Study on High Yield Strength Monolith NbTi Superconducting Wire for MRI Magnets in WST

NbTi strands are widely used in magnetic resonance imaging (MRI) and other superconducting magnets for their good processing characteristics, low cost, and good superconducting performance. With the huge demand for high yield strength monolith wire for MRI using less liquid helium, improving the yield strength of monolith NbTi wire becomes a problem that urgently needs to be solved. In this study, we adopted a new fabrication process by "enameling insulation before rolling and forming" to improve the yield strength of the wire. By choosing the suitable insulation material and adjusting the working rate, the insulation property has been improved. The results show that the polyvinyl formal (PVF) is the best material for the "rolling and forming" process and the fact also shows that the working rate should be controlled between 15% to 25%. The final monolith NbTi wires show good insulation performance, while the forming size is controlled within ± 0.003 mm and the average value of 0.1% yield strength increases from ∼120 MPa to ∼350 MPa.