NbTi (NbTi) superconducting material is a typical quantum material. Its superior comprehensive performance accounts for over 80% of the global usage of superconducting materials. For a long time, the NbTi materials necessary for many high-end applications such as magnetic resonance imaging (MRI), large-scale scientific projects, etc. in China have all relied on imports, and the prices are very high. At the same time, with the rapid development of advanced new superconducting applications such as advanced medical high-field superconducting MRI, fast-pulse high-energy accelerators, advanced light sources, high-speed magnetic levitation, quantum computing, etc., increasingly strict requirements are being put forward for the performance and industrialization capabilities of NbTi materials. How to obtain NbTi superconducting long lines with high critical current density (J), high thermal stability, and low AC loss and achieve mass production has become a competitive hotspot in the international superconducting field. New technologies must be developed and industrialized.
This project has undergone more than twenty years of research and development, conducting systematic research on NbTi flux pinning control technology and wire comprehensive force-heat-electromagnetic stabilization technology. High-performance NbTi superconducting materials have been invented and mass-produced through this technology and have been realized on a large scale, filling the domestic gap. High-performance NbTi superconducting wires have achieved large-scale application worldwide, accounting for more than 55% of the global market share in 2024, ranking first in the world. The main scientific innovations include:
The invention of high critical current density wire flux pinning control technology introduced special "aging heat treatment + cold deformation" technology. Nano-scale a-Ti sheet-like precipitated phases and high-density dislocations were used as effective pinning centers, and medium-temperature, long-time, and multiple (385°C x 40h x 5 times) aging heat treatment and large-strain cold deformation were used to control the size and distribution of the flux pinning centers, increasing the J. at 4.2K and 5T to 3251A/mm2 compared to the wire used in the international tokamak fusion experiment reactor (ITER), an increase of 13%.
The Nb artificial pinning technology was developed to increase the density of effective pinning centers. For the first time, NbTi multi-core superconducting wire with a content of up to ~30% and uniformly dispersed pinning centers was prepared. The overall magnetic flux pinning center (a-Ti + Nb) was increased to ~50%, and the J at 4.2K and 2T was increased by 67% to 8778 A/mm2. The Ta doping technology was invented to enhance the upper critical magnetic field, thereby increasing the critical current density. The first high-uniformity and high-Ta-content (10wt.%) NbTiTa alloy was prepared, and a medium-temperature, short-time, and few-cycle (385°C x 5h x 3 times) aging heat treatment regime was developed. The J at 4.2K and 9T was increased by 47% to 787 A/mm2. The successful breakthrough of this technology laid a technical foundation for NbTi superconducting materials to fully meet new applications.
The design of a new structure for high-temperature stable NbTi superconducting wire and the preparation technology have developed a new type of NbTi/Cu superconducting wire with a high copper ratio and excellent thermal stability. The "superconducting core + U-shaped copper slot wire" continuous embedded welding conductor design and preparation technology has been invented. An internal circulation copper-solder coating copper slot, with a low processing rate and high-precision composite special tooling, has been independently developed to achieve defect-free welding of the core wire and the U-shaped copper slot wire. The first set of online embedded welding copper-covered special equipment has been designed and developed, and a production line integrating surface activation, embedded welding, and online non-destructive testing has been built. A copper superconducting wire with a length of 10,000 meters and a copper ratio of up to 55 and a residual resistance ratio of up to 263 has been batch-produced with a high copper ratio of up to 55. The technology for developing a polyester filament weaving insulation technology and equipment has been developed, which improves the mechanical and thermal properties of the wire while maintaining the insulation strength. A production line with an annual capacity of 5,000 tons of high-temperature stable NbTi superconducting wire for MRI has been built. The micro-level ultra-fine core wire NbTi superconducting wire conductor structure design and processing technology has been invented. The micro-level ultra-fine core wire NbTi superconducting wire conductor structure design and processing technology has been proposed, which uses Cu5Ni alloy as the base material and can achieve good plastic cooperative deformation with the aged NbTi core wire. At the same time, its high resistance characteristics effectively reduce the eddy current loss of the wire. The cold threading assembly and processing technology for ultra-fine core composite bodies has been invented, completely solving the problem of four-component cooperative deformation under a 99.999% large plastic deformation processing volume. The 360° short torsion and high-precision twisting technology and dedicated equipment have been developed. Through high twisting speed, low unwinding speed, and high-precision coordination, ultra-fine core wire NbTi superconducting wire with a diameter of 1.9 um and a torque of 6 mm has been twisted for the first time, solving the problems of wire breakage under high shear stress and large J degradation.
Finally, the world's first NbTi superconducting long line with the largest number of cores (75,276 cores) and the thinnest core wires (1.9 μm) was successfully prepared. Compared with the wire material used in ITER at 4.2 K and ±3T, the AC loss was reduced by 68% (reaching 19.9 mJ/cm2), providing a core material guarantee for applications such as high-speed magnetic levitation and fast pulse accelerators in alternating magnetic fields. 4. Superconducting coaxial cable assembly technology for quantum computers This project invented the "automatic centering" rolling technology, enabling the automatic centering of NbTi tubes during rolling deformation, and obtaining high-uniformity tubes with a diameter of 0.86 mm and a wall thickness of 0.10 mm, with a wall thickness tolerance of only +3 μm, completely solving the technical problem of high-precision processing of NbTi tubes.
Developed high-precision nesting technology and specialized equipment, embedding the inner conductor after insulation into the capillary tube, invented the "self-coaxialization" cable manufacturing technology, conducting 2% small processing rate drawing on the coaxial cable to achieve uniform plastic deformation of the NbTi capillary tube, with the eccentricity of the inner and outer conductors being only 5 um, completely solving the problem of controlling the concentricity of the three components (inner, outer conductors and insulation layer). Finally, a batch of NbTi coaxial cables with a diameter of 0.86 mm (outer conductor wall thickness 0.10 mm, inner conductor diameter 0.20 mm) was mass-produced. At 5 GHz, the signal attenuation was ≤ 0.2 dB/m, which was better than the Japanese counterparts (≤ 0.5 dB/m), filling the domestic gap and breaking the situation where this type of superconducting coaxial cable was "hindered". It has been applied in the field of superconducting quantum computers in China.
