TBC to compensate for thermal expansion differences between it and the base material. The ASPS process presents an economical alternative to EB-PVD to produce durable columnar TBCs.
Yttrium Silicate Coatings by Sol Precursor Plasma Spraying for Environmental Barrier Applications
Authors: Quet A. , Bianchi L. , Darthout E. , Gitzhofer F. , Leluan J. L. , Rebillat F.
Published: November 2022

Yttrium silicates are among the candidates for protection of silicon-based ceramics in high temperature and moist environments due to chemical and mechanical compatibility with substrate, low volatility and moisture resistance. Here we reported on the development of yttrium silicate coatings by sol precursor plasma spraying. The use of a sol feedstock allowed easy composition flexibility. The microstructure and the structure of as-sprayed and heat-treated coatings were investigated. Finer microstructure was obtained compared to micrometric powder plasma spraying traditionally used to produce environmental barrier coatings (EBC). XRD analyses on as-sprayed coatings revealed amorphous or crystalline layers depending on plasma parameters. In EBC application, a volume change from crystallization or phase transformation was envisaged to be damaging due to induced stresses and fully crystalline phases are a key durability requirement for EBC from conventional plasma spraying. Yttrium silicates are characterized by an important polymorphism and the ability to form amorphous coatings. Therefore, special attention was so paid to the amorphous degree of the coatings.
Wear Behaviour of HVOF-Sprayed Nanostructured WC-CoCr Coatings
Authors: Bergonzini E. , Bolelli G. , Bonferroni B. , Lusvarghi L. , Varis T. , Kanerva U. , Suhonen T. , Oksanen J. , Söderberg O. , Hannula S.-.P
Published: November 2022

HVOF-sprayed WC–10wt%Co–4wt.%Cr coatings were obtained using experimental feedstock powders (manufactured by spray-drying + sintering), containing nanometric carbide particles. Three reference coatings were also deposited using commercially-available powders containing sub-micrometric carbide particles. The coatings obtained from nanostructured powders, although affected by decarburisation phenomena, contained very fine carbide particles (~200 nm size). Those obtained from commercially-available powders simultaneously exhibited sub-micrometric (~400 nm size) and micrometric carbide particles, and were much less decarburised. Sliding wear tests performed at room temperature against sintered Al2O3 balls showed the occurrence of brittle fracture wear (detachment of near-surface material by local brittle cracking) on the nanostructured coatings, which were embrittled by decarburisation. The reference coatings, by contrast, exhibited either ductile wear behaviour (plastic deformation, pull-out of single carbide particles) or a mix of both ductile and brittle wear mechanisms. When the decarburisation of the nanostructured coatings was not too extensive, their wear loss was comparable to that of the reference ones. At 500 °C, the wear behaviour of all coatings was dominated by abrasive grooving, on account of thermal softening. The most decarburised nanostructured coatings, however, still experienced brittle cracking as well.
Microstructure and Mechanical Properties of 7075 Al Matrix SiC Reinforced Composite Coatings Produced by the Cold Gas Dynamic Spraying Process
Authors: Meydanoglu O. , Jodoin B. , Sabri Kayali E.
Published: November 2022

Microstructure and mechanical properties of 7075 Al alloy matrix and SiC reinforced composite coatings deposited on a T6 6061 Al alloy by cold spray are investigated. Feedstocks are prepared as mixtures of 7075 Al alloy and SiC powders with SiC content varying between 0 to 40 vol. %. Microstructural characterization is carried out by optical and scanning electron microscopic examinations and X-ray diffraction (XRD) analysis. The coatings mechanical behavior is evaluated using hardness measurements and wear tests. Wear tests are conducted under dry conditions using a ball-on disc tester under atmospheric conditions. The presence of SiC improves the coatings hardness and wear resistance when compared to pure 7075 Al coatings. The coating hardness increases with increasing SiC content; however SiC content higher than 10 vol.% does not lead to further increase in wear resistance. In this respect, the optimum composition of the coating is determined to be 92 vol. % 7075 Al + 8 vol. % SiC.
Application of Structure-Based Models of Mechanical and Thermal Properties on Plasma Sprayed Coatings
Authors: Vilémová M. , Matějíček J. , Mušálek R.
Published: November 2022

