A preparation method for high-performance multi-core niobium-tin composite wire and the composite wire

Abstract

The present invention discloses a method for preparing a high-performance multi-core niobium-tin composite wire and the composite wire, which relates to the technical field of superconducting composite wires. The method comprises the following steps: separately loading Nb rods and NbTaHf rods into oxygen-free copper tubes to prepare CuNb single-core rods and doped CuNb single-core rods; loading hexagonal copper core rods, CuNb single-core rods, and doped CuNb single-core rods into NbTaHf alloy tubes, and collectively loading them into the oxygen-free copper tube to form a composite sheath; preparing the composite tube; loading SnTi rods into the composite tube to obtain circular subcomponents; forming hexagonal subcomponents and fan-shaped subcomponents; assembling them into Ta tubes, and collectively loading them into the oxygen-free copper tube to form the composite wire, and finally forming the multi-core niobium-tin composite wire. By utilizing NbTaHf rods and NbTaHf alloy tubes, combined with a specific preparation process, the present application improves the critical current density of the multi-core niobium-tin composite wire while also enabling long-wire preparation.

Description

Technical Field

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

[0002] The target critical current density of the niobium-tin superconducting material required for the magnet performance design of controlled nuclear fusion projects exceeds 2700A / mm² (4.2K, 12T), approaching the current performance design limit of niobium-tin wire. To achieve this extremely high performance, the current common technical solution is to increase the grain boundary density of niobium-tin wire through elemental doping, thereby further improving the wire's performance. A common doping method is to add Ta, Hf, Zr, and corresponding oxides to Nb, followed by the preparation of niobium-tin superconducting wire through powder tube technology. This elemental doping method for improving the performance of niobium-tin superconducting wire has been widely proven.

[0003] In the prior art, Chinese patent CN115295243A discloses a method for preparing element-doped niobium-tin superconducting strands with high critical current density. Specifically, the process involves: loading Nb-XY into a copper tube and treating it to obtain a Cu / Nb-XY single-core rod; loading oxide powder into a copper tube and treating it to obtain a Cu / oxide single-core rod; pouring molten Sn into an oxygen-free copper cylinder to obtain a Cu / Sn billet, which is then subjected to multiple cold forging, drawing, and forming steps to obtain a Cu / Sn single-core rod; bundling the Cu / Nb-XY single-core rod and the Cu / oxide single-core rod into a copper tube, which is then drawn and formed to obtain a Nb module; bundling the Nb module and the Cu / Sn single-core rod into a Ta tube, which is then loaded into a copper tube and drawn multiple times to complete the process.

[0004] However, due to the limitation that doping atoms will cause the plastic processing performance of the wire to drop sharply, although the above-mentioned existing technology can improve the critical current density of niobium-tin superconducting wire, there are huge technical obstacles in the preparation of long wires (kilometer level), and it is impossible to take into account both high critical current density and long wire preparation. Summary of the Invention

[0005] The present application provides a method for preparing a high-performance multi-core niobium-tin composite wire and the composite wire, which is used to solve the problem that the existing niobium-tin superconducting wire preparation technology cannot take into account both high critical current density and long wire preparation.

[0006] In one aspect, the present application provides a method for preparing a high-performance multi-core niobium-tin composite wire, comprising the following steps:

[0007] In step 1, Nb rods and NbTaHf rods are respectively placed into oxygen-free copper tubes, and are sequentially subjected to hot isostatic pressing, extrusion, straightening, and multiple cold drawing processes to prepare CuNb single-core rods and doped CuNb single-core rods, respectively.

[0008] Step 2: The hexagonal copper core rod, the CuNb single core rod and the doped CuNb single core rod are densely packed into a NbTaHf alloy tube, and then are all packed into an oxygen-free copper tube to form a composite sheath.

[0009] Step three: subjecting the composite sheath to hot isostatic pressing, extrusion, straightening, multi-pass cold drawing, and drilling processes in sequence to prepare a composite tube.

[0010] Step 4: Place the SnTi rod into the composite tube, and obtain a circular subcomponent through multiple cold drawing and cleaning processes.

