The aim of this study is to develop for thermal barrier applications a new process in which coatings exhibit properties between those of APS and EBPVD. This process includes two conventional D.C. plasma torches working in a chamber whose pressure can vary between 30 and 100 kPa. Micro-sized yttria stabilized zirconia powders are injected in both plasma jets to vaporize them, at least partially, and produce finely-structured coatings from vapor and micro-droplets deposition. The torch arrangement allows separating the vapor and the very small particles (less than 1 µm) from the partially vaporized bigger ones. The diagnostics are based on optical emission spectroscopy, pyrometry, imaging of particles trajectories and coating microstructural characterization.

This study deals with a plasma technique that combines two plasma spray torches to produce finely-structured zirconia coatings. Ideally, the deposition process path involves the vaporization of most of the particles injected in the plasma jet and the transport of the vapor to the substrate where it re-condenses. The arrangement of the plasma torches makes it possible to limit the deposition of non-completely evaporated particles onto the substrate. The experimental design of the vapor deposition process has been assisted by experimental characterization of the plasma temperature field and numerical simulations of the two plasma flow interactions and powder vaporization.