A silicon nitride sintered body and its manufacturing method

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PROBLEM TO BE SOLVED : To provide a silicon nitride sintered compact which has excellent strength in a high-temperature area near 1, 000 deg.C from room temperatures and has high toughness and a long fatigue life and a method for manufacturing the same. SOLUTION : This sintered compact consists of β type silicon nitride crystal phases, grain boundary crystal phases consisting of rear earth elements, silicon, aluminum, oxygen and nitrogen and grain boundary amorphous phases. The βtype silicon nitride crystal phases of <=10 μm are 70 to 90% in an area ratio. The sintered compact contains 10 to 30% β type silicon nitride crystal phases of 40 to 100 μm and the thickness of the amorphous phase among the silicon nitride crystal phases is <=2 nm and the thicknesses of the β type silicon nitride crystal phases and the amorphous phases among the grain boundary crystal phases are specified to <=5 nm.