Research On Key Preparation Technologies Of Iridium/Rhenium/Carbon-Carbon Thrust Chamber

Currently, the liquid engine used for attitude and orbit control is developing in the direction of high specific impulse,lightweight and long life,which makes it a challenge for the materials prepared for the thrust chamber. Rhenium/Iridium/C-C composites chamber combines the advantages of Rhenium/Iridium for its high strength,long life and anti-oxidtion properties at high temperature and C-C composites for its low density and high specific strength.So this paper aims at the preparation of Rhenium/Iridium/C-C composites chamber and lay the emphasis on the key technology confronting in the process.The feasibility of two technical projects(inner to outer project and outer to inner project)was first studied.Numerical simulation was conducted to solve the problem of uniformity in the CVD process of rhenium coating.At last,a more uniform deposition result was obtained by the optimization of deposition reactor and process parameters.SiC coating was tried to prepared on the outer C/C composites by reactive melt infiltration in case of oxidation during the test process.At last,the chamber was tested by a series of methods to assess the anti-thermal shock and anti-ablation properties. Main conclusions were summarized as follows:(1) The outer to inner project is full of technical problems and uncertain factors despite of the shorter process.Cracks exist in the rhenium coating on the C/C composite tube after the CVD process.Defects are inevitable on the inner surface of the tube during the electrodeposition of iridium in the molt salt.While dense, defect-free rhenium and iridium coating could be obtained in the inner to outer project.What is more,the microstructure of the coating could be examined layer by layer easily.This latter project is more feasible in spite of the long process and preparation period.So we adopt the latter project after a deliberate comparison.(2) Mathematic model of the CVD reactor was first established after a series of reasonable assumption and simplification.The gas flow pattern,distribution of concentration as well as the deposition rate of rhenium on the substrate were simulated by FLUENT 6.3.26.At last,a more uniform deposition result was obtained by optimization of the shape of CVD reactor and process parameters.(3) SiC coating could be obtained on the outer C/C composites by reactive melt infiltration to improve the anti-oxidation property.However Si atoms would react with rhenium coating at the interface between the C/C composites and thick rhenium coating to form ReSi2 and continue to diffuse to the inner coating which makes the iridium coating failure by segregating and forming low melt-point alloy in the grain boundary.Then infiltration method was improved by a two-step process,Ti86.5Si13.5 and pure Si respectively.The result show that TiC layer was first formed at the interface mentioned above to prevent the reaction between Re and Si successfully.But unfortunately it fails to block the diffusion of Si to the inner Ir coating,which would reduce the failure of chamber.(4) The pressure resistant property,anti-thermal shock and anti-ablation properties of the chamber were tested by a series of methods.Results show that the chamber has a compact and dense inner wall and remain good shape and property after the tests,which claims that the chamber has reached the desired performance.