Microstructure and Superconducting Properties of Copper Sheathed MgB2 Wires With Ti Barrier Fabricated by in Situ Powder-in-Tube Method

An intrinsic powder-in-tube technique is used to fabricate Cu-sheathed MgB
₂
with and without a Ti barrier. The effect of heat treatment on reaction layers between the Cu sheath, Ti barrier, magnesium and boron is evaluated by scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray powder diffraction. Annealing the Cu (sheath)/Ti (barrier) prior to in situ heat treatment of the Mg + 2B reaction improves formation of a pure MgB
₂
core and eliminates subsequent reactions between B powder and the Ti barrier. Microstructural study of the interface between pure MgB
₂
and annealed Ti/Cu sheath does not show any evidence of reaction and diffusion between B and Ti which is beneficial for superconducting properties. Magnetization measurements of MgB
₂
superconducting wires have shown that the critical current density, J
_c
, of a Cu-sheathed wire combined with a Ti barrier can significantly enhance performance compared with a Cu-sheathed MgB
₂
wire without a Ti barrier. This enhancement is due to elimination of a MgCu
₂
interface layer between the copper sheath and magnesium powder for wires when a Ti barrier is involved. Pre-annealing of the Cu (sheath)/Ti (barrier) does not affect the J
_c
of MgB
₂
wires. This could make a positive effect on the J
_c
of the wires with finer filaments.