bluuebunny/crossref_metadata_2025 huggingface dataset:
Improving the Reproducibility and the Comparability of Bond Strength Values
Authors: Kopp C.A. , Bobzin K. , Ernst F. , Richardt K. , Schläfer T.
Published: September 2022

One of the most popular test methods for the evaluation of thermally sprayed coatings and substrate pre-treatment is the bond strength test in accordance to the standard EN 582 (in Europe) or ASTM C633-79 (in the U.S.). An interlaboratory test, carried out in 2003, has shown that bond strength tests of samples that were joined by different institutions in accordance to DIN EN 582 lead to bond strength values that varied by the factor 2, even if the same adhesive was used. The test not only made clear that the adhesives used to join the loading block to the substrate block but also many other parameters have a tremendous influence on the results of the bond strength tests. It was also clarified that the DIN standard needs to be supplemented in order to improve the comparability and the reproducibility of the bond strength test results. The first aim of this work was to identify the influencing parameters by carrying out Failure Mode and Effect Analyses (FMEA) together with namable institutions. Based on these results, a work instruction based on the DIN standard will be composed in order to avoid its weak spots. Later, a second interlaboratory test will be carried out to evaluate the quality of the work instruction.
Transmission Electron Microscopy of Cold Sprayed Titanium
Authors: King P.C. , Jahedi M.
Published: September 2022

The processes of microstructural evolution in titanium during deposition by cold spray were investigated. Titanium particles underwent plastic deformation at very high strain rates, resulting in (a) extensive refinement and (b) large inhomogeneities in microstructure. There were large nanostructured areas (several micrometres in extent) with high dislocation densities and subgrain sizes less than 100 nm. Dense dislocation tangles and elongated subgrains were observed in other places. It is hoped that by further understanding the microstructural changes that occur during cold spray, improvements in mechanical properties may be realised.
Wear Behaviour and Performance of a Cost-Effective Iron-Based, Carbide-Reinforced, Sintered Coating
Authors: Lugbauer M. , Badisch E. , Kröll A.
Published: September 2022

In every industry wear plates and parts are demanded in heavy duty standards at cost effectiveness and environmental friendliness. For that reasons a new kind of coating technology was developed, and first applied on parts for agricultural machinery for getting results from the field. Simultaneously lab tests were done to compare the wear behaviour and performance of these sintered iron-based coatings with mainly chromium-carbides and borides in it, with other well known wear-resistant coatings like hard chrome, thermal sprayed coatings (Ni-matrix/WC), PTA welded coatings (Ni-matrix/WC, high speed steel) and processed steel like Hardox. Wear tests were performed under 3-body-abrasion as well as combined impact/abrasion conditions, respectively. Dry-sand rubber-wheel procedure according ASTM G65 was used to investigate low stress abrasion, whereas for high stress abrasion investigations a steel wheel was used. A special designed impeller-tumbler apparatus was used for combined impact and abrasion wear tests. Analysis after testing was done quantitatively by gravimetric mass loss, and qualitatively using SEM microscopy (edge stability, wear mechanisms). The ambition of this investigation is to secure the wear performance of the sintered iron-based coating at low production costs compared to well known anti-wear solutions applied in wear intensive industries.
New Conventional Plasma Gun with High Performance: ProPlasma HP
Authors: Allimant A. , Billières D.
Published: September 2022

Saint-Gobain Coating Solutions new ProPlasma HP gun, based on conventional plasma gun design (single anode-single cathode), has been evaluated for typical demanding applications of the thermal spray industry. A general overview of this gun main features is presented. Aim of its development was to fulfill the whole range of applications of plasma spraying, from high feed rate –high deposit efficiency (DE) to high velocity. First, plasma spraying performance of ProPlasma is exposed through 2 typical examples of materials extensively sprayed: yttria stabilized zirconia (YSZ) and chromia, both needing high DE at high feed rates. A set of spraying parameters was developed for YSZ Saint-Gobain #204 hollow spherical powder showing 57% DE at 150g/min and exhibiting 13 to 15% porosity as typically requested for thick TBCs. Two sets of parameters were developed for chromia at 120g/min leading either to 3% porosity - 51% DE or 2% porosity - 42% DE. Then, the possibility to reach a high velocity mode is shown through the presentation of the anode development made for a typical high velocity application material: WC-Co. After a first design showed experimental promising results with low porosity, the anode design has been further improved based on experiment and CFD modeling.
TriplexPro-200 Gun Platform: Impacting All Operational Aspects of Thermal Spraying
Authors: Hawley D. , Dambra C. , Molz R.
Published: September 2022

Triplex is a second generation plasma gun technology that offers multiple benefits in term of rates of application and deposit efficiencies. This paper focuses on Triplex technology as it relates to daily operational aspects of a typical thermal spray facility. Today, Triplex is the only plasma technology that features "fixed" parameter operation for extended run times which has significant impact at multiple levels within the spray shop. Data presented will compare Triplex to first generation plasma technology with regards to quality, training, simplification, and process repeatability.
Yttria Deposition by a Novel Plasma Torch
Authors: Pershin L. , Mostaghimi J.
Published: September 2022

