Effect of applied pressure and sintering aid on phase separation and crystallization behavior of amorphous Si₃N₄-BN composite powder

Si₃N₄-BN nanocomposites are formed via phase separation and crystallization of amorphous Si₃N₄-BN composite powder during sintering. Amorphous Si₃N₄-BN composite powders were prepared by a vapor phase reaction method. To clarify the effect of applied pressure and sintering aid on the phase separation and crystallization behavior, the composite powders were hot-pressed and pressurelessly sintered with and without Y₂O₃-Al₂O₃ sintering aid. Si₃N₄ crystallized into α-phase at 1600°C without sintering aid, and into β-phase at 1400°C with sintering aid. It was found that the crystallization of Si₃N₄ and BN was promoted by applied pressure and sintering aid. On the other hand, the phase separation of BN from Si₃N₄ occurred around 1400°C regardless of applied pressure and sintering aid.