Study On The Fabrication And Transport Properties Of 122-type Iron-based Superconducting Multi-filamentary Wires And Tapes

New iron-based superconductors have attracted extensive attention from researchers since they were discovered in 2008.Due to its outstanding characteristics such as high transition temperature,ultrahigh upper critical fields,low anisotropy and high transmission performance,122-type superconductor becomes the most promising iron-based superconducting material.At present,the critical current density of single-core tape has surpassed 1.5×10~5 A/cm~2 at 4.2 K and10 T by adopting the conventional power-in-tube(PIT)method,exhibiting great promise for high-field applications.However,with poor anti-interference ability and high AC loss,the single-core wire or tape is difficult for conductor design and practical use,but must be made into multi-filamentary wires or tapes,which have high stability and low flux jumping.Therefore,this paper tries to develop the 7-and37-filamentary iron-based superconducting tapes.By studying the effects of related factors on superconducting core deformation and the performance during the preparation,including outer sheath material and thickness,rolling direction as well as rolling pass,to find out the optimum process parameters of multi-filamentary tape,and provide direction and reference for subsequent optimization.The main contents are as follows:Based on the thin-walled(5*0.5mm)single core wire,the 7-filamentary tape prepared with 8*1mm pure silver sheath has the highest performance for critical current density(J_c),which exceeds 3.5×10~4 A/cm~2 at 4.2 K and 10 T,but the superconducting core shows obvious rupture.By adapting the bidirectional rolling technology,the non-uniform deformation of superconducting core can be eliminated,and the integrity of superconducting cores can be guaranteed,therefore,the critical engineering current density(J_e)is increased to 1×10~4 A/cm~2 for the first time.The higher hardness of silver alloy can enhance the density of superconducting core so as to improve the performance of the tape,which is up to 3.5×10~4 A/cm~2 at 4.2 K and 10 T.However,the core ratio is only 22%,which is obviously lower than that of pure silver 7-filamentary tape.Meanwhile,both Jc and Je are improved when the silver alloy tube with thinner wall thickness(6.4*0.5 mm)is used as the sheath material,indicating that 6.4*0.5 mm is more suitable for the preparation of the7-core silver alloy tape.In addition,it is found that 5 passes rolling is more favorable to the uniform deformation of the superconducting core,which has almost no"sausage effect".The J_c of the first silver alloy 37-filamentary tape exceeds 2.3×10~4 A/cm~2(4.2K,10 T).Moreover,according to the analysis and improvement of problems such as too low core ratio and serious“saddle effect”appeared in the first 37-filamentary tape,the optimized tape achieved high core ratio and even deformation of superconducting core.