| 摘要 |
PROBLEM TO BE SOLVED: To produce a silicon nitride-based member having a small difference between the inside and the outside in strength without requiring grinding working of the surface in a thick-wall member having >=10 mm diameter of the maximum inscribed sphere and to provide a method for producing the silicon nitride-based member. SOLUTION: This silicon nitride-based member is produced by baking a formed compact consisting essentially of silicon nitride and containing a group 3a element of the periodic table in an amount of 2.0-9.5 mol% expressed in terms of an oxide, aluminum in an amount of 2.0-7.6 mol% expressed in terms of an oxide and excessive oxygen in an amount of 3.0-9.5 mol% expressed in terms of silicon dioxide and capable of forming a shape so as to have >=10 mm diameter of the maximum inscribed sphere after baking in a nitrogen-containing atmosphere at 1 650-1,800 deg.C and at a lower temperature than the temperature at which the nitrogen partial pressure in the baking atmosphere equals the equilibrium nitrogen partial pressure in a decomposing reaction of the silicon nitride by >=120 deg.C, further heat-treating the baked material at 800-1, 200 deg.C after the baking and crystallizing a part of the grain boundary phase. The resultant silicon nitride-based member has >=950 MPa strength at normal temperature, >=800 MPa strength at 1,000 deg.C and >=950 MPa strength at normal temperature in a position at 300 μm depth from the surface left after baking. |
