Research On The Microvascular Self-healing Material For Thermal-protection Application

The utility of reuseble spacecraft, which will be the inevitable trend of development, is the effective way to reduce the transport cost and to improve the operational efficiency. During spacecraft re-entery, the aerodynamic heating give rise to a ultra-high surface temperature. So, the thermal protection system of spacecraft is the key factor for retaining its shape , and keeping longer service life and maintenance convenience.To obtain a light-weight, self-healing thermal-protection material of the reuseable spacecraft, the present investigations on the biomimetic Al/Al₂O₃ TPS structures with self-healing phase- transformation energy-absorption capabilities have been carried out in present project. The micro-vascular and Al core/Al₂O₃ shell structures as the first generation self-healing structures, were designed, prepared and disscussed, respectively. This is the first time to introduce the liquid-solid coupling self-healing patterns from polymeric to ceramic materials.The preparation methods of self-healing Al core/Al₂O₃ shell structure have been studied via direct oxidation and micro-arc oxidation (MAO) routes. During research, the lowest solid-state synthesis temperature, 400℃, of MgAl2O4 spinel was reached in heating the mixture of Mg(NO3)2.6H2O and boehmite powders. A light-weight and high-strength self-healing Al core/Al₂O₃ shell structure can be obtained via MAO process. After heating at the temperatures higher than 1000℃, the pre-produced cracks were healed by the scaring effect, i.e. the oxidation of the molten Al, which bleeding out of Al₂O₃ shell.The whole self-healing process is kinetically controlled by the Al bleeding out of Al₂O₃ shell and in-situ oxidation of the molten Al into Al₂O₃ scar. By estimation, the Al core in self-healing Al core/Al₂O₃ shell structure can repair the cracks for 20 times at the temperatures higher than 1000℃.Gel-casting and Al / SiC / PCS precursor metohds were applied in prepareing a high-tempreature ceramic matrix bulk composite containing above-mentioned micro-vascular self-heaing Al core/Al₂O₃ shell foam structure.During Gel-casting, the best fludity of slurry was obtained with the viscosity of 179mPa·s at pH9 by adding0.5wt% dispesant after 4 hours'ball-milling,which was used in filling the Al core/Al₂O₃ shell foam,The sintering linear shrinkage of sintered body is 2%, which results in a large amount of surface cracking.In Al / SiC / PCS precursor with 60vol% Al and PCS, the linear shrinkage rate of green body is near zero, as the result of the formation of AlN, which can compensate the shrinkage of PCS decompsotion. After sintering the matrix of obtained final composite was identified as SiC and AlN.