Multi-core Nb3Sn composite wire preparation method and composite wire

Abstract

The invention discloses a preparation method of a multi-core Nb3Sn composite wire and the composite wire. The method comprises the following steps: loading an Nb rod into an oxygen-free copper pipe to obtain a CuNb single-core rod; the CuNb single-core rods and the hexagonal copper core rods are sequentially arranged in a CuMn alloy pipe at intervals to obtain a multi-core CuNb composite sheath, and then the multi-core CuNb composite sheath is machined into a CuNb composite rod; the CuNb composite rod is machined into a CuNb composite pipe; the SnTi alloy bar is loaded into the CuNb composite tube to obtain a sub-component; a hexagonal CuMn subcomponent is obtained through machining; the hexagonal CuMn subcomponent and the SnCu alloy bar are assembled into a Ta tube and then integrally assembled into an oxygen-free copper tube to obtain a composite wire, and the composite wire is processed to obtain the Nb3Sn superconducting wire. CuNb single core rods on the outermost layer are adjusted to be in discontinuous close arrangement, the problem that machining cracking is prone to occurring in the subcomponent preparation stage due to the fact that Cu on the outer portions of the single core rods is little is solved, the deformation consistency of the wire in the composite wire machining stage is further enhanced by using the CuMn alloy on the outer portions of the subcomponents, it is also guaranteed that the wire cannot crack when stretched, and the service life of the wire is prolonged. The fan-shaped SnCu alloy bars are additionally arranged, so that sufficient Sn is ensured when the wire Nb generates Nb3Sn.

Description

Technical Field

[0001] The present invention relates to the field of air purification, and particularly to a preparation method of a multi-core Nb3Sn composite wire and the composite wire. Background Art

[0002] The Nb3Sn superconducting material has been widely used in large controllable thermonuclear fusion devices, electron colliders, extremely high magnetic field magnet devices, etc. In order to meet the market demand for higher magnetic field usage scenarios in the future, the critical current density performance of Nb3Sn superconducting wires needs to be continuously improved. However, high-performance designed wires usually mean a continuous reduction in the Cu content that plays a role in co-deformation, which will cause problems such as wire cracking and uneven deformation during wire processing. Summary of the Invention

[0003] Embodiments of the present invention provide a preparation method of a multi-core Nb3Sn composite wire and the composite wire, which are used to solve the problems of wire cracking and uneven deformation that easily occur during wire processing caused by the continuous reduction of the Cu content that plays a role in co-deformation in the prior art.

[0004] On the one hand, embodiments of the present invention provide a preparation method of a multi-core Nb3Sn composite wire, including: Putting Nb rods into oxygen-free copper tubes to obtain CuNb single-core rods; Arranging the outermost CuNb single-core rods and hexagonal copper core rods in the CuMn alloy tube at intervals in a close-packed hexagonal form to obtain a multi-core CuNb composite sheath; Processing the CuNb composite sheath into a CuNb composite rod; Drilling the center of the CuNb composite rod to obtain a CuNb composite tube; Putting SnTi alloy rods into the CuNb composite tube to obtain sub-elements; Processing the sub-elements to obtain hexagonal CuMn sub-elements; Assembling the hexagonal CuMn sub-elements and fan-shaped SnCu alloy rods into a Ta tube and then assembling the whole into an oxygen-free copper tube to obtain a composite wire; Processing the composite wire to obtain Nb3Sn superconducting wire.

[0005] In a possible implementation manner, before putting the Nb rods into the oxygen-free copper tubes to obtain CuNb single-core rods, it further includes hot isostatic pressing, extrusion, straightening, and cold drawing of the Nb rods and the oxygen-free copper tubes.

[0006] In a possible implementation manner, processing the CuNb composite sheath into a CuNb composite rod is to process the CuNb composite sheath through hot isostatic pressing, extrusion, straightening, skinning, and multi-pass cold drawing processes to obtain the CuNb composite rod.

