Sintering Behavior of Si3N4 Ceramics at Low Temperature in Air Atmosphere Furnace

Abstract

Abstract Si3N4 ceramics have been densified in air atmosphere furnace at low temperatures of 1600∼1650°C with Li2O-Al2O3sintering additives. Molar ratio of 0.4∼1.6:1 of Li2O and Al2O3 were used to study the effects of additives on sintering behavior of Si3N4 materials. It is found that the densities of sintered samples increased and then decreased with the increase of molar ratio accordingly. Highest densities in excess of 95%oftheoretical are obtained with the ratio of 0.7:1. Densification process is accompanied by phase transformation. Therefore, the primarily phases in sintered specimens areβ-Si3N4and α-Si3N4, with a small amount of Si2N2O existed because of minor oxidation of the specimens during sintering. However, relatively low α- to βSi3N4 transformation (∼63%β-Si3N4) took place in the present densification conditions. The microstructures of the sintered samples exhibited typical β-Si3N4 elongated grain morphologies with small amount of homogeneously distributed residual pores. The sintered Si3N4 materials have the hardness of 14GPa and fracture toughness of 5.08MPa·m1/2, indicating a potential method for low-cost processing of Si3N4-basedceramics.