Features of corrosion resistance of AlN–SiC ceramics in air up to 1600°C

Abstract

The kinetics and mechanism of (80% AlN + 20% SiC) and (50% AlN + 50% SiC) powders and ceramics oxidation in air up to 1600°C were studied with the aid of TG, DTA, XRD, EPMA, SEM and metallographic analysis methods. The ceramics samples were obtained by hot pressing fine-dispersion AlN and SiC powders with an average particle size of 1μm at 1800°C for 2h. This ensures a fine-grain material structure with a uniform distribution of phase components. It was shown that in a nonisothermal regime, a three-stage oxidation mechanism takes place. It was established that the scale formed consists of three oxide layers. In the inner layer, Al10N8O2 oxynitride and β-SiO2 (cristobalite) phases were observed; in the intermediate layer, β-SiAlON was found for samples with a relatively low SiC content whereas α-Al2O3 was present in samples with a greater SiC content. The outer layer contains 3Al2O3.2SiO2 (mullite) as a main phase, the latter ensuring highly protective properties of the scale. The materials investigated can be considered as having extremely high resistance to corrosion up to 1550°C.