JPH06309965A - Method for manufacturing NbTi superconducting wire - Google Patents

Abstract

(57) [Summary] [Purpose] NbTi that can maintain good soundness of NbTi filaments and obtain good superconducting properties.
A method of manufacturing a superconducting wire is provided. [Structure] The present invention has an NbTi filament diameter of 1 to 5
NbT in the range of 0 μm and having a critical current density of 2,000 A / mm ² or more at a temperature of 4.2 K and a magnetic field of 5 T
An i superconducting wire designing and manufacturing method is disclosed. In the plastic working in the manufacturing process, the ratio of the cross-sectional area of the Nb barrier layer to the cross-sectional area of the portion consisting of the NbTi filament and the Nb barrier layer S _Nb / S _{(NbTi + Nb)} is (Here, Df is the final NbTi filament diameter (μm)
Indicates. In order to satisfy the above condition, a Nb layer having a predetermined film thickness is compounded around the NbTi rod.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for designing and manufacturing NbTi multifilamentary superconducting wire used in electric power application equipment such as generators and transformers.

[0002]

2. Description of the Related Art Usually, a NbTi multicore superconducting wire having a large number of NbTi filaments embedded in a matrix is
It is manufactured according to the processing steps shown in FIG.

However, during the production of the wire rod, the matrix Cu and NbTi chemically react with each other due to the temperature rise for hot extrusion and wire drawing processing, and the heat generated during processing during the intermediate heat treatment, whereby Ti ₂ Cu, ( Intermetallic compounds such as TiNb) ₂ Cu may form.

Since this material is harder than the NbTi alloy,
NbTi filament penetrates during wire drawing and NbTi
Since the filament is damaged, the current may be attenuated during use in the permanent current mode, resulting in a remarkable deterioration of superconducting properties.

Therefore, in order to solve the above problems, a diffusion barrier layer made of Nb is provided at the boundary between Cu and NbTi filaments of the matrix, as disclosed in JP-A-59-26772. This prevents the formation of intermetallic compounds due to the heat received during the processing step,
NbTi superconducting wire rods have been proposed which have no deterioration in superconducting properties.

[0006]

In manufacturing such NbTi superconducting wire, the diffusion barrier layer generally made of Nb has been empirically set at a certain ratio.

However, in the NbTi superconducting material designed and manufactured as described above, the thickness of the diffusion barrier layer made of Nb may become too small or may become larger than necessary.

If the thickness of the diffusion barrier layer made of Nb is too small, the diffusion reaction between Ti and Cu proceeds through the diffusion barrier layer due to the influence of heat in the processing step to form an intermetallic compound. Therefore, there is a problem that the original purpose of the diffusion barrier layer made of Nb cannot be sufficiently achieved.

On the other hand, when the thickness of the diffusion barrier layer made of Nb is unnecessarily large, deterioration of superconducting characteristics due to damage of the NbTi filament is prevented, but the wire material is equivalent to the excess diffusion barrier layer. N in total
There has been a problem that the amount of bTi is reduced and the critical current of the wire is reduced.

The present invention provides a diffusion barrier layer made of Nb having an optimum thickness for the thermal history during the manufacturing process,
It is intended to provide a method for producing an NbTi superconducting wire capable of obtaining good superconducting properties while maintaining high soundness of the NbTi filament.

[0011]

SUMMARY OF THE INVENTION The present invention provides a final NbTi
The filament diameter is 1 to 50 μm and the temperature is 4.2.
K, magnetic field 5T, critical current density (Jc) is 2,000A
The present invention provides a method for designing and manufacturing NbTi superconducting wire rods having a thickness of 1 mm2 / mm ² or more.

According to the method of the present invention, a layer made of Nb is provided around a core made of NbTi, Cu or a Cu alloy is compounded around the layer, and plastic working is performed in a temperature range of 0 to 900 ° C. to obtain NbTi. The first step of producing a single-core wire and the bundle of a plurality of single-core wires obtained in the first step are 0 to 900.
A second step of producing a NbTi multifilamentary wire rod by performing plastic working in a temperature range of ° C.
NbTi filaments and N
N with respect to the cross-sectional area of the portion composed of the barrier layer composed of b
Ratio of cross-sectional area of barrier layer consisting of b S _Nb / S
_{(NbTi + Nb)} is

[0013]

[Equation 2]

In order to satisfy (here, Df represents the final NbTi filament diameter), a layer of Nb having a predetermined thickness is compounded around the core material of NbTi in the first step in advance. Characterize.

