Preparation Of ?Zr,Ti?B₂-SiC And ?Zr,Hf?B₂-SiC Modified C/C Composites Via A Reaction Melt Infiltration Method And Their Antiablation Properties

C/C composites show excellent high-temperature properties,however,they are easily oxidized and ablated at high temperature and rich oxygen conditions,which greatly limit the wide application of them.Introducing high-temperature ceramics via a matrix modification technology is an effective method to improve the ablation resistance of C/C composites.In this thesis,?Zr,Ti?C modified C/C composites,?Zr,Ti?B₂-SiC modified C/C composites and?Zr,Hf?B₂-SiC modified C/C composites were respectively prepared by reactive melt infiltration method and pack cementation medhod using zirconium powder,titanium powder and hafnium powder as raw materials.The phase composition,microstructure and morphology of the prepared samples and specimen were characterized by XRD,SEM and EDS,and the ablation performance of the specimen was tested using plasma ablation equipment.The related results and conclusions are as follows:1.The infiltration temperature has an obvious effect on the ablation resistance preformance of?Zr,Ti?C modified C/C composites.The anti-ablative performance of the prepared specimen first increased and then decreased when the infiltration temperature rised.The tested specimen obtained by infiltrining at 2200^oC showed better anti-ablative performance with mass ablation rate of 1.16 mg·s^-1 and linear ablation rate 1.06?m·s^-1after ablation for 30 s.This is mainly because much low–viscosity ZrTiO₄ was formed to combine ZrO₂ tightly and formed a continuous dense oxide protective layer on the surface of the specimen during ablation.2.The?Zr,Ti?B₂-SiC modified C/C composites prepared by introducing both B and Si show excellent ablation resistance and the mass ablation rate and linear ablation rate were 0.74 mg·s^-11 and1.18?m·s^-1 respectively after ablation for 120 s.While at the same conditions,the mass ablation rate and linear ablation rate were 2.61 mg·s^-1and 3.74?m·s^-1 for just adding B,and 2.29 mg·s^-1 and 4.55?m·s^-1 for just adding Si,respectively.After introducing B and Si,high-viscosity B₂O₃-SiO₂-ZrO₂ oxide layer was formed on the surface of composites to protect thenm from ablation.3.?Zr,Hf?B₂-SiC modified C/C composites exhibited good ablation resistance.The mass ablation rate and linear ablation were 0.21 mg·s^-1 and 1.14?m·s^-1 after ablation for120 s.During the process of ablation,a ZrO₂?HfO₂?ZrSiO₄?SiO₂ and B₂O₃ complex oxide layer was formed on the surface of composites,and various oxides exhibited synergistic effect.Then these oxides provided effective protection for C/C composites under high temperature and speed particle flow in oxidizing environment.