Carbon dioxide (CO2) and hydrocarbons (such as CH4) gas mixtures generate plasmas with much higher enthalpy and thermal conductivity, leading to higher spray process efficiency and improved heat transfer to the sprayed powder. We have employed a DC plasma torch operated with CO2+CH4 gas mixture, which has been developed at the Centre for Advanced Coating Technologies (CACT) at the University of Toronto, to deposit various coatings. This study was focused on the effect of this plasma gas mixture on the in-flight particle parameters during plasma spraying of Yttria (Y2O3). The results were compared with a similar coating applied by the SG-100 torch (Praxair) with Ar+He gas mixture. The particulate plume scans show that with the CACT torch, all particles in measured volume were overheated at a distance of 120 mm. Cross-sections through the sprayed coatings were polished and examined under a scanning electron microscope. The dielectric properties of the two coatings were also compared with each other.
Investigation of Atmospheric Plasma Sprayed Tungsten Carbide Cobalt Coatings Using Statistical Design of Experiments
Authors: Tillmann W. , Vogli E. , Krebs B.
Published: September 2022

The interaction between thermal spray parameters and coating characteristics of atmospheric plasma sprayed WC-12Co was investigated by means of statistically designed experiments. A central composite design was employed to study the influence of the process parameters’ ratio Ar/H2, plasma gas volume flow, powder feed rate and stand-off distance on the deposition efficiency, tensile strength, porosity, roughness, particle temperature, particle velocity and the percentage of molten carbides. The process parameters’ volume flow and powder feed rate showed a considerable impact on the microstructure and morphology of the coatings, which could be traced back to a change in the melting degree of the powders as well as a change in particle temperature and velocity. On the basis of the statistical experiments, mathematical expressions were found to describe the coating characteristics. The quality of the mathematic model was scrutinized in a subsequent evaluation stage.
Thermally Sprayed Oxidation Protection Coatings for γ-TiAl Substrates
Authors: Bobzin K. , Schläfer T. , Warda T. , Brühl M.
Published: September 2022

Due to excellent mechanical properties and low density compared to super alloys (e.g. Ni-based alloys) Titanium Aluminide is often used as base material in the aerospace industry. But the thermodynamic conditions within turbines limit the capabilities of the material. At the moment γ-TiAl is used for parts, which have to withstand temperatures up to 700 °C. Above this temperature oxidation kinetics cause a thick oxide layer consisting of several oxides, which tend to fast chipping. Therefore the surface of the γ-TiAl is being destroyed and the material loses its excellent mechanical properties. To enable the use of this material at higher temperatures, the development of an oxidation protection coating is necessary. Several coating techniques e.g. EB-PVD were tried in the last years, but the oxidation behaviour of the γ-TiAl could not be significantly improved. Protective thermal spray coatings so far seem to be a promising technology in order to protect γ-TiAl components against oxidation. Therefore this technique was used within this work, which aims for the development of new oxidation protection coatings. A multilayer system was developed. The multilayer consists of a ceramic ZrO2-7Y2O3 coating with a NiCoCrAlY top coat. In this case the ceramic coating avoids the diffusion of Ti or Al of the γ-TiAl into the MCrAlY coating or the other way around. The NiCoCrAlY coating improved the oxidation behaviour of the Titanium Aluminide by building a dense oxide layer on top of the multilayer. The paper will give an overview about the results of the oxidation tests with the new developed multilayer concept for protection of the γ-TiAl against oxidation.
Oxidation Behaviour of MCrAlY Bond Coats Manufactured by Plasma, HVOF and Cold Gas Dynamic Spraying
Authors: Richer P. , Yandouzi M. , Beauvais L. , Jodoin B.
Published: September 2022

This paper examines the oxidation behaviour of CoNiCrAlY coatings manufactured by APS, HVOF and CGDS deposition techniques when subjected to isothermal heat treatments. Comparison of the as-deposited coating microstructures is achieved by means of scanning electron microscopy (SEM). Investigation of the oxide compositions and growth dynamics is achieved by SEM, X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). Oxide growth rates were determined by a series of mass gain measurements. Results from this study demonstrate that lower coating porosity and oxide contents lead to lower oxide growth rates. Results also demonstrate that low-temperature processing of CoNiCrAlY bond coats is beneficial to their oxidation behaviour as it favours the formation of alumina in preference to other detrimental fast-growing mixed oxides.
HVOF Spraying of Ultrahigh Boron-High Carbon Tool Steel Coating for Wear Resistance Applications
Authors: Rajasekaran B. , Mauer G. , Vaßen R. , Röttger A. , Weber S. , Theisen W.
Published: September 2022

The objective of this study is to investigate the feasibility of high velocity oxy-fuel (HVOF) spraying of tool steel coating containing high boron and high carbon. A full factorial experimental design was established to investigate the influence of process parameters on the coating formation. The microstructural investigations revealed that the tool steel containing ultrahigh boron and high carbon can be coated using HVOF. The coating microstructure does not seem to be conventional lamellar structure and consists of high density micro-cracks. However, the coating features superior hardness of about 980 HV and shows the potential for wear resistance applications.
Computational Investigation of Warm Spray
Authors: Tabbara H. , Gu S. , McCartney G.
Published: September 2022

