| 摘要 |
PURPOSE:To obtain a silicon nitride sintered compact having such structure that the predominant silicon nitride grains and the grain boundary thereof contain at least a rare earth element compounds, also controlled in oxygen level and grain boundary crystal phase level, thus excellent in the mechanical strength of its surface layer at room temperature and elevated temperatures. CONSTITUTION:This silicon nitride sintered compact has the following characteristics: (1) the main crystal is composed of silicon nitride; (2) the boundary phase between silicon nitride grains adjacent to each other contains at least a rare earth element compound; and (3) the quantity of oxygen in the surface layer is less than that in the inside (the latter being pref. >=2.9wt.%) and the quantity of grain boundary crystal phase in the surface layer is more than that in the inside. Even in the form of a high-temperature structural member or complicated assign with thick-walled and thin-walled portions, this sintered compact is high in the mechanical strength of its surface layer at room temperature and elevated temperatures. |
