| 摘要 |
PROBLEM TO BE SOLVED: To provide a silicon nitride sintered product excellent in grindability, as sustaining low thermal expansion, light weight and high toughness. SOLUTION: A mixture of a powder of silicon nitride of <=80% of the α-form content with an average particle size of 2-6μm with a powder of sintering additives is formed to a formed product having a composition of 75-95wt.% of silicon nitride, 1-7wt.% of rare earth elements oxides, 1-10wt.% of alumina and 1-8wt.% of silica. The formed product is fired in a nonoxidative atmosphere at 1,600-1,750 to provide a silicon nitride sintered product containing the silicon nitride β-crystalline phase and the granular phase including rare-earth elements, silicon, aluminum, oxygen and nitrogen. This sintered product can be improved in its grindability by adjusting its properties as follows: density to 2.90-3.15g/cm<3> , Young's modulus to 240-270Gpa, maximum void diameter to <=100μm, toughness (KIc) to 3-6Mpa.m<1/2> and 4-point flexural strength to 300-500Mpa. |
