High-performance dense MgB 2 superconducting wire fabricated from mechanically milled powder

Owing to the relatively high critical temperature and the low manufacturing cost, MgB 2 superconducting wires are promising for liquid helium-free superconducting applications. Today, commercially available MgB 2 wires are manufactured by either an in situ or ex situ powder-in-tube process, the in situ process being more effective to obtain high critical current density. In in situ -processed wires, however, the critical current density is seriously suppressed by the high porosity of MgB 2 filaments. To resolve this problem, we propose an innovative method of using precursor powder prepared by mechanical milling of magnesium, boron, and coronene powders. This precursor powder has a metal–matrix–composite structure, in which boron particles are dispersed in a magnesium matrix. The plastic deformation of the precursor powder through wire processing leads to compact packing, and a dense MgB 2 filament is generated after heat treatment. As a result, the limitation of critical current density that occurs for the typical in situ process is overcome, and the practical critical current density of 10 3 A mm −2 is obtained at 10 K and 6.1 T, at 15 K and 4.8 T, and at 20 K and 3.3 T.