采用粉末装管法(PIT)已经可以制备出千米量级MgB2超导长线,但依然没有完全满足应用需求,如何继续提高线材的单根长度仍然是MgB2超导材料研究领域的一个重要方向.在传统的原位PIT法制备MgB2超导线材的过程中,引入挤压工艺对其进行加工处理.分别用Cu和Cu-Nb作为中心增强材料,组装两个37芯MgB2包套,通过挤压、拉拔工艺对其进行加工处理.采用金相显微镜(OM)和扫描电子显微镜(SEM)对线材截面和断口的微观形貌进行分析,采用1μV·cm-的电压判据和标准四引线法测量样品在4.2K下的Ic-B曲线,得出样品在该温度下的Jc-B曲线,Ic为临界电流,B为磁场强度,Jc为临界电流密度.结果发现挤压过程所有组元变形基本同步,挤压工艺有效地增加了芯丝致密度.制备的直径3.0 mm Cu芯线材在4T,4.2K下Jc达到2.48 ×104 A·cm-2;Cu-Nb芯线材在4T,4.2K下Jc达到1.59×104A·cm-2.采用挤压工艺加工MgB2复合包套的途径是可行的,但挤压过程中复合体一次变形量超过90％,目前采用的导体结构需要进一步优化,将有助于提高所制备线材的长度和性能.
MgB2 superconducting wire of kilometers could be prepared by powder in tube method (PIT).But it still could not fully meet the requirements of application.How to improve the length of single wire was still an important research field of MgB2 superconducting material.In the traditional PIT process,the extrusion method was introduced.Two MgB2 composite wires were fabricated with the extrusion procedure,where Cu and Cu-Nb bars were adopted as central strengthening cores,respectively.Two superconducting wires with a diameter of 3 mm were processed by extrusion and drawing.The morphology of the cross section and fracture surface was analyzed by means of optical microscope (OM) and scanning electron microscope (SEM).The Icc-B curve of the sample was measured with 1 μV ·cm-1 voltage criterion and standard four-probe method.The Jc-B curves of the samples at the temperature were calculated.Ic was critic current,B was magnictic field strength,Jc was critic current density.The deformation of all components of the extrusion process was found to be synchronized.The extrusion technology could effectively increase the density of core wire.At 4 T,4.2 K,the Jc of MgB2 with Cu and Cu-Nb core reached 2.48 × 104 A·cm 2 and 1.59 × 104 A·cm-2.It was feasible to process the MgB2 superconducting wires by extrusion technology,but the current use of the conductor structure needed to be further optimized.
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