Features forming of structure and phase composition in yttria-stabilized zirconia ceramics

Exposure to the ultrasound (US) during compaction process leads to the formation of a homogeneous structure of agglomerates. Moreover, the particles in the compact activated during vibration interaction. It makes us possible to intensify the sintering, decrease the temperature, control the grain growth, and stabilize grain boundaries. The size distribution of fragments became narrower when the US power increases. The morphology of initial powder remained unchanged for US power less than 1.2 kW. The most narrow size distribution of grains was observed at W=2 kW. Crystallites completely disappeared at W=3 kW and agglomerates can be formed. All samples of YSZ ceramics were polycrystalline, tetragonal modification. The monoclinic modification was observed for the samples exposured to 1.2 kW. It was found that US exposure leads to an intensification of high-temperature diffusion of Yttrium from grain volume into the grain boundary area and reduce the Y$_2$O$_3$ concentration in inner grain area. Such a redistribution during pressing leads to the formation of a cubic phase in the interface regions and a monoclinic phase in the grain volume. It was found that samples compacted at P = 150 MPa, W = 2 kW cleave by trans-granular mechanism. That fact indicates a decrease in the strength of the crystallites (grains) caused by the formation of monoclinic phase regions. The analysis of the transport properties of thermal phonons at helium temperature showed that the main reason of phonon scattering is phase inhomogeneities in the grain structure.