Short-term oxidation of a ternary composite in the system AlN-SiC-ZrB2

The present study investigates the oxidation behaviour in air of a structural ceramic composite with the following volumetric composition: 55% AlN-15% SiC-30% ZrB2. This kind of ternary composite is electroconductive (3 x 10(-4) Omega cm) and has significant strength (similar to 700 MPa) and toughness (4MPa m(1/2)) up to 1000 degrees C. Oxidation tests were carried out in a TG equipment from 700 to 1300 degrees C with exposition time of 30 h. Significant weight gain is observed at T > 1000 degrees C. In the range 700-900 degrees C, the process is dominated by the oxidation of ZrB2 into zirconia and boria and the kinetic is nearly parabolic. At temperatures in the range 1000-1100 degrees C, boria reacts with alumina forming aluminium borate and. borosilicate glass and the kinetic largely deviates from parabolic behaviour. In the samples oxidized at temperatures in the range 1200-1300 degrees C, aluminium borate and mullite crystallize on the surface. The kinetics is para-linear in this temperature range but at 1300 degrees C, the rupture of the outer layer, results in accelerated damage of the sample. The composite is recommended for applications up to 1100 degrees C. (c) 2004 Elsevier Ltd. All rights reserved.