A nbti material for superconducting wire and method of making

Abstract

The application belongs to the technical field of superconducting wire, and relates to a NbTi material for superconducting wire and a preparation method thereof. The preparation method of the NbTi material comprises the following steps: melting, forging and forming NbTi ingots to obtain the NbTi material; at least once aging heat treatment is performed before the forging after the melting of the NbTi ingots; 1-3 times of aging heat treatment is performed during the forging; and 1-3 times of aging heat treatment is performed after the forging. The application solves the technical problems of low heat treatment efficiency and long production cycle during the preparation of the superconducting wire.

Description

Technical Field

[0001] This invention belongs to the field of superconducting wire technology, and relates to an NbTi material for superconducting wires and its preparation method. Background Technology

[0002] NbTi / Cu superconducting wires possess excellent processing characteristics, stable superconducting properties, and relatively low cost, making them widely used in superconducting magnets. With the development of superconducting technologies such as magnetic resonance imaging (MRI) and nuclear magnetic resonance imaging (NMR), the demand for high critical current density niobium-titanium superconducting materials is constantly increasing. However, niobium-titanium superconducting wires require multiple (≥3) aging heat treatments to generate a pinned phase in order to achieve a high critical current density. The total heat treatment time ranges from 100 to 500 hours, requiring significant resources such as manpower, electricity, furnace gas, and circulating water, thus lengthening the production cycle. Furthermore, during heat treatment, superconducting materials can only be coiled, leaving the central part of the heat treatment furnace empty and underutilized. Summary of the Invention

[0003] The purpose of this invention is to solve the technical problems of low heat treatment efficiency and long production cycle in the preparation of superconducting wires.

[0004] To achieve the above objectives, the present invention provides an NbTi material for superconducting wires and a method for preparing it to meet this need in the art.

[0005] On one hand, the present invention relates to a method for preparing NbTi material for superconducting wires, comprising: melting, forging and forming an NbTi ingot to obtain NbTi material;

[0006] After the NbTi ingot is smelted, at least one aging heat treatment is performed before the forging process; during the forging process, one to three aging heat treatments are performed.

[0007] After forging is completed, 1 to 3 aging heat treatments are performed.

[0008] Furthermore, in the method for preparing NbTi material for superconducting wires provided by the present invention, the total number of aging heat treatments performed before obtaining the NbTi material is 3 to 5.

[0009] On the other hand, the present invention relates to an NbTi rod for superconducting wires, comprising: preparing NbTi material using the above-described method for preparing NbTi material for superconducting wires, and forming the NbTi material into a rod shape to obtain the NbTi rod.

[0010] On the other hand, the present invention relates to a method for preparing a multi-core NbTi / Cu composite wire, which includes: using Nb as a barrier layer, loading the NbTi rod as described in claim 4 into a Cu tube to obtain an NbTi / Nb / Cu single-core ingot.

[0011] The NbTi / Nb / Cu single-core ingot is subjected to extrusion, multi-pass stretching, and at least one aging heat treatment to obtain NbTi / Nb / Cu single-core wire;

[0012] Multiple strands of the aforementioned NbTi / Nb / Cu single-core wires are soldered together using molten solder and a mold to obtain the multi-core NbTi / Cu composite wire.

[0013] Furthermore, in the method for preparing multi-core NbTi / Cu composite wire provided by the present invention, the temperature of the molten tin is 200-400°C, and the speed of passing through the molten tin is 30m / min-100m / min.

[0014] Furthermore, in the method for preparing multi-core NbTi / Cu composite wire provided by the present invention, the multi-strand consists of 7 to 1000 strands.

[0015] On the other hand, the present invention relates to a multi-core NbTi / Cu composite wire, which is prepared by the above-mentioned method for preparing multi-core NbTi / Cu composite wire.

[0016] Furthermore, in the method for preparing NbTi material for superconducting wires provided by the present invention or the method for preparing multi-core NbTi / Cu composite wires provided by the present invention, the aging heat treatment temperature is 295-520°C and the time is 3-60h.

[0017] On the other hand, the present invention relates to NbTi materials prepared by the above-mentioned method for preparing NbTi materials for superconducting wires, or NbTi rods for superconducting wires as described above, or the application of the above-mentioned multi-core NbTi / Cu composite wires in the preparation of superconducting wires.

