CONCEPTUAL PROTECTION MODEL FOR STRONGLY HEAT-RESISTANT MATERIALS IN HYPERSONIC OXIDIZING JET FLOWS

Abstract

The article is a continuation of authors’ publications in the field of multi-function protective coatings for strongly heat loaded structural elements of hypersonic systems. The paper suggests a new physical and chemical model of heat-proof coating operation in a high-enthalpy oxidizing gas jet flow. The model considers and eliminates the main causes of surface destruction by the gas flow. The concept is efficiently used to produce a number of Si–TiSi2–MoSi2–B–Y system alloys intended for thin-layer coating formation using any layer deposition method capable of reconstituting the structure, phase composition and morphology of the deposited material. Deposition involves forming a microcomposite layer constructed from the refractory silicide framework with cells filled with a fusible (as compared with the framework phase) eutectic component. This layer transforms into a multilayer system during the high-temperature interaction with oxidizing media (synergetic effect). This multilayer structure contains anti-catalytic, reradiative, anti-erosion, heat-proof, barrier compensating function layers of micron and sub-micron thicknesses. Protection is ensured by a self-healing oxide glassy film formed based on alloyed silica. The self-healing effect consists in the rapid filling of incidental defects by the viscous plastic eutectics and faster (as compared with the known coatings) protection film forming. The branched dendrite cellular refractory framework ensures high resistance to erosion mass loss. The MAI D5 and MAI D5U protective coatings created as part of the presented concept were tested successfully in high-enthalpy oxygen-containing gas flows. The various specimens made of strongly heat-resistant materials were used to depose the coating such as niobium alloys, carbon-carbon and carbon-ceramic composites as well as graphitized carbon materials. The 80–100 μm thick coatings subjected to jet flows with M = 5÷7 and enthalpy 30–40 MJ/kg have shown the protection capacity above 600 s (Tw = 1800 °С), 200 s (Tw = 1900 °С), and 60 s (Tw = 2000 °С) for structural components with sharp edges as well.