Air plasma-sprayed Y2O3 coatings for Al2O3/Al2O3 ceramic matrix composites

Al2O3/Al2O3 ceramic matrix composites (CMC) are candidate materials for hot-gas leading components of gas turbines. Since Al2O3/Al2O3 CMC are prone to hot-corrosion in combustion environments, the development of environmental barrier coatings (EBC) is mandatory. Owing to its favorable chemical stability and thermal properties, Y2O3 is considered a candidate EBC material for Al2O3/Al2O3 CMC. Up to 1 mm thick Y2O3 coatings were deposited by means of air plasma spraying (APS) on Al2O3/Al2O3 CMC with a reaction-bonded Al2O3 bond-coat (RBAO). APS Y2O3 coatings exhibit a good adherence in the as-deposited state as well as upon isothermal annealing up to 1400 °C. Moreover, furnace cyclic testing performed at 1200 °C revealed an excellent durability. This is explained by the formation of a continuous, approximately 1 μm thick reaction zone at the APS Y2O3/RBAO interface. The reaction zone between Y2O3 and Al2O3 comprises three layers of thermodynamically stable yttrium-aluminates exhibiting strong bonding, respectively.