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 × 10−4 Ω cm) and has significant strength (∼700 MPa) and toughness (4 MPa m1/2) up to 1000 °C. Oxidation tests were carried out in a TG equipment from 700 to 1300 °C with exposition time of 30 h. Significant weight gain is observed at T > 1000 °C. In the range 700-900 °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 °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 °C, aluminium borate and mullite crystallize on the surface. The kinetics is para-linear in this temperature range but at 1300 °C, the rupture of the outer layer, results in accelerated damage of the sample. The composite is recommended for applications up to 1100 °C.