bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical Properties and Microstructure of HVOF Sprayed Co and Ni Alloy Coatings
Authors: Zhang D. , Harris S.J. , McCartney D.G.
Published: September 2022

A high velocity oxy-fuel spraying system using liquid fuel (HVOLF) has produced Stellite 6 (CoCrWC) and NiCoCrAlY coatings from gas atomised powders of both alloys. Comparative coatings were prepared by weld 0verlay (Stellite 6) and vacuum plasma spraying (VPS) of NiCoCrAlY. The original powders and coatings were characterised by Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD). The presence or absence of cored dendritic microstructures in etched surfaces was used to interpret the degree of melting which took place during spraying, i.e. >80% in VPS and <20% in HVOLF. Low levels of oxide were formed in HVOLF coatings due to the reduced level of thermal transfer during the short heating cycle involved in spraying. For the same reason less melting occurred which permitted sufficient plastic deformation of the solid fraction to occur, reducing voidage between particles and then allowing the liquid fraction to weld them together. This pattern of short cycle heating with both NiCoCrAlY and Stellite 6 particles influenced second phase formation. In NiCoCrAlY coatings the β (Co Ni Al) phase remained as relatively coarse precipitates in the as - sprayed condition whilst in Stellite 6 little carbide eutectic formed. HVOLF spraying can produce coatings with different hardness values when compared with VPS coatings and weld overlays. This may widen the range of coating applications as well as reduce costs.
Experimental Correlation between Flattening Degree and Reynolds Number of Spray Particles
Authors: Li C.-J. , Liao H.-L. , Gougeon P. , Montavon G. , Coddet C.
Published: September 2022

The particle parameters including particle size, velocity and temperature influence significantly splat formation process in thermal spraying. The flattening degree of subsequent splat determines the coating structure and properties. Both theoretical analysis and simulation of splatting process indicate that the flattening degree depends on Reynolds number (Re) of spray particles. The experimental correlations suggest that the theoretical models overestimate the flattening degree. In the present study, with careful control of particle size and measurement of particle velocity and temperature, the relationship between the flattening degree and particle Reynolds number is examined experimentally. Copper powders of small size range are used to ensure valid of mean particle size. Plasma spraying is carried out under different conditions to change particle velocity and temperature. The particle velocity and temperature are measured using DPV- 2000. Splats were deposited on preheated polished stainless substrate surface. The diameter of individual splat was measured. The flattening degree was estimated using average diameter of splats and spray particles for individual spray condition. Using the exponential formula of Re with a power of 0.2, it was found that experimental correlation yielded a coefficient about half of that given by Madjeski’s model.
Evaluation of Sn and Al2O3 Splats by Fractal Geometry
Authors: Hikari R. , Amada S. , Uematsu S.
Published: September 2022

The quality of thermal sprayed coatings greatly depends on the individual flattened splats. Generally they are characterized by two main factors, flattening ratio and splat profile. The flattening ratio is specified straightforward, but it is difficult what factor should be selected from the various properties for the splat profiles. Fractal geometry is introduced to the profile evaluation of the splats which are formed by the free-fall metal droplets and by the alumina coatings using plasma spraying method. The fractal dimension of each splat was measured by SIA (Slit Island Analysis) technique which measures the ratio of area to contour length of the island appeared on the horizontally sliced plane of the splat. The obtained fractal dimension was related to with Re and We numbers in a bi-linear form, which is the same characteristics as the unevenness ratio obtained previously. It was concluded that fractal dimension is an effective measure to evaluate the splat profile.
Effect of Reynolds Number of Molten Spray Particles on Splat Formation in Plasma Spraying
Authors: Li C.-J. , Liao H.-L. , Gougeon P. , Montavon G. , Coddet C.
Published: September 2022

A thermal spray coating is formed through successive impact, flattening, rapid cooling and solidification processes of a stream of spray droplets. Splashing may occur during droplet flattening process. Recent studies suggested that splashing can be suppressed when a molten droplet impacts on a preheated flat substrate. In this study, the splatting behavior in plasma spray is examined using molten spray droplets of different Reynolds number. Splats are deposited on preheated flat stainless steel surface. The morphology of splats is examined using optical microscopy and scanning electron microscopy. To adjust Reynolds number of spray droplets, copper droplets are produced using both Ar-H2 and Ar-He-H2 plasma jets under different operating conditions. As a result, the Reynolds number of spray droplets have been varied from about 18,000 to 90,000. It has been found that Reynolds number will influence splashing phenomena during splatting and consequent splat morphology. At low Reynolds number, splats present a regular disc morphology. However, when Reynolds number was increased up to about 5x104, the severe splashing around periphery of splat droplet was clearly observed despite the preheating of substrate. Based on the morphology of splats, a model for the spreading of molten droplet is proposed to explain the effect of Reynolds number on the flattening behavior of molten spray droplet.
Influence of Substrate Temperature on Formation of Micrometric Splats Obtained by Plasma Spraying Liquid Suspension
Authors: Fazilleau J. , Delbos C. , Violier M. , Coudert J-F. , Fauchais P. , Bianchi L. , Wittmann-Ténèze K.
Published: September 2022

