ＭｇＢ２―材料と超電導特性―Ｉｎ‐ｓｉｔｕ ＰＩＴ法によるＣｕおよびＣｕ合金シースＭｇＢ２線材の作製

Abstract

We investigated the applicability of Cu and Cu-alloy sheaths to MgB2 wires prepared by the in-situ synthesis powder-in-tube (PIT) method. Raw materials pellets of Mg and B mixed with ZrH2 and/or C powder were inserted into Cu, Cu-Zr, Cu-Cr, Cu-Sn and Cu-Be sheath tubes. We fabricated round MgB2 wires 1.0mm in diameter utilizing rotary swaging, drawing and two-axial rolling at room temperature. The wires were annealed at 500 - 800°C for 2 h in an Ar gas atmosphere. Compared with Cu sheath wires, the critical current characteristics of some of the Cu-alloy sheath wires were improved. For example, the four-probe transport measurements at 4.2 K in a self-field showed that a MgB2/Cu short sample with a 1.0mm diameter had an IC of 726 A (JC = 545 kA/cm2), while that of the MgB2/Cu-Cr sample was 846 A (JC = 635 kA/cm2). This improvement may be due to the higher core density of the MgB2 wires fabricated using Cu-Cr sheaths with higher hardness. Futhermore, decreasing the Cu:Core ratio in the cross-section of the MgB2/Cu wire from 4.9 to 2.0, is was possible to increase the IC from 726 A to 1219 A.