AIN-Based Ceramics - an Alternative to Si<sub>3</sub>N<sub>4</sub> and SiC in High-Temperature Applications?

Aluminium nitride ceramics retain a high level of mechanical properties at temperatures above 1000°C and possess good oxidation resistance due to the formation of protective alumina-based scales. Although silicon-based ceramics dominate high-temperature engineering applications, new composites based on AIN can challenge the leading position of Si 3 N 4 and SiC ceramics. This paper presents a brief analysis of the oxidation behaviour of AlN-based materials using experimental results obtained in the framework of the INTAS project High Temperature Corrosion and Protection of Engineering Ceramics. Two major groups of AlN-based materials that can be considered for structural applications at high-temperatures are: 1. AlN-SiC solid solutions and multiphase composites which can form mullite scales with better protective properties compared to SiO 2 , particularly in combustion atmospheres. 2. AlN-boride (TiB 2 , ZrB 2 and other) composites which form self/healing oxide scales containing refractory aluminium borates. These compositions can be used as bulk ceramics or protective coatings for C/C composites or other materials with low oxidation resistance. Advantages and limitations of AlN-based composites are discussed.