Influence of Yb2Si2O7 doping concentration on mechanical properties and thermal conductivity of Yb2SiO5-Yb2Si2O7 composite ceramics

Ytterbium silicate is one of the most promising candidate materials for environmental barrier coatings. (1-x)Yb2SiO5-xYb2Si2O7 (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, mol. %) composite ceramics were prepared by high-temperature sintering method at 1500 °C. The microstructure, phase composition, mechanical properties, thermal conductivity and high-temperature sintering behavior of Yb2SiO5-Yb2Si2O7 composite ceramics were investigated. The results showed that the (1-x)Yb2SiO5-xYb2Si2O7 composite ceramics were composed of X2-Yb2SiO5 and β-Yb2Si2O7 phases, and no other phases were formed. The hardness (3.93 ± 0.11 GPa) and fracture toughness (1.53 ± 0.03 MPa·m1/2) of 0.5Yb2SiO5-0.5Yb2Si2O7 ceramic were about 50% higher than those of pure Yb2SiO5 ceramic. The thermal conductivity of 0.5Yb2SiO5-0.5Yb2Si2O7 ceramic was 1.39 W·m−1·k−1 at 1073 K, and maintained at a lower level. The microstructure and phase composition of 0.5Yb2SiO5-0.5Yb2Si2O7 ceramic were still stable after sintered at 1400 °C for 100 h, exhibiting excellent high-temperature structural stability.