U.S. patent number RE32,178 [Application Number 06/577,906] was granted by the patent office on 1986-06-10 for process for producing compound based superconductor wire.
This patent grant is currently assigned to Mitsubishi Denki K.K.. Invention is credited to Kiyoshi Yoshizaki.
United States Patent |
RE32,178 |
Yoshizaki |
June 10, 1986 |
Process for producing compound based superconductor wire
Abstract
A process for producing a compound-based semiconductor wire
having a high mechanical strength and which can be coiled so as to
be cooled efficiently. A starting composition is formed by blending
at least one metal powder selected from among Nb-based and V-based
particles having at least a partial surface coating of an alloy or
metal selected from Cu-Sn-based and Ga-based metal layers with at
least one of Cu-based, Sn-based, Ga-based, Cu-Sn-based and
Cu-Ga-based metal or alloy powder. The cross-sectional area of the
composition is reduced followed by a heat treatment. The
composition is then drawn into a wire of desired diameter.
Inventors: |
Yoshizaki; Kiyoshi (Sagamihara,
JP) |
Assignee: |
Mitsubishi Denki K.K. (Tokyo,
JP)
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Family
ID: |
13307986 |
Appl.
No.: |
06/577,906 |
Filed: |
February 7, 1984 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
264325 |
May 18, 1981 |
04363675 |
Dec 14, 1982 |
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Foreign Application Priority Data
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May 19, 1980 [JP] |
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55-66166 |
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Current U.S.
Class: |
419/3; 29/599;
505/823; 505/921 |
Current CPC
Class: |
B22F
1/025 (20130101); C22C 1/045 (20130101); H01L
39/2409 (20130101); Y10T 29/49014 (20150115); Y10S
505/823 (20130101); Y10S 505/921 (20130101) |
Current International
Class: |
B22F
1/02 (20060101); C22C 1/04 (20060101); H01L
39/24 (20060101); H01L 039/24 () |
Field of
Search: |
;148/11.5P,11.5F
;29/599 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1004179 |
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Sep 1965 |
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GB |
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1070691 |
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Jun 1967 |
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GB |
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1137427 |
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Dec 1968 |
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GB |
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1177728 |
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Jan 1970 |
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GB |
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1209490 |
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Oct 1970 |
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GB |
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1370257 |
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Oct 1974 |
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GB |
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Other References
Tsuei, C. C., Applied Physics Letters, vol. 25, No. 5, Sep. 1,
1974, p. 318. .
Flukiger, R. et al., IEEE Transactions on Magnetics, vol. Mag. 15,
No. 1, Jan. 1979, p. 689..
|
Primary Examiner: Stallard; Wayland
Attorney, Agent or Firm: Sughrue, Mion, Zinn, Macpeak &
Seas
Claims
What is claimed is:
1. A process for producing a Nb.sub.3 Sn or V.sub.3 Ga
compound-based superconductor wire comprising the steps of: forming
a composition by blending at least one metal powder selected from
the group consisting of Nb-based and V-based particles at least
part of the surface of which is covered with at least one layer
selected from the group consisting of .[.Cu-Sn-based.]. .Iadd., in
the case of Nb.sub.3 Sn compound-based superconductor wire,
Cu-based and Sn-based, and in the case of V.sub.3 Ga compound-based
superconductor wire, Cu-based .Iaddend.and Ga-based, metal layers
with at least one metal powder or alloy powder selected from the
group consisting of Cu-based, Sn-based, Ga-based, Cu-Sn based and
Cu-Ga-based .Iadd.particles.Iaddend.; reducing the cross-sectional
area of said composition; heat treating said composition; and
drawing the heat-treated composition into a wire.
2. The process according to claim 1 wherein at least part of the
surfaces of individual particles of said group consisting of Nb-
and V-based metal particles is covered with an alloy layer selected
from the group consisting of Cu-Sn-based and Cu-Ga-based alloy
layers.