A new thermal spray process is under development in order to produce thin coatings (thickness lower than 50 µm), with a fine microstructure (grain size smaller than 1 µm). It consists in injecting in a Direct Current (D.C.) plasma jet a suspension containing submicronic particles of the material to be deposited. To study the interaction between the plasma jet and the suspension, a system based on a pendulum allows the collection of particles at different distances from the injection point. In this paper the effect of substrate temperature upon the formation of micrometric zirconia splats was studied, glass and stainless steel were used as substrate materials.
Partially Melted Particle and Its Splat Morphology
Authors: Zhang H. , Xiong H.B. , Zheng L.L. , Vaidya A. , Li L.
Published: September 2022

The melting behavior of in-flight particle and its impact on splat morphology are studied. A group parameter, “melting index”, has been derived to correlate the melting status of inflight particles with particle size, velocity, and temperature which can be measured experimentally. Numerical simulations have been used to determine the unknown parameters in the melting index. The effect of particle size on its melting behavior has been investigated.
Synthesis of BCN Coatings in Thermal Plasma Jets
Authors: Wank A. , Wielage B.
Published: September 2022

The system B-C-N contains the hardest known materials like diamond, cubic boron nitride and boron carbide, which also show excellent chemical resistance. The oxidation resistance is shifted to higher temperatures in comparison to pure diamond. But pure BCN coatings cannot be produced by conventional thermal spray processes, as the materials lack both a liquid phase and sufficient ductility to permit deposition. Conventional VPS equipment is successfully applied in Thermal Plasmajet CVD processes for high deposition rate synthesis of diamond coatings. The feasibility of SiCN or boron carbide synthesis by this method has also been proven. The use of liquid precursors results in outstanding deposition rates and improved operational safety. Methylized borazine is applied for synthesis of BCN coatings in thermal plasma jets. The use of single source precursors is advantageous with concern to the homogeneity of the coating forming species stoichiometry. For long-term storage cooling is necessary, but also under ambient conditions the precursor shows sufficient stability. Plasma gun nozzles with different diameter and design are applied and evaluated with concern to the resulting coating properties. Deposition rates of up to 1,500 µm/h have been achieved with homogeneous coating thickness and morphology on areas with 50 mm diameter. No porosity is detected in SEM investigations on cross sections and fracture surfaces show a fine columnar coating morphology. XRD investigations point at an amorphous structure. Only for very high substrate temperatures the formation of crystalline boron carbide B8C and h-BN or graphite phases is detected. Oxygen contamination results in boric acid formation and therefore has to be avoided carefully. During coating deposition on mild steel substrates the formation of boride and nitride reaction zones is observed. VPS sprayed nickel or molybdenum interlayers permit to inhibit the evolution of reaction zones. Thereby BCN coatings with thicknesses of up to 10 µm are deposited without local delamination. Space resolved emission spectroscopic analyses are carried out in order to detect coating forming and intermediate species. As Thermal Plasmajet CVD is a pure gas phase deposition process, the control of the space resolved emission permits easy process control.
Research on Fluid Properties of Low Energy, High Efficiency and Non-transferred Arc Plasma Jet
Authors: Yan Zhijun , An Liantong , Gao Yang , Huang XiaoOu
Published: September 2022

A mathematical model was used to describe the fluid flow, electromagnetic and heat flow of the plasma jet in the non-transferred model. A computer program has been developed to simulate the fluid properties of the low energy and high efficiency plasma jet. The numerical results approximate the measurements by using the enthalpy probe.
Neural Networks, Design of Experiments and Other Optimization Methodologies to Quantify Parameter Dependence of Atmospheric Plasma Spraying
Authors: Guessasma S. , Montavon G. , Coddet C.
Published: September 2022

Off-line control of thermal spraying generally implements the quantification of the energetic, environmental, injection and geometric conditions. The interdependence of these parameters with regard to the deposit properties were studied with different statistical methodologies. The aim was to point out the large possibilities of the Artificial Neural Network methodology in the process optimization. In that way, experiments were designed considering atmospheric plasma spraying and the following operating parameters: arc current intensity, powder feed rate, carrier gas flow rate, total plasma gas flow rate, primary hydrogen content and scanning step. These parameters were related to the coating porosity level and hardness (HK). For each case, simple correlations were studied with none linear regressions, design of experiments and a Multilayer Perceptrons (MLP, with two hidden layers). Non linear correlations were compared with MLP based on the Average Sum of Absolute Error (ASAE) and other correlation factors (RSS, R2, Ra2, STD, RS and AR).
On the Study of the Thermal Fluxes Transferred during the HEATCOOL Process
Authors: Bolot R. , Deng H. , Liao H. , Coddet C.
Published: September 2022

