Microstructural development during final-stage sintering of nanostructured zirconia based ceramics

The microstructural evolution of nanostructured zirconia based ceramics during pressureless final-stage sintering in vacuum was followed using X-ray diffraction, high resolution scanning electron microscopy and small-angle neutron scattering (SANS). The ultra-fine zirconia and yttria powders were synthesized by the inert gas condensation technique, the ultra-fine alumina by chemical vapor condensation. Powder compacts of ZrO2 and dispersion mixed 5 mol% Y2O3 partially stabilized ZrO2 and ZrO2+14 wt.% Al2O3 were sintered at temperatures between 1000 and 1200°C for 2 h. Densification and concurrent grain growth as a function of temperature revealed a significant suppression of grain growth in the zirconia/alumina composite. Due to a homogeneous distribution of the alumina second phase in the zirconia matrix nearly full density and grain sizes <40 nm were achieved. Changes in the microstructure of monoclinic zirconia sintered at T>1050°C were detected by SANS and could be attributed to the detrimental effects of the monoclinic to tetragonal martensitic phase transformation. The log-normal pore size distributions were also evaluated for the ceramics.