Tungsten Copper Throat Insert

Solid rocket motor spray tube by controlling the expansion of the combustion chamber exhaust gas generated energy is efficiently converted to kinetic energy, so as to provide the required power for the aircraft. Throat insert located in the larynx of the spray tube, which plays an important role in restricting the throat area expansion by ablations and the decreases of the thrust. Throat insert usually need to be heated from room temperature to more than 2000℃  and produces a great temperature gradient and thermal stress when the engine working, which is also the main reason for the cracks and failure of throat insert materials. Furthermore, such high-performance engine for rocket often uses metal powders (such as Al) as propellants combustion at high temperature of about 3000 ℃ high burning rate entrained flow of solid particles or liquid droplets (Al2O3) and scoured the throat insert intensely. It is difficult to ensure a stable aerodynamic shape even the fragmentation occurred if the throat insert has severe ablation, so it will has an bad effect on the thrust and efficiency of the engine.

With the application of throat insert becoming wider and wider, such as rocket boosters, long-range missiles, solid rocket engine and so on, and the more and more types of the metal additives, the materials properties for throat insert has been confronted with the higher requirements, which is also a key to the solid rocket technology developments. In general, throat insert materials used for solid rocket engine include refractory metal, graphite, carbon and carbon-based composite material, reinforced plastics and ceramic-based composite materials, etc. Among them, tungsten copper is one of the very suitable materials for throat insert fabricating. In addition, throat insert heat conduction can be divided into three steps: 1.Engine ignition instant impact heating; 2. Ablation when working steady; 3. The cooling process of flameout; wherein the thermal shock of throat insert often occurs at the moment of the ignition.

Tungsten copper throat insert fabricated by the infiltration process, which not only has high hardness, high density, high strength, high melting point, low coefficient of thermal expansion and excellent wear and corrosion resistance of W, but also has excellent ductility, thermal and electrical conductivity of Cu. What’s more, since there is a great difference in the melting point between W and Cu, at high temperature higher than the melting point of Cu, Cu will evaporate and take away the most of heat and the hard phase W left. So it ensures the stability of throat insert works, and tungsten copper is also known as sweating heat sink material.

Through related experiments the researchers found that coarse grain has better performance in thermal shock resistance and poor in ablation resistance, conversely. Rocket spray tube entrained within particles or liquid phase stream high burning rate will continue to scour throat insert, and this two-phase flow weakly oxidizing, such throat insert constantly ablated, which is a complex physical and chemical process covered by heat conduction, mass conduction, transmission capacity and chemical reactions. According to different ablation principles, it can be specifically divided into thermal ablation, melted ablation and mechanical erosion. When the surface temperature of tungsten copper throat insert is higher, melted copper was deposited on the inner surface, which will cause thermal effect and prevent heat transfer to the inside of the material.

In addition, when the gas temperature below the melting point of tungsten, tungsten skeleton does not melt, ablation occurs at this time of the melting of copper and tungsten substrate by gas particles (such as Al2O3) erosion produced by mechanical erosion. Currently, copper tungsten throat insert prepared have been able to successfully applied to 3600 ℃, 6.88MPa under thermal environment at this temperature above the melting point of W, tungsten skeleton is also possible to melt ablation. From the view point of throat insert structure, improving the roughness and prolonging the length of the straight section can remarkably improve the ablation resistance of throat insert.

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