Many precious metals such as Ir, Pl, Rh, Hi and so on have high melting point characteristics of metal iridium melting point as high as 2410℃ due to its high temperature oxygen permeability coefficient and low oxygen diffusion coefficient so has excellent high temperature oxidation resistance. However, in order to avoid the metal iridium directly exposed to high temperature atmosphere, the vapor pressure of the oxide is higher, it is necessary to add other components coating on the outer layer of the metal Ir. The Ir-Si-Al anti-oxidation coating prepared by V. Terentieva et al. 2 on tantalum alloy substrate has an oxidation weight of 6.9mg/cm² after 200 hours at 1650℃ oxidation atmosphere, while the Ir-Al coating works at 1700 ℃ oxidation atmosphere for 120 hours The weight gain after oxidation is only 4.26mg/cm². Due to the high cost of precious metal coating, only a few experiments have been carried out under laboratory conditions. The Mo-Si-Hr anti-oxidation coating prepared by foreign scholars W.S. Worel et al. can withstand the oxidation atmosphere of 1790℃ for 3h without significant change P. The anti-oxidation coating showed good thermal shock resistance and anti-scour performance under the condition of high temperature oxidation airflow scour experiment. The results show that the antioxidant coating is Hf. The refractory phase structure of z0s MonmuoSi has cracks around it and the cracks produced by MoSi, SiHi3-s and HiSi; Completely sealed so that the coating can block the penetration of oxidation atmosphere at high temperature and improve the high temperature oxidation resistance of the coating. Al-Sn coating on Ta-10W surface was prepared by Royal Company by fusion slurry method. The coating thickness was 75μm, and the protective life was 37h at 1500℃. The coating was successfully applied in the thrust chambers of 7.3kg and 90.7kg of the secondary propulsion system of Arjinna rocket, and the normal cumulative working time was 6 250s and 2000s.
Noble metal coating has good corrosion resistance and ductility, which can overcome stress deformation and elastic-plastic deformation caused by high temperature creep of matrix. At present, CVD method is usually used to prepare noble metal oxidation resistant coatings on refractory metal surface, but there are still technical bottlenecks in this technology.
There is an inevitable thermal expansion difference between tantalum and tantalum alloy material matrix and coating material, which is also the main reason for the crack of coating. Coating cracks of tantalum and tantalum alloy materials can be eliminated by the preparation of sealing layer and gradient coating. Gradient coating can make the coating and matrix two-phase concentration and the composition of the multiphase coating is continuous distribution, eliminate the stress between all surfaces, and the surface without cracks, and finally achieve the purpose of high temperature oxidation.
