Study On Preparation And Properties Of Carbon Fiber Reinforced ZrB₂-SiC Composites

Due to their extremely high melting point?>3000°C?and excellent resistance to oxidation and ablation,ultra-high temperature ceramics can be used for a long time in an oxidizing environment above 2000°C and maintain non-ablation and structural integrity.The ultra-high temperature non-ablation type heat-proof material with great application prospects is an important or even primary candidate material for key thermal structural parts such as nose cone and leading edge of hypersonic aircraft.However,the poor fracture toughness of ultra-high temperature ceramic materials has become a bottleneck that restricts the engineering application of such materials.Carbon fiber is considered to be the most potential toughening phase due to its excellent room temperature and high temperature mechanical properties.However,carbon fiber will cause structural damage during the preparation of composite materials,and the preparation of non-damaged carbon fiber toughened ultra-high temperature ceramic composite materials has become the focus of research.In this paper,a low-temperature and pressureless densification method combining vibration grouting,vacuum impregnation and precursor impregnation cracking method was used to prepare a needle-punched continuous carbon fiber toughened Zr B₂-Si C composite material,and the prepared composite material was macroscopically Cf/Zr B₂-Si C composites prepared by low-temperature and pressureless densification were examined by microstructure analysis,mechanical performance analysis,and anti-oxidation ablation performance analysis.In terms of mechanical properties,this paper applies a method of applying a pyrolytic carbon coating to carbon fiber to protect the carbon fiber,prevent structural damage to the carbon fiber during the preparation process,and limit the carbon fiber's excellent toughening effect and high temperature performance.The pyrolytic carbon coating can also form a weak interface between the carbon fiber and the Zr B₂-Si C ultrahigh temperature ceramic matrix,promoting fiber pull-out,fiber bridging,crack bifurcation,and crack deflection toughening mechanisms to avoid Cf/Zr B₂-Si C compounding The devastating destruction occurs when the material has an external force.The flexural strength of the composite material is 203±14MPa,the fracture toughness is 5.26±0.25 MPa·m1/2,and the fracture work is 1446J/m2,which has achieved a significant improvement in the mechanical properties of the composite material.In terms of thermal physical properties,the specific heat capacity,thermal conductivity and thermal diffusion coefficient of acupuncture Cf/ ZRB₂-SIC composites were measured.The specific heat capacity of Cf/ Zr B₂-Si C composites increases gradually with the increase of temperature,and decreases slightly when the temperature rises to 1000?.The thermal conductivity of Cf/ Zr B₂-Si C composites began to decrease slightly at 1000?.It can be found that both thermal conductivity and specific heat capacity will rise with the increase of temperature,but they will slightly decrease after 1000?.With the increase of temperature,the thermal diffusion coefficient decreases gradually until 1000? has an upward trend.The static oxidation experiment of acupuncture Cf/Zr B₂-Si C composites was carried out at 1500 ? for 1h.The static oxidation behavior of acupuncture Cf/Zr B₂-Si C composites was comprehensively studied through multi-angle characterization such as oxidation profile and surface microstructure and chemical composition analysis.The oxide layer was mainly composed of Si O2 in the outer layer and Zr O2+Si O2 in the inner layer.After static oxidation,the structure of carbon fibers in the transition region between the oxide layer and the matrix remains good without serious corrosion.During the static oxidation experiment at 1500?/1h,the Py C interface layer plays a certain protective role on carbon fibers.Then examines the needle type dynamic of Cf/Zr B₂-Si C composites anti-oxidation ablative performance of Py C the introduction of interface layer,reducing the carbon fiber surface oxidation rate,to a certain extent,improved antioxidant ablative performance,and comprehensive study of the needle type Cf/Zr B₂-Si C the static oxidation behavior of Si C composites,the oxide layer is mainly composed of the outer layer of Si O2,the middle layer of Zr O2+Si O2 and inner Zr O2,oxide layer and substrate transition area of the carbon fiber in the static structure to maintain good after oxidation,without serious corrosion phenomenon,Under the condition of 1800?/800 s oxyacetylene test,the performance was near zero ablation,which realized the synergy of toughening and oxidation resistance.