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 cm) and has significant strength (~700MPa) and toughness (4MPam1/2) up to 1000 oC. Oxidation tests were carried out in a TG equipment from 700 to 1300 oC with exposition time of 30 h. Significant weight gain is observed at T > 1000 oC. In the range 700-900 oC, 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 oC, 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 oC, aluminium borate and mullite crystallize on the surface. The kinetics is para-linear in this temperature range but at 1300 oC, the rupture of the outer layer, results in accelerated damage of the sample. The composite is recommended for applications up to 1100 oC.