Effects of Y 2 O 3 –MgO nanopowders content on mechanical and dielectric properties of porous BN/Si 3 N 4 composites

Porous BN/Si3N4 composites with different Y2O3–MgO nanopowders have been fabricated by a pressureless sintering method. The densification, phase evolution, microstructure, mechanical properties and dielectric properties of the BN/Si3N4 composites were investigated. The density and mechanical properties of the porous BN/Si3N4 composite ceramics firstly increased with addition of Y2O3–MgO up to 20wt% and then decreased, while the dielectric properties gently declined as the Y2O3–MgO contents increased. For the porous BN/Si3N4 composites with 20wt% Y2O3–MgO nanopowders, the porosity, flexural strength and dielectric constant reached 21.9%, 243.6MPa and 5.5, respectively, which indicated that the composites could be one of the candidates for wave-transparent applications.