[0011] Step 5: Fill the hexagonal oxygen-free copper tube and the fan-shaped oxygen-free copper tube with tin oxide powder, and respectively load the circular subcomponents 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 hexagonal subcomponents and fan-shaped subcomponents.

[0012] Step 6: Assemble the hexagonal sub-components and the fan-shaped sub-components into a Ta tube and place them together into an oxygen-free copper tube to form a composite wire, which is then subjected to multiple cold drawing and heat treatment processes to form a multi-core niobium-tin composite wire.

[0013] 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.

[0014] The Nb rod and the NbTaHf rod have the same size, both with diameters of 100-305 mm. The mass proportion of Ta atoms in the NbTaHf rod is 4%, and the mass proportion of Hf atoms is 0.5%-4%.

[0015] 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.

[0016] In step 1, the hot isostatic pressing temperature is 650-720°C, the extrusion temperature is 450-550°C, the extrusion speed is 10-20 mm / s, the straightening accuracy is no more than 1 mm per 3 meters, and the inter-pass processing rate of multi-pass cold drawing is 15%-30%.

[0017] In a possible implementation, in step 2, the hexagonal copper core rods are densely arranged in the center of the NbTaHf alloy tube, and the CuNb single core rods and the doped CuNb single core rods are densely arranged outside the hexagonal copper core rods.

[0018] 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.

[0019] 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.

[0020] In a possible implementation, in step three, the outer diameter of the composite tube is 40-100 mm, and the drilling size is 12-45 mm.

[0021] In step 3, the hot isostatic pressing temperature is 650-720°C, the extrusion temperature is 450-550°C, the extrusion speed is 10-20 mm / s, the straightening accuracy is no more than 1 mm per 3 meters, and the inter-pass processing rate of multi-pass cold drawing is 15%-30%.

[0022] In a possible implementation, in step 4, the mass proportion of Ti atoms in the SnTi rod is 0.7% to 2%.

[0023] In step 4, the inter-pass processing rate of the multi-pass cold drawing is 15% to 30%, the outer Cu thickness of the cleaned circular subcomponent is 0.2 to 0.5 mm, and the diameter of the circular subcomponent is 1.8 to 5.5 mm.

[0024] In a possible implementation, in step five, the cross-section of the hexagonal oxygen-free copper tube is hexagonal on the outside and circular on the inside, with an outer hexagonal width of 3 to 7 mm and an inner diameter of 2.8 to 6.5 mm.

[0025] The cross section of the fan-shaped oxygen-free copper tube is fan-shaped outside and circular inside. The outer fan-shaped tube matches the shape of the hexagonal oxygen-free copper tube and has the same inner diameter as the hexagonal oxygen-free copper tube.

[0026] The mass proportion of O atoms in the tin oxide powder is 1% to 5%.

[0027] The thickness of the tin oxide powder in the hexagonal sub-component and the fan-shaped sub-component is 0.5 mm. The copper ratio of the hexagonal sub-component and the fan-shaped sub-component is the same, which is 0.1-0.27.

[0028] In a possible implementation, in step six, 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.

[0029] The hexagonal subcomponents and the fan-shaped subcomponents are densely packed into the Ta tube, the number of the hexagonal subcomponents is 31 to 163, the number of the fan-shaped subcomponents is 6, the outer diameter of the Ta tube is 47 mm, and the thickness is 1 mm.

[0030] 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.

[0031] The processing rate between passes of the multi-pass cold drawing of the composite wire is 8% to 15%.

[0032] The heat treatment includes: 340°C / 96h+550°C / 200~300h+650°C / 72~150h.

[0033] On the other hand, the present application provides a high-performance multi-core niobium-tin composite wire, which is prepared using the above-mentioned method for preparing a high-performance multi-core niobium-tin composite wire.

[0034] The preparation method and composite wire of a high-performance multi-core niobium-tin composite wire in this application have the following advantages:

[0035] By using NbTaHf rods and NbTaHf alloy tubes, combined with a specific fabrication process, the critical current density of multi-core niobium-tin composite wires is increased while also enabling the production of long wires. The use of NbTaHf rods provides the wire with doping elements that refine the niobium-tin grains; the use of NbTaHf alloy tubes ensures that oxygen atoms enter the wire structure only during the subsequent composite wire stage, significantly reducing the number of wire processing passes after oxygen doping and providing a source of oxide doping for further improved wire performance. By using NbTaHf rods and NbTaHf alloy tubes, combined with the specific fabrication process steps one through six, the critical current density of multi-core niobium-tin composite wires is increased while enabling the production of kilometer-long wires, reducing the processing difficulty of niobium-tin superconducting wires.

