122型铁基超导线带材实用化研究进展

Recent progress of 122-type iron-based superconducting wires and tapes

在种类众多的新型铁基超导材料中,122型铁基超导体具有高转变温度、超高上临界场、低各向异性、高临界电流密度等优点,因此成为高场应用领域最具竞争力的铁基超导材料.目前122型铁基超导线带材在4.2 K,10 T下的传输临界电流密度已经超过10~5 A/cm^2这一实用化门槛值,表现出十分广阔的应用前景.本文回顾了新型铁基超导体的发现及发展历程,结合122型铁基超导体的自身特点,就如何制备高性能122型铁基超导线带材展开讨论,同时对粉末装管法制备流程中影响线带材性能的几大关键因素进行了详细分析.重点介绍了近年来122型铁基超导线带材的实用化研究进展,包括高强度线带材的制备、圆线的研制、多芯线材及长线的制备、超导接头的研究、力学性能及各向异性的研究等.对122型铁基超导线带材实用化研究进行了总结,并对其未来的发展趋势进行了展望.

With high transition temperature Tc（-38 K）, high upper critical field H（c2）（ 100 T）, superior transport Jc（-10^6 A/cm2） and extremely small anisotropy（1.5-2.0）,the 122-type iron-based superconductors show great promise in high-field applications such as next-generation high energy physics accelerator and high-field magnetic resonance imaging（MRI）. Power-in-tube（PIT） method is widely adopted to fabricate the iron-based superconducting wires and tapes due to low cost and easiness of large-scale fabrication. In the past few years, substantial efforts have been made to improve the transport performances of 122-type iron-based superconducting wires and tapes by ex-situ PIT technique.In this review, the recent progress of 122-type iron-based superconducting wires and tapes is presented. Firstly, we focus on the techniques for fabricating high-performance 122-type wires and tapes. We also discuss the key factors affecting the final performances of wires and tapes during the PIT process, including the preparation of high-quality precursor,the effect of chemical doping, the improvement of core density and grain connection. Recently, due to the improving of degree of c-axis texture and connectivity of grains, the transport Jc value of 122/Ag tapes reached 1.5 × 10^5 A/cm2 at4.2 K and 10 T, which exceeds the practical level of 10^5 A/cm2 and demonstrates their promise in high-field applications.Then, the progress of practical application of 122-type wires and tapes is summarized. In order to reduce the fabrication cost and improve the mechanical strengths of superconducting wires and tapes, an additional outer sheath such as Fe,Cu and stainless steel was used in combination with Ag. Besides, a favourable transport Jc was also obtained in the Cu-, or Fe-sheathed 122 tapes. For round wires, the highest Jc value reached 3.8 × 10^4 A/cm2 in Cu/Ag composite sheathed wires at 4.2 K and 10 T, obtained by the hot-isostatic-press technology. From the viewpoint of practicality,the fabrication of multifilamentary wires and tapes is an indispensable step. The 7-, 19-and 114-filament 122 wires and tapes were successfully fabricated by the PIT method, and these multifilamentary tapes exhibited weak field dependence of Jc. Based on the experience of high-performance short samples and multifilamentary wires process, the scalable rolling process has been used to produce the first 115-m-long 7-filament Sr（1-x）KxFe2 As2/Ag superconducting tape, confirming the great potential for large-scale manufacture. Moreover, the mechanical property, anisotropy and superconducting joint of 122 tapes are also studied. Finally, a perspective for the future development of 122-type wires and tapes in practical applications is given.