[0007] In a possible implementation, obtaining the hexagonal CuMn sub-component by processing the sub-component is to subject the sub-component to multi-pass cold drawing to obtain the hexagonal CuMn sub-component.

[0008] In a possible implementation, before assembling the hexagonal CuMn sub-component and the fan-shaped SnCu alloy rod into a Ta tube and then assembling the whole into an oxygen-free copper tube to obtain a composite wire, the following steps are further included: Closely packing and assembling the hexagonal CuMn sub-component and the fan-shaped SnCu alloy rod inside the Ta tube.

[0009] In a possible implementation, before processing the composite wire to obtain Nb3Sn superconducting wire, the following steps are further included: Performing multi-pass cold drawing and heat treatment processes on the composite wire.

[0010] On the other hand, an embodiment of the present invention provides a multi-core Nb3Sn composite wire, and the multi-core Nb3Sn composite wire is prepared by the method described in any one of the above.

[0011] A method for preparing a multi-core Nb3Sn composite wire and the composite wire in the present invention have the following advantages: (1) By adjusting the outermost CuNb single-core rod of the CuNb composite sheath to non-continuous close packing, the problem of easy processing cracking due to less external Cu in the sub-component preparation stage is solved.

[0012] (2) By using a CuMn alloy outside the sub-component, the deformation consistency of the wire during the composite wire processing stage is further enhanced, and it is also ensured that the wire will not crack during stretching.

[0013] (3) By adding a fan-shaped SnCu alloy rod, it is ensured that there is sufficient Sn when Nb in the wire generates Nb3Sn. Description of the Drawings

[0014] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0015] Figure 1 It is a flowchart of a method for preparing a multi-core Nb3Sn composite wire provided by an embodiment of the present invention; Figure 2 It is a structural diagram of a multi-core Nb3Sn composite wire provided by an embodiment of the present invention; Figure 3A CuNb single core rod for a multi-core Nb3Sn composite wire provided by an embodiment of the present invention; Figure 4 A CuNb composite rod for a multi-core Nb3Sn composite wire provided by an embodiment of the present invention; Figure 5 An assembled CuMn-type sub-element for a multi-core Nb3Sn composite wire provided by an embodiment of the present invention; Figure 6 An SnCu alloy rod for a multi-core Nb3Sn composite wire provided by an embodiment of the present invention. Detailed implementation manners

[0016] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0017] Figure 1 A flowchart of a preparation method for a multi-core Nb3Sn composite wire provided by an embodiment of the present invention; an embodiment of the present invention provides a preparation method for a multi-core Nb3Sn composite wire, including: Putting the Nb rod into an oxygen-free copper tube to obtain a CuNb single core rod; Arranging the outermost CuNb single core rod and the hexagonal copper core rod in the CuMn alloy tube at intervals in a close-packed hexagonal form to obtain a multi-core CuNb composite sheath; Processing the CuNb composite sheath into a CuNb composite rod; Drilling the center of the CuNb composite rod to obtain a CuNb composite tube; Putting the SnTi alloy rod into the CuNb composite tube to obtain a sub-element; Processing the sub-element to obtain a hexagonal CuMn sub-element; Assembling the hexagonal CuMn sub-element and the fan-shaped SnCu alloy rod into a Ta tube and then assembling the whole into an oxygen-free copper tube to obtain a composite wire; Processing the composite wire to obtain Nb3Sn superconducting wire; Before putting the Nb rod into the oxygen-free copper tube to obtain the CuNb single core rod, it further includes subjecting the Nb rod and the oxygen-free copper tube to hot isostatic pressing, extrusion, straightening, and cold drawing; Processing the CuNb composite sheath into a CuNb composite rod is to process the CuNb composite sheath through hot isostatic pressing, extrusion, straightening, peeling, and multi-pass cold drawing processes to obtain the CuNb composite rod; The hexagonal CuMn subgroup element is obtained by subjecting the subgroup element to multi-pass cold drawing; Before assembling the hexagonal CuMn subgroup element and the sector-shaped SnCu alloy rod into the Ta tube and then assembling the whole into the oxygen-free copper tube to obtain the composite wire, the following steps are further included: Closely packing the hexagonal CuMn subgroup element and the sector-shaped SnCu alloy rod inside the Ta tube; Before processing the composite wire to obtain the Nb3Sn superconducting wire, the following steps are further included: Performing multi-pass cold drawing and heat treatment processes on the composite wire.

