bluuebunny/crossref_metadata_2025 huggingface dataset:
Injection Conditions and In-Flight Particle States in Suspension Plasma Spraying of Alumina and Zirconia Nano-Ceramics
Authors: Oberste Berghaus J. , Bouaricha S. , Legoux J.-G. , Moreau C.
Published: August 2022

Plasma spraying of ceramic nano-powders suspended in a liquid carrier medium is an emerging technology, which allows the formation of thinner coatings with microstructures more refined than conventional plasma spraying. An external injection system, where the suspension enters the plasma jet radially, is installed on a F4-Sulzer Metco dc torch for the production of nanostructured Al2O3 and ZrO2 coatings. The effect of injection parameters, such as initial droplet diameter, droplet velocity and suspension flow rate is studied. The suspension droplets are continuously generated through an exchangeable micron-sized nozzle with a superimposed pulse of variable ultrasonic frequency. The heat transfer from the plasma to the liquid feed is optimized at high droplet velocity, moderate counter-current injection angle and flow rates not exceeding a threshold value, which depends on the plasma enthalpy and the latent heat of the suspension medium. A significant effect of initial droplet size (220 – 500 µm) or solid concentration (5 – 15 %) is not observed. In-flight particle states are measured for different plasma conditions, and are related to the resulting microstructures by SEM and XRD. High particle temperatures give rise to a refinement in crystallite size, while the particle velocities govern the deposition efficiencies and porosity levels. The results show that the particles follow closely the gas flow in the free stream, as well as in the stagnation boundary layer close to the substrate by virtue of their limited inertia. The prominent difference in microstructure between highly porous alumina and very dense zirconia coatings is explained in terms of particle impact velocities, which are simulated for typical operating conditions as a function of particle size and free-stream gas velocity.
Comparative Study of the Properties of WC-Co Nanostructured and Bimodal Coatings, Sprayed by High Velocity Oxy-Fuel (HVOF)
Authors: Guilemany J.M. , Dosta S. , Nin J. , Miguel J.R.
Published: August 2022

Over the last years, the grain size reduction to the nanometric scale has experienced an increasing interest because of its enhanced properties. This study is based on WC-Co cermet materials, which have a great application in the wear resistance materials field. In the Thermal Spray Center (CPT) of the University of Barcelona, two coatings using nanostructured and bimodal WC-Co cermet powders have been obtained by means of High Velocity Oxygen-Fuel (HVOF) technique. Both were sprayed under the same spraying parameters. Structural characterization for both feedstock materials and coatings have been performed using XRD, SEM and TEM. The friction wear resistance of the coatings has been studied by Ball-on-Disk test (ASTM G99-90), and the abrasive wear resistance has been quantified by Rubber-Wheel test (ASTM G65-91). Finally, the corrosion resistance has been studied by electrochemical techniques and a salt fog spray test. The nanostructured coating shows more hardness, but the bimodal coating shows better abrasive and friction wear resistance. Both coatings shows good corrosion resistance, better than the conventional coatings of WC-Co. The bimodal powder have the added advantage of being not as expensive as the nanostructured powder, and even providing better properties.
Formation of Nanoscale Composite Coatings via HVOF and Wire-Arc Spraying
Authors: Branagan D.J. , Marshall M.C. , Meacham B.E.
Published: August 2022

In the materials world, there are two distinct usages of the term nanotechnology; Particulate Materials Nanotechnology (PMN) and Bulk Materials Nanotechnology (BMN). Both approaches have been used in attempts to produce nanoscale coatings with characteristic length scales from 10 to 100 nm. While particulate strategies are widespread, a different approach is presented which focuses on producing coatings through a solid / solid state transformation which results in the refinement of the microstructural scale (i.e. phase / grain size) down to the nanoscale regime. The essential features of BMN are the 2-d grain and phase boundary defects and achieving this nanoscale regime is key to enhancing bulk properties. This paper will attempt to clarify the terminology, definitions, and usages of the term nanoscale to clear up misconceptions and clearly show the salient features allowing for the production of nanoscale microstructures on an industrial scale. A clear demonstration of this achievement will be presented with a case study on the formation of amorphous / nanocomposite coatings while processing in air using off the shelf thermal spray technology using conventionally sized feedstock. Examples of nanostructured HVOF and wire-arc as-sprayed and heat treated coatings with average phase sizes of 50 nm and 80 nm respectively will be presented using detailed TEM micrographs.
Study of Ni/Al2O3 Deposition on Metallic Surface using RF Plasma Process
Authors: Oukacine L. , Gitzhofer F. , Abatzoglou N. , Gravelle D.V.
Published: August 2022

