JP3031477B2 - Nb Lower 3 Method for Manufacturing Sn Superconducting Wire - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a Nb ₃ Sn superconducting wire, particularly a low AC loss Nb ₃ Sn superconducting wire suitable for AC use.

[Prior art] Nb ₃ Sn wire has a much higher critical temperature than NbTi wire, so if a low AC loss Nb ₃ Sn wire is developed, it will have a large impact on power systems such as generators and transformers. Make an impact.

In superconducting wire for the purpose of AC applications, in order to reduce the hysteresis loss due to pinning force of the superconductor, it is necessary to minimize the filament diameter, in theory Nb ₃ Sn in 0.05 .mu.m, NbTi Then
It is said that 0.1 μm is optimal.

However, the hysteresis loss does not always correspond one-to-one with the filament diameter of the superconductor. When the filament interval becomes less than a certain limit, the proximity effect occurs and the hysteresis loss increases. Therefore, even in the case of a wire having a filament diameter which is theoretically optimized, the hysteresis loss is not necessarily reduced in relation to the filament interval.

Until now, the filament diameter of Nb ₃ Sn wire rod has been reduced by the internal diffusion method or the external diffusion method for AC applications.
Wires of 0.1 μm or less have been trial manufactured. However, when the diameter of the Nb filament is processed to 1 μm or less, the Nb filament is deformed into a ribbon shape, and the filaments locally remarkably come close to each other, and further, partially coalesce after the heat treatment. For this reason, the filament interval becomes smaller than the theoretical value when the filament is processed while maintaining the circular cross section, the hysteresis loss of the wire increases due to the so-called proximity effect, and the effective filament diameter is several times to several times the theoretical value. The result is calculated to be 10 times the value.

[Problems to be Solved by the Invention] When a wire structure is used in which the filament interval is so large that the proximity effect does not occur even if ribbon-like deformation of the Nb filament occurs, the volume ratio of the matrix material to the Nb ₃ Sn superconductor, that is, the matrix The ratio increases, and the critical current density with respect to the wire cross-sectional area decreases, which is not practically preferable. Therefore, in order to reduce the hysteresis loss without lowering 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 above-mentioned disadvantages of the prior art,
Improved critical current density and low AC loss
An object of the present invention is to provide an Nb ₃ Sn superconducting wire.

[Means for Solving the Problems] The gist of the present invention resides in that an Nb-based alloy is used as a core material in an Nb ₃ Sn superconducting wire for AC use, thereby reducing the filament diameter to 1 μm or less. The present invention suppresses the ribbon-like deformation of the filament, and achieves a high critical current density and a low AC loss.

In the case of the present invention, as an alloy element in the Nb-based alloy,
Ti, Hf or Ta is effective, and its addition amount is suitably 0.1 to 5 atomic%. If the addition amount exceeds 5 atomic%, the critical temperature of the wire is undesirably lowered. In addition, the addition amount is 0.1
If the content is less than atomic%, the effect of suppressing ribbon-shaped deformation when the filament diameter becomes small is lost.

When the addition amount is in the range of 0.1 to 5 atomic%, in addition to the effect of suppressing the ribbon-like deformation, there is an effect of accelerating the generation of Nb ₃ Sn during the heat treatment, and the critical current characteristics are also improved.

The Cu-Sn alloy matrix, but can produce easily as Nb ₃ Sn Sn amount is large, Sn when Sn content exceeds 8.5 atomic% does not total amount dissolved in Cu, workability is impaired.

Since the degree of ribbon-like deformation of the filament is also related to the deformation resistance and work hardening characteristics of the matrix material, when the above-mentioned Nb-based alloy is used for the core, the Sn amount is 3 atomic% or more with respect to the Cu-Sn alloy. As a result, the effect of suppressing ribbon-like deformation becomes remarkable.

[Example] Hereinafter, an example of the present invention will be described.

Conventionally, Nb, Nb-1at.% Ti, Nb-1at.% Hf and Nb-1at.% Ta are prepared as the core material, Cu-5at.% Sn as the matrix material, and Ta as the barrier. In the same manner as described above, an outer periphery stabilized copper-type Nb ₃ Sn wire having the specifications shown in Table 1 was produced.

Processing is performed while performing intermediate annealing at 450-500 ° C for 30 minutes.
Finally, the outer diameter (mm) / filament diameter (μm) are each 0.
Finished to 28 / 0.5, 0.38 / 0.7, 0.48 / 0.9 wire. Next, these wires were subjected to a heat treatment at 500 to 600 ° C. in order to generate Nb ₃ Sn.

