Modeling of plasma spraying of two powders (original) (raw)
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Controlling particle injection in plasma spraying
Journal of Thermal Spray Technology, 2001
This paper reviews experimental and analytical techniques that examine the efficiency of systems for the injection of powders in plasma jets used in spray coating. The types of injectors, the experimental techniques for observing particle trajectories and distributions, and the mathematical models used to investigate the momentum and heat-transfer phenomena between particles, carrier gas, and plasma jet are described. Experimental data are presented from numerous examples from the plasma spraying of ceramic powders.
Plasma-particle interactions in plasma spraying systems
Metallurgical Transactions B, 1992
A mathematical formulation is presented to represent the interactions between the plasma jet exiting a nontransferred arc plasma torch and injected solid particles. This is a generic problem in plasma spraying operations. The calculations are based on the solution of the two-dimensional equation of motion and the thermal energy balance for the particles. Additionally, the plasma temperatures and velocities in the torch and plume are calculated using a mathematical model based on a simplified set of conservation equations. In the formulation, we allow for departure from continuum conditions, particle vaporization, and temperature gradients within the particles. The calculations are compared with previously published experimental measurements of alumina particles injected into a room-temperature, turbulent air jet and into the plume of a commercial plasma torch operating in a turbulent mode. The second set of experiments provides simultaneous measurement of particle temperature, size, and velocity and so form an excellent basis for testing our model. The comparison of the model and the measurements brings new insight into the behavior of particles in plasma jets.
Particle statistical size distribution of an alumina powder is generated and fed (3D) with a carrier gas through an injector into the plasma jets calculated in part I. The initial velocity of each particle is randomized through a law resulting of experimental observations. Characteristic residence times of the particles from the injector to the target and characteristic times for the melting of the particles are obtained. Also size, temperature and velocity distributions of particles impacting on the target are calculated to characterize the coating deposition.
Modelling and Experimental Investigation of A Plasma Spraying System
Ph.D. Dissertation, 2009
In this study, the relationship between the parameters of the atmospheric plasma spraying process and the in-flight properties of the particles was determined experimentally using an optical measurement system, DPV2000. The coating microstructure was investigated using analysis of SEM (Scanning Electron Microscope) images. The morphology of individual splats was studied to shed light on the relationship between the in-flight particle properties and the coating characteristics. The results demonstrate that changing the vertical position of the torch relative to the sensing head of DPV2000 has a strong effect on the particles velocities and temperature distributions. Also changing the distance between the torch and the sensing head increases the velocity gradient. Coating microstructure was studied by changing the spraying parameters, e.g. the stand-off distance, arc current, powder feed rate, and the Ar/ He mixture as a plasma gas. A Matlab code was constructed for porosity analysis of the SEM images of the coating. The coating cross-section analysis showed that the total porosity of the coating increased by decreasing the arc current, increasing the stand-off distance, decreasing powder feed rate and increasing helium flow rate. Two different material were used for the APS coating; the regular (r-YSZ) feed stoke and the nano size (n-YSZ) agglomerated powder, the results illustrate that the r- YSZ coating has higher total porosity at higher arc currents than n-YSZ coating. The splat flattening behavior was examined at different substrate temperatures, and different surface roughness for both powders. The results indicate that the flattening degree increases for high polished substrate with high temperature for the two material but the values for n- YSZ were higher than r-YSZ. Circularity of the splats increased as the arc current increased and stand-off distance decreased. A numerical 2-D model was prepared to study the effect of changing the plasma parameters on the particle behavior inside the plasma plume. It was found that an increase in the plasma gas flow rate, with all other process parameters unchanged, results in a higher particle velocity but lower particle temperature. The particle was modeled as discrete lagrangian entities while the injection process performed the diameter and particle injection velocity was changed. The results indicate that the particle temperature reaches its beak value at approximately 20 to 30 mm from the point of injection after that start to decrease slowly. The temperature of the smaller particles is larger than the larger particle. The velocity of the smaller particles increases faster than larger particles.