[0018] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects or advantages:

[0019] (1) Unlike traditional niobium-titanium superconducting wires, which undergo aging heat treatment only during processing, this invention introduces multiple aging heat treatments during the production of NbTi material from NbTi ingots. This allows for the earlier formation of the superconducting pinned α-Ti phase, significantly increasing the critical current density of the niobium-titanium superconducting wire at high fields. If the number of heat treatments is less than 3, the performance is lower. If the number of heat treatments is more than 5, there is no significant improvement in performance.

[0020] (2) Unlike traditional niobium-titanium superconducting wires, which undergo aging heat treatment only during processing, this invention introduces multiple aging heat treatments during the NbTi ingot fabrication process. Copper is not introduced at this stage, avoiding the copper heat treatment inherent in traditional methods. This significantly improves heat treatment efficiency, increasing it by nearly three times. Using the same heat treatment furnace, this patented method can produce 9 tons of superconducting wires, while traditional methods can only produce 3 tons. This technique also reduces the risk of copper contamination of the superconducting phase during heat treatment, a risk associated with traditional methods.

[0021] (3) Tin liquid is a good welding agent that can effectively connect NbTi / Cu superconducting core wires. Tin has good thermal conductivity and can quickly dissipate the heat generated when applied to superconducting magnets, thus protecting the superconducting magnets. Detailed Implementation

[0022] The technical solution of the present invention will be described below with reference to the embodiments. However, the present invention is not limited to the following embodiments.

[0023] Unless otherwise specified, the experimental and detection methods described in the following embodiments are conventional methods; unless otherwise specified, the reagents and materials are commercially available.

[0024] Example 1

[0025] This embodiment provides a process for preparing a multi-core NbTi / Cu composite wire.

[0026] First, NbTi ingots are smelted. An aging heat treatment is performed once before forging the NbTi ingots, and twice during forging. After forging, the NbTi ingots undergo a final aging heat treatment. The aging heat treatment temperature is 300℃, the time is 60 hours, and the total number of heat treatments is 4. A large amount of superconducting pinned phase precipitates during the aging heat treatment.

[0027] Next, the NbTi rod, Nb plate, and Cu tube were cleaned. After cleaning, the NbTi rod was completely wrapped with the Nb plate and then inserted into the Cu tube to prepare an NbTi / Nb / Cu single-core ingot. NbTi / Nb / Cu single-core wire was obtained through extrusion, stretching, and a single aging heat treatment. Seven strands of NbTi / Nb / Cu single-core wire were welded together with molten tin and a mold to prepare a high-performance, multi-core NbTi / Cu composite wire. The single aging heat treatment resulted in a diameter of Φ12.87 mm, and the final single-core wire diameter was Φ1.0 mm with a final strain of 5.11. The total heat treatment time was 290 hours.

[0028] Example 2

[0029] This embodiment provides a process for preparing a multi-core NbTi / Cu composite wire.

[0030] First, NbTi ingots are smelted. An aging heat treatment is performed once before forging the NbTi ingots, and once more during forging. After forging, the NbTi ingots undergo a third aging heat treatment. The aging heat treatment temperature is 400℃, the time is 38 hours, and the total number of heat treatments is 3. A large amount of superconducting pinned phase precipitates during the aging heat treatment.

[0031] Next, the NbTi rod, Nb plate, and Cu tube were cleaned. After cleaning, the NbTi rod was completely wrapped with the Nb plate and then inserted into the Cu tube to prepare an NbTi / Nb / Cu single-core ingot. NbTi / Nb / Cu single-core wire was obtained through extrusion, stretching, and a single aging heat treatment. 520 strands of NbTi / Nb / Cu single-core wire were then welded together with molten solder and a mold to prepare a high-performance, multi-core NbTi / Cu composite wire. The single aging heat treatment resulted in a diameter of 7.00 mm, and the final wire diameter was 1.50 mm with a final strain of 3.08. The total heat treatment time was 164 hours.

[0032] Example 3

[0033] This embodiment provides a process for preparing a multi-core NbTi / Cu composite wire.