3. The process according to claim 1 or 2 wherein said metal powder
comprises at least one metal powder selected from the group
consisting of Nb- and .[.Ga-based.]. .Iadd.v-based
.Iaddend.particles at least a part of the surface of which is
covered with at least one layer selected from the group consisting
of Cu-based, Sn-based, Ga-based, Cu-Sn-based and Cu-Ga-based
layers, said particles being further covered with at least one
layer selected from the group consisting of Sn-based, Ga-based,
Cu-Sn-based and Cu-Ga-based layers.
4. The process according to claim 1 or 2 wherein said Nb-based and
V-based metal particles are blended with particles selected from
the group consisting of Cu-based, Cu-Sn-based, Cu-Ga-based
particles, Nb-based composite particles, and V-based composite
particles by forming individual metal or alloy layers into a
desired shape at a temperature of from room temperature to
1050.degree. C. and sintering, whereupon part of all of said metal
or alloy layers on surfaces of adjacent metal layers are joined
together.
5. The process according to claim 1 or 2 wherein said Nb-based and
V-based metal particles are blended with particles selected from
the group consisting of Cu-based, Cu-Sn-based, Cu-Ga-based
particles, Nb-based composite particles, and V-based composite
particles by extrusion at an extrusion temperature of from room
temperature to 1050.degree. C. with an extrusion ratio of more than
2, whereupon part of all of said metal or alloy layers on surfaces
of adjacent metal layers are joined together.
6. The process according to claim 1 or 2 wherein said at least one
layer selected from the group consisting of Cu-Sn-based and
Cu-Ga-based alloy layers contains a material selected from the
group consisting of tin in one of a range of from 0.1 to 14 wt %
and from 50 to 100 wt %, and gallium in one of a range of from 0.1
to 25 wt % and from 50 to 100 wt %.
7. The process according to claim 1 or 2 wherein said step of heat
treating comprises sintering in a vacuum to form a metallurgically
integral bar.
8. The process according to claim 1 or 2 wherein said step of heat
treating comprises hot extrusion.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a process for producing a
compound-based superconductor wire.
Superconductor wires made of intermetallic compounds such as
Nb.sub.3 Sn and V.sub.3 Ga are characterized by a number of
continuous fibers of intermetallic compound which are buried in the
matrix phase. Wires having such a construction exhibit a high
superconductivity but because of the intermetallic compound used,
they are inherently brittle and permit an elongation of only less
than 1.0% and are very vulnerable to mechanical tensile stress and
bending stress. Therefore, the reliability of manufacturing such
superconductor wires and winding them into a coil is low, and what
is more, they cannot be cooled with liquid helium effectively.
In recent years, attempts have been made to produce a
superconductor by using the "tunnel effect", also known as the
proximity effect or filament effect, in which a number of very
fine, discontinuous fibers of superconducting compounds are buried
in the matrix phase very close to each other. Unfortunately, the
superconducting characteristics of wire produced by this method are
too low to satisfy practical requirements. A superconductor wire
made of discontinuous fibers of a compound such as Nb.sub.3 Sn is
produced typically by a process in which Cu and Nb are melted to
form an ingot with spherical or acicular particles of Nb scattered
within the Cu matrix and the ingot is drawn to the final dimensions
and Sn is diffused into the Cu matrix from its surface or a process
in which a Cu-based metal tube is filled with a mixture of Nb and
Cu powders and the tube is drawn to the final dimensions and Sn is
diffused into the Cu matrix from its surface to form a coating of
Nb.sub.3 Sn on the Nb fibers. In the former method, if Cu is mixed
with more than 25 vol % of Nb, it becomes difficult to melt and
cast the mixture in a mold, and an ingot containing a sufficient
percentage of Nb to provide improved superconducting
characteristics cannot be formed. In addition, the casting is very
difficult to draw. For these reasons, it has been practically
impossible to make a wire having good superconducting
characteristics using this method. In the latter method, the Nb
powder in the Cu matrix does not form a sufficiently elongated
fiber upon drawing and consequently it often breaks during the
drawing step and thereby fails to provide a structure wherein a
number of discontinuous Nb fibers elongated in the drawing
direction are buried within the Cu matrix. Therefore, both
processes have a low reliability and are capable of producing only
a wire having poor superconducting characteristics.
