Internal friction peak in silicon nitride sintered without additives

A silicon nitride sintered without additives was tested by mechanical spectroscopy. The as-sintered material contained a few amount of glassy phase and, as a consequence, a small internal friction peak was detected at 1203 K. To investigate the role of the YSiAlON crystalline phases at very high temperature, the as-sintered material was annealed at 1873 K and then rapidly cooled to the room temperature before testing. In the annealed material, the internal friction spectrum exhibited a higher internal friction peak comparable to results obtained in silicon nitrides containing an important amount of intergranular glassy phase. These results indicate that the material contains a liquid phase at 1873 K.