This work is aimed at acquiring knowledge on successive deposition of alumina and nickel coatings on a metallic substrate using an RF plasma torch. The composition and morphology of various Ni/Al2O3 steam reforming catalysts, prepared by plasma spraying of precursor nickel suspensions, are studied in this work. As Ni/γ-Al2O3 is a well known reforming catalyst it was decided to study the deposition of a particular catalytic formulation on a metallic substrate. The purpose of this study was to find the means of building 2D monolithic catalysts by plasma deposition. Since 2D monolithic catalysts are non-porous, their specific areas available for hosting the catalytic reactions are low. Thus, It is essential to have very good dispersion of the active catalytic sites. Such dispersion is only possible only if the deposit can take place at the nanometer scale. The suspension plasma spraying is assessed for its ability to produce such structures. This method permits the formation of nanocrystalline structures within a few seconds. The main difficulty is the control of the various spraying parameters in order to obtain satisfactory deposition. The Ni/γ-Al2O3 catalysts so obtained are characterized by scanning electron microscopy, field electron microscopy and X-Ray diffraction.
Examining the Variations in Splat Properties within the Footprint of a Spray Stream
Authors: Srinivasan V. , Vaidya A. , Streibl T. , Li L. , Sampath S.
Published: August 2022

It is known that particles injected in a plasma stream follow differing trajectories which in turn leads to different thermal and kinetic history dependent on the location of particle in the plume. The variation in particle characteristics (temperature and velocity) across the plume has been the focus of research over the years. The corresponding variation in impacting particles, particularly in terms of their splat characteristics have not been explored as systematically. This is important for a complete understanding of the coating build-up phenomena and the variations in coating properties. This paper presents the results of a study in which the spatial variation in particle properties is mapped to the spatial variation in splat properties. This has been accomplished using a procedure to collect splats using a shutter mechanism that allows us to expose the substrate for approximately 50 milliseconds. Splats of Alumina and a Ni- Cr-B-Si-Mo have been collected on polished substrates maintained at 250ºC and studied. Micrographs reveal differing splat morphologies across the spray plume – from missing-cores in one part to complete disc-shaped splats in the other. Extent of flattening and fragmentation have been quantified and found to vary within the ‘splat map’. Correlation between the location of particle in the plume and the resulting splat has been constructed using this data. Abstract only; no full-text paper available.
Improvement of DC Thermal Plasma Spraying by Reducing the Cold Gas Entrainment Effect
Authors: Henne R.H. , Arnold J. , Schiller G. , Kavka T.
Published: August 2022

Plasma jets for thermal spraying are strongly affected in a negative sense by the interaction with the relatively static surrounding atmosphere, particularly at atmospheric spray conditions. Turbulences at the jet fringes arise resulting in entrained cold gas, in slowing and cooling down of the jet and in causing eventually its disintegration. All means suppressing or delaying this phenomenon, called cold gas entrainment, help to improve the interaction of plasma and spray material and hence lead to better product quality and higher deposition efficiency of the process. To observe the cold gas entrainment, to investigate the thermal and kinetic properties of DC plasma jets at different operating conditions and to study the effect of plasma source and powder injection modifications a diagnostic equipment with Schlieren optics, enthalpy probe and mass spectrometry was installed. By modification of the internal and external anode nozzle contours and also by application of a shroud nozzle around the plasma jet exit encouraging results with reduced penetration of cold ambient air into the jet could be obtained.
Particle Properties During Plasma-Spraying of Yttria Stabilized Zirconia Using a Triplex-II Torch
Authors: Döring J.-E. , Marqués J.-L. , Vaßen R. , Stöver D.
Published: August 2022

The triplex-torch design providing three stable arcs in power and geometry promises a stable, quasi-laminar plasma jet leading to an uniform plasma and thus an uniform particle distribution. Additionally, the three powder injectors lead to an extended powder feed rate, resulting in a lower spraying time. This paper deals with particle properties of YSZ (SM 204NS) with respect to their injection location and powder feed rate and the resulting coating microstructure and porosity levels. Concerning the injection conditions, the three powder jets can be clearly identified. Their location depends on the spraying distance and less pronounced on the injection velocity. Interestingly, if the different powder-sizes are grouped and the jet cross-section is plotted for the different size cuts, the position of each size cut varies. Thus, a local separation of the powder takes place in the jet. The powder feed rate was varied from 30 to 320 g/min. Accordingly to this variation, the particles mean temperature was lowered from 3050°C down to 2650°C, and the velocity values dropped from 230 m/s to 155 m/s. Regarding the achieved coating thickness, up to a powder feed rate of approximately 210 g/min the thickness is increasing with no dramatic change in the porosity values. More powder does not lead to a thicker coating but results in a significantly higher porosity. Moreover, the microstructure of the coatings obtained by using a higher feed rate exhibits more segmentation cracks.
Plasma Spray Process Control with Neural Network
Authors: Jakimov A. , Hertter M. , Abdullahi H. , Staudacher S.
Published: August 2022

In current aircraft engines challenging coatings or coating systems with different functions are used. Many of these coatings are applied to different components with thermal spray processes. Thermal spraying is a very sensitive and very complex process, which is influenced by numerous controllable variables like the powder feed rate, the gas flow rates, etc. as well as not controllable variables like the torch wear, varying powder properties, etc. With conventional process control based on linear algorithms it is not possible to enduringly create constant coating properties, because they cannot describe the complexity of all influencing variables. In this work, the possibility of a closed loop was investigated exemplarily for an atmospheric plasma spray process (APS). During serial production a data base was collected, consisting information about torch and plume conditions as well as powder and coating properties. This data base was used to train different neural networks (NN). With regard to the automation of the APS, the NN obtained target values of relevant coating properties and should calculate the needed control variables. The result of this work shows the difficulties in the quantification of relevant influencing variables and the feasibility of the plasma spray process control with neural network.
Computational Evaluation of Thermal Barrier Coating Characteristics Under Plasma Spraying
Authors: Solonenko O. , Sato T. , Nishiyama H.
Published: August 2022

