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

Abstract

Nanostructured silicon nitride and aluminium nitride powder mixtures have been successfully produced by high-energy mechanical activation. Subsequent high sintering activity and beta-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 degrees C lower, as compared with the samples prepared from the non-activated powder mixture. Al-27 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 degrees C for 60 min, beta-sialon samples had a Young's modulus of 281 GPa, microhardness of 12.8 GPa, fracture toughness of 4.6 MPa m(0.5) and flexural strength of 632 +/- 129 MPa. The unique structure and bi-modal grain size distribution that is retained after conventional sintering at 1600 degrees C opens up new possibilities for tailoring the microstructure and related properties of these materials. (C) 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.