含LiAlO2-Y2O3复合助烧剂的氮化硅陶瓷低温致密化研究

Low temperature densification of silicon nitride ceramics with LiAlO2-Y2O3 as composite sintering additive

以高α相含量的Si3N4粉体为主要原料,LiAlO 2-Y2O3作为复合助烧剂,在无压条件下烧结Si3N4陶瓷,研究了LiAlO2-Y2O3助烧剂体系对Si3N4陶瓷烧结致密化过程、相变过程和显微结构的影响。结果表明:LiAlO2-Y2O3助烧剂对Si3N4陶瓷致密化温度的降低和相转变速率的提高有明显作用,在1500℃有低共熔点液相LiAlSi 3O 8生成,且α-Si3N4向β-Si3N4的相转变开始进行,埋碳烧结时被氧化部分为试样表面。在LiAlO2-Y2O3助烧剂体系中,对Si3N4陶瓷低温致密化起主导作用的是LiAlO 2,当LiAlO 2加入量为8%(w)时试样的相对密度达到98.1%,且可以得到发育良好的柱状β-Si3N4晶粒。而Y2O3对α-Si3N4向β-Si3N4的相转变速率有明显提高,随着Y2O3加入量的增加,β-Si3N4转化率随之提高。当Y2O3加入量为8%(w)时β-Si3N4转化率达到91%。

Si3N4 ceramics were prepared by pressureless sintering using highα-phase content Si3N4 powder as the main raw material and LiAlO2-Y2O3 as the composite sintering additive.The effect of LiAlO2-Y2O3 sintering additive on the sintering densification,the phase transformation and the microstructure of Si3N4 ceramics was researched.The results show that the addition of LiAlO2-Y2O3 can play a significant role in reducing the sintering densification temperature and promoting the phase transformation rate of the Si3N4 ceramics;at 1 500℃,a low melting point phase LiAlSi3O8 is formed andα-Si3N4 begins to transform toβ-Si3N4;the oxidized part of the specimen during cabon embedded sintering is the surface.In the system of LiAlO2-Y2O3 sintering additive,LiAlO2 plays as a leading role in the low-temperature densification of Si3N4 ceramics.When the LiAlO2addition is 8 mass%,the relative density of the specimen reaches 98.1%,and the well developed elongated β-Si3N4 grains can be obtained.Y2O3 can promote the phase transformation rate of α-Si3N4 to β-Si3N4,which increases with the rising Y2O3 addition.When the Y2O3 addition is 8 mass%,the conversion rate of β-Si3N4 is 91%.