Highly densed silicon nitride ceramics with various #alpha#/#beta# phase ratios were produced by pulse electric current sintering process. The #beta#-phase content of Si_3N_4 in sintered materials varied from 20 to 100 wt percent depending on th sintering condition. H microstructure was observed by scanning electron microscopy and investigated by image analysis. Young's modulus, hardness, fracture toughness, and strength were strongly dependent on the #alpha#/#beta# phase ratio. The fracture toughness increased from 4.6 MPa m~(1/2) for 20-wt percent #beta#-phase content to 8.2 MPa m~(1/2) for 95-wt percent #beta#-phase content, and the fracture strength showed a maximum value of about 1.6 GPa at 60-to-80-wt percent #beta#-phase content.
展开▼
