Stabilization Multifilamentary Superconductors

On the other hand, aluminum-stabilized superconductors are desirable because aluminum has excellent low-temperature electrical conductivity, low magnetoresistance, low heat capacity during cooldown, and low density. The great differences in mechanical properties between high-purity aluminum and NbTi alloys, however, make it very difficult to fabricate an aluminum-stabilized multifilamentary superconductor. 

The method described here for the manufacture of an aluminum-stabilized multifilamentary superconductor is essentially a two-step process, as illustrated in Fig. 1. First, a composite of multifilamentary NbTi embedded in an aluminum alloy (1100 Al or 6061 Al) matrix is prepared in the usual manner. The extruded NbTi-Al alloy composite is then inserted into a high-purity Al tube, and the whole composite is drawn in a Cu jacket. In this way, the high-strength NbTi filaments are supported in a stronger and work-hardenable Al matrix. As far as the softer, self-annealing pure Al is concerned, the center core, i.e., the NbTi-Al composite, can be considered as a unit, such as a NbTi monofilament. The whole composite can be reduced without localized nonhomogeneous deformation. 

Fabrication of an Al-stabilized multifilamentary NbTi superconductor was made possible by a two-step process. First, a composite of multifilamentary NbTi... 

Recent measurements have indicated a degradation of the critical current of NbTi [ ] and NbaSn [ ] multifilamentary composites under static tensile stress. In this paper these static stress results are summarized and preliminary measurements of the effects of cyclic stress on the critical current, mechanical strength, and stability of these superconductors are reported. 

The effect of the v/o of NbaSn on composite ductility was investigated by tensile testing a series of multifilamentary NbsSn superconductors. The v/o of the NbaSn in these conductors was varied by adjusting the fraction of stabilizing copper, the size of the filaments, the bronze composition, and the time and temperature used for NbaSn formation. L measurements were made, which verified that useful conductors could be produced with reasonable ductility. 

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