Mechanical and thermal properties of thermally sprayed coatings, especially ceramics, are strongly influenced by cracks and pores that are present in the coating microstructure. In the recent past, there have been efforts to find an analytical model describing the coating properties based on the microstructural characteristics. Various analytical models were developed and published in the literature. In this study, several major models were applied to ceramic and metal coatings to describe their elastic modulus and thermal conductivity. The sensitivity of the models to the variations in the microstructure and relevancy of their use in specific cases were examined. The results were compared with those obtained by FEM modeling and experimentally measured values.
Heat and Mass Transfer within an Evaporating Solution Droplet in a Plasma Jet
Authors: Hu Y. , Shan Y.
Published: November 2022

A mathematical model is developed to analyze thermo-physical phenomenon within an individual solution precursor droplet travelling in the high temperature plasma jet. The model involves the motion and evaporation of the droplet and the heat and mass transfer within the droplet. The influence of Stefan flow and the variable physical properties of the environment gas around the droplet are considered. The internal circulation due to the relative velocity between the droplet and the plasma jet, which can be described by the Hill’s spherical vortex, is considered as well. The trajectory, temporal droplet surface temperature and radius variation are predicted. The temperature and concentration distribution inside the droplet as well as the difference between the droplets with different injection parameters are presented.
Homogenization of Coating Properties in Atmospheric Plasma Spraying – Results and Outlook of a DFG (German Research Foundation)-Funded Research Group
Authors: Bobzin K. , Schläfer T. , Petković I. , Hartz-Behrend K. , Landes K. , Forster G. , Kirner S. , Marqués J.-L. , Zimmermann S. , Schein J. , Prehm J. , Xin L. , Erne M. , Möhwald K. , Bach Fr.-W.
Published: November 2022

The goal of this research group is to homogenize properties of three-cathode plasma sprayed coatings on basis of numerical simulations and advanced diagnostics. Results of the first project phase as well as an outlook to future work are presented. A numerical model for investigation of plasma flow in the free jet, produced by three-cathode torch was developed. Modelling results are verified by plasma diagnostics (Computer Tomography). In order to include particle shrinking effects, coating formation simulation is accomplished by a newly developed model, based on Computational Fluid Dynamics coupled with the Finite Element method, whereat diagnostics carried out in the fields of particle diagnostics. During the next phase of the project, the investigation of the plasma free jet and particle injection by advanced diagnostics and simulation respectively is scheduled. In a subsequent stage the transition from conventional particles to suspensions will be considered. Coating formation simulations are scaled up to dimensions of macroscopic tensile tests. By combining these overarching investigations, appropriate process parameters for homogenized coatings will be obtained.
Titanium Dioxide Coatings Sprayed by a Water Stabilized Plasma Gun (WSP) With Argon and Nitrogen as the Powder Feeding Gas: Differences in Structural, Mechanical and Photocatalytic Behavior
Authors: Ctibor P. , Pala Z. , Neufuss K. , Štengl V. , Píš I. , Zahoranová T. , Nehasil V.
Published: November 2022

Titanium dioxide coatings were sprayed by a water stabilized plasma gun (WSP) to form robust self-supporting bodies with a photocatalytically active surface. Agglomerated nanometric powder was used as a feedstock. In one case argon was used as a powder-feeding as well as coating-cooling gas whereas in the other case nitrogen was used. Stainless steel was used as a substrate and the coatings were released after the cooling. Over one millimeter thick self-supporting bodies were studied by XRD, HR-TEM, XPS, Raman spectroscopy, UV-VIS spectrophotometry and photocatalytic tests. Majority of the tests was done at the surface as well as at the bottom side representing the contact surface with the substrate during the spray process. Porosity was studied by image analysis on polished cross sections where also microhardness was measured. Dominant phase present in the sprayed samples was rutile whereas anatase was the main minor component. Hydrogen content in the nitrogen assisted coating was higher, but the character of the optical absorption edge remained the same for both samples. Photoelectron spectroscopy revealed differences in the character of O 1s peak between both samples. The photocatalytic activity was tested by decomposition of acetone at UV illumination, whereas also the end products - CO and CO2 - were monitored. The nitrogen-assisted coating was revealed as more efficient photocatalyst.
Oxidation Behaviour of CoNiCrAlY Bond Coats Produced by APS, HVOF and CGDS at Temperatures of 1000 °C and 1100 °C
Authors: Roy J.-M. , Richer P. , Beauvais L. , Jodoin B.
Published: November 2022

