Study Of CVD Process Optimization For Large Diameter Pure Tungsten Liner And Penetration Performance

The high density(19.3g/cm3), high acoustic velocity(4.03km/s) and high dynamicfracture elongation rate make tungsten one of the most attractive candidate materials forpure metal shaped charge liners (SCLs). The preparation of pure tungsten SCLs largelyaffects their ability to form jet, thus affects the penetration performance of pure tungstenSCLs. Because high purity, high density of pure metal coating can be easily achieved bychemical vapor deposition (CVD) technology, which attracts widespread attention andstudy on the preparation of pure tungsten Liner by CVD technology. At present, althoughChina has carried out research on the preparation and penetration performance of puretungsten SCLs. Related research merely stops at CVD preparation and penetrationperformance of pure tungsten SCLs about65mm diameter, yet research on larger diameterCVD pure tungsten SCLs and their penetration performance is blank.In order to research the penetration performance of larger diameter pure tungstenSCLs, our research group developed a kind of CVD deposit system that can prepare varioustypes of pure tungsten SCLs. The deposit system can satisfy the demands for accuratecontrol of gas flow and stable deposition temperature. Based on static penetration testrequirements for the preparation of large diameter pure tungsten SCLs, we conducted aseries of optimization to deposition equipment. We not only solved the problems such aspoor air tightness and jamming of pipeline, but also successfully controlled the depositiontemperature at the preset temperature value with deviation in the range of±5℃and the H2and WF6gas flow precise stable near the preset flow value. Uniformity and grain size oforiginal structure can greatly affect the continuity of jet formed by pure tungsten SCL. Thus,improving the uniformity and reducing the grain size of pure tungsten SCL can effectivelyimprove the continuity of pure tungsten jet and thus improve its penetration performance.Optimized CVD deposit system was used to research the effect of deposition temperatureand gas flow on the microstructure of CVD pure tungsten. The research results show that in500~540℃range, higher deposition temperature reduces the uniformity of pure tungstenmicrostructure and best uniformity of pure tungsten microstructure can be obtained underthe condition of500℃. Pure tungsten grains can be refined by reducing gas flow ratio of H2to WF6under the condition of500℃. When the gas flow ratio is less than260ml/g, puretungsten microstructure of relatively uniform and fine grains can be obtained. Along with the deep comprehension and accumulated practice, it found that production problems suchas deformation, cracking and thickness of inequality phenomenon incurred during thepreparation process of large diameter pure tungsten SCLs can be solved effectively byimproving the structure of the heating wire. It also found that the presence of water vapor inH2gas seriously affect the stability of WF6flow and cause the growing of surface relief onthe surface of pure tungsten. Improving the dry degree of the H2can greatly improve thestability of the WF6flow and the surface quality of pure tungsten SCLs.In static penetration test with burst height of2times the diameter of the pure tungstenSCL, pure tungsten SCL of100mm diameter, and60°cone angle, and208g has been testedto penetrate45#steel target and obtained penetration depth of495millimeter.Micro-regions of different ballistic location were analyzed and both the whole process ofthe jet penetrating the target and mechanism were researched. The research results showthat the formation of acute angle cracks reduced effective mass of tungsten jet and theintensity of interaction between the jet and the target weakened during the whole jetopening-pit phase. When jet entered into the quasi-steady phase, the intensity of interactionbetween jet and target exacerbated again and kept stable until the effective mass andvelocity of tungsten decreased to a certain extent. With the gradually consumption of themass and gradually reduction of velocity of the tungsten jet, the intensive of interactionbetween the jet and target weakened gradually and jet eventually stopped sundering armor.