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1-6 of 6
Modeling and Measurement of Splat Phenomenon
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Proceedings Papers
ITSC1997, Thermal Spray 1997: Proceedings from the United Thermal Spray Conference, 619-626, September 15–18, 1997,
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In thermal spray processes, the coating structure is the result of flattening and cooling of molten droplets on the substrate. The study of the cooling time and evolution of the splat size during impact is then of the highest importance to understand the influence of the spray parameters and substrate characteristics on the coating structure. Measurement of particle temperature during impact requires the use of a high-speed 2-color pyrometer to collect the thermal emission of the particle during flattening. Simultaneous measurement of the splat size with this pyrometer is difficult since the size of the particle can change as it cools down. To measure the splat size independently, a new measurement technique has been developed. In this technique the splat size is measured from the attenuation of the radiation of a laser beam illuminating the particle during impact. Results are presented for plasma sprayed molybdenum particles impacting on a glass substrate at room temperature. It is shown that the molybdenum splat reaches its maximum extent about 2 microseconds after the impact. In this work, we show that this increase of the splat surface is followed by a phase during which the splat size decreases significantly during 2 to 3 microseconds.
Proceedings Papers
ITSC1997, Thermal Spray 1997: Proceedings from the United Thermal Spray Conference, 627-633, September 15–18, 1997,
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This paper is devoted to the investigation of the transient pressure occurring at the impact of a molten particle onto a flat substrate surface under different thermal spray conditions. In this paper, the mathematical model developed is based on the following assumptions: laminar, viscous and incompressible fluid; the mixed velocity-pressure model is employed to construct the finite element model. The choice of pressure penalty coefficient, which depends on the Reynolds number, is crucial for the results. This is discussed in this paper. The numerical results show that the pressure at the particle-substrate interface is strongly affected by the processing parameters, especially by the particle density and the impact velocity. The influence of spray parameters and material properties are also discussed.
Proceedings Papers
ITSC1997, Thermal Spray 1997: Proceedings from the United Thermal Spray Conference, 635-643, September 15–18, 1997,
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A numerical model has been developed to study the rapid solidification of an alumina splat in thermal spray deposition. The model focuses on the melt undercooling, the selection of the various phases of Al 2 O 3 , and the subsequent non-equilibrium rapid solidification process. A thin molten layer is assumed to be brought into contact with the substrate at time t = 0. One-dimensional heat transfer is considered through splat and substrate along with a thermal contact resistance between them. The classical theory of nucleation kinetics is used to determine the nucleation temperature, assuming that nucleation takes place heterogeneously on the substrate surface. The most likely nucleated crystalline phase is investigated, based on the nucleation kinetics of various phases. Once the particular phase is identified and the nucleation temperature is calculated, the solidification starts assuming a planar interface between the solid and the liquid. Non-equilibrium kinetics of the chosen phase is applied at the moving interface to calculate the interface velocity from the interface melt undercooling. In this paper, the effect of splat variables on the solidification and cooling process of the splat are analyzed. Special attention is paid to the value of the wetting angle between the growing nucleus and the substrate, which affects greatly the nucleation temperature.
Proceedings Papers
ITSC1997, Thermal Spray 1997: Proceedings from the United Thermal Spray Conference, 645-652, September 15–18, 1997,
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A high resolution numerical model has been developed to simulate the simultaneous spreading and solidification of single and multiple-splat on a cold substrate. The model combines the level set formulation with curvilinear adaptive finite volume scheme to predict the deforming shape of the splat's free surface as well as the solidification interface shape and dynamics. An adaptive grid generation captures the solidification front and the level set formulation allows the free surface deformation caused by merging and separation. Numerical results on spreading, merging and solidification of a single splat and two splats are presented to demonstrate the capability of the scheme. It also shows that this model can be extended to predict porosity in thermal spray coatings.
Proceedings Papers
ITSC1997, Thermal Spray 1997: Proceedings from the United Thermal Spray Conference, 653-656, September 15–18, 1997,
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Engineering analytical formulas describing variations of the final values of the splat thickness and radius during flattening of composite particles in thermal spraying are obtained. The effective values of the droplet parameters (impact velocity and viscosity) and the Reynolds number are introduced taking into account a composition of the composite particles. Analytical results obtained agree well with the experimental data available.
Proceedings Papers
Modeling and Experimental Studies of Particles Velocity and Temperature in Plasma Spraying Processes
ITSC1997, Thermal Spray 1997: Proceedings from the United Thermal Spray Conference, 657-663, September 15–18, 1997,
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Mathematical and computer models of movement and heating of particles in low pressure conditions are developed. The mathematical models are based on the molecular-kinetics theory of gases. A program complex for computer realization of models is developed. It contains a built-in data base of temperature dependent properties of substances, system of processing and graphic visualization of simulation results. For verification of the developed models, computer simulation and experimental measurments of Al 2 O 3 particle temperature and velocity are conducted. These materials were sprayed in Plasma-Technik equipment at pressure 60 mBar in argon. Particle velocity was measured with a special optical device, particle temperature was defined by intensity radiation method. It was established that the developed models are adequate to real process (error of 5-8 %) and may be used for study and improvement of VPS processes.