中文摘要：

在压力为5.2～5.7GPa,温度为1100～1300℃,保温保压时间为15min的条件下,对添加有Y2O3、Al2O3助剂的α-Si3N4微粉进行了高温高压烧结实验,以探索α-Si3N4的相变.对样品进行了X射线衍射、扫描显微观察及密度测量.实验结果表明,α→β相转变开始于1100～1200℃之间,其相转变程度随温度、压力的升高均有所提高,在5.7GPa/1300℃时,发生完全的相转变.相转变完成的烧结样品由长柱状β-Si3N4晶粒组成,晶粒间相互交错,结构均匀致密,断面有明显的晶粒拔出现象.根据实验数据拟合了大致的两相相界方程,并讨论了相关的相变机制.

英文摘要：

In order to investigate the phase transition of silicon nitride （Si3N4 ）, α-Si3N4 with Y2O3 and Al2O3 as additives was sintered under 5.2 - 5.7 GPa at 1 100 - 1300℃ for 15 rain. The sintered samples were analyzed by X-ray diffraction, scanning elec- tron microscopy and density measurement. The results showed that α→βphase transition started in 1 100 - 1200℃ and the ratio of transformation from a to β phase increased with increasing temperature and pressure, α-Si3N4 was completely transformed to β3-Si3N4 under 5.7 GPa at 1300 ℃. The β-Si3N4 was composed of elongated β-Si3N4 rod crystals with disordered orientation and had intergranular interlocks and uniform and compact microstructure. Pulled-out crystal grains on the fractured cross sections were obviously observed by SEM. The boundary equations of the two phases were roughly fitted on the base of obtained data. The related mechanism of phase transformation was discussed.