Feasibility research of Yb3Al5O12 garnet as environmental barrier coating materials

Abstract

In this work, Yb3Al5O12 (YbAG) garnet, as a new material for environment barrier coating (EBC) application, was synthesized and prepared by atmospheric plasma spraying (APS). The phases and microstructures of the coatings were characterized by XRD, EDS and SEM, respectively. The thermal stability was measured by TG-DSC. The mechanical and thermal-physical properties, including Vickers hardness (Hv), fracture toughness (KIC), Young's modulus (E), thermal conductivity (κ) and coefficient of thermal expansion (CTE) were also measured. The results showed that the as-sprayed coating was mainly composed of crystalline Yb3Al5O12 and amorphous phase which crystallized at around 917 °C. Moreover, it has a hardness of 6.81 ± 0.23 GPa, fracture toughness of 1.61 ± 0.18 MPa m1/2, as well as low thermal conductivity (0.82–1.37 W/m·K from RT-1000 °C) and an average coefficient of thermal expansion (CTE) (∼6.3 × 10−6 K−1 from RT to 660 °C). In addition, the thermal shock and water-vapor corrosion behaviors of the Yb3Al5O12-EBC systems on the SiCf/SiC substrates were investigated and their failure mechanisms were analyzed in details. The Yb3Al5O12 coating has an average thermal shock lifetime of 72 ± 10 cycles as well as an excellent resistance to steam. These combined properties indicated that the Yb3Al5O12 coating might be a potential EBC material. Both the thermal shock failure and the steam recession of the Yb3Al5O12-EBC systems are primarily associated with the CTE mismatch stress.