Each of the obtained wires was subjected to SEM (scanning electron microscope) observation of a tensile fracture surface, measurement of critical current characteristics, measurement of magnetization characteristics, and the like.

FIG. 1 shows Nb-1 atomic% H having a filament diameter of 0.9 μm.
2 shows an enlarged cross section of an f-core wire rod. The first
In the figure, reference numeral 1 denotes Cu as a stabilizing material, 2 denotes a barrier made of Ta, 3 denotes a core of Nb-1 at% Hf (151 pieces), and 4 denotes C
2 shows a matrix of u-5 atomic% Sn.

In the SEM observation of the tensile fracture surface of the wire, compared with the Nb core wire, 1 atomic% of Ti, Hf or Ta was added to Nb.
It was observed that the wire having the base alloy as the core had the ribbon-like deformation of the core suppressed more clearly.

Fig. 2 shows the filament diameter which was heat treated at 600 ° C for 100 hours.
The SEM photograph of the tensile fracture surface of the 9 μm Nb core wire is shown in FIG.
The figure also shows the filament diameter which was heat treated at 600 ° C for 100 hours.
It is the SEM photograph of the tensile fracture surface of a 9 micrometer Nb-1 atomic% Ti core wire.

2 and 3, reference numeral 5 denotes an Nb ₃ Sn compound layer, 6 denotes an unreacted core, and 7 denotes a matrix of a Cu—Sn alloy.

As is clear from FIGS. 2 and 3, even under the same heat treatment conditions, it was observed that the alloy core wire had a thicker Nb ₃ Sn layer, and the addition of a small amount of Ti, Hf or Ta was ₃ Sn
It has an effect of promoting the generation of

Fig. 4 shows the relationship between the critical current density per non-copper cross-sectional area (non Cu Jc) and the magnetization history loss at 1T (tesla) with respect to the filament diameter when the wires shown in Table 1 were heat-treated at 575 ° C for 100 hours. It is shown. Regardless of the filament diameter, this ratio is higher for the alloy core wire than for the Nb core wire, and high critical current and low hysteresis loss are achieved with the alloy core wire to which Ti, Hf or Ta is added. I understand.

[Effects of the Invention] As is clear from the above description, according to the present invention, Nb ₃ S having a filament diameter of 1 μm or less for AC use is used.
In n-wires, N with a small amount of Ti, Hf or Ta added to the core
By using the b-based alloy, the ribbon-like deformation of the filament is suppressed, the proximity effect is reduced, and the addition of the alloy element also has an effect of promoting the generation of Nb ₃ Sn, so that a low AC loss, and a high critical current There is an effect that an Nb ₃ Sn wire can be easily obtained.

[Brief description of the drawings]

FIG. 1 is a partial schematic diagram of a micrograph showing a cross-sectional shape of a superconducting wire according to an embodiment of the method according to the present invention, and FIG. 2 is a schematic diagram of a microscopic photograph showing a state of a tensile fracture surface of a conventional superconducting wire. FIG. 3 is a schematic diagram of a micrograph showing a state of a tensile fracture surface of a superconducting wire according to an embodiment of the present invention, and FIG. 4 is a graph showing a relationship between a critical current density and a magnetization history loss with respect to a filament diameter of each wire. is there. 3: Nb-1 at% Hf core, 4: Cu-5 at% Sn matrix, 5: Nb ₃ Sn compound layer

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Kyoji Tachikawa 1117 Kita-Kaneme, Hiratsuka-shi, Kanagawa Prefecture Tokai University Faculty of Engineering, Department of Metallic Materials Engineering (56) References JP-A-57-54260 (JP, A)

Claims (1)

(57) [Claims] To 1. A Nb material and wire the composite obtained by reduction process while subjected to intermediate annealing between the Cu-Sn alloy, Nb ₃ Sn for alternating the heat treatment for producing a Nb ₃ Sn In the method for producing a superconducting wire, any one of Ti, Hf and Ta is used as the composite in 0.1%.
The present invention is characterized in that the filament diameter of the Nb-based alloy material is reduced to 1 μm or less by using a composite of an Nb-based alloy material containing 5 to 5 atomic% and a Cu-based alloy material containing 3 to 8.5 atomic% Sn. Nb
Manufacturing method of ₃ Sn superconducting wire.