Stability of interfaces in hybrid EBC/TBC coatings for Si-based ceramics in corrosive environments

• Published in: International journal of refractory metals & hard materials Vol. 49; pp. 339 - 349
• Main Authors: Xu, J., Sarin, V.K., Dixit, S., Basu, S.N.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.03.2015
• Subjects: Ceramic matrix composites; Chemical vapor deposition; Coatings; Corrosion prevention; Deposition; Environmental barrier coatings; Exposure; Functional grading; Mullite; Silicon carbide; Thermal barrier coatings; YSZ; Yttria stabilized zirconia; Thermal barrier coatings; Environmental barrier coatings; YSZ; Functional grading; Mullite
• ISSN: 0263-4368; 2213-3917
• DOI: 10.1016/j.ijrmhm.2014.08.013

SiC/SiC ceramic matrix composites (CMCs) are being used increasingly in the hot-sections of gas turbines, especially for aerospace applications. These CMCs are subject to recession of their surface if exposed to a flow of high-velocity water vapor, and to hot-corrosion when exposed to molten alkali salts. This research involves developing a hybrid system containing an environmental barrier coating (EBC) for protection of the CMC from chemical attack and a thermal barrier coating (TBC) that allows a steep temperature gradient across it to lower the temperature of the CMC for increased lifetimes. The EBC coating is a functionally graded mullite (3Al2O3•2SiO2) deposited by chemical vapor deposition (CVD), and the TBC layer is yttria-stabilized zirconia (YSZ) deposited by air plasma spray (APS). The stability of this system is investigated, which includes the adhesion between the two coating layers and the substrate, the physical and chemical stability of each layer at high temperature, and the performance under severe thermal shock and during exposure to hot corrosion. The effect of vertical cracks in the TBC on the EBC layer below it is also examined. •Dense, uniform and phase pure mullite-based EBCs were deposited on SiC/SiC CMCs by CVD and overlaid by APS YSZ TBCs.•The EBCs were graded from stoichiometric mullite at the EBC/CMC interface to alumina-rich mullite at the EBC/TBC interface.•The coating system performed better than plasma sprayed coatings systems based on similar design with segmentation cracks.•The segmentation cracks in the TBC propagated into the EBC for the plasma sprayed samples.•The plasma sprayed mullite/CMC interface was weak while the CVD mullite/CMC interface was strong.