[0018] Exemplarily, as Figure 2 、 3 shown in 4, 5, and 6, the inner diameter of the oxygen-free copper tube for loading the Nb rod into the oxygen-free copper tube to obtain the CuNb single-core rod is 100 - 310 mm, the outer diameter is 115 - 335 mm, and the size of the Nb rod is 100 - 305 mm; the hexagonal forming size of the CuNb single-core rod is 2.2 - 11 mm, and the copper ratio is 0.1 - 0.32; the hot isostatic pressing temperature during processing is 650 - 720 °C, the extrusion temperature is 450 - 550 °C, the extrusion speed is 10 - 20 mm / s, the straightening accuracy is an error of 1 mm per 3 meters, and the cold drawing processing rate between passes does not exceed 30%.

[0019] The size of the hexagonal copper core rod is 2.2 - 11 mm, the inner diameter of the CuMn alloy tube is 86 - 430 mm, the outer diameter is 96 - 450 mm, and the atomic proportion of the Mn element in the CuMn alloy is 0.5 - 6%; The center of the CuMn tube is closely packed with the hexagonal copper core rod, the outermost layer of CuNb single-core rods and the hexagonal copper core rod are alternately and closely packed, and the outermost layer of CuNb single-core rods is not continuously arranged.

[0020] The size of the CuNb composite rod is Φ25 - Φ100 mm; the hot isostatic pressing temperature for processing the CuNb composite sheath into the CuNb composite rod is between 650 - 720 °C, the extrusion temperature is between 450 - 550 °C, the extrusion speed is 10 - 20 mm / s, the straightening accuracy is an error of 1 mm per 3 meters, the peeling amount is between 2 - 5%, peeling is performed once, and the cold drawing processing rate between passes does not exceed 30%.

[0021] When drilling the center of the CuNb composite rod to obtain the CuNb composite tube, the drilling size is between 10 - 45 mm, and the atomic proportion of the Ti element in the SnTi alloy rod is 0.7 - 2%; The cold drawing processing rate of the subgroup element in multi-pass does not exceed 30%, the forming size of the hexagonal CuMn subgroup element is 3 - 6 mm, and the copper ratio is between 0.1 - 0.27.

[0022] In the composite wire, the CuMn subgroup elements have a close-packed structure, and the number of subgroup elements is 61 to 169; In the SnCu alloy, the proportion of Cu atoms is 1 to 3%. The SuCn alloy rod is in a fan shape and is used to fill the voids of the close-packed CuMn subgroup elements near the Ta tube. The number is 6. The remaining voids inside the composite wire are filled with CuMn alloy rods with a diameter of Φ2 mm, and the Mn content is the same as the corresponding content in the subgroup elements; The Ta tube has a size of Φ47 mm and a thickness of 1 mm. The outer diameter of the oxygen-free copper tube is Φ53 to Φ72 mm, and the inner diameter is Φ48 mm. The copper super ratio of the composite wire is 0.3 to 1.5; When the diameter of the composite wire is greater than Φ10 mm, the multi-pass cold drawing processing rate is 15 to 30%. When the diameter of the composite wire is less than Φ10 mm, the multi-pass cold drawing processing rate is 8 to 15%; The heat treatment process is: 340°C / 96h + 600°C / 72h + 650°C / 96h.

