Modification And Properties Of Wide Temperature Domain C/C-SiC-ZrC Composites

Carbon fiber reinforced silicon carbide/zirconium carbide based（C/C-SiC-ZrC）composite is a new type of composite material which can maintain excellent mechanical properties,erosion resistance and oxidation resistance under high temperature environment.It is widely used in nose cone,leading edge,engine nozzle and other extreme thermal environment parts of high-speed aircraft.Although C/C-SiC-ZrC composites have many excellent properties,the oxidation resistance of C/C matrix is poor under high temperature aerobic atmosphere.When the temperature reaches 350℃,the oxidation begins,and the oxidation rate increases when the temperature exceeds 500℃.In low temperature domain（500-1200℃）for long time,the dense oxygen barrier layer cannot be formed.This results in the destruction of composites,which limits the application of C/C-SiC-ZrC composites in medium and low temperatures to a great extent.In this paper,B₄C and Zr B₂were introduced into C/C-SiC-ZrC composites by simple and low-cost slurry process and infilteation and pyrolysis process.By forming a compact oxide film in the low temperature domain,the wide temperature domain oxidation ablation resistance of C/C-SiC-ZrC composites can be improved.The main research contents include the following sections:（1）Preparation technology:The slurry impregnation and impregnation pyrolysis method were adopted.Boron carbide powder was introduced,and the effects of dispersant content,p H value,solid content and binder content on the stability of boron carbide slurry were investigated.The slurry parameters for sully preparation were determined as p H=8,solid content of 15 wt.%,dispersant content of 0.5 wt.%and binder content of 2.5 wt.%.The influence of vacuum,vibration,ultrasonic and other parameters on the impregnation efficiency was studied.When the ultrasonic time was controlled at 30 minutes,the weight gain of the fabric preform after impregnation with slurry was the highest,which was about 31%,and the density was close to 1.0 g/cm³.After the density of composite material reached 1.8 g/cm³,the slurry impregnation method was continued.The Zr B₂-SiC ceramic particle layer was prepared by sintering with zirconium disilicate and boron carbide at 1600℃（2）Mechanical properties of composite materials:The mechanical properties of composite materials before and after slurry modification were compared.With the increase of slurry particles,the mechanical properties of composite materials showed a downward trend.Taking the tensile properties as an example,they decreased from 109 MPa to 59 MPa.Finally,it was determined that the introduction of B₄C should be controlled within 15%.（3）Wide temperature range oxidation resistance:the oxidation resistance of composites at different stages and times was tested.Before modification,C/C-SiC-ZrC composites had good oxidation resistance at high temperature stage,but could not form a good protective film below1000℃,resulting in a lot of damage to carbon fibers;The modification of boron carbide can improve the oxidation resistance of composite materials at 600℃,and the introduction of zirconium boride can improve the oxidation resistance of composite materials in the range of500～2000℃.Through the combination of microscopic morphology and energy spectrum analysis,the modified composites were tests by static oxidation at 600℃,oxy-acetylene ablation at 1500℃,and wind tunne ablation at 1800℃.The C/C-B₄C-SiC-ZrC-Zr B₂materials could maintain structural integrity and were covered with dense oxide film,forming a relay of oxide layer and achieving great oxidation resistance effect in a wide temperature range.