多孔Si_3N_4/BN复相陶瓷的常压烧结制备

以微米级Si3N4和h-BN粉末为原料,Yb2O3-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%的多孔Si3N4/25%h-BN复相陶瓷。研究了Yb2O3添加量对Si3N4/25%BN复相陶瓷力学性能的影响,通过X射线衍射和扫描电子显微镜分析了复相陶瓷的物相组成和显微结构。结果表明:随着Yb2O3添加量增加,制备的Si3N4/25%BN复相陶瓷的气孔率逐渐增大,收缩率变小,相对密度减小。Yb2O3添加量为2%(质量分数)时,Si3N4/25%BN复相陶瓷的气孔率为15.1%,相对密度为72.8%;当Yb2O3添加量提高至15%时复相陶瓷的气孔率增加至32.1%,相对密度则降至60.3%。同时随着Yb2O3添加量增加,复相陶瓷的室温抗弯强度先增大后减小,Yb2O3含量为4%时,室温抗弯强度呈现最大值,可达264.3MPa。

PREPARATION OF POROUS Si3N4/BN COMPOSITE CERAMICS BY PRESSURELESS SINTERING

Porous Si3N4/25%BN（in volume,h-BN） composite ceramics were fabricated by pressureless sintering using micron-sized α-Si3N4 and h-BN powders as starting materials and Yb2O3,Al2O3 and Y2O3 as sintering additives. The effects of the Yb2O3 content on the mechanical properties of the Si3N4/25%BN composites were investigated,and the phase composition and microstructure of the Si3N4/25%BN multiphase composite ceramics were analyzed by X-ray diffraction and scanning electron microscopy. The experimental results show that as Yb2O3 content increases,the porosity of Si3N4/BN composite ceramics increases,and its shrinkage and relative density decrease. The apparent porosity of composites increases from 15.1% to 32.1%,and its relative density decreases from 72.8% to 60.3% with the increase of Yb2O3 content in mass from 2% to 15%. The flexural strength of the samples fistly increases and then decreases as the amount of Yb2O3 increases. When the amount of the Yb2O3 is 4% in mass,the Si3N4/25%BN composite ceramic has the highest flexural strength reaching to 264.3 MPa under room-temperature.