To enhance the efficiency of computational experiment covering all links of a technological chain ‘generation of plasma jet – injection of particles – formation of dust-laden plasma jet – coating deposition from drops of a melt’ it is very attractive to integrate the experimentally tested analytical solutions characterizing splats formation along with 2-D/3-D models describing dust-laden technological flow. The authors of the present paper carried out a computer simulation of a plasma spraying process from zirconia particles injection to a coating formation conducted by integrating particle-laden plasma flow, metal oxide splat formation and coating formation models with reference to the thermal barriers. The velocity and temperature of both plasma flow and zirconia particles under an applied RF electromagnetic field were clarified by using the first model. Radial distributions of particle impact location, velocity and temperature were obtained based on both an unsteady effect of a plasma flow and distributions of particle size and injection velocity. Secondly, splat thickness and diameter after zirconia droplets impact onto substrate were clarified by using the earlier experimentally probated analytical solution. Finally, the coating thickness distributions were evaluated by using the last model. Abstract only; no full-text paper available.
Photocatalytic Properties of Nanostructured TiO2 and TiO2-Al Coatings Elaborated by HVOF Spraying
Authors: Toma F.-L. , Chwa S.-O. , Bertrand G. , Liao H. , Klein D. , Coddet C.
Published: August 2022

In the present study, TiO2 and TiO2-Al composite coatings were prepared by HVOF spraying using reconstituted nanosized feedstock powders prepared via the spray drying technique. In the flame, the powders were injected by two methods: internal injection i.e. as in conventional HVOF process and external injection i.e. outside the torch nozzle. The microstructure of the coatings was characterized by scanning electron microscopy and X-ray diffraction. It was found that the amount of anatase in the coatings depends on the nature of the powder and also on the type of the injection method. The coatings were tested for their photocatalytic properties regarding the conversion rate of nitrogen oxides. Coatings elaborated by external injection presented a better photocatalytic activity than those obtained by the conventional HVOF process.
In-Flight Particle Characterization of HVOF-Arc Hybrid Gun
Authors: Kosikowski D. , Batalov M. , Mohanty P.S.
Published: August 2022

The high-velocity oxy-fuel (HVOF) gun represented a major development towards forming dense coatings. But, compared to the electric arc-spray process, the HVOF process is more difficult to apply and in general more costly. Therefore, some process development efforts have aimed at exploiting the attributes of both the electric arc-spray technique combined with those of the HVOF technique. Specifically, this hybrid process utilizes the electric arc spray benefits of using wire stock and high deposition rates combined with the higher coating densities obtained using HVOF. This paper presents an in-depth, in-flight particle characterization of a hybrid spray gun. A DPV-2000 particle diagnostics sensor was used to measure particle velocity, temperature, size and distribution. The influence of feed material, electric arc-spray parameters, and HVOF parameters on the particle characteristics is presented. It is observed that the velocity of the particles in the hybrid mode are slightly lower than the velocity of particles by HVOF alone but significantly higher than typical electric arc-spray velocities. In addition, the particle temperature in the hybrid mode isn’t significantly different than those by HVOF only. The particles produced by the hybrid gun tend to be more uniform and smaller compared to traditional electric arc-spray coatings.
Friction and Wear Behavior of Plasma Sprayed Al2O3 and Cr2O3 Coatings Against Copper Alloy Under High Load Dry Sliding
Authors: Tao S. , Zhou X. , Ding C.
Published: August 2022

Al2O3 and Cr2O3 coatings were deposited by atmospheric plasma spraying. The tribological properties of coatings against copper alloy were evaluated with a block-on-ring configuration under dry friction conditions at room temperature. Microstructure of powders and coatings were observed using scanning electron microscopy (SEM) and optical microscope (OM). Some thermo-physical properties of coatings were measured. Results showed that the Cr2O3 coating exhibits cracking failure in the sliding condition with a normal load of 500N and a sliding velocity of 0.84 m/s. This failure of the plasma sprayed Cr2O3 coating is explained in terms of its low thermal conductivity.
Measuring Thermal Contact Resistance Between Molten Aluminum Droplets and a Steel Plate
Authors: Heichal Y. , Xue M. , Chandra S. , Mostaghimi J.
Published: August 2022

