Oxidation behavior of electrically conductive alpha/beta SiAlON composites with segregated network of TiCN

Abstract

The oxidation behavior of novel electrically conductive alpha/beta SiAlON composites with a continuous network of 2.5-10 vol% TiCN particulates was investigated. Composites, produced by coating spray dried granules with nano TiCN particles by a simple blending method, were gas pressure sintered at 1990 degrees C for 1h under 10 MPa N-2 pressure. Oxidation tests were carried out between 800 degrees C and 1200 degrees C in air for 2 and 48 h in atmosphere of dry air. Below 1000 degrees C, the formation of TiO2 crystals on the surfaces of TiCN particles was observed. Before the glass transition temperature of intergranular phase (T-g < 1000 degrees C), it was revealed that oxidation is controlled by the diffusion of oxygen into pre-formed TiO2 particles. Above Tg, liquid glass dissolves the intergranular phase elements such as Ti, Y, and Si at the interface between TiCN and SiAlON particles. Migration of T-g towards the (opening point of the TiCN network) surface was found to be the main reason for the formation of subsurface porosity that slows down Ti diffusion through the surface. Moreover, it was detected that at high temperatures surface porosity filled by the intergranular glassy phase. Consequently, the oxidation rate was found to be decreased due to the slower oxygen diffusion