Investigation of Destruction Mechanisms for Heat-Resistant Coatings in Hypersonic Flows of Air Plasma

The authors present the results of investigations of degradation processes that occur in the structure of heat-resistant coating of the Si-TiSi2-MoSi2-B-Y system in hypersonic flows of air plasma. It is found that coating operating capacity at surface temperatures Tw ≤ 1820÷1830°C is provided by the structural-phase state of its microcomposite main layer and formation on the coating surface of a heterogeneous passivating protective film. It is based on borosilicate glass reinforced by rutile microneedles. The mechanism of coating destruction at Tw ≥ 1850÷1860°C is erosion loss of oxide film as well as generation and growth of gas-filled cavities at the "coating main layer–oxide film" interface. As the pressure of saturated vapor of gaseous oxidation products (SiO, CO, MoO3 and B2O3) exceeds that of the ambient, the oxide film integrity is disrupted and oxidation process becomes active. The rates of erosion loss and sublimation grow as operating temperature increases and ambient pressure decreases.