Improved performance of silicon nitride-based high temperature ceramics

Results are presented regarding experiments intended for improving the strength and toughness of hot-pressed Si3N4 (HPSN), improving the strength and oxidation resistance of reaction-sintered Si3N4 (RSSN), and improving the strength and oxidation resistance of sinterable Si-Al-O-N compositions. It is shown that the use of ZrO2 instead of MgO as a sintering aid improved the room-temperature and high-temperature flexural strength of HPSN, in addition to enhancing the rupture strength and Charpy impact resistance. The use of crushable energy absorbing layers increased the impact resistance of HPSN. Impregnation of RSSN with solutions that oxidize to Al2O3 or ZrO2 resulted in increased bending strength at room temperature. Beta-prime Si-Al-O-N sintered to full density by means of the sintering aids CeO2, Y2O3, and ZrO2 yielded the greatest strength with Y2O3 and the greatest oxidation resistance with ZrO2.