[0036] 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 the multi-core niobium-tin composite wire is further improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0038] Figure 1 A schematic flow chart of a method for preparing a high-performance multi-core niobium-tin composite wire provided in an embodiment of the present application;

[0039] Figure 2 A cross-sectional view of the multi-core niobium-tin composite wire provided in an embodiment of the present application;

[0040] Figure 3 This is a cross-sectional electron microscope scan of the multi-core niobium-tin composite wire provided in an embodiment of the present application. DETAILED DESCRIPTION

[0041] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0042] like Figure 1 As shown, the embodiment of the present application provides a method for preparing a high-performance multi-core niobium-tin composite wire, comprising the following steps:

[0043] In step 1, Nb rods and NbTaHf rods are respectively placed into oxygen-free copper tubes, and are sequentially subjected to hot isostatic pressing, extrusion, straightening, and multiple cold drawing processes to prepare CuNb single-core rods and doped CuNb single-core rods, respectively.

[0044] Step 2: The hexagonal copper core rod, the CuNb single core rod and the doped CuNb single core rod are densely packed into a NbTaHf alloy tube, and then are all packed into an oxygen-free copper tube to form a composite sheath.

[0045] Step three: subjecting the composite sheath to hot isostatic pressing, extrusion, straightening, multi-pass cold drawing, and drilling processes in sequence to prepare a composite tube.

[0046] Step 4: Place the SnTi rod into the composite tube, and obtain a circular subcomponent through multiple cold drawing and cleaning processes.

[0047] Step 5: Fill the hexagonal oxygen-free copper tube and the fan-shaped oxygen-free copper tube with tin oxide powder, and respectively load the circular subcomponents 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 hexagonal subcomponents and fan-shaped subcomponents.

[0048] Step 6: Assemble the hexagonal sub-components and the fan-shaped sub-components into a Ta tube and place them together into an oxygen-free copper tube to form a composite wire, which is then subjected to multiple cold drawing and heat treatment processes to form a multi-core niobium-tin composite wire.

[0049] Specifically, in this embodiment, the tin oxide powder refers to tin powder doped with oxygen.

[0050] The embodiment of the present application further provides a high-performance multi-core niobium-tin composite wire, which is prepared using the above-mentioned method for preparing a high-performance multi-core niobium-tin composite wire.

[0051] like Figure 2 As shown, it is a cross-sectional view of the multi-core niobium-tin composite wire; Figure 3 The figure shows a cross-sectional electron microscope image of the multi-core niobium-tin composite wire. It can be seen from the electron microscope image that the niobium-tin grains in the multi-core niobium-tin composite wire of the present application have been refined, thereby improving the current carrying capacity of the multi-core niobium-tin composite wire.

[0052] Example 1:

[0053] For example, in step 1, 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 are of the same size, both with a diameter of 100 mm. The mass proportion of Ta atoms in the NbTaHf rod is 4%, and the mass proportion of Hf atoms is 0.5%. The hexagonal forming size of the CuNb single-core rod and the doped CuNb single-core rod are both 2.2 mm, and the copper ratio is the same, both 0.2. In step 1, 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 no more than 1 mm per 3 meters, and the inter-pass processing rate of the multi-pass cold drawing is 15% to 30%.

[0054] Exemplarily, in step 2, the hexagonal copper core rod is densely packed in the center of the NbTaHf alloy tube, and the CuNb single core rod and the doped CuNb single core rod are densely packed outside the hexagonal copper core rod. In step 2, the oxygen-free copper tube has an inner diameter of 86 mm and an outer diameter of 130 mm, and the hexagonal copper core rod is 2.2 mm in size. The NbTaHf alloy tube has the same composition as the NbTaHf rod, an outer diameter of 86 mm, and a thickness of 0.2 mm, which is 0.1 of the diameter of the Nb rod in the composite sheath.

