Two cores in one grain in the microstructure of silicon nitride prepared with aligned whisker seeds

The microstructure of silicon nitride with aligned silicon nitride whisker seeds was examined by electron microscopy. Silicon nitride sintered with yttria and alumina showed a “core-rim” structure. A few grains of the sample sintered with yttria and alumina had more than one core within one grain. This was explained in terms of coalescence of the grains growing from separate cores. A boundary with small misfit was observed by TEM, also supporting the possibility of grain coalescence.