Preparation method of high-performance multi-core Ni3Sn composite wire and composite wire

Abstract

The invention discloses a preparation method of a high-performance multi-core Ni3Sn composite wire and the composite wire, and relates to the technical field of superconducting composite wires, and the preparation method comprises the following steps: respectively loading an Nb rod and an NbTaHf rod into an oxygen-free copper pipe, preparing a CuNb single-core rod and a doping type CuNb single-core rod, loading a hexagonal copper core rod, the CuNb single-core rod and the doping type CuNb single-core rod into an NbTaHf alloy pipe, loading the NbTaHf alloy pipe into the oxygen-free copper pipe together, and preparing the high-performance multi-core Ni3Sn composite wire. Forming a composite sheath; preparing a composite pipe; the SnTi rod is loaded into the composite tube, and a circular sub-component is obtained; a hexagonal sub-component and a fan-shaped sub-component are formed; and assembling into a Ta tube, and jointly loading into an oxygen-free copper tube to form a composite wire, and then forming the multi-core niobium-tin composite wire. The NbTaHf rod and the NbTaHf alloy pipe are adopted, and a specific preparation process flow is combined, so that the critical current density of the multi-core Ni3Sn composite wire is improved, and meanwhile, the long wire preparation capacity is achieved.

Description

Technical Field

[0001] This application relates to the technical field of superconducting composite wires, and particularly to a preparation method and a composite wire of a high-performance multi-core niobium-tin composite wire. Background Art

[0002] The target value of the critical current density of the niobium-tin superconducting material required for the magnet performance design of the controllable nuclear fusion project exceeds 2700 A / mm2 (4.2K, 12T), which is already close to the limit of the current niobium-tin wire performance design. In order to obtain niobium-tin wires that meet such extremely high performance, the current common technical solution is to improve the niobium-tin grain boundary density by means of element doping, thereby further improving the performance of the wires. The common doping methods are doping Ta, Hf, Zr and corresponding oxides in Nb, and then realizing the preparation of niobium-tin superconducting wires through the powder-in-tube technical solution. This technical solution of improving the performance of niobium-tin superconducting wires by element doping has been widely verified.

[0003] In the prior art, Chinese Patent CN115295243A discloses a preparation method of an element-doped niobium-tin superconducting strand with a high critical current density. Specifically: loading Nb-X-Y into a copper tube, and obtaining a Cu / Nb-X-Y single-core rod after treatment; loading oxide powder into a copper tube, and obtaining a Cu / oxide single-core rod after treatment; pouring molten Sn into an oxygen-free copper cylinder to obtain a Cu / Sn blank, and obtaining a Cu / Sn single-core rod after multi-pass cold precision forging, drawing and forming; bundling the Cu / Nb-X-Y single-core rod and the Cu / oxide single-core rod and loading them into a copper tube, and obtaining a Nb module after drawing and forming; bundling the Nb module and the Cu / Sn single-core rod and loading them into a Ta tube and then into a copper tube, and performing multi-pass drawing.

[0004] However, limited by the fact that doping atoms will cause a sharp decrease in the plastic processing performance of the wire, although the above prior art can improve the critical current density of the niobium-tin superconducting strand, there are huge technical obstacles in the preparation of long wires (kilometer level), and it is impossible to balance high critical current density and long wire preparation. Summary of the Invention

[0005] This application provides a preparation method and a composite wire of a high-performance multi-core niobium-tin composite wire to solve the problem that the existing niobium-tin superconducting wire preparation technology cannot balance high critical current density and long wire preparation.

[0006] On the one hand, this application provides a preparation method of a high-performance multi-core niobium-tin composite wire, including the following steps: Step 1, respectively loading Nb rods and NbTaHf rods into oxygen-free copper tubes, and successively passing through hot isostatic pressing, extrusion, straightening, and multi-pass cold drawing processes to respectively prepare CuNb single-core rods and doped CuNb single-core rods.

[0007] Step 2: Load the hexagonal copper core rod, the CuNb single core rod, and the doped CuNb single core rod into the NbTaHf alloy tube in a close-packed form, and then load them together into an oxygen-free copper tube to form a composite sheath.

[0008] Step 3: Subject the composite sheath to hot isostatic pressing, extrusion, straightening, multi-pass cold drawing, and drilling processes in sequence to prepare a composite tube.

[0009] Step 4: Load the SnTi rod into the composite tube, and obtain circular sub-elements through multi-pass cold drawing and cleaning processes.

[0010] Step 5: Fill tin oxide powder into the hexagonal oxygen-free copper tube and the fan-shaped oxygen-free copper tube, and load the circular sub-elements into the hexagonal oxygen-free copper tube and the fan-shaped oxygen-free copper tube in the form of extruding the tin oxide powder to form a hexagonal sub-element and a fan-shaped sub-element.