[0055] For example, in step 3, the outer diameter of the composite tube is 40 mm, and the drill hole size is 12 mm. In step 3, 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 no more than 1 mm per 3 meters, and the inter-pass processing rate of the multi-pass cold drawing is 15% to 30%.

[0056] For example, in step 4, the mass fraction of Ti atoms in the SnTi rod is 0.7%. In step 4, the inter-pass processing rate of the multi-pass cold drawing is 15% to 30%, the outer Cu thickness of the cleaned circular subcomponent is 0.2 mm, and the diameter of the circular subcomponent is 1.8 mm.

[0057] Exemplarily, in step 5, the cross-section of the hexagonal oxygen-free copper tube is an outer hexagonal inner circular, the outer hexagonal width is 3 mm, and the inner diameter is 2.8 mm. The cross-section of the fan-shaped oxygen-free copper tube is an outer fan-shaped inner circular, 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%. 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, both 0.1.

[0058] For example, in step six, the outer diameter of the oxygen-free copper tube is 67 mm, the inner diameter is 48 mm, and the copper excess ratio of the composite wire is 1. The hexagonal subcomponents and the fan-shaped subcomponents are densely packed into the Ta tube. The number of hexagonal subcomponents is 163, and the number of fan-shaped subcomponents is 6. The Ta tube has an outer diameter of 47 mm and a thickness of 1 mm. The gap between the outermost hexagonal subcomponents and the Ta tube is filled with an oxygen-free copper rod with a diameter of 1 mm. The inter-pass processing rate of the multi-pass cold drawing of the composite wire is 8% to 15%. The heat treatment includes: 340°C / 96h + 550°C / 200h + 650°C / 72h.

[0059] In Example 1, in step 6, a 3m long composite wire was cold stretched multiple times to a diameter of 0.8mm, producing two kilometer-long wires of 1142 meters and 3380 meters. The length of a single wire exceeded 3000 meters, meeting the length requirements of niobium-tin superconducting wires used in existing controlled nuclear fusion projects. The critical current density after heat treatment is 3120A / mm 2 (4.2K, 12T), much higher than the existing undoped niobium-tin superconducting wire of about 2500A / mm 2 The average performance level of (4.2K, 12T) is higher than the highest performance of known undoped niobium-tin superconducting wires.

[0060] Example 2:

[0061] Exemplarily, in step 1, 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 are of the same size, both with a diameter of 150 mm. The mass proportion of Ta atoms in the NbTaHf rod is 4%, and the mass proportion of Hf atoms is 4%. The hexagonal forming size of the CuNb single-core rod and the doped CuNb single-core rod is 5.5 mm, and the copper ratio is the same, both 0.2. In step 1, the hot isostatic pressing temperature is 700°C, the extrusion temperature is 500°C, the extrusion speed is 15 mm / s, the straightening accuracy is no more than 1 mm per 3 meters, and the inter-pass processing rate of the multi-pass cold drawing is 15% to 30%.

[0062] Exemplarily, in step 2, the hexagonal copper core rod is densely packed in the center of the NbTaHf alloy tube, and the CuNb single core rod and the doped CuNb single core rod are densely packed outside the hexagonal copper core rod. In step 2, the oxygen-free copper tube has an inner diameter of 195 mm and an outer diameter of 240 mm, and the hexagonal copper core rod is 5.5 mm. The NbTaHf alloy tube has the same composition as the NbTaHf rod, an outer diameter of 195 mm, and a thickness of 0.9 mm, which is 0.18 of the diameter of the Nb rod in the composite sheath.

[0063] For example, in step 3, the outer diameter of the composite tube is 70 mm, and the drill hole size is 25 mm. In step 3, the hot isostatic pressing temperature is 700°C, the extrusion temperature is 500°C, the extrusion speed is 15 mm / s, the straightening accuracy is no more than 1 mm per 3 meters, and the inter-pass processing rate of the multi-pass cold drawing is 15% to 30%.