This work compares the oxidation behaviour of CoNiCrAlY coatings manufactured by the HVOF, APS and CGDS processes when submitted to temperatures of 1000°C and 1100°C. The as-sprayed coating microstructural features were characterised using SEM and XRD analysis before being subjected to isothermal heat treatments in an air furnace. Oxide scale composition was determined using XRD, SEM and EDS analysis while the oxide growth rates were obtained using mass gain measurements. The as-sprayed HVOF and CGDS coatings exhibit similar microstructures while the APS samples have a significantly higher porosity and oxide content levels. Results from the oxidation experiments indicated that the oxide growth rate of HVOF and CGDS were lower than that of the APS samples. The results also indicated that samples oxidised at 1100°C have a lower oxide growth rate than those oxidised at 1000°C. Analysis of the oxidation process up to 100 hours indicates that the formation of dense α-Al2O3 is more favourable at 1100°C while a transition alumina, θ-Al2O3 is more favourable at 1000°C. Furthermore, the surface profile of the samples oxidised at 1100°C were more uniform and free of protrusions.
Biocompatibility of Titanium Coatings Deposits on CoCr by Cold Spray
Authors: Trentin A. , Vezzù S. , Rech S. , Gulizia S. , Jahedi M.
Published: November 2022

The excellent corrosion resistance and biocompatibility of titanium make of it the material to choose for biomedical applications. Cold spraying, as a new coating technique, can be used to deposit protective Ti coatings onto less performing materials such as stainless steel and Co-Cr alloys, commonly used for biomedical implants. In addition, Cold Spray has the advantage, in comparison with conventional thermal spray techniques, to permit the deposition of oxygen-sensitive materials. In this study, Cold Sprayed Ti coatings were prepared on Co-Cr alloy substrates by using different spray process conditions. The microstructure of coatings was observed by SEM and the inner porosity was estimated by image analysis. Oxygen and nitrogen contents were investigated on a set of free standing deposits obtained using different process parameters. In the same way, the roughness and microhardness of deposits, such as the adhesion strength with the substrate, were measured. Finally, the corrosion performance of the coatings was evaluated by mean of open circuit potential measurement (OCP) and potentiodynamic polarizations scans. The electrochemical response was therefore discussed and compared to the corrosion behaviour of the Co-Cr alloy substrate and the bulk Titanium.
Measurement of Specific Enthalpy under Very Low Pressure Plasma Spray Condition
Authors: Zhang N. , Sun F. , Zhu L. , Planche M. P. , Liao H. , Dong C. , Coddet C.
Published: November 2022

Very low pressure plasma spraying has been intensively studied in recent years especially the properties of plasma jet. These properties are affected by plasma generating and working conditions. These operating parameters such as arc power, plasma gas flow rate and chamber pressure have influences on specific enthalpy and temperature of plasma jet. In this work, the measurements under very low pressure were performed using enthalpy probe which was previously modified (increase of the internal diameter and depositing TBC coating (Ni/Al and ZrO2+ Y2O3) on the head). Different parameters, for instance, current intensity, hydrogen gas flow rate and detecting distance were changed in order to point out their effect on the characteristics of plasma jet. The specific enthalpy, temperature and quantity of heat in this situation were obtained.
Development and Characterization of Oxide Ceramic APS Coatings for Microwave Absorption
Authors: Müller P. , Floristán M. , Killinger A. , Gadow R. , Cardella A. , Li C.
Published: November 2022

Thermonuclear fusion is a promising source of clean energy for the future. Max-Planck-Institute für Plasmaphysik (IPP, Greifswald, Germany) is currently working on the new type of fusion reactor, the stellarator Wendelstein 7-X. The extreme operating conditions of fusion reactor devices have lead to an increasing interest in the field of high performance materials. The present work describes the development of coating systems acting as efficient absorbers for 140 GHz radiation, which is the microwave frequency to which the analyzed components of Wendelstein 7-X are subjected. Several types of oxide ceramic coatings were applied by Atmospheric Plasma Spraying. Different powders were used as feedstock material for the coating operation. The influence of the process parameters on the coating properties and microwave absorbing capability was analyzed. The coatings microstructure and mechanical properties were characterized in terms of porosity, microhardness, roughness, adhesion and residual stresses. XRD and SEM were carried out. It was found that thickness and microstructure of the coatings have a significant influence on microwave absorption behavior. For Al2O3/TiO2 coatings, absorption values over 90% were obtained. After optimization of the coating structure, the coating process was adapted to several real reactor components that will work in Wendelstein 7-X.
Cavitation Erosion Mechanism in Fe-Mn-Cr-Si-Ni Arc Thermally Sprayed Coatings
Authors: Pukasiewicz A. G. M. , Capra A. R. , Paredes R. S. C.
Published: November 2022