A study of thermal fluxes transferred during the HEATCOOL process is proposed. The concept of this process, specially designed to enhance the residual stresses relaxation, consists in the use of a consecutive three-step procedure during the coating elaboration (heating / spraying / cooling). The present study focuses on thermal exchanges occurring during the heating step. For this, the elaborated experimental equipment incorporates a series of ten holes aligned equidistantly with 5 mm separation. A burning gas mixture (premixed acetylene and oxygen) is injected through these holes and the burning gas jets impinge and heat the substrate. The stand-off distance between the heating device and the substrate may be adjusted between 30 and 90 millimeters. Concerning thermal fluxes transferred using this experimental device, a front work piece incorporating several thermocouples was used to perform heat flux measurements. In a first step, the case of a single hole was considered. Since this method is not able to provide the thermal flux directly, the corresponding thermal fluxes were deduced using an inverse heat conduction problem method that was specially developed. Results obtained using this inverse problem method based on experimental measurements are then compared with numerical predictions obtained using a computational fluid dynamic model representing the system. For this part, the PHOENICS software was used to perform the corresponding computations.
Conjugated Gradient Method for Estimating Inversely the Flux Distribution of Cooling Jets
Authors: Liao Hanlin , Deng Hao , Coddet Christian
Published: September 2022

It is necessary to cool specimens during spraying in the case APS or HVOF, because process-induced heat rises the specimen temperature and leads to oxidation and spalling of coatings. A reasonable cooling just after spraying improves some properties such as microhardness, adhesion and cohesion of the coating/substrate system. In the modelling of specimen temperature and residual stress, it is necessary to know the flux distribution of the cooling jet like compressed air, CO2 liquid jet etc. Therefore, the evaluation of the flux becomes important. In order to measure and analyse the distribution of cooling flux imposed on the substrate, the theory of the inverse problem of heat conduction was applied and an experimental apparatus was designed to mesure the transient temperature. Because of its insensibility to the effect of measuring error, the conjugate gradient method, an effective method of inverse problems was chosen among several mathematical optimisation methods. The flux distributions of cooling jet can be estimated by using the measured data and a program written according to the conjugate gradient method.
In-Flight Oxidation of Metallic Particles in Plasma Spraying
Authors: Syed A.A. , Denoirjean A. , Deniorjean P. , Labbe J.C. , Fauchais P.
Published: September 2022

Air engulfment by the plasma jet in Air Plasma Spraying (APS) causes in-flight oxidation of metallic particles. This oxidation, often complex and difficult to explain by classical diffusion-controlled oxidation, is governed by several mechanisms. This paper highlights the possible in-flight oxidation mechanisms in metallic particles with a focus on convective oxidation. Two different types of austenitic stainless steel particles, Metco 41C (-106+45 µm) and Techphy (-63+50 µm) were air plasma sprayed using a dc plasma gun (PTF4 type) and were collected in an argon atmosphere. Preliminary experiments indicated that different mechanisms are likely to occur during the in-flight oxidation of particles. Mass transfer from surface to interior of particle occurred forming oxide islands in particles. The mass transfer is governed by convective movements inside liquid particles within plasma jet core due to higher plasma-particle kinematic viscosities ratio and particles Reynolds number higher than 20. The islands were composed of metastable phases consisting of mixed oxide of Fe and Cr, likely in a nonstoichiometric form of FeCr2O4. Convective movements within particles cease roughly outside of the plasma jet core and classical surface oxidation was found to be the dominating phenomenon forming the surface oxide layer. Moreover, the molten surface oxide outside the jet core is entrained to the tail of the particle if plasma conditions promote higher particle temperature, velocity and Re number.
Insights to Spraying Conditions, Microstructure and Properties and Their Statistical Correlation for Different Thermal Spraying Processes Using Complementary Characterization Methods
Authors: Margadant N. , Siegmann S. , Keller T. , Wagner W. , Kulkarni A.
Published: September 2022

In many empirical studies on the structure and properties of thermally sprayed coatings, a set of two predefined parameters (e.g. porosity and elastic modulus) is correlated over a narrow range of structural variation assuming a continuous correlation function. Such a data evaluation assumes the existence of physical correlation’s between material behavior and microstructure. The experimental approach, undertaken in this study, comprises a maximum range of morphologies for starting materials with nearly identical chemical compositions to reveal the influence of microstructural changes of diverse defect species on different coating properties. The large matrix of structural and physical data is statistically correlated without any preconceived assumptions concerning the mathematical functions or the physicochemical nature of the property-microstructure-correlation’s. The divergent morphologies are realized by using different coating processes such as vacuum (VPS) and atmospheric (APS) plasma spraying, water stabilized plasma spraying (WSP), wire arc (WAS)- and flame spraying (FS), including variation of process specific parameters. The microstructure is systematically analyzed along length scales starting from defects in the micrometer down to the nanometer range. The microstructure and its anisotropy is quantified by small angle neutron scattering (SANS). The phenomenological coating behavior is successively investigated starting from basic properties such as electrical and thermal conductivity, elastic constants, residual stresses up to application oriented properties such as wear resistance. Property combinations presuming high sensitivity to microstructural changes are preferentially characterized and statistically correlated.
Field Electron Emission from Surface of Plasma Sprayed and Laser Engraved AI2O3+13TiO2 and Al2O3+40TiO2 Coatings
Authors: Znamirowski Z. , Czarczynski W. , Campana F. , Janssen J.-P. , Rivenet M. , Vannier R.-N. , Pawlowski L.
Published: September 2022