In the present invention, "the cross-sectional area of a portion composed of a diffusion barrier layer composed of NbTi filaments and Nb" means a diffusion barrier composed of NbTi filaments and Nb in a cross section obtained by cutting perpendicularly to the longitudinal direction of the wire. The term "area occupied by the layer" means "the cross-sectional area of the diffusion barrier layer made of Nb" means the area occupied by the diffusion barrier layer made of Nb in a cross section obtained by cutting perpendicularly to the longitudinal direction of the wire. I will say.

In the present invention, the ratio of the cross-sectional area of the barrier layer made of Nb to the cross-sectional area of the portion made of the barrier layer made of NbTi filaments and Nb S _Nb / S
A predetermined thickness T of the barrier layer made of Nb to be compounded around the core material made of Nb before the plastic working in the first step so that _{(NbTi + Nb)} satisfies a predetermined range determined by the final filament size. _S can be obtained as follows, where D _S is the initial diameter of the core material made of Nb.

[0017] In a first step, the cross-sectional area of the layer made of Nb before plastic working S 'and _Nb, the cross-sectional area of the portion consisting of a layer consisting of a core material and a Nb consisting of NbTi S'
If _{(NbTi + Nb), S '} Nb, S' (NbTi + Nb) is respectively given by the following equation.

[0018]

[Equation 3]

[0019]

[Equation 4]

From the equations (1) and (2), in the first step, the ratio of the cross-sectional area of the layer made of Nb to the cross-sectional area of the portion made of the core made of NbTi and the layer made of Nb before plastic working is S If ′ _Nb / S ′ _{(NbTi + Nb)} is calculated,

[0021]

[Equation 5]

The ratio of the cross-sectional area of the layer made of Nb to the cross-sectional area of the portion made of the core material made of NbTi and the layer made of Nb before plastic working obtained here _S'Nb / S '
_{(NbTi + Nb)} is the ratio of the cross-sectional area of the barrier layer made of Nb to the cross-sectional area of the portion made of the Nb filament and the barrier layer made of Nb in the final wire rod after plastic working, S _Nb / S ₍ It can be treated almost equivalent to ( _{NbTi + Nb)} .

[0023]

[Equation 6]

Therefore, the following equation (5) is established.

[0025]

[Equation 7]

From the above, in the first step, the predetermined film thickness T _S of the layer made of Nb compounded around the core made of NbTi before the plastic working can be obtained by the following equation (6). it can.

[0027]

[Equation 8]

In the method of the present invention, when the desired filament diameter D _f in the final wire is given in the designing step of the wire, in the plastic working of the first step and the second step,
An appropriate range of the ratio S _Nb / S _{(NbTi + Nb)} of the cross-sectional area of the barrier layer made of Nb to the cross-sectional area of the portion made of the NbTi filament and the barrier layer made of _Nb can be determined. When the value of S _Nb / S _{(NbTi + Nb)} is determined, it is possible to simulate an appropriate thickness of the layer made of Nb to be compounded around the core made of NbTi in the first step.

[0029]

The present inventors have made various studies in order to set a barrier layer made of Nb having an appropriate thickness that can completely prevent the formation of intermetallic compounds in the processing step of the NbTi superconducting wire which is affected by heat. It was

As a result, in the plastic working accompanied by heat, the thickness X of the barrier layer made of Nb necessary for preventing the formation of the intermetallic compound at the interface between the Cu of the matrix and the NbTi filament is the plastic working accompanied by heat. It was newly found that it can be obtained by the equation (7) from the thermal experience temperature M of the wire rod in the process and the thermal experience time T of the wire rod.

[0031]

[Equation 9]

As suggested by the above equation, the appropriate thickness X of the barrier layer made of Nb is defined by the plastic working conditions such as the thermal experience temperature M of the wire and the thermal experience time T of the wire.

