Reaction-based Processing of Thermal and Environmental Barrier Coatings for All-Oxide Ceramic Matrix Composites

Abstract

The protection of all-oxide ceramic matrix composites (CMC) based on alumina and mullite is a key issue for their long-term high-temperature application in corrosive atmosphere. Alumina and mullite are prone to high-temperature chemical corrosion, mainly in highly dynamic combustion atmospheres. The application of corrosion-resistant environmental barrier coatings (EBCs) is considered the only way to overcome the corrosion problem of all-oxide CMCs. Besides corrosion, alumina and mullite fibers suffer from high-temperature creep and strength loss caused by thermally induced grain growth. Therefore the development of thermal barrier coatings with low thermal conductivity is essential for all-oxide CMCs. In order to reduce costs and to improve flexibility, the deposition of coatings via reaction-based techniques is highly attractive. Reaction-bonding can be performed at moderate temperatures not exceeding the CMC processing temperature. Thermal and environmental barrier coatings have been deposited on porous WHIPOX-type CMC substrates by means of dip-coating and subsequent reaction-bonding. Examples include the deposition of reaction-bonded alumina coatings, reaction-bonded zirconia coatings, composite and multilayer coatings.