The powders of alloys Al2O3+13wt.%TiO2 and Al2O3+40wt.% TiO2 were plasma sprayed onto aluminum rolls coated initially with Ni20Cr bond deposits. The coatings were subsequently ground, polished and submitted to laser engraving. The engraving, similar to that applied for anilox rolls manufacturing, enabled production of three different patterns with the line densities of 60, 100 and 200 1/cm and depths of about 80, 50 and 10 µm correspondingly. The patterns were engraved under angle of 60° that corresponds to a honeycomb geometry of cells. Emission current, for the electric fields up to 150 V/µm, was in the range of 10-7-10-4A for coatings containing 13 wt.% of titania and, in the range 10-11–10-9 A for that of 40 wt.% of titania. The SEM observations of engraved coating morphology was made in order to find the electron emission spots.
Effect of Particle Size and Spray Distance on the Features of Plasma Sprayed Cast Iron
Authors: Morks M.F. , Shoeib M.A. , Tsunekawa Y. , Okumiya M.
Published: September 2022

Superior wear resistance property of cast iron coatings is strongly linked to their microstructure. Graphite formation in plasma sprayed cast iron deposit is the main reason for this distinct phenomenon owing to its self-lubricant property. Since solidification rate affects graphite formation, optimization of spray conditions such as substrate temperature, chamber pressure, particle size and spray distance are required to slow down the solidification rate. The adhesion property of cast iron coating depends strongly on the adhesive strength between the first deposited layer and the substrate. It is important to improve the adhesive strength of splats by optimization of spray parameters. In this paper, cast iron splats were sprayed on aluminum substrate by plasma spray method using high Si and Al cast iron powders in Ar atmosphere. The effect of particle size and spray distance on splat microstructure (including graphite distribution) and its adhesive strength has been investigated. A correlation between microstructure and solidification rate was also introduced. Spraying by using large particle size leads to an increase in the number fraction of disk splats and a decrease in the splat’s adhesive strength. In contrast, the number fraction of star-shaped splats and their adhesive strength increase by spraying using small particle size. Longer spray distances lead to a decrease in number fraction of disk splats and their adhesive strength. The rear-side observation of cast iron splats sprayed with different spray distances show no distinct difference.
Effect of the Chamber Pressure on the Structure of a Plasma Jet
Authors: Bolot R. , Klein D. , Coddet C.
Published: September 2022

The aim of the present study concerns the effect of the chamber pressure on the structure of a plasma jet. Conventional vacuum plasma spray equipments are currently designed to operate at chamber pressures higher than 10 mbar. Nevertheless, recently, the exploration of lower pressure level conditions seems to have become a new challenge. In the present study, pressure levels as low as 0.5 mbar have been achieved and tested. It is shown that a decrease in the chamber pressure provides a longer and enlarged plasma jet whose length may be longer than one meter for the lowest pressure levels considered. CFD modeling results and photographs performed under vacuum conditions are proposed for the case a standard conical nozzle. Some additional characterizations (using thermocouples and emission spectroscopy) were also conducted but the results are currently being analyzed.
Control of Particle Temperature, Velocity, and Trajectory in the Thermal Spray Process
Authors: Fincke J.R. , Swank W.D. , Bewley R.L. , Haggard D.C. , Gevelber M. , Wroblewski D.
Published: September 2022

The plasma-spray process features complex plasma-particle interactions that can result in process variations that limit process repeatability and coating performance. This paper reports our work on the development of real-time diagnostics and control for the plasma spray process. The strategy is to directly monitor and control those degrees of freedom of the process that are observable, controllable, and affect resulting coating properties. This includes monitoring of particle velocity and temperature as well as the shape and trajectory of the spray pattern. Diagnostics that have been developed specifically for this purpose and integrated with a closed loop process controller are described.
Sensitivity Study of Four On-Line Diagnostic Systems for Plasma Spraying
Authors: Nylén P. , Lemaitre J. , Wigren J.
Published: September 2022

The introduction of sensor techniques has lead to a major change in the possibility to on-line control the plasma spraying process. By the use of such techniques reproducibility of the process can be enhanced by a more precise process control of flame and particle in-flight characteristics. In this paper a comparative study of four different on-line diagnostic systems and their sensitivity is presented. The systems evaluated are: the Particle Flux Imaging (PFI) from Zierhut Messtechnik GmbH, the PlumeSpector from Tecnar Automation Ltee., the Spray and Deposit Control (SDC) from the University of Limoges/Snecma Inc. and the DifRef M from Flumesys GmbH. Tests were performed using plasma spraying of a Nickel- Aluminium alloy. A statistical design of experiments (DOE) was defined using a ± 5% variation of the five process parameters current, argon flow rate, hydrogen flow rate, powder feed rate and carrier gas flow rate. System principles, sensitivity results are given and the systems suitability for use in industrial production is discussed.
Particle Temperature and Velocity Measurements by Two-Wavelength Streak Imaging
Authors: Craig J.E. , Parker R.A. , Lee D.Y. , Wakeman T. , Heberlein J. , Guru D.
Published: September 2022

