Abstract
A slurry process was employed to develop advanced environmental barrier coatings (EBCs) for SiC based composites. Yb2Si2O7 and mullite (3 Al2O3⋅2 SiO2) were chosen as the base materials for the bond coat to enable temperatures beyond the melting point of the current silicon bond coat (1414 °C). Various sintering aids, such as mullite, Yb2Si2O7, Al2O3, and silicon enabled sintering at 1500 °C – 1550 °C. Yb2Si2O7 was used as the top coat to provide water vapor recession resistance. A HfSiO4 intermediate layer prevented the 1500 °C eutectic reaction at the mullite/Yb2Si2O7 interface. Parabolic oxidation behavior and good adhesion as well as chemical and microstructural stability were observed after 500 h / 500 cycle steam oxidation at 1427 °C in 90 % H2O-10 % O2 steam. Kinetic analyses on Yb2Si2O7-coated SiC showed the independence of TGO growth rates on EBC thickness indicating that the oxidant permeation through the silica scale is the rate controlling factor.
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