Superconductivity is a fundamental phenomenon in physics in which a material acquires zero electrical resistance upon reaching a certain temperature called the critical superconductivity temperature.
Superconducting (cryogenic) alloys are specially developed materials possessing superconducting properties within certain temperature ranges at a specified density of electric charge flow, magnetic field strength, and intensity. They are characterized by high resistance to external factors when three conditions are observed:
- Service temperature does not exceed the critical temperature at which transition from the superconducting state to the normal one occurs.
- Magnetic field parameters are below the upper critical value.
- Electric current density is less than the critical indicator (determined at a temperature below the transition temperature).
Superconducting precision alloys can be subjected to cold drawing after preliminary heat treatment, as well as hot deformation, but within strictly established temperature intervals.
Grades of superconducting precision alloys
The group of presented cryogenic materials includes seven alloys: 35BT, 50BT, 65BT, 70TM, 70TM-VD, BTTs, and BTTs-VD. Let us consider the most popular of them:
- 35BT — the alloy base is titanium (from 60% to 64%) and niobium (at least 33.5% and not more than 36.5%); zirconium (1.7–4.3%) acts as an alloying addition. The metal is characterized by high specific toughness, as well as weak dependence of conducting properties on the dimensions of products made from it.
- 65BT — has the same chemical elements in composition as 35BT, but in other ratios: Ti — 22–26%, Nb — 63–68%, Zn — 8.5–11.5%. It has the highest value of critical electric current density and magnetic field. Characterized by elevated yield strength and tensile strength. Widely used to manufacture internal core elements.
- BTTs-VD — a precision alloy based on niobium (from 98.76% to 99.73%) alloyed with titanium (0.07–0.2%) and zirconium (0.2–1%). Resistant to atmospheric corrosion and oxidation in aggressive chemical environments. Manufacturing method — vacuum-arc melting.
- 70TM-VD — a titanium-molybdenum steel alloyed with iron. The percentage ratio of chemical elements is: Ti — 73–76%, Mo — 24–26%, Fe — not more than 2.5%. It has high specific resistance that changes little when temperature rises or falls in the range from −289.15°C to −249.15°C.
In the markings of the presented steels the letter B indicates presence of niobium, and the numbers before it — its percentage ratio. The letter T indicates presence of titanium in the alloy, Ts — zirconium, M — molybdenum. The letters VD at the end of material names mean their melting method (vacuum-arc).
Properties of cryogenic precision alloys and their application areas
Superconducting precision alloys have a number of unique physical-mechanical characteristics that make them attractive for various industrial areas and technological research. For example:
- Medical equipment — superconducting materials are used in creating highly sensitive equipment for magnetic resonance imaging (MRI) and magnetoencephalography (MEG). They make it possible to create powerful magnetic fields with minimal energy loss, which improves quality and resolution of medical images and allows more accurate disease diagnosis.
- Quantum computing — the presented alloys have high potential for creating quantum bits (qubits) in quantum computers. Elevated accuracy of physical-mechanical qualities and resistance to external factors make such steels promising “candidates” for implementing stable quantum operations.
- Transport — the ability to create powerful magnetic fields makes superconducting metals suitable materials for creating magnetic systems of high-speed transport such as maglev trains — trains on a magnetic cushion.
- Energy — applying superconducting alloys in energy systems can raise efficiency and reliability of electricity transmission, as well as reduce losses when transmitting electricity over long distances.
- Physics research — the presented materials are widely used in physical experiments requiring creation of powerful magnetic fields to study properties of various materials and phenomena.
Despite many advantages, superconducting precision alloys also have some drawbacks. One of them is complexity of production and high cost of chemical elements in the composition. However, research in this area continues, and scientists constantly seek new ways to improve properties and reduce the cost of superconducting materials.
