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

The kinetics and mechanism of (80% AIN + 20% SiC) and (50% AIN + 50% SiC) powders and ceramics oxidation in air up to 1600 degrees C Mere studied with the aid of TG, DTA, XRD, EPMA, SEM and metallographic analysis methods. The ceramics samples were obtained by, hot pressing fine-dispersion AIN and SiC powders with an average particle size of I mu m at 1800 degrees C for 2 h. This ensures a fine-grain material structure with a uniform distribution of phase components. It was shown that in a non-isothermal regime, a three-stage oxidation mechanism takes place. It,was established that the scale formed consists of three oxide layers. lit the inner layer, Al10N8O2 oxynitride and beta-SiO2 (cristobalite) phases were observed, in the intermediate layer, beta-SiAlON uas found for samples with a relatively, low SiC content whereas alpha-Al2O3 was present in samples with a greater SiC content. The outer lay er contains 3Al(2)O(3 .)2SiO(2) (mullite) as a main phase, the latter ensuring highly protective properties of the scale. The Materials investigated call be considered as having extremely high resistance to corrosion up to 1550 degrees C. (C) 1999 Elsevier Science Limited. All rights reserved.