Preparation And Performance Of C_f/HfC Composite By Liquid Impregnation Combined Reactive Melt Infiltration

C/C composite is one of the widely used advanced structural materials which possess a lot of outstanding properties such as low density,high specific strength.However,the long fabrication period with high cost and feasibility of oxidation and ablation at high temperature and aerobic environment limits its widely applications in aviation aerospace and metallurgy areas.The matirix modification method,with large amounts of anti-oxidation particles or ultra high temperature ceramics introduced into matrix,is an effective way to improve the oxidation and ablation resistance of C/C composite.Reactive melt infiltration?RMI?is the most effective measure to modife C/C composite by ceramic components,which can not only improve the oxidation and ablation resistance of C/C composite,but also effectively decrease the preparation period and cost.The melting point of hafnium carbide?HfC?is 3890?,and its oxide Hf O₂ has a high melting point and low evaporation rate,thus HfC modified C/C compsite possesses excellent oxidation and ablation resistance.Aiming at the preparation of C_f/HfC composite,this paper studies the organization and properties of modified C/C composite,infiltrated organization of composite after hafnium alloy infiltrated C/C preform,and properties of C_f/HfC composite.Our expectation is that C_f/HfC composite which possesses excellent oxidation and ablation resistance can be obtained by liquid impregnation combined reactive melt infiltration method.Using ball mill mixture,various particles such as Zr B₂,B₄C,Ta Si₂ were well dispersed in barium-phenolic resin.The modified C/C composite was prepared by liquid imprgnation technique.The impregnation efficiency of Zr B₂ modified barium-phenolic resin impregnant was studied,and the most efficient hybrid scale was 3.5 to 1,proportion by weight.The oxidation and ablation resistance of single component modified C/C composte was unsatisfied,however,multiple components introudced into C/C composite simultaneously can enhance the oxidation and ablation resistance of the composite significantly.The linear ablation rate of Zr B₂+Ta Si₂+Hf O₂ modified C/C composite was 0.0146mm/s,whose density was 1.34g/cm³ and contained 9wt.%modified components.The flexural strength of the composite was 178.52MPa,displaying a brittle behavior.The Hf-Si-B,Hf-Zr-Si-Ta,Hf-Zr-Si-Ta-B alloys were designed and prepared,then infiltrated into C/C preforms at 1900?.Results showed that with the increasing of Ta content,the distribution of phases in infiltrated organization became more homogeneous,the porosity of C_f/HfC composite decreased,yet the linear ablation rate of the composite increased.Introduction of B element can enhance the ablation resistance of C_f/HfC composite.The linear ablation rate of Hf-Si-B alloys infiltrated samples decreased with the increasing of B content,among which the the linear ablation rate of Hf10Si6B alloy infiltrated sample was 0.0044mm/s.The ablation resistance of C_f/HfC composite improved obviously after the introduction of B element into Hf-Zr-Si-Ta quarternary alloys.The density and open porosity of 40Hf36Zr10Si10Ta4B alloy infiltrated sample were 4.15g/cm³ and 8.77%,respectively,and an oxide layer which was mainly consisted of Hf O₂,Zr O₂ formed on the surface of composite after oxyacetylene flame ablated 60s.The surface of test sample was flat,there was no obvious ablation pit on it,and the linear ablation rate of the composite was 0.0109mm/s.Two kinds of C_f/HfC composites were prepared by liquid impregnation combined reactive melt infiltration technique.The density and open porosity of C_f/HfC composite which contained ZrB₂+HfO₂+TaSi₂ particles were 2.98g/cm³ and 12.95%.A compact oxide layer formed on the composite after oxyacetylene flame ablated 60s,which was consisted of Hf O₂,Zr O₂,Ta₂O₅ and Si O₂,the the linear ablation rate of the composite was 0.0171mm/s.The flexural strength of the sample was 173.73 MPa,displaying a pseudo-ductile fracture behavior.The ablation resistance of C_f/HfC models,which were prepared by reactive melt infiltration and liquid impregnation conbined reactive melt infiltration technique,respectively,was tested in the high-frequency plasma wind tunnel?HFWT?.The RMI model,whose density was 5.29g/cm³,was tested for 1000s with the heat flux of2.83MW/m².The stagnation temperature was around 2301?,the shape and the dimension of the model were changed insignificant after HFWT test,with the linear ablation rate of 0.0011mm/s after removed the oxide layer.The combined method model,whose density was 3.87g/cm³,was tested for 180s with the heat flux of3.53MW/m².The stagnation temperature was around 2293?,and the linear ablation rate of which was 0.0017mm/s after removed the oxide layer,which indicated that the C_f/HfC composite prepared by liquid impregnation combined reactive melt infiltration technique possesses excellent ablation property.