An adapted HVOF system has been computationally investigated in order to test the effects of injecting a cooling gas on both the gas phase dynamics and particle behaviour through the system. An existing liquid-fuelled HVOF thermal spray gun is modified by introducing a centrally located mixing chamber. The gas phase model incorporates liquid fuel droplets which heat, evaporate and then exothermically combust within the combustion chamber producing a realistic compressible, supersonic, turbulent jet. The trajectory of each discrete phase powder particle is tracked using the Lagrangian approach, with the inclusion of heating, melting and solidification through each particle. The results obtained give an insight to the complex interrelations present between the gas and particle phases, and demonstrates the usefulness of this modelling approach in aiding the development of thermal spray devices.
NIR (Near-Infra-Red) Sensor – An Alternative Diagnostic Tool for the Online Process Control of Thermal Spray Processes
Authors: Schwenk A. , Wank A. , Wallendorf T. , Marke S.
Published: September 2022

According to the present state of the art “in situ, real-time control systems” are absolutely necessary in modern applications within the field of Thermal Spray technology with regard to the quality and reproducibility of thermal spray coatings for a wide range of industrial applications. Compared with the already existing diagnostic systems and their algorithms which are developed on the basis of CCD cameras, an algorithm can be developed for in situ, real-time control systems, which possesses a by far closer physical approach for the determination of the particle characteristics due to the measurement principle. Thus, about 300 particles can be detected per millisecond as well as average particle velocities within the range of 30 - 1200 m/s and average particle surface temperatures between 700 - 3000 °C can be determined. A statistical distribution of approximately 3000 particles is considered for the computation of the online measured average particle velocities and surface temperatures. The accuracy of the measurement determines the use of an online process control during Thermal Spray processes.
The Shear Test for Thermally Sprayed Coatings in Quality Management
Authors: Winkler R. , Hartmann S. , Deuerler F.
Published: September 2022

The shear test in accordance with DIN EN 15.340 is a method to test the bond between substrate and coating in thermal spraying. It has been developed in order to avoid the disadvantages of the test mainly in use, the adhesion test (DIN EN 582). In quality management in a thermal spraying job shop often results of coating analyses are necessary within a very limited time frame; very important is a low number of necessary specimens and a fast and reliable test method. It is described how the shear test can be implemented into the practice of a job shop and the experiences of the OBZ innovation GMBH, which has used the shear test for more than four years, are explained.
Colferoloy—an Iron-Based Alternative for Wear Resistance Applications
Authors: Stratford G. C. , Battenbough A. J. , Allnatt P. J. , Burkard H.
Published: September 2022

Wall Colmonoy Ltd has developed a new generation of Iron-based powder alloys providing superior resistance to dry wear and excellent corrosion resistance. These alloys are economically interesting because they contain none or very low levels of expensive and market sensitive metals such as nickel and cobalt. These powders are marketed under the trade name Colferoloy. This paper details the properties and advantages of Colferoloy when compared to current “traditional” surface treatment methods and consumables. Metallurgical examination of the Colferoloy deposits showed that the alloy formed sub-micron structures which afford excellent dry-wear resistance, whilst the high chromium content provides good resistance to corrosion. Colferoloy alloys were applied using HVOF techniques to engineering components producing dense coatings with a hardness in the range of 950-1000 Vickers. The cost benefits of using an Iron-based alloy with low density hard phases were studied and comparisons with traditional materials were performed. This study showed that Colferoloy is a viable alternative to current hardfacing alloys and treatments.
Cold Spraying of Zn and Zn-Alloy Coatings for Print
Authors: Onizawa K. , Jansen J. , Schulze M. , Gärtner F. , Klassen T.
Published: September 2022

Zn, Zn-Al and Zn-Mg coatings have been produced by cold spraying. By careful tuning alloy compositions and spray conditions, dense coatings are produced with a hardness of 200 HV0.01 that are up to four times harder than pure bulk Zn, thus meeting the requirements for print applications. These new developments open opportunities for producing harder and more wear resistant coatings, which may allow for the production of larger number of copies without compromising quality.
Evaluation of the Photocatalytic Activity of TiO2-Coatings Prepared by Different Thermal Spray Techniques
Authors: Gutzmann H. , Kliemann J.-O. , Albrecht R. , Gärtner F. , Klassen T. , Toma F.-L. , Berger L.-M. , Leupolt B.
Published: September 2022

The metastable anatase structure of titanium dioxide (TiO2) is photocatalytically active and thus able to purify air and water. This makes anatase TiO2 a desirable material for instance in environmental technology. The present work provides a comparative study on the photocatalytic activity of TiO2 coatings, prepared by different spray methods: conventional atmospheric plasma spraying, HVOF spraying, suspension spraying and cold spraying. The spray experiments were performed with anatase powder as feedstock and the spray parameters were optimized in order to obtain coatings with high photocatalytic performance. With respect to spray technique and spray conditions, different amounts of the photocatalytic active anatase phase could be retained. The photocatalytic activity of the coatings was evaluated by degradation of dichloroacetic acid. The results show that the photocatalytic activity is highly dependent on the amount of preserved anatase structure obtained under the different spray techniques.
The Performance of Different WC-Based Cermet Coatings in Oil and Gas Applications – A Comparison
Authors: Meng H. , Neville A. , Gourdji P. , Hu X.
Published: September 2022