[0023] In a possible embodiment, examples are listed according to the above method as follows: Example 1 1) Assemble a Nb rod with a diameter of 100 mm into an oxygen-free copper tube with an outer diameter of 115 mm and an inner diameter of 100 mm, and then pass the whole through processes such as hot isostatic pressing, extrusion, straightening, and cold drawing to prepare a hexagonal CuNb single-core rod with a size of 2.2 mm and a copper ratio of 0.2. The hot isostatic pressing temperature is 650°C, the extrusion temperature is 450°C, the extrusion speed is 20 mm / s, the straightening accuracy is 1 mm error per 3 meters, and the cold drawing processing rate between passes does not exceed 30%.

[0024] 2) Assemble the CuNb single-core rod in step 1) and a hexagonal copper core rod with a size of 2.2 mm into a CuMn alloy tube in a close-packed hexagonal form. The center of the CuMn tube is filled with the hexagonal copper core rod in a close-packed manner to form a multi-core CuNb composite sheath. The outermost CuNb single-core rod is in a non-continuous close-packed arrangement, alternately close-packed with the hexagonal copper core rod. The inner and outer diameters of the CuMn alloy tube are Φ86 / Φ96 mm, and the proportion of Mn atoms is 0.5%.

[0025] 3) Pass the CuNb composite sheath through processes such as hot isostatic pressing, extrusion, straightening, skiving, and multi-pass cold drawing to prepare a CuNb composite rod with an outer diameter of Φ25 mm. The hot isostatic pressing temperature is 650°C, the extrusion temperature is 450°C, the extrusion speed is 15 mm / s, the straightening accuracy is less than 1 mm deviation per 3 meters, the skiving amount is 2.1%, and the multi-pass cold drawing processing rate is within 15 to 30%.

[0026] 4) Drill a hole with a diameter of Φ10 mm in the center of the CuNb composite rod to form a CuNb composite tube. Then, insert the SnTi alloy rod into the drilled hole of the composite tube to form an assembled sub-component, and form a hexagonal CuMn sub-component through multiple cold drawing processes. The content of Ti atoms in SnTi is 1.5%. When the sub-component undergoes multiple cold drawing processes, the processing rate is within 15 - 30%. The forming size of the hexagonal CuMn sub-component is 3.0 mm, and the copper ratio is 0.22. Compared with conventional multi-core sub-components, there is no processing cracking phenomenon in the preparation process of the sub-components in the present invention.

[0027] 5) Tightly arrange and assemble the CuMn sub-component and the SnCu alloy rod into the Ta tube, and then integrally assemble the Ta tube into the oxygen-free copper tube to form an assembled composite wire. Then, subject the composite wire to multiple cold drawing and heat treatment processes to form the final Nb3Sn superconducting wire. The CuMn sub-component in the composite wire has a close-packed structure, the number of sub-components is 163, the number of SnCu alloy rods is 6, the SnCu alloy rod is in a fan shape, and the proportion of Cu atoms is 2%. The remaining voids inside the composite wire are filled with CuMn alloy rods with a diameter of Φ2 mm, and the Mn content is the same as the corresponding content in the sub-component. The size of the Ta tube is Φ47 mm and the thickness is 1 mm. The inner and outer diameters of the oxygen-free copper tube are Φ48 / Φ72 mm respectively, and the copper-to-super ratio of the composite wire is 1.5. When the diameter of the composite wire is greater than Φ10 mm, the processing rate of multiple cold drawing is 15 - 30%. When the diameter of the composite wire is less than Φ10 mm, the processing rate of multiple cold drawing is 8 - 15%.

[0028] When the 3-meter-long assembled composite wire is stretched to Φ0.8 mm, the number of broken wires of the composite wire is 5 times, and the average output length is 4300 meters, which is much greater than the average output length of existing Nb3Sn composite wires. The heat treatment process is: 340°C / 96h + 600°C / 72h + 650°C / 96h. After heat treatment, the critical current density is 2703 A / mm2 (4.2K, 12T), which is higher than the average performance level of about 2500 A / mm2 (4.2K, 12T) of existing batch-produced Nb3Sn products.

