Niobium titanium superconducting alloy is one of the most widely used superconducting materials in current superconducting electric technology. Nb-Ti alloy with mass ratio nearly L: 1 has good superconducting electric properties. Its superconducting critical transition temperature Tc= 9.5K, which can operate at liquid helium temperature. It can transmit current density Jc≥105A/cm2(4.2K) in a magnetic field of 5T(50,000 Gs). The maximum application field is 10T(100,000 Gs)(4.2K). The alloy also has excellent processing properties, which can be used to obtain superconducting wire and strip products by traditional smelting, processing and heat treatment. Therefore, after the research began in the 1960s, it quickly entered the industrial scale production. The United States produced 100 tons by the end of the 1970s; China also built trial production lines around the 1980s. Practical Nb-Ti superconducting materials are mostly simple binary alloys containing 35% ~ 55% Nb. Some tantalum and zirconium can be added to improve superconductivity. Due to the stability of superconducting, Nb-Ti superconducting materials are usually made of pure copper, pure aluminum or Cu-Ni alloy as the matrix materials, and are combined into composite multi-core superconducting materials by inserting multiple Nb-Ti thin cores.
A superconducting wire may contain dozens to tens of thousands of Nb-Ti cores with a minimum diameter of 1 m. In addition, according to the use of different occasions, also often to twist and transposition of the multicore wire, to reduce the loss and increase the electromagnetic stability effect. The basic processing technology of Nb-Ti superconducting material is: using consumable electric arc furnace or plasma furnace to melt pure titanium and pure niobium into alloy ingot, then hot extruding, hot rolling and cold drawing into bar; Then Nb-Ti alloy rod was inserted into the anaerobic copper tube as the matrix material to form a single mandrel. After many times of composite assembly, it is processed into multi-core Nb-Ti superconducting wire and strip. It is necessary for the material to undergo several large cold processing (processing rate above 90%) and low temperature (below 400℃) aging heat treatment to obtain enough effective nailing centers and improve the superconducting electrical properties of superconducting materials. Nb-Ti superconductor is especially suitable for electrical applications with large current and strong magnetic field due to the zero-resistance effect of superconductor, which brings no joule heat loss, and the ability of Nb-Ti superconductor to carry high transport current under strong magnetic field. For example: high field magnets, generators, motors, magnetohydrodynamic power generation, controlled thermonuclear reactions, energy storage devices, high-speed maglev trains, ship electromagnetic propulsion and transmission cables. So far, the most successful applications of Nb-Ti alloy superconducting materials are large cyclotron high-energy accelerator with a diameter of more than 1km and magnetic resonance imaging diagnostics widely used in medical sectors. In the mid-1980s scientists discovered high-temperature copper-oxide superconductors that operate at liquid nitrogen temperatures (77K).
However, niobium titanium alloy superconducting material is still the most important practical superconducting material in the world with its unique excellent processing performance, good low temperature superconducting electrical performance, relatively low cost and decades of research, production and application development experience.