[0011] Step 6: Assemble the hexagonal sub-element and the fan-shaped sub-element into a Ta tube, and then load them together into an oxygen-free copper tube to form a composite wire. Then, through multi-pass cold drawing and heat treatment processes in sequence, a multi-core niobium trisilicide composite wire is formed.

[0012] In a possible implementation, in Step 1, the inner diameter of the oxygen-free copper tube is 100 - 310 mm, and the outer diameter is 115 - 335 mm.

[0013] The Nb rod and the NbTaHf rod have the same size, with a diameter of 100 - 305 mm. The mass fraction of Ta atoms in the NbTaHf rod is 4%, and the mass fraction of Hf atoms is 0.5% - 4%.

[0014] The hexagonal forming sizes of the CuNb single core rod and the doped CuNb single core rod are both 2.2 - 11 mm, and the copper ratios are the same, both 0.1 - 0.2.

[0015] In Step 1, the temperature of the hot isostatic pressing is 650 - 720 °C, the temperature of the extrusion is 450 - 550 °C, the extrusion speed is 10 - 20 mm / s, the straightening accuracy is no more than 1 mm error per 3 meters, and the processing rate between passes of the multi-pass cold drawing is 15% - 30%.

[0016] In a possible implementation, in Step 2, arrange the hexagonal copper core rod in the center of the NbTaHf alloy tube in a close-packed manner, and arrange the CuNb single core rod and the doped CuNb single core rod on the outside of the hexagonal copper core rod in a close-packed manner.

[0017] In Step 2, the inner diameter of the oxygen-free copper tube is 86 - 430 mm, the outer diameter is 130 - 480 mm, and the size of the hexagonal copper core rod is 2.2 - 11 mm.

[0018] The composition of the NbTaHf alloy tube is the same as that of the NbTaHf rod. The outer diameter of the NbTaHf alloy tube is 86 - 430 mm, the thickness is 0.2 - 3 mm, and the thickness is 0.1 - 0.3 of the diameter of the Nb rod in the composite sheath.

[0019] In a possible implementation, in Step 3, the outer diameter of the composite tube is 40 - 100 mm, and the drilling size is 12 - 45 mm.

[0020] In Step 3, the temperature of hot isostatic pressing is 650 - 720 °C, the temperature of extrusion is 450 - 550 °C, the extrusion speed is 10 - 20 mm / s, the straightening accuracy is no more than 1 mm error per 3 meters, and the processing rate between passes of multi-pass cold drawing is 15% - 30%.

[0021] In a possible implementation, in Step 4, the mass proportion of Ti atoms in the SnTi rod is 0.7% - 2%.

[0022] In Step 4, the processing rate between passes of multi-pass cold drawing is 15% - 30%, the external Cu thickness of the circular sub-element after cleaning is 0.2 - 0.5 mm, and the diameter of the circular sub-element is 1.8 - 5.5 mm.

[0023] In a possible implementation, in Step 5, the cross-section of the hexagonal oxygen-free copper tube is hexagonal outside and circular inside, the width of the outer hexagon is 3 - 7 mm, and the inner diameter is 2.8 - 6.5 mm.

[0024] The cross-section of the sector-shaped oxygen-free copper tube is sector-shaped outside and circular inside. The outer sector shape matches that of the hexagonal oxygen-free copper tube, and the inner diameter is the same as that of the hexagonal oxygen-free copper tube.

[0025] The mass proportion of O atoms in the tin oxide powder is 1% - 5%.

[0026] The thickness of the tin oxide powder in both the hexagonal sub-element and the sector-shaped sub-element is 0.5 mm, and the copper ratios of the hexagonal sub-element and the sector-shaped sub-element are the same, both being 0.1 - 0.27.

[0027] In a possible implementation, in Step 6, the outer diameter of the oxygen-free copper tube is 54 - 82 mm, the inner diameter is 48 mm, and the copper super ratio of the composite wire is 0.3 - 2.

[0028] The hexagonal sub-elements and the sector-shaped sub-elements are closely packed into the Ta tube. The number of the hexagonal sub-elements is 31 to 163, the number of the sector-shaped sub-elements is 6, the outer diameter of the Ta tube is 47 mm, and the thickness is 1 mm.

[0029] The gap between the outermost hexagonal sub-elements and the Ta tube is filled with oxygen-free copper rods with a diameter of 1 mm.

[0030] The processing rate between passes of the multi-pass cold drawing of the composite wire is 8% to 15%.

[0031] The heat treatment includes: 340°C / 96 h + 550°C / 200 - 300 h + 650°C / 72 - 150 h.

