A method of producing a pre-textured bi-2212 wire

Abstract

The application discloses a preparation method of pre-textured Bi-2212 wire, which comprises the following steps: 1, Bi-2212 precursor powder is loaded into a silver tube, and is drawn and rolled into a flat strip; 2, the flat strip is loaded into the silver tube after being cut to a certain length and cut off, and then is drawn to process into a hexagonal sub-element wire; 3, the hexagonal sub-element wire is loaded into a silver-magnesium alloy tube after being cut to a certain length and cut off, to obtain a secondary composite, and then is drawn to obtain the pre-textured Bi-2212 wire. The application introduces the flat strip core wire into the round wire structure, improves the texture orientation of the core wire in the a and c directions, promotes the ordered arrangement of the crystal grains, is beneficial to sharpening the biaxial orientation of the Bi-2212 crystal grains, reduces the misfit angle of the Bi-2212 crystal grains, reduces the weak connection, improves the current-carrying performance of the Bi-2212 wire, and is suitable for preparing an ultra-high field magnet.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature superconducting material preparation technology, specifically relating to a method for preparing pre-textured Bi-2212 wire. Background Technology

[0002] Practical high-temperature superconducting materials mainly include three materials: REBa2Cu3O y (REBCO) coated conductor, Bi2Sr2Ca2Cu3O y (Bi-2223) and Bi2Sr2CaCu2O y (Bi-2212). REBCO coated conductors generally employ physical deposition to prepare oxide buffer layers and superconducting layers on a metal substrate. By sharpening the biaxial orientation of the grains and reducing mismatch angles, high-performance strips are obtained. Bi-2223 introduces rolling orientation into the strip through heat treatment combined with rolling technology, forming c-axis aligned Bi-2223 grains. Compared to the previous two strips, Bi-2212 has a circular wire structure. Through melt recrystallization growth, the Bi-2212 grains are aligned along the a-axis, and the texture orientation is relatively weak.

[0003] Bi2Sr2CaCu2O y The crystal structure of (Bi-2212) is a layered tetragonal system. During the melt-recrystallization growth process, the growth rate of grains along the a-axis or b-axis is significantly greater than that of grains along the c-axis. In the local environment of a circular core wire, Bi-2212 grains will deflect, the preferred orientation of the core wire deteriorates, and the increased mismatch angle leads to a decrease in wire performance.

[0004] Traditional powder-coated tubular methods for preparing multi-core round wires generally struggle to adjust the core wire orientation within the wire. Rolling Bi-2212 round wire typically results in core wire breakage, increased liquid phase residue during melting, leading to impurity phase residue and increased destructive bridging. This is significantly different from the solid-state reaction of Bi-2212. The melting growth of Bi-2212 is influenced by the silver layer; introducing a flat silver layer in the initial stage can help improve the grain arrangement of the wire. Summary of the Invention

[0005] The technical problem to be solved by this invention is to provide a method for preparing pre-textured Bi-2212 wire, addressing the shortcomings of the prior art. This method introduces flat core wires into the round wire structure, improving the texture orientation of the core wires in the a and c directions, promoting orderly grain arrangement, reducing the mismatch angle of Bi-2212 grains, decreasing weak connections, and improving the current-carrying capacity of the Bi-2212 wire. This solves the problem that traditional methods produce Bi-2212 wires with only a weak a-axis orientation, high mismatch angles between grains, and weak connections, which reduce current-carrying capacity.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for preparing pre-textured Bi-2212 wire, characterized in that the method includes the following steps: Step 1: Load Bi-2212 precursor powder into a silver tube, draw it into wire, and roll the wire into flat strips of different sizes. Step 2: After the flat strip from Step 1 is cut to length and placed into a silver tube, it is drawn to obtain a primary composite containing the flat strip. Then, the primary composite is processed into hexagonal sub-component wires. Step 3: After cutting the hexagonