Microstructural development and mechanical properties of pressureless sintered Al2O3/SiC composites

Abstract

Al2O3 green bodies containing 5 vol% SiC were prepared by slip coating. In order to obtain stable slips, the zeta potential of the SiC was adapted by chemical modificaiton of the surface using functional silanes (e.g. amino ethyl amino propyltrimethoxysilane). Another route for the preparation of homogeneous slips was developed by heterocoagulation of Al2O3 and SiC under well controlled pH conditions and by stabilizing of the heterocoagulated system with a non-ionic surfactant. Both routes led to homogeneous aqueous slips which could be slip-casted to green compacts with densities around 60% of theory showing an excellent distribution of the SiC within the Al2O3 matrix. Green compacts were pressureless sintered at 1800°C to densities above 98.5% showing a homogeneous microstructure with average grain sizes between 2 and 2.5 µm, a fracture strength of about 650 MPa and fracture toughness around 3.0 MPa m0.5.