Abstract
We study the application of the millimeter wave heating method to the silicon nitride, which includes Ytterbium oxide (Yb_2O_3) and alumina (Al_2O_3) as additives. Millimeter wave heating method has capability in enhancing densification of sintered bodies. As a result, we successfully obtained high-density sintered bodies with 5-wt% Yb_2O_3 and 3-wt% Al_2O_3. The sintering temperature was 1650℃, which was 200℃ lower compared with the conventional external heating method. Moreover, the annealing at 1220℃ with millimeter wave heating method after the sintering was proved to be effective. The sintered bodies showed excellent mechanical properties at room and high temperatures. The Vickers hardness was 7.5 GPa at 1400℃ in a vacuum, 17.4 GPa at room temperature in the air, and fracture toughness K_<IC> was 9.3 MPa m^<1/2> at room temperature in the air. These experimental results showed that the application of the millimeter wave heating method to the silicon nitride is very effective.
