Preparation of Si3N4 Ceramics with 3 wt % Y2O3–Al2O3 (2 : 1, 1 : 1, 3 : 5) Additions by Spark Plasma Sintering

α-Si₃N₄-based powder composites containing 3 wt % Y₂O₃–Al₂O₃ sintering aids with 2 : 1, 1 : 1, and 3 : 5 stoichiometries have been prepared by the Pechini process and spray drying. We have studied four ceramic samples produced by spark plasma sintering of the powder composites. The sintering process was run under a load of 70 MPa at a heating rate of 50°C/min as long as shrinkage of the powder composites continued. We have analyzed the shrinkage behavior of the powder composites during the sintering process; evaluated the activation energy for sintering; and measured the density, microhardness, and fracture toughness (cracking resistance) of the ceramic samples. The highest hardness, H_V = 16.5 GPa, in combination with a fracture toughness K_Ic = 3.8 MPa m^1/2, was offered by the material with an Y₂O₃ : Al₂O₃ molar ratio of 3 : 5 sintered at 1860°C. The corresponding densification factor was 99.0%. The starting mixture for this material was synthesized using spray drying.