DE19612274B4 - Process for the production of a superconducting wire with Nb3Sn - Google Patents

Abstract

A method for producing a superconducting composite strand with Nb ₃ Sn representing an A ₃ B type compound, comprising the following steps:
a) positioning one or more Nb core materials (1) in a billet (2) made of a Cu-Sn alloy;
b) Forming a pure Cu layer (3) on the outer periphery of the billet (2) from a Cu-Sn alloy by inserting the billet into a Cu tube (3), with a ratio of the cross-sectional area of the pure Cu layer to the cross-sectional area of the Cu-Sn alloy billet composed of the Nb core materials (1) from 0.03 to 0.1;
c) Isostatic hot pressing of the Cu tube of the composite billet;
d) pulling the composite billet into a composite strand with a predetermined diameter, at the same time using a surface wire drawing so that the pure Cu layer (3) is completely removed and
e) subjecting the composite strand to a diffusion heat treatment to produce an Nb ₃ Sn compound.

Description

The present invention relates to a method for producing a superconducting wire or superconductor with Nb ₃ Sn, which represents an A ₃ B-type connection.

An A ₃ B type surproductive compound (also called A15 superconducting compound), such as Nb ₃ Sn, Nb ₃ Al and V ₃ Ga, is an intermetallic compound and is quite difficult to process to make superconducting wires. Conventionally, a manufacturing method is used in which a composite billet of a metal A with a high melting point and a metal B with a low melting point, which form the above-mentioned superconductor with A ₃ B-type connection, is drawn into a composite wire and subjecting the composite wire material to diffusion for heat treatment; wherein the above-mentioned low-melting metal B diffuses in and reacts with the above-mentioned high-melting metal A to produce a superconducting wire having the above A ₃ B-type connection.

A known method of manufacturing a Nb ₃ Sn superconducting wire, which is a typical A ₃ B type superconductor, is the known bronze process. The process for producing a superconducting Nb ₃ Sn wire using the bronze process is described below. bores are formed in a rod made of a Cu-Sn alloy (hereinafter referred to as bronze), which further serve as a matrix. An Nb core material is inserted into each hole to form a composite billet. The composite billet is drawn to produce a composite wire, such as by extrusion or wire drawing. Optionally, the composite billet mentioned above is used as a composite primary billet which is inserted into an outer shell such as a bronze tube or a pure copper tube to form a composite secondary billet (composite endstick), and wherein composite secondary billet is pulled into a composite wire.

To form a composite stick higher In some cases, the composite wire becomes orderly used as a strand. To the packing density when assembling the composite stick has to enlarge the strand desirably a hexagonal cross section. For the case that a composite strand by wire drawing with a prescribed diameter was made, the strand for changing the circular cross-section in an approximate hexagonal cross section, for example, drawn or rolled.

The composite wire material mentioned above has a structure with Nb fibers or wires which are embedded in a matrix metal. While the composite wire material for diffusion is subjected to a heat treatment by heating at 550 ° C to 700 ° C, the Sn diffuses in the bronze and reacts with the Nb fiber to produce Nb ₃ Sn. The Nb fiber thus becomes a superconducting Nb ₃ Sn fiber, from which a superconducting wire, the structure of which has a large number of cores, is produced. There is also the so-called outer diffusion process, in which the outer periphery of the above composite wire material is covered with Sn, and then diffusion heat treatment is carried out.

Meanwhile, a supporting metal to enlarge the resistance of the superconductive State of a superconductive Wire generally positioned in the middle or outermost part of the superconducting wire. If a Cu tube is used as the outer sheath in the manufacture of a superconducting wire Assembling the above composite end stick is used this, positioned outermost Part, as support metal. If a pure copper rod or the like positioned in the middle of the composite stick , this serves optionally as a in the middle of the superconducting wire positioned support metal. Furthermore, a method is used in which an Nb barrier material or a Ta barrier material at the interface between the mentioned above pure copper tube or the pure copper rod and the bronze tube, and thereby prevents that Sn in the bronze of the bronze tube in the support metal diffused.

