The properties of SiAlON ceramics are strongly affected by the composition and structure of the intergranular phase, which are controlled by dopants, sintering conditions and starting silicon nitride (Si3N4) powder characteristics. In this study, 25 alpha:75 beta SiAlON compositions were designed with different molar ratios of Y:Srn:Ca (9:0.5:0.5 and 3:6:1). The effects of cation ratios, different cooling profiles (50 degrees C/min and 5 degrees C/min) and further heat treatment under different conditions (at 1600 degrees C for 2, 4 and 6 h) on the final phase composition, the type of the intergranular phase (amorphous or crystalline) formation, the resulting microstructures and the machining performance were studied. It is found that slow cooling and heat treatment have a great influence on crystallisation behaviour and in turn the crystallisation enhance the machining performance of SiAlON materials in cutting tool applications. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.