Metal treatment – Process of modifying or maintaining internal physical... – Superconductive metal or alloy
Patent
1993-01-08
1994-11-08
Roy, Upendra
Metal treatment
Process of modifying or maintaining internal physical...
Superconductive metal or alloy
29599, 148 96, 148901, 428930, H01B 1200
Patent
active
053623312
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a Nb.sub.3 Al superconducting wire, and more particularly, to a process for making an electromagnetically stable Nb.sub.3 Al superconducting wire which has a high current density at the high level of magnetic field such as 20 tesla and is coated with a stabilizing material, and an apparatus for making such a Nb.sub.3 Al superconducting wire.
BACKGROUND ART
As disclosed in Applied Physics Letter 52(20), May 16, 1988, pp. 1724-1725, one of conventional Nb.sub.3 Al superconducting wires has been made by cold drawing a composite consisting of a Nb matrix and a large number of Al-alloy cores into a wire having ultrafine multicores and then heat-treating the cold drawn wire at a temperature ranging from 750.degree. to 950.degree. C. to form a Nb.sub.3 Al multifilamentary wire (refer to Composite Forming Process).
Japanese Laid Open Patent Publication No. 29017/87 discloses a Nb.sub.3 Al superconducting wire made by mixing Nb and Al powders, forming the mixture into a wire, irradiating an electron beam to the formed wire, and heat treating the irradiated wire at a temperature ranging from 500.degree. to 1000 .degree. C. to provide a final Nb.sub.3 Al superconducting wire (refer to Electron Beam Irradiation Process).
The composite forming process described above has several disadvantages, i.e. a stabilizing metal such as Cu or Al can not be compounded with a matrix; a stoichiometric composition of Nb.sub.3 Al cannot be obtained unless an ultrafine filament less than 1 .mu.m in diameter is formed; the Nb.sub.3 Al multifilamentary wire thus produced has a relatively low critical temperature and a critical magnetic field; and the critical current density falls is steeply at a high level of magnetic field such as 20 tesla.
The electron beam irradiation process described above can not, provide a Nb.sub.3 Al superconducting wire having an electromagnetically stable multifilamentary wire structure.
DISCLOSURE OF INVENTION
Accordingly, it is an object of the present invention to provide a process for making an electromagnetically stable Nb.sub.3 Al multifilamentary superconducting wire having high current density at a high level of magnetic field such as 20 T, and covered with an electromagnetically stabilizing material, and an apparatus for making such an electromagnetically stable Nb.sub.3 Al multifilamentary superconducting wire.
According to the present invention, there is provided a process for making a Nb.sub.3 Al multifilamentary superconducting wire comprising the steps of cold-drawing a composite consisting of a large number of Al or Al alloy core materials and a Nb matrix into a composite multi cores wire, and heat treating the cold drawn composite multicore wire, wherein the cold drawn composite multicore wire is dipped into a molten metal to solidify the molten metal around the composite multicore wire for forming an electromagnetically stabilizing metal coating on the periphery of the superconducting wire. Each of the Al or Al alloy core wires of the cold drawn composite multicore wire has a diameter or thickness ranging from about 0.1 to about 10 .mu.m, and the molten metal consists of Cu , Cu alloy, Ag or Ag alloy.
In the present invention, it is preferred to coat the periphery of the Nb.sub.3 Al superconducting wire with an electromagnetically stabilizing metal by dipping a cold drawn composite multicore wire consisting of a large number of Al alloy core wires and a Nb matrix into a molten metal bath such as Cu or Cu alloy, Ag or Ag alloy healed to a temperature higher than 1200.degree. C. for coating the composite wire, rapidly cooling the coated composite wire,and then heat treating the cooled composite wire at a temperature ranging from about 700.degree. to about 950.degree. C.
It is also preferred to increase the critical current density of the Nb.sub.3 Al superconducting wire at the high magnetic field by cold drawing the large number of Al alloy core materials into fine wires within the range of inducing no proximity effect, heating the fine wires to a
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Inoue Kiyoshi
Kamata Kunihisa
Tada Naohumi
Wadayama Yoshihide
Hitachi , Ltd.
Hitachi Cable Ltd.
National Research Institute for Metals
Roy Upendra
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