Mechanical Properties and Microstructure of Silicon Nitride Ceramics by Pressureless Sintering

The mechanical properties and microstructure of silicon nitride ceramics with MgO-Al2O3-SiO2 as additives produced by pressless sintering were investigated by XRD, SEM, TEM, EDS, and HRTEM. The relationship among preparation processing, microstructure, and mechanical properties was emphatically discussed. Intensifying blend by planetary blender, silicon nitride ceramics sintered at 1780℃ for 3h has an uniform microstructure with bigger aspect ratio of elongated grains (diameter in 0.3-0.8μm, length in 3-6μm, aspect ratio in 7-10), flexure strength of 1.06GPa, HRA hardness of 92, Hv hardness of 14.2GPa, and fracture toughness of 6.6 MPa·m0.5.