[0032] On the other hand, the present application provides a high-performance multi-core niobium-tin composite wire, which is prepared by using the preparation method of a high-performance multi-core niobium-tin composite wire described above.

[0033] The preparation method and the composite wire of a high-performance multi-core niobium-tin composite wire in the present application have the following advantages: By using NbTaHf rods and NbTaHf alloy tubes and combining with a specific preparation process flow, while improving the critical current density of the multi-core niobium-tin composite wire, it has the ability to prepare long wires. Among them, by using NbTaHf rods, doping elements that can refine the niobium-tin grains are provided inside the wire; by using NbTaHf alloy tubes, it is realized that oxygen atoms enter the wire structure only in the subsequent composite wire stage, greatly reducing the number of processing passes of the wire after oxygen atom doping, and also providing an oxide doping source for further improving the wire performance; by using NbTaHf rods and NbTaHf alloy tubes and combining with the specific preparation process flow from step 1 to step 6, while improving the critical current density of the multi-core niobium-tin composite wire, it can produce long wires of kilometers, reducing the processing difficulty of niobium-tin superconducting wires.

[0034] The proposed heat treatment includes: 340°C / 96 h + 550°C / 200 - 300 h + 650°C / 72 - 150 h. By using a specific heat treatment process, the critical current density of the multi-core niobium-tin composite wire is further improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to these drawings.

[0036] Figure 1 Schematic flow chart of a method for preparing a high-performance multi-core niobium tin composite wire provided by an embodiment of the present application; Figure 2 Cross-sectional photograph of a multi-core niobium tin composite wire provided by an embodiment of the present application; Figure 3 Cross-sectional electron microscope scan of a multi-core niobium tin composite wire provided by an embodiment of the present application. Detailed implementation manners

[0037] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts shall fall within the protection scope of the present application.

[0038] As Figure 1 shown, an embodiment of the present application provides a method for preparing a high-performance multi-core niobium tin composite wire, including the following steps: Step 1: Respectively load Nb rods and NbTaHf rods into oxygen-free copper tubes, and successively go through hot isostatic pressing, extrusion, straightening, and multi-pass cold drawing processes to respectively prepare CuNb single-core rods and doped CuNb single-core rods.

[0039] Step 2: Load a hexagonal copper core rod, the CuNb single-core rod, and the doped CuNb single-core rod into a NbTaHf alloy tube in a close-packed form, and jointly load them into an oxygen-free copper tube to form a composite sheath.

[0040] Step 3: Subject the composite sheath to hot isostatic pressing, extrusion, straightening, multi-pass cold drawing, and drilling processes in sequence to prepare a composite tube.

[0041] Step 4: Load a SnTi rod into the composite tube, and obtain circular sub-elements through multi-pass cold drawing and cleaning processes.

[0042] Step 5: Fill tin oxide powder into a hexagonal oxygen-free copper tube and a fan-shaped oxygen-free copper tube, and load the circular sub-elements into the hexagonal oxygen-free copper tube and the fan-shaped oxygen-free copper tube in the form of extruding the tin oxide powder to form a hexagonal sub-element and a fan-shaped sub-element.

[0043] Step 6: Assemble the hexagonal sub-element and the fan-shaped sub-element into a Ta tube, and jointly load them into an oxygen-free copper tube to form a composite wire, and then successively go through multi-pass cold drawing and heat treatment processes to form a multi-core niobium tin composite wire.

[0044] Specifically, in this embodiment, the tin oxide powder refers to tin powder doped with oxygen element.

[0045] The embodiment of the present application also provides a high-performance multi-core niobium tin composite wire, which is prepared by using the preparation method of the high-performance multi-core niobium tin composite wire described above.

[0046] As Figure 2 shown, it is a cross-sectional photograph of the multi-core niobium tin composite wire; as Figure 3 shown, it is a scanning electron microscope image of the cross-section of the multi-core niobium tin composite wire. It can be seen from the scanning electron microscope image that the niobium tin grains in the multi-core niobium tin composite wire of the present application are refined, thereby improving the current-carrying capacity of the multi-core niobium tin composite wire.

[0047] Example 1: Exemplarily, in step one, the inner diameter of the oxygen-free copper tube is 100 mm, and the outer diameter is 115 mm. The Nb rod and the NbTaHf rod have the same size, and the diameter of both is 100 mm. The mass fraction of Ta atoms in the NbTaHf rod is 4%, and the mass fraction of Hf atoms is 0.5%. The hexagonal forming sizes of the CuNb single-core rod and the doped CuNb single-core rod are both 2.2 mm, and the copper ratios are the same, both being 0.2. In step one, the temperature of hot isostatic pressing is 650 °C, the temperature of extrusion is 450 °C, the extrusion speed is 20 mm / s, the straightening accuracy is no more than 1 mm error per 3 meters, and the processing rate between passes of multi-pass cold drawing is 15% - 30%.

