Preparation of m-ZrO2 compacts by microwave sintering

Dense un-doped monoclinic ZrO2 (m-ZrO2) compacts were prepared successfully by microwave sintering with a TE666 resonant mode and temperature ranges from 1350 °C to 1550 °C. XRD and SEM techniques were used to characterize the samples. A dense and homogeneous microstructure was observed with the grain size of 1 μm, which is smaller than that of conventional sintered ones. A monoclinic ZrO2 phase without detectable tetragonal ZrO2 (t-ZrO2) was found for both microwave sintered and conventional sintered samples. Density of samples was measured according to the Archimedes principle. The results showed a relative density of 99.0% for microwave sintered samples which is higher than that of conventional sintered ones. The microhardness was investigated by indentation test with the highest value of 4.0 GPa. Meanwhile, microcracks were observed on the edges of the indentation but not at the tips for microwave sintered samples which indicated good toughness. Optimized microwave sintering temperature of m-ZrO2 compacts was 1450 °C for 30 min with the microhardness of 4.0 GPa and relative density of 99.0%.