[0029] Example 2 1) Assemble a Nb rod with a diameter of 150 mm into an oxygen-free copper tube with an outer diameter of 170 mm and an inner diameter of 150 mm, and then subject the whole to processes such as hot isostatic pressing, extrusion, straightening, and cold drawing to prepare a hexagonal CuNb single-core rod with a size of 5.75 mm and a copper ratio of 0.32. The temperature of hot isostatic pressing is 650°C, the extrusion temperature is 550°C, the extrusion speed is 15 mm / s, the straightening accuracy is an error of 1 mm per 3 meters, and the cold drawing processing rate between passes does not exceed 30%.

[0030] 2) Assemble the CuNb single core rod and the hexagonal copper core rod with a size of 5.75 mm in the close-packed hexagonal form into the CuMn alloy tube in step 1). The center of the CuMn tube is filled with the hexagonal copper core rod with a size of 5.75 mm in a close-packed manner to form a multi-core CuNb composite sheath. The outermost CuNb single core rods are arranged in a non-continuous close-packed pattern, alternately and closely packed with the hexagonal copper core rods. The inner and outer diameters of the CuMn alloy tube are Φ195 / Φ220 mm respectively, and the atomic ratio of Mn is 1.0%.

[0031] 3) Subject the CuNb composite sheath to a series of processes including hot isostatic pressing, extrusion, straightening, peeling, and multi-pass cold drawing to prepare a CuNb composite rod with an outer diameter of Φ70 mm. The hot isostatic pressing temperature is 650 °C, the extrusion temperature is 550 °C, the extrusion speed is 20 mm / s, the straightening accuracy is less than 1 mm deviation per 3 meters, the peeling amount is 2.4%, and the multi-pass cold drawing processing rate is within 15 - 30%.

[0032] 4) Drill a hole with a diameter of Φ35 mm in the center of the CuNb composite rod to form a CuNb composite tube. Then, insert the SnTi alloy rod into the drilled hole of the composite tube to form an assembled sub-element, and form a hexagonal CuMn sub-element through multi-pass cold drawing. The Ti atomic content in SnTi is 1.5%. The processing rate during multi-pass cold drawing of the sub-element is within 15 - 30%. The formed size of the hexagonal CuMn sub-element is 3.5 mm, and the copper ratio is 0.27. Compared with the conventional multi-core sub-elements, there is no processing cracking phenomenon during the preparation process of the sub-elements in the present invention.

[0033] 5) Assemble the CuMn sub-elements and the SnCu alloy rods in a close-packed manner into the Ta tube, and then assemble the Ta tube as a whole into the oxygen-free copper tube to form an assembled composite wire. Then, subject the composite wire to a series of processes including multi-pass cold drawing and heat treatment to form the final Nb3Sn superconducting wire. The CuMn sub-elements in the composite wire are in a close-packed structure, the number of sub-elements is 121, the number of SnCu alloy rods is 6, the SnCu alloy rods are in a fan shape, and the atomic ratio of Cu is 3%. The remaining voids inside the composite wire are filled with CuMn alloy rods with a diameter of Φ2 mm, and the Mn content is the same as the corresponding content in the sub-elements. The size of the Ta tube is Φ47 mm with a thickness of 1 mm, the inner and outer diameters of the oxygen-free copper tube are Φ48 / Φ53 mm respectively, and the copper-to-super ratio of the composite wire is 0.3. When the diameter of the composite wire is greater than Φ10 mm, the multi-pass cold drawing processing rate is 15 - 30%. When the diameter of the composite wire is less than Φ10 mm, the multi-pass cold drawing processing rate is 8 - 15%.

[0034] When the 3-meter-long assembled composite wire is stretched to Φ0.8 mm, the number of wire breakages of the composite wire is 3 times, and the average output length is 4,100 meters, which is also greater than the average output length of the existing Nb3Sn composite wire. The heat treatment process is: 340°C / 96 h + 600°C / 72 h + 650°C / 96 h. After the heat treatment, the critical current density is 2,787 A / mm2 (4.2 K, 12 T), which is higher than the average performance level of about 2,500 A / mm2 (4.2 K, 12 T) of the existing batch-produced Nb3Sn products.

