Influence of planetary high-energy ball milling on microstructure and mechanical properties of silicon nitride ceramics

The influence of ball-milling methods on microstructure and mechanical properties of silicon nitride (Si3N4) ceramics produced by pressureless sintering for a sintering additive from MgO-Al2O3-SiO2 system was investigated. For planetary high-energy ball milling, the mechanical properties of Si3N4 ceramics were evidently improved and a homogeneous microstructure developed. In contrast, some exaggerated elongated grains were developed due to the local enrichment of sintering additives in the specimen prepared by general ball milling. For Si3N4 ceramics produced by planetary ball milling, flexure strength of 1.06 GPa, Vickers hardness of 14.2 GPa, and fracture toughness of 6.6 MPa (.) m(0.5) were achieved. The differences in the mechanical properties of Si3N4 ceramics produced by different processing seem to arise mainly from the changes in microstructural homogenization and sinterability. The planetary high-energy ball-milling process provides a good route to mix starting powders for developing ceramics with uniform microstructure and promising mechanical properties.