C/C-ZrC composites were prepared by precursor infiltration and pyrolysis using the organic zirconium as precursor.The conversion mechanisms of the precursors such as the thermal behavior,structural evolution,phase composition,microstructure,composition of the precursors and products were analyzed by thermal gravimetric analyzer,Fourier transform infrared spectrometer,X-ray diffraction and scanning electron microscope.The results indicate that the ZrC precursor transforms to inorganic ZrO2 from room temperature to 1200 ℃,then reduces to ZrC at 1600 ℃ through the carbothermal reduction reaction.The microstructure of the C/C-ZrC composites was also investigated.The composites exhibit an interesting structure,a coating composed of ZrC ceramic covers the exterior of the composite,and the ZrC ceramic is embedded in the pores of the matrix inside the composite.
A novel SiC?ZrB2 coating was prepared using a two-step technique by slurry-sintering and chemical vapor reaction on carbon/carbon (C/C) composites. The SiC?ZrB2 coating was composed of the scattered ZrB2 phase and the continuous SiC phase. It was observed that a good adhesion was built between the coating and the C/C composites. The SiC?ZrB2 coating samples exhibited a better ablation resistance in comparison with the uncoated C/C composites. The SiO2?ZrO2 barrier layer, the heat dissipation of the gaseous products and the pinning effect of ZrO2 all contributed to the good ablation resistance of the SiC?ZrB2 coated composites.
C/C composites with banded structure pyrocarbon were fabricated by fast chemical vapor infiltration（CVI）,with C3H6 as carbon source,N2 as carrier gas,and three-dimensional（3D） 12K PAN-based carbon fabric with high density of 0.94 g/cm3 as preform.Experimental results indicated that the fracture characteristics of C/C composites were closely related to the frequency of high-temperature treatment（HTT） at the break of CVI process.According to the load？displacement curves,C/C composites showed a pseudoplastic fracture after twice of HTT.After three times of HTT,load？displacement curves tended to be stable with a decreasing bending strength at 177.5 MPa.Delamination failure and intrastratal fiber fracture were observed at the cross-section of C/C composites by scanning electronic microscope.Because the content of pyrocarbon and fibers has a different distribution in layers,the C/C composites show different fracture characteristics at various regions,which leads to good toughness and bending strength.
