Marie-Pierre Planche

Relationships between in-flight particle characteristics and coating microstructure with a twin wire arc spray process and different working conditions

Abstract The aim of this study is to get a better understanding of the build up of coatings obtained through twin wire arc spray process. Properties of in-flight steel particles, i.e. diameter, velocity and temperature, were determined using a dpv system, for different working conditions. Due to very large size distribution, specific experimental set-up has been developed in order to collect particles at a given spraying distance. As a result, the dpv diameter parameter was calibrated and well-marked tendencies on particle velocity and diameter have been found while changing input parameters. Then, the morphology of the splats has been studied in terms of flattening degree and shape factor. Finally, some correlations have been established between input parameters and properties of coatings in relation with particle characteristics and splats analysis.

Influence of HVOF spraying parameters on in-flight characteristics of Inconel 718 particles and correlation with the electrochemical behaviour of the coating

The high velocity oxy fuel (HVOF) process is currently used to produce metallic coatings on a wide variety of surfaces, imparting to the base material improved wear, high temperature or electrochemical corrosion resistance. However, HVOF spraying of metals in the atmosphere typically leads to the formation of embedded oxides within a coating. In many service applications, the presence of oxides results in poor coating performance. The gas dynamics of the HVOF spray are particularly important in terms of oxide contents. Therefore, the objective of the present work is to determine the effect of the oxygen/fuel ratio on the particle characteristics during their flight in the jet. A comparison between the oxide contents in Inconel 718 coatings was established as a function of the spray parameters. Electrochemical measurements were performed, giving information on the role of the oxides present in the coating in relation to its corrosion behaviour. Finally, directions are proposed to optimise coating properties obtained with the HVOF process in relation to the in-flight particle characteristics.

In-flight characteristics of plasma sprayed alumina particles: Measurements, modeling, and comparison

The key phenomena controlling the properties of sprayed coatings are the heat and momentum transfer between the plasma jet and the injected particles. Modern on-line particle monitoring systems provide an efficient tool to measure in-flight particle characteristics in such a way that factors that could affect the coating quality can be identified during the spray process. In this work, the optical sensing device, DPV-2000 from Tecnar, was used for monitoring the velocity, temperature, and diameter of in-flight particles during the spraying of alumina with a Sulzer-Metco F4 plasma torch. Evolution of particle velocity, temperature, diameter, and trajectory showed well-marked trends. Relationships between the position of the in-flight particles into the jet and their characteristics were pointed out, thus delivering valuable information about their thermal treatment. Moreover, a numerical model was developed and predictions were compared with experimental results. A good agreement on particle characteristics was found between the two different approaches.

Investigation of Deposition Behavior of Cold-Sprayed Magnesium Coating

Two types of magnesium powders with different particle size distributions were deposited by cold spraying at different main gas temperatures. The effects of gas temperature and particle size distribution on the deposition efficiency of particles were studied. The microstructure of coatings was observed, and the porosity of coatings was evaluated. The deposition efficiency of particles increased, and the porosity of coatings decreased with the increase of gas temperature. The deposition efficiency of particles increased when using the powder with a smaller particle size distribution. Stainless steel and aluminum plates were used as substrates. The bonding strength and mechanism between the coating and substrate were studied. The commercial finite element software ABAQUS was used to help us better understand the deformation behavior of particles and substrates. The mean bonding strength slightly increased when aluminum plates were used as substrates. The bonding mechanism of Mg coatings on stainless steel and aluminum substrates was discussed.

Intelligent system for prediction and control: Application in plasma spray process

Parametric drifts and fluctuations occur during plasma spraying. These drifts and fluctuations originate primarily from electrode wear and intrinsic plasma jet instabilities. One challenge is to control the manufacturing process by identifying the parameter interdependencies, correlations and individual effects on the in-flight particle characteristics. Such control is needed through methods that (i) consider the interdependencies that influence process variability and that also (ii) quantify the processing parameter-process response relationships. Due to the large amplitudes of the drifts and fluctuations, the strategy to adopt would depend on the required corrections to apply to the in-flight particle characteristics. Artificial intelligence is a pertinent tool to reach this objective. The system is flexible in order to permit a full control based on pre-defined rules aiming at maintaining at constant values in-flight particle characteristics (average surface temperature and velocity) by adjusting in real time the arc current intensity, the total plasma gas flow and the hydrogen content whatever the fluctuations.

In-flight particle characterization and coating formation under low pressure plasma spray condition

Yttria-stabilized zirconia (YSZ) coatings were deposited by low pressure plasma spray (LPPS) in 1.0×104 Pa, 1.5×104 Pa, and 2.5×104 Pa. Both in-flight particle diagnostic detected by DPV-2000 system and ANSYS-FLUENT software were used to study the connection between the parameters of flying particles and the coating formation, which might help to recognize the relationship between the operation parameters and the coatings quality. The results of simulation showed that particles in a lower spray pressure could achieve a higher velocity. The particle velocity was around 380 m/s at a distance of 35 cm from the nozzle at 1.0×104 Pa while only 300 m/s at 2.5×104 Pa in actual measurement. The results showed that the velocity of particles increased with decreasing the spray pressure, which might enhance the flattening rate of coatings and thereby decreased the porosity. The deposited YSZ coating with the lowest porosity can be gained under 1.0×104 Pa condition.

Effect of suspension characteristics on in-flight particle properties and coating microstructures achieved by suspension plasma spray

This paper focuses on the influence of suspension properties on the manufacturing of coatings by suspension plasma spraying (SPS). For this purpose, alumina suspensions were formulated with two different liquid phases: water and ethanol. Suspensions were atomized with a twin-fluid nozzle and injected in an atmospheric plasma jet. Suspension injection was optimized thanks to shadowgraphy observations and drop size distribution measurements performed by laser diffraction. In-flight particle velocities were evaluated by particle image velocimetry. In addition, splats were collected on glass substrates, with the same conditions as the ones used during the spray process. Scanning electron microscopy (SEM) and profilometry analyses were then performed to observe the splat morphology and thus to get information on plasma / suspension interactions, such as particle agglomeration. Finally, coatings were manufactured, characterized by SEM and compared to each other.

Effect of in-flight particle temperature on the microstructure and gas tightness of atmospheric plasma-sprayed YSZ coating

The microstructure, gas tightness and ionic conductivity of plasma-sprayed yttrium stabilised zirconia coating is evaluated. Results show that the gas permeability and ionic conductivity of coating was improved by increasing the in-flight particle temperature.