The superconducting wire with a supporting metal positioned in the middle is often used as a superconducting wire, for example for superconducting magnets. This is necessary because the Nb ₃ Sn fibers or wires must be designed to connect the ends of the superconducting wires.

When producing a superconducting wire from an A ₃ B-type compound, the B-metal alloy as a matrix metal tends to break or tear during cold processing due to its poor elongation. If the A ₃ B-type compound is Nb ₃ Sn, since the Cu-Sn compound contained in the bronze (Cu-Sn) has very little elongation, it tends to break or tear during cold processing. If a bronze with a low concentration of Sn is used, the reduction in machinability can be somewhat avoided, but the diffusion of Sn necessary for the formation of Nb ₃ Sn becomes insufficient, so that a superconducting wire can be used high quality properties cannot be obtained.

In recent years, many make a bronze with an Sn content of 14% by weight or more is used. If such a bronze with a high Sn content is used, are there the Cu-Sn content mentioned above in large Amount is included - the Problems that the workability is bad and the wire. while of wire drawing tends to break or the like. Therefore, it is required machinability to improve the matrix metal.

From the DE 28 35 974 B2 and the DE 42 08 678 A1 The so-called bronze technique or the so-called bronze process is known, whereby for the production of a superconducting wire with an A ₃ B-type connection, A-metal core materials are introduced into a B-metal alloy matrix, subjected to a cross-sectional machining and then to form the intermetallic superconducting phase A ₃ B are subjected to an annealing treatment by diffusion. In addition, it is from the DE 28 35 974 B2 and the DE 42 08 678 A1 It is known to combine a plurality of matrix elements composed in this way, to process them in a cross-section-reducing manner and then to subject them to an annealing treatment for diffusion.

From the DE 32 03 222 C2 there is known a billet for producing a superconducting wire, the billet being wound on a laminate rolled around a copper core rod with a bronze layer under a layer of stretched niobium metal. The billet thus wound is then provided with a layer of an expanded material which acts as a diffusion barrier and onto which a copper sheathing is applied to facilitate the processing of the wire thus produced with a view to reducing the cross-section.

From the US 45 32 703 A method for producing a superconducting wire with an A ₃ B connection is known, the matrix material provided with a plurality of A metal core materials being provided on a B metal alloy with a layer serving as a diffusion barrier and a copper sheathing arranged thereon to improve the machinability of the superconducting wire to be manufactured with regard to machining reducing the cross section.

The DE 27 33 511 C3 discloses to provide a matrix material with core materials with a sheath made of high-purity aluminum and this in turn with a sheath made of copper and to draw a wire from this composite.

The US 51 74 830 discloses a superconducting wire, in which an A-metal core is coated with several alloys containing A-metal, which in turn are surrounded by an A-metal diffusion barrier and finally by a copper sheath.

In view of the above prior art, intensive studies have been conducted leading to the present invention. The object of the present invention is to provide a method for producing a superconducting wire with an A ₃ B-type connection without precisely those which occur when handling a matrix material with poor machinability, such as, for example, a bronze with a high Sn concentration problems.

• a) Positionieren eines oder mehrerer Nb-Kernmaterialien in einem Knüppel aus einer Cu-Sn-Legierung;
• b) Bilden einer reinen Cu-Lage auf der äußeren Peripherie des Knüppels aus einer Cu-Sn-Legierung durch Einsetzen des Knüppels in ein Cu-Rohr mit einem Verhältnis der Querschnittsfläche der reinen Cu-Lage zu der Querschnittsfläche des mit den Nb-Kernmaterialien zusammengesetzten Knüppels aus der Cu-Sn-Legierung von 0,03 bis 0,1;
• c) Isostatisches Warmpressen des Cu-Rohrs des zusammengesetzten Knüppels;
• d) Ziehen des zusammengesetzten Knüppels zu einem zusammengesetzten Strang mit einem vorbestimmten Durchmesser, wobei gleichzeitig ein Oberflächendrahtziehen angewandt wird, so daß die reine Cu-Lage vollständig entfernt wird und
• e) Aussetzen des zusammengesetzten Strangs einer Diffusionswärmebehandlung, um eine Nb₃Sn-Verbindung zu erzeugen.

