Enhanced densification and phase transformations during rapid microwave sintering of alumina – yttria-stabilized zirconia ceramics

Alumina – 7.5 wt% yttria-stabilized zirconia (YSZ) ceramic composites were sintered using 24 GHz microwave heating at rates of 10 – 200 °C/min with zero isothermal hold. The starting powders were nanophase η-Al₂O₃ and YSZ prepared by a laser evaporation method. The final densities of the sintered samples were up to 97.5 % of the theoretical value. The samples exhibited rapid densification until transformation to the α-Al₂O₃ phase. The temperature of the densification rate peak (and hence of the phase transformation) decreased consistently with increasing microwave electromagnetic field intensity (varied by using different susceptor materials). The densification peak temperature difference between microwave and conventional sintering experiments exceeded 200 °C.