Metal treatment – Process of modifying or maintaining internal physical... – Superconductive metal or alloy
Reexamination Certificate
2001-04-06
2003-01-21
Kopec, Mark (Department: 1751)
Metal treatment
Process of modifying or maintaining internal physical...
Superconductive metal or alloy
C505S806000, C505S815000, C420S901000, C029S599000, C174S125100
Reexamination Certificate
active
06508889
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to process for the production of Nb
3
Al extra-fine multifilamentary superconducting wire. More particularly, the invention concerns a process for the production of Nb
3
Al extra-fine multifilamentary superconducting wire which can produce simply and inexpensively high-performance Nb
3
Al extra-fine multifilamentary superconducting wire having three greatly-improved critical values, Tc, Hc
2
and Jc, without the addition of third elements such as Ge, Si and Cu, the process being promising as a practically applied technology.
2. Description of the Related Art
A process for producing Nb
3
Al extra-fine multifilamentary wire has been proposed in which a rapid heating and quenching treatment is applied to a composite wire of Nb and Al to form an Nb-25 at % Al supersaturated bcc alloy solid solution phase, and then an additional heat treatment at 700-900° C. is conducted to transform the Nb—Al supersaturated bcc alloy solid solution phase to an Al5.Nb
3
Al phase.
The Nb
3
Al extra-fine multifilamentary wires produced by this process have three critical values, Tc, Hc
2
and Jc, higher than those of the Nb
3
Al wires by the conventional diffusion process and, therefore, have much hope as a next practically used wire for strong magnetic fields. Although the maximum magnetic field generated by superconducting magnets using conventional metallic superconducting wires was 21.7 T, it is expected that the use of the aforementioned Nb
3
Al extra-fine multifilamentary wires will achieve the upper limit of magnetic field generated as high as 21 T at 4.2K and 24 T at 1.8K.
On the other hand, the improvement of performances of Nb
3
Al extra-fine multifilamentary wires is under studying.
For example, it has been found that the addition of Ge or Si to Nb
3
Al results in the direct formation of Al5 phase after rapid heating and quenching treatment, greatly enhancing Tc and Hc
2
.
In this case, however, it has been pointed out that a large amount of impurities are also formed, Jc becomes not so high and the addition of Ge and Si greatly reduces workability of Nb/Al wires. The production of long-length wires requires enough research.
On the other hand, it has been also found that the addition of Cu results in the direct formation of the Al5 phase after a rapid heating and quenching treatment, improving characteristics. Tc reaches 18.2 T and Hc
2
reaches about 29 T. Furthermore, Jc is also a high value in strong magnetic fields.
For practical applications of this technology, however, there are problems in workability or the like.
SUMMARY OF THE INVENTION
The invention according to this application is created in light of such circumstances and intends to provide a process for the production of an Nb
3
Al extra-fine multifilamentary superconducting wire which can produce simply and inexpensively a high-performance Nb
3
Al extra-fine multifilamentary superconducting wire having three greatly-improved critical values, Tc, Hc
2
and Jc, without the addition of third elements such as Ge, Si and Cu, the process being promising as a practically applied technology.
To solve the above problems, the invention according to this application provides, in a first aspect, a process for the production of an Nb
3
Al extra-fine multifilamentary superconducting wire, the process comprising the steps of: applying a first rapid heating and quenching treatment to an Nb/Al composite wire having an atomic ratio of Al to Nb from 1:2.5 to 1:3.5 and having extra-fine multifilamentary structure to form a BCC alloy phase comprising Nb with Al supersaturatedly dissolved therein wherein the first treatment comprises heating the composite wire up to a temperature not lower than 1900° C. within two seconds and then introducing it into a molten metal at a temperature not higher than 400° C. to rapidly quench it; applying a second rapid heating and quenching treatment to form an Al5 pahse-Nb
3
Al compound having a low degree of crystalline order but having a composition near the stoichiometric one wherein the second treatment comprises heating the wire up to a temperature not lower than 1500° C. within two seconds and then introducing it into a molten metal at a temperature not higher than 400° C.; and applying, after the second rapid heating and quenching treatment, an additional heat treatment at 600-850° C. to the composite wire to improve the degree of crystalline order of the Al5 phase.Nb
3
Al compound.
The invention according to this application also provides, in a second aspect, the process further comprising a step, conducted before or after the additional heat treatment, of coating the composite wire with Cu. The invention provides, in a third aspect, one of the processes further comprising a step, conducted before the first rapid heating and quenching treatment, of compounding Cu or Ag for stabilizing in a state where a diffusion barrier is incorporated. The invention also provides, in a fourth aspect, one of the processes further comprising a step, conducted between the first rapid heating and quenching treatment and the second rapid heating and quenching treatment, of cold working at reduction of area of 70% or less.
REFERENCES:
patent: 4088512 (1978-05-01), Pickus et al.
patent: 4917965 (1990-04-01), Inoue et al.
patent: 5628835 (1997-05-01), Tada et al.
patent: 6372054 (2002-04-01), Kikuchi et al.
patent: 6376099 (2002-04-01), Inoue et al.
Iijima Yasuo
Inoue Kiyoshi
Kikuchi Akihiro
Kopec Mark
National Institute for Materials Science
Wenderoth , Lind & Ponack, L.L.P.
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