Effect of oxide additives on the sintered texture of amorphous Si ₃N ₄-BN composite powder

The crystallization behavior and sintered texture of amorphous Si ₃N ₄-BN composite powder were investigated in the range 1200-1800°C with sintering aids from the Y ₂O ₃-Al ₂O ₃ and Y ₂O ₃-TiO ₂-AlN systems. With the Y ₂O ₃-Al ₂O ₃ system, no crystalline phase was observed at 1200°C. α- and β-Si ₃N ₄ were detected by XRD at 1400°C, and α-Si ₃N ₄ was transformed to β-Si ₃N ₄ and h-BN appeared at 1600-1800°C. On the other hand, with the Y ₂O ₃-TiO ₂-AlN system, a small peak of TiN was detected at 120°C.Si ₂N ₂O was detected with α- and β-Si ₃N ₄ at 1400°C At 1600-1800°C, β-Si ₃N ₄ and h-BN were detected and Si ₂N ₂O disappeared. In the sintered texture at 1800°C, flaky BN particles with a length of about 1 μm were observed in an equiaxed Si ₃N ₄ grain matrix in the Y ₂O ₃-Al ₂O ₃ system, whereas rod-like Si ₃N ₄ grains with a length of 2-3 μm and flaky BN particles with a length of about 1.5 μm were observed in the Y ₂O ₃-TiO ₂-AlN system.