[0034] First, NbTi ingots are smelted. An aging heat treatment is performed once before forging the NbTi ingots, and three more aging heat treatments are performed during forging. After forging, the NbTi ingots undergo a final aging heat treatment. The aging heat treatment temperature is 500℃, the time is 10 hours, and the total number of heat treatments is 5. A large amount of superconducting pinned phase precipitates during the aging heat treatment.

[0035] Next, the NbTi rod, Nb plate, and Cu tube were cleaned. After cleaning, the NbTi rod was completely wrapped with the Nb plate and then inserted into the Cu tube to prepare an NbTi / Nb / Cu composite ingot. NbTi / Nb / Cu composite wire was obtained through extrusion, stretching, and a single aging heat treatment. 900 strands of NbTi / Nb / Cu single-core wire were welded together with molten solder and a mold to prepare a high-performance, multi-core NbTi / Cu composite wire. The single aging heat treatment resulted in a diameter of Φ16.50mm, and the final wire diameter was Φ0.50mm with a final strain of 6.99. The total heat treatment time was 100 hours.

[0036] Comparative Example 1

[0037] Similar to Example 1, except that an aging heat treatment was performed once before forging the NbTi ingot and once during forging, for a total of two heat treatments. The performance at the critical current density was comparable to that of Examples 1-3. The total heat treatment time was 230 hours.

[0038] Comparative Example 2

[0039] Similar to Example 1, except that a conventional multi-core NbTi / Cu composite wire fabrication process was used (fabrication steps refer to CN104201278A; the NbTi rod was not subjected to aging heat treatment, but aging heat treatment was performed during the fabrication of single-core rods and composite rods). The performance at the critical current density was comparable to that of Examples 1-3. The total heat treatment time was 480 hours.

[0040] The critical current density measurement results of the niobium-titanium superconducting wires prepared in Examples 1 to 3 and Comparative Examples 1 to 2 are shown in Table 1.

[0041] Table 1 Critical Current Density of Niobium-Titanium Superconducting Wires

[0042] <![CDATA[Jc(4.2K,5T)A / mm 2 ]]> Example 1 3090 Example 2 3100 Example 3 3150 Comparative Example 1 2600 Comparative Example 2 3095

[0043] As can be seen from Examples 1-3 and Comparative Examples 1-2 in Table 1, unlike conventional niobium-titanium superconducting wires which undergo aging heat treatment only during processing, this invention introduces multiple aging heat treatments when converting NbTi ingots into NbTi materials. This allows for the earlier formation of the superconducting pinned α-Ti phase, significantly increasing the critical current density of the niobium-titanium superconducting wire at high fields. If the number of heat treatments is less than three, the performance is lower.

[0044] As described above, the basic principles, main features, and advantages of the present invention have been well described. The above embodiments and specifications are merely descriptions of preferred embodiments of the present invention, and the present invention is not limited to the above embodiments. Various changes and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit and scope of the present invention should fall within the protection scope defined by the present invention.

Claims

1. A method for preparing a multi-core NbTi / Cu composite wire, characterized in that, include: NbTi ingots are smelted, forged, and shaped to obtain NbTi material, and the NbTi material is shaped into rods to obtain NbTi rods; After melting the NbTi ingot, at least one aging heat treatment is performed before forging; during forging, 1 to 3 aging heat treatments are performed. After forging is completed, 1 to 3 aging heat treatments are performed. The total number of aging heat treatments performed before obtaining the NbTi material is 3 to 5. Using Nb as a barrier layer, the NbTi rod is inserted into a Cu tube to obtain an NbTi / Nb / Cu single-core ingot; The NbTi / Nb / Cu single-core ingot is subjected to extrusion, multi-pass stretching, and at least one aging heat treatment to obtain NbTi / Nb / Cu single-core wire; The multi-core NbTi / Nb / Cu composite wire is prepared by welding multiple strands of the NbTi / Nb / Cu single-core wire together with molten solder and a mold. The aging heat treatment described herein is performed at a temperature of 295~520℃ for a time of 3~60h.

2. The method for preparing multi-core NbTi / Cu composite wire according to claim 1, characterized in that, The molten tin is passed through a molten tin at a temperature of 200-400°C and at a speed of 30-100 m / min.

3. The method for preparing multi-core NbTi / Cu composite wire according to claim 1, characterized in that, The number of shares mentioned refers to 7 to 1000 shares.