Microstructurally determined electromagnetic properties of copper-sheathed in situ MgB2 wires

The critical current performance of Cu-sheathed in situ MgB
₂
wires can be substantially influenced by controlling - rate of rapid reactive interdiffusion between copper and magnesium and resulting formation of MgCu
₂
intermetallic percolated network. The presented results are exploring both: doping of the Mg-2B core with Cu nanoparticles at 9 at% level to slow down the directional diffusion of the copper atoms from the external matrix, and application of the ex-situ MgB
₂
barrier to suppress the formation of MgCu
₂
compound. Wires manufactured by the in situ technique, diffusing magnesium atoms to boron particles experienced ~ 25.5% decrease in density from the initial value after cold deformation, due to the phase transformation from Mg + 2(β-B) → MgB
₂
. To improve the intergrain connectivity and therefore minimise the voids created, an external pressure needs to be induced during sintering process to close up voids and consolidate the superconducting core. Because copper external sheet subjected to the Mg-2B sintering conditions at ~ 750°C becomes mechanically soft there is necessity to provide an additional external compressive reinforcement by externally induced pressure or electromagnetically or by gas. Microstructurally defined complex co-existing grain-boundary and artificial pinning sites are effecting electromagnetic properties of above Cu sheathed [ex situ/in situ] MgB
₂
wires.