JP2886202B2 - Method for producing NbTi alloy superconducting wire - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing an NbTi alloy superconducting wire.

[Conventional technology]

In a conventional method of manufacturing a NbTi alloy superconducting wire, first, a homogenizing heat treatment is applied following the melting and casting steps to produce a highly uniform NbTi alloy ingot. Then, the ingot as the starting material, and repeating the appropriate cold working to distribute it and precipitation heat treatment of alpha-Ti phase for the J _c improvement, was prepared the NbTi alloy superconducting wire. Observation of the internal microstructure of the NbTi alloy superconducting wire obtained in this way shows that the precipitation distribution of the α-Ti phase is not uniform, and high density and low density are mixed. the distribution becomes uneven, improvement of J _c was inhibited. This is due to fluctuations in the Ti concentration distribution of the NbTi alloy ingot, which is the starting material, so that a highly uniform control of the Ti concentration in the ingot was required.

[Problems to be Solved by the Invention] However, in the conventional method of manufacturing an NbTi alloy ingot, it is difficult to achieve a high uniformity of the Ti concentration, and it has been a limit to suppress the variation to at most ± 2% in a micro region. .

[Means and actions for solving the problem]

The present invention provides a method for producing an NbTi alloy superconducting wire that solves the above-mentioned problems, by subjecting an NbTi alloy material to processing of ε ≧ 3, and then performing hot extrusion in a temperature range of 650 ° C. to 850 ° C. And then performing heat treatment and wire drawing. Here, ε is defined by the following equation.

As described above, by actively introducing strong working and high-temperature heat treatment before the α-Ti phase precipitation heat treatment and the cold working to disperse it, the Ti concentration distribution can be controlled microscopically and uniformly. It is possible to The reason for this is that by applying processing, strain energy is introduced into the inside of the material, which is used as a driving force for recrystallization. In this way, the diffusion of atoms is promoted during the heat treatment at the time of hot extrusion, and the concentration fluctuation is reduced.

If the hot extrusion concentration is 850 ° C. or higher, the reaction between Cu and NbTi proceeds to generate an intermetallic compound of Cu _x Ti _y, which adversely affects the subsequent processing, which is not suitable. Also, 65
If the temperature is lower than 0 ° C., the reaction rate of the recrystallization becomes slow, which is not suitable. That is, if the temperature is 650 ° C. or lower, the heat treatment requires a long time, and the reaction of the Cu / NbTi interface proceeds in the composite as described above, which is inappropriate.

The reason why the epsilon ≧ 3 are that epsilon <strain energy as 3 the driving force is insufficient, because the crystal grains become disadvantageous for the optimization of the coarsened subsequent J _c.
It is desirable to use hot extrusion or the like as the strong working of ε ≧ 3.

〔Example〕

 Hereinafter, the present invention will be described based on examples.

Insert a single Nb-46.5wt% Ti ingot that has been heat-treated into a Cu tube with an outer diameter of 45mmφ and an inner diameter of 39mmφ, and cover it.
Hot extrusion was performed at a high temperature of 800 ° C. Ε = 6.2 (ε =
l _n (A ₀ / A), A ₀ : Cross-section before processing, A: Cross-section after processing), reduce the diameter and pack it again in Cu tube, 800 ℃
A second hot extrusion was performed at a high temperature of. Next, an intermediate heat treatment for α-Ti phase precipitation at 380 ° C. for 40 hours is performed on the material,
Intermediate processing of ε = 0.6 to 0.7 for dispersing the α-Ti phase was repeated five times. After final heat treatment, giving the process of epsilon = 4 to 6 J _c
Was measured. As a comparative example, changing the second round of extrusion temperature, other heat treatment processing conditions was measured J _c also materials were the same. Table 1 shows the results.

As is clear from Table 1, the higher the temperature in the second hot extrusion, the higher the _Jc value. this is,
Uniformity of the Ti concentration is promoted during extrusion between the second heat, conducted uniform precipitation in the subsequent alpha-Ti precipitation treatment is considered to be because an effective pinning center to J _c improved are uniformly dispersed.

Note that changing the ε after hot extrusion, a second round of extrusion temperature 800 ° C., and other processing conditions shows the result of measuring the J _c as described above in Table 2.

This result, epsilon is made when J _c also increases greatly.

〔The invention's effect〕

As described above, according to the present invention, the NbTi alloy material is subjected to strong working of ε ≧ 3, and then hot-extruded in the range of 650 ° C. to 850 ° C. to make the Ti concentration uniform, pinning centers can be uniformly introduced by heat treatment and wire drawing, there is excellent effect that J _c is improved.

────────────────────────────────────────────────── ─── front page continued (51) Int.Cl. ⁶ identifications FI C22F 1/00 683 C22F 1/00 683 684 684Z 685 685Z 694 694A 694B H01B 12/02 ZAA H01B 12/02 ZAA 13/00 563 13 / 00563Z (58) Fields investigated (Int. Cl. ⁶ , DB name) C22F 1/00 B21C 23/00 H01B 13/00 563 H01B 12/02

Claims (1)

(57) [Claims] Claims 1. An NbTi alloy material is subjected to processing of ε ≧ 3,
A method for producing an NbTi alloy superconducting wire, comprising performing hot extrusion in a temperature range of 650 ° C. to 850 ° C., and then performing heat treatment and wire drawing. Here, ε is defined by the following equation.