[0064] For example, in step 4, the mass fraction of Ti atoms in the SnTi rod is 1%. In step 4, the inter-pass processing rate of the multi-pass cold drawing is 15% to 30%, the outer Cu thickness of the cleaned circular subcomponent is 0.3 mm, and the diameter of the circular subcomponent is 3.5 mm.

[0065] Exemplarily, in step 5, the cross-section of the hexagonal oxygen-free copper tube is an outer hexagonal inner circular, 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 an outer fan-shaped inner circular, 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 2%. 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, both 0.27.

[0066] For example, in step six, the outer diameter of the oxygen-free copper tube is 72 mm, the inner diameter is 48 mm, and the copper excess ratio of the composite wire is 1.5. The hexagonal subcomponents and the fan-shaped subcomponents are densely packed into the Ta tube. The number of hexagonal subcomponents is 55, and the number of fan-shaped subcomponents is 6. The outer diameter of the Ta tube is 47 mm and the thickness is 1 mm. The gap between the outermost hexagonal subcomponents and the Ta tube is filled with an oxygen-free copper rod with a diameter of 1 mm. The inter-pass processing rate of the multi-pass cold drawing of the composite wire is 8% to 15%. The heat treatment includes: 340°C / 96h + 550°C / 250h + 650°C / 96h.

[0067] In Example 2, in step 6, a 3m long composite wire was cold stretched to a diameter of 0.8mm through multiple passes, producing three kilometer-long wires of 1760m, 1232m, and 2270m, meeting the length requirements of niobium-tin superconducting wires for existing controlled nuclear fusion projects. The critical current density after heat treatment is 3274A / mm 2 (4.2K, 12T), much higher than the existing undoped niobium-tin superconducting wire of about 2500A / mm 2 The average performance level of (4.2K, 12T) is higher than the highest performance of known undoped niobium-tin superconducting wires.

[0068] Example 3:

[0069] For example, in step 1, the inner diameter of the oxygen-free copper tube is 310 mm and the outer diameter is 335 mm. The Nb rod and the NbTaHf rod are of the same size, both with a diameter of 305 mm. The mass proportion of Ta atoms in the NbTaHf rod is 4%, and the mass proportion of Hf atoms is 2%. The hexagonal forming size of the CuNb single-core rod and the doped CuNb single-core rod is 11 mm, and the copper ratio is the same, both 0.1. In step 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 no more than 1 mm per 3 meters, and the inter-pass processing rate of the multi-pass cold drawing is 15% to 30%.

[0070] Exemplarily, in step 2, the hexagonal copper core rod is densely packed in the center of the NbTaHf alloy tube, and the CuNb single core rod and the doped CuNb single core rod are densely packed outside the hexagonal copper core rod. In step 2, the oxygen-free copper tube has an inner diameter of 430 mm and an outer diameter of 480 mm, and the hexagonal copper core rod is 11 mm in size. The NbTaHf alloy tube has the same composition as the NbTaHf rod, an outer diameter of 430 mm, and a thickness of 3 mm, which is 0.3 of the diameter of the Nb rod in the composite sheath.

[0071] For example, in step 3, the outer diameter of the composite tube is 100 mm, and the drill hole size is 40 mm. In step 3, 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 no more than 1 mm per 3 meters, and the inter-pass processing rate of the multi-pass cold drawing is 15% to 30%.

[0072] For example, in step 4, the mass fraction of Ti atoms in the SnTi rod is 2%. In step 4, the inter-pass processing rate of the multi-pass cold drawing is 15% to 30%, the outer Cu thickness of the cleaned circular subcomponent is 0.5 mm, and the diameter of the circular subcomponent is 3.6 mm.

[0073] Exemplarily, in step 5, the cross-section of the hexagonal oxygen-free copper tube is an outer hexagonal inner circular, the outer hexagonal width is 5.1 mm, and the inner diameter is 4.6 mm. The cross-section of the fan-shaped oxygen-free copper tube is an outer fan-shaped inner circular, 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 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, both 0.24.