A first embodiment of the present invention provides a method of making a superconducting composite strand with Nb ₃ Sn representing an A ₃ B type compound, comprising the steps of:

• a) positioning one or more Nb core materials in a Cu-Sn alloy billet;
• b) Forming a pure Cu layer on the outer periphery of the Cu-Sn alloy billet by inserting the billet into a Cu pipe with a ratio of the cross-sectional area of the pure Cu layer to the cross-sectional area of the composite with the Nb core materials Cu-Sn alloy billets from 0.03 to 0.1;
• c) Isostatic hot pressing of the Cu tube of the composite billet;
• d) pulling the composite billet into a composite strand of a predetermined diameter, simultaneously using a surface wire drawing so that the pure Cu layer is completely removed and
• e) subjecting the composite strand to a diffusion heat treatment to produce an Nb ₃ Sn compound.

• a) Bilden einer reinen Cu-Lage auf der äußeren Oberfläche eines Bronzerohres aus einer Cu-Sn-Legierung durch Einsetzen des Bronzerohres in ein sauerstofffreies Cu-Rohr;
• b) Positionieren eines auf der äußeren Oberfläche mit Nb beschichteten sauerstofffreien Kupferstabes in der Mitte des Bronzerohres;
• c) Einsetzen einer Vielzahl zusammengesetzter Stränge, die gemäß der ersten Ausführung der vorliegenden Erfindung hergestellt sind, in den Freiraum zwischen dem Bronzerohr und dem Kupferstab, wobei ein zusammengesetzter Sekundär-Knüppel ausgebildet wird;
• d) Extrudieren und Drahtziehen des zusammengesetzten Sekundär-Knüppels und Entfernen der reinen Cu-Lage durch Oberflächendrahtziehen während des Drahtziehens zu einem zusammengesetzten Draht; und
• e) Aussetzen des zusammengesetzten Drahts einer Diffusionswärmebehandlung, um eine Nb₃Sn-Verbindung zu erzeugen.

A second embodiment of the present invention provides a method of manufacturing a superconducting wire with Nb ₃ Sn representing an A ₃ B type connection, comprising the steps of:

• a) forming a pure Cu layer on the outer surface of a bronze tube made of a Cu-Sn alloy by inserting the bronze tube into an oxygen-free Cu tube;
• b) positioning an oxygen-free copper rod coated with Nb on the outer surface in the middle of the bronze tube;
• c) inserting a plurality of composite strands made in accordance with the first embodiment of the present invention into the space between the bronze tube and the copper rod, forming a composite secondary billet;
• d) extruding and wire drawing the composite secondary billet and removing the pure Cu layer by surface wire drawing during the wire drawing to a composite wire; and
• e) subjecting the composite wire to a diffusion heat treatment to produce an Nb ₃ Sn compound.

1 Figure 12 shows a view of a composite primary billet in accordance with an embodiment of the present invention.

2 shows in a view the state in which a composite secondary stick is assembled according to an embodiment of the present invention.

In a first execution a pure copper layer with good machinability on the outer periphery a single composite stick provided so that the surface of the Wire material can hardly be broken or torn during wire drawing.

Accordingly, the occurrence breakage of the wire material can be suppressed, and it can be a composite wire material or a composite strand with good machinability be generated. The effect of an improvement in the above machinability can also be achieved when a bronze with a low Sn concentration for the B-metal alloy is used. The effect is particularly remarkable in the event in which a bronze is used which has a Sn content of 10% by weight or more contains.

