Sr1-xKxFe2As2超导圆线的微观结构与临界电流提高机制研究

Iron-based superconductors, which were discovered in 2008, have great potential in electrical and high-field applications, since they show ultrahigh upper critical fields (Hc2) above 100 T with very small Hc2 anisotropy, and can be made into wires and tapes by low-cost powder-in-tube (PIT) method. Therefore, the development of iron-based superconducting wires and tapes is of great significance for high field applications. At present， by mechanical pressing to achieve the densification and grain texture of superconducting core, the transport critical current density (Jc) of iron-based superconducting tapes have been greatly increased. However, due to the advantage of geometry, round wires are more suitable for high-field applications compared to flat tapes, and so far the current carrying property of iron-based superconducting round wires still need to be improved. In this project, we will fabricate Sr1-xKxFe2As2 superconducting round wires by hot isostatic pressing (HIP) technique. By controlling the parameters of HIP process, we will systematically study the microstructure including mass density, grain size and grain orientation in the superconducting cores, find out the crucial factors which determine the performance of round wires, so as to further enhance the transport Jc in iron-based superconducting wires. Our research will provide a better understanding of the Jc improvement mechanism, and also further promote the application of iron-based superconductors.

铁基超导体是2008年发现的一种新型超导材料，因其具有极高的上临界场（大于100 T）以及较小的各向异性，能够采用成本较低的粉末装管法制备成超导线带材，在强电和强磁场方面具有独特的应用潜力。目前，铁基超导带材通过采用机械加压的方法实现超导芯的致密化和织构化，载流性能已得到大幅度提高。然而，与带材相比，超导圆线由于其形状上的优势更适用于高场应用，但目前铁基超导圆线的载流性能还亟待提高。本项目将采用热等静压技术制备Sr1-xKxFe2As2铁基超导圆线，通过工艺参数的调控，从超导芯致密度，晶粒生长以及晶粒取向三个方面对圆线的微观结构进行深入系统的研究，明确圆线中载流性能提高的关键因素，提高铁基超导圆线的传输临界电流密度。 本研究无论是对深化我们对铁基超导线材电流提高机制的认识，还是对推进铁基超材料的实际应用，都具有重要的意义。

2008年发现的铁基超导体是一种新型实用化超导材料，具有极高的临界磁场及各向异性小等独特优势，在下一代高场超导磁体，高能粒子加速器，核磁共振谱仪等领域极具应用潜力。本项目以122型铁基超导圆线的微观结构与性能为研究对象，基于热等静压这一先进材料制备技术，制备了不同复合金属包套的线带材，对线材热处理工艺参数进行了调控优化，并对拉拔、平辊轧制、孔型轧制等多种机械加工工艺进行探索和系统研究。在实现超导相致密化的基础上，对超导相的元素成分、晶粒生长以及晶粒织构进行了重点研究。开展的系列研究包括：1）铜银复合包套铁基超导圆线的制备与性能研究；2）Monel合金/银复合包套铁基超导线带材的制备与性能研究；3）铁基超导圆线的性能优化与EBSD表征；4）铁基超导线材不同变形工艺与性能提高。通过研究深化了对铁基超导线材临界电流提高机制的认识，建立了铁基超导圆线超导性能与微观结构特点之间的联系，并最终有效提高了铁基超导圆线的电流传输性能，其传输临界电流密度达到3.1×10^4 A/cm2 （4.2 K，10 T），对推动铁基超导材料的在高场强电领域的实际应用有重要意义。