A two-wavelength particle imaging sensor has been developed to measure temperature and velocity of individual particles in most thermal spray devices. The sensor provides continuous updates to particle condition profiles, histograms and correlation’s. The software locates particle streaks, determines the intensity ratio and dimensions of each streak, and calculates the particle temperature and velocity. Many forms of advanced materials processing technologies, such as thermal spray, spray-forming and atomization have considerable need of process control sensor technology. These measurements provide the basis for application of the sensor to many of these processes. Particle temperature and velocity measurements of plasma-sprayed ceramic powder were obtained using the sensor. The average temperature varied from 2800 K to 3000 K as the current to the plasma was increased from 700 amps to 900 amps. The average velocity varied from 85 m/s to 99 m/s over the same range. These results compare favorably with similar measurements, reported in the literature. With its full-stream field of view, the vision-based particle sensor can be applied to control strategies for the purpose of providing stable particle temperatures and velocities over long duration plasma spray processes.
Simple Self-Selective Method of Velocity Measurement for Particles in Spray Coating
Authors: Lebedev M. , Akedo J.
Published: September 2022

A simple, low-cost technique for measuring the velocity of particles for spray coating methods is presented. The accuracy of measurement is determined by the precision of the only quantity of geometrical size of the deposited layer. Self-selection of the particles with parameters suitable for deposition occurs. For typical deposition conditions, a velocity of 650 m/s was detected. This technique allows in situ velocity monitoring during process.
Real-Time Control for Plasma Spray: Production Issues and Distribution Implications
Authors: Gevelber M. , Cui C. , Vattiat B. , Wroblewski D. , Fincke J.R. , Swank W.D.
Published: September 2022

This paper investigates the advantages that an advanced control system can provide for plasma spray deposition in terms of variation reduction and greater ability to engineer coating structure. We report our work on implementing a feedback control system that automatically adjusts system inputs to maintain the desired particle states in spite of process variations. The limitations and performance capabilities of both feed forward and real-time control are evaluated. Important system characteristics needed to develop such controllers are discussed including dominant nonlinearalities, dynamics, cross-coupling, distributions, and sensor issues. Performance is evaluated in terms of engineering coating structure and production objectives.
Integration of a Feedback Controller into a Standard In-Flight Particle Sensor
Authors: Blain J. , Pouliot L. , Nadeau F. , Bisson J.-F. , Vaudreuil G. , Moreau C.
Published: September 2022

This paper first presents some typical results that illustrate the need for closed-loop stabilization of plasma spraying processes. A strategy to identify the most efficient control actuators is then explained, followed by a description of a robust operator closed-loop feedback method. This method can be directly implemented on current commercial sensors and applied to older spraying equipment than cannot easily be interfaced to modern computers. The method is also capable of implementing tight computer-controlled closed-loop feedback on more modern equipment. A discussion of minimum sensor requirements is also given.
Modern Gas Supply Systems for Thermal Spraying
Authors: Park Dave , Krömmer W. , Heinrich P.
Published: September 2022

Industrial gas product supply has a dramatic influence on the quality, consistency, and performance of thermal spray coatings and their application equipment. The various thermal spray processes test the limits of common gas supply modes in the areas of safety, pressure, purity, storage, and recovery. Selection criteria for the gas and supply mode, using the latest methods, are discussed for plasma, HVOF and cold spray techniques.
How to Improve the Reliability and Reproducibility of Plasma Sprayed Coatings
Authors: Fauchais P. , Vardelle M.
Published: September 2022

This paper presents what is our actual knowledge in the development of the on-line control of the plasma spray process. First the influence of the different parameters on coating properties is recalled. The dependence of particle parameters at impact on macroscopic parameters such as the gas composition, its enthalpy, the injection conditions… is discussed together with the possible actions to compensate for the voltage drop due to electrodes erosion. The transient aspect of the plasma jet due to the arc root fluctuations and their consequence on particle parameters is also presented. Then the different sensors able to work in booths harsh environment are described. The way they are used, informations they provide, the possibility they give to monitor the spray parameters for a good working area is discussed. At last what would really be necessary for a real on-line control is presented and it is concluded that we are still far to achieve this objective.
The Influence of Spray Parameters on Ni20Cr Coating Properties Using On-line Optimization Process
Authors: Guilemany J.M. , Nin J. , Miguel J.R. , Navarro J. , Gaona M.
Published: September 2022

