Preparation of large size ZTA ceramics with eccentric circle shape by microwave sintering

Ultra-large zirconia toughened alumina (ZTA, mass ratio of Al₂O₃ and ZrO₂ is 78:22) ceramics with eccentric circle shape were successfully sintered by microwave sintering with a multi-mode cavity at 2.45 GHz. The dimension of ZTA ceramics (green body) is 165 mm (outer diameter) × 25 mm (thickness). The optimized sintering temperature of microwave sintering is about 1500 ℃ for 30 min, and the total sintering time is about 4 h which is much shorter than that of conventional sintering. An auxiliary-heating insulation device was designed based on the principle of local caloric compensation to guarantee the intact sintered samples. With the increasing of sintering temperature, more and more microwave energy is absorbed within the entire sample, volumetric densification performs, and phases shift from m-ZrO₂ phase to t-ZrO₂ phase and cause Al₂O₃ grain growth.