Cavitation erosion is a common phenomenon that occurs in hydraulic turbine blades and result in mass loss. Welding is the most common technique used to recover the geometrical profile of these cavitation eroded turbine blades, however it is known that tensile residual stress can develop. The development of manufacture process that could reduce or eliminate the residual stress level will contribute for a longer service life of this component. It is aimed in this study evaluate cavitation erosion mechanism of Fe- Mn-Cr-Si-Ni arc thermally sprayed coating. Coatings were analyzed by optical and scanning electronic microscopy, microhardness, cavitation tests (ASTMG32-92) and the analysis of eroded surface areas after ultrasonic cavitation tests with DRX and SEM. The results showed that lamellae morphology, oxide volume fraction and porosity modified by changings in parameters deposition, modified cavitation mass loss mechanisms. After ultrasonic cavitation tests, it was verified that mass loss occurred by interlamellae oxide removal and splats surface deformation in initial stages, followed by rupture and finally detachment of the lamellae. Splashing droplets promote greater mass loss in some localized areas because they lower intersplat cohesion.
Thermal Barrier Coatings on Novel High Temperature Cobalt Rhenium Substrates
Authors: Seiler P. , Rösler J. , Mukherji D. , Kopka T.
Published: November 2022

Presently, highly stressed components in gas turbines are mainly made of single crystal nickel based alloys and the maximum application temperature (without coatings) is typically limited to 1100°C. Superalloys are now reaching limits posed by their melting temperatures. Increasing the substrate temperature beyond 1200°C will increase the efficiency of the turbine significantly. A new generation high temperature Co-Re alloys are aimed for use at +100°C above present single crystal nickel-superalloys. The substrates will be protected against the higher gas temperatures by thermal barrier coatings. For Co-Re alloy substrates CoReCrSi is a promising bond-coat material. CoReCrSi is thermo-chemically compatible to Co-Re due to the very similar mechanical and chemical properties. The oxide formation and the adhesion of the top coat are being investigated by studying a simplified coating system. The coating system consists of a CoReCrSi bond coat bulk material, and an yttria-stabilised zirconia top coat. The system was tested under cyclic conditions at 1200°C. This study provides a first insight into the TGO growth, the basic failure mechanism of the top coat, and the diffusion processes at the top coat/bond coat interface. It is shown that CoReCrSi with 2 at.% silicon promotes a good adhesion of the top coat by forming a dense chromium oxide layer. The critical TGO thickness beyond which the TGO fails by spallation was determined to be 25 microns and is roughly 2.5 times the critical thickness in MCrAlY based system in nickel-alloys.
Advanced Thermal Barrier Coatings from Ti-Doped YSZ Systems
Authors: Jarligo M. O. , Mauer G. , Mack D. , Vassen R. , Stöver D.
Published: November 2022

Fracture toughness and phase stability are crucial properties of thermal barrier coatings (TBC) during highly loaded thermomechanical operations in gas turbines. While several alternative TBC materials have exhibited excellent thermal resistance, their potential applicability has been limited due to poor endurance to cyclic stresses. The addition of TiO2 to the non-transformable tetragonal t´-YSZ has been found to effectively enhance the fracture toughness and phase stability of YSZ at high temperature exposures. Thermal cycling tests in a burner rig were conducted on TBCs prepared from atmospheric plasma sprayed titania-doped YSZ to verify this phenomena. Exposure temperature was 1400°C at the surface and thermal gradient across the sample was provided by simultaneous back-cooling treatment. Cycling tests reveal that the slight increase in the tetragonality of the deposited coatings with increasing amount of dopant did not cause a significant effect to the lifetime of the TBCs. Moreover, increasing amount of Ti-substitution did not influence the fracture toughness of the bulk YSZ.
Scratch Test Mechanical Properties of Suspension Plasma Sprayed TiO2 Coatings
Authors: Łatka L. , Pawłowski L. , Petit F. , Kozerski S.
Published: November 2022