Thermal and kinetic history of particles inside the jet plume of atmospheric plasma spray (APS) provide the particles with a certain velocity and temperature prior to the impact onto the substrate. Adjusting these velocity and temperature allows to control final coating's properties. The properties of the obtained coatings mostly depend on particle's conditions prior to the impingement. A set of experiments were done in order to optimize an atmospheric plasma process by means of an online monitoring system. The study is done by changing some spraying parameters that certainly affect the velocity and the temperature of the in-flight particles. Plasma gas flow rates and spraying distance were the parameters changed in this work, whereas all the other spraying conditions were kept constant. On-line monitoring system Spray-Watch (Oseir Ltd.) was used to achieve the parameters optimization by the measurement of velocity, temperature and spatial distribution of the Ni20Cr inflight particles. The study of the coated samples includes microstructure characterization by means of Optical Microscopy (OM), Scanning Electron Microscopy (SEMEDS) and X-ray diffraction to study the effect of the spraying parameters in phase composition. Roughness measurements and mechanical properties are also included.
On-Line Monitoring Assisted Spray Process Optimization of Thermal Barrier Coatings
Authors: Tricoire A. , Legros E. , Vardelle A. , Ahmaniemi S. , Vuoristo P. , Mäntylä T.
Published: September 2022

The objective of this study is to increase the deposition rate in the plasma-spray manufacturing of thermal barrier coatings without altering the quality of the coatings. The experimental part involves the measurement of in-flight particle characteristics and analysis of coatings properties when varying the hydrogen content of the plasma-forming gas, the torch nozzle diameter and the powder feed rate. The experimental results of particle measurements are discussed in the light of the gas flow fields projected by a 3-D model of the plasma spray process.
Influence of Secondary Hydrogen on the Microstructure of Plasma-Sprayed Yttria-Stabilized Zirconia Coatings
Authors: Bisson J.F. , Moreau C. , Dorfman M. , Dambra C. , Mallon J.
Published: September 2022

The influence of secondary hydrogen and current on the deposition efficiency (DE) and microstructure properties of yttria-stabilized zirconia (YSZ) coatings was evaluated. In order to better understand the influence of the spray process on coating consistency, an YSZ powder, -125+44 µm, was sprayed with nitrogen/hydrogen parameters and a 9MB gun. DE and coating porosity produced using two different spray gun conditions yielding the same input power were compared. Amperage was allowed to vary between 500 A and 560 A and hydrogen was adjusted in order to maintain constant power, while nitrogen flow was kept at a fixed level. Several power conditions, ranging from 32 to 39 kW, were tested. Different injection geometries, i.e., radial with and without a backward component, were also compared. The latter was found to produce higher in-flight temperatures due to a longer residence time of the powder particles in the hotter portion of the plasma. Porosity was based on cross-sectional photomicrographs. In-flight particle temperature and velocity measurements were also carried out with the DPV-2000 for each condition. Test results showed that DE and coating density could vary significantly when a different hydrogen flow rate was used in order to maintain constant input power. On the other hand, DE was found to correlate very well with the temperature of the in-flight particles. Therefore, to obtain more consistent and reproducible DE and microstructures, it is preferable to maintain constant the in-flight particle temperature instead of keeping the input power constant by adjusting the secondary hydrogen flow rate for obtaining more consistent and reproducible DE and microstructures.
Production Experience of On-Line Diagnostic Systems in Plasma and Flame Spraying
Authors: Wigren J. , Nylén P.
Published: September 2022

In order to ensure reproducibility of thermal sprayed coating characteristics, process control by a sensor system is essential. Volvo Aero has more than 5 years experience of using different sensor systems in plasma and flame spraying. This article presents two examples where such systems have been used for quality control in production. In the first example the DPV2000 system was used in plasma spraying to control the tensile strength of an abrasive application. The study showed that the particle in-flight properties and the tensile strength were very sensitive to the carrier gas flow rate. In the second example the PlumeSpector system was used to control erosion and tensile strength in flame spraying of a composite powder composed of a core of Bentonite clay coated with a shell of NiCrAl alloy. The results show that the capability could be increased by a factor of two using on-line diagnostic control.
Fluid Dynamic Effects on Plasma Torch Anode Erosion
Authors: Sun X. , Heberlein J.
Published: September 2022

Anode erosion in plasma spray torches results in coating deterioration. The usable life of a torch anode is strongly dependent on the fluid dynamic behavior of the plasma inside the torch, which in turn depends on the geometric design of the anode and the operating parameters. In order to study the relative importance of these effects, cold flow investigations have been performed with a torch having a glass anode with the same geometric dimensions as a Praxair-TAFA SG 100 torch. The density differences between the arc and the cold gas were simulated by injecting heated helium from the tip of the cathode into the cold argon gas flow from the regular gas injector. Flow visualization was achieved by seeding the flow with micron-sized particles. A finite element CFD code was used to simulate the cold flow structure. The results were compared with erosion patterns observed with an actual plasma torch. The results indicate that recirculation eddies inside the torch will force a preferred anode attachment which is different for different gas injectors. Minimization of such recirculation regions by appropriate fluid dynamic design will result in more random attachment of the arc and prolonged anode life.
Microstructure and Properties of Micro-Plasma Sprayed Cu Coating
Authors: Li C.-J. , Sun B. , Wang M. , Han F. , Wu T.
Published: September 2022