The above-mentioned pure Cu layer is designed that this relationship the cross-sectional area the pure Cu layer to the cross-sectional area of the individual composite stick Is 0.03 to 0.1. If the ratio is less than 0.03, this can occur when pulling the wire onto the outer surface of Act on the wire so that the Bronze has poor machinability. on the other hand is the effect at a ratio above 0.1 saturated and the diameter of the composite billet is made unnecessarily large, what with regard to the equipment or systems, for example for the capacity of the extruder, is not preferable.

The pure Cu layer is removed during wire drawing. If the strands with the single remaining pure Cu layer were placed in an outer shell to assemble a composite secondary billet, the A-metal space factor of the above composite secondary billet, for example an Nb core material, would be undesirably reduced. Since the B of the B-metal alloy, for example the Sn in the bronze, diffuses into the Nb core material and into the pure Cu layer during the diffusion heat treatment, the supply of Sn for producing Nb ₃ Sn would be reduced. In addition, it is necessary to completely remove the pure Cu layer, since uneven stresses are exerted on the strand during wire drawing if parts of the pure Cu layer remain, which in some cases result in the wire breaking or tearing.

When removing the pure copper layer by wire drawing, although the pure copper layer mentioned above is used for wire drawing Completely can be removed at once, this gradually by repeated Wire drawing can be removed. In this case it is advantageous if the pure Cu layer in terms of machinability may remain until the last wire drawing. The machinability in the subsequent wire drawing also gets worse if the pure Cu layer is removed prematurely. As a method of removing the pure Cu layer above during wire drawing can be, for example, the known conventional one Surface Wire Drawing be used.

The conventional surface wire drawing is known for example from Nonferrous Wire Handbook, Volume 2 - Bare Wire Processing, 1981 by Otto J. Tassi, published by THE WIRE ASSOCIATION INTERNATIONAL, INC., Guilford, Connecticut.

First embodiment

The following will refer to 1 described a first embodiment in detail, wherein Nb ₃ Sn was established as an A ₃ B connection.

Each round bronze bar (length 600 mm and diameter 230 mm) consisting of 14 wt .-% of Sn, 0.2 wt .-% of Ti and the rest essentially of Cu was with 19 through holes, which were distributed approximately evenly with with a diameter of 25 mm and was then machined to produce a bronze tube with a diameter according to Table 1. Nb rods with a diameter of 24.5 mm were inserted into the through holes. The bronze tube was in an oxygen-free copper tube with an outer diameter of 210 mm and an inner diameter, the value of which is given in Table 1, was used. Oxygen-free copper washers (not shown) were welded to opposite ends of the tube. The interior was evacuated and sealed to create a vacuum. The tube was then hot isostatically pressed and machined to give an outer diameter of 200 mm. The primary stick thus obtained 4 is in 1 shown. In the figure, the above Nb rod corresponds to an Nb core, the bronze tube corresponds to a Cu-Sn alloy matrix 2 , and the above oxygen-free copper tube corresponds to a pure Cu layer 3 , The inner diameter of the pure Cu layer and the ratio of the cross-sectional area of the pure Cu layer to the cross-sectional area of the composite primary billet 4 are given in Table 1.

In order to bring the diameter to 40 mm, the composite primary stick was 4 Extruded at 650 ° C and drawn several times to obtain a composite strand with a diameter of 2 mm. At the same time, the pure copper layer was completely removed by pulling the surface wire. The composite strand thus produced was further wire drawn and deformed to produce a hexagonal strand to obtain a hexagonal cross section with a distance between opposite sides of 1.7 mm. In order to build a higher order composite billet (composite secondary billet), this hexagonal strand was used to create a superconducting wire by subsequent drawing.

