Mechanical Properties and Thermal Conductivity of Ytterbium-Silicate-Mullite Composites

Various Ytterbium-Silicate-Mullite composites were successfully fabricated by adding Yb(2)SiO(5) into mullite ceramics and then using pressureless sintering at 1550 °C. The influence of Yb(2)SiO(5) addition on the microstructure, mechanical properties, and thermal conductivity of ytterbium-silicate-mullite composites was investigated. Results show that the composites mainly consisted of a mullite matrix and some in situ formed Yb(2)Si(2)O(7) and Al(2)O(3) phases. By the addition of Yb(2)SiO(5), the Vickers hardness of composites reached ~9.0 at an additive concentration of 5 mol %. Fracture toughness increased to ~2.7 MPa·m(1/2) at the additive concentration of 15 mol %, owing to the trans-granular fracture and crack deflection of the pinning effect of the Al(2)O(3) phase in the composites. With the increase of the Al(2)O(3) phase in the composite, the thermal conductivity for the 15YbAM reached around 4.0 W/(m·K) at 1200 °C. Although the thermal conductivity increased, it is still acceptable for such composites to be used as environmental barrier coatings.