OXIDATION BEHAVIOR OF SIC WHISKER-REINFORCED AL2O3/ZRO2 COMPOSITES

The oxidation behaviour of hot-pressed SiC whisker-reinforced Al2O3/ZrO2 composites is characterized. The influence of composition, additives and impurities is studied and discussed. These composites have a good oxidation resistance up to temperatures between 1000...1200-degrees-C, depending on the additive content. At higher temperatures the oxidation products of whiskers can form new phases with the matrix and thus reduce the oxidation resistance. The oxidation process follows a parabolic rate law. The activation energy, obtained in the present investigation, was in the range 350...420 kJ/mol. Diffusion of oxygen through the matrix and oxide product appears to be the rate controlling process. During oxidation, gaseous phases (CO), amorphous phases (SiO2 and SiO2-rich aluminosilicate) and crystalline phases (mullite and aluminosilicate) are formed, depending on time and temperature. At low temperatures and short time spans only amorphous phase is formed; after longer time periods and at higher temperatures, crystalline phases occur. The oxidation rate of SiC(w)-reinforced Al2O3/ZrO2 depends more strongly on additive and impurity contents than on the amount of whiskers. Preoxidation treatments indicate no distinct influence on the creep curve under the conditions of these tests.