Vasiliy Shmakov

The combination of various oxide ceramics in layered and functionally graded composites allows for the development of novel materials, including for high-temperature applications. This study demonstrates the possibility of obtaining a thick ZrO₂-based coating on a ZrB₂–SiC ceramic substrate by the immersion method. For better wettability, the porous ZrB₂–SiC substrate is treated with cold plasma without changing the structure and phase composition of the surface. Immersion of the substrate in a ZrO₂-based slurry results in the formation of a gradient transition layer due to ZrO₂ particle penetration into the pore volume. The interfacial residual microstresses are evaluated experimentally. The residual macrostresses in the samples are calculated by finite element simulation. It is shown that the thermal residual stresses in the ZrB₂–SiC substrate are compressive and do not exceed 43 MPa. In the ZrO₂ coating and transition layers of the composite, the residual stresses are tensile. Their values increase as they get closer to the outer layer of the ZrO₂ coating and reach 1525 MPa. This confirms the conclusions about the presence of tensile residual stresses made in the experimental part of the work when observing crack propagation in the surface layers during indentation.

The work is devoted to the study of the kinetics of the microstructure of oxide ceramics based on zirconium, magnesium and their composite. The investigated ceramics have bimodal porosity. Sintering was accompanied by a long isothermal exposure from 10 to 600 minutes at 1600 °C. It is shown that the dependence of the volume shrinkage and the size of micro- and macropores on the duration of isothermal exposure reflects the stages of solid-phase sintering of powder compacts. It has been found that changes in the average pore size are determined by various diffusion mechanisms.