Fabrication Process and Properties of Si<sub>3</sub>N<sub>4</sub>-SiC Ceramics by a Two Step Sintering Method

Abstract

A new composite ceramics of Si3N4/ SiC were prepared by a two step sintering method with SiC powders and Si powders as main material. Its properties and structures were characterized by the porosity, bulk density, flexural Strength, XRD, SEM and EDS. The effects of particle grade and sintering temperature on its properties were studied. The results show that bulk density of powders is the largest when coarse powder of SiC (average diameter 120 um) is about 40% (by weight), with average diameter 80um of SiC is about 20% (by weight) and fine powder (average diameter 35 um) of of SiC is 10% (by weight). A minimum porosity, a maximum bulk density and flexural Strength were achieved by nitriding at 1450 °C for 2h and then two states sintering at 1700 °C. XRD analysis indicated that the the main crystalline phase of the ceramic made from α-SiC, α-Si3N4and β-Si3N4. SEM and EDS analysis indicated that a larger of wisker like α-Si3N4and some little β-Si3N4are found coating with SiC, giving its excellent mechanical properties.