Design, synthesis and characterization of multilayer environmental barrier coatings

Abstract

The formation of cristobalite thermally grown oxides (TGO) is a major life limiting factor for environmental barrier coatings (EBCs) with Si bond coat exposed to high temperature steam environments due to its reversible phase transformation and the resultant cracking behaviour during thermal cycling. Therefore, controlling or avoiding cristobalite TGO formation by engineering coating chemistry and architecture will be desirable for a highly durable EBC system. In this work, a multilayer Si/Al-Si-N/Yb2Si2O7 EBC was produced using a hybrid vapor deposition process. The oxidation behavior of the EBC was evaluated in flowing 90% H2O (g) + 10% air at 1316 °C. After 100 h and 510 h steam test, crack-free mullite and Al-Si-O-N layers formed above Al-Si-N layer and no SiO2 scale formation of Si bond coat was observed. Detailed TEM analyses show that the Al-Si-N layer successfully prevented the oxidation of underlying Si bond coat and avoided the formation of detrimental cristobalite phase.