The impact and solidification of 4 mm molten aluminum alloy 380 droplets on a tool steel substrate was studied both analytically and experimentally. Temperature histories at different radial location on the substrate surface under impacting droplets were recorded using an array of thin film thermocouples with response times less than 1 µs. Photographs were taken of droplet impact onto the substrate. Initial substrate temperature was varied from room temperature to 300°C and average surface roughness from 0.5 to 5.0 µm. Estimates of thermal contact resistance were made by matching measured substrate temperatures with an analytical solution for surface temperature variation. A model of the true area of contact between molten metal and a rough surface was developed in order to predict how contact resistance changes with surface roughness and contact pressure. Impact of molten aluminum alloy droplets was simulated using a three-dimensional numerical. Using values of thermal contact resistance predicted by the model gave good agreement between computed and observed droplet shapes during impact.
Shear Testing for Characterizing the Adhesive and Cohesive Coating Strength Without the Need of Adhesives
Authors: Siegmann St. , Dvorak M. , Grützner H. , Nassenstein K. , Walter A.
Published: August 2022

The characterization of the adhesive and cohesive strength of thermally sprayed coatings is often evaluated according to given standardized testing procedures. These tests require the preparation of normally large coupons which have to be fixed together using an appropriate adhesive. Additionally they need time for preparation (e.g. annealing/curing of the adhesive) and require test equipments normally not available at job shops for coating development. One of the largest limitations of these tests is the applicability only for non-porous coatings, and in some cases the limited strength of the adhesive. Within a European CRAFT research project on “standards, measurements and testing”, a new shear test method was developed to characterize the mode and value of failure of thermally sprayed layers in a more reliable and less limited manner. This new shear test does not need any adhesive and yields more intrinsic information on coating quality than conventional tensile tests.
Nanostructures in Thermal Sprayed Hydroxyapatite (HA) and HA/Nano-Zirconia Coatings and their Influence on Coating Properties
Authors: Li H. , Khor K.A. , Cheang P.
Published: August 2022

Nanostructured hydroxyapatite (HA) and HA/nano-zirconia powders were sprayed by both plasma and HVOF spraying. Microstructure characterization on the nanostructured coatings were conducted using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffractometry (XRD), and Raman spectroscopy. Results showed that the nanostructures of the HA feedstock retained to some extent after the thermal spraying depending on the melt state of the powders. The microstructural features of individual HA splats were also characterized through TEM observing both as-sprayed and ion-milled splats. A nanostructure (with ~ 30nm grains) within the surrounding parts of the HA splats was revealed, while significant grain growth (a size up to 5 µm) depending on flattening state was found at the center of the splats. It also revealed that the nano-sized zirconia particles (< 90 nm) retained their fine size after HVOF deposition, and were evenly distributed within the coating. The crystallite size of tetragonal zirconia in the coating was found to be less than 13 nm. The biocompatibility of the coatings was characterized using in vitro incubation testing in simulated body fluid and osteoblast cell culturing. It showed that the presence of the nanostructures in the coatings improved the stability of the coatings (delayed the dissolution). The addition, the presence of the nanostructures contributes to improved mechanical properties.
Development of Highly Wear Resistant Iron Based PTAW Hardfacing Alloys
Authors: Branagan D. , Marshall C. , Meacham B.
Published: August 2022

Typically, highly wear resistant PTA materials for mining and mineral processing applications are developed by adding ceramics like tungsten carbide to appropriate matrices. The problem is that failure during abrasion can often occur as a result of preferential wearing of the soft matrix material or crack formation through the highly loaded brittle ceramic phases. In this paper, the development of new highly wear resistant plasma transferred arc (PTAW) iron based alloys will be detailed. In this case, the matrix material itself was found to have excellent abrasion resistance with high hardness obtained in the weld deposits up to Rc 66 from the development of a fine structure consisting of a high volume fraction of complex M23(BC)6 and M7(CB)3 borocarbides phases. The matrix material is found to additionally exhibit high toughness up to 73.3 MPam1/2 due to an effective distribution of fine carbide and boride phases in a ductile dendrites / cells. When adding WC particles to the starting powder and welding, the matrix was found to effectively wet the WC particles forming a strong tough matrix which avoids the typical “pull-out” or cracking found in conventional PTAW hardfacing materials. Specific weight loss measurements were conducted using ASTM G-65 wear testing and will be correlated to the structure achieved during PTAW. Abstract only; no full-text paper available.
New Concepts for Plasma Sprayed Zirconia TBCs for Aeronautical Applications
Authors: Tricoire A. , Vardelle M. , Fauchais P. , Braillard F. , Malié A. , Bengtsson P.
Published: August 2022

The aim of this work, devoted to yttria stabilised zirconia (YSZ) thermal barrier coatings, is to produce by DC plasma spraying a single thick pass macro cracked orthogonally to the substrate. YSZ was plasma sprayed in air atmosphere on Hastelloy X substrates, with a NiCrAlY bond coat. A three-zone microstructure is observed, where lamellae and columns are present. The measurements of deposition stresses during spraying allow explaining the macrocrack formation.
Formation of TiN-Al2O3-ZrO2 Composite Coatings by Gas Tunnel Type Plasma Spraying
Authors: Kobayashi A.
Published: August 2022

