Slurry-based protective coatings for Oxide/Oxide ceramic matrix composites

摘要

In a pilot study zirconia/zircon, and zirconia/yttrium-monosilicate composite coatings for oxide ceramic matrix composites (Ox-CMC) with highly porous matrices were fabricated by deposition of powder dispersions (‘slurries’) and subsequent firing. During firing, thermal degradation of Ox-CMC as well as constrained sintering of powder compacts deposited on the rigid CMC substrate are key challenges. The oxidation-related volume expansion of zirconium-disilicide starting powders and reactivity of oxidation products zirconia and silica were used to compensate shrinkage and provide consolidation of powder compacts at process temperatures of 1300 °C. Similar processes are commonly referred to as ‘reaction-bonding’. Well-adherent, crack-free reaction-bonded coatings could be fabricated on Whipox-type Ox-CMC. Resulting microstructures are strongly depending on the composition, morphology, and reactivity of constituents, in particular of transient oxide phases. Zirconia/zircon reaction-bonding systems yield composite coatings with relative low porosity whereas as much lower densification capability of the zirconia/yttrium-monosilicate system was observed.