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Author: Sadaf Mohammadi
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Thermal spray technology is a widely used technique in the industry in which surfaces of components are coated by spraying a wide range of metals or ceramics. Considering the growing interest in building nanostructured coatings due to their unique characteristics, a new technique called suspension plasma spraying is developed. Suspension plasma spraying (SPS) is one of the promising methods that can be used to achieve coatings with fine microstructure and superior properties. Several significant parameters make this SPS process complex to understand and control. In particular, the velocity and diameter of in-flight particles near the substrate, which depend on the plasma and injection conditions, have a strong influence on the coating columnar structure. In this work, the velocity of in-flight particles in the vicinity of the substrate and free jet was investigated by the particle image velocimetry (PIV) method. This study is aimed at providing a better understanding of the behavior of in-flight particles in the SPS process. A suspension of titania particles is used here taking advantage to the abundance and chemical stability of titania and its use in different SPS applications. Observations and results of this work showed that the trajectory and velocity of micron-size particles, due to their small Stokes number, are strongly influenced by the presence of the substrate. The PIV results make it possible to visualize the suspension injection into the plasma with titania aqueous suspension. Particle velocity reported by PIV method corresponded likely to un-molten particles in SPS process. The PIV measurements were finally compared with velocity measurements carried out with a thermal-emission particle sensor in the same spray condition as the PIV run.
Author: Sadaf Mohammadi
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Thermal spray technology is a widely used technique in the industry in which surfaces of components are coated by spraying a wide range of metals or ceramics. Considering the growing interest in building nanostructured coatings due to their unique characteristics, a new technique called suspension plasma spraying is developed. Suspension plasma spraying (SPS) is one of the promising methods that can be used to achieve coatings with fine microstructure and superior properties. Several significant parameters make this SPS process complex to understand and control. In particular, the velocity and diameter of in-flight particles near the substrate, which depend on the plasma and injection conditions, have a strong influence on the coating columnar structure. In this work, the velocity of in-flight particles in the vicinity of the substrate and free jet was investigated by the particle image velocimetry (PIV) method. This study is aimed at providing a better understanding of the behavior of in-flight particles in the SPS process. A suspension of titania particles is used here taking advantage to the abundance and chemical stability of titania and its use in different SPS applications. Observations and results of this work showed that the trajectory and velocity of micron-size particles, due to their small Stokes number, are strongly influenced by the presence of the substrate. The PIV results make it possible to visualize the suspension injection into the plasma with titania aqueous suspension. Particle velocity reported by PIV method corresponded likely to un-molten particles in SPS process. The PIV measurements were finally compared with velocity measurements carried out with a thermal-emission particle sensor in the same spray condition as the PIV run.
Author: Kourosh Pourang
Publisher:
ISBN:
Category :
Languages : en
Pages : 99
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Book Description
Thermal spray technology is a widely used technique in industry in which surfaces of materials are coated by spraying a wide range of metals or ceramics. Considering the growing interest in building nanostructured coatings due to their significant characteristics a new technique called suspension plasma spraying is developed. In this method, a coating is formed by injecting a suspension of nano or sub-micron sized particles into a plasma flame. Obtaining a uniform coating on mechanical parts is one of the industrial challenges in suspension plasma spraying. Through a three dimensional numerical analysis, this study is aimed at providing a better understanding of the effect of substrate position and curvature on in-flight particle temperature, velocity and trajectory. The high temperature and high velocity plasma flow is simulated inside the plasma torch using a uniform volumetric heat source in the energy equation. The suspension of yttria stabilized zirconia (YSZ) particles is used here due to its vast applications in forming thermal barrier coatings. Suspension is molded in this study as a multicomponent droplet while catastrophic breakup regime is considered for simulating the secondary break-up when the suspension interacts with the plasma flow. A two-way coupled Eulerian-Lagrangian approach along with a stochastic discrete model was used to track the particle trajectory. Particle size distribution in the vicinity of the substrate at different standoff distances has been investigated. Then the effect of substrate curvature on in-flight particle characteristics is discussed. The results show that sub-micron particles obtain higher velocity and temperature compared to the larger particles. However, due to the small Stokes number associated with sub-micron particles, they are more sensitive to the change of the gas flow streamlines in the vicinity of the substrate.
