Superplasticity of the nanostructured binary systems of zirconia-alumina-spinel ceramics by spark plasma sintering process

Three biphase composites (zirconia-alumina, alumina-spinel and zirconia-spinel) of the zirconia-alumina-spinel ceramic were processed separately from nanosized alumina, zirconia and magnesia powders. The samples became nearly fully dense after spark plasma sintering at 1050-1100 °C, with the grain sizes between 50 nm and a few hundreds of nanometers. Specimens cut from the sintered compacts were tested under compression at elevated temperatures (1300-1500 °C) and at strain rates ranging from 10 ^-1 to 10 ^-5 s ^-1. Strain sensitivities and activation energies of the biphase composites were compared with that of the triphase composite. Additionally, microstructures of the binary systems before and after the superplastic deformation were studied by SEM. Lastly, grain boundaries and phase boundaries that were most prone to sliding were investigated in conjunction with mechanical parameters in order to shed more light on the rate controlling mechanisms.