Study of the microstructure and efficiency of YSZ-SPS finely structured ceramic coatings ; Etude de la microstructure et des performances des revêtements céramiques YSZ finement structurés obtenus par projection plasma de suspension

Thanks to the using of liquid carrier, suspension plasma spray (SPS) enables the manufacture of finely structured coatings. As for conventional plasma spraying (APS), the microstructures of SPS coatings can be tailored by controlling the spray conditions. However, SPS is more complicated than APS due to its number of modifiable parameters.This thesis aims to provide a more fundamental understanding of the relationship between SPS process parameters and the properties of YSZ coatings by identifying generic models based on the use of mathematical statistical methods for the study of influence and sensitivity of the individual parameters.Systematic experiments were carried out to study the influence of six parameters (plasma power, suspension mass load, powder size, projection distance, projection step and substrate roughness) on the microstructure of coatings which were also analyzed in terms of the properties (mechanical, thermal, tribological, etc.). The porosity of the coatings was studied in detail and the measurements were carried out using three different techniques: the image analysis method, the X-ray transmission and the USAXS (Ultra-Small Angle X-ray Scattering) method. Multivariate analyzes of the collected experimental data were performed and several mathematical models were proposed to predict the properties of the coatings and then guide towards an optimization of the microstructure of the coating for specific applications.In this context of optimizing the mechanical and tribological performance of ceramic coatings, different amounts and sizes of h-BN powder have been added in the YSZ suspension. The YSZ/h-BN composite coatings were manufactured by SPS process and their analysis showed a clear reduction in the coefficient of friction and the wear rate when the size and the amount of addition powder are optimized together. Three wear mechanisms have finally been identified and been discussed. ; Grâce à l'utilisation d'un porteur liquide, la projection plasma de suspension (SPS) permet la fabrication ...