Author: Ali Akbarnozari
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Suspension plasma spray (SPS) is an emerging coating process for making surfaces with superior properties. In the SPS process, ceramic particles are mixed with water or ethanol to form a suspension. A plasma torch provides the heat and momentum to evaporate liquid phase of the injected suspension, melt the coating particles, propel the in-flight particles toward a substrate, and eventually form a coating layer. However, the SPS process relies strongly on the coupon test and trials to find optimum spray conditions for plasma, suspension injection, and substrate location. At the end, an optimum spray condition set in a spray booth may not reproduce the same coating result in other booths. An effective control over the spray process improves the reproducibility of the spray conditions and consequently coating structures. Therefore, monitoring systems are employed to better understand and control the required spray condition. The monitoring included accessing state of droplets after the atomization of suspension and state of in-flight particles near the substrate. For further development of the SPS process, the suspension can be injected by an effervescent atomizer. This research aims to contribute in further improving the process and developing the diagnostic tools in SPS. For a further improvement of the SPS process, an effervescent atomizer was investigated as an alternative way instead of the current methods of injection of the suspension in the plasma jet. Performance of the effervescent atomizer was investigated at room temperature by phase Doppler particle anemometry (PDPA). Size of droplets and shape of the atomized spray in a crossflow configuration was almost independent of the suspension concentration. Size of droplets depends on the atomization at the exit of the orifice and the breakup in the crossflow. Velocity of droplets at downstream is the velocity of the crossflow. It was found that the shape of spray was conserved in the crossflow and relatively smaller droplets were enveloped by the larger droplets. As a contribution to adapt a diagnostic system for SPS, a two-color pyrometer was modified and investigated to measure temperature of in-flight particles. The in-flight particles are released after evaporation of the liquid phase of suspension droplets. A high cooling rate of the in-flight particles in terms of distance from the torch and radiation of plasma are main challenges for temperature measurement. To remove these limitations, the temperature was measured by a single-point measurement system based on thermal emission which equipped by readjusted bandpass filtering. The result of online temperature and velocity measurement was in a good agreement with the offline validation by collecting the splats and analyzing the samples. Moreover, the measurement condition has an impact on temperature, and the impact can be minimized by elimination of the stray radiation. As a fundamental research work to develop a diagnostic system for SPS, a light diffraction (LD) system was adapted and investigated to measure size of in-flight particles. Refraction of the laser in the measurement volume and radiation from plasma were two main challenges of the size measurement. A shield of an optimized aperture was employed to control the condition of measurement volume. By applying a narrow bandpass filter at a right wavelength and selecting a right angle to collect the scattered signal from the in-flight particles, the size of particles was measured. A good agreement between the result of online measurements under the plasma condition and studying the feedstock particles in the wet cell unit in the room condition validated the size measurement.
Author: R. Suryanarayanan
Publisher: World Scientific
ISBN: 9789810213633
Category : Science
Languages : en
Pages : 318
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Book Description
The recent advances in plasma spraying are discussed in this book which divides into two sections — theory and application. The book presents sophisticated experimental techniques, diagnostics, theoretical models and computer simulations which not only improve the understanding and uses of the spraying process but also help to increase the reliability factor of the manufacturing components. Applications that are metallurgical, aeronautical, automobile, chemical, etc. are also shown. More importantly, applications that include silicon for solar cells, magnets and superconductors are also discussed for the first time. Advanced graduate students in materials science and engineering, research scientists, engineers and industries involved in plasma spray applications will benefit from this book.
Author: Pierre L. Fauchais
Publisher: Springer Science & Business Media
ISBN: 0387689915
Category : Technology & Engineering
Languages : en
Pages : 1587
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Book Description
This book provides readers with the fundamentals necessary for understanding thermal spray technology. Coverage includes in-depth discussions of various thermal spray processes, feedstock materials, particle-jet interactions, and associated yet very critical topics: diagnostics, current and emerging applications, surface science, and pre and post-treatment. This book will serve as an invaluable resource as a textbook for graduate courses in the field and as an exhaustive reference for professionals involved in thermal spray technology.
Author: Elham Dalir
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Suspension plasma spraying (SPS), a relatively new deposition technique in thermal spray coating technology, has been increasingly applied to deposit high-quality thermal barrier coatings using sub-micron particles. An accurate simulation of the process includes developing a realistic plasma model both within and outside the torch. In the current work, a three-dimensional time-dependent model has been developed to simulate magneto-hydrodynamic fields inside a direct current (DC) plasma torch, including arc fluctuations. Reynolds stress model (RSM) is used to simulate the time-dependent turbulent plasma flow. A two-way coupled Eulerian-Lagrangian method is employed to investigate the effects of arc fluctuations on the droplets' trajectory, temperature, and speed. Sub-micron yttria-stabilized zirconia (YSZ) solid particles suspended into ethanol are modeled as multicomponent droplets. Kelvin-Helmholtz Rayleigh-Taylor (KHRT) breakup model is used to simulate the droplets' atomization. This model considers the effects of both aerodynamic forces (Wave model) and Rayleigh-Taylor instabilities on the atomization process combing a liquid core region (Levich model). Particles are also tracked after completion of suspension breakup and evaporation to obtain inflight particles' conditions (trajectory, size, speed, and temperature). The developed model is then employed to study the droplets' shape and solid concentration on the SPS process. A dynamic drag law is applied to analyze the effect of droplets/particles' shape on the SPS process. It was concluded that the percentage of molten particles in applying dynamic drag law (non-spherical particles) decreases significantly compared to using the spherical particles. The effect of suspension concentration is also studied. It was shown that using a higher solid concentration (20 compared to 10 wt.% YSZ) provides a denser coating as a result of the larger molten landed particles with higher velocities. Finally, the developed model is used to study the in-flight droplets/particles' atomization in the SPS process. Nine case studies are investigated to see the effect of KH, RT instabilities, and breakup length on the droplets/particles' atomization. A massive difference is represented in quantity, droplets' atomization pattern, and quality of the final landed particles over the substrate of some cases. The obtained size distributions of the trapped particles over the substrate are compared to the existing data to find the suggested ranges for the breakup model's constants.
Author: Bishoy Aziz
Publisher:
ISBN:
Category :
Languages : en
Pages : 100
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Book Description
The temperature of in-flight particles in suspension plasma spraying (SPS) is one of the key parameters affecting the coating microstructure. Temperature measurement has been carried out before for in-flight particles in air plasma spray (APS) and other thermal spraying processes. Suspension plasma spray (SPS) is an emerging coating deposition technology that permits the deposition of nanostructured coatings with unique structural characteristics. The particles size in SPS is smaller than the one that is commonly used is APS and other spray processes leading to specific challenges for determining its temperature. The aim of this work is to assess the feasibility of two-color pyrometer for in-flight particles in suspension plasma spraying. To do so, spectroscopic analysis in the visible to near infrared range was carried out on the jet stream when suspension of 20 wt. % YSZ particles in pure ethanol was sprayed. The analysis takes into account the radiation scattered by the particles (Mie scattering) as well as the radiation directly detected from the plasma in the jet stream, and it was found that the effect of the scattered radiation by the particles on temperature measurement is negligible along the center axis of spraying at the melting point of Zirconia. Moreover, the main and dominant source of error on temperature measurement is the plasma radiation, the vapors and the free electrons in the background of the continuum. One the other hand, it was found that going for a longer wavelength from 1 ?m to 2.5 ?m is not a promising wavelength range for temperature measurement. Finally, the measurements carried out in this thesis favors future development for the current configuration of a commercial diagnostic sensor to have a better iv precision for the value of temperature measurement, as it was found that the error because of the current configuration can reach 540 ° C degrees.
Author: Farzad Jabbari
Publisher:
ISBN:
Category :
Languages : en
Pages : 105
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Book Description
Plasma Spraying is a coating process designed to deposit accelerated molten or semi-molten coating materials on prepared substrates. Suspension Plasma Spraying (SPS) is one type of Plasma Spraying with enhanced characteristics. Numerical modeling of this process helps us to find optimum operating parameters such as suspension injection position and standoff distance for substrates. A three-dimensional model of a plasma spraying system with radial suspension injection is studied in this work. To model turbulent flow of plasma, Reynolds Stress Model (RSM) is utilized. In addition, Lagrangian approach is used to track particles and two-way coupling is used to consider the effect of suspension on the gas flow. It should be mentioned that when mass flow rate of suspension is very high, the plasma plume cannot melt all particles that fly near the centerline. It is found that with optimum suspension mass flow rate, in general, almost all particles flying near the centerline are melted and reach high temperature. Furthermore, the effect of angle of suspension injection is studied. One can find that angles toward the gun give more penetration of suspension in the plasma plume, resulting in better melting and higher speed of particles. Finally, particle temperature, velocity and size distributions are studied at different standoff distances with respect to the plasma gun exit. It is shown that optimum standoff distance for the studied particles and plasma plume properties is between 3 to 6 cm. Less than 3 cm standoff distance, particles have no time to reach the melting point and the base liquid would not evaporate completely; and with more than 6 cm standoff distance, particles’ velocity will be significantly reduced. It should be mentioned that trajectory and penetration of suspension completely depends on velocity of suspension on one hand, and on the other hand temperature and velocity of the plasma plume. It is clear that for each condition, mass flow rate and velocity of plasma, the related modeling should be done to find velocity and temperature of particles.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 7
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Book Description
This is the second paper of a two part series based on an integrated study carried out at the State University of New York at Stony Brook and Sandia National Laboratories. The goal of the study is the fundamental understanding of the plasma-particle interaction, droplet/substrate interaction, deposit formation dynamics and microstructure development as well as the deposit property. The outcome is science-based relationships, which can be used to link processing to performance. Molybdenum splats and coatings produced at 3 plasma conditions and three substrate temperatures were characterized. It was found that there is a strong mechanical/thermal interaction between droplet and substrate, which builds up the coatings/substrate adhesion. Hardness, thermal conductivity, and modulus increase, while oxygen content and porosity decrease with increasing particle velocity. Increasing deposition temperature resulted in dramatic improvement in coating thermal conductivity and hardness as well as increase in coating oxygen content. Indentation reveals improved fracture resistance for the coatings prepared at higher deposition temperature. Residual stress was significantly affected by deposition temperature, although not significant by particle energy within the investigated parameter range. Coatings prepared at high deposition temperature with high-energy particles suffered considerably less damage in wear tests. Possible mechanisms behind these changes are discussed within the context of relational maps which are under development.
Author: Ian F. Thomson
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
An optical diagnostic system was built to measure the in-flight parameters of thermal spray particles. A ratio pyrometer was built to measure mean particle temperatures to within 100 K. Particle velocities and acceleration were recorded using a particle-tracking velocimetry system consisting of three pulsed lasers; a filtered, intensified CCD camera; and an image analysis macro in the software package OPTIMAS. Flow visualization of the emerging plasma jet was accomplished using smoke pellets for seeding and a laser sheet for illumination. The system was used to evaluate the performance of a new curvilinear gas shroud attachment and compare it with a commercially available conical attachment. The curvilinear attachment was found to increase particle temperatures by 300 K, leading to more complete particle melting. These favourable particle conditions resulted in higher quality coatings, displaying higher adhesion strength, lower porosity, and a more uniform microstructure than those applied with the conical nozzle. A new design for shrouding gas injection through a circular slot was tested and found to offer better protection to the particles in flight. The system was also used to measure impact conditions of nickel particles sprayed onto a preheated substrate. Individual nickel splats were examined under an electron microscope. A substrate transition temperature was found above which particle splashing ceases and splats become circular disks. Substrate preheating could potentially be applied in industry, as coating properties are highly dependent on interactions between splats. Measured particle impact conditions were also used to validate a numerical model of droplet spreading and solidification.
