ABSTRACT
In the first stage of the project, 3 mol% Y2O3-ZrO2 (Y-TZP) was uniaxially dry pressed at various pressures, and then microwave sintered using a hybrid heating system in a commercial 2.45 GHz microwave chamber. Most samples were successfully sintered to high densities in a relatively short time, although a few were slightly warped and cracked. The results of this work showed that microwave sintering is similar to conventional sintering in that increasing green densities result in increased sintered densities, albeit at shorter hold times.
In the project’s second stage, 3 mol% Y2O3-ZrO2 and 9 mol% MgO-ZrO2 (Mg-PSZ) powders were microwave sintered using a similar technique. For the yttria-zirconia rapid heating and cooling rates resulted in the formation of a dense, basically tetragonal zirconia polycrystal (TZP) material with an average grain size of ~0.2 μm. Fracture toughness of the Y-TZP material was low, and comparison of X-ray diffraction patterns before and after grinding of the surface indicate that the tetragonal to monoclinic transformation did not occur using this stressing method. The Mg-PSZ samples were subjected to a variety of longer heating and cooling cycles. Only one heat treatment cycle resulted in precipitate growth. Ageing of some Mg-PSZ samples in a conventional furnace at 1400°C produced a non-uniform distribution of precipitates whose size was dependent on aging time.
This work has shown that microwave sintering may have some application for production of single phase and TZP zirconia ceramics, but that difficulties may be associated with the development of optimal PSZ material.