[0074] For example, in step six, the outer diameter of the oxygen-free copper tube is 54 mm, the inner diameter is 48 mm, and the copper excess ratio of the composite wire is 0.3. The hexagonal subcomponents and the fan-shaped subcomponents are closely packed into the Ta tube. The number of hexagonal subcomponents is 55, and the number of fan-shaped subcomponents is 6. The outer diameter of the Ta tube is 47 mm and the thickness is 1 mm. The gap between the outermost hexagonal subcomponents and the Ta tube is filled with an oxygen-free copper rod with a diameter of 1 mm. The inter-pass processing rate of the multi-pass cold drawing of the composite wire is 8% to 15%. The heat treatment includes: 340°C / 96h + 550°C / 300h + 650°C / 150h.

[0075] In Example 3, in step 6, a 3m long composite wire is cold stretched multiple times to a diameter of 0.8mm, producing a 1492m long wire, which meets the length requirements of niobium-tin superconducting wire used in existing controlled nuclear fusion projects. The critical current density after heat treatment is 3235A / mm 2 (4.2K, 12T), much higher than the existing undoped niobium-tin superconducting wire of about 2500A / mm 2 The average performance level of (4.2K, 12T) is higher than the highest performance of known undoped niobium-tin superconducting wires.

[0076] Example 4:

[0077] For example, in step 1, 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 are of the same size, both with a diameter of 210 mm. The mass proportion of Ta atoms in the NbTaHf rod is 4%, and the mass proportion of Hf atoms is 2%. The hexagonal forming size of the CuNb single-core rod and the doped CuNb single-core rod is 5.4 mm, and the copper ratio is the same, both 0.15. In step 1, the hot isostatic pressing temperature is 700°C, the extrusion temperature is 500°C, the extrusion speed is 15 mm / s, the straightening accuracy is no more than 1 mm per 3 meters, and the inter-pass processing rate of the multi-pass cold drawing is 15% to 30%.

[0078] Exemplarily, in step 2, the hexagonal copper core rod is densely packed in the center of the NbTaHf alloy tube, and the CuNb single core rod and the doped CuNb single core rod are densely packed outside the hexagonal copper core rod. In step 2, the oxygen-free copper tube has an inner diameter of 240 mm and an outer diameter of 270 mm, and the hexagonal copper core rod is 5.4 mm in size. The NbTaHf alloy tube has the same composition as the NbTaHf rod, an outer diameter of 240 mm, and a thickness of 0.9 mm, which is 0.18 of the diameter of the Nb rod in the composite sheath.

[0079] For example, in step 3, the outer diameter of the composite tube is 70 mm, and the drill hole size is 25 mm. In step 3, the hot isostatic pressing temperature is 700°C, the extrusion temperature is 500°C, the extrusion speed is 15 mm / s, the straightening accuracy is no more than 1 mm per 3 meters, and the inter-pass processing rate of the multi-pass cold drawing is 15% to 30%.

[0080] For example, in step 4, the mass fraction of Ti atoms in the SnTi rod is 1%. In step 4, the inter-pass processing rate of the multi-pass cold drawing is 15% to 30%, the outer Cu thickness of the cleaned circular subcomponent is 0.3 mm, and the diameter of the circular subcomponent is 5.5 mm.

[0081] Exemplarily, in step 5, the cross-section of the hexagonal oxygen-free copper tube is an outer hexagonal inner circular, 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 an outer fan-shaped inner circular, 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%. 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, both 0.15.

[0082] For example, in step six, the outer diameter of the oxygen-free copper tube is 82 mm, the inner diameter is 48 mm, and the copper excess ratio of the composite wire is 2. The hexagonal subcomponents and the fan-shaped subcomponents are closely packed into the Ta tube. The number of hexagonal subcomponents is 31, and the number of fan-shaped subcomponents is 6. The outer diameter of the Ta tube is 47 mm, and the thickness is 1 mm. The gap between the outermost hexagonal subcomponents and the Ta tube is filled with an oxygen-free copper rod with a diameter of 1 mm. The inter-pass processing rate of the multi-pass cold drawing of the composite wire is 8% to 15%. The heat treatment includes: 340°C / 96h + 550°C / 300h + 650°C / 150h.

