Influence of long term oxidation on the microstructure, mechanical and electrical properties of pressureless sintered AlN-SiC-MoSi2 ceramic composites

The effects of long term oxidation on the microstructural modification and on the electrical resistivity and mechanical strength of a AlN-SiC-MoSi2 electroconductive ceramic composite are presented. The microstructure of the pressureless sintered composite is described and the oxidation behaviour is discussed. The formation of protective mullite layer at temperatures above 1000°C provides good oxidation resistance for use at higher temperatures. At temperatures below 1000°C, the AlN/SiC matrix disables the “pesting” phenomena and strength degradation, despite the fact that at these temperatures MoSi2 oxidizes rapidly. The surface modification induced by oxidation on AlN-SiC-MoSi2 composites do not affect mechanical strength, while the electrical conductivity strongly decreases.