Search Results for particle analysis

The aim of this study was to point out the role of each electrode in the droplets formation in twin arc spraying. This way, two consumable wires of different properties, namely steel and copper, were sprayed simultaneously. The DPV 2000 diagnostic system was used to determine the size, temperature and velocity of in-flight particles, detected at the same locations than those previously tested on particles collection. Then, a model based on the particle temperature was developed to separate particles from the anode and the cathode wires. Results showed significant modifications in term of size, velocity, temperature and repartition when changing material electrodes. To validate the proposed model, modelling results were first compared to results found on properties of collected particles, i.e. sizes and percentages. Then, important differences of in-flight particles characteristics, velocity and temperature, were pointed out depending on the electrode nature and on radial locations in the spray jet. Finally, some coatings were sprayed at the same locations and analyzed in term of thickness. Results showed that the thickness distribution was largely dependent on the anode nature, which was in close agreements with in-flight particles analysis.

The conditions of particle injection into the side of plasma jets play an important role in determining the microstructure and properties of sprayed deposits. However, few investigations have been carried out on this topic. The current work presents the results of an experimental and computational study of the influence of injector geometry and gas mass flow rate on particle dynamics at injector exit and in the plasma jet. Two injector geometries were tested: a straight tube and a curved tube with various radii of curvature. Zirconia powders with different particle size range and morphology were used. A possible size segregation effect in the injector was analyzed from the space distribution of particles collected on a stick tape. The spray pattern in the plasma jet was monitored from the thermal radiation emitted by particles. An analysis of the particle behavior in the injector and mixing of the carrier-gas flow with the plasma jet was carried out using a 3-D computational fluids dynamics code.

Solution precursor plasma spraying has been used to deposit ceramic coatings with submicron/nanocrystalline structures. Previous studies revealed that the deposition mechanism in the solution precursor plasma spraying differs from that in the conventional plasma spraying. To increase the understanding of the deposition mechanism in the solution precursor plasma spraying, a numerical model is used to predict the particle conditions on the substrate. Five types of particle conditions, melted particles; small sintered particles; dry agglomerates; wet agglomerates; and wet droplet are assumed based on the computed temperature distribution of the particles. An analysis of the deposition mechanism in the solution precursor plasma spraying is performed. Experiment results s are also collected to verify the numerical prediction and the analysis of the deposition mechanisms.

Plasma spray for depositing thermal barrier coatings features large distributions of particle states that result in significant variations in coating quality. These variations arise from distributions of particle sizes, large spatial gradients of plasma thermal-fluid fields, and temporal variations of the arc and jet. This paper describes a simplified approach for studying how particle state distributions are influenced by torch conditions and powder distributions, and the implications for deposition rate monitoring and control. The approach combines a simplified jet model with a more detailed particle model. The important fluid-thermal spatial gradients in the plasma jet are captured using a three zone model: a core region, modeled by growth of a turbulent shear layer around a laminar core, a transition region and a similarity region. Plasma-particle momentum and thermal interactions, particle phase transitions, internal particle temperature gradients, and collapse of in-flight hollow particles have been modeled using a multi-lumped particle model. Effects of distributions of particle size, particle morphology, injection velocity, and carrier gas flow were studied for YSZ spray in an Ar-He plasma. The results provide guidance on sensor design and operation and on approaches for plume location control.

In this study, axisymmetric two-dimensional numerical analysis was performed to clarify the particle behavior in supersonic hybrid aerosol deposition (HAD). The predicted result showed that the small particles, which can deposit via HAD, impact the substrate on a wide region while the large particles, which can abrade the surface of film and substrate, impact around the center.