High performance Thermal Barrier Coating (TBC) has been expected for use under extream conditions in advanced industrial fields. A high performance of zirconia (ZrO2) composit coating was achieved by gas tunnel type plasma spraying. The zirconia-alumina (ZrO2-Al2O3) composite coating has a high hardness layer at the surface side of the coating, which shows the graded functionality of hardness, and is expected to use as a Thermal Barrier Coating (TBC). TiN thick coatings which has excellent properties have also been formed at high deposition rate by means of the gas tunnel type plasma reactive spraying. In this study, the fundamental characteristics of this method were investigated by measuring the properties of the titanium nitride (TiN) coatings formed on traversed stainless steel substrate. Some coating characteristics of TiN which depend on the spraying distance, the environmental gas, traverse number etc. were then clarified. The functionally graded property of the ZrO2-Al2O3 composite coating was clarified to make TiN-Al2O3 -ZrO2 Composite Coatings. The TiN coating was overcoated on the ZrO2-Al2O3 coating, in order to enhance the performance of such high hardness composite coating. The Vickers hardness of the TiN layer was increased at the coating surface, which corresponded to the result that the coating surface became dense. The graded functionality of the hardness in the thickness direction was increased remarkably in the TiN-Al2O3 -ZrO2 Composite Coatings by Gas Tunnel Type Plasma Spraying. In addition, the performance of TiN thick composite coating was discussed as a heat resistant TBC.
Thermal Conductivity Evaluation and Comparsion of APS Low Density and Dense Vertically Segmented Advanced Thermal Barrier Coatings
Authors: Bolcavage A. , Feuerstein A. , Hitchman N.
Published: August 2022

This study on ceramic thermal barrier coatings (TBCs) presents baseline thermal conductivity data on as-deposited 7-8 wt.% YSZ and a paired-cluster rare-earth oxide doped YSZ, prepared using air plasma spray (APS). The thermal diffusivity for each coating was measured up to 1100°C using the laser flash method, and from these values, the thermal conductivity was calculated. The maximum benefit for thermal conductivity reduction in TBCs with a (GdO2, Yb2O3)-doped YSZ composition was highest for APS dense, vertically macrocracked microstructures, whereas in the case of low density APS TBCs, the reduction in conductivity was found to be more strongly influenced by horizontally-oriented, sub-critical defects and porosity within the coating microstructure.
A Comparison of Cr3C2-NiCr Coatings Obtained by HVOF using Propylene and Hydrogen as Fuel Gases
Authors: Guilemany J.M. , Espallargas N.
Published: August 2022

Due to its oxidation resistance, HVOF thermal sprayed Cr3C2-NiCr coatings have been widely used for wear resistance at elevated temperatures up to 850ºC. During HVOF spraying deposition, compositional degradation occurs through dissolution of the carbide phase into the metal matrix. The occurrence of carbide dissolution and the high working temperatures affects on the final properties of the coating. The aim of this work is to study the effect on the structure and wear properties at elevated temperatures of Cr3C2- NiCr coatings using hydrogen as a fuel gas against propylene. The structural characterization was done by SEM-EDS, XRD, and Scanning White Light Interferometry (SWLI). Wear properties at room and high temperatures have been evaluated by Ball-on-Disk (ASTM G99-90). Oxidation resistance of all coatings was carried out using a calorimetric technique Abstract only; no full-text paper available.
Properties of HVOF Sprayed Multi-Scale Polymer/Silica Composite Coatings
Authors: Gupta V. , Knight R. , Ivosevic M. , Cairncross R.A. , Twardowski T.E. , Taghizadeh S.
Published: August 2022

The high velocity oxy-fuel (HVOF) combustion spray process has been demonstrated to be a suitable technique for the deposition of nano-reinforced polymer matrix composite coatings by controlling both the particle dwell time and the substrate temperature. HVOF-sprayed polymer matrix composites incorporating reinforcements with size scales ranging from 7 nm to 100 µm are being studied to bridge between the nano and conventional scale regimes. Microstructural characterization has been used to characterize the dispersion and distribution of the ceramic reinforcements within the polymer matrix. The effect of particle size distribution on reinforcement dispersion and distribution has been studied, and the influence of substrate temperature on coating adhesion has also been investigated. Changes in crystallinity, as determined by Differential Scanning Calorimetry (DSC), are being correlated to coating microstructure, reinforcement loading and process parameter variations. Results of optical and scanning electron microscopy, scratch testing and DSC characterization of the feedstock materials and sprayed coatings are presented. Coatings of nominal 60 µm Nylon 11 with 10 vol. % of nano and micron size hydrophilic silica reinforcements exhibited a ~22 % improvements in scratch resistance compared to pure Nylon 11 coatings. An ~15 % improvement in scratch resistance was obtained for coatings containing 10 vol. % nano scale hydrophilic silica reinforcement.
Carbide Containing Materials for Hard Chromium Replacement by HVOF-Spraying
Authors: Kirsten A. , Oechsle M. , Moll R.F.
Published: August 2022

