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 0.5μm were used to prepare α-β SiAlON ceramics by gas-pressure sintering. Elongated β-SiAlON grain morphology was identified in the samples prepared using 0.5μm particle size β-Si₃N₄ powder. Low-aspect ratio grain morphology was observed in samples prepared from starting powders with coarse particles (2μm and 1μm). 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 12.4-14.2GPa and 5.1-6.4 MPam^1/2 respectively. It was revealed that fracture toughness increases with decrease in particle size of starting β-Si₃N₄ powder.