| Directional solidification oxide eutectic ceramic is affected with its excellent resistance to high temperature, anti-oxidation, corrosion resistance, high strength, high hardness etc properties. It is considered as one of the most promising candidates for new generations of ultra-high-temperature structural materials, and has important application prospects on the ultra high temperature aerospace engine.In this experiment, Al2O3/MgAl2O4/ZrO2 eutectic ceramic has been prepared by zone-melting method. This experiment mainly includes two aspects:(1) The preparation and characterization of pre-sintered ceramic. The best process parameters for pre-sintered were determined by measuring the porosity, analysing phase composition through XRD. The powders were ball milled with water for 3h to obtain a homogenous slurry that was subsequently dried in a drying oven. The strip samples were prepared by pressuring at 20MPa with the mixed powder and then sintered at 1550℃ for 3h to obtain the pre-sintered ceramics, which have a certain strength and density.(2) The preparation and characterization of eutectic ceramic. Tungsten crucible as the best one, whose inner diameter is 8mm and wall thickness is 1.5mm, is selected in graphite crucible molybdenum crucible and tungsten crucible. The crucible wall temperature is 2200℃ and the crucible rate is 1～6mm/h. A dense rod eutectic ceramic with smooth surface was prepared under the best conditions of the above. By measuring the density reached 99%, achieved the full densification. The XRD pattern shows that the eutectic consists of Al2O3 phase MgAl2O4 phase and ZrO2 phases the same phases composition as in the pre-sintered ceramics. Its microstructure shows that the phases are homogenously distributed and interconnected with each other without grain boundary, no micro porosity and crack. By measuring and calculated λ2v≈2.5 conform to the λ2v=constant.Its microstructure reveals that the Al2O3-MgAl2O4 phase is the matrix, the ZrO2 stick sets in the matrix. With the increase of the crucible rate, the eutectic spacing and the hardness reduce, the fracture toughness are opposite with the hardness. Its hardness reaches 11.68GPa, is about 1.6 times of the sintered sample. Its fracture toughness at temperature reaches 7.21 MPa·m1/2, is about 2 times of the sintered sample. The disappearance of the grain boundaries and pores, and the dispersion of the fine ZrO2 phases with round shape in the matrix result in the improvement of the material’s hardness and fracture toughness. |
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