| Carbon/carbon(C/C) composites exhibit excellent high-temperature mechanical properties such as low density, low coefficient of thermal expansion(CTE), high specific strength and good thermal shock resistance, so they are considered as promising candidate materials for applications in aeronautics and astronautics fields. However, the oxidation of these composites at temperatures above 500℃ in oxidizing atmosphere limits their application as high-temperature materials.Several approaches have been considered to prevent C/C composites from oxidation at high temperature. Among these, coating is one of the promising methods to solve the problems. MoSi2 has been proved to be an excellent anti-oxidation material because of the self-sealing performance at high temperature and the high melting temperature of 2030℃, which dictates a potential upper use temperature of about 1600℃. ZrB2, a representative of ultra-high-temperature ceramics(UHTCS), has excellent oxidation-resistant property due to B2O3 glaze which is one kind of oxides formed by ZrB2 and oxygen at 1273 K. Moreover, ZrO2 from the oxidation of ZrB2 is a typical thermal barrier material. So ZrB2 and MoSi2 are hopeful materials for anti-oxidation coating.The spherical ZrB2-Mo Si2 composite powders were successfully prepared by spray drying and vacuum sintering. Then dense and homogeneous ZrB2-MoSi2 composite coatings were deposited on C/C composites by plasma spraying. The structures and properties of powder and coating were characterized via scanning electron microscope(SEM), energy dispersive spectroscopy(EDS), X-ray diffraction(XRD), differential scanning calorimeter(DSC) and laser particle size analyzer, etc. The main contents and detailed results obtained are as follows:(1) Zr B2-MoSi2 composite powders which are suitable for plasma spraying were successfully prepared by spray drying and vacuum sintering. The effect of sintering temperature on mobility and strengh of spray-dried powder has been researched. The results show that strengh of spray-dried powder increase with increasing sintering temperature, but the mobility and loose density decrease wih increasing sintering temperature. The mobility and strength of spray-dried ZrB2-MoSi2 composite powders are suitable for plasma spraying when the sintering temperature is 1200℃.(2) With the spray-dried and mechanically-mixed ZrB2-MoSi2 composite powders as raw material, the spray-dried and mechanically-mixed ZrB2-MoSi2 composite coatings were manufactured by low pressure plasma spray(LPPS), respectively. Then homogeneity of these two kinds of coatings was comparatively studied. The results show that the Si of spray-dried ZrB2-MoSi2 composite(SZM) coating distributed much more uniformly than that of mechanically-mixed ZrB2-MoSi2 composite(MZM) coating. Besides, the SZM coating exhibited lower void content in comparison with those of MZM coating.(3) The SZM coatings with different content of MoSi2 were deposited on C/C composites by atmospheric plasma spraying(APS). Then the structures and basic properties of coatings were researched. The results show that with the content of MoSi2 increasing, the powder melting in plasma spraying process is better, but the internal stress was increased. ZrB2-40 wt.%MoSi2 composite coatings exhibit a dense and homogeneous structure. And the bonding strength is up to 7.2MPa.(4) The anti-oxidation ability of SZM coatings with different content of MoSi2 at 1500℃ were investigatied in detail. The results show that SZM coatings all exhibit poor anti-oxidatin ability when the content of MoSi2 is too high or too low. The mass loss of C/C composites coated by ZrB2-40 wt.%MoSi2 coating is 1.7% after 9h in air at 1500℃. The coating exhibits good self-sealing performance and excellent anti-oxidation ability. |
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