High performance in-situ MgB 2 wires processed using rapid-hot-rolling-quenching reel-to-reel technology

Abstract In-situ reaction has become one of the mainstream methods for preparing high performance MgB 2 (Magnesium diboride) wire due to the good grain connectivity and small particle size of in-situ reaction MgB 2 . However, a large number of pores inside the in-situ MgB 2 wire seriously hinders the further performance improvement of MgB 2 wire since it decreases the volume fraction of superconducting phase in the wire. In this article, a rapid-hot-rolling-quenching (RHRQ) technology is developed to effectively improve this problem through ohmic self-heating and hot-rolling wire. Comparative experiments were conducted on a 30 core in-situ MgB 2 precursor wire prepared by powder-in-tube method. Microstructure analysis shows that RHRQ treatment effectively squeezes out a large number of pores left by Mg–B diffusion reaction, and the effective area ratio of the strip-shaped particle region in the optimal sample can reach about 88%, thereby significantly improving its current carrying performance throughout the entire testing temperature and magnetic field range. For the optimal sample, under a 1 T field, the magnetic J c value at 4.2 K and 20 K reached J c @(4.2 K,1 T) = 1.36 × 10 5 A cm −2 and J c @(20 K,1 T) = 4.52 × 10 4 A cm −2 , improved by 23.6% and 25.2%, respectively, compared with the conventional in-situ MgB 2 samples. Under a 4 T field, J c @(4.2 K,4 T) = 3.05 × 10 4 A cm −2 and J c @(20 K,4 T) = 3.90 × 10 3 A cm −2 , with a performance improvement of 32.1% and 148%, respectively. Transport measurement reveals that core- J c Tr of the optimal sample can reach 7.17 × 10 5 A cm −2 and 1.16 × 10 5 A cm −2 at 4.2 K under 2 T and 6 T respectively. Furthermore, the irreversibility field and flux pinning force were also comprehensively enhanced. Our research demonstrated that RHRQ technology can effectively combine hot pressing sintering, Ohmic-self-heating, and reel-to-reel processes while retaining the inherent advantages of in-situ reactions, thereby significantly increasing the volume fraction of superconducting phases in wires and improving performance. Therefore, it can serve as an effective new approach for continuously preparing high-performance in-situ MgB 2 wire.