Niobium-Titanium superconducting alloys

In the existing superconducting technology, niobium-titanium superconducting alloy is one of the most widely used superconducting materials.

The Nb-Ti alloy with mass ratio close to 1: 1 has good superconducting electrical properties. Its critical transition temperature Tc= 9.5K can operate at liquid helium temperature, and its transfer current density Jc≥105A/cm²(4.2K) in a magnetic field of 5T(50,000GS). The maximum application field can reach 10T(100000 GS)(4.2K).

The superconducting wire and strip products can be obtained by traditional smelting, processing and heat treatment.

Therefore, after starting research in the 1960s, it quickly entered the industrial scale production.

America produced 100 tons a year in the late 1970s;Trial-production lines were also built in China around the 1980s.

The practical Nb-Ti superconducting materials are mostly simple binary alloys containing 35% ~ 55% niobium. Some tantalum and zirconium can be added to improve superconductivity.

Due to the stability of superconducting material, Nb-Ti superconducting material is usually made of pure copper, pure aluminum or Cu-Ni alloy as the matrix material, and the composite multi-core superconducting material is made by inserting multiple Nb-Ti fine cores.

A superconducting wire can contain dozens to tens of thousands of Nb-Ti cores, the core diameter of the minimum up to 1μm.

In addition, according to the use of different occasions, but also often to the multi-core wire for torsion and transposition, to reduce the loss and increase the effect of electromagnetic stability.

The basic processing technology of Nb-Ti superconducting material is as follows: smelting pure titanium and niobium into alloy ingots with consumable electric arc furnace or plasma furnace, then opening the blank by hot extrusion, and forming bars by hot rolling and cold drawing; Then, the Nb-Ti alloy rod was inserted into the oxygen-free copper tube as the matrix material to form a single mandrel. After many times of composite assembly, the multi-core Nb-Ti superconducting wire and strip are processed.

The material needs to undergo several large cold processing (processing rate of more than 90%) and low temperature (below 400℃) aging heat treatment, so that the superconductor to obtain enough effective nailing center, improve the superconducting electrical properties of the superconducting material.

Nb-Ti superconducting materials are especially suitable for electrical applications with large current and strong magnetic field due to the characteristics of no Joule heat loss caused by the zero-resistance effect of superconductors and the ability of Nb-Ti superconductors to carry high current under strong magnetic field.

For example: high field magnets, generators, motors, magnetic fluid power generation, controlled thermonuclear reactions, energy storage devices, high speed maglev trains, ship electromagnetic propulsion and transmission cables, etc.

To date, the most successful applications of Nb-Ti alloy superconducting materials are large cyclotron accelerators with a diameter of more than 1km and magnetic resonance imaging diagnostic instruments widely used in the medical sector.

Although in the mid-1980s scientists discovered high-temperature copper oxide superconductors capable of operating at liquid nitrogen temperatures (77K);However, niobium titanium alloy superconducting material is still the most important practical superconducting material in the world by virtue of its unique excellent processing properties, good low-temperature superconducting electrical properties, relatively low cost and decades of research, production and application and development experience.