Mechanical and superconducting properties of PIT-processed MgB2 wire after heat treatment

Abstract

The mechanical and superconducting properties of MgB2 wires heat treated at various conditions have been investigated. Superconducting MgB2 wires, fabricated by the powder-in-tube (PIT) method, show a transition temperature Tc at 32.4 K for the as-rolled wire as shown by dc-resistivity measurement. It is found that the Tc is improved (37.3–38.4 K) by subsequent Ar annealing treatment under various sintering temperatures and times. Remarkably, the annealed samples show significant improvement in the overall quality of the samples. On annealing at 1323 K for 0.6 ks, we obtained the best quality sample with a Jc of 470 A mm−2 at 2.0 T. In order to find out the irreversible field (Birr), the technique of the Kramer plot was applied. The Birr obtained was 7.6 and 9.6 T, for the as-rolled as well as the annealed samples at 1073 K for 3.6 ks, respectively. The mechanical properties were measured under tensile load. The yield stress was 450 MPa for the as-rolled sample and decreased by annealing at 1323 K for 0.6 ks to 110 MPa. After the wires were heat treated at temperatures between 1073 and 1323 K and tensile-stressed up to their yield stress at room temperature. The critical current measurements were carried on such samples at 4.2 K under applied magnetic fields of 2 and 5 T. The stress level for the 95% tolerance of critical current was determined to 97 MPa.