[0048] Exemplarily, in step two, the hexagonal copper core rod is densely arranged in the center of the NbTaHf alloy tube, and the CuNb single-core rod and the doped CuNb single-core rod are densely arranged outside the hexagonal copper core rod. In step two, the inner diameter of the oxygen-free copper tube is 86 mm, the outer diameter is 130 mm, and the size of the hexagonal copper core rod is 2.2 mm. The composition of the NbTaHf alloy tube is the same as that of the NbTaHf rod. The outer diameter of the NbTaHf alloy tube is 86 mm, and the thickness is 0.2 mm, which is 0.1 of the diameter of the Nb rod in the composite sheath.

[0049] Exemplarily, in step three, the outer diameter of the composite tube is 40 mm, and the drilling size is 12 mm. In step three, the temperature of hot isostatic pressing is 650 °C, the temperature of extrusion is 450 °C, the extrusion speed is 20 mm / s, the straightening accuracy is no more than 1 mm error per 3 meters, and the processing rate between passes of multi-pass cold drawing is 15% - 30%.

[0050] Exemplarily, in step four, the mass fraction of Ti atoms in the SnTi rod is 0.7%. In step four, the processing rate between passes of multi-pass cold drawing is 15% - 30%. The external Cu thickness of the cleaned circular sub-element is 0.2 mm, and the diameter of the circular sub-element is 1.8 mm.

[0051] Exemplarily, in step five, the cross-section of the hexagonal oxygen-free copper tube is hexagonal on the outside and circular on the inside, with the width of the outer hexagon being 3 mm and the inner diameter being 2.8 mm. The cross-section of the sector-shaped oxygen-free copper tube is sector-shaped on the outside and circular on the inside, with the outer sector being matched with the shape of the hexagonal oxygen-free copper tube and the inner diameter being the same as that of the hexagonal oxygen-free copper tube. The mass percentage of O atoms in the tin oxide powder is 1%. The thickness of the tin oxide powder in both the hexagonal sub-element and the sector-shaped sub-element is 0.5 mm, and the copper ratios of both the hexagonal sub-element and the sector-shaped sub-element are the same, both being 0.1.

[0052] Exemplarily, in step six, the outer diameter of the oxygen-free copper tube is 67 mm and the inner diameter is 48 mm, and the copper super-ratio of the composite wire is 1. The hexagonal sub-elements and the sector-shaped sub-elements are closely packed into the Ta tube. The number of the hexagonal sub-elements is 163, and the number of the sector-shaped sub-elements is 6. The outer diameter of the Ta tube is 47 mm and the thickness is 1 mm. The gap between the outermost hexagonal sub-element and the Ta tube is filled with an oxygen-free copper rod with a diameter of 1 mm. The processing rate between passes of the multi-pass cold drawing of the composite wire is 8% - 15%. The heat treatment includes: 340°C / 96 h + 550°C / 200 h + 650°C / 72 h.

[0053] In Example 1, in step six, when a 3-m long composite wire is cold-drawn through multiple passes to a diameter of 0.8 mm, two kilometer-long wires of 1142 m and 3380 m are produced, and the length of a single wire exceeds 3000 m, meeting the length requirements of the niobium-tin superconducting wire for existing controlled nuclear fusion projects. The critical current density after heat treatment is 3120 A / mm 2 (4.2K, 12T), which is much higher than the average performance level of about 2500 A / mm 2 (4.2K, 12T) of the existing undoped niobium-tin superconducting wire, and higher than the highest performance of the known undoped niobium-tin superconducting wire.

[0054] Example 2: Exemplarily, in step one, the inner diameter of the oxygen-free copper tube is 150 mm and the outer diameter is 170 mm. The Nb rod and the NbTaHf rod have the same size, with a diameter of 150 mm. The mass percentage of Ta atoms in the NbTaHf rod is 4%, and the mass percentage of Hf atoms is 4%. The hexagonal forming sizes of both the CuNb single-core rod and the doped CuNb single-core rod are 5.5 mm, and the copper ratios are the same, both being 0.2. In step one, the temperature of hot isostatic pressing is 700°C, the temperature of extrusion is 500°C, the extrusion speed is 15 mm / s, the straightening accuracy is no more than 1 mm error per 3 m, and the processing rate between passes of multi-pass cold drawing is 15% - 30%.

