Evolution of the phase composition of ZrB2-35MoSi2-15Al composite coating at annealing

In this article, new composite coatings ZrB2-35MoSi2-15Al were deposited on the surface of a carbon-carbon composite using a multi-chamber detonation accelerator. The evolution of the phase composition of ZrB2-35MoSi2-15Al coatings was analyzed with differential scanning calorimeter (DSC) and X-ray diffractometry (in situ HT-XRD) at temperatures from room temperature (∼ 25°C) to 1400°C (normal atmosphere and pressure). The coating before annealing according to X-ray diffractometry data is tetragonal (t-ZrO2) and monocline (m-ZrO2) zirconium dioxide, monocline silicon oxide (m-SiO2), hexagonal zirconium diboride (h-ZrB2), tetragonal molybdenum disilicide (t-MoSi2), cubic aluminum (c-Al) and cubic yttrium oxide (c-Y2O3). It was found that the coating crystallizes in m-ZrO2 at 460ºC, and then mullite with rhombic crystal lattice appears at 960ºC. When the temperature reaches 1050ºC the m-ZrO2, ZrSiO4, t-ZrO2, m-SiO2 and mullite phases formed in the coating. At 1400 º C, cubic zirconium dioxide appears in the coating. Experimental results can become the basis for the application of ceramic coating ZrB2-35MoSi2-15Al, which can improve the properties of carbon-carbon composites in an oxygen-containing environment at elevated temperatures.

Research of properties of protective coating applied to the surface of reaction-sintered ceramic materials

The study describes the properties of the protective coating deposited on the surface of the reaction-sintered silicon carbide and molybdenum disilicide. The technology of increasing the protective ability of the coating of products deposited on the surface on the basis of reactive sintered carbide of silicon and molybdenum disilicide, which operate in an oxidizing environment at high temperature and a sharp change of thermal regime, is investigated. The obtained results showed that the presence of a protective slip layer significantly increases the stability of the deposited silicoboride coating, thus blocking the interaction of silicon hexaboride with the environment, slowing down almost all diffusion processes at the transition of the interaction of diffusion. It has been established that the simultaneous use of both diffusion and slurry coatings enables maximum protection of reaction-sintered ceramic materials based on silicon carbide and molybdenum disilicide against high-temperature gas corrosion. The developed coating ensures maximum resistance to repeated changes in temperature conditions, while cyclic changes destroy products of silicon carbide and molybdenum disilicide without applied protective coating. The proposed protective coating can be recommended for the protection of reaction-sintered ceramic materials operated in high temperatures.