JPH0443513A - Manufacture of nb3sn superconductive wire material - Google Patents

Abstract

PURPOSE:To increase the critical current density and to reduce the AC loss by using an Nb-based alloy in which a minute amount of Ti, Hf, or Ta is added to the core. CONSTITUTION:In the manufacturing of Nb3Sn superconductor wire material, a compound material of an Nb-based alloy material including 0.5 to 5 atomic % of either one sort of Ti, Hf, or Ta, and a Cu-based alloy material including 3 to 8.5 atomic % of Sn is used as the said compound material, and processed. As a result, a ribbon-form deformation of a filament is suppressed, and the proximity effect is reduced. And since the adding of the alloy elements has a growth promoting effect of Nb3Sn, an Nb3Sn wire material of a low AC loss and a high critical current can be manufactured easily.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing an N b a S n superconducting wire, particularly a N b S S n superconducting wire with low AC loss suitable for AC applications. .

[Prior art] N b s S n wire has a much higher critical temperature than Nb Ti wire, so N b a S n wire has low AC loss.
Once N-wires are developed, they will have a major impact on power systems such as generators and transformers.

In superconducting wires intended for AC applications, the filament diameter must be made as small as possible in order to reduce hysteresis loss caused by the pinning force of the superconductor, and theoretically, N b 3S n has a diameter of 0. 05μ
It is said that 0.1 μm is optimal for NbTi.

However, the hysteresis loss does not necessarily have a one-to-one correspondence with the filament diameter of the superconductor, and when the filament spacing falls below a certain limit, a proximity effect occurs and the hysteresis loss increases. Therefore, even if the wire has a theoretically optimal filament diameter, the hysteresis loss will not necessarily be reduced in relation to the filament spacing.

Up to now, NbaSn wires with filament diameters of 0.1 μm or less have been prototyped using internal diffusion methods or external diffusion methods for the purpose of AC applications. However, when the diameter of the Nb filament is processed to be 1 μm or less, the Nb filament is deformed into a ribbon shape, and each filament locally becomes extremely close to each other, and furthermore, coalescence occurs partially after heat treatment. For this reason, the filament spacing becomes smaller than the theoretical value when the filament is processed while maintaining its circular cross section, and the hysteresis loss of the wire increases due to the so-called proximity effect, and the effective filament diameter ranges from several times the theoretical value to several times the theoretical value. The result was calculated to be 10 times more expensive.

[Problems to be Solved by the Invention] If the wire structure is such that the filament spacing is large enough to prevent the proximity effect from occurring even if ribbon-like deformation of the Nb filaments occurs, the volume ratio of the matrix material to the Nb3Sn superconductor can be reduced. That is, the matrix ratio increases and the critical current density with respect to the cross-sectional area of the wire decreases, which is not preferred in practice. Therefore, in order to reduce the hysteresis loss without reducing the critical current density of the wire, it is effective to suppress the ribbon-like deformation of the Nb filament as much as possible.

An object of the present invention is to eliminate the drawbacks of the prior art described above, and to provide an improved N
An object of the present invention is to provide a baSn superconducting wire.

[Means for Solving the Problems] The gist of the present invention is to use a Nb-based alloy as a core material in a NbaSn superconducting wire for AC use, thereby reducing the filament diameter to 1 μm or less. suppresses the ribbon-like deformation of the filament when
It is designed to achieve high critical current density and low AC loss.

In the case of the present invention, alloying elements in the Nb-based alloy include:
Ti, Hf or Ta is effective, and the amount added is 0.1
~5 atomic % is suitable. If the amount added exceeds 5 at %, the critical temperature of the wire will drop, which is undesirable. Furthermore, if the amount added is less than 0.1 atomic %, the effect of suppressing ribbon-like deformation when the filament diameter becomes small is lost.

When the amount added is in the range of 0.1 to 5 atomic %, in addition to the above-mentioned effect of suppressing ribbon-like deformation, there is an effect of promoting the formation of Nb Sn during heat treatment, and the critical current characteristics are also improved.

Regarding the matrix Cu-Sn alloy, the more 5njl, the easier it is to generate N b s S n , but 5
When njl exceeds 8.5 atomic %, Sn is not completely dissolved in Cu, impairing workability.

The degree of ribbon-like deformation of the filament is also related to the deformation resistance and work hardening properties of the matrix material.
The effect of suppressing ribbon-like deformation becomes remarkable for the above Cu-Sn alloys.

[Example] Examples of the present invention will be described below.

