Development of oxide-based High temperature environmental barrier coatings for ceramic matrix composites via the slurry process

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 degrees C). Various sintering aids, such as mullite, Yb2Si2O7, Al2O3, and silicon enabled sintering at 1500 degrees C - 1550 degrees C. Yb2Si2O7 was used as the top coat to provide water vapor recession resistance. A HfSiO4 intermediate layer prevented the 1500 degrees 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 degrees C in 90 % H2O-10 % O-2 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.