Development Ofygdbco Strip Lead Solder And Exploration Of Superconducting Connection Technology

Due to the high critical current density,upper critical magnetic field and excellent mechanical properties of Re Ba₂Cu₃O_7-?(Re:Y,Gd and other rare earth elements)superconducting coating conductor in liquid nitrogen temperature region,Re BCO coated conductor is the second generation high temperature superconducting strip,which has a wide range of applications in the fields of power,energy,transportation,biomedicine,aerospace development and national defense and military.Among many applications of superconducting materials,superconducting magnets are the biggest engineering applications at present.Restricted by the processing technology,the current strip length can not meet the needs of coil winding.At the same time,in order to meet the different magnetic field shape,field intensity and closed-loop current mode,the superconducting magnet needs to connect each coil through the joint.In addition,the superconducting magnet in the closed-loop constant current mode,the current attenuation is almost zero,can produce extremely stable magnetic field,and the formation of the closed coil,can not be separated from the superconducting joint.In this paper,the preparation of superconducting solder on the superconducting layer of YGd BCO strip was taken as the starting point.On the one hand,the current carrying capacity of YBCO coated conductor was increased by improving the film thickness;on the other hand,the goal was to effectively alleviate the interface of ceramic properties,which could not achieve high-quality connection only by relying on high temperature melting.The preparation technology of YBCO superconducting solder and the superconducting connection technology of YGd BCO high-temperature superconducting strip are mainly studied,and the practical problems encountered in the preparation of superconducting joints are deeply explored,which lays a foundation for the preparation of superconducting joints.In this study,YBCO(4 mm wide YGd BCO)silver strip from Shanghai Superconducting Company(SHSC)was used as the support to prepare YBCO(YBCO)superconducting solder by spinning YBCO film on the superconducting layer of the strip.The surface corrosion of superconducting layer of YGd BCO strip with propionic acid as solvent precursor solution and methanol as solvent precursor solution was studied.The results show that propionic acid can corrode the surface of the strip superconducting layer more and more seriously at room temperature and under dry conditions,but methanol can not corrode the surface of the strip superconducting layer at room temperature and dry conditions.Through the research on the preparation of superconducting solder,it is found that the structure,surface morphology and superconducting properties of YGd BCO high-temperature superconducting strip will not be damaged during the process of solution coating and low temperature heat treatment of tubular furnace drying.The oxygen content in the strip will decrease at low temperature,which will decrease the critical current value of the strip.However,the critical current value of the strip can be restored to the base metal level after the oxygenation treatment.The optimal temperature and growth time of YGd BCO strip superconducting layer were determined to be 795?and 60 min.Under these conditions,the structure,microstructure and superconducting properties of the sample strip superconducting layer would not be destroyed,and the critical current value could be kept within the normal range.The effect of the pressure uniformity of the die and the different joint structures on the morphology of the strip superconducting layer was studied.Through the exploration of the high-temperature connection technology,it is determined that the optimal temperature and growth time of the single crystal film during the preparation of the YGd BCO strip superconducting joint are 820?and 30 min.After the oxidation annealing treatment at450?for 5 h,the structure and superconducting properties of the single crystal film sample strip can be restored to the level of the parent material.It is found that the edge stress concentration effect can destroy the superconducting layer of the strip.After the joint is connected at high temperature,the polycrystalline films can grow as single crystals in a closed joint environment.The method of preparing the second generation high temperature superconducting strip superconducting joint with YBCO superconducting solder was explored.The superconducting solder was prepared by heat treatment at the joint,and then the superconducting joint was prepared.The preliminary study shows that this method is very feasible to fabricate superconducting joints with high performance.