氟化钙对常压烧结Si3N4/BN复相陶瓷结构与性能的影响

以微米级Si3N4和h-BN粉末为原料,CaF2–Al2O3–Y2O3为烧结助剂,采用常压烧结工艺制备了BN体积含量为25%的Si3N4/BN复相陶瓷。研究了CaF2添加量对Si3N4/BN复相陶瓷材料力学性能的影响,并通过X射线衍射和场发射扫描电镜分析了复相陶瓷的物相组成和显微组织。结果表明：随着CaF2添加量增加,制备的Si3N4/BN复相陶瓷材料气孔率逐渐增大,收缩率变小,相对密度减小。添加量为2%（质量分数）时,Si3N4/BN复相陶瓷的室温抗弯强度达145.5MPa。添加适量的CaF2可在Si3N4/BN复相陶瓷材料常压烧结过程中较大程度地破坏h-BN的卡片房式结构,将微米级的h-BN颗粒变成纳米级颗粒。

Effect of CaF2 on Microstructure and Mechanical Properties of Pressureless Sintered Si3N4/BN Composites

Si3N4/BN composites with h-BN of 25% in volume were fabricated via pressureless sintering with micron-sized α-Si3N4 and h-BN powders as starting materials and CaF2,Al2O3 and Y2O3 as sintering additives.The effect of CaF2 content on the mechani-cal properties of Si3N4/BN composites was investigated,and the phase composition and microstructure of the Si3N4/BN composites were analyzed by X-ray diffraction and scanning electron microscopy.The results show that as CaF2 content increases,the porosity of Si3N4/BN composites increases,and its shrinkage and relative density decrease.When the amount of CaF2 is 2% in mass,the Si3N4/BN composite has the highest flexural strength of 145.5 MPa at room-temperature.A moderate amount of CaF2 in Y2O3-Al2O3 sintering aids can destroy the card-house structure during the pressureless sintering process of Si3N4/BN composites,causing the fracture of micron-sized h-BN particles into nano-sized BN segments.