Thermal cycle test performances of environmental barrier coatings of HfO2-SiO2/Yb2Si2O7 in the steam environment at 1475 °C

The novel bi-layer environmental barrier coatings (EBCs) with HfO2-SiO2/Yb2Si2O7 structure (70HfO2-30SiO2/ Yb2Si2O7: 70HS/YbDS, 50HfO2-50SiO2/Yb2Si2O7: 50HS/YbDS, molar ratios) was tested in 90%H2O-10%O2 conditions between room temperature and 1475 degrees C in an Al2O3 tube furnace, then its performance was evaluated. The YbDS layer was contaminated by alumina impurities under steam conditions. After 22 cycles, the 70HS/YbDS completely separated from the SiC substrate, while the 50HS/YbDS and SiC did not separate, even though cracks formed at the 50HS/SiC interface and the TGO layer. Furthermore, the thermally grown oxide (TGO) layer formed at the HfO2-SiO2/SiC interface. Formation and growth of the TGO led to the formation and propagation of cracks at the HfO2-SiO2/TGO interface and TGO interior, which was the culprit leading to the failure of EBCs. These results demonstrated that the 50HS/YbDS EBCs have the potential to protect SiC in steam conditions at 1475 degrees C.