| Continuous carbon fiber reinforced silicon carbide(Cf/SiC)composites are considered as a mature technique of high technology materials for the aerospace applications because of their low density,high strength,high temperature resistance,and wash out resistance.However,Cf/SiC become invalid by oxidative stress corrosion,high water vapor corrosion and high-temperature corrosion environment when used in the new kind of rocket propellant where the working temperature is over 1400? and the water vapor content are more than 70%.In this paper,based on the review of progress on anti-oxidation techniques of C/SiC composites,pyrochlore-type lanthanum zirconate(La2Zr2O7)coatings were deposited via electrophoretic deposition(EPD)on Cf/SiC substrates which were prepared by polymer infiltration and pyrolysis.Some properties of them,such as fabrication,microstructure evolution,anti-oxidation properties and mechanism of coatings,were investigated.Properties of LZO were modified by Y2O3 adoption with the thermal expansion coefficient(TEC)and sintering behavior of Y2O3 doped LZO powders are investigated in this work.It was observed that when the addition of Y2O3 in LZO is 15% the TEC of LZO can be largely decreased.The TEC of LZO is 2~4×10-6K-1 after doped,and the modified powders are more approaches that of C/SiC composites.Electrophoretic suspension was invested.The result showed that the size of La2Zr2O7(LZO)particles is the minimum when the ball-milling time is about 24 h.Ethanol provides good dispersion,iodine charges ceramic particles and polyvinyl butyral(PVB)provides good stability.The conductivity and stability of the suspension is excellent when the quality of iodine and PVB is 4% and 0.2‰,respectively.And the absolute value of Zeta potential can be improved from 20 mV to 30-40 mV as well as the surface structure of the coatings is smooth and dense when the addition of PVB is 0.2‰.Constant voltage and constant current were applied to produce LZO green coatings,respectively.Study showed that thick,compact and less vicious coatings can be prepared difficultly under the way of constant voltage.And SEM observations revealed that the deposit morphologies of LZO coatings can be unfluence by current density and electrode distance,deeply.The deposition mass increased as the applied current density increased.Moreover,the surface structure of the coatings is smooth and dense when the current density is 1 mA/cm2 and the electrode distance is 2 cm.The coating bonding strength is 0.806 MPa and the relative density is 50.37% after sintered for 1 h at 1300?.The diffusion coefficient and thermal conductivity can be reduced slightly.Performance of coated C/SiC composites was tested under the high temperature and high water vapor environment.The strength retention of C/SiC with La2Zr2O7 coatings is increased from 81% to 92% after testing at 1200 °C for 30 min in water vapor.And after 10 times for 10 min every time of thermal shock from RT to 1200? under air,the quality retention rate and the strength retention of coated C/SiC composites are 87% and 50.28%,respectively. |
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