Effect of TiO2 and AlN Additions on the Sintering Behavior of the Si3N4-Y2O3-Al2O3 System

Si3N4-Y2O3-Al2O3 system bodies with TiO2 and AlN additions were fired at 1300-1900 C for 1 h. TEM and EDS analysis showed that spherical TiN particles were located in the grain boundary and grain. A sample containing both TiO2 and AlN fired at 1700 C had a bulk density above 3.25 g/cm3. In-situ measurement of shrinkage during sintering was carried out. The shrinkage of a green body in the Si3N4-Y2O3-Al2O3-TiO2-AlN system started at a lower temperature than that of the Si3N4-Y2O3-Al2O3 system. Although three peaks of the shrinkage rate in the sample without TiO2 and AlN were seen, the third peak disappeared in the case of TiO2 and AlN addition. Furthermore, it was confirmed that the maximum temperature in the shrinkage rate dropped about 70 C in the sample with TiO2 and AlN addition. XRD analysis showed that the alpha-to-beta phase transformation in the sample with TiO2 is delayed and that with TiO2 and AlN addition was advanced in comparison to that without TiO2 and AlN. Thermodynamics suggest that added TiO2 should react with Si3N4 in the case of only TiO2 addition and with AlN in the case of simultaneous addition of TiO2 and AlN to form SiO2 and Al2O3, respectively. 2 refs.