WC-based thermally sprayed coatings are now widely used in a range of industries to improve the mechanical strength of the components, but also enhance the resistance of the substrate to wear and corrosion. High velocity oxygen fuel thermal spraying has been accepted as a pre-eminent technology to deposit composite coatings with high density, superior bond strengths and relatively low decarburization due to the high particle velocities and relatively low particle temperatures induced in the deposition process. Many types of tungsten carbide/metal cermet coatings have been developed by alloying with different chemical elements, in an attempt to enhance corrosion and even erosion-corrosion resistance of coatings produced by HVOF for industrial applications, for example oil and gas industries. In this paper the galvanic series and the erosion-corrosion behaviour of three types of tungsten carbide coatings and three different sealing technologies in simulated oil and gas industry environments are compared. The ultimate goal is to have an understanding of how optimum choice of coating for a given application can be made for applications in the oil and gas industry.
Comparison of Al2O3 and Al2O3-TiO2 Coatings Manufactured by Aqueous and Alcoholic Suspension Plasma Spraying
Authors: Darut G. , Valette S. , Montavon G. , Ageorges H. , Denoirjean A. , Fauchais P. , Klyatskina E. , Segova F. , Salvador M. D.
Published: September 2022

Alumina-titania plasma spray coatings are widely used for their tribological performances. The combination of these two ceramics in a particular mix percentage permits to manufacture coatings with better wear resistance in comparison to those made of pure alumina. Suspension plasma spraying permit to manufacture sub-micrometer structure coatings very fine structure thanks to precursors which have an initial size of 10 to 300 nm. The use of a liquid feedstock, aqueous or alcoholic, allows the use of nanometer particles directly without the need to agglomerate them to obtain conventional nanostructured micrometer-sized powders. This study aims at studying Al2O3 and Al2O3-TiO2 coatings made from aqueous and alcoholic suspensions produced by suspension plasma spraying. Microstructures and phase evolutions are considered. Manufactured coatings present different architectures depending of operating parameters and feedstock particle sizes; the lower the particle diameter, the thinner the microstructure. Phases composition are discussed and compared to conventional micrometer-sized structure Al2O3 and Al2O3-TiO2 coatings.
Duration and Reliability of Axial Suspension Plasma Spray Process
Authors: Tang Z. , Hartell P. , Masindo G. , Bogdanovic N. , Yaroslavski I. , Kim H. , Restrepo J. , Ellsworth D. , Burgess A.
Published: September 2022

Suspension plasma spraying is gaining greater interest for emerging applications such as new thermal barrier coatings, next generation environmental barrier coatings and ceramic membranes as in solid oxide fuel cells. Mettech developed an axial injection plasma process coupled with an automatic suspension feed system, and demonstrated its capability to overcome the complexities of the process and deliver quality coatings. This paper aims at determining the durability and stability of the gun, suspension feeder and their components. A 120-hour duration test was performed, and the plasma torch and suspension feed parameters and performances were recorded. The test results indicate that the equipment and process are stable and reliable, and ready for industrial applications.
Crystal and Micro Structures of Plasma Sprayed Yttrium Oxide Coatings by Axial Injection of Fine Powder Slurries
Authors: Kitamura J. , Mizuno H. , Sato K. , Tang Z. , Burgess A.
Published: September 2022

Yttrium oxide (Y2O3) coatings have been prepared with high power axial injection plasma spraying using fine powder slurries. It is clarified that the coatings have high hardness, low porosity and high erosion resistance against CF4 contained plasma in the previous study. This suggests that the plasma spraying of Y2O3 with slurry injection techniques is applicable to fabricating equipments for semiconductor devices, such as dry etching. Surface morphologies of the slurry coatings with splats are almost similar to conventional plasma-sprayed Y2O3 coatings, identified from microstructural analysis by field emission SEM in this study. However, no lamellar structure has been seen from cross sectional analysis, which is apparently different from the conventional coatings. It has also been found that crystal structure of the slurry Y2O3 coatings mainly composed of metastable phase of monoclinic structure, whereas the powders and the conventional plasma spray coatings have stable phase of cubic structure. Mechanism of coating formation by plasma spraying with fine powder slurries will be discussed based on the findings.
Influence of Feedstock Powder for Fabrication of Aluminum Nitride in Reactive Atmospheric Plasma Spray Process
Authors: Shahien M. , Yamada M. , Yasui T. , Fukumoto M.
Published: September 2022

It was possible to fabricate cubic-AlN (c-AlN) based coating through the reaction between Al powder and the N2/H2 plasma in APS system. The fabricated coating was about 100 μm with hardness about 540 Hv, which is much higher than the hardness of Al. The formation of the cubic phase in APS is directly related to the rapid solidification phenomena of plasma spraying process. The sprayed powder particles show rapid cooling rates upon impact with the substrate, which prevent its complete crystal growth. The nitride content increased with the spray distance due to increase the flight time of Al particles in the N2 plasma. Using smaller particle size improved the nitriding reaction at short spray distance due to increasing the particle temperature. However increasing the particle temperature leads to excessive vaporization of Al particles and completing nitriding reaction during flight, therefore suppressing the coatings thickness. The nitriding reaction of the larger particle size Al powders can be enhanced through NH4Cl powders addition. That NH4Cl addition changed the reaction pass way from liquid-gas to vapor-phase intermediate mechanism.
Vapor Phase Deposition Using a Plasma Spray Process
Authors: Niessen K. von , Gindrat M.
Published: September 2022

