结构材料对Bi2212超导线材临界性能影响机理研究

Due to the high critical performance at very high magnetic fields (~30T), Bi2212 round wire is currently considered as a candidate for magnets technology development for the future fusion reactors (CFETR), accelerator and so on. However, Bi2212 is a brittle ceramic material, and the sheath of the round wire is Ag/Ag alloy with high plasticity and low strength. Subjecting to enormous stresses (i.e. electromagnetic stress) during operation under a high field will cause a strain on the round wire and furtherly to decrease its critical performance. The superconductivity stability of Bi2212 magnets can be improved by cabling the Bi2212 wire with high strength materials. Moreover, the oxidation of the high strength material as well as the reactions happened between the Bi2212 wire and the high strength material will affect the Bi2212 formation and cause a decrease in critical performance. So far, researches on the effects of high strength material on critical performance of Bi2212 round wire during heat treatment are seldom carried out and the relevant mechanisms are unclear. In this project, the Bi2212 round wires will be cabled with various high strength materials and heat treated for Bi2212 phase formation. Then the formed defects (like Cu-free particles, voids/bubbles, breaks and so on) together with the critical performance of the wires will be studied. The relevance between the critical performance and the defect type/quantity is expected to be understood. Underlying mechanisms those defects’ formation will be clarified, which will give guidance for high strength material optimization. Besides, these researches will provide basis for higher strength material development that are also compatible with Bi2212. Finally, the results will be a reference for high performance Bi2212 magnets design.

未来聚变堆、加速器等装置要求磁场强度高于15T，甚至高达20T, Nb3Sn等超导材料应用受限。Bi2212超导线材临界性能高，5~30T高场下临界性能几乎无衰减，是各强磁场装置超导磁体首选超导材料之一。但Bi2212超导线材机械性能低，高场下电磁力等负载会引起线材损坏或应变致临界性能衰退，磁体研制需要高强度、高韧性同时具有低热膨胀系数及高导电性能的结构强化材料以强化超导缆。然而，在Bi2212成相热处理中，结构材料的氧化及其与线材元素间的反应将引起线材微结构缺陷，进而导致临界性能衰减。本项目拟采用高性能结构材料与Bi2212超导线材进行超导缆研制模拟，对Bi2212线材在成相热处理过程中形成的缺陷类型及形成机理进行判别，揭示结构材料对线材临界性能影响的微观作用机制，进而提出结构材料的优化方案，为高场用Bi2212超导磁体结构强化材料的研制及高性能Bi2212超导导体和磁体的设计提供参考。

Bi2212超导线材具有低温高场高临界载流特性，且其具有各向同性，是应用于下一代聚变堆、加速器等高场超导磁体应用的优选材料之一。但是，Bi2212超导线材通常由金属银基材料和Bi2212陶瓷粉末通过粉末装管（PIT）法制备而成，具有强度低的特点，因此，高电磁负载极易引起线材损伤和载流性能的衰退。此外，Bi2212超导成相需要氧气及高温高压环境，这也给其应用带来了一定的困难，主要体现在氧气环境高温高压热处理过程中结构材料与Bi2212超导线材易发生相互反应，进而对结构材料及超导线材性能产生影响。本项目首先通过对结构材料的低温力学行为演变分析，遴选出具有低温高性能候选材料，并采用其与Bi2212超导线材进行超导缆研制模拟，对Bi2212线材在成相热处理过程中形成的缺陷类型及形成机理进行判别，获得了结构材料对超导线材临界性能影响的作用机制，提出Bi2212高场应用CICC导体潜在可用的结构材料，为高场用Bi2212超导导体及磁体的设计提供参考。同时，通过该项研究，资助发表论文2篇，获得受理/授权专利2项。培养硕士生2名。