Effect of high energy milling on the formation and properties of sialon ceramics prepared from silicon nitride-aluminium nitride precursors

Nanostructured silicon nitride and aluminium nitride powder mixtures have been successfully produced by high-energy mechanical activation. Subsequent high sintering activity and β-sialon formation at low temperature resulted from activation milling at high acceleration. Densification of the samples prepared from the activated powders commenced at temperatures by about 200 °C lower, as compared with the samples prepared from the non-activated powder mixture. 27Al MAS NMR spectra clearly showed the effect of mechanical activation on the structural changes and phase evolution of the sialon precursor during heat treatment. After pressureless sintering at 1600 °C for 60 min, β-sialon samples had a Young’s modulus of 281 GPa, microhardness of 12.8 GPa, fracture toughness of 4.6 MPa m0.5 and flexural strength of 632±129 MPa. The unique structure and bi-modal grain size distribution that is retained after conventional sintering at 1600 °C opens up new possibilities for tailoring the microstructure and related properties of these materials.