Plasma spray – physical vapor deposition (PS-PVD) is a low pressure plasma spray technology to deposit coatings out of the vapor phase. PS-PVD is part of the family of new hybrid processes recently developed by Sulzer Metco AG (Switzerland) on the basis of the well established low pressure plasma spraying (LPPS) technology. Included in this new process family are plasma spray - chemical vapor deposition (PS-CVD) and plasma spray - thin film (PS-TF) processes. In comparison to conventional vacuum plasma spraying (VPS) and low pressure plasma spraying (LPPS), these new processes use a high energy plasma gun operated at a work pressure below 2 mbar. This leads to unconventional plasma jet characteristics which can be used to obtain specific and unique coatings. An important new feature of PS-PVD is the possibility to deposit a coating not only by melting the feed stock material which builds up a layer from liquid splats but also by vaporizing the injected material. Therefore, the PS-PVD process fills the gap between the conventional physical vapor deposition (PVD) technologies and standard thermal spray processes. The possibility to vaporize feedstock material and to produce layers out of the vapor phase results in new and unique coating microstructures. The properties of such coatings are superior to those of thermal spray and EB-PVD coatings. In contrast to EB-PVD, PS-PVD incorporates the vaporized coating material into a supersonic plasma plume. Due to the forced gas stream of the plasma jet, complex shaped parts like multi-airfoil turbine vanes can be coated homogeneously with columnar thermal barrier coatings using PS-PVD. This paper reports on the progress made by Sulzer Metco to develop a thermal spray process to produce coatings out of the vapor phase.
Selective Impact of Industrial Gases on the Thermal Spray Process
Authors: Krömmer W. , Heinrich P.
Published: September 2022

The trend in thermal spraying is more and more towards a globally uniform level of high-grade spray coatings. It is therefore extremely important that auxiliaries such as spray materials or industrial gases undergo precise examination in order to exactly define their influence. A further point is of particular significance in today’s business world. With ever-increasing raw material prices, it is absolutely essential that spray processes are optimized to the maximum. This is not only made possible by selecting the right system, but also by choosing the right gas and gas mixture. The optimization of costs, extended lifetime of systems and tailoring of coating properties to suit specific applications are just some of these influencing variables. Gas producers test countless facilities and thermal spray systems in their own laboratories and are therefore always in a position to provide the right solution for existing and new applications.
Potential of Cold Gas Spraying in Power Electronic Applications
Authors: Donner K.-R. , Gaertner F. , Klassen T.
Published: September 2022

A successful combination of isolating substrates with conducting metal coatings produced by cold spraying could open new industrial application areas like the fabrication of power electronic components. For minimizing the number of industrial process steps, isolating ceramic layers should ideally be processed by thermal spray techniques. Thus, the present study investigates the impact behaviour and coating formation of ductile metallic feedstock powders onto brittle ceramic coatings. With respect to high electrical conductivity of the metallic lines and good electrical isolation of the ceramic interlayer, copper was cold gas sprayed on previously thermally sprayed Al2O3 coatings. Successful cold coating formation requests different strategies for the activation of the ceramic layer to increase adhesion and to avoid brittle failure. Both can be achieved by applying a bondcoat on the ceramic layer or by using heated substrates during the cold spray process.
Thermophysical Studies on Thermally Sprayed Tungsten Carbide-Cobalt Coatings
Authors: Thiele S. , Sempf K. , Jaenicke-Roessler K. , Berger L.-M. , Spatzier J.
Published: September 2022

The development of new hardmetal coating applications such as fatigue-loaded parts, structural components and tools for metal forming is connected with improvement of their performance and reliability. For modelling purposes the knowledge of thermophysical, mechanical and other material data is required. However, this information is still missing today. In the present work the thermophysical data of a WC-17Co coating sprayed with a liquid-fuelled HVOF-process from a commercial agglomerated and sintered feedstock powder from room temperature up to 700 °C was determined as an example. The dependence of the heat conductivity on temperature was obtained through measurement of the coefficient of thermal expansion, the specific heat capacity and the thermal diffusivity. Heat conductivities ranging from 29.2 W/(mK) at 50°C to 35.4 W/(mK) at 700 °C were determined. All measurements were performed twice (as-sprayed and after the first thermal cycle) in order to take into account the structural and compositional changes. Extensive XRD and FESEM studies were performed in order to characterize the phase compositions and microstructures in the as-sprayed and heat-treated states. Bulk samples obtained by spark plasma sintering from the feedstock powder were studied for comparison.
Microstructure and NO2 Sensing Performance of APS ZnO Coatings
Authors: Zhang C. , Debliquy M. , Liao H.
Published: September 2022

