Theoretical modeling and experimental study of thermal barrier coatings

An automated plasma spray apparatus was designed to investigate experimentally the formation of splats (spread and solidified melted particles) by fully controlling key physical parameters (the velocity, temperature and size of the molten droplets impacting a substrate, and the temperature and surface condition of the substrate). The plasma spray apparatus made it possible to obtain a representative set of yttria-stabilized zirconia (YSZ) splats deposited on polished metal substrates (stainless steel or polished CoNiCrAlY sub-layers sprayed on nickel alloy substrates by low pressure plasma spraying) with full control of key physical parameters. The set of splats allowed verification of the theoretical characterization of metal oxide splat formation. Even without introducing empirical coefficients to the theoretical equations, quite good agreement between the calculated and experimental diameters and thicknesses of YSZ-splats was obtained over a wide range of various values of the key physical parameters. The results obtained will be first of all interest for optimizing the deposition of thermal barrier coatings and also for optimizing the deposition of the first monolayer of coatings of metal oxides sprayed onto metal substrates.