Hybrid Microwave Sintering of Yttria Stabilized Zirconia

Sintering of 7–8 wt.% yttria-stabilized zirconia (8 YSZ) was investigated using hybrid microwave (HMW) processing at 2.45 GHz. The phases evolution and the microstructural changes behavior of 8 YSZ during HMW processing were investigated. Commercial 8 YSZ powder was investigated where the powder was pressed and molded into green body disk using uniaxial press before it was later sintered using HMW processing. 8 YSZ prepared green disks were heat-heated at 3 different temperatures: 1350 ℃, 1400 ℃ and 1450 ℃ with a holding time of 2 h before they were allowed to cool down to room temperature. The HMW sintered disks were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The crystal size of HMW sintered samples was calculated to be around 46–49 nm using Scherrer equation. Furthermore, SEM micrographs of the HMW heat-treated samples had showed the typical sintered microstructure. HMW processing was successfully used to sinter 8 YSZ samples where the transformation of the stable tetragonal (t-ZrO₂) phase into monoclinic (m-ZrO₂) phase was suppressed which might be attributed to the huge number of oxygen vacancies formation during HMW processing. So, HMW was slowing down the typical martensite transformation and consequently decreasing the formation of the undesired microcracks from such transformation that usually lower the mechanical properties of YSZ. Furthermore, the cubic (c-ZrO2) phase was stabilized in the HMW sintered samples especially at higher heat-treatment temperatures due to that generated vacancies. Hybrid microwave processing is considered as a promising technique to sinter YSZ materials.