Effect of wire diameter, tape thickness, and rolling ratio on the superconducting properties of monocore Fe/MgB2 conductors

Abstract

This study investigates the influence of initial wire diameter and subsequent cold deformation on the superconducting properties of MgB₂ wires and tapes fabricated using the in situ powder-in-tube method. We manufactured wires and tapes by filling the iron tube with unreacted Mg + 2B powder. The 15 mm diameter tube underwent a groove rolling process to reduce its diameter to 3 mm to produce wire. The wire underwent a multi-stage cold drawing process down to 1.3 mm diameter. During this process, appropriate lengths of wire were cut at specific drawing stages as the diameter reached 2.5 mm, 2.0 mm, 1.7 mm, and 1.3 mm. Some wire pieces were spared in wire form. The wires, each with different diameters, were cold flat rolled into tapes of 1.2 mm, 0.9 mm, 0.6 mm, and 0.4 mm. The intermediate heat treatments were applied between some processing steps to reduce the mechanical stress induced due to the mechanical deformation processes. Wire and tape samples of about 160 mm long were cut and heat treated at 700 °C for 2 h using a tube furnace, then tested for determination of their superconducting properties. The samples used for the tests were approximately 25 mm long and taken from the middle of heat-treated samples. Current–voltage measurements were carried out at 25 K between 3.5 T and 5.2 T magnetic fields. Resistance–temperature characterizations were conducted at zero and 4 T magnetic fields. The fabricated wires and tapes were analyzed to understand the relationship between processing, structure, and superconducting performance.