Microstructure and mechanical properties of silicon nitride ceramics prepared by pressureless sintering with MgO–Al 2O 3–SiO 2 as sintering additive

Abstract

The microstructure and mechanical properties of pressureless sintered Si 3N 4 ceramics prepared both by conventional ball-milling and planetary high-energy ball-milling for a sintering additive from the MgO–Al 2O 3–SiO 2 system were investigated by XRD, SEM, TEM, HRTEM, and EDS. For pressureless sintered Si 3N 4 ceramics prepared by planetary ball-milling, a flexure strength of 1.06 GPa, Vickers hardness of 14.2 GPa, and fracture toughness of 6.4 MPa·m 0.5 were achieved. The microstructure of the sintered materials consists of elongated grains with almost identical size and aspect ratio that uniformly distributed throughout the body. The improved mixing efficiency by planetary ball-milling has simply reduced the particle size and improved the distribution of sintering additives, leading to a slightly improved densification and microstructural homogenization that are responsible for the promising properties of Si 3N 4 ceramics. In comparison with traditional ball-milling route, the planetary high-energy ball-milling is an efficient processing to produce high homogeneous microstructure and promising mechanical properties.