Impact of Precursor Thermal Decomposition Reactions on YSZ Coatings Deposited with a Low-Power Plasma Torch at Short Spray Distance
Résumé
Yttria-stabilized zirconia (YSZ) deposition at short spray distance is of great interest for the aeronautic industry, especially to perform a thermal barrier coating (TBC) local repair. Typical thermal spray techniques usually employed to deposit such coatings are not designed for this type of application due to the powers involved. This work focuses on a plasma torch operating at atmospheric pressure, at low power (\ 1 kW) and at short spray distance (4 mm). Precursor solutions are directly injected in the plasma afterglow to be sprayed and deposited onto a substrate. During flight time, precursor conversion is initiated. However, because of the low afterglow temperature (600 °C), droplets are not fully converted into YSZ when they impact the substrate. Typically, posttreatment is applied to improve the conversion of precursors into oxides, but this operation is very time-and therefore moneyconsuming. This study is focused on exploring a way to maximize the heat transfer to droplets already deposited by generating exothermicity using a redox reaction between zirconium and yttrium nitrates with ammonium acetate. This work highlights how exothermic precursor decomposition reactions as well as the gel-like consistency of the deposited clusters can improve both chemical conversion and coating microstructure.
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