Sintering and mechanical properties of oxide-oxide composite based on ZrO₂-MgO mixtures

Porous ceramics ZrO₂-MgO with a 50 vol. % pore volume and bimodal pore size distribution were studied. The samples were produced by cold uniaxial pressing followed by sintering at temperature of 1600°C and a holding time from 10 min to 10 hours. Bimodal pore structure was obtained by adding of ultrahigh molecular weight polyethylene pore-forming particles with average size 50 μm to the initial powder mixtures. The pore volume for all samples was constant - 50±3 vol. %. With increasing of sintering holding time the average size of the macropores decreased and the micropores increased. The coherent diffraction domains average size of components increases with increasing of MgO concentration and the time of the sintering, while the microdistortions of crystal lattice decrease. With an increase of the sintering holding time more than 5 hours, an insufficient stabilization of cubic ZrO₂ takes place for the low MgO concentrations. The dependences of the tensile strength and the Young's modulus on the microstresses in the ceramic composite structure are investigated. Estimation of the microstresses on the basis of X-ray diffraction analysis has shown that the tensile strength mainly determined by microstresses and its increasing leads to a strength decrease.