In this paper, the phenomenological behaviour of gas flow and particles motion during cold spraying has been studied. Observations of particles behaviour show two features: a uniform jet over a short distance ahead of the nozzle exit and then, a progressive dispersion. These behaviours are explained using a computational analysis based on a direct numerical simulation of the gas flow and the kinematic interactions with the particles. The CFD computation demonstrates that the gas stream starts to be unstable inside the nozzle with more turbulence as it moves towards the exit of the nozzle. The flow is self-oscillated along the flow direction and drives the motion of the Cu particles outside the nozzle. The zone of gas flow instability does correspond to the zone of experimental particle dispersion. Outside the nozzle, the particles form a straight jet over a certain distance that corresponds to the zone of the experimental uniform particles jet. Then, they are deviated and become more and more dispersed towards a very sparse jet along the flow direction. This phenomenon is explained by a Magnus lift force that deviates the particles trajectory when the gas flow becomes highly turbulent while developing a vorticity shedding.

The properties of thermally sprayed coatings significantly depend on the alloy composition and the adjusted process parameters. In addition to the powder certificate it may be useful to analyse the chemical composition of the sprayed powder during the spraying process itself. The principle of composition analysis is similar to the chemical analysis in an ICP plasma but the boundary conditions are more complex because the sprayed powder should not be completely evaporated in a thermal spray process. Nevertheless all thermal spraying processes lead to a certain evaporation of the species and to excitation of atomic states. The transition into the ground state occurs under emission of characteristic lines. The intensity of these lines is influenced by the plasma temperature, the particle temperature, the temperature dependent evaporation rate of the alloying elements and the powder feed rate. In consideration of the boundary conditions and the information from a detailed analysis of the emitted spectra the lines can be used to quantify the chemical composition of the sprayed alloys online. The theory of the principle for on-line analysing the chemical composition will be deduced and the first experimental validation will be presented.

The industrial flame spraying process has been analyzed by three-dimensional Computational Fluid Dynamics (CFD) simulation. The actual process is employed at the Volvo Aero Corporation for coating of fan and compressor housings. It involves the Metco 6P gun where the fuel, a mixture of acetylene and oxygen, flows through a ring of 16 orifices, while the coating material, a powder of nickel-covered bentonite, is sprayed through the flame with a stream of argon as a carrier gas by a central orifice. The gas flow was simulated as a multi-component chemically reacting incompressible flow. The standard, two equations, k-e turbulence model was employed for the turbulent flow field. The reaction rates appeared as source terms in the species transport equations. They were computed from the contributions of the Arrhenius rate expressions and the Magnussen and Hjertager eddy dissipation model. The particles were modeled using a Lagrangian particle spray model. In spite of the complexity of the system, the complex geometry and the numerous chemical reactions, the simulations produced fairly good agreement with experimental measurements. The powder size distribution was found to play a critical role in the amount of unmelted fraction of particles. The modeling approach seems to give a realistic description of the physical phenomena involved in flame spraying, albeit some model refinement is needed.

Recent advances has made possible to obtain Ultra High Molecular Weight Polyethylene (UHMWPE) coatings by cold spray technique with nano-ceramic additives with the feedstock. However, the exact role of nano particles is largely not understood. In this work, isolated depositions of UHMWPE particles with 0%, 2%, 4%, 10% of fumed nano alumina (FNA) on Al surface were performed at different gas/particle temperatures. Particle velocities and particle temperatures were controlled by varying the carrier gas pressure and temperature. The impact behavior of UHMWPE was analyzed using SEM, FIB and high-speed camera. Increase in gas temperature and percentage of FNA showed a significant variation in the deposition volume. FIB analysis showed that successful depositions were influenced by degree of deformation of particle. Further, addition of FNA helped in deposition of particles that have required a lesser degree of deformation. Finally, high speed camera showed that particles are moving at an incidence velocity of 180-200m/s and rebound velocity of 40-50m/s. This suggests that particles lose a significant amount of their kinetic energy during the impact.