Titanium oxide coatings were suspension plasma sprayed onto different substrates. The suspension was formulated using fine rutile pigment in the mixture of water with ethanol. The zeta potential of the suspension was determined. The spray process parameters were designed using a full factorial plan using spray distance and torch scan velocity as the variables. The temperature at spray process was monitored using a pyrometer. The X-ray diffraction (XRD) analysis enabled to find out the crystalline phases in sprayed deposits and, in particular, the anatase content. Scanning electron microscope (SEM) enabled to characterize the coatings’ microstructure. The coatings included well molten lamellas and zones of loosely agglomerated and sintered grains. The scratch test of the coatings enabled to determine their mechanical properties such as critical load and scratch hardness.
Characterization of Detonation Sprayed Coatings
Authors: Shtertser A. A. , Ulianitsky V. Yu. , Tsarakhov K. A. , Grinberg B. E.
Published: November 2022

Characterization of coatings made with the help of Computer Controlled Detonation Spraying (CCDS) was performed. The applied coatings include hard alloys (WC/Co -75/25, WC/Co - 88/12, WC/Co/Cr - 86/10/4, and Cr2C3 / NiCr), aluminum oxide, nickel-chromium self-fluxing alloy, titanium, bronze, and stainless steel. Tribological investigations of coatings were provided using abrasion test (ASTM standard G65), erosion test (ASTM standard G76), and hydro-abrasive test. To make hydro-abrasive tests special device and method were elaborated based on the interaction of water jet saturated with corundum particles with a coating surface.
Impact Particle Behavior in Cold Gas Dynamic Spray of Composite Coatings
Authors: Leshchynsky V. , Papyrin A. , Bielousova O. , Yadroitsava I. , Smurov I.
Published: November 2022

The cold gas dynamic spray process offers a unique advantage to form composite coatings by applying powder mixtures. The powder mixture constituents are supposed to interact with each other during impact. In this study, Al and Cu-based powder mixtures are used with the aim to define specific features of the coating formation. Composite coatings with different Al2O3, SiC, and Ti content are sprayed. Impact behavior of various powder mixtures is analyzed based on scanning electron microscopy images. The Al2O3 and SiC phases of the initial powder are found to be fractured on impact and preserved in the coatings. Another advantage of the kinetic spray process is the ability to mix materials which would normally react with each other and form a composite coating. Some experimental data of such reactions are discussed. Within the composite coating, each constituent changes the initial properties of the sprayed powder material: for example, the soft matrix is strengthened, and hard particles are fractured. The fracture and deformation behavior of the particles and their reactions induced by the impact are determined by micromechanical tests and EDX analysis. Morphology, physical and mechanical properties of the sprayed coatings are discussed.
Novel Manufacturing Method for Producing Stacked Wire Mesh Compact Heat Exchangers Using Cold Spray
Authors: Assaad J. , Corbeil A. , Richer P. , Jodoin B.
Published: November 2022

Heat exchangers play a vital role in ongoing efforts to conserve energy. Plate-type heat exchangers typically consist of two flat separated flow paths in which heat transfer enhancing matrices are inserted. The combined effects of small irregular hydraulic diameters along with elevated heat transfer areas results in highly-efficient heat transfer to the external fluid. This allows for very versatile and compact heat exchanger designs. Typical plate-type heat exchanger fabrication methods such as brazing are labour intensive and limit post-processing operations like welding. In this paper, a novel micro-heat exchanger fabrication method using recently patented technologies is presented. The approach uses thermal spray processes such as Pulsed Gas Dynamic Spraying (PGDS) as an alternative to brazing for the production of a pressure barrier and integration of flow headers. Mesh wafer surfaces sealed using PGDS
New Cold Spray Based Technique of FeAl Intermetallic Compound Coating Synthesis
Authors: Maev R. Gr. , Leshchinsky E. , Maeva E.
Published: November 2022

