Improved mechanical properties of dense β-Si3N4 ceramics fabricated by spark plasma sintering with Al2O3-YSZ additives

In this work the influence of sintering conditions on structure and mechanical properties of Si3N4 ceramics was investigated. Nearly full dense beta-Si3N4 ceramics with excellent mechanical properties and interlock microstructure of elongated grains was fabricated using Al2O3 and yttria-stabilized zirconia (YSZ with 3 mol% Y2O3) as sintering additives by spark plasma sintering (SPS) at relatively low temperature of 1600 degrees C for 15 min. X-ray diffraction analysis shows that the SPSed sample is pure beta-Si3N4 phase without any secondary crystalline phase. The elements Al, Zr, Y and O of the additive can diffuse into Si3N4 lattice forming beta-Si3N4 based solid solution. The residual additive formed an amorphous phase at the beta-Si3N4 grain boundaries. The beta-Si3N4 ceramics obtained by SPS using 6.0 wt. % Al2O3 and 6.0 wt. % YSZ as additives shows interlock elongated beta-Si3N4 grains of 500 nm in width and 3000 nm in length, high density of 3.29 g/cm(3), Vickers hardness of 16.15 GPa and high fracture toughness K-IC of 6.75 MPa m(1/2).