| 摘要 |
PROBLEM TO BE SOLVED: To obtain a silicon nitride-based sintered material having a stronger strength at it burnt skin layer than that at the inside of main body part of the sintered material by forming the main body part having a specific burnt skin layer. SOLUTION: This silicon nitride-based sintered material containing disilicate crystalline phase only in the burnt skin layer formed on the surface of the main body part, is obtained by weighing each prescribed amount of a silicon nitride powder of either α-type or β-type containing 1-3wt.% oxygen element content and extremely small amount of other impurities, and a sintering assistant containing rare-earth elements such as Yb, Y and Er and preparing a mixture, then adding a binder thereto, forming and sintering, then heat-treating the obtained silicon nitride-based sintered material under an oxidizing atmosphere at 1,100-1,500 deg.C to oxidize a granular boundary phase in the silicon nitride-based sintered material. As necessary, the strength of the main body part having the burnt skin layer is increased by using the sintering assistant containing, e.g. Al2 O3 or AlN which, contains Al, V, W, Cr, etc., also including 5ReO3 , Si3 N4 , Al2 O3 crystalline phase or a merrillite crystalline phase in the main body part, and heat-treating. |