Demands on functional coatings with high dimensional accuracy and high surface quality has led to increasing interest in processing of very fine powder grades in a particle size range < 25 µm. Fine powders are not only showing a distinct potential for application of thin and dimensionally accurate coatings, but are also very promising for the production of dense and homogeneous coatings with improved mechanical properties. The large specific surface of fine powders is allowing for relatively low thermal energy levels that are introduced into the process. Nevertheless this also requires a very sensitive temperature control, to prevent overheating of the particles. The reduction of the thermal energy level is resulting in significant advantages particularly for the usability of the HVOF process for coating of inner diameters. Within this work in-flight particle properties of ultrafine carbide powders were analyzed. The studied HVOF process allows the adjustment of a broad parameter range by utilization of a hydrogen stabilized liquid fuel combustion process. A conventional straight nozzle type as well as a curved nozzle for internal spraying was studied. For a further assessment of the potential of ultrafine carbide powders also spray trials with a plasma spraying system have been made.

Particle melting is one of the key issues in air plasma spraying of high-temperature ceramics such as YSZ. This study aims to estimate the molten content of the spray stream from in-flight particle temperature measurements. Particle temperature distribution is delineated into particle states (unmolten, partially molten, completely molten) as a first approximation, which is then used to estimate the molten content in the spray stream. The estimated percentage of molten content is shown to correlate well with deposition efficiency measurements for a wide range of process conditions and feedstock characteristics. The use of this estimation technique for other materials and processes is also discussed.

This study compares the performance of circular and rectangular cold spray nozzles based on numerical simulations and experimental results. It shows how nozzle geometry and gas pressure affect the velocity and temperature of copper particles at various points in their travel. The goal of the investigation is to establish a nozzle design that achieves a uniform spray pattern with suitable particle impact velocity for the materials and temperatures involved. It was found that a rectangular nozzle with an expansion ratio in the range of 11-12 can provide a more uniform particle velocity with high deposition efficiency at a reasonable gas pressure.

The thermal spray industry identified the need for repeatable and reproducible feedstock powder characterization methods, especially particle size distribution (PSD), for cost effective manufacturing of thermal barrier coatings. The PSD measurement by a laser light scattering method was identified as the technique most widely used in the industry. This technique offers high resolution, rapid measurements and ease of use. A round robin study by nine laboratories using different models of a commercial light scattering instrument has been completed as the first step towards the development of a Standard Reference Material (SRM) for the calibration of light scattering instrument. Other measurement techniques were also employed for additional comparison. The PSD measurements employing light scattering techniques evidenced some method dependence, despite the use of identical sample preparation procedures. The round robin results will serve as reference values for the development of the SRM.

The flame spraying process has been analysed using three-dimensional Computational Fluid Dynamics (CFD) simulations. The process employed at the Volvo Aero Corporation for the coating of fan and compressor housings has been modelled. The gas combustion was simulated as a multi-component chemically reacting flow. The standard, two equations, k-ε turbulence model was employed. A statistical analysis of the computer simulation experiments revealed that particle velocity and particle temperature were dependent on four process parameters, namely the acetylene flow rate, the carrier gas flow, the powder feed rate and the spray distance. The most important factors influencing particle velocity and temperature were the acetylene flow rate and the carrier gas flow. The carrier gas flow rate was shown to have an unexpectedly large influence on particle in-flight properties. Simulations were repeated with particles of different median diameters. The study revealed that a very high correlation existed between particle temperature and particle velocity for particles of the same median diameter. Furthermore, the particle median diameter, when compared with the investigated process parameters, was found to have a more pronounced influence on both particle temperature and velocity. It would appear that the use of powder lots comprised of sufficiently fine-grained powders is the most promising single contribution towards increasing deposition efficiency that can be applied to the current process.