SUMMARY OF THE INVENTION
An object of the invention is to provide a process for producing a
Nb.sub.3 Sn or V.sub.3 Ga compound-based superconductor wire that
has great mechanical strength, can be cooled efficiently and which
has improved superconducting characteristics.
To achieve this object, a composition wherein at least one metal
powder selected from Nb-based and V-based particles at least a part
of the surface of which is covered with at least one layer selected
from the group consisting of Cu-based, Sn-based and Ga-based metal
layers blended or otherwise brought into intimate contact with at
least one metal or alloy powder selected from Cu-based, Sn-based,
Ga-based, Cu-Sn-based and Cu-Ga-based particles is subjected to a
treatment of reducing the cross-sectional area of the composition
and a heat treatment.
Using the process of the invention, a compound-based superconductor
wire that has great mechanical strength, which can be cooled
efficiently and which has improved superconducting characteristics
is obtained.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described in detail with reference to the
following examples taken in conjunction with the accompanying
drawings, wherein:
FIG. 1 schematically shows a cross-section of a composite particle
according to a preferred embodiment of the invention;
FIG. 2 is a chart showing the critical current characteristics of a
Nb.sub.3 Sn superconductor wire produced according to a preferred
embodiment of the invention and two Nb.sub.3 Sn superconductor
wires produced by the conventional process; and
FIGS. 3 to 6 show schematically a cross-section of composite
particles produced according to other embodiments of the
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred embodiments of the invention will be described with
reference to specific examples.
EXAMPLE 1
Niobium particles (generally indicted at 1 in FIG. 1) having an
average size of about 40 .mu.m whose surface was cleaned by a
chemical treatment were covered with a copper layer 2 of a
thickness of about 5 .mu.m by electrodeposition. The resulting
composite particles (as already mentioned, a particle having at
least two metal layers is referred to as a composite particle) was
blended with copper particles in a ratio of 1:0.6. The blend was
subjected to a preliminary forming with a rubber press and further
formed into a bar having a diameter of 30 mm and a length of 200
mm. The bar was sintered continuously with a hot press in a vacuum
at 950.degree. C. to thereby form a metallurgically integral
composite metal bar wherein Nb particles were scattered within the
Cu matrix. The space factor of Nb in the bar was about 50 vol
%.
The bar was cold-drawn into a 0.3 mm.phi. wire by a conventional
technique. No annealing was performed during the drawing step. The
wire was covered with a tin layer formed by electroplating and
subsequently heated at 700.degree. C. for 50 hours to diffuse tin
and form a Nb.sub.3 Sn coating on the surfaces of Nb fibers.
Microscopic observation of a cross-section of the resulting
Nb.sub.3 Sn wire revealed the presence of Nb.sub.3 Sn fibers
elongated in the longitudinal direction of the wire. The diameter
of each fiber and the average distance between adjacent compound
layers were on the order of several hundred angstroms. The Nb.sub.3
Sn wire was placed in liquid helium and its critical current
characteristics were measured by applying to it a biasing magnetic
field (10 teslas) at 4.2.degree. K. and a bending strain. The
results are shown in FIG. 2 by a curve A. For comparison, a very
thin commercial wire composed of a number of continuous fibers and
a wire composed of discontinuous fibers produced by the
conventional process were subjected to the same test under the same
conditions. The results are shown in FIG. 2 by curves B and C,
respectively.
FIG. 2 shows that the wire produced according to the invention had
a larger critical current for zero strain than the very thin
commercial wire composed of a number of continuous fibers. The
value of critical current for zero strain of the wire of the
invention was substantially maintained even when the strain was
about 2%, and it decreased only gradually as greater strains were
applied. The critical current for the very thin commercial wire
with a number of continuous fibers dropped suddenly when the strain
became more than 0.5%. The wire composed of discontinuous fibers
exhibited low critical currents for all levels of strain. As is
clear from these data, the wire produced by the process of this
invention exhibited much better superconducting and mechanical
characteristics than the conventional products.
