Study On Preparation Of Metal Coatings On Hollow Microspheres And Properties Research

Hollow microsphere is an important fuel container in inertial confinement fusion(ICF)experiments.And metal coating is a necessary part of microsphere shell.It can improve the gas retention performance,increase impact resistance,strength compression efficiency and decrease the Rayleigh Taylor instability(RT)function and so on.So metal coating on the microsphere with uniformed thickness,compacted structure and low surface roughness can be better used in the ICF research.It is a pity that the researches about metal coated microspheres are still less.There also lacks systematic studies on growth mode and morphology evolution of the coating.And the quality of coating needs to be improved.In addition,the coating growth on microsphere is quite different from that on plane(studies of coating on plane have also been widely conducted).Then,based on the current situation,we developed a research about metal coatings on microspheres.Fabrication of the high quality coating on microsphere is the ultimate objective of our work.In order to achieve this objective,we first carried out the study on changing the working parameters during sputtering process which is related to the growth of coating.And then to find optimum preparation process,on this basis,the research on excitation of microspheres movement was carried out.As a result,the key factors and influence rules of the coating were analyzed,and methods to control the coating of best quality were summarized.Finally,in order to further improve the comprehensive properties of metal coatings on microspheres,the multilayer coatings on microspheres were investigated,and related experiments of aluminum-tungsten multilayer coatings were explored first.And the result is shown as following:(1)By changing the argon flow rate in the vacuum chamber,the corresponding relationship between the working pressures and the quality of the coating were analyzed.It can be find that with the working pressures increased,the deposition rate of aluminum coating decreased,the surface roughness showed a trend of decreased first and then increased,the best working pressure was stabilized between 0.2 Pa~0.4 Pa.When the target-to-substrate distance increased,the deposition rate of aluminum coating decreased and its thickness uniformity increased.And surface roughness increased first and then decreased.The best target-to-substrate distance is 10cm(2)we made special comparison of difference about the growth mode on the surface of microspheres and the plane.A hypothesis of microspheres motion model is proposed,and then the probe of motion excitation was carried out.The growth process and the final morphology of the coating were analyzed in detail by the diffusion potential barrier,the shadowing effect and angle change of the sputtering atoms.It was found that the frication of the rotating tray can make the microspheres rotate for a period of time,this motion mode of microspheres lead to the smaller surface roughness of aluminum coating,but the thickness of coating is more discrete.When the rotation speed is 45 r/min,the quality of aluminum coating is relatively the best.The hollow microspheres can basically realize constant movement under knocking effect.The wall thickness uniformity was significantly enhanced and the structure of the coating was compact columnar crystals.There existed a transition of coating growth pattern from the initial layer growth to integration of layer growth and island growth.Unsatisfactorily,the surface roughness would be increased.When tapping interval is 15 s,The comprehensive quality of aluminum coating on microspheres is optimal.The wall thickness uniformity is 93.5%,the surface roughness is low to 30.43 nm and the residual stress value is least of preferred crystal(111)surface.This has come to a high level during ICF experiment.(3)The multilayer coatings were explored on the microspheres.It was found that the overall microstructure and internal residual stress of the multilayer coatings were mainly affected by the underlying coating.In this paper,the microstructure and internal residual stress of multilayer coatings were greatly influenced by the bottom aluminum coating.The aluminum coating with a compacted structure and spherical particles provided a good template for the growth of tungsten coating.This not only changes the particle morphology of the tungsten coating,but also significantly reduces the residual stress of the coating,and thickness uniformity of all coatings is more than 90%.This study also explored the influence of the change of working pressure on the comprehensive quality of the composite multilayer coating.The analysis shows that the surface morphology and surface roughness of the multilayer coating are greatly influenced by the working pressure.When the working pressure is 0.5 Pa,the comprehensive quality of aluminum-tungsten multilayer is best.Coating thickness uniformity is more than 90%,the surface roughness of the coating layer is low to 196.5 nm and the residual stress is minimal.