[0055] Exemplarily, in step two, the hexagonal copper core rod is closely arranged at the center of the NbTaHf alloy tube, and the CuNb single core rod and the doped CuNb single core rod are closely arranged outside the hexagonal copper core rod. In step two, the inner diameter of the oxygen-free copper tube is 195 mm, the outer diameter is 240 mm, and the size of the hexagonal copper core rod is 5.5 mm. The composition of the NbTaHf alloy tube is the same as that of the NbTaHf rod. The outer diameter of the NbTaHf alloy tube is 195 mm, and the thickness is 0.9 mm, which is 0.18 of the diameter of the Nb rod in the composite sheath.

[0056] Exemplarily, in step three, the outer diameter of the composite tube is 70 mm, and the drilling size is 25 mm. In step three, the temperature of hot isostatic pressing is 700 °C, the temperature of extrusion is 500 °C, the extrusion speed is 15 mm / s, the straightening accuracy is no more than 1 mm error per 3 meters, and the processing rate between passes of multi-pass cold drawing is 15% - 30%.

[0057] Exemplarily, in step four, the mass proportion of Ti atoms in the SnTi rod is 1%. In step four, the processing rate between passes of multi-pass cold drawing is 15% - 30%. The outer Cu thickness of the circular sub-element after cleaning is 0.3 mm, and the diameter of the circular sub-element is 3.5 mm.

[0058] Exemplarily, in step five, the cross-section of the hexagonal oxygen-free copper tube is hexagonal outside and circular inside. The outer hexagonal width is 5.1 mm, and the inner diameter is 4.5 mm. The cross-section of the fan-shaped oxygen-free copper tube is fan-shaped outside and circular inside. The outer fan shape matches the shape of the hexagonal oxygen-free copper tube, and the inner diameter is the same as that of the hexagonal oxygen-free copper tube. The mass proportion of O atoms in the tin oxide powder is 2%. The thickness of the tin oxide powder in both the hexagonal sub-element and the fan-shaped sub-element is 0.5 mm, and the copper ratios of the hexagonal sub-element and the fan-shaped sub-element are the same, both being 0.27.

[0059] Exemplarily, in step six, the outer diameter of the oxygen-free copper tube is 72 mm, the inner diameter is 48 mm, and the copper super ratio of the composite wire is 1.5. The hexagonal sub-elements and the fan-shaped sub-elements are closely arranged in the Ta tube. The number of hexagonal sub-elements is 55, and the number of fan-shaped sub-elements is 6. The outer diameter of the Ta tube is 47 mm, and the thickness is 1 mm. The gap between the outermost hexagonal sub-element and the Ta tube is filled with oxygen-free copper rods with a diameter of 1 mm. The processing rate between passes of multi-pass cold drawing of the composite wire is 8% - 15%. The heat treatment includes: 340 °C / 96 h + 550 °C / 250 h + 650 °C / 96 h.

[0060] In Example 2, in Step 6, when a 3m long composite wire is cold drawn through multiple passes to a diameter of 0.8mm, 1760m, 1232m, and 2270m of 3 km long wires are produced, meeting the length requirements of niobium-tin superconducting wires for existing controlled nuclear fusion projects. The critical current density after heat treatment is 3274 A / mm 2 (4.2K, 12T), much higher than the average performance level of about 2500 A / mm 2 (4.2K, 12T) of existing undoped niobium-tin superconducting wires, and higher than the highest performance of known undoped niobium-tin superconducting wires.

[0061] Example 3: Exemplarily, in Step 1, the inner diameter of the oxygen-free copper tube is 310mm and the outer diameter is 335mm. The Nb rod and the NbTaHf rod have the same size, both with a diameter of 305mm. The mass fraction of Ta atoms in the NbTaHf rod is 4%, and the mass fraction of Hf atoms is 2%. The hexagonal forming sizes of the CuNb single-core rod and the doped CuNb single-core rod are both 11mm, and the copper ratios are the same, both 0.1. In Step 1, the temperature of hot isostatic pressing is 720°C, the temperature of extrusion is 550°C, the extrusion speed is 10mm / s, the straightening accuracy is no more than 1mm error per 3m, and the processing rate between passes of multi-pass cold drawing is 15% - 30%.

[0062] Exemplarily, in Step 2, the hexagonal copper core rod is closely arranged at the center of the NbTaHf alloy tube, and the CuNb single-core rod and the doped CuNb single-core rod are closely arranged outside the hexagonal copper core rod. In Step 2, the inner diameter of the oxygen-free copper tube is 430mm and the outer diameter is 480mm, and the size of the hexagonal copper core rod is 11mm. The composition of the NbTaHf alloy tube is the same as that of the NbTaHf rod. The outer diameter of the NbTaHf alloy tube is 430mm and the thickness is 3mm, which is 0.3 of the diameter of the Nb rod in the composite sheath.

