Environmental barrier coatings (EBCs) protect fiber-reinforced ceramics (such as SiC/SiC composites) from water vapor recession, which is observed in modern gas turbines. These coatings are often made by thermal spray deposition methods; a standard coating material system for EBCs is a ytterbium disilicate topcoat with a silicon bond coat. The paper will describe the recent results of our group on advanced EBCs.
First of all, different spraying processes such as atmospheric plasma spraying (APS), suspension plasma spraying (SPS), and very low-pressure plasma spraying (VLPPS) can be used to produce these coatings and will be described along with the corresponding properties of the coatings. Major targets for EBC development are a high degree of crystallinity after deposition, a low porosity level, and a minor loss of silicon during spraying. The influence of the different coating processes on these properties will be discussed.
Furthermore, results on the development and performance of combined environmental and thermal barrier coatings using yttria-stabilized zirconia (YSZ) as thermal barrier coating will be presented.
Finally, the results of thermogravimetric measurements of SiC samples coated with silicon bond coat and dense ytterbium disilicate topcoat will be shown. The comparison with samples only coated with a silicon bond coat showed a reduced oxidation rate of the sample revealing the low permeation rate of the top coat.