Novel ceramic spray powders for abradable coatings

Abradable coatings are used in turbines to reduce the clearance between the blade tips and the casing. Abradable seals improve the overall efficiency of the turbine which leads to reduced fuel consumption and likewise lower carbon dioxide emissions. At operation temperatures above 900°C, mainly ceramic powders are used for the coatings. These powders are often mixed with additional pore formers and/or solid lubricants to improve the rub performance of the resulting coatings.

In this study, specially designed powders with different chemical compositions, e.g. yttria stabilized zirconia, gadolinium zirconate and others,  were used to produce theses abradable coatings by atmospheric plasma spraying. The coatings were applied by a high-enthalpy plasma spray system (Progressive Surface 100HE®) that allowed for high powder feed rates combined with high deposition efficiency.  The study shows the influence of different spray parameters on the porosity and hardness of the coatings. Porosity was determined at SEM pictures of the coating cross sections using the open source software ImageJ. The hardness was measured by a HR15Y indentation test. The lifetime of the abradable coatings was compared to conventional thermal barrier coatings in a furnace thermal cycling test.