This work studied the possibility of using a sensor based on plasma-sprayed zinc oxide (ZnO) sensitive layer for NO2 detection. The atmospheric plasma spray process was employed to deposit ZnO gas sensing layer and the obtained coating structure was characterized by scanning electron microscopy and X-ray diffraction analysis. The influences of gas concentration, working temperature, water vapor in testing air on NO2 sensing performance of the ZnO sensors were studied. ZnO sensors showed a good sensitivity and selectivity to NO2 at an optimal working temperature.
The Influence of Particle Temperature, Particle Velocity and Coating Surface Temperature on the Sliding Wear Performance of TiO2-Cr2O3 Coatings
Authors: Trache R. , Berger L.-M. , Saaro S. , Lima R.S. , Marple B.R.
Published: September 2022

In this work the sliding wear resistance of HVOF and APS-sprayed coatings from two experimental TiO2-10-20 wt.%Cr2O3 fused and crushed feedstock powders was investigated. During the spraying process the particle temperatures and velocities were mapped in the cross section of the spray jet at different spray distances. In addition, the coating surface temperature was monitored. Coating microstructures and phase composition were studied by SEM and XRD, respectively. The elastic modulus (E) and hardness (H) values were measured via in-depth sensing indentation. The unidirectional ball-on-disk sliding wear test was performed at room temperature against a tungsten carbide ball (sliding speed 0.05 m/s, normal force 90 N). The increase of the particle temperature and velocity leads to an increase of hardness and Young’s modulus of the coatings, thereby increasing their sliding wear resistance. The sliding wear resistance can be correlated with the H3/E2 ratio better than with the hardness alone. The sliding wear resistance was also sensitive to the coating surface temperature reached during deposition.
Cold Spraying for Titanium Dioxide Coatings with High Photocatalytic Bactericidal Activity
Authors: Kliemann J.-O. , Gutzmann H. , Gärtner F. , Klassen T. , Gabriel H.
Published: September 2022

Titanium dioxide in anatase phase structure has high antibacterial activity. For this study, titanium dioxide coatings on stainless steel were produced by cold spraying. The bactericidal effect of the coatings was tested with Pseudomonas aeruginosa bacteria at a high concentration of more than 107 CFU (colony-forming units) per milliliter. The bacteria were applied on the surface and exposed to UV light with a peak intensity of 360 nm. A kill rate of 99,99% was already achieved after 5 minutes, while the raw stainless steel reference did not show any significant reduction even after 60 min. The results show that cold-sprayed titanium dioxide coatings can serve as self-disinfecting surfaces.
Columnar Structured Thermal Barrier Coatings (TBCs) by Thin Film Low Pressure Plasma Spraying (LPPS-TFTM)
Authors: Hospach A. , Mauer G. , Vaßen R. , Stöver D.
Published: September 2022

The very low pressure plasma Spray (VLPPS) process has been developed with the aim of depositing uniform and thin coatings with large area coverage by plasma spraying. At typical pressures of 100-200 Pa, the characteristics of the plasma jet change compared to conventional low pressure plasma spraying processes (LPPS) operating at 5 – 20 kPa. The combination of plasma spraying at low pressures with enhanced electrical input power has led to the development of the LPPS-TF process (TF = thin film). At appropriate parameters it is possible to evaporate the powder feedstock material providing advanced microstructures of the deposits. This technique offers new possibilities for the manufacturing of thermal barrier coatings (TBCs). Besides the material composition, the microstructure is an important key to reduce thermal conductivity and to increase strain tolerance. In this regard, columnar microstructures deposited from the vapor phase show considerable advantages. Therefore, physical vapor deposition by electron beam evaporation (EB-PVD) is applied to achieve such columnar structured TBCs. However, the deposition rate is low and the line of sight nature of the process involves specific restrictions. In this paper, the deposition of thermal barrier coatings by the LPPS-TF process is shown. It is investigated how the evaporation of the feedstock powder could be improved and to what extend the deposition rates could be increased.
Effect of Heat Treatment on Porosity and Corrosion Performance of Cold Sprayed Titanium Deposits
Authors: Hussain T. , McCartney D.G. , Shipway P.H. , Marrocco T.
Published: September 2022

Cold gas dynamic spraying (CGDS) can be used to deposit oxygen sensitive materials, such as titanium, without significant chemical degradation of the powder and with minimal heating of the substrate. The process is thus believed to have potential for the deposition of corrosion resistant barrier coatings. However, to be effective a barrier coating must not allow ingress of a corrosive liquid and hence must have minimal interconnected porosity. Thus the aim of the present study was to investigate the effects of processing, including a post-spray annealing treatment, on the deposit meso- and microstructures and corrosion behavior. Commercially pure titanium powder was deposited using pre-heated nitrogen as main and powder carrier gas using a CGT Kinetiks 4000 system to produce coatings on stainless steel. Selected coatings were debonded from the substrate, and the resultant free standing deposits heat treated at 1050° C in vacuum for 60 minutes. Changes in microhardness were measured and correlated with microstructural changes. Optical microscopy, scanning electron microscopy, X-ray diffraction (XRD), helium pycnometry and mercury porosimetry were all employed to examine the microstructural characteristics of coatings and free standing deposits, before and after heat treatment. Their corrosion performance was also investigated using potentiodynamic polarization tests in 3.5 wt% NaCl. The influences of heat treatment and corrosion behavior will be analyzed and discussed in terms of pores structure evolution and microstructural changes.
A Preliminary Study of the Oxidation Behavior of TBC with Cold Spray CoNiCrAlY Bond Coat
Authors: Chen W.R. , Irissou E. , Legoux J.-G. , Wu X. , Marple B.R.
Published: September 2022

