The oxidation of Si3N4-TiN ceramics in AlR-1vol%SO2

The last decade has seen increased interest in the development of ceramic matrix composite materials for high technology applications. In this time the substantial progress achieved in the area of production has led to important improvements in physical and mechanical properties. Changes due to the introduction of a second phase mean that detailed property characterisation must be carried out in order to gain a good insight into the likely performance of this new class of materials under practical conditions of use. In this work the thermal stability of an electrically conductive Si3N4-30vol% TiN composite in a 1vol% SO2-air mixture was evaluated in the temperature range 800-1400 degrees C and compared to the behaviour of the matrix Si3N4. The behaviour of the materials was evaluated by means of oxidation kinetics and studies of the microstructural changes occurring as a result of oxidation attack. The results show that the presence of TiN increases the rate of weight change and a deep zone of Ti depletion in the sub-surface region of the ceramic is formed.