In order to evaluate the machinability in the manufacture of the composite strand before assembling the above composite secondary billet, observations of the appearance of the composite strand produced during wire drawing and eddy current investigations were conducted to investigate defects, in order to determine whether cracks were present in the surface of the composite strand. The composite strand in whose surface cracks were found was classified as defective. The production yield calculation of non-defective composite strands was based on the amount of Nb needed to assemble the original composite billet 4 was used. The yield (weight) of the composite strands obtained was then measured. These results are shown in Table 1.

Comparative execution to first embodiment and execution according to the well-known bronze process

In a known version a composite strand using a round bronze bar similar to that first execution by forming 19 through holes that are distributed approximately evenly were produced with a diameter of 25 mm. To an outer diameter of To form 210 mm, the bronze tube was machined. The outer periphery the bronze tube was not covered with an oxygen-free copper tube. Similar to the first time the composite strand thus obtained was used further, around a composite stick higher Order (composite secondary billet) build up and by subsequently pulling a super conductive wire manufacture. A comparison was made similar to the first version of the the present invention, with the exception that the Cross-sectional area ratio of the pure Cu layer had the value given in Table 1. The Presence or absence of cracks in the strand surface, the Production yield, and the yields of the composite thus obtained Strands of known execution and the comparison execution are also given in Table 1.

As can be seen from Table 1, point No. 1 and No. 2 of the execution of the present invention in comparison with No. 3 of the known execution demonstrably a much better machinability on, for example, the number of cracks in the surface is less and the production yield of the composite strand is larger. No. 4 of the comparison execution, where the cross-sectional area ratio of the pure Cu layer was 0.0268, showed poor machinability and production yield. On the other hand was the production yield the comparison execution No. 5 low, although the cross-sectional area ratio of the pure Cu layer is 0.1183 and it had good machinability. Because the compound strands the first execution of the present invention in comparison with those of the known execution and the comparison execution much better workability and production yield have, it is possible the production cost for superconductive wires or leader according to the procedure of the present invention.

Second embodiment

In the following it should refer to 2 a second embodiment will be explained. Any oxygen-free copper tube 7 with the inner diameter given in Table 2 and an outer diameter of 220 mm was over each bronze tube 6 (consisting of 14 wt .-% of Sn, 0.2 wt .-% of Ti, and the rest essentially of Cu) with the outer diameter and an inner diameter given in Table 2 knife of 180 mm, and a length of 600 mm. The composite strand (round wire with a diameter of 2 mm) from number 3 of the first embodiment above was further drawn to form a hexagonal strand 5 with the distance between the opposite sides of 1.7 mm. The hexagonal strands were, as in the 2 shown in the bronze tube 6 inserted. In the middle of the bronze tube 6 became an oxygen-free copper rod 9 with a diameter of 90 mm, that of an Nb film 8th was wrapped with a thickness of 1 mm.

Then oxygen-free copper washers (not shown) on opposite Welded ends. To the outer diameter To bring it to 200 mm, the tube was hot isostatically pressed and machined processed. On the outer periphery the secondary billet thus obtained was a pure Cu layer according to the above oxygen-free copper tube. The inner diameter the pure copper layer and the relationship the cross-sectional area of the pure Cu layer to the cross-sectional area of the assembled secondary billet given in Table 2. In order to bring the diameter to 40 mm, the composite secondary billet was extruded at 650 ° C and wire-drawn several times to finally create a composite Obtain 0.8mm wire. While of wire drawing, the above-mentioned pure Cu layer was made by surface wire drawing Completely away. The examination results of observation of phenomena while of wire drawing and the investigation of cracks in the surface of the composite strand through eddy current studies for defect research, the production yield is calculated on the basis of that during assembly of the composite secondary stick used Amount of Nb and the yield amount (weight) of the superconducting wires or Conductors are given in Table 2.