EXAMPLE 2
Niobium particles having an average size of about 40 .mu.m whose
surface was cleaned by a chemical treatment were covered with a
copper layer of a thickness of about 9 .mu.m by vapor deposition.
The resulting composite particles were pressed into a bar 150 mm in
diameter and 400 mm long. The bar was hot-extruded (extrusion
ratio: 10, extrusion temp.: 1050.degree. C.) into a tubular form
(OD: 50 mm, ID: 15 mm). A metallurgical integral composite metal
tube was thus provided with elongated niobium particles scattered
within the Cu matrix. The space factor of Nb in the tube was about
50 vol %.
A 14.5 mm.phi. bar was fitted into the composite metal tube which
was fitted into a tantalum tube (OD: 53.8 mm, ID: 50.2 mm) which
was in turn fitted into a copper tube (OD: 76 mm, ID: 54 mm). The
resulting tubular structure was cold-drawn to a 1.4 mm.phi. wire by
a conventional technique. The wire was heated at 700.degree. C. for
50 hours to form a Nb.sub.3 Sn superconductor wire having a
stabilizing Cu layer. The wire was then covered with an insulating
coating and wound into a coil (OD: 200 mm, ID: 100 mm). When a
magnetic flux density of 12 teslas was generated with a combination
of the coil and a bias coil, the characteristics of the Nb.sub.3 Sn
coil were almost as good as those of a short sample. No such
small-scale and high-performance coil could be fabricated easily
with the conventional Nb.sub.3 Sn wire.
EXAMPLE 3
Niobium particles (generally indicated at 1 in FIG. 3) having an
average size of about 40 .mu.m whose surface was cleaned by a
chemical treatment were covered sequentially with a copper layer 2,
a tin layer 3 and a copper layer 2 by electrodeposition. Each layer
had a thickness of about 40 .mu.m. The resulting composite
particles were fitted into a tantalum tube (OD: 20 mm, ID: 18 mm)
which was fitted into a copper tube (OD: 28 mm, ID: 20.2 mm). The
resulting tubular structure was cold-drawn into a wire having a
square cross-section (4.times.4 mm) by a conventional technique.
The wire was given a heat treatment as described above to provide a
Nb.sub.3 Sn wire of a square cross-section having a stabilizing
copper layer.
The critical current characteristics of the wire were measured by
applying various degrees of bending at 4.2.degree. K. under a
magnetic flux density of 10 teslas. The value of critical current
decreased little even when a bending stress causing about 2% strain
was applied. This indicated a large current-carrying capacity, high
ability to be cooled and good mechanical characteristics of the
wire produced by the process of this invention.
EXAMPLE 4
Niobium particles (generally indicated at 1 in FIG. 4) having an
average size of about 40 .mu.m whose surface was cleaned by a
chemical treatment were covered with an alloy (Cu-13 wt % Sn) layer
4 of a thickness of about 10 .mu.m by electroplating. The resulting
composite particles were pressed into a bar 150 mm in diameter and
400 mm long. The bar was hot-extruded (extrusion ratio: 22,
extrusion temp.: 550.degree. C.) into a wire (OD: 32 mm). The wire
was metallurgically integral and had a structure wherein elongated
niobium particles were scattered within the Cu-Sn matrix. The wire
was fitted into a tantalum tube (OD: 37 mm, ID: 34 mm) which was
fitted into a copper tube (OD: 46 mm, ID: 38 mm). The resulting
tubular structure was subjected to repeated cycles of cold drawing
and annealing (400.degree. C..times.1 hr) to form a 1.4 mm.phi.
wire. The wire was then heated at 700.degree. C. for 50 hours to
provide a Nb.sub.3 Sn superconductor wire having a stabilizing
copper layer.
The wire was put in liquid helium and subjected to measurement of
the critical current characteristics under the same conditions as
in Example 1. The value of critical current for zero strain was
maintained until the strain was about 0.2%. This indicated the very
good mechanical characteristics of the wire.
