Effects of sintering aids on the microstructure and mechanical properties of laminated Si 3N 4/BN ceramics

Abstract

Laminated Si 3N 4/BN ceramics with two types of sintering aids, MgO–Y 2O 3–Al 2O 3 (MYA) and La 2O 3–Y 2O 3–Al 2O 3 (LYA), were fabricated through roll compaction and hot-pressing. Sintering aids influence evidently the microstructure and mechanical properties of laminated Si 3N 4/BN ceramics. In comparison with La 2O 3–Y 2O 3–Al 2O 3, MgO–Y 2O 3–Al 2O 3 sintering aid is easier to form a glassy phase with lower viscosity and lower eutectic temperature, which is much easier to migrate into BN interlayers. This results in the denser interlayer microstructure and good bending strength of laminated Si 3N 4/BN ceramics at room temperature, but poor work of fracture (WOF) at room temperature, low strength and work of fracture at elevated temperature. In addition, the LYA sintering aid is good for forming elongated and interlocked β-Si 3N 4 grains and beneficial to the mechanical properties of the laminated Si 3N 4/BN ceramics.