Execution after the known bronze process and comparison for the second embodiment

In a known embodiment, a composite secondary billet was made similar to the second embodiment of the present invention, except that the bronze tube 6 instead of using an oxygen-free copper tube 7 with a bronze tube (consisting of 14% by weight of Sn, 0.2% by weight of Ti, and the rest essentially of Cu) with a length of 600 mm, an inner diameter of 180 mm and an outer diameter of 220 mm was covered, and a composite wire material similar to the embodiment of the present invention was made. In a comparative embodiment, the second embodiment of the present invention was repeated, except that the cross-sectional area ratio of the pure Cu layer had the value shown in Table 2. The results of the investigation of cracks in the surface, the production yield, and the yield amount of the superconducting wires of the known embodiment and the comparative embodiment are also shown in Table 2.

As can be seen from Table 2, no. 6 and No. 7 of the second version of the present invention compared to No. 8 of the known embodiment a much better machinability, for example the number of cracks in the surface is low and the production yield high. No. 9 of the comparative version, in which the cross-sectional area ratio of the pure Cu layer 0.0258 there were many cracks in the surface of the strand and determine the machinability and production yield lower. On the other hand, the production yield was lower, though the editability in No. 10 of the comparative version, where the cross-sectional area ratio of the pure Cu layer was 0.1089, better.

The method for producing a superconducting Nb ₃ Sn wire according to the present invention allows the production of superconducting wires or conductors, as already explained, with both a high production yield and a high quality, and furthermore improves the productivity and thus provides one remarkable contribution to the industry.

1

A metal-

2

B-metal alloy

3

Cu layer

4

Primary billet

5

hexagonal strand

6

Bronze tube

7

Cu tube

8th

Nb foil

9

copper steel

Claims (5)

A method of making a superconducting composite strand with Nb ₃ Sn representing an A ₃ B type compound, comprising the steps of: a) positioning one or more Nb core materials ( 1 ) in a stick ( 2 ) from a Cu-Sn alloy; b) formation of a pure Cu layer ( 3 ) on the outer periphery of the stick ( 2 ) made of a Cu-Sn alloy by inserting the stick into a Cu pipe ( 3 ), with a ratio of the cross-sectional area of the pure Cu layer to the cross-sectional area of the with the Nb core materials ( 1 ) Cu-Sn alloy billets from 0.03 to 0.1; c) Isostatic hot pressing of the Cu tube of the composite billet; d) pulling the composite billet into a composite strand of a predetermined diameter, simultaneously using a surface wire drawing so that the pure Cu layer ( 3 ) is completely removed and e) exposing the composite strand to a diffusion heat treatment to produce an Nb ₃ Sn compound. A method of manufacturing a superconductive composite strand with Nb ₃ Sn according to claim 1, which further comprises the steps of welding an oxygen-free Cu disc to the opposite ends of the Cu tube ( 3 ) and an evacuation of the interior of the Cu pipe ( 3 ) to form a vacuum prior to hot isostatic pressing. A method of manufacturing a superconducting composite strand with Nb ₃ Sn according to claim 1 or 2, wherein the billet is made of a Cu-Sn alloy containing not less than 10% by weight of Sn. A method of making a superconducting wire with Nb ₃ Sn representing an A ₃ B type compound, comprising the steps of: a) forming a pure Cu layer on the outer surface of a bronze tube ( 6 ) made of a Cu-Sn alloy by inserting the bronze tube ( 6 ) in an oxygen-free Cu pipe ( 7 ); b) positioning one on the outer surface with Nb ( 8th ) coated oxygen-free copper rod ( 9 ) in the middle of the bronze tube ( 6 ); c) inserting a plurality of composite strands, which are produced according to one of claims 1 to 3, into the space between the bronze tube ( 6 ) and the copper rod ( 9 ), wherein a composite secondary billet is formed; d) extruding and wire drawing the composite secondary billet and removing the pure Cu layer by surface wire drawing during the wire drawing to a composite wire, and e) subjecting the composite wire to a diffusion heat treatment to produce an Nb ₃ Sn compound. A method of manufacturing a Nb ₃ Sn superconducting wire according to claim 4, further comprising the step of: welding oxygen-free Cu disks to the opposite ends of the Cu tube ( 7 ).