The fabrication method where a duplex alloy is mechanically reduced to wires or tapes by simple metallurgical processes, that is rolling, swaging and wire-drawing after ingot-casting is an approach for producing composite materials. The composite produced by this method is called the in situ formed composite. This process was first applied to the production of superconducting materials by Tsuei and thereafter many works have been carried out extensively. This in situ formed superconducting composite has following characteristics.
(1) Aligned superconducting filaments are fine but discontinuous.
(2) The strength of composites is relatively high.
(3) The superconducting properties, especially
Jc, are stable against stress.
The recent improvement of the fabrication method enables to produce the in situ formed composites with a large volume fraction of Nb
3Sn filaments. Such composites show good superconducting properties with an overall
Jc of 10
6A/cm
2 at 4.2K and O field, which is comparable to that of the commercial Nb
3Sn composite. Although the possible mechanisms of superconductivity in the in situ formed superconducting composite are considered to be filament effect, proximity effect and the direct contact of superconducting filaments, the latter two mechanisms will become important with increment of the volume fraction of superconducting filaments. More work remains to be done in improving
Jc at high field and the stress effect of
Jc.
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