Comparison of the effect of chromium oxide and magnesium oxide on the mechanical properties and microstructure of alumina-mullite-zirconia composites

Alumina-mullite-zirconia composites were prepared by the reaction sintering method between alumina and zircon powders and the effect of two additives (chromium oxide and manganese oxide)were investigated on their properties. 2 and 4 wt% of each oxide were added to the raw material composition and after pressing, the samples were sintered at 1630°C. The results showed that chromium oxide decreased the density, strength, and hardness of the samples, while manganese oxide increased the density, strength, and hardness. The microstructure of the composite made with Chromium oxide was also uniform and homogeneous and the grain size was relatively smaller; whereas, unlike the improved mechanical properties with manganese oxide, this additive resulted in the growth of grains. The boundary phase which was formed between the grains in the samples containing manganese oxide was also investigated. The effect of chromium oxide and manganese oxide on the composition of the final phases (formation of mullite and zirconia) was different.