[0063] Exemplarily, in Step 3, the outer diameter of the composite tube is 100mm and the drilling size is 40mm. In Step 3, the temperature of hot isostatic pressing is 720°C, the temperature of extrusion is 550°C, the extrusion speed is 10mm / s, the straightening accuracy is no more than 1mm error per 3m, and the processing rate between passes of multi-pass cold drawing is 15% - 30%.

[0064] Exemplarily, in Step 4, the mass fraction of Ti atoms in the SnTi rod is 2%. In Step 4, the processing rate between passes of multi-pass cold drawing is 15% - 30%. The external Cu thickness of the cleaned circular sub-element is 0.5mm, and the diameter of the circular sub-element is 3.6mm.

[0065] Exemplarily, in step five, the cross-section of the hexagonal oxygen-free copper tube is hexagonal on the outside and circular on the inside. The width of the outer hexagon is 5.1 mm, and the inner diameter is 4.6 mm. The cross-section of the fan-shaped oxygen-free copper tube is fan-shaped on the outside and circular on the inside. The outer fan shape matches the shape of the hexagonal oxygen-free copper tube, and the inner diameter is the same as that of the hexagonal oxygen-free copper tube. The mass percentage of O atoms in the tin oxide powder is 5%. The thickness of the tin oxide powder in both the hexagonal sub-element and the fan-shaped sub-element is 0.5 mm, and the copper ratios of both the hexagonal sub-element and the fan-shaped sub-element are the same, both being 0.24.

[0066] Exemplarily, in step six, the outer diameter of the oxygen-free copper tube is 54 mm, and the inner diameter is 48 mm. The copper super ratio of the composite wire is 0.3. The hexagonal sub-elements and the fan-shaped sub-elements are closely packed into the Ta tube. The number of hexagonal sub-elements is 55, and the number of fan-shaped sub-elements is 6. The outer diameter of the Ta tube is 47 mm, and the thickness is 1 mm. The gap between the outermost hexagonal sub-element and the Ta tube is filled with an oxygen-free copper rod with a diameter of 1 mm. The processing rate between passes of the multi-pass cold drawing of the composite wire is 8% - 15%. The heat treatment includes: 340 °C / 96 h + 550 °C / 300 h + 650 °C / 150 h.

[0067] In Example 3, in step six, when a 3 m long composite wire is cold drawn in multiple passes to a diameter of 0.8 mm, a 1492 m long kilometer wire is produced, meeting the length requirements of the niobium-tin superconducting wire for existing controlled nuclear fusion projects. The critical current density after heat treatment is 3235 A / mm 2 (4.2K, 12T), much higher than the average performance level of about 2500 A / mm of existing undoped niobium-tin superconducting wires 2 (4.2K, 12T), and higher than the highest performance of known undoped niobium-tin superconducting wires.

[0068] Example 4: Exemplarily, in step one, the inner diameter of the oxygen-free copper tube is 210 mm, and the outer diameter is 225 mm. The Nb rod and the NbTaHf rod have the same size, with a diameter of 210 mm. The mass percentage of Ta atoms in the NbTaHf rod is 4%, and the mass percentage of Hf atoms is 2%. The hexagonal forming sizes of both the CuNb single-core rod and the doped CuNb single-core rod are 5.4 mm, and the copper ratios are the same, both being 0.15. In step one, the temperature of hot isostatic pressing is 700 °C, the temperature of extrusion is 500 °C, the extrusion speed is 15 mm / s, the straightening accuracy is no more than 1 mm error per 3 m, and the processing rate between passes of multi-pass cold drawing is 15% - 30%.

[0069] Exemplarily, in step two, the hexagonal copper core rod is closely arranged at the center of the NbTaHf alloy tube, and the CuNb single core rod and the doped CuNb single core rod are closely arranged outside the hexagonal copper core rod. In step two, the inner diameter of the oxygen-free copper tube is 240 mm, the outer diameter is 270 mm, and the size of the hexagonal copper core rod is 5.4 mm. The composition of the NbTaHf alloy tube is the same as that of the NbTaHf rod. The outer diameter of the NbTaHf alloy tube is 240 mm, and the thickness is 0.9 mm, which is 0.18 of the diameter of the Nb rod in the composite sheath.

[0070] Exemplarily, in step three, the outer diameter of the composite tube is 70 mm, and the drilling size is 25 mm. In step three, the temperature of hot isostatic pressing is 700 °C, the temperature of extrusion is 500 °C, the extrusion speed is 15 mm / s, the straightening accuracy is no more than 1 mm error per 3 meters, and the processing rate between passes of multi-pass cold drawing is 15% - 30%.

[0071] Exemplarily, in step four, the mass proportion of Ti atoms in the SnTi rod is 1%. In step four, the processing rate between passes of multi-pass cold drawing is 15% - 30%. The external Cu thickness of the circular sub-element after cleaning is 0.3 mm, and the diameter of the circular sub-element is 5.5 mm.

