We used a three-dimensional model of droplet impact and solidification to simulate the effect of surface roughness on the impact dynamics and the splat shape of an alumina droplet impinging onto a substrate. The substrate surface was patterned by a regular array of cubes spaced at an interval twice their size. Three different cube sizes were considered, and the results were compared to the case of droplet impact onto a smooth substrate. To understand the effect of solidification on the droplet impact dynamics and splat morphology, the simulations were run with and without considering solidification. Comparing the results, we have concluded that solidification plays a major role in determining splat shape on a rough surface. We also present results of the distribution of voids between the splat and the substrate.

This work deals with a 3-D transient simulation of the air plasma spraying of ceramic powders using a C.F.D. commercial code ESTET v3.4 that has been adapted to thermal plasma conditions. The mathematical model computes the distribution of particle velocity, temperature, molten state and size at impact and predicts the heat transfer to the substrate by plasma jet and particles. It incorporates the conversion from electrical to thermal energy in the torch nozzle as well as coating formation on the substrate. It makes it possible to predict the shape of the coating footprint when the torch and the substrate are fixed. The projections of the model are compared with experimental results that involve flow characteristics, time-dependant particle behavior in the flow and heat flux to the substrate.

We used an object oriented finite element numerical method to examine residual stress build-up in a simulated crosssection of coating. The cross-section image of coating was the result of simulation produced by a 3-D stochastic model of thermal spray coatings, which model features of coating microstructure including internal pores and surface roughness. An adaptive meshing technique was used to fit a grid in a section through the simulated coating, and stresses in the coating calculated using a finite element method. The results showed that stresses are sensitive to the thickness and roughness of the coating.

The objective of this study is to increase the deposition rate in the plasma-spray manufacturing of thermal barrier coatings without altering the quality of the coatings. The experimental part involves the measurement of in-flight particle characteristics and analysis of coatings properties when varying the hydrogen content of the plasma-forming gas, the torch nozzle diameter and the powder feed rate. The experimental results of particle measurements are discussed in the light of the gas flow fields projected by a 3-D model of the plasma spray process.

The effect of substrate characteristics on the formation of plasma-sprayed alumina splats was studied using both experiments and numerical simulation. Knowledge of the particle and substrate conditions is critical in understanding coating formation and in validating computational models. The size, velocity and temperature of the alumina particles prior to impact were measured using a particle in-flight diagnostic system. Experiments were performed on two substrate materials: stainless steel and glass. Substrate temperatures were varied in a range of 20-500°C and controlled with an electric heater. For each substrate material, a transition temperature was observed above which there was no fingering/splashing and the splats had a circular disk shape. A 3D computational model of free surface flows with heat transfer and solidification was used to simulate the impact of alumina particles in conditions given by the experiments. The splat shapes from numerical model were comparable to those of the experiments for hot stainless steel substrate. For a cold substrate, the numerical model did not show any fingering/splashing. In the experiments, however, we observed two types of splat shapes: intensive splashing with no central core and circular disk splat. Substrate surface contamination, not considered in the numerical model, was the probable cause of droplet splashing on the cold substrate.

This paper presents a numerical simulation of the plasma spraying of alumina particles using a three-dimensional commercial fluid dynamics code ESTET 3.4 . The objective of this study is to investigate the effect of (i) turbulence model and turbulence radial profiles at the torch exit on plasma flow and particle behavior, (ii) particle injection conditions on particle trajectories and heating and (iii) plasma jet fluctuations on temperature and velocity flow fields. The comparison of predictions with experimental measurements of gas and particle velocity and temperature, makes it possible to determine the influential parameters and set them to pertinent values.

A three dimensional model of coating formation has been developed. Using the model we are able to simulate coating formation by deposition of large numbers of droplets. The properties of impacting particles are assumed to vary stochastically using a normal probability density function. Splat curl up is assumed to be the source of porosity formation. The model is able to predict coating porosity, thickness and roughness as a function of spray parameters.

Various models exist of the 2D impact of a molten thermal spray particle onto a flat solid surface. Such models, however, cannot be used to examine 3D effects such as the asymmetric splashing and breakup which are common under thermal spray conditions. The focus of the present work is on such effects. A 3D model of droplet impact has been developed which predicts splashing and the subsequent formation of small satellite droplets. The model is a 3D version of RIPPLE (LA12007- MS), an Eulerian fixed-grid finite volume code utilizing a volume tracking algorithm to track the droplet free surface. Simulations are presented of the impact and splashing of a molten tin droplet, and the results compared with photographs. A simple model, based on Rayleigh-Taylor instability theory, yields an estimate of the number of satellite droplets which form during impact. Finally, a simulation of droplet impact under thermal spray conditions demonstrates breakup, although in the form of a corona which separates from the bulk of the fluid.