In situ nano-SiC doped MgB 2 wires were fabricated from MgH 2 and B powders. Hydrostatic extrusion, followed by rotary swaging and two-axial rolling, were applied as the forming processes. The critical current J c of MgB 2 wires, made from MgH 2 and B powders, was significantly improved by nano-SiC doping. Nano-SiC doping substantially increased the upper critical (irreversibility) field B c2 above 20 T. The maximum J c values were measured for samples having 6 at.% SiC in low field and for those having 12 at.% SiC in high field, above 10 T. During the final sintering at 670 • C, the SiC decomposed and formed an Si-rich layer at the inner circumference of the Fe sheath. The composition of the core of SiC doped wires is more inhomogeneous in comparison to undoped ones, with MgO, Mg 2 Si and probably Mg 2 SiO 4 as the major segregated phases. Strong segregation of Si within the MgB 2 core was also observed. The highest T c−mid = 39.3 K was measured for undoped wire. For the optimal SiC doping amount ∼6 at.%, at high field, there was no difference in J c between hydrostatically extruded and hydrostatically extruded plus two-axially rolled wire. This can be attributed to the beneficial effect of hydrostatic extrusion, which causes higher density of the core in comparison to traditional deformation processes.

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In order to improve the overall critical current characteristics of Cu sheathed in situ MgB2 wires a special architecture of the wire, and processing parameters were used. The study presents the influence of the ex situ MgB 2 chemical barrier between ex situ core and Cu, suppressing the reaction of Cu with Mg. Wires, doped with 10 at.% SiC of 18 nm average grain size, were fabricated from MgH 2 and B or from Mg and B powders, using the powder-in-tube method. The methods of rotary swaging or drawing were used as the alternating wire-forming processes. The samples were annealed under high Ar gas pressure (hot isostatic pressing) at 750• C and 1.0 GPa for 15 and 30 min. A significant difference in Cu distribution across the wires for a long and short time of sintering was observed. The formation of microstructure in the powder-in-tube process and the relationship between the microstructure and critical current density Jc values, are discussed in this paper.