Each of Nb, Nb-1 atomic% Ti, Nb-1 atomic% Hf and Nb-1 atomic% Ta was prepared as the core material, Cu-5 atomic% Sn was prepared as the matrix material, and Ta was prepared as the barrier. A periphery-stabilized copper type N b 3S n wire material having the specifications shown in Table 1 was manufactured by processing in the same manner as before.

During processing, intermediate annealing was performed at 450 to 500°C for 30 minutes, and the final outer diameter (w)/filament diameter (μm) was 0.2810.5.0.3810.7.0.4B1.
It was finished into a wire rod with a diameter of 0.9. Next, N is added to these wires.
Heat treatment was performed at 500 to 600°C to generate baSn.

Table 1 Each of the obtained wire rods was subjected to SEM (scanning electron microscopy) observation of the tensile fracture surface, measurement of critical current characteristics, measurement of magnetization characteristics, etc.

FIG. 1 shows an enlarged cross section of an Nb-1 atomic % Hf core wire with a filament diameter of 0.9 μm. In addition,
In Fig. 1, numeral 1 is Cu as a stabilizing material, 2 is a barrier made of Ta, and 3 is a core of Nb-1 atomic % Hf (1
51), 4 indicates a Cu-5 atomic % Sn matrix.

In SEM observation of the tensile fracture surface of the wire, ribbon-like deformation of the core was more clearly observed in the wire with a Nb-based alloy containing 1 at% of Ti, Hf, or Ta than in the Nb-core wire. observed to be suppressed.

Figure 2 shows an SEM photograph of the tensile fracture surface of a Nb core wire with a filament diameter of 0.9 μm heat-treated at 600°C for 100 hours, and Figure 3 shows a Nb-core wire with a filament diameter of 0.9 μm heat-treated at 600°C for 100 hours. This is a SEM photograph of a tensile fracture surface of a 1 atomic % Ti core wire.

In addition, in FIG. 2 and FIG. 3, the code 5 is N b 3
The Sn compound layer, 6 is an unreacted core, and 7 is a Cu-8n alloy matrix.

As is clear from FIGS. 2 and 3, even under the same heat treatment conditions, it was observed that the Nb2Sn layer was formed thicker in the alloy core wire, and the addition of a small amount of Ti1Hf or Ta It can be seen that it has the effect of promoting the generation of Sn.

Figure 4 shows the critical current density (non-Cu
This figure shows the relationship between J c) and the ratio of magnetization hysteresis loss. At any filament diameter, this ratio is higher for the alloy core wire than for the Nb core wire;
It can be seen that high critical current and low hysteresis loss can be achieved with the alloy core wire containing Hf or Ta.

[Effects of the Invention] As is clear from the above description, according to the present invention, Nb with a filament diameter of 1 μm or less intended for AC use
In the 3S n-wire, by using an Nb-based alloy with a small amount of Ti, Hf, or Ta added to the core, the ribbon-like deformation of the filament is suppressed and the proximity effect is reduced, and the addition of the alloying element is s S n
It also has the effect of promoting the formation of Nb a S n wire with low AC loss and high critical current.

[Brief explanation of drawings]

■ 1st △ is a photomicrograph showing the cross-sectional shape of a superconducting wire according to an embodiment of the method according to the present invention, Fig. 2 is a photomicrograph showing the condition of a tensile fracture surface of a superconducting wire according to the prior art, and Fig. 3
The figure is a micrograph showing the state of the tensile fracture surface of a superconducting wire according to an example of the present invention, and FIG. 4 is a graph showing the relationship between critical current density and magnetization hysteresis loss with respect to the filament diameter of each wire. 3: Nb-1 atomic% Hf core, 4: Cu-5 atomic% Sn matrix, 5: N
b 3S n compound layer. Fig. 1 Fig. 4 Agent Patent attorney Fujio Sato Filament diameter (μrn1 Procedural amendment, Kae, 2 Name of the invention

Claims (1)

[Claims] 1. A method for producing an Nb_3Sn superconducting wire, in which a wire obtained by reducing the area of a composite of a Nb material and a Cu-Sn alloy material while subjecting it to intermediate annealing is subjected to heat treatment to generate Nb_3Sn, in which the composite as Ti, Hf or T
Processing is carried out using a composite of a Nb-based alloy material containing 0.5 to 5 at.% of any one of a. and a Cu-based alloy material containing 3 to 8.5 at.% of Sn. Method for manufacturing Nb_3Sn superconducting wire