Oxidation behaviour of Si3N4-ZrN-AlN ceramics

The oxidation behaviour of Si3N4-ZrN-AlN ceramics at 1300 C and 1050 C ∼ 1150 C was studied. The weight gain of Si3N4-0.7%AlN-6.3%ZrN after oxidation at 1300 C for 120h is 1.9g / m2, lower than that of Si3N4-6.6%Y2O3-9.5%La2O3 (2.8g/m2). The superior oxidation resistance of Si3N4-ZrN-AlN is attributed to reduced amount of intergranular phase and increase of its viscosity and softening temperature. Catastrophic failure occurred in Si3N4-ZrN-AlN specimens with ZrN > 10.8% and in Si3N4-ZrN specimens with ZrN 24%, but was not found in Si3N4-ZrN specimens with ZrN < 15%. The catastrophic failure is suggested to be attributed to large volume expansion (> 1%) due to the transformation of ZrO or ZrN to ZrO2(m). Because a dense surface of tridymite formed which prevented rapid inward diffusion of oxygen, catastrophic failure in specimens Si3N4-10.8%ZrN-5%AlN did not occur during oxidation at 1300 C. (orig.)