[0072] Exemplarily, in step five, the cross-section of the hexagonal oxygen-free copper tube is hexagonal outside and circular inside, the outer hexagonal width is 7 mm, and the inner diameter is 6.5 mm. The cross-section of the fan-shaped oxygen-free copper tube is fan-shaped outside and circular inside, the outer fan shape matches the shape of the hexagonal oxygen-free copper tube, and the inner diameter is the same as that of the hexagonal oxygen-free copper tube. The mass proportion of O atoms in the tin oxide powder is 1%. The thickness of the tin oxide powder in both the hexagonal sub-element and the fan-shaped sub-element is 0.5 mm, and the copper ratios of the hexagonal sub-element and the fan-shaped sub-element are the same, both being 0.15.

[0073] Exemplarily, in step six, the outer diameter of the oxygen-free copper tube is 82 mm, the inner diameter is 48 mm, and the copper super ratio of the composite wire is 2. The hexagonal sub-elements and the fan-shaped sub-elements are closely arranged in the Ta tube. The number of hexagonal sub-elements is 31, and the number of fan-shaped sub-elements is 6. The outer diameter of the Ta tube is 47 mm, and the thickness is 1 mm. The gap between the outermost hexagonal sub-element and the Ta tube is filled with an oxygen-free copper rod with a diameter of 1 mm. The processing rate between passes of multi-pass cold drawing of the composite wire is 8% - 15%. The heat treatment includes: 340 °C / 96 h + 550 °C / 300 h + 650 °C / 150 h.

[0074] In Example 4, in Step 6, when a 3-meter-long composite wire is cold-drawn through multiple passes to a diameter of 0.8 mm, two kilometer-long wires of 1524 meters and 3504 meters are produced, meeting the length requirements of niobium-tin superconducting wires for existing controlled nuclear fusion projects. The critical current density after heat treatment is 3274 A / mm 2 (4.2K, 12T), much higher than the average performance level of about 2500 A / mm 2 (4.2K, 12T) of existing undoped niobium-tin superconducting wires and higher than the highest performance of known undoped niobium-tin superconducting wires.

[0075] In the embodiments of the present application, by using NbTaHf rods and NbTaHf alloy tubes and combining specific preparation process flows, while improving the critical current density of multi-core niobium-tin composite wires, the ability to prepare long wires is achieved. Among them, by using NbTaHf rods, doping elements that can refine niobium-tin grains are provided inside the wire; by using NbTaHf alloy tubes, it is realized that oxygen atoms enter the wire structure only at the subsequent composite wire stage, greatly reducing the number of processing passes of the wire after oxygen atom doping and also providing a source of oxide doping for further improving the wire performance; by using NbTaHf rods and NbTaHf alloy tubes and combining the specific preparation process flows from Step 1 to Step 6, while improving the critical current density of multi-core niobium-tin composite wires, kilometer-level long wires can be produced, reducing the processing difficulty of niobium-tin superconducting wires.

[0076] The proposed heat treatment includes: 340°C / 96h + 550°C / 200 - 300h + 650°C / 72 - 150h. By adopting a specific heat treatment process, the critical current density of multi-core niobium-tin composite wires is further improved.

[0077] Although the preferred embodiments of the present application 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 interpreted to include the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0078] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalent technologies, the present application is also intended to include these modifications and variations.

Claims

1. A method for preparing a high-performance multi-core niobium-tin composite wire, characterized in that: The following steps are involved: Step 1, respectively putting Nb rods and NbTaHf rods into oxygen-free copper tubes, and sequentially subjecting them to hot isostatic pressing, extrusion, straightening, and multiple cold stretching processes to prepare CuNb single-core rods and doped CuNb single-core rods, respectively; Step 2, the hexagonal copper core rod, the CuNb single core rod and the doped CuNb single core rod are densely packed into the NbTaHf alloy tube, and are loaded into the oxygen-free copper tube together to form a composite sheath; Step 3, subjecting the composite sheath to hot isostatic pressing, extrusion, straightening, multi-pass cold drawing, and drilling processes in sequence to prepare a composite tube; Step 4, placing the SnTi rod into the composite tube, and obtaining a circular subcomponent through multiple cold drawing and cleaning processes; Step 5, filling the hexagonal oxygen-free copper tube and the fan-shaped oxygen-free copper tube with tin oxide powder, and respectively loading the circular subcomponent into the hexagonal oxygen-free copper tube and the fan-shaped oxygen-free copper tube in the form of extruded tin oxide powder to form a hexagonal subcomponent and a fan-shaped subcomponent; Step six, assembling the hexagonal sub-components and the fan-shaped sub-components into a Ta tube, and loading them into an oxygen-free copper tube together to form a composite wire, and then sequentially undergoing multiple cold drawing and heat treatment processes to form a multi-core niobium-tin composite wire.

