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Thermal spraying using liquid feedstock has emerged as a promising technology for the deposition of finely structured ceramic coatings. In order to provide a comparative assessment of the deposition mechanisms occurring when spraying suspension or solution feedstock, suspensions of 300 nm-sized ZrO2–4.5 mol.% Y2O3 particles dispersed in water and in ethanol and solutions of zirconium and yttrium salts, corresponding to ZrO2–4.5 mol.% Y2O3 and ZrO2–8 mol.% Y2O3 stoichiometries, were processed by plasma spraying using different parameter settings. In-flight diagnostics of sprayed droplets, together with the morphological, microstructural and phase analysis of individual lamellae collected onto polished substrates, performed by SEM, FIB, AFM and micro-Raman spectroscopy, led to the identification of deposition mechanisms, which were subsequently verified through the characterisation of complete coating layers

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International audienc

Suspension plasma spraying (SPS) enables the production of various coating microstructures with unique mechanical and thermal properties. Aeronautical manufacturers have been working for fifty years to improve the thermal barrier coating (TBC) performances in gas turbines. Commercial plasma torches with a segmented anode that are characterized by stable plasma jets should enable a better control of the TBC microstructure. The addition of diatomic gases such as hydrogen in the plasma-forming gas affects the plasma jet formation and causes some instabilities. However, it enhances the thermal conductivity of the gas flow, the plasma mass enthalpy and the heat transfer to particles. This study aims to characterise and describe the coating microstructure changes of yttria-stabilised zirconia when gradually adding hydrogen with argon into the plasma gas mixture. The effect of hydrogen is weighted out due to the gas mass enthalpy, mean velocity at the nozzle exit and “hot zone” length of the plasma jet. The coating microstructures, which depend on these plasma jet parameters, will be mapped from feathery and porous to dense and cracked deposits depending on the spraying conditions.