Properties of MWCNTs added Si3N4 composites processed from oxidized silicon nitride powders

Abstract

Si3N4/3 wt.% multi-walled carbon nanotubes (MWCNTs) composites were prepared from oxidized α-Si3N4 powders and sintering additives by hot isostatic pressing (HIP). The Si3N4 powders were oxidized at 1000 °C in ambient air environment for 10 and 20 h and the powder mixture was sintered at 1700 °C for 3 h under the pressure of 20 MPa in nitrogen. The relationship between oxidation, microstructure, tribology and mechanical properties was studied. The dispersion of MWCNTs was not optimal, as they were found mainly in the form of bundles between the β-Si3N4 grains. Neither Si2N2O nor other oxide phase were observed after the sintering. This was probably caused by the presence of MWCNTs at the grain boundaries of the Si3N4 grains causing reduction of oxide phases. The density, hardness, bending strengths and friction coefficient of the composites increased with the oxidation time of the Si3N4 powder.