[0083] In Example 4, in step 6, a 3m long composite wire was cold stretched to a diameter of 0.8mm through multiple passes, producing two kilometer-long wires of 1524m and 3504m, meeting the length requirements of niobium-tin superconducting wires for existing controlled nuclear fusion projects. The critical current density after heat treatment is 3274A / mm 2 (4.2K, 12T), much higher than the existing undoped niobium-tin superconducting wire of about 2500A / mm 2 The average performance level of (4.2K, 12T) is higher than the highest performance of known undoped niobium-tin superconducting wires.

[0084] The embodiment of the present application uses NbTaHf rods and NbTaHf alloy tubes, combined with a specific preparation process, to improve the critical current density of multi-core niobium-tin composite wire while also having the ability to produce long wires. Specifically, the use of NbTaHf rods provides the interior of the wire with doping elements that can refine the niobium-tin grains; the use of NbTaHf alloy tubes ensures that oxygen atoms enter the wire structure only in the subsequent composite wire stage, greatly reducing the number of wire processing passes after oxygen atom doping and providing a source of oxide doping to further improve wire performance; the use of NbTaHf rods and NbTaHf alloy tubes, combined with the specific preparation process of steps one to six, improves the critical current density of multi-core niobium-tin composite wire while being able to produce kilometer-long wires, reducing the processing difficulty of niobium-tin superconducting wires.

[0085] 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 the multi-core niobium-tin composite wire is further improved.

[0086] Although the preferred embodiments of the present application have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present application.

[0087] Obviously, those skilled in the art may make various changes and modifications to this application without departing from the spirit and scope of this application. Thus, if these modifications and variations of this application fall within the scope of the claims of this application and their equivalents, this application is intended to include these modifications and variations.

Claims

1. A method for preparing a multi-core niobium-tin composite wire, characterized in that: The following steps are involved: Step 1: Nb rods and NbTaHf rods are respectively placed into oxygen-free copper tubes, and are sequentially subjected to hot isostatic pressing, extrusion, straightening, and multiple cold drawing 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 a NbTaHf alloy tube, and then are collectively packed into an oxygen-free copper tube to form a composite sheath; Step 3: subjecting the composite sheath to hot isostatic pressing, extrusion, straightening, multiple cold drawing, and drilling processes in sequence to prepare a composite tube; Step 4: Place the SnTi rod into the composite tube, and obtain a circular subcomponent through multiple cold drawing and cleaning processes; Step 5: Filling tin oxide powder into the hexagonal oxygen-free copper tube and the fan-shaped oxygen-free copper tube, 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 6: Assembling the hexagonal sub-components and the fan-shaped sub-components into a Ta tube and placing them together into an oxygen-free copper tube to form a composite wire, which is then subjected to multiple cold drawing and heat treatment steps to form a multi-core niobium-tin composite wire; In step 2, the hexagonal copper core rods are densely arranged in the center of the NbTaHf alloy tube, and the CuNb single core rods and the doped CuNb single core rods are densely arranged outside the hexagonal copper core rods; The heat treatment includes: 340°C / 96h+550°C / 200~300h+650°C / 72~150h.

2. The method for preparing a 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 having a diameter 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 size 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 hot isostatic pressing temperature is 650-720°C, the extrusion temperature is 450-550°C, the extrusion speed is 10-20 mm / s, the straightening accuracy is no more than 1 mm per 3 meters, and the inter-pass processing rate of multi-pass cold drawing is 15%-30%.

3. The method for preparing a multi-core niobium-tin composite wire according to claim 1, characterized in that: 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; 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 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 3, the hot isostatic pressing temperature is 650-720°C, the extrusion temperature is 450-550°C, the extrusion speed is 10-20 mm / s, the straightening accuracy is no more than 1 mm per 3 meters, and the inter-pass processing rate of multi-pass cold drawing is 15%-30%.

5. The method for preparing a 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 inter-pass processing rate of the multi-pass cold drawing is 15% to 30%, the outer Cu thickness of the cleaned circular subcomponent 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 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, with an outer hexagonal width of 3 to 7 mm and an inner diameter of 2.8 to 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 has the same inner diameter as 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 sub-component and the fan-shaped sub-component is 0.5 mm. The copper ratio of the hexagonal sub-component and the fan-shaped sub-component is the same, which is 0.1-0.

27.

7. The method for preparing a 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%.

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

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