While twin wire arc spraying, strong dependences are usually noticed between elaboration process parameters and coating properties. Therefore, control is needed for increasing coating performances. The aim of this paper is to investigate the coating properties in relation with in-flight particle characteristics and with the impact modes. Measurements were achieved on iron particles when changing either the current intensity or the air flow rates. In-flight particle characteristics were determined by using the DPV diagnostic system 200 mm from the gun exit and for three different radial locations. The same locations were kept for the impact analysis. Then, the morphology of the splats was evaluated by its flattening and shape factors when the substrate is preheated or not. Finally, the coating properties were characterized in terms of porosity, oxide contents, microhardness and thickness. Through the determination of related interactions, a better knowledge of coating elaboration conditions will lead to improve reliability and properties of the deposits.

Plasma-sprayed ceramic coatings are deposited such that flattened splats together with some nonmelted particles are present in the coatings. In this study, the nonmelted particles in plasma-sprayed alumina coatings were examined by scanning electron microscopy, confocal Raman analysis, and X-ray diffraction analysis with the aim of quantitative evaluation of the coating microstructure. Results showed that the nonmelted particles can be clearly identified from the cross-sectional microstructure due to the morphology that results from the high hardness of the nonmelted particles. The obvious gap at the interface between nonmelted particles and the surrounding splats suggests weak interface bonding. Raman analysis revealed that there was little α-Al 2 O 3 phase in the flattened splats region, which confirms that this phase in the coating appears only from nonmelted particles. Attention should be paid to the weak bonding of the nonmelted particles relative to the flattened splats during the preparation of samples for quantitative characterization of coating microstructure.

In this work, the possibility of controlling the thermally sprayed TBC microstructure is in order to improve the overall TBC system performance. The control is possible primarily by metallic bond coat surface microtexturization prior to ceramic top coat spraying. Such pretreated bond coat was modeled to investigate the influence of the substrate topography on the plasma stream behavior as well as the feedstock particle thermophysical properties and trajectories in the substrate closest proximity. The microscale computational domain was considered here. It was extracted from entire spraying domain and located in the microtextured substrate boundary layer. Then, advanced flow models were introduced to the governing equations to define heat flux to the substrate, turbulent flow, and plasma jet / feedstock droplets interaction. Feedstock discrete phase was defined by the means of Discrete Phase Model (DPM) including particle drag laws and DPM source modelling. The motivation for this study was to model and investigate the influence of the bond coat microtexturization on the behavior of the feedstock particles in the substrate boundary layer. This opens the possibility of better understanding the TBC build-up mechanism and strictly controlling the microstructure of such TBCs.

In this study, cold spay particle impact behavior of a typical copper material is examined using ABAQUS finite element analysis software. Various combinations of calculation settings are explored, such as element type, adaptive meshing, contact interaction, and material damage, with the main focus on element distortion and its effect on output. The influence of mesh size on modeling accuracy is also discussed as are fundamental aspects of modeling cold spray particle deformation.

The purpose of this work is to study the effect of laser radiation on powder particles transported by gas during laser cladding. The temperature and velocity of particles entering the light field of a CO 2 laser were determined by measuring particle radiation as well as the scattered radiation of the diode laser, two independent methods. It is shown that under the action of laser radiation, the particles acquire additional acceleration due to the vapor pressure from the irradiated part of the particle surface. This sonic recoil vapor pressure can significantly affect the in-flight characteristics of powder particles in a gas jet. Particle velocities due to laser acceleration exceeded 100 m/s in a carrier gas with a flow rate less than 30 m/s. Particle temperature depends on several factors and was found to vary from ambient temperature to the boiling point of the powder.

The paper analyzes different working gases and their mixtures for possible application in cold gas spraying (CGS). The gases considered include Ar, CO 2 , and steam, alone and in combination. Typical pressures and temperatures were used, along with CFD simulation software, to calculate gas velocity profiles along the axis of a convergent-divergent nozzle. The profiles are compared with that of nitrogen, the standard gas for cold spray, flowing under the same conditions. Velocity and temperature profiles were also calculated for copper particles in the various gas flows as well as nitrogen. Differences in temperature and velocity are explained based on sonic velocities, viscosities, and thermal conductivities of the respective gases.