Comparative Study on Liquid Plasma Sprayed Lanthanum Aluminate Oxide Coatings Using Different Feedstock Materials for Potential TBC Application

TBC’s are used in aerospace and automotive industry with the aim to provide thermal protection to superalloy materials from excessive temperatures and hot corrosion. Conventional TBC systems consist of superalloy bondcoats, usually MCrAlYs, serving as an oxidation resistant and thermal expansion coefficient mediator layer between the substrate and the ceramic top-coat heat resistant layer. A successful TBC system exhibits high thermal shock resistance, low thermal conductivity, hot corrosion protection as well as long-term stability at high temperatures.  

Lately several studies focus on alternative to YSZ top-coat materials for applications above 1100^oC. Operation environments with temperatures higher than 1100^oC result in densification, phase transformation and Young’s modulus increase thus limiting long term stability due to deterioration of the whole system.

Coatings development using the Liquid Plasma Spraying (LPS) technique requires liquid feedstock materials in form of suspension or solution. The use of precursor solutions has the advantage of phase formation through chemical reaction during droplet travel time through the plasma in a single step procedure. This way promising nanostructured ceramic coatings can be deposited presenting unique microstructural characteristics, uniform pore distribution and absence of large splat boundaries.

In our study, a detailed investigation concerning the effect of different feedstock LaAlO₃ materials on thermally sprayed perovskite coatings development has been performed. Feeding materials were i) suspension inks of home-made fine LaAlO₃ perovskite type oxide powders (prepared using liquid chemistry methods) and ii) solutions developed using nitrate La and Al salts as precursor materials. LPS parameters correlation and consequent optimization of process yield, deposition rate and microstructure quality of the developed coatings has been done. Good quality coatings can be deposited, with different thickness for potential use in TBC.

Support by THEBARCODE project (№310750-FP7) is gratefully acknowledged.