| Ultra-high temperature ceramics stand out among the many high temperature materials due to their unique physical and chemical properties and have a wide range of applications,especially in the aerospace and equipment sectors.Given the diversity of the preparation of this material and the advanced nature of the equipment technology as well as the non-uniformity of the external environment,the properties of the resulting material show variations.However,due to the intrinsic characteristics of the material itself,the following problems exist in the currently prepared ultra-high temperature ceramics:（1）difficult sintering,（2）low fracture toughness,（3）easy oxidation,（4）poor thermal shock resistance.For these reasons,the application of ultra-high temperature ceramics is limited.For this reason,this project focuses on the sintering method and uses in situ synthesis combined with discharge plasma sintering to improve the sintering difficulties of ultra-high temperature ceramics.The presence of Si C also improves the oxidation properties of the composite ceramics.In addition,the ablation resistance of the composite ceramics was improved by introducing short-cut carbon fibres into the Zr C-Zr B2-Si C three-phase composite ceramics.The three parts of the research carried out are as follows:（1）Reactive sintering densification processes with ZrH2,B4C and Zr Si2as the main raw material powders under reactive discharge plasma sintering（RSPS）were investigated.The dense Zr C-Zr B2-Si C complex-phase ceramics were successfully prepared at 1600°C-20 MPa.Z3Z6S1 exhibited optimum mechanical properties with a bending strength of 681±32 MPa,a hardness of 19.8±0.1 GPa and a fracture toughness of 4.7±0.2 MPa·m1/2.The main reason for this was the uniform distribution of the three phases and the fine average grain size.Z1Z8S1 has the highest thermal conductivity.The high thermal conductivity provides for increased heat dissipation to other parts,contributing to a reduction in the thermal gradient within the component and thus reducing thermal stresses in the internal material and improving thermal shock resistance.（2）On this basis,the ablation properties of ZrC-ZrB2-SiC（Cf）ceramics with different contents of short-cut carbon fibres added under the same synthesis process were investigated.The thermal shock resistance of the material was evaluated under both rapid heat and cold conditions.In addition,a gradient structure was designed with the aim of better preventing catastrophic damage to the ceramics in the presence of both rapid heat and cold.The results show that the presence of carbon fibres interlaced within the composite,forming a web-like structure woven within the matrix,enhances the ablation resistance of the composite.（3）Although carbon/carbon（C/C）composites are the most important thermal protection materials in the aerospace industry,their inherent low oxidation resistance limits their application.Zr B2-Zr C-Si C-Mo-C/C（ZZS-Mo-C/C）composites were synthesised at low temperatures using the reactive spark plasma sintering（RSPS）technique.The densification process,microstructure,interfacial bonding,ablation properties and mechanism of the ZZS-Mo-C/C composites were investigated.Before and after ablation,the specimens showed good interfacial bonding,indicating that the presence of the Mo foil transition layer resulted in an optimum connection between ZZS and C/C.In addition,SEM analysis shows that the ZZS ceramics have a dense structure,which prevents further diffusion of oxygen into the substrate.The results show that ZZS-Mo-C/C exhibits excellent oxidation resistance and ablation properties under an oxygen-acetylene flame（4170 KW/m2 heat flow density）. |
