OPERATING CAPACITY OF ANTI-OXIDIZING COATING IN HYPERSONIC FLOWS OF AIR PLASMA.

In this paper, we present the results of investigations of degradation processes that occur in the structure promising high-temperature anti-oxidizing of heat-resistant coating of the Si–TiSi2–MoSi2–B–Y system in hypersonic flows of air plasma. The coating is designed to protect a wide range of heat-resistant materials (carbon–carbon and carbon–ceramic composites, coal–graphite materials, alloys based on Nb, Mo, W, etc.). It is found that the coating operating capacity at surface temperatures T w ≤ 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 T w ≥ 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. [ABSTRACT FROM AUTHOR]