Hard chromium, electrochemical deposited, is a widely used and established coating solution for surface protection against wear and corrosion as well as for decorative applications. Due to the possibility to coat bulk goods also, this technique is well suitable to protect small pieces and mass-produced goods. However, the most disadvantage of that technique is the appearance of highly carcinogenic hexa-valence chromium. Because of human health and environmental aspects the replacement of this coating technique is more and more required. At least for bigger parts with larger surfaces H(igh) V(elocity) O(xy) F(uel) -spraying can already produce competitive coatings to galvanic hard chromium with equal or even better properties. Especially thermal sprayed carbide coatings with in terms of corrosion resistance tailored metallic matrices offering the best potential to replace hard chromium in various applications. Beside of the material properties also the spraying conditions have essential influence on the corrosion resistance of those coatings. The present paper will give an overview of different carbide containing materials for HVOF-spraying and their properties with special respect to the replacement of galvanic hard chromium. The closest attention will be on the corrosion resistance of HVOF-coatings of those materials in different aqueous solutions compared with hard chromium. For a liquid fuel high velocity spraying system also the trends will be shown in which way the spraying parameters are influencing the general corrosion behaviour of such coatings. Those tendencies by conviction of the authors are also transferable to other HVOF systems.
Analysis of Thermal Fluxes Transferred by an Impinging HVOF Jet
Authors: Bolot R. , Verdy C. , Coddet C. , Cornu D. , Choulant M.
Published: August 2022

In the present paper, both CFD computations and experiments were carried out in order to quantify thermal fluxes from an impinging HVOF jet. The case of a CDS gun fed by natural gas is considered. Standoff distances ranging from 50 mm up to 300 mm were investigated. The CFD model implements a 2-layer extension to the Chen-Kim k-? turbulence model for a better quantification of thermal exchanges with the front body surface. Experiments were performed using two different methods. The first device incorporates two square calorimeters positioned side by side. It was elaborated in order to attempt defining the radial profile of the transferred thermal flux. Additionally, an infrared thermal camera was used to measure the front part surface temperature.
Nanoreinforced HVOF-Sprayed Ceramic Coatings
Authors: Turunen E. , Varis T. , Hannula S.-P. , Keskinen J. , Lintunen P. , Fält T.
Published: August 2022

HVOF thermal spraying has been developed to deposit dense Al2O3-coatings with improved protective properties for various applications. Nanocrystalline coatings have been found to offer better thermal shock resistance, lower thermal conductivity and better wear resistance than their conventional counterparts. In this paper we describe the development of nanocrystalline Al2O3 and Al2O3-Ni -coatings, where the grain size of Al2O3 has been decreased and a few percents of nickel has been added in order to toughen the coating. Coatings were manufactured by HV- 2000 HVOF using spray parameters determined based on the on-line spray diagnostics. Parameters were selected aiming at different melting stages of the powder. The resulting microstructure of the coatings and its influence on the coating properties is discussed
Influence of Post Heat Treatment on Microstructure and Wear Properties of Thermally Sprayed WC-Co Coatings
Authors: Vuoristo P. , Laurila J.
Published: August 2022

In this study we studied the influence of post heat treatment of thermally sprayed WC-Co coatings on coating microstructure, phase structure and wear resistance. The coatings were prepared from two different spray powders by detonation gun process, with two different spray conditions. The as-sprayed coatings showed very different microstuctures and wear properties. After heat treatment, the coatings showed very similar good wear performance, although the phase structures showed large differences. Abstract only; no full-text paper available.
High Rate Deposition of Protective Coatings by High Power Diode Laser (HPDL)
Authors: Naumann T. , Scharek S. , Nowotny S. , Vuoristo P. , Tuominen J. , Latokartano J. , Vihinen J.
Published: August 2022

Laser cladding is a surface treatment technology in which thick, dense and metallurgically adhered metallic layers are deposited on various structural steels with relatively low heat input, high accuracy and reproducibility. Laser cladding processes used in industrial cladding are largely based on the use of CO2 or Nd:YAG lasers. High power diode lasers (HPDL) with rectangular beam spots are regarded as ideal laser sources for laser cladding processes, due to their compact size, high electrical to optical efficiency, easy operation, and low investment and running costs. In laser cladding of large surface areas, the affectivity of the laser cladding process becomes more important, i.e. high laser powers, wide laser beam spots, and high coating material feedrates are regarded as beneficial. In order to optimise the cladding process for such applications, special attention has to be put on devices used to deliver the coating power to the process. In the present work, various parameters in effective HPDL cladding are described and new approaches to optimised HPDL cladding process are described. The performance of a new HPDL cladding powder delivery nozzle will be presented and discussed. Abstract only; no full-text paper available.
Characteristics of BSCCO Thin Films Fabricated by using the Layer by Layer Deposition and Evaporation Deposition Method
Authors: Cheon M.W. , Park Y.-P.
Published: August 2022

The BSCCO thin film fabricated by using the layer by layer deposition method was compared with the BSCCO thin film fabricated by using the evaporation method. Reevaporation in the form of Bi atoms or Bi2O3 molecules easily bring out the deficiency of Bi atoms in thin film due to the long sputtering time of the layer by layer deposition. On the other hand, the respective atom numbers corresponding to BSCCO phase is concurrently supplied on the film surface in the evaporation deposition process and leads to BSCCO phase formation. Also, it is cofirmed that by optimizing the deposition condition, each single phase of the Bi2201 phase and the Bi2212 phase can be fabricated, the sticking coefficient of Bi element is clearly related to the changing of substrate temperature and the formation of the Bi2212 phase.
Corrosion Resistance and Microstructure of Arc-Sprayed Zn-Al and Zn-Al-Mg Coatings
Authors: Liu Yan , Zi-Xin Zhu , Yong-Xiong Chen , Xu B. , Ma Shining , Li Z.
Published: August 2022

