Niobium-Titanium Superconducting Alloy Technology Progress and Market Application

Niobium-titanium superconducting alloys began to be studied by Americans in the 1950s, and were initially not quickly developed and produced due to the large current densities at high fields that were not obtained. By 1961, the Americans Ham (J.K. Halm) and others in the country's "Physical Review" publication for the first time reported a niobium-titanium superconducting alloys Tc. 1962, the Americans Berlincounrt (T.G. Berlincounrt) and others were the first to publish a niobium-titanium superconducting alloys of Hc2 with a high Jc, in the same year, the Americans Mathias (B.T. Mathias) in the U.S. patent reported the first niobium-titanium superconducting material magnet. Since then, niobium-titanium superconducting alloy materials in the international application of the development stage.

Niobium-titanium superconducting alloys are one of the most used superconducting materials in existing superconducting technology. Mass ratio of nearly 1:1 Nb-Ti alloy has good superconductivity, its superconducting critical transition temperature Tc = 9.5K, can be operated at the temperature of liquid helium, it is in the 5T (50,000 Gs) magnetic field, the transmission current density Jc ≥ 105A / cm2 (4.2K); the highest application of the field up to 10T (100,000 Gs) (4.2K). The alloy also has excellent processing performance, can be obtained through the traditional melting, processing and heat treatment process superconducting wire and strip products. Therefore, from the 60's after the beginning of research, soon entered the industrialized scale production. The United States in the late 70's annual production reached a hundred tons; China in the 80's around the same time also built a pilot production line. Most of the practical Nb-Ti superconducting materials are simple binary alloys containing 35% to 55% Nb; some tantalum and zirconium can be added to improve the superconducting properties. Due to the stability of superconductivity, Nb-Ti superconducting materials commonly used pure copper, pure aluminum or copper-nickel alloy as the matrix material, embedded into the multiple strands of Nb-Ti fine core combination into a composite multi-core superconducting materials. A superconducting wire can contain dozens to tens of strands of Nb-Ti core, the core diameter of the smallest to 1 μm. In addition, according to the use of different occasions, but also often have to twist the multi-core wire and transposition, to achieve the effect of reducing losses and increase the stability of the electromagnetic Nb-Ti superconducting materials of the basic processing process is: self-consumption arc furnace or plasma furnace will be pure titanium and niobium melting into an alloy ingot, and then hot extrusion of billets, hot rolled and cold drawn into rods, hot rolled and cold-drawn into a rod. Through hot rolling and cold drawing into rods; then Nb-Ti alloy rods inserted into the oxygen-free copper tube as the base material, composite into a single-core rod; and after several composite assembly, processing into multi-core Nb-Ti superconducting wire and strip. The material needs to be subjected to multiple 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 pinning center, to improve the superconducting properties of superconducting materials. Due to the zero resistance effect of superconductors brings no joule heat loss, and Nb-Ti superconductors in the strong magnetic field can carry a very high transport current ability, so that the Nb-Ti superconducting materials are particularly suitable for the application in the field of high current, strong magnetic field of electrical engineering. Examples include high-field magnets, generators, electric motors, magnetic fluid power generation, controlled thermonuclear reactions, energy storage devices, high-speed magnetic levitation trains, electromagnetic propulsion for ships, and power transmission cables. To date, the most successful applications of Nb-Ti alloy superconducting materials are: large cyclotron high-energy gas pedals with diameters of more than 1km and magnetic resonance imaging diagnostic instruments widely used in the medical sector. Although scientists in the mid-80s discovered a copper-oxygen compound high-temperature superconductor that can operate at liquid nitrogen temperatures (77K); however, Nb-Ti alloy superconducting materials with their own unique excellent processing performance, good low-temperature superconducting properties, relatively low cost and decades of research, production and application development experience, niobium-titanium alloys are still the world's most important practical superconducting materials.