Cold gas dynamic spray (CGDS) utilizes a supersonic gas jet to accelerate fine solid powders above a critical velocity at which particles impact, deform plastically, and bond to the substrate material in the ambient environment. This process is potentially beneficial for thermal barrier coating (TBC) bond coat deposition because it would avoid oxidation of the feedstock powder that normally occurs when higher temperature thermal spray processes are employed. Therefore, there would be no prior aluminum depletion in as-deposited bond coats produced by the CGDS technique. This paper presents the oxidation behaviour of a TBC with CGDS-produced CoNiCrAlY bond coat, in comparison with TBCs with APS- and HVOF-CoNiCrAlY bond coats. Oxidation behaviors of these TBCs were evaluated in terms of microstructural evolution, kinetics of thermally-grown-oxides (TGO), as well as cracking behaviour during thermal exposure at 1050 °C.
Characterization of Thermo-Mechanical Properties for Thermal Sprayed NiCoCrAlY Coatings
Authors: Fasth A. , Nylén P. , Markocsan N. , Mušálek R.
Published: September 2022

The thermo-mechanical properties of a thermal barrier bond coat (BC) play an important role in governing the life-time of a coating system. The presented work aims to determine these properties for NiCoCrAlY coatings sprayed on Hastelloy X substrates sprayed under different process conditions. Temperature dependent Young’s modulus values are determined for both Atmospheric Plasma Sprayed (APS) and HVOF sprayed coatings using the four-point bending test. Particular attention is paid to microstructure-property relationships during heating. Young´s modulus was determined up to 950°C and evaluated for coatings loaded in both tension and compression. Results are discussed in the context of the effect of feedstock material, process conditions and microstructure characteristics. The methods and results presented are attractive, particularly for the thermal spray industry, since these properties are a prerequisite when the BC is to be considered in component design.
Deposition of NiO/YSZ Composite and YSZ by Suspension Plasma Spray on Porous Metal
Authors: Wang Y. , Legoux J.-G. , Neagu R. , Hui R. , Maric R. , Marple B.R.
Published: September 2022

The use of a liquid feedstock carrier in suspension plasma spray (SPS) permits injection of fine powders, providing the possibility of producing sprayed coatings that are both thin and dense and have fine microstructures. These characteristics make SPS an attractive process for depositing highly efficient electrodes and electrolytes for solid oxide fuel cell (SOFC) applications. In the present study, NiO-yttria stabilized zirconia (YSZ) anode and YSZ electrolyte half cells were successfully deposited on porous Hastelloy X substrates by SPS. The NiO-YSZ anode deposition process was optimized by design of experiment. The YSZ electrolyte spray process was examined by changing one parameter at a time. The results from the design-of-experiment trials indicate that the porosity of the as-deposited coatings increased with an increase of suspension feed rate while it decreased with an increase of total plasma gas flow rate and standoff distance. The deposition efficiency increased with an increase of total plasma gas flow rate, suspension feed rate and standoff distance. The microstructure examination by SEM shows that the NiO and YSZ phases were homogeneously distributed and that the YSZ phase had a lamellar structure. It was observed that the density of the YSZ electrolyte layer increased as input power of the plasma torch increased.
Development of a Low-Temperature, Oxy-Fuel (LTOF) Thermal Spray Gun
Authors: Dhiman R. , Farhadi F. , Pershin L. , Chandra S. , Mostaghimi J.
Published: September 2022

This paper presents the development of a new thermal spray gun for the so-called warm spraying process in which powder particles are not melted but heated to temperatures much higher than those typically found in a cold spray process. The increased heating leads to a reduction in the particle impact velocity required to deposit the coating and hence reduces operating cost. The new gun utilizes methane-oxygen combustion for particle heating and features a swirl-type combustion chamber to create a turbulent mixture of the fuel and oxidizer for efficient combustion. Powder can be fed axially or radially into the gun. To control particle temperature independently, combustion gases are diluted by adding nitrogen gas through axial or radial ports provided in the gun. A converging-diverging nozzle with a downstream cylindrical barrel accelerates the burnt gases to supersonic velocities. The design of the nozzle and barrel was optimized using numerical simulations. Mass flow rates of methane, oxygen, and nitrogen were calculated using energy balance, stoichiometric combustion, and nozzle flow rate equations. The gun is designed to operate up to 200 kW and is water-cooled. Experiments were conducted to test the performance of the new gun in which tungsten carbide coatings were deposited on aluminum substrates. Coatings were analyzed using standard methods and showed promising results.
Comparison of Cold Spray and Detonation Coatings Properties
Authors: Smurov I. , Pervushin D. , Ulianitsky V. , Zlobin S. , Sova A.
Published: September 2022

