| 摘要 |
PURPOSE:To enhance toughness, strength and flaw resistance by constituting this sintered material of the composition which consists of ZrO2, ZrN and the combined phase of Mg-Si-Zr-O-N system, beta-Si3N4 of acicular crystal and inevitable impurities and allowing a specified surface oxidative layer to be present. CONSTITUTION:A green compact is obtained by mixing (i) 1-27wt.% ZrN powder, (ii) 0.5-5wt.% SiO2 powder, (iii) 1-10wt.% MgO powder and (iv) the balance Si3N4 powder preferably consisting of alpha-Si3N4 as a main component and molding this mixture. Then when this green compact is primarily sintered at 1500-2000 deg.C at 1-50atm in a nitrogen atmosphere and secondarily sintered at 1700-2000 deg.C at 100-2000atm in a nitrogen atmosphere, the green compact is held for 30 minutes to 3 hours in an oxidative atmosphere contg. 5-1000ppm concn. of O2 at a prescribed temp. of 500-1300 deg.C in the temp. rising stage in the primary sintering and/or after secondary sintering, the sintered body is held for 30 minutes to 3 hours at a prescribed temp. of 500-1000 deg.C in the atmosphere. Thereby the material is obtained which consists of 0.1-20vol.% ZrO2, 0.1-14vol.% ZrN, 3-15vol.% combined phase of Mg-Si-Zr-O-N system, the balance beta-Si3N4 of acicular crystal and inevitable impurities and has a surface oxidative layer of 10-1000mum thickness wherein the concn. of ZrO2 is made higher as this layer approaches the surface side. |