It is to be noted that tubes could be subsequently reduced in their
cross-sectional area only when they used niobium particles covered
with Cu-Sn alloys containing 0.1 to 14 wt % or 50 to 100 wt % of
tin.
EXAMPLE 5
Composite particles as shown schematically in FIGS. 5 and 6 were
drawn and heat-treated as in Example 4 to form Nb.sub.3 Sn
superconductor wires. They exhibited as good results in measurement
of critical current characteristics as the wire produced in Example
4.
EXAMPLE 6
Vanadium particles having an average size of about 40 .mu.m whose
surface was cleaned with a chemical treatment were covered with an
alloy (Cu-23 wt % Ga) layer of a thickness of about 10 .mu.m by
electroplating. The resulting composite particles were pressed into
a bar 150 mm in diameter and 400 mm long. The bar was hot-extruded
(extrusion ratio: 22, extrusion temp.: 500.degree. C.) into a wire
(OD: 32 mm). The wire was metallurgically integral and had a
structure in which elongated vanadium particles were scattered in
the Cu-Ga matrix. The wire was subjected to repeated cycles of
cold-drawing and annealing (350.degree. C..times.1 hr) to form a
0.3 mm.phi. wire. The wire was then heated at 650.degree. C. for 50
hours to provide a V.sub.3 Ga base superconductor wire.
The wire was put in liquid helium and subjected to a measurement of
its critical current characteristics under the same conditions as
in Example 1. The value of critical current for zero strain was
maintained until the strain was about 0.2%. This indicated very
good mechanical characteristics of the wire. It is to be noted that
wires could be subsequently reduced in their cross-sectional area
only when they used vanadium particles covered with Cu-Ga alloys
containing 0.1 to 25 wt % or 50 to 100 wt % of gallium.
The scope of the invention is not limited to the foregoing examples
and it can be applied with equal advantage to the manufacture of
V.sub.3 Si, Nb.sub.3 (Sn-In), Nb.sub.3 (Sn-Ga), Nb.sub.3 Al and
other compound-based wires that can be produced by the same method
as that for producing Nb.sub.3 Sn and V.sub.3 Ga-based wires. In
other words, Pb, Ge, Si, which are of the same group as Sn, and In
and Al, which are of the same group as Ga, can also be diffused
into the matrix phase as effectively as Sn and Ga to produce
compound-based superconductor wires by the process of the
invention.
Various modifications can be made to the processes of the invention
described above. For example, inert elements can be added to base
materials such as Nb, V, Cu, Sn and Ga, or Nb and Cu particles or
Nb, Cu and Sn particles can be blended in a different manner for
preparing composite particles. Also, Cu particles, Sn particles or
Cu-Sn alloy particles can further be added to these composite
particles. Still further, the method of making a shaped article of
the composite particles can be changed. These modifications can be
made without adversely affecting the characteristic features and
advantages provided by the invention.
As described above, the process of the invention yields a Nb.sub.3
Sn or V.sub.3 Ga compound-based superconductor wire using Nb- or
V-based composite particles wherein at least part of the surface of
Nb- or V-based metal particles is covered with at least one layer
selected from the group consisting of Cu-, Sn- and Ga-based metal
layers. By so doing, a compound-based superconductor wire that has
excellent mechanical characteristics such as high bending strength
and tensile strength and which undergoes only a very small decrease
in superconducting characteristics under stress can be manufactured
very easily and in a consistent manner. In addition, because of its
good mechanical properties, an electrical conductor of a shape that
can be cooled with liquid helium effectively can be formed of the
wire. Furthermore, the wire can be wound easily to form a
compound-based superconducting coil having a high reliability and
improved coil characteristics. The wire has a high industrial
utility; for example, it makes possible the economical production
of a magnet of high magnetic field strength. As a further
advantage, the process of the invention facilitates the deposition
of a high-purity copper of aluminum layer necessary for providing a
wire that is stable and can be cooled with liquid helium with a
high efficiency.
* * * * *