Cold and detonation spraying methods are based on the interaction of high-velocity particles with substrate. High quality coatings from various powder materials can be deposited. In both processes, the substrate experiences insignificant thermal effect. Thermally sensitive powder can be sprayed with no oxidation and decomposition. The initial powder microstructure and even nanostructure can be preserved under properly selected spraying conditions. This study is based on a comparative analysis of the mechanical, electrical, and heat transfer properties of a series of coatings deposited by cold and detonation spraying technologies. The coatings are produced from copper and aluminum powders using a commercial Cold Spray equipment CGT-4000 and an original computer-controlled detonation spraying (CCDS) installation developed by the authors. The coating microhardness, density, electrical and heat conductivity, adhesion, cohesion, etc. are measured and compared. Particular advantages and drawbacks of both spraying methods are discussed.
Correlations Between the Oscillation Modes of Arc Voltage and Pressure in Cathode Cavity of Dc Plasma Torches
Authors: Rat V. , Coudert J.-F.
Published: September 2022

The development of coating elaboration processes involving electric arcs depends on process stability and the capacity to ensure a constant reproducibility of coatings properties. This is particularly important when considering the plasma treatment of submicron or nanosized particles in Suspension Plasma Spraying (SPS). Submicron particles closely follow plasma instabilities and have non-homogeneous plasma treatment. Recently, it has been shown that arc voltage fluctuations in dc plasma torches, showing dominant fluctuation frequencies between 4 – 6 kHz, are linked to pressure oscillations in cathode cavity in the rear part of the plasma torch. These resonant oscillations are linked to plasma torch geometry. In this paper, first, we will present a method to isolate the different oscillations modes in measured arc voltage and pressure signals by the use of signal processing methods. Second, correlations between the different modes of oscillations are analyzed following the plasma torch operating parameters.
Investigation of Impact Behavior of Cold-Sprayed Large Annealed Copper Particles and Characterizations of Coatings
Authors: Li W.-Y. , Guo X.P. , Liao H. L. , Coddet C.
Published: September 2022

In this research, large gas-atomized copper powder was selected as the feedstock. Some powder was annealed in a vacuum circumstance to avoid to the greatest extent the effect of grain boundaries on the high velocity impact behavior of particles during cold spraying. Some powder was oxidized in a resistance furnace to clarify the effect of surface oxide films. Both the annealed and the oxidized Cu powders were deposited by cold spraying with respect to the single impacts and coating deposition under the same gas condition. In addition, the rebounded copper particles were collected for morphology analysis compared to the adhered particles. The results show that the average size of the rebounded particles is apparently increased compared to the starting powder because of the rebound of the larger particles and the intensive plastic deformation of particles. For the deposited particles, obvious plastic deformation causes the higher hardness of the coatings. The last but not the least finding in this study is the rebounded particles also experienced large deformation and possible shear instability at the impact interfaces.
Characterization and Performance Evaluation of a Helium Recovery System Designed for Cold Spraying
Authors: Legoux J.-G. , Irissou E. , Desaulniers S. , Bobyn J. , Harvey B. , Wong W. , Gagnon E. , Yue S.
Published: September 2022

This paper describes and evaluates the performance of a Helium Recovery System (HRS) designed for cold spraying. A flexible, automated, full scale HRS system has been designed and installed in the McGill Aerospace Materials & Alloy Development Center Cold Spray Facility, located at and in collaboration with the National Research Council of Canada. The fully automated HRS has been designed to recover helium from the cold spray chamber with sufficient purity (>99%) and flow capacity (5 to 220 Nm3/h), allowing for a cost-effective operation by insuring a recovery rate of above 85%. In addition, a comparison of titanium coating properties obtained by using both He and N2 as propellant gas is presented.
Mechanical Properties and Behaviour of BSAS/Mullite-Based Environmental Barrier Coatings Exposed to High Temperature in Water Vapour Environment
Authors: Cojocaru C.V. , Kruger S.E. , Lima R.S. , Moreau C.
Published: September 2022

Si-based ceramics (e.g., SiC and Si3N4) are known as promising high-temperature structural materials in various components where metals/alloys reached their ultimate performances (e.g., advanced gas turbine engines and structural components of future hypersonic vehicles). To alleviate the thickness recess that Si-based ceramics undergo in a high-temperature environmental attack (e.g., H2O vapour), appropriate refractory oxides are engineered as environmental barrier coatings (EBCs). Presently, the state-of-the art EBCs comprise multilayers of silicon (Si) bond coat, mullite (Al6Si2O13) intermediate layer and BaO-SrO-Al2O3-SiO2 (BSAS) top coat. Evaluating and understanding their mechanical properties, such as, the elastic modulus (E) and the strain-stress relationship is essential for their practical application and reliable employment. It was investigated via depth-sensing indentation the role of high-temperature treatment (1300°C), performed in H2O vapour environment (for time intervals up to 500 h), on the mechanical behaviour of air plasma sprayed Si/mullite/BSAS layers deposited on SiC substrates. Laser-ultrasonics was employed to evaluate the E values of as-sprayed coatings and to validate the indentation results. The fully crystalline, crack-free and near crack-free as-sprayed EBCs were engineered under controlled deposition conditions. The (i) absence of phase transformation and (ii) stability of the low elastic modulus values (e.g., ~60-70 GPa) retained by the BSAS top layers even after harsh environmental exposures provides a plausible explanation for the almost crack-free coatings observed. The measured mechanical properties of the EBCs and their microstructural behaviour during the high-temperature exposure are discussed and correlated.