Preparation Process And Properties Of TiC In-situ Modified Graphite Collector Materials For High Power Microwave Source

The collector applied to high-power microwave(HPM)source is a device used for receiving high-current electron beam after beam-wave coupling.It is one of the most important devices in the HPM source for the fact that its service life directly determines the life of high-power microwave weapons.Considering the drawbacks like easy gas release,oxidation and carbon pollution in the vacuum system of graphite collector,the titanium carbide(TiC)surface modification method was used to improve the performance of graphite collector in this paper.Through the comparison of various in-situ reaction processes,the in-situ reaction TiC gradient coating was prepared on the surface of the graphite substrate by powder embedding process,and the in-situ reaction mechanism was analyzed by HSC Chemistry 6 thermodynamic calculation software.Combining the experimental and calculational results,the influence of process parameters on the morphology and structure of TiC coatings were analyzed.Based on this,the feasibility of forming Ti3SiC2 coating by in-situ reaction of Ti and Si in step with graphite was explored.Finally,the effect of TiC modification on the performance of graphite collectors for HPM source was analyzed by the test results of the basic properties and electron beam bombardment resistance of graphite modified by in-situ TiC.In order to improve the bonding strength of the TiC coating to the graphite substrate,the TiC should be prepared by in-situ chemical reaction and infiltrate into the graphite substrate.Based on the principle of in-situ reaction of titanium-containing gas with graphite to form TiC surface gradient coating,the in-situ reaction of Ti vapor,titanium iodide gas and titanium chloride gas in-situ reaction process and solid powder embedding process were respectively studied in this paper.The powder embedding process was finally selected to prepare the TiC gradient coating for the advantages that lower in-situ reaction temperature,more uniform morphology of TiC coating,and easier to operate..Ti powder,TiO2 powder,TiC powder and NH4Cl were used as the Ti sources in the powder embedding process.The thermodynamic simulation results show that TiC is formed by the reaction of TiCl3 gas formed in the Ti sources with the graphite substrate during the embedding process.TiO2 does not act as an inert filler,but participates in the reaction process and promotes the formation of TiC,which is obviously different from the mechanism of forming TiC on the surface of carbon steel.Also,the experimental results indicate that the penetration depth of the TiC gradient coating increases firstly and then decreases with the increase of temperature.This can be explained as that increasing the experimental temperature increases the diffusion rate of TiCl3 and increases the thickness of the gradient coating,on the other hand,it increases the rate of TiCl3 and graphite in-situ to form TiC and reduces the permeability of the reaction gas.In addition,with the increase of the pressure,the partial pressure of the reaction gas decreases,and the driving force for diffusion into the graphite substrate is decreased,results in the decrease of the penetration depth of the coating.With the increase of the proportion of TiC in the Ti sources,the grain size of TiC in the coating increases,and the coverage integrity of the coating on the graphite surface increases.Moreover,with the increase of the ratio of NH4Cl in the Ti sources,the penetration depth of TiC decreases,which results from the increase of pressure due to the decomposition of NH4Cl.Besides,The thickness of TiC gradient coating can be increaseed by prolonging the holding time to 2h.However,when the time exceeds 2h,the concentration of NH4Cl decreases due to its decomposition and dissipation,and the influence of the holding time on the thickness of the coating is gradually weakened.Under the conditions of 1000? and 0.04 MPa,a TiC gradient coating with a thickness of 150 ?m can be obtained,and a TiC surface coating with a thickness of 15?m can be obtained under 1500? and 0.04 MPa.The experimental study on the in-situ reaction of Ti and Si with graphite shows that the Ti3SiC2 coating can be formed on the graphite surface by the process that in-situ reacting with silicon vapor firstly and then reacting with titanium vapor.The bond strength between the coating and the substrate is poor and it is easy to fall off.According to the performance requirements of collector materials for HPM sources,the fundamental properties of TiC modified graphite materials prepared by powder embedding method were tested.The results show that TiC coating modification can effectively block off the pores on the surface of graphite substrate by reducing the pore size and the porosity.Furthermore,the surface conductivity of the TiC modified graphite is one to two orders of magnitude higher than that of the graphite,the elastic modulus increases by 77 percent after the modification of TiC coating.Also,TiC coating can effectively improve the oxidation resistance of graphite.Finally,the electron beam bombardment resistance of TiC modified graphite samples were tested.The TiC gradient coating can effectively improve the performance of the graphite when it is used as high-current electron beam collector.