Industrially, niobium-titanium alloy foil (NbTi Alloy Foil/Strip) generally refers to strips or foils with a thickness ≤0.1mm (ultra-thin foils can reach 0.02～0.05mm) obtained by precision rolling using an Nb-Ti binary alloy (typically Nb-46.5wt%Ti or Nb-47wt%Ti, i.e., approximately 50/50 by weight, sometimes written as NbTi50) as the base material.
NbTi foil is a precision-machined product of refractory metal alloys. A typical process flow is as follows: 1. Alloy smelting (ingot making): High-purity niobium rods/blocks are mixed with high-purity titanium in a set ratio (usually Ti 46-48 wt%) using vacuum arc remelting (VAR) or electron beam melting (EBM). Generally, 2-3 remeltings are required to ensure uniform composition and reduce O/N/C impurities (O < 100 ppm is required to prevent low-temperature brittleness). 2. Hot working: The ingot is hot-forged/hot-extruded under vacuum or inert atmosphere protection at approximately 900-1100℃, then hot-rolled to a thickness of several millimeters into a hot-rolled plate/strip, breaking up the casting structure and refining the grains. 3. After hot-rolled/cold-rolled foil sheets are pickled to remove the oxide layer, they undergo multiple cold rolling passes. Each pass has a processing rate of 5%–15%, and when the cumulative deformation reaches 50%–70%, intermediate annealing (vacuum annealing, 700–900℃, holding for tens of minutes to several hours) is required to eliminate work hardening. Repeated rolling and annealing cycles ultimately reduce the foil to the target thickness (commonly 0.03mm, 0.05mm, 0.1mm), with a width of 100–300mm. Finished product heat treatment and surface treatment: Final recrystallization annealing: Vacuum or high-purity argon protection, 800–950℃, to obtain a uniform recrystallized structure, ensuring low-temperature plasticity and superconducting properties. The surface is then pickled (HF+HNO₃ system) or electrolytic polished to remove the oxide layer, achieving a bright or matte surface (Ra < 0.5μm). Cutting and vacuum packaging are then performed to prevent oxidation. Quality Control Key Points: Chemical composition deviation controlled within ±0.5wt%; strict control of oxygen, nitrogen, and carbon impurities (affecting low-temperature toughness and critical current density); thickness tolerance typically ±5% to ±10%, monitored by ultrasonic or X-ray thickness measurement.
Superconducting Magnet Components – Core Applications: MRI Magnets; Solenoid magnets wound with NbTi superconducting wires (made from NbTi rods drawn into composite copper) generate strong magnetic fields of 1.5T/3.0T; NbTi foil itself can be used as experimental samples, transition connecting sheets, or low-temperature current lead auxiliary layers in particle accelerators/synchrotron radiation devices. The Large Hadron Collider (LHC) and Shanghai Synchrotron Radiation Facility employ NbTi multi-core superconducting coils; NbTi foil is used for interlayer insulation pads in magnets, low-temperature equalization plates, or laboratory-grade superconducting tape prototypes. The circumferential/poloidal field magnets of the device use NbTi superconducting wires; NbTi foil can be used as a low-temperature shielding layer, magnet end reinforcement foil, or a substrate for superconducting tape research.
In the intermediate process of manufacturing superconducting composite wires/tapes, NbTi is first rolled into 0.1–0.3 mm foil in the preparation of artificially pinned center (APC) type NbTi superconducting wires. This foil is then alternately layered and wound around an Nb rod with pure Nb foil. Finally, a Cu sheath is inserted, extruded, and drawn to form an α-Ti pinned phase-reinforced superconducting composite wire. This is the most distinctive "semi-finished product" application of NbTi foil—not directly used as an end-product, but as a crucial form before composite processing. Low-temperature electronic and superconducting devices: Superconducting quantum interference device (SQUID) connectors/transition joints utilize the zero resistance and good mechanical connectivity of NbTi at 4.2 K. Superconducting nanowire single-photon detector (SNSPD) substrates or composite targets.