Cu coating was deposited by microplasma spraying system under a low power of 2.8 to 4.2kW. The effects of the main processing parameters including plasma arc power, operating gas flow and spray distance on particle velocity during spraying, and the microstructure and properties of the coating were investigated. The coating microstructure was examined with optical microscopy. The coating properties were characterized by cross sectional microhardness. The particle velocity during in-flight was examined using a particle velocity/temperature measurement system based on thermal radiation. The experiment results showed that particle velocity was increased with the increase in operating gas flow, and was not influenced significantly by plasma arc power and spray distance. Moreover, the microhardness of the coating was increased with the increase in arc power and with the decrease in spray distance. The operating gas flow showed no significant influence on the microhardness of the coating. The analysis suggested that the microhardness of the coating is influenced significantly by particle temperature. The comparison showed that the microhardness of the Cu coating deposited by microplasma spray is comparable to that of the coating deposited by conventional plasma spray system at power level of 30kW.
Improvement of the Properties of Thermally Sprayed Ceramic Coating by the Infiltration of the Adhesives
Authors: Li C.-J. , Yang G.-J. , Ohmori A.
Published: September 2022

Thermally sprayed ceramic coating consists generally of porosity up to over ten percent. The existence of voids in the coating will degrade mechanical performance and corrosion resistance. The infiltration technique has been used to enhance the coating performance. In the present work, the adhesives of high strength are used as infiltrator for plasma sprayed alumina coatings to investigate the effect of the infiltration on the adhesive strength and erosion resistance. The adhesive strength of coating after infiltration is tested following ASTM-C-633 standard with the same adhesive. The commercial adhesives used are liquid types of adhesives. Alumina coatings are deposited by plasma spraying to a thickness about 500ìm. The adhesive strength of as-sprayed coating was tested using another epoxy resin adhesive. The test pieces are prepared without infiltration of adhesive into the coating. The results revealed that the infiltration of adhesive to alumina coating can improve significantly the adhesive strength and erosion resistance. The adhesive strength from 40 to 55 MPa can be obtained in spite of deposition conditions. The erosion resistance of the coating at 90 degrees can be improved by a factor about 3.
Optical Emission Spectroscopic Diagnostics of Atmospheric Argon Radio Frequency Inductively Coupled Plasma
Authors: Gao G. , Pershin L. , Mostaghimi J.
Published: September 2022

An experimental study is conducted to determine the property fields of 40 MHz argon radio frequency inductively coupled plasma using optical emission spectroscopy. The pure argon plasma was operated at the input power of 0.3 kW and under atmospheric pressure. 29 atomic argon lines with upper level energies ranging from 12.9 to 15.5 eV, continuum emission and line width are used to evaluate plasma parameters such as temperature and electron number density. Since 40 MHz plasma is in almost complete nonequilibrium, the validaty and accuracy of most usual spectroscopic methods are questioned. Analysis based on the Boltzmann diagram, line-to-continuum intensity ratio, population of continuum extrapolated level, and continuum intensity reveals the departure from thermodynamic equilibrium in the plasma. Among these methods, the Boltzmann diagram method is shown to provide reliable plasma excitation temperature as long as the Boltzmann plot is drawn based on enough spectra lines covering from infrared to ultraviolet regions. The continuum emission at wavelengths within visible region can give good estimation of the electron density by using excitation temperature in the continuum relation. The line-to-continuum is not a reliable method for the temperature measurement of nonequilibrim plasma. The electron density obtained from the Saha plot can provide rough estimation of the electron density. It is shown that the electron-atom interaction contribution to the continuum radiation is more important than being expected before for the argon plasma in our study. The non-axisymmetric distribution of the emission was found to exist within the coil zone of the plasma, which may affect the estimation of the local emission coefficient, and consequently the measured plasma fields.
Analysis of Electronic Properties of TiO2 (001) Surface Based on Band Calculations
Authors: Kellou A. , Toma F-L. , Aourag H. , Klein D. , Coddet C.
Published: September 2022

The electronic structure of the bulk and the surface of rutile titanium dioxide (TiO2) are analyzed from band calculation based on quantum mechanics formalism. The surface density of states and charge distributions of bulk and (001) surface are compared to better understand the mechanism of adsorption and photodegradation processes.
Influences of Substrate Roughness and Temperature on Adhesive Strength in Thermal Spray Coatings
Authors: Fukanuma H. , Ohno N.
Published: September 2022

