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Superconducting materials refer to materials that have the properties of exhibiting resistance equal to zero and repelling magnetic lines of force under certain low temperature conditions.

Alloy superconducting materials refer to superconducting materials that fuse two or more metal elements to form superconducting properties. There are 27 metallic elements that are superconducting, and their Hc and Jc are relatively low. The Hc2 of the lead-bismuth (Pb-Bi) eutectic alloy discovered in 1930 was less than 2T. Later it was discovered that thousands of alloys are superconducting substances, but only a few have practical value.

Alloy superconducting materials with practical value are almost all niobium-based alloys, mainly including niobium-zirconium (Nb-zr), niobium-titanium (Nb-Ti) and niobium-zirconium-titanium (Nb-Zr-Ti). Their compositions The range (%) is Nb—(25～35)Zr, Nb—(45～55)Ti and Nb—42Zr—10Ti respectively, Tc is 11～11.5K, 9～9.5K and 10.3K respectively, at 4.2K temperature The Hc2 under 4.2K5T are 8~9.5T, 11.5~12.5T and 10.5T respectively. The Jc under 4.2K5T are 1000A/mm2, 3800A/mm2 and 2800A/mm2 respectively. Among them, Nb-Ti still has Jc value of 1600A/mm2.

Before 1961, the field strength of superconducting magnets made of niobium wire, molybdenum-thorium (Mo-Th) wire and niobium-titanium wire did not exceed 1.5T. In 1957, Kunzler discovered that niobium-zirconium alloy has superconductivity. It was not until 1962 that Hacker and others made several superconducting magnets using niobium-zirconium wires. In the mid-1960s, the manufacturing process of niobium-titanium single-core wires matured, and multi-core wires began to be developed. Some progress has also been made in multi-component alloys based on Nb-Ti and Nb-Zr. The Hc2 of Nb-Ti-Ta, Nb-Ti-Ta-Zr and Nb-Ti-Ta-Hf are all higher than the best Nb-Ti binary alloy, but the increase is not much at 4.2K temperature, only 0.3T , Hc2 is significantly improved only at lower temperatures. For example, the Hc2 of Nb-43Ti-25Ta at 2K is 15.5T, which is 1.3T higher than the best Nb-Ti alloy. This superconducting material will be used to make 12T Experimental model of nuclear fusion. The Jc of Nb-42Zr-6Ti is not low, but it cannot be made into multi-core wires. The Jc of Nb-40Zr-10Ta at 4.2K and 5T is 2000A/mm2.

At present, the most widely used superconducting material is niobium-titanium, which accounts for more than 95%. It is mainly used to make superconducting magnets below 9T. It has been successfully used in MRI devices, NMR spectrometers, MHD power generation, SSC accelerators and Laboratory magnets.

High-magnetic field superconducting materials are all Type II superconductors, which contain magnetic flux lines between Hc1 and Hc2. When current passes through the conductor, the Lorentz force will cause the magnetic flux lines to move and cause resistance. In order to improve the current carrying capacity, dislocation density, grain boundaries and second phase particles are usually increased to pin the magnetic flux lines. Frictional heat generated by mechanical disturbances, sudden changes in magnetic field or current, will cause the magnetic flux to jump and cause local heating. This is the instability of superconducting materials. In order to prevent quench caused by magnetic flux jump, stabilization measures should be taken for the conductor, using one or more of freeze stabilization, adiabatic stabilization and dynamic stabilization. Composite conductors are usually made by embedding superconductors in oxygen-free copper with a high residual resistance ratio (200-300). The copper can quickly transfer the heat generated by the magnetic flux jump to the liquid helium, causing the conductor to return to a zero-resistance state. . In order to prevent the proximity coupling effect between core wires, part of the high-purity copper is replaced with copper-nickel alloy or copper-manganese alloy. Copper-nickel has a resistance scattering effect, and manganese has a spin inversion scattering effect.