[0035] Example 3 1) Assemble a Nb rod with a diameter of 305 mm into an oxygen-free copper tube with an outer diameter of 335 mm and an inner diameter of 310 mm, and then pass the whole through processes such as hot isostatic pressing, extrusion, straightening, and cold drawing to prepare a hexagonal CuNb single-core rod with a size of 11 mm and a copper ratio of 0.1. The hot isostatic pressing temperature is 720°C, the extrusion temperature is 550°C, the extrusion speed is 10 mm / s, the straightening accuracy is 1 mm error per 3 meters, and the cold drawing processing rate between passes does not exceed 30%.

[0036] 2) Assemble the CuNb single-core rod in step 1) and the hexagonal copper core rod with a size of 11 mm into a CuMn alloy tube in a close-packed hexagonal form. The center of the CuMn tube is filled with the hexagonal copper core rod with a size of 11 mm in a close-packed manner to form a multi-core CuNb composite sheath. The outermost CuNb single-core rods are arranged in a non-continuous close-packed manner, alternately spaced with the hexagonal copper core rods in a close-packed manner. The outer and inner diameters of the CuMn alloy tube are Φ430 / Φ450 mm respectively, and the Mn atom content is 6.0%.

[0037] 3) Pass the CuNb composite sheath through processes such as hot isostatic pressing, extrusion, straightening, skinning, and multi-pass cold drawing to prepare a CuNb composite rod with an outer diameter of Φ100 mm. The hot isostatic pressing temperature is 720°C, the extrusion temperature is 550°C, the extrusion speed is 10 mm / s, the straightening accuracy is less than 1 mm deviation per 3 meters, the skinning amount is 5.0%, and the multi-pass cold drawing processing rate is within 15 - 30%.

[0038] 4) Drill a hole with a diameter of Φ45 mm in the center of the CuNb composite rod to form a CuNb composite tube. Then, insert the SnTi alloy rod into the drilled hole of the composite tube to form an assembled sub-element, and form a hexagonal CuMn sub-element through multi-pass cold drawing. The Ti atom content in SnTi is 2%. The processing rate during the multi-pass cold drawing of the sub-element is within 15 - 30%. The formed size of the hexagonal CuMn sub-element is 5.1 mm, and the copper ratio is 0.1. Compared with the conventional multi-core sub-elements, there is no processing cracking phenomenon in the preparation process of the sub-elements in the present invention.

[0039] 5) The CuMn subgroup elements and SnCu alloy rods are closely packed and assembled into a Ta tube, and then the Ta tube is integrally assembled into an oxygen-free copper tube to form an assembled composite wire. The composite wire is then subjected to multiple cold drawing and heat treatment processes to form the final Nb3Sn superconducting wire. The CuMn subgroup elements in the composite wire are in a close-packed structure, with 55 subgroup elements, 6 SnCu alloy rods, and the SnCu alloy rods are fan-shaped, with the Cu atom proportion being 3%. The remaining voids inside the composite wire are filled with CuMn alloy rods with a diameter of Φ2 mm, and the Mn content is the same as the corresponding content in the subgroup elements. The Ta tube has a size of Φ47 mm and a thickness of 1 mm, and the inner and outer diameters of the oxygen-free copper tube are Φ48 / Φ60 mm respectively, and the copper-to-super ratio of the composite wire is 0.65. When the diameter of the composite wire is greater than Φ10 mm, the multi-pass cold drawing processing rate is 15 - 30%, and when the diameter of the composite wire is less than Φ10 mm, the multi-pass cold drawing processing rate is 8 - 15%.

