Influence of β-Si3N4 particle size and heat treatment on microstructural evolution of α:β-SiAlON ceramics

In the present study, we report the effects of starting β-Si3N4 particle sizes and post-sintering heat treatment on microstructure evolution and mechanical properties of prepared α–β SiAlON ceramics. Three different β-Si3N4 starting powders, with particle sizes of 2, 1 and 0.5 μm were used to prepare α–β SiAlON ceramics by gas-pressure sintering. Elongated β-SiAlON grain morphology was identified in the samples prepared using 0.5 μm particle size β-Si3N4 powder. Low-aspect ratio grain morphology was observed in samples prepared from starting powders with coarse particles (2 μm and 1 μm). The sintered samples were further heat treated to develop desired microstructure with elongated grains. The hardness and indentation fracture toughness values of sintered and heat treated samples were found to lie in the range of 12.4–14.2 GPa and 5.1–6.4 MPa m1/2 respectively. It was revealed that fracture toughness increases with decrease in particle size of starting β-Si3N4 powder.