The FeAl intermetallic compound offers a combination of attractive properties such as thermal barrier, good strength at intermediate temperatures and an excellent corrosion resistance at elevated temperatures under oxidizing, carburizing and sulfidizing atmospheres. So they have attracted considerable attention as potential candidates for structural and coatings applications at elevated temperatures. However, the application of these intermetallics has been limited due to lack of deposition techniques and their low ductility at room temperature. To overcome the drawbacks we apply Low Pressure Cold Spray (LPCS) with following sintering for improving coating ductility and structure. The aim of this paper is to present the first results of FeAl intermetallic compound synthesis with this technique. A CS deposit is built up by the successive impact of individual powder particles that are the ‘‘building blocks’’ of the deposit. Sintering is applied to utilize reactions between the particles and obtain complex intermetallic compound. The microstructures and properties of the coatings were characterized by SEM, EDX and thermal diffusivity tests to define the structure formation mechanisms.
Automatic Generation of Robot Trajectory for Free-form Surfaces in Thermal Spraying
Authors: Fang D. , Deng S. , Liao H. , Coddet C.
Published: November 2022

Automatic robot trajectory generation for thermal spray applications is considered necessary for advanced automatic manufacturing. Achieving coating uniformity on the free-form surfaces is the principal challenge due to the complexity of their geometries. The purpose of this study is to develop a new function of Thermal Spray Toolkit with user-friendly interface for automatic generation of robot trajectory on the irregular workpieces according to the spray parameters, such as the torch speed, the spray distance, the spray angle, etc. This software toolkit is based on RobotStudio which is an off-line programming and simulation software by ABB company. The results showed that the robot trajectories can be generated rapidly, accurately and automatically on the free-form surfaces by using Thermal Spray Toolkit.
Comparison of Oxidation and Microstructures of Warm-Sprayed and Cold-Sprayed Titanium Coatings
Authors: Kim K. H. , Kuroda S. , Watanabe M. , Huang R. , Fukanuma H. , Katanoda H.
Published: November 2022

Thick titanium coatings were prepared by warm spraying (WS) and cold spraying (CS) process to investigate the oxidation and microstructure of the coating layers. Prior to the coating formations, the temperature and velocity of in-flight titanium powder particle were numerically calculated. Significant oxidation occurred in WS process using higher gas temperature conditions with low nitrogen flow rate, which is mixed to the flame jet of an HVOF spray gun in order to control the temperature of the propellant gas. Oxidation, however, decreased strikingly as the nitrogen flow rate increased. In CS process using nitrogen or helium as a propellant gas, little oxidation was observed. Although most of the cross-sections of the coating layers prepared by conventional mechanical polishing looked dense, coating cross sections prepared by an ion-milling method revealed the actual microstructures containing small pores and unbounded interfaces between deposited particles. Even when scanning electron microscopy or x-ray diffraction method did not detect oxides in the coating layers by WS using high nitrogen flow rate or CS using helium, the inert gas fusion method revealed minor increase of oxygen content below 0.3 wt%.
The Synthesis of Titanium Dioxide Powders for Cold Spray
Authors: Tjitra Salim N. , Yamada M. , Nakano H. , Isago H. , Shima K. , Fukumoto M.
Published: November 2022

Titanium dioxide (TiO2) is a unique material that can be used as an excellent photocatalyst, hence it will be very useful to solve the current world pollution problem. For photocatalytic application, the cold spray process, which uses supersonic high velocity technique at moderate temperature is considered to be a suitable technique as it will inhibit the phase transformation of TiO2. It is known that obtaining a thick coating of TiO2 is difficult as it is a hard ceramic material. However, we have successfully synthesised TiO2 powders that can be cold sprayed. Our synthesis technique is a simple hydrolysis method of titanyl sulphate (TiOSO4) in distilled water. It was discovered that the cold sprayability of TiO2 powders is depended on the powder morphology and using our synthesis method, powder morphology can be easily altered. Addition of (NH4)2SO4 during hydrolysis and post synthesis hydrothermal treatment result in a unique oriented aggregated nanostructure of TiO2. Only TiO2 with this nanostructure can be cold sprayed.
Influence of Gas Conditions in Cold Spraying on WC Cermet Coatings
Authors: Sato K. , Seo D. , Furukawa H. , Kitamura J. , Ogawa K.
Published: November 2022

