A new injection system for spraying liquid nitrates in a low power plasma reactor: Application to local repair of damaged thermal barrier coating

• Published in: Surface & coatings technology 2019-01, Vol.357, p.195-203
• Main Authors: Rousseau, F., Quinsac, A., Morvan, D., Bacos, M.-P., Lavigne, O., Rio, C., Guinard, C., Chevillard, B.
• Format: Article
• Language: English
• Subjects: Aqueous solutions; Fracture mechanics; Infiltration; Low-power plasma reactor; Nano-microstructure; Nitrates; Oxide coatings; Particle image velocimetry; Physical vapor deposition; Plasma jets; Plasma physics; Protective coatings; Reactors; Repair; Seals; Spalling; Spraying; Stability analysis; Substrates; Thermal barrier coatings; Velocity measurement; Yttria-partially stabilized zirconia
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2018.09.069

In addition to the search for new Thermal Barrier Coating (TBCs) systems with increased reliability over very long time periods, the repair of current systems is a technological and economic issue for both civilian and military engine end-users. This paper describes the latest version of the deposition process known as the Low-Power Plasma Reactor (LPPR) process, specially developed to repair locally damaged TBCs. The LPPR process enables micro/nanostructured TBCs to be made from nitrate salts in aqueous solutions, which are sprayed in an Ar/O2 plasma discharge at low power (240 W) and transformed into oxide coatings. A new injection device was designed to produce a fairly homogenous and reproducible spray to repair partially spalled APS and EB-PVD TBCs deposited on small flat coupons. The microstructure and the stability of the LPPR TBCs were assessed, in particular using SEM observations, during ageing tests under various time/temperature conditions. The Particle Image Velocimetry (PIV) technique and associated modeling have proved that the nitrates impact the substrate in a liquid state even in the presence of plasma and a vacuum. Due to the liquid state of the precursors, the new LPPR TBC seals the damaged areas and deeply infiltrates all porosities and failure cracks in the original coatings. This research has enabled the new version of the LPPR process to be validated as a simple, efficient, cheap and promising way to repair locally damaged TBCs. •A new injection device was specially adapted to a Low-Power Plasma Reactor.•Droplets of precursors impact the substrate in a liquid form.•The liquid state favors the infiltration of the repair barrier.•Damaged APS or EB-PVD TBCs deposited on small samples were successfully repaired.