Gas-pressure sintering of silicon nitride with Yb4Si2O7N2 phase

Silicon nitride containing Yb2O3 as a sintering additive was gas-pressure s intered, A dilatometric study indicates that the liquid formation temperatu re of this additive is higher than that of commonly used additives, The mat erial containing 3.6 mol% of additive densified up to 99% of the theoretica l density by sintering at 1950 degreesC for 4 h. The grain boundary phase o f this material crystallized as Yb4Si2O7N2. The bending strength of this ma terial was 460 MPa at room temperature, This value is rather low because of voids formed during gas pressure sintering in the specimens, However, stre ngth degradation at high temperature was limited because of the highly refr actory Yb4Si2O7N2 grain boundary phase.