Slip Casting And Properties Characterization Of ZrB₂-SiC Ultra-high Temperature Ceramics

ZrB2is mainly used in the front head of supersonic aircraft, sealing surface, wing leading edge, and other heterosexual parts as typically Ultra-high temperature ceramics materials. Several of methods have been used to prepare ZrB2ceramic, such as hot press sintering, isostatic pressing, as well as dry pressing. However, only ceramic products with simple shape can be prepared by the above methods. Therefore, much attention has been paid on precision machining processes in order to obtain components of ZrB2ceramic with complex shapes. It is noted that it is difficult to process ZrB2ceramic which has high strength and high hardness. On the basis of this, slip casting molding-pressureless sintering is used in this paper to prepare ultra-high temperature ZrB2ceramic with complex shapes. The best volume ratio of ZrB2and SiC was obtained through a serious of contrast experiments. The effect of pH, dispersing agent (PEI), and milling conditions on properties of slurry were explored. Meanwhile, the microstructure, strength at high temperature, and resist burn corrosion properties for this ultra-high temperature ceramic were also tested.During the process to obtain the best volume ratio between ZrB2and SiC, much attention also focused on researching the effect of milling time on the diameter of ZrB2powder. The result showed that the best milling time of ZrB2powder was6h, and the corresponding diameter was1.32μm; when the best volume ratio between ZrB2and SiC was80:20, the density, bending strength, and fracture toughness were5.33g/cm3,233MPa,4.94MPa-m1/2, respectively.A system researches were made to investigate the effect of pH, the amount of PEI, milling speed, the ratio of balls to materials and graduation of balls, the amount of solid content and body reinforcing agent (GA-472) on the properties of slurry during the process of preparing slurry. Base on the volume ratio of ZrB2to SiC was80to20, it was demonstrated that the best properties of slurry was produced when the pH of the solution was11, the percentage in volume of PEI to mixed powder was0.3, the milling rate was400r/min, the ratio of balls to materials was1:1in presence of the same amount of big and small balls (the corresponding diameter of big and small balls is30mm and10mm, respectively), and then the solid content was55vol%, the percentage in volume of body reinforcing agent to mixed powder was0.2.The high-temperature bending strength of the as-prepared samples was measured, and the results showed that the bending strength of high temperature ceramic went through, rising, and then keeping the same tend followed by falling, three different change processes when the temperature was elevated from room temperature to900℃. In addition, we also investigated the loss on line ignition, loss on quality ignition, the thickness of center area, as well as the changes of bending strength to ablation time, and demonstrated that the weight of the sample and the thickness of centre areas had little changes when ablation time was less than50s; the bending strength of the sample before and after ablation almost kept the same changes tend when ablation time was less than70s, and then obtained samples with good ablation resistance and oxidative stability, X-ray diffraction pattern was used to analysis the principal phase compositions of samples oxidized at60s.