Preparation And Properties Of Modified C/C Composite By The Combination Of Spraying And Melt Infiltration

C/C composite has excellent properties such as low density,high specific strength,low thermal expansion coefficient and good fatigue resistance.It has broad application prospects in high temperature structural materials.However,the poor oxidation resistance in high temperature oxidizing environment restricts the practical application of C/C composites in the field of high temperature materials.Reactive infiltration,which is the one of the matrix modification methods for C/C Composite,has the problems of poor applicability for large,heterogeneous and complex components and high requirement of equipment.This paper explores the modification of C/C composites by the combination of spraying and infiltration.First of all,the melt infiltration alloy was prepared into spraying powder.And the alloy coating was prepared on the surface of C/C composites by the method of plasma thermal spraying.Then the alloy coating infiltrates into the pores of C/C composites with the infiltration process.The alloy reacts with the matrix carbon to produce carbide ceramics in situ.Si as spraying infiltration agent,spray infiltration method was used to prepare spray infiltrated Si modified C/C composite.In order to prepare a good fluidity,high powder rate of the alloy powder coating,spray powder preparation process was studied.The paper optimized the plasma thermal spray process,to prepare a combination of good,high-quality alloy spray coating.Then the paper optimized infiltration process to form SiC-SiC/C-C/C gradient structure on the surface of C/C composite,which can improve the anti-oxidation ablation performance.Si powder with-180～+320 mesh and good fluidity was used to prepare the good Si spraying layer by spraying power of 350A and 60V.Then the Si modified C/C composite was prepared by infiltration of 30min at1550℃in vacuum.Under the same ablation condition（1250～1350℃,10min）,the mass loss rate of unmodified C/C composites and modified C/C composites is 60.2%and 9%respectively,and the oxidation and ablation resistance are improved significantly.It also proves the feasibility and advantages of the modified C/C composites by spraying infiltration method,and expands the applicability of the reaction infiltration process.In order to improve the oxidation and ablation resistance of C/C composites modified by spray infiltration in super-high temperature,Si-Zr alloy was used to replace Si to modify C/C composites by melt infiltration.In order to reduce the melting percolation temperature and improve the process feasibility,Si-Zr10 eutectic alloys as spraying infiltration agent,Si-Zr infiltration alloy spray powder was prepared,and the Si-Zr modified C/C composites were prepared by spray infiltration method at lower infiltration temperature.The（ZrC+SiC）-（ZrC+SiC）/C-C/C gradient structure was formed on the surface of C/C composite to improve the oxidation and ablation properties.The introduction of the Zr element can reduce the melting point of the molten alloy and the melting temperature,and enhance the oxidation resistance of the modified C/C composite at a higher temperature.However,ZrO₂ has isomeric phase change with temperature change,which leads to the change of ablative layer volume in the cooling process of ablative sample,and the ablative layer is easy to pulverize.So it’s difficult to be reused.In order to solve the problems caused by ZrO₂ phase transition,Ta₂O₅ was introduced to stabilize ZrO₂.ZrSiTaB spray powder was prepared by mechanical mixing and atomization drying granulation of Zr powder、Si powder、Ta powder and B powder.Sprayed ZrSiTa B modified C/C composite was prepared with56Zr30Si10Ta4B granulation powder.The research shows that the method has the problem of low powder rate and the preparation process needs to be improved.In the process of atmospheric plasma spraying,Zr and Ta have appeared obvious oxidation,resulting in the formation of ZrO₂ and Ta₂O₅.In the following research,the alloy layer should be prepared by vacuum or atmosphere protective plasma spraying.