[0040] When a 3-meter-long assembled composite wire is stretched to Φ0.8 mm, the number of wire breaks in the composite wire is 8 times, and the average output length is 2000 meters, which is equivalent to the average output length of the existing Nb3Sn composite wire. The heat treatment process is: 340°C / 96 h + 600°C / 72 h + 650°C / 96 h. After heat treatment, the critical current density is 2734 A / mm2 (4.2K, 12T), which is higher than the average performance level of about 2500 A / mm2 (4.2K, 12T) of the existing batch-produced Nb3Sn products.

[0041] Example 4 1) A Nb rod with a diameter of 205 mm is assembled into an oxygen-free copper tube with an outer diameter of 225 mm and an inner diameter of 210 mm, and then the whole is processed through hot isostatic pressing, extrusion, straightening, cold drawing and other processes to prepare a hexagonal CuNb single-core rod with a size of 5.5 mm and a copper ratio of 0.1. The hot isostatic pressing temperature is 670°C, the extrusion temperature is 550°C, the extrusion speed is 15 mm / s, the straightening accuracy is 1 mm error per 3 meters, and the cold drawing processing rate between passes does not exceed 30%.

[0042] A Nb rod with a diameter of 5 mm is assembled into an oxygen-free copper tube with an outer hexagonal size of 5.5 mm and an inner circular diameter of 5.05 mm to form a CuNb single-core rod, and the copper ratio of the CuNb single-core rod is 0.1.

[0043] 2) The CuNb single-core rod in step 1) and the hexagonal copper core rod with a size of 5.5 mm are assembled into a CuMn alloy tube in a close-packed hexagonal form, and the center of the CuMn tube is filled with a close-packed hexagonal copper core rod with a size of 5.5 mm to form a multi-core CuNb composite sheath. The outermost layer of CuNb single-core rods is in a non-continuous close-packed arrangement, and is alternately close-packed with the hexagonal copper core rods. The inner and outer diameters of the CuMn alloy tube are Φ240 / Φ270 mm respectively, and the Mn atom proportion is 2.2%.

[0044] 3) The CuNb composite sheath is successively processed through hot isostatic pressing, extrusion, straightening, peeling, multi-pass cold drawing and other processes to prepare a CuNb composite rod with an outer diameter of Φ70 mm. The hot isostatic pressing temperature is 670 °C, the extrusion temperature is 550 °C, the extrusion speed is 20 mm / s, the straightening accuracy is less than 1 mm deviation per 3 meters, the peeling amount is 2.4%, and the multi-pass cold drawing processing rate is within 15 - 30%.

[0045] 4) A Φ35 mm center hole is drilled in the CuNb composite rod to form a CuNb composite tube. Then, the SnTi alloy rod is inserted into the drilled hole of the composite tube to form an assembled sub-element, and a hexagonal CuMn sub-element is formed through multi-pass cold drawing. The Ti atomic content in SnTi is 0.7%. The processing rate during multi-pass cold drawing of the sub-element is within 15 - 30%. The forming size of the hexagonal CuMn sub-element is 4.2 mm, and the copper ratio is 0.25. Compared with conventional multi-core sub-elements, there is no processing cracking phenomenon in the preparation process of the sub-elements in the present invention.

[0046] 5) The CuMn sub-elements and SnCu alloy rods are closely packed and assembled into a Ta tube, and then the Ta tube is integrally assembled into an oxygen-free copper tube to form an assembled composite wire. The composite wire is then processed through multi-pass cold drawing, heat treatment and other processes to form the final Nb3Sn superconducting wire. The CuMn sub-elements in the composite wire are in a closely packed structure, the number of sub-elements is 85, the number of SnCu alloy rods is 6, the SnCu alloy rods are in a fan shape, and the Cu atom proportion is 1%. The remaining voids inside the composite wire are filled with CuMn alloy rods with a diameter of Φ2 mm, and the Mn content is the same as the corresponding content in the sub-elements. The size of the Ta tube is Φ47 mm and the thickness is 1 mm. The inner and outer diameters of the oxygen-free copper tube are Φ48 / Φ60 mm respectively, and the copper-to-super ratio of the composite wire is 0.65. When the diameter of the composite wire is greater than Φ10 mm, the multi-pass cold drawing processing rate is 15 - 30%. When the diameter of the composite wire is less than Φ10 mm, the multi-pass cold drawing processing rate is 8 - 15%.

