Key durability issues with mullite-based environmental barrier coatings for Si-based ceramics

Abstract

Plasma-sprayed mullite (3Al 2 O 3 2SiO 2) and mullite/yttriastabilized-zirconia (YSZ) dual layer coatings have been developed to protect silicon-based ceramics from environmental attack. Mullitebased coating systems show excellent durability in air. However, in combustion environments, corrosive species such as molten salt or water vapor penetrate through cracks in the coating and attack the Sibased ceramics along the interface. Thus the modification of the coating system for enhanced crack-resistance is necessary for longterm durability in combustion environments. Other key durability issues include interfacial contamination and coating/substrate bonding. Interfacial contamination leads to enhanced oxidation and interfacial pore formation, while a weak coating/substrate bonding leads to rapid attack of the interface by corrosive species, both of which can .cause a premature failure of the coating. Interfacial contamination can be minimized by limiting impurities in coating and substrate materials. The interface may be modified to improve the coating/substrate bond.