Perspective heat-resistant coating for protection of C$_{\rm f}$/SiC composites in air plasma hypersonic flow

The investigation results on development and testing of heat-resistant coating with experimental composition of $\rm Si$–$\rm TiSi_2$–$\rm MoSi_2$–$\rm TiB_2$–$\rm CaSi_2$ for protection of C$_{\rm f}$/SiC composites from oxidation and highspeed erosion in high-speed gas flows are presented. This coating was formed by slip firing technology out of slip compositions with filler based on heterophase powder of the system of interest. The results of fire bench tests of samples with coating under conditions of flow-around and off balance heating by air plasma streams with $\rm M = 5.5$–$6.0$ and enthalpy of $40$–$45$ MJ/kg. The effectiveness of the protective action of coating at surface temperature $T_w = 1810$–$1820^{\circ}$C is kept not less than $920$–$930$ s, at $T_w \ge 1850$–$1860^{\circ}$C—not less than $420$–$430$ s. It was found that the effectiveness of coating is provided by structural-phase state of the base coating and formation of heterogeneous oxide film on its surface formed by borosilicate glass with titanium and calcium segregation heterogeneity and $\rm TiO_2$ reinforce micro-needles in the form of rutile. The decrease in saturated steam pressure level in oxide film–coating system induced by increase in the level of external layer heterogeneity was experimentally confirmed.