Effect of Y<sub>2</sub>O<sub>3</sub> on the Sintering, Mechanical and Dielectric Properties of Mullite/h-BN Composites

Mullite/10 wt. %h-BN composites with 5 wt. % Y 2 O 3 additive were fabricated by pressureless sintering at different temperatures. The densification, phase composition, microstructure, mechanical and dielectric properties of the mullite/h-BN composites were investigated. With the addition of Y 2 O 3 , the sintering temperature of the mullite/h-BN composites declined, while the density, mechanical and dielectric properties all increased. The addition of Y 2 O 3 promoted the formation of liquid phase at high temperature, which accelerated the densification. Besides, Y 2 O 3 particles which were located at the grain boundaries inhibited the grain growth of mullite matrix. For the mullite/h-BN composites with Y 2 O 3 additive, the appropriate sintering temperature was about 1600°C. The relative density, flexural strength, fracture toughness and dielectric constant of the Y 2 O 3 doped mullite/h-BN composite sintered at 1600 °C reached 82%, 135 MPa, 2.3 MPa·m 1/2 and 4.9, respectively.