Preparation And Properties Of C_f/ZrC-SiBCN Composite

Due to the excellent physical properties and chemical stability,ultra-high temperature ceramic materials have met the ever-increasing demands of hypersonic vehicles in recent years.Especially the continuous fiber toughened ceramic matrix composites has overcome the brittleness of ceramic and poor thermal shock resistance,which has attracted the attention of aerospace researchers.ZrC is a transition metal carbide with high melting point and high hardness,which makes it the preferred material for aircraft fuselage.However,the domestically produced ZrC powders are characterized with coarse particles and uneven size distribution.Based on this situation,this work prepared ZrC powder by the sol-gel and carbothermal reduction.Then,the synthesized ZrC powder was combined with SiBCN ceramic as composite material,which has the good oxidation resistance.The C_f/ZrC-SiBCN composites were prepared by the slurry impregnation and PIP.The mechanical properties and oxidation resistance of the material were tested in this work.This work used inexpensive sucrose as the carbon source,ZrO₂ as the zirconium source.They were well mixed by method of sol-gel,and turned into the ZrC powder in the suitable carbothermal reduction process.In the carbothermal reduction process,the effects of heating temperature,zirconium/carbon ratio and raw material size on the final powder were investigated.By SEM and XRD analysis,the final ZrC powder has a higher purity and uniform particle size at the temperature of 1550°C and the best zirconium/carbon ratio is 1:4.By the slurry impregnation and PIP process,ZrC powder and SiBCN ceramics can be smoothly impregnated into the interior of the matrix.And the composite material has a density of 70%in a short preparation cycle.By testing the flexural strength of the composite,it was found that the increase of the ZrC content would reduce the mechanical properties of the material.The water quenching method was used to test the thermal shock resistance of the material.The result shows that the mechanical properties of the material would decrease greatly due to the surface defects above 600°C.The critical thermal shock temperature of the composite is calculated to be 736°C.At the same time,it was found that there was no macro crack on the surface of the material above 1000°C The oxidation resistance of the composites was investigated by static oxidation tests at different temperatures and time.The results show that the material has the bad oxidation resistance in the range of 1000-1200°C.The main reason is the difference in thermal expansion coefficient and the volatilization of gaseous substances.The results show that the material exhibits poor oxidation resistance in the temperature range of 1000-1200°C,mainly due to the difference in thermal expansion coefficient of each phase component and oxidation of surface materials.In the temperature range of 1400-1550°C,the material exhibits good oxidation resistance,mainly because the molten SiO2 has good fluidity under high temperature,can bridge the defects of the material surface,reduce the oxygen channel,and avoid The oxidation of the substrate.As the temperature increases,the thickness of the oxide layer on the surface of the material decreases from 430μm to 103μm.