In the conventional method, the barrier layer made of Nb is empirically formed from the NbTi filament and Nb based on experience without considering the plastic working conditions applied to the wire, for example, the heat experience temperature M of the wire and the heat experience time T of the wire. Was uniformly set so as to occupy about 4 to 8% of the portion consisting of the barrier layer, but from the above equation, the plastic working conditions applied to the wire,
For example, it has become clear that it is preferable to define the thickness of the barrier layer made of Nb within a certain range according to the thermal experience temperature M of the wire and the thermal experience time T of the wire.

From this point of view, as a result of further research and examination, as a result of the desired final filament diameter Df, NbT was obtained in the plastic working of the first step and the second step.
The ratio S _Nb / S _{(NbTi + Nb)} of the cross-sectional area of the barrier layer made of Nb to the cross-sectional area of the portion made of the barrier layer made of i filament and Nb is

[0035]

[Equation 10]

(Where Df is the final NbTi filament)
Shows the diameter (μm). ) Of the first process
In the process, a predetermined Nb is applied around the core made of NbTi.
NbTi filament diameter of 1-5
It is in the range of 0 μm, and the temperature is 4.2K and the magnetic field is 5T.
Field current density (Jc) is 2,000A / mm ²Is over
In realizing NbTi superconducting wire, NbTi filament
Can prevent the formation of intermetallic compounds that impair the integrity of the
Being able to secure a barrier layer made of Nb with an appropriate thickness
I found it.

In the present invention, the ratio of the sectional area of the barrier layer made of Nb to the cross-sectional area of the portion made of the barrier layer made of NbTi filaments and Nb S _Nb / S
_{(NbTi + Nb)} is

[0038]

[Equation 11]

In order to satisfy (where, Df represents the final NbTi filament diameter (μm)), in the first step, a layer made of Nb is compounded around a core material made of NbTi. , NbTi filament and N
N with respect to the cross-sectional area of the portion composed of the barrier layer composed of b
Ratio of cross-sectional area of barrier layer consisting of b S _Nb / S
_{If (NbTi + Nb)} is smaller than the range specified in the present invention, a barrier layer made of Nb may be provided at the interface between the NbTi filament and Cu in the matrix, as shown in the following examples. Nevertheless, the thickness of the barrier layer made of Nb becomes insufficient, and it is impossible to completely prevent the formation of intermetallic compounds in the process affected by heat. The critical current density (Jc) is about 3,000 A / mm ² ,
When the ratio of the cross-sectional area of the barrier layer made of Nb to the cross-sectional area of the portion made of the NbTi filament and the barrier layer made of _Nb S _Nb / S _{(NbTi + Nb)} exceeds 0.33, the temperature is 4.2K. This is because the critical current density (Jc) in the portion composed of the NbTi filament and the barrier layer composed of Nb at a magnetic field of 5 T cannot be achieved at 2,000 A / mm ² or more.

[0040]

EXAMPLES The effects of the method of the present invention will be clarified below based on examples.

Example 1 NbTi filament diameter was 3 μm and temperature was 4.2.
K, magnetic field 5T, critical current density (Jc) is 2,000A
A NbTi superconducting wire having a thickness of at least 1 / mm ² is manufactured. Based on this assumption, the manufacturing design of the wire rod was performed.

Applying the method of the present invention,

[0043]

[Equation 12]

(Here, Df represents the final NbTi filament diameter (μm).)
The ratio of the cross-sectional area of the Nb barrier layer to the cross-sectional area of the portion composed of the i filament and the Nb barrier layer S _Nb / S
_The range of _{(NbTi + Nb)} should be calculated as follows.

0.044 ≦ S _Nb / S _{(NbTi + Nb)} ≦ 0.33 Four kinds of S _Nb / S _{(NbTi + Nb)} satisfying this range are set,
From the set value, the appropriate thickness of the Nb layer to be wound around the NbTi rod was calculated by the above equation (6).

Based on this manufacturing design, an Nb sheet was wound around an NbTi rod having a diameter of 10 mm so as to have a predetermined thickness, and the outer diameter was 15 to 20 mm and the inner diameter was 10 to 15 m.
After being inserted into a Cu pipe of m, a wire drawing process was performed to produce a hexagonal Cu / NbTi single-core composite wire with a distance between opposite sides of 2.5 mm.