It is essential to understand and clarify what causes adhesive strength between the thermally sprayed deposit and the substrate. It is known that the adhesive bond strength is strongly related to the roughness of the substrate surface, however, we are yet to know why and how the roughness affects the strength. Although the roughness works as a socalled anchor or interlocking effect, we cannot show how the effect quantitatively relates to the strength. Before we use the word “roughness”, we need to define roughness as a strict meaning in connection with the adhesive strength to avoid any ambiguity in expressing the roughness itself. Seeking the true roughness to relate to the bond strength, we have introduced a newly developed roughness indicator correlated closely with the adhesive strength. This indicator is derived by theory on the basis of the assumption that the bond strength is primarily caused by the mechanical friction between the deposit and the substrate. It was supposed that chemical and physical adhesions were secondary effects except that the molten particle, the substrate temperature or both of them are high enough to form these bonds by thermal interaction. The increase in contact area between the splat and the substrate could raise the friction force between them. The higher substrate temperature could increase the contact area when the molten particle interacts with the substrate, because the molten particle could wet better on the high temperature substrate. The substrate temperature influence on the adhesive strength was also investigated.
Structure and Magnetic Properties of Iron-Based Alloys Obtained by APS Thermal Spraying
Authors: Fenineche N.E. , Cherigui M. , Kellou A. , Aourag H. , Coddet C.
Published: September 2022

The development of amorphous and nanocrystalline materials took a significant part in search on materials these last years. Indeed, the magnetic, chemical and mechanic properties of materials are greatly modified when the size of crystallites becomes nanometric. The absence of crystal structure involves a macroscopic behaviour of the alloy, which is completely different from the same alloy in a polycrystalline state, particularly magnetic and mechanical properties. We have carried out coatings by APS plasma thermal spraying on a copper substrate using three types of powders, FeB (17,5% wt-B), FeSi (6,5% wt-Si) and FeNb (67,2% wt-Nb). Structure of these coatings was characterized by SEM and X-rays. We have also tested the magnetic properties of these deposits. Results obtained showed that the FeNb alloys are amagnetic with a partially amorphous structure, however FeSi and FeB alloys presented a microcrystalline structure with soft magnetic properties.
Study of Unique Microstructure in SPS Ceramic NanoCoatings
Authors: Ma X.Q. , Roth J. , Xiao T.D. , Gell M.
Published: September 2022

Ceramic oxide coatings were made with a unique microstructure using solution plasma spray (“SPS”), a novel variant on the conventional powder plasma spray techniques. In the SPS process, a precursor solution is fed into an air plasma torch using a liquid injector, and a nanocrystalline ceramic coating is formed directly on various substrates without post heat treatment. It was found that the microstructure of the SPS coating depended on control of process parameters for liquid feed and plasma spray to a large extent. This study deals with the formation of SPS deposited yttria stabilized zirconia coatings with a well-controlled microstructure addressing porosity, cracking and adhesion. The SPS-deposited YSZ coatings have demonstrated unique microstructural characteristics including adjustable porosity, vertical microcracks and the absence of splat boundaries. Such zirconia-base coatings show great potential for the applications of high-density electrolyte layers in solid oxide fuel cells (“SOFC”s) and high porosity/low conductivity thermal barrier coatings for industrial and gas turbines.
Thermally Grown Oxides on Electroplated Bond Coats under APS TBC
Authors: Khan Abdus , Duda Thomas , Taylor Alan , Moore Peter , Rutter Peter , Foster John
Published: September 2022

MCrAlY bond coats were deposited on nickel base substrate by electroplated process. The bond coats were plated using ‘CrAlY’ precursor powders suspended in an electrolytic bath containing nickel and cobalt in solution. The CrAlY powders used had size in the range generally below 10 um. The as-deposited coatings were heat-treated in a vacuum at elevated temperature. The roughness of the as-deposited coatings was on the range from 2 to 4 um (average). Yttria stabilized zirconia thermal barrier coatings, 7YSZ were deposited by air plasma spray. The thickness of the both bond coats and TBCs was varied in order to determine the effects of thickness in the stability of the thermal barrier coatings. The coated samples were tested in a static furnace and also in a thermal shock test rig where the samples could be cooled rapidly from 1000°C to 100°C at a predetermined rate. The TGO formed at temperatures in the range from 800 to 1050°C was characterized by optical, scanning electron microscope and electron beam microprobe.
Synthesis and Oxidation Behavior of Nanocrystalline MCrAlY Bond Coats
Authors: Ajdelsztajn Leonardo , Tang Feng , Schoenung Julie M. , Picas Josep , Kim Geoge E. , Provenzano Virgil
Published: September 2022

Thermal barrier coating (TBC) systems protect turbine blades against high-temperature corrosion and oxidation. They consist of a metal bond coat (MCrAlY, M = Ni, Co) and a ceramic top layer (ZrO2/Y2O3). In this work the oxidation behavior of conventional and nanostructured HVOF NiCrAlY coatings has been compared. Commercially available NiCrAlY powder was mechanically cryomilled and HVOF sprayed on a nickel alloy foil to form a nanocrystalline coating. Free-standing bodies of conventional and nanostructured HVOF NiCrAlY coatings were oxidized at a 1000°C for different time periods in order to form the thermally grown oxide (TGO) layer. The experiments show an improvement in oxidation resistance in the nanostructured coating when compared to that of the conventional one. This behavior is a result of the formation of a continuous Al2O3 layer on the top surface of the nanostructured HVOF NiCrAlY coating. This layer protects the coating from further oxidation and avoids the formation of mixed oxide protrusions present in the conventional coating.