[0047] When a 3-meter-long assembled composite wire is stretched to Φ0.8 mm, the number of broken wires of the composite wire is 5 times, and the average output length is 3300 meters, which is higher than the average output length of existing Nb3Sn composite wires. The heat treatment process is: 340 °C / 96 h + 600 °C / 72 h + 650 °C / 96 h. After heat treatment, the critical current density is 2784 A / mm2 (4.2K, 12T), which is higher than the average performance level of about 2500 A / mm2 (4.2K, 12T) of existing batch-produced Nb3Sn products.

[0048] Figure 2Structural diagram of a multi-core Nb3Sn composite wire provided by an embodiment of the present invention; An embodiment of the present invention provides a multi-core Nb3Sn composite wire, and the multi-core Nb3Sn composite wire is prepared by any one of the above methods.

[0049] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they know the basic creative concept. Therefore, the appended claims are intended to be construed to include the preferred examples as well as all changes and modifications falling within the scope of the present invention.

[0050] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A method for preparing a multi-core Nb3Sn composite wire, characterized in that: include: The Nb rod is placed into the oxygen-free copper tube to obtain a CuNb single-core rod; The outermost CuNb single core rod and the hexagonal copper core rod are sequentially arranged in a CuMn alloy tube in a close-packed hexagonal form to obtain a multi-core CuNb composite sheath; Processing the CuNb composite sheath into a CuNb composite rod; Drilling a hole at the center of the CuNb composite rod to obtain a CuNb composite tube; Inserting the SnTi alloy rod into the CuNb composite tube to obtain a subcomponent; Processing the subcomponent to obtain a hexagonal CuMn subcomponent; Assembling the hexagonal CuMn subcomponent and the fan-shaped SnCu alloy rod into a Ta tube and then assembling the whole into an oxygen-free copper tube to obtain a composite wire; The composite wire is processed to obtain a Nb3Sn superconducting wire.

2. The method for preparing a multi-core Nb3Sn composite wire according to claim 1, characterized in that: Before the Nb rod is loaded into the oxygen-free copper tube to obtain the CuNb single-core rod, the method further includes hot isostatic pressing, extrusion, straightening and cold stretching the Nb rod and the oxygen-free copper tube.

3. The method for preparing a multi-core Nb3Sn composite wire according to claim 1, characterized in that: Processing the CuNb composite sheath into a CuNb composite rod is to process the CuNb composite sheath through hot isostatic pressing, extrusion, straightening, peeling and multiple cold stretching steps in sequence to obtain the CuNb composite rod.

4. The method for preparing a multi-core Nb3Sn composite wire according to claim 1, characterized in that: Processing the subcomponent to obtain the hexagonal CuMn subcomponent involves subjecting the subcomponent to multiple cold stretching passes to obtain the hexagonal CuMn subcomponent.

5. The method for preparing a multi-core Nb3Sn composite wire according to claim 1, characterized in that: Before assembling the hexagonal CuMn subcomponent and the fan-shaped SnCu alloy rod into a Ta tube and then assembling the whole into an oxygen-free copper tube to obtain a composite wire, the process further includes: The hexagonal CuMn subcomponent and the fan-shaped SnCu alloy rod are closely packed and assembled in the Ta tube.

6. The method for preparing a multi-core Nb3Sn composite wire according to claim 1, characterized in that: Before the composite wire is processed to obtain the Nb3Sn superconducting wire, the method further comprises: The composite wire is subjected to multiple cold drawing and heat treatment processes.

7. A multi-core Nb3Sn composite wire, characterized in that: The multi-core Nb3Sn composite wire is prepared by the method according to any one of claims 1-6.

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