Fabrication of practical NbTi alloy superconductors

① Alloy Melting. The optimal alloy ration contains T in 46% to 50% (mass percent).
② NbTi alloy rod processing, high uniformity of Nbi rods in addition to uniformity of composition, and uniformity of mechanical properties.
③ cladding stabilization materials, so that hundreds of NbTi filaments buried in the role of stabilization of highly conductive oxygen-free copper or high-purity aluminum to prevent thermal loss of super or to provide current bypass. Residual resistance ratio (RRR) is often used to illustrate the quality of stabilized materials, RRR is the resistivity at room temperature 293K divided by the resistivity of the ratio of low temperature (4.2K), usually superconducting magnets require stabilization of the material RRR ratio should be in 30 and above.
Nb is a widely used barrier layer material, the purpose of which is to avoid the formation of intermetallic compounds such as TiCu4 between NbTi alloy and Cu matrix, preventing the pulling of wire breakage of the core and significantly reducing the critical current density (Jc).
⑤ Combination design of multi-core composite, the combination design is carried out before hot extrusion, and the design is based on the parameter requirements of the finished superconducting wires, such as the wire diameter, core diameter, copper ratio, etc. to project the size of the sheath barrier layer, the size of the NBi rods, and the number of extrusions. Multi-core composite wire in the NbTi core wires are tightly arranged between the core to the outside are arranged in hexagonal layers, the number of roots of each layer in order to form an equidistant progression of the relationship between the layers, such as 6, 12, 18, 24, 30, 36, ....
(vi) Extrusion and stretching, where extrusion is used to form a jig bond with high bonding strength between the NT bar, the Nb barrier layer, and the Cu layer matrix .