In this study, cored wires and high velocity arc spraying technique (HVAS) were applied to produce Zn-Al and Zn-Al-Mg alloy coatings on low carbon steel substrates. The microstructures and mechanical properties were studied by SEM, EDS, XRD, and Vickers micro-indentor. The electrochemical corrosion behaviors of Zn-Al and Zn- Al-Mg coatings were investigated comparing with Zn and Al coatings in 5%NaCl. The results show that, Zn-Al and Zn-Al-Mg coatings have good quality of uniform microstructure and low porosity. The corrosion resistance of Al coating deteriorated rapidly after nearly 16h immersion, and then kept at a relative stable value. In the contrast, the corrosion potential of the coatings containing Zn decreased a little and then increased towards the noble potential. The potentiodynamic polarization tests show that the icorr value of Zn-Al coating changed greatly at different steps, and it trended to increase continuously which may imply that the coating is easy to be corroded. Comparatively, no obvious change had been found in the Zn-Al-Mg coating which may indicate that the corrosion resistance enhanced with the addition of Mg, and the role of Mg appears to be associated with the self sealing process. Abstract only; no full-text paper available.
Stress Gradients in Plasma Sprayed Chromia Coatings
Authors: Dubsky J. , Materna A. , Chraska P. , Prask H.J. , Gnaeupel-Herold T.
Published: August 2022

It is generally known that plasma sprayed coatings exhibit rather a low strength thanks to their characteristic microstructure with porosity and microcracks. To determine the role of varying types of deformation in different parts of the coatings profile, 1.8 mm thick chromia coatings on a steel substrate were made using WSP plasma spray. Stress gradients were then measured "in-situ" on a four-point bending device during bend deformation of the coated beam using neutron diffraction. Only compressive loading in coatings increased the resulting stresses. From the plot of stresses vs. applied strain (linear dependence) the Young’s moduli of the substrate and the coating were determined. Both values agree well with those obtained by mechanical testing. In general it is believed that, in a simplified way, interlamellar voids (cohesion defects) roughly parallel to the substrate decrease the tensile strength in the direction perpendicular to the substrate, while intralamellar cracks, roughly perpendicular to the substrate, significantly affect the Young’s modulus of coating. It is supposed that the tensile deformation of coatings opens the cracks and no stress increase is observed. On the other hand the applied compressive deformation in the coating closes the intralamellar microcracks and the internal stresses increase, as suggested by obtained results.
High Crystallinity Degree Hydroxyapatite Coatings using HVOF Spraying
Authors: Fernández J. , Guilemany J.M. , Gaona M.
Published: August 2022

Biomaterial coatings must have high degrees of crystallinity and phase purity, good adhesive and cohesive integrity and adequate porosity to promote bone ingrowth. The most used coating method is atmospheric plasma spraying. However, the main drawback of this technique is the generation of an amorphous phase and other calcium phosphate phases after the spraying process, which are not present in the feedstock and are not desirable. The use of HVOF as a process for obtaining hydroxyapatite coatings on Ti-6Al-4V was used successfully. With optimised HVOF process parameters, coatings with similar bond strength to plasma sprayed HAp coatings, good microstructure and higher crystallinity degree than atmospheric plasma sprayed ones where hydroxyapatite was the only crystalline phase present were obtained. Coating characteristics were analysed with XRD, EDS, SEM, FTIR which indicated that the coatings had a high degree of crystallinity and good bond strength. Moreover, in vitro response were also evaluated and the strength of the coating to the substrate.
On the Influence of the Substrate Hardness on Cold-Sprayed Nickel Coating
Authors: Raletz F. , Ezo’o G. , Brenot P. , Vardelle M.
Published: August 2022

Cold spray process is an emerging technique that produces high density coatings. Particles are carried by a supersonic gas stream through a De Laval nozzle and, finally, impact on a substrate with high kinetic energy. Low gas temperatures make it possible to maintain sprayed material in solid state during the whole process. Beyond a given velocity, called “particle critical velocity”, particles can bind to the surface and create a coating. This velocity is clearly dependent on both sprayed material and substrate properties. This study deals with the investigation of the influence of the substrate hardness on nickel coating properties. Substrates with different hardness but same chemical composition were used. Samples are then coated with pure nickel or NiCrAlY under the same operating conditions. The measurements of some coating properties and process parameters (deposition efficiency (D.E.), level of porosity, micro hardness) allow the analysis of the effect of substrate hardness on sprayability. It was found that only D.E. is widely influenced by hardness of the substrate. It decreases drastically (especially for NiCrAlY) since hardness of the substrate is higher than hardness of the particle. Porosity level and coating hardness remain constant whatever substrate hardness is.
Study of Laser Ablation in Conjunction with Wire Arc Spraying of Al-5Mg Coating Onto 7075 Al Alloy
Authors: Arsenault B. , Gougeon P. , Coddet C.
Published: August 2022

