氮气压力对多孔氮化硅陶瓷显微组织和力学性能的影响

Effects of Nitrogen Pressure on Microstructure and Mechanical Performance of Porous Silicon Nitride Ceramics

以α-Si3N4为原料,Y2O3为烧结助剂,在三种不同的氮气压力(0.12、0.32和0.52 MPa)下烧结制备了多孔氮化硅陶瓷。研究了氮气压力对氮化硅的烧结行为、显微组织和力学性能的影响,分别通过SEM观察显微组织并统计晶粒的长径比,通过XRD对物相进行分析,并对烧结试样进行三点弯曲强度测试。随着氮气压力的提高,多孔陶瓷的线收缩率降低、气孔率提高,这是由于低熔点的液相中N含量随氮气压力的提升而增加,导致了液相粘度提高,抑制陶瓷致密化。随着氮气压力的提高,组织中的棒状β-Si3N4生长良好,晶粒长径比增大,其原因是高的液相粘度抑制了β-Si3N4形核,有利于β-Si3N4生长。由于β-Si3N4棒状晶的作用,陶瓷弯曲强度随氮气压力的升高得到改善,但是气孔率的升高降低陶瓷的强度。在0.52 MPa的氮气压力下烧结的多孔陶瓷气孔率达58%,弯曲强度为140 MPa。

Porous silicon nitride ceramic was fabricated by using Gt-Si3N4 as raw material and Y203 as a sintering ad- ditive, with nitrogen pressure of 0.12 MPa, 0.32 MPa and 0.52 MPa. Effects of the nitrogen pressure on grain mor- phology and mechanical properties of the resultant porous Si3N4 ceramics were characterized by SEM, XRD and flex- ural strength. With the increasing of nitrogen pressure, sintering shrinkage decreased, with a corresponding increased porosity. Due to the increase of nitrogen pressure, the viscosity of liquid phase increased due to increased N solubility, leading to the low densification in the sintering. Fibrous β-Si3N4 grains were developed in the porous microstructure and the grain morphology and aspect ratio were greatly affected by the nitrogen pressures. The high viscosity of the liquid phase in nitrogen at high pressure led to restraining of the 13-Si3N4 nucleation, and preferential growth of ^-SiaN4 Due to the formation of elongated β-SiaN4, flexural strength of the porous Si3N4 ceramic was improved by the increase of nitrogen pressure, while decreased with the increase of porosity. The porous Si3N4 ceramics with porosity of 58% and flexural strength of 140 MPa were obtained at the nitrogen pressure of 0.52 MPa.