STRUCTURE AND PROPERTIES OF SINTERED Si₃N₄ TOUGHENED BY ZrO₂(Y₂O₃)

The sintered Si₃N₄ toughened by ZrO₂(Y₂O₃) was prepared at high temperature (1400℃) and ultra high pressure (4.2GPa). The phase structure and the mechanical properties were investigated by XRD and the measurements of compressive strength and micro hardness. The results show that the sintered Si₃N₄ was toughened by Y₂O₃ partially stabilized ZrO₂ with Al addition.The phase transformation and toughness were increased with Y₂O₃ content in less than 2.5mol% Y₂O₃.The toughness increasing came from t m transformation and micro cracks. Almost 100% t ZrO₂ were retained in more than 2.5mol% Y₂O₃ but the toughening effect was weakened by less transformation. The hardness was increased with Y₂O₃ content because Y₂O₃ can promote Si₃N₄ sintered as liquid at high temperature.