In order to broader thermal spraying applications and reduce constraints and time due to conventional surface preparation before thermal spraying, the PROTAL process was developed over the last decade. This process integrates laser ablation, using a Q-switched Nd-YAG laser to prepare the surface simultaneously to the coating build-up during Plasma or HVOF Spraying. The present paper aimed at evaluating the feasibility to use the Protal technology in conjunction with the Twin Wire Arc deposition (Arc spraying) onto the 7075 Aluminum based alloy and to define the optimal Protal process parameters. Coating adhesion, micro-gap at coating-substrate interface and the coating residual stresses are evaluated. The Protal parameters investigated are: the laser energy density onto the substrate and the coating layers, the number of laser passes and the time delay between the laser impact. This study results indicate that it is feasible to use the Protal technology in-situ with the Arc spray process in spite of the challenging overspray and the large plume size of the Arc process. Good adherence and absence of interface micro-gap is obtained with an appropriate range of laser energy density to ablate the substrate. The use of a low energy ablation prior each coating layers reduces coating tensile residual stresses and improves furthermore the bond strength. The elimination of the process ablation dust and overspray dust prior the coating deposition onto the plane substrate was found critical to obtain a good bond strength. This research results from collaboration between the LERMPS in France and National Research Council Canada. Abstract only; no full-text paper available.
Suitability of High Power Diode Laser for Plasma-Augmented-Laser-Cladding (PALC)
Authors: Wilden J. , Bergmann J.P. , Aicher M. , Dolles M.
Published: August 2022

Laser cladding offers several advantages as low dilution, low thermal influence and distortion of the components and a fine microstructure due to the high cooling rate. Nevertheless the set of laser cladding in the industrial production is nowadays limited to few applications, as the efficiency of laser sources is still too low and the running costs are too high. The absorption behaviour of metal surfaces, as for example steel, towards diode laser (up to approx. 42%) is very high compared to Nd:YAG (approx. 35%) and CO2-Laser sources (approx. 11%), so that some benefits can be expected. One of the disadvantages of diode laser was the low intensity and the difficulty to couple it in a fibre. The development of the last years reached to overcome these boundaries. High power diode lasers are nowadays available till 6 kW and can be coupled in fibres, allowing an easier processing. Investigations regarding laser alloying with high power diode laser confirm the appreciable reliability of this laser class. In order to improve efficiency of laser surface processing the hybrid process plasma-augmented-laser-cladding (PALC) with an Nd:YAG laser source was presented and confirmed that due to the pre-heating of the powder through the plasma transferred arc and the activation of the metallic surface a higher processing velocity (factor three) and efficiency could be reached by summing only one third of the energy with a PTA-equipment. Further more when processing with higher velocity the energy loss due to conductivity decreases so that a further positive increase of efficiency can be depicted. The suitability of fibre coupled high power diode laser for PALC hasn’t yet been investigated, even if the set of this laser type would be very advantageous. In this paper investigations regarding the process design and the necessary set up of the hybrid PALC-process with a 3 kW fibre coupled high power diode laser and wire coating metal are reported.
In-Flight Particle Diagnostic of Water Stabilized Plasma Spray Process
Authors: Chraska T. , Neufuss K. , Oberste-Berghaus J. , Lamontagne M. , Moreau C.
Published: August 2022

Individual particles of various ceramic materials sprayed by water stabilized plasma torch (WSP) were characterized in flight by an optical sensing device DPV-2000. Temperature, velocity, and diameter of individual particles were measured at the center of particle plume and maps of the particle plume cross-section were acquired as well. Plasma jet and consecutively particle plume of the WSP torch is much larger compared to gas stabilized torches and even larger than the maximum span of the DPV-2000 sensing head. In summary, temperatures of particles varied from 2000 to 2600°C and their velocities from 60 to 140 m/s depending on the powder feedstock cut size, particle density, feeding distance, spraying distance, and feed rate. The last three parameters were varied to study their effect on the particle states and their distribution in the plasma jet and to correlate these results with selected properties of the corresponding coating. Some of the spraying parameter effects are difficult to interpret, nevertheless, general trends have been established.
Characterization of the Particle Jet of Different HVOF Guns by Means of LDA
Authors: Wank A. , Wielage B. , Grund T. , Rupprecht C. , Zimmermann S. , Landes K.
Published: August 2022

For constant conditions concerning substrate state, feedstock and environment properties of thermal spray coatings depend only on temperature and velocity of particles at impact on the substrate. Two different HVOF spraying guns, the kerosene fuel system Tafa JP5000 with radial powder injection and the ethylene fuel system Sulzer Metco Diamond Jet Hybrid 2700 with axial powder feeding, are characterized concerning the evolution of space resolved velocity and density of particles by LDA. Also influence of process parameter variations is examined. The region of shock diamonds is studied specifically. The influence of different characteristics concerning impact velocity and trajectories on the coatings microstructure is determined by means of optical microscopy and microhardness testing.