The hexagonal composite wire thus obtained was cut into a regular size to prepare 7,000 hexagonal segments. The 7,000 hexagonal segments are bundled and densely packed in a Cu pipe having an outer diameter of 300 mm and an inner diameter of 250 mm, and a cap made of copper or a copper alloy is covered on both ends of the head end and sealed by an electron beam (EB) to form Cu / An NbTi multi-core superconducting billet was obtained. After subjecting this superconducting billet to surface reduction processing by hot extrusion at 500 ° C., a final wire rod having a wire diameter of 0.8 mm was obtained through the steps of wire drawing, heat treatment and twisting.

With respect to the wire rods of Examples 1 to 4 of the present invention thus obtained, the NbTi filament diameter and the thickness of the Nb barrier layer were measured, respectively, and the cross-sectional area of the portion of the wire rod after the production, which was composed of the NbTi filament and the Nb barrier layer, was measured. Against N
The ratio S _Nb / S _{(NbTi + Nb)} of the cross-sectional area of the b barrier layer was determined.

The temperature of the wire rods of Examples 1 to 4 of the present invention was 4.2.
The critical current density (Jc) was measured at k and a magnetic field of 5T. Further, the surface of the NbTi filament was observed with an electron microscope to examine whether or not a CuTi compound was produced. The results are shown in Table 1.

Next, as a comparative example, four sets of S _Nb / S _{(NbTi + Nb)} were set outside the range specified by the method of the present invention, and the NbTi rod was wound around the NbTi rod from the set value according to the above formula (6). The thickness of the Nb layer to be attached was calculated, and an NbTi wire rod was produced according to the same manufacturing process as in the example of the present invention.

With respect to the wire rods of Comparative Examples 1 to 4 thus obtained, the NbTi filament diameter and the thickness of the Nb barrier layer were measured, respectively, and the cross-sectional area of the portion of the wire rod after the production, which was composed of the NbTi filaments and the Nb barrier layer, was measured. The ratio S _Nb / S _{(NbTi + Nb)} of the cross-sectional area of the Nb barrier layer to was calculated.

The temperature of the wires of Comparative Examples 1 to 4.2 was 4.2.
The critical current density (Jc) was measured at k and a magnetic field of 5T. Further, the surface of the NbTi filament was observed with an electron microscope to examine whether or not a CuTi compound was produced. The results are collectively shown in Table 1.

[0053]

[Table 1]

Example 2 NbTi filament diameter was 1 μm and temperature was 4.2.
K, magnetic field 5T, critical current density (Jc) is 2,000A
A NbTi superconducting wire having a thickness of at least 1 / mm ² is manufactured. Based on this assumption, the manufacturing design of the wire rod was performed.

Applying the method of the present invention,

[0056]

[Equation 13]

(Here, Df represents the final NbTi filament diameter (μm).)
The ratio of the cross-sectional area of the Nb barrier layer to the cross-sectional area of the portion composed of the i filament and the Nb barrier layer S _Nb / S
_The range of _{(NbTi + Nb)} should be calculated as follows.

0.125 ≦ S _Nb / S _{(NbTi + Nb)} ≦ 0.33 Four kinds of S _Nb / S _{(NbTi + Nb)} satisfying this range are set,
From the set value, the appropriate thickness of the Nb layer to be wound around the NbTi rod was calculated by the above equation (6).

Based on this manufacturing design, Nb sheets were wound around NbTi rods having a diameter of 10 mm so that each had a predetermined thickness, and the outer diameter was 15 to 20 mm and the inner diameter was 10 to 15 m.
After being inserted into a Cu pipe of m, a wire drawing process was performed to produce a hexagonal Cu / NbTi single-core composite wire with a distance between opposite sides of 2.5 mm.

The hexagonal composite wire thus obtained was cut into a regular size to prepare 7,000 hexagonal segments. The 7,000 hexagonal segments are bundled and densely packed in a Cu pipe having an outer diameter of 300 mm and an inner diameter of 250 mm, and a cap made of copper or a copper alloy is covered on both ends of the head end and sealed by an electron beam (EB) to form Cu / An NbTi multi-core superconducting billet was obtained. After subjecting this superconducting billet to surface reduction processing by hot extrusion at 500 ° C., a final wire rod having a diameter of 0.13 mm was obtained through the steps of wire drawing, heat treatment and twisting.