2. The method for preparing a high-performance multi-core niobium-tin composite wire according to claim 1, characterized in that: In step 1, the inner diameter of the oxygen-free copper tube is 100-310 mm, and the outer diameter is 115-335 mm; The Nb rod and the NbTaHf rod have the same size, both with diameters of 100 to 305 mm. The mass proportion of Ta atoms in the NbTaHf rod is 4%, and the mass proportion of Hf atoms is 0.5% to 4%. The hexagonal forming dimensions of the CuNb single core rod and the doped CuNb single core rod are both 2.2-11 mm, and the copper ratio is the same, both 0.1-0.2; In step 1, the temperature of hot isostatic pressing is 650-720°C, the temperature of extrusion is 450-550°C, the speed of extrusion is 10-20 mm / s, the accuracy of straightening is no more than 1 mm per 3 meters, and the processing rate between passes of multi-pass cold drawing is 15%-30%.

3. The method for preparing a high-performance multi-core niobium-tin composite wire according to claim 1, characterized in that: In step 2, the hexagonal copper core rod is densely arranged in the center of the NbTaHf alloy tube, and the CuNb single core rod and the doped CuNb single core rod are densely arranged outside the hexagonal copper core rod; In step 2, the inner diameter of the oxygen-free copper tube is 86-430 mm, the outer diameter is 130-480 mm, and the size of the hexagonal copper mandrel is 2.2-11 mm; The composition of the NbTaHf alloy tube is the same as that of the NbTaHf rod. The outer diameter of the NbTaHf alloy tube is 86-430 mm, and the thickness is 0.2-3 mm, which is 0.1-0.3 of the diameter of the Nb rod in the composite sheath.

4. The method for preparing a high-performance multi-core niobium-tin composite wire according to claim 1, characterized in that: In step 3, the outer diameter of the composite tube is 40-100 mm, and the drilling size is 12-40 mm; In step three, the temperature of hot isostatic pressing is 650~720°C, the temperature of extrusion is 450~550°C, the speed of extrusion is 10~20mm / s, the accuracy of straightening is no more than 1mm per 3 meters, and the processing rate between passes of multi-pass cold drawing is 15%~30%.

5. The method for preparing a high-performance multi-core niobium-tin composite wire according to claim 1, characterized in that: In step 4, the mass proportion of Ti atoms in the SnTi rod is 0.7% to 2%; In step 4, the processing rate between passes of the multi-pass cold drawing is 15% to 30%, the outer Cu thickness of the circular subcomponent after cleaning is 0.2 to 0.5 mm, and the diameter of the circular subcomponent is 1.8 to 5.5 mm.

6. The method for preparing a high-performance multi-core niobium-tin composite wire according to claim 1, characterized in that: In step 5, the cross-section of the hexagonal oxygen-free copper tube is hexagonal on the outside and circular on the inside, the width of the outer hexagon is 3-7 mm, and the inner diameter is 2.8-6.5 mm; The cross section of the fan-shaped oxygen-free copper tube is fan-shaped on the outside and circular on the inside, the outer fan-shaped tube matches the shape of the hexagonal oxygen-free copper tube, and the inner diameter is the same as that of the hexagonal oxygen-free copper tube; The mass proportion of O atoms in the tin oxide powder is 1% to 5%; The thickness of the tin oxide powder in the hexagonal subcomponent and the fan-shaped subcomponent is 0.5 mm, and the copper ratio of the hexagonal subcomponent and the fan-shaped subcomponent is the same, which is 0.1-0.

27.

7. The method for preparing a high-performance multi-core niobium-tin composite wire according to claim 1, characterized in that: In step 6, the outer diameter of the oxygen-free copper tube is 54-82 mm, the inner diameter is 48 mm, and the copper excess ratio of the composite wire is 0.3-2; The hexagonal subcomponents and the fan-shaped subcomponents are closely packed into the Ta tube, the number of the hexagonal subcomponents is 31 to 163, the number of the fan-shaped subcomponents is 6, and the outer diameter of the Ta tube is 47 mm and the thickness is 1 mm; The gap between the outermost hexagonal subcomponent and the Ta tube is filled with an oxygen-free copper rod with a diameter of 1 mm; The processing rate between passes of the multi-pass cold drawing of the composite wire is 8% to 15%; The heat treatment includes: 340°C / 96h+550°C / 200~300h+650°C / 72~150h.

8. A high performance multi-core niobium-tin composite wire, characterized in that: The high-performance multi-core niobium-tin composite wire is prepared by the preparation method of any one of claims 1 to 7.

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