Study On The CVD Iridium Coated Rhenium Composite

The composite of Ir/Re was prepared by chemical vapor deposition (simply CVD) first in china. Iridium coatings and rhenium substrates were bonded together metallurgically.Ir films were prepared by MOCVD (metal-organic chemical vapor deposition) using Iridium-acetylacetonate precursors on molybdenum substrates. The effects of substrate temperature, precursor temperature and flow of argon on deposition rates of iridium were studied firstly. The relationship between the deposition rate and the substrate temperature did not accord with Arrhenius formula: there was a parabola relation in them. The deposition rate of iridium reached maximum at 750℃. The deposition rate increased linearly with the rising of temperature of iridium-acetylacetonate, whereas decreased obviously with the increasing flow of argon. The microstructure of surface and the composition of iridium films were determined by SEM. CVDIr films grow with particles of 0.1 micron in diameter. The contents of carbon and oxygen in iridium films were less than 0.8wt% and 1.0wt% respectively.Rhenium was prepared by CVD. The effects of substrate temperature and flow of chlorine gas on deposition rates of rhenium were studied. The relationship between the deposition rate of rhenium and the substrate temperature accords with Arrhenius formula; The deposition rate increased linearly with the increasing flow of chlorine gas. It is of the typical characteristic of mass transmission control process.The effects of deposition conditions on microstructure of rhenium were studied in this work. Deposit microstructure could be controlled by manipulating the degree of rhenium supersaturation in the gas phase and the deposition (substrate) temperature. The most common microstructure of rhenium was discontinuous columnar prepared by discontinuous deposition. The typical dendritic surface morphology was obtained when the deposition temperature reached 1250℃ CVDRe with the dendritic microstructure was coated in the outersurface of Re/Ir rocket nozzle.ABSTRACTThe tensile strength of CVDRe exceeds 50kg/mm2, which is independent on the deposition temperature and the flow of chlorine gas; the density of CVDRe is 20.92g/cm3, close to the theoretic density of rhenium; the Vickers hardness of CVDRe is high but the Cronic hardness is lower. The Vickers hardness increases obviously with the increasing of deformation of CVDRe. When the deformation is more than 20%, the material cracks.Examination of the microprobe photographs and of the scans clearly indicates that diffusion of Re into Ir coating predominates with little diffusion of Ir into the Re. For this case, the semi-infinite medium can be used to model the diffusion of Re into Ir coating. The diffusion coefficients have been obtained in the temperature range 1 400-2000 , which have an Arrhenius dependence. The life time of Ir/Re composite has been predicted from the results of the experiments, which is 47.6 hours.The oxidation behavior of CVDRe was firstly studied by thermogravimetric analyses(TGA). For the long period of oxidation, the Wagner's law for thick film oxidations was obeyed above 1000, that is the parabola relationship exists between the oxidation rate and the oxidation time, whereas there exists a linear dependence between them as the temperature is lower than 1 000 . Arrhenius plots were obtained for the weight loss and the temperature relation either for PMRe or for CVDRe. There is no significant difference of activation energies for different oxidation time.