With respect to the wire rods of Examples 1 to 4 of the present invention thus obtained, the diameter of the NbTi filament and the thickness of the Nb barrier layer were measured, and the cross-sectional area of the portion of the wire rod after the production, which was composed of the NbTi filament and the Nb barrier layer, was measured. Against N
The ratio S _Nb / S _{(NbTi + Nb)} of the cross-sectional area of the b barrier layer was determined.

The temperature of the wire rods of Examples 1 to 4 of the present invention was 4.2.
The critical current density (Jc) was measured at k and a magnetic field of 5T. Further, the surface of the NbTi filament was observed with an electron microscope to examine whether or not a CuTi compound was produced. The results are shown in Table 2.

Next, as a comparative example, four sets of S _Nb / S _{(NbTi + Nb)} were set outside the range specified by the method of the present invention, and from the set values, winding was performed around the NbTi rod according to the above formula (6). The thickness of the Nb layer to be attached was calculated, and an NbTi wire rod was produced according to the same manufacturing process as in the example of the present invention.

With respect to the wire rods of Comparative Examples 1 to 4 thus obtained, the diameter of the NbTi filament and the thickness of the Nb barrier layer were measured, and the cross-sectional area of the portion of the wire rod after the production, which was composed of the NbTi filament and the Nb barrier layer, was measured. The ratio S _Nb / S _{(NbTi + Nb)} of the cross-sectional area of the Nb barrier layer to was calculated.

The temperature of the wires of Comparative Examples 1 to 4.2 was 4.2.
The critical current density (Jc) was measured at k and a magnetic field of 5T. Further, the surface of the NbTi filament was observed with an electron microscope to examine whether or not a CuTi compound was produced. The results are shown in Table 2 together.

[0066]

[Table 2]

As is clear from the results of Tables 1 and 2, in the superconducting wire according to the example of the present invention manufactured by applying the method of the present invention, CuTi is formed on the surface of the NbTi filament.
It was confirmed that no formation of compounds was observed and the critical current characteristics assumed before the wire production was obtained.

On the other hand, in the superconducting wire of Comparative Example,
Despite the provision of the Nb barrier layer, it was found that due to the insufficient thickness of the Nb barrier layer, a CuTi compound was generated on the surface of the NbTi filament and the critical current characteristics did not reach the level expected. Also,
In the superconducting wire of Comparative Example, formation of the CuTi compound was not observed on the surface of the NbTi filament, but Nb
It can be seen that the ratio occupied by the barrier layer becomes too large, so that the critical current density is reduced in some cases.

[0069]

As described above, Nb according to the present invention
According to the method for producing a Ti superconducting wire, it is possible to efficiently obtain an NbTi superconducting wire having good superconducting properties while maintaining high soundness of the NbTi filament.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a manufacturing process of a conventional NbTi superconducting wire.

Claims (1)

[Claims] 1. The NbTi filament diameter is 1 to 50 μm.
NbT that has a critical current density (Jc) of 2,000 A / mm ² or more in a temperature range of 4.2 K and a magnetic field of 5 T
i A method for producing a superconducting wire, comprising providing a layer made of Nb around a core made of NbTi,
Cu or Cu alloy is compounded around it, 0-900
A first step of producing an NbTi single-core wire rod by performing plastic working in a temperature range of ℃, and bundling a plurality of single-core wire rods obtained in the first step
A second step of producing a NbTi multifilamentary wire by performing plastic working in a temperature range of 900 ° C., in the plastic working of the first step and the second step, from a barrier layer made of NbTi filaments and Nb The ratio S _Nb / S _{(NbTi + Nb)} of the cross-sectional area of the barrier layer made of Nb to the cross-sectional area of (Here, Df is the final NbTi filament diameter (μm)
Indicates. In the first step, a layer made of Nb having a predetermined film thickness is compounded around the core made of NbTi so as to satisfy the above condition (1).