Cold spraying is well known as an attractive coating process that prevents degradation of materials, such as oxidation, decomposition and undesirable reaction due to overheating. High velocity oxy-fuel (HVOF) spraying has been recognized as the most popular technique in particular to produce tungsten carbide (WC) cermet coatings in industrial fields. However, the degradation of WC cermet occurs using HVOF that is quite different from sintered hard metal, which can be defined as an ideal material. Thus, low temperature processes, such as cold and warm spraying, are actively researched to achieve WC cermet coatings, similar to sintered one. In this study, influence of gas conditions in cold spraying on WC cermet coatings has been investigated, where WC-Co, WC-CrC-Ni and WC-Fe alloy are selected. The study reveals that nitrogen gas is effective to form thick, dense and hard coatings of WC-CrC-Ni and WC-Fe alloy compared to helium gas. This suggests optimal temperature and velocity of powder jet has been formed when using nitrogen gas.
Corrosion and Wear Resistance of Molybdenum Containing Arc Spray Composite Coatings
Authors: Laurila J. , Niemi K. , Vuoristo P. , Vajala J.
Published: November 2022

In twin wire arc spraying process it is possible to use feedstock wires of two different compositions at the same time. As a result of this procedure it can be achieved composite coatings called also as pseudo alloys with modified physical properties. In this study nickel and cobalt based super alloy materials were arc sprayed with pure molybdenum wire to tailor corrosion and wear resistance of the coatings. Coatings for the tests were sprayed using two different twin wire Sulzer Metco arc-spraying units, Smart Arc and OSU 300, operating with suitable spray parameters to produce coatings of good quality. It was already known that these twin wire configurations are producing coatings with differing microstructures. Coating sprayed with the OSU system was clearly finer in structure and one purpose of this study was to measure the effect of the micro structural size on the corrosion and wear properties of the final coatings. Microstructures of the coating materials were studied and analyzed from cross-sectional specimens. Volume fraction of pure molybdenum in the coating matrices was evaluated with simple line method and according to the results volume fraction of pure molybdenum metal is over 50 volume-% in all of these tested composite coatings and higher in materials sprayed with OSU unit. Also the microstructure of the coatings was seen to be finer when OSU was used as was expected. Wear resistance was measured with modified ASTM G65 rubber wheel sand abrasion wear test and corrosion resistance was tested in low pH values and chlorine containing environment according to the ASTM G48 corrosion testing standard. Corrosion testing was carried out at room temperature 22°C and also at higher 50°C temperature. Molybdenum addition is clearly improving the abrasion wear resistance of the tested coating systems. At room temperature also the corrosion resistance is getting better with molybdenum addition but at higher temperature this effect is not so clear.
Turbulence Effects in a DC Plasma Torch
Authors: Bolot R. , Allimant A. , Billières D. , Coddet C.
Published: November 2022

The development of new plasma spray torches reinforced the use of numerical modelling to help in the design steps. Most of the thermal spray material providers are thus now interested in understanding the arc behaviour inside the torch so that CFD studies focussed on this topic become numerous. Our first calculations performed on the ProPlasma HP gun assuming a laminar hypothesis have shown underestimations of the torch voltage and of the thermal losses in the cooling circuit, and a subsequent overestimation of the thermal efficiency of the torch. In the present study, the setup of different turbulence models was performed and a comparison was made between the results obtained using either the laminar assumption or several turbulence models. The calculations indicate that the results obtained using conventional turbulence models such as k-ε or k-ω type models do not significantly differ from those obtained using a laminar assumption, thus only more sophisticated models can be expected to improve the simulations.
Effects of Power and Concentration and Dispersion Phase on Nano-Zirconia Coatings Prepared by Sol Plasma Spraying
Authors: Yang H. , Chen L.
Published: November 2022

ZrOCl2•8H2O and NH4OH were regarded as original materials to prepare zirconia sol by co-precipitation, and nano-zirconia coatings were prepared by sol plasma spraying. The structure of the coatings was analyzed by SEM, XRD, and influence of power and stabilizer, concentration and dispersed phase on the coatings was investigated primarily. The result showed that the sol was non-crystal structure after spontaneously dried, the coatings were mixed of nanostructure of monoclinic and cubic phase after plasma jet heated. Increasing power decreased the content of non-crystal phase, adulterating yttria had good crystal phase stabilization, and the content of monoclinic phase decreased greatly. Coatings were denser when higher concentration and ethanol qua dispersed phase were used. Porosity of coatings decreased prior and increased later along with concentration increasing.