In this work, a numerical model of the cold spray process was developed to reproduce microstructures obtained in coatings by simulating the deformation of impinging particles and resulting coating build-up. The model employs a library of particle images generated by x-ray microtomography. To each image, a velocity is assigned and the deformation that would be produced by particle impact is estimated by means of finite element analysis and stored for later use. Based on the results, the ing approach has good potential for simulating coating microstructures that can be achieved through cold spraying.

In the present study, X-ray microtomography is used to examine cold-sprayed tantalum splats on copper substrates. To resolve tantalum splats intermeshed with other splats of the same chemical composition, a contrasting medium of some sort is required. For this purpose, the feedstock powder is coated with an iron layer by means of fluidized-bed chemical vapor deposition. Experimental tests were coupled with finite element simulations to determine how stresses generated during the impact of a spherical iron-coated particle affect the integrity of the added contrasting layer.

Moving from a 2-dimensional to a 3-dimensional approach to microstructure and properties has been expected eagerly for a long while to result in a dramatic increase in the knowledge of thermally-sprayed processes and coatings. To meet these expectations, in the present work, microtomography and electrochemical impedance spectroscopy (EIS) were carried out to simulate the microstructure of plasma-sprayed alumina. As-sprayed and excimer laser-processed deposits were studied. Some unexpected but relevant results, e.g. regarding pore orientation in the coatings, could be obtained. EIS simulation led to the establishing of an electrical circuit equivalent to the microstructure which simulated the insulating properties as a function of interfaces and pore interconnection. The latter was studied by microtomography. From this 3-dimensional simulation, a finite element analysis of mechanical properties was developed and compared to experimental measurements. Using this approach to microstructure and properties, excimer laser surface processing was shown to be an innovative process to modify insulating characteristics of plasma-sprayed alumina.

Porosity is a key feature of thermally-sprayed coating microstructure. Porosity is made of pores and cracks of various orientations. Both pores and cracks can be intralamellar or interlamellar due to coating build-up which leads to lamellae from impinging of droplets. Pores are interconnected with cracks, which results in a 3-dimensional porosity network. Direct observation of this network is intricate and remains somewhat limited. A 3-dimensional simulation of this network was therefore developed in this work based on the building-up of objects which simulated the lamellae in the sprayed microstructure. These objects were constructed from morphological measurements using confocal microscopy of actual lamellae, i.e. “splats”, obtained from “linescan”-typed plasma-sprayed experiments. This simulation, in the lamella building-up, involves randomly cracks and pores the characteristics of which (i.e. content, orientation, size, …) were determined from thorough quantitative image analysis of cross-section plasma-sprayed alumina microstructures. Using 3-dimensional images resulting from the simulation, finite element calculations were performed to study dielectric properties of plasma-sprayed alumina as a function of porosity. The influence of anisotropy is discussed in particular and calculated values compared to experimental values.

Plasma spraying is known to be one of the main promising processes for the manufacturing of Ti/SiC long fiber composites. However, some improvements remain to be done for this process to be applied in a routine industrial route. These include: oxygen contamination of the sprayed material through that of Ti particles before and during spraying damaging of fibers due to a high level of thermal stresses induced at the spraying stage adequate deposition of Ti-based powder to achieve a low-porosity matrix and good impregnation of the fiber array. This contribution deals with work in the 3 previously mentioned fields, which resulted in a whole 3-fold study of the process. Oxidation was studied using electron microprobe analysis of elementary particles quenched and trapped into a closed box at various given flight distances. Oxygen diffusion phenomena within the particles are discussed from a preliminary theoretical approach coupled with experimental data. Isothermal and thermo-mechanical calculations were made using ABAQUS code to determine stresses arising from contact of a liquid Ti-6Al-4V particle onto a SiC fiber. On a higher scale, i.e. that of the sprayed powder flow, a 2-dimensional original model simulating the deposition of droplets onto a substrate was developed. This model is based on a lattice-gas automaton which reproduces the hydrodynamical behavior of fluids.