Modelling the Plasma Jet in Multi-Arc Plasma Spraying
Journal of Thermal Spray Technology, 2016
Particle in-flight characteristics in atmospheric plasma spraying process are determined by impulse and heat energy transferred between the plasma jet and injected powder particles. One of the important factors for the quality of the plasma-sprayed coatings is thus the distribution of plasma gas temperatures and velocities in plasma jet. Plasma jets generated by conventional single-arc plasma spraying systems and their interaction with powder particles were subject matter of intensive research. However, this does not apply to plasma jets generated by means of multi-arc plasma spraying systems yet. In this study, a numerical model has been developed which is designated to dealing with the flow characteristics of the plasma jet generated by means of a three-cathode spraying system. The upstream flow conditions, which were calculated using a priori conducted plasma generator simulations, have been coupled to the plasma jet simulations. The significances of the relevant numerical assumptions and aspects of the models are analyzed. The focus is placed on to the turbulence and diffusion/demixing modelling. A critical evaluation of the prediction power of the models is conducted by comparing the numerical results to the experimental results determined by means of emission spectroscopic computed tomography. It is evident that the numerical models exhibit a good accuracy for their intended use.
Journal of Thermal Spray Technology, 2003
A three-dimensional computational fluid dynamic (CFD) analysis using Fluent V5.4 was conducted on the in-flight particle behavior during the plasma spraying process with external injection. The spray process was modeled as a steady jet issuing from the torch nozzle via the heating of the arc gas by an electric arc within the nozzle. The stochastic discrete model was used for the particle distribution. The particle temperature, velocity, and size inside the plasma plume at a specified standoff distance have been investigated.The results show that carrier gas flow rate variation from 2 standard liters per minute (slm) to 4.0 slm can increase the centerline particle mean temperature and mean velocity by 10% and 16%, respectively, at the specified standoff distance. A further increase of the carrier gas flow rate to 6 slm did not change the particle temperature, but the particle velocity was decreased by 20%. It was also found that an increase in the total arc gas flow rate from 52 slm to 61 slm, with all other process parameters unchanged, resulted in a 17% higher particle velocity, but 6% lower particle temperature. Some of these computational findings were experimentally confirmed by Kucuk et al. For a given process parameter setting, the kinetic and thermal energy extracted by the particles reached a maximum for carrier gas flow rate of about 3.5-4.0 slm.
Numerical Analysis of the Interactions between Plasma Jet and Powder Particles in PS-PVD Conditions
Coatings, 2021
Plasma spray-physical vapor deposition (PS-PVD) refers to a very low-pressure (~100 Pa) deposition process in which a powder is injected in a high-enthalpy plasma jet, and mostly vaporized and recondensed onto a substrate to form a coating with a specific microstructure (e.g., columnar). A key issue is the selection of the powder particle size that could be evaporated under specific spray conditions. Powder evaporation takes place, first, in the plasma torch between the injection location and nozzle exit and, then, in the deposition chamber from the nozzle exit to the substrate location. This work aims to calculate the size of the particles that can be evaporated in both stages of the process. It deals with an yttria-stabilized zirconia powder and two commercial plasma torches operated at different arc powers with gas mixtures of argon and helium or argon and hydrogen. First, it used computational fluid dynamics simulations to calculate the velocity and temperature fields of the pla...
Modeling of particles impacting on a rigid substrate under plasma spraying conditions
Journal of Thermal Spray Technology, 1995
Finite-element methods have been applied for the spreading process of a ceramic liquid droplet impacting on a flat cold surface under plasma spraying conditions. The goals of the present investigation are to predict the geometrical form of the splat as a function of process parameters, such as initial temperature and velocity, and to follow the thermal field developing in the droplet up to solidification. A nonlinear finite-element procedure has been extended to model the complex physical phenomena involved in the impact process. The dynamic motion of the viscous melt in the drops as constrained by elastic surface tensions and in interaction with the developing contact with the target has been coupled to transient thermal phenomena to account for the solidification of the material. A model is used to study the impact of spherical particles of liquid ceramic of given temperature and velocity on a flat, cool rigid surface. The deformation of the splat geometry as well as the evolution of the thermal field within the splat are followed up to the final state and require adaptive discretization techniques. The proposed model can be used to correlate flattening degrees with the initial process parameters.
Numerical modelling of plasma spray process
Journal of Physics: Conference Series, 2010
Reproduction of the coating quality in the plasma spraying is tough task. To overcome this problem, it is necessary to understand the behaviour of the arc inside the torch, plasma jet and particles in a plasma jet. Various experimental and modelling works have been carried out on these topics. In this article, a few of our new results of plasma arc inside the torch are presented and some of our simulated results of plasma jets and particle behaviour in a plasma jet are summarized. Electro-thermal efficiencies predicted using two different models are close to the measured one. The effect of atmosphere, where the plasma jet is issued, on temperature field is stronger than on velocity field. The influence of the carrier gas and particle loading on the plasma jet thermo-fluid fields is discussed. The effects of particle loading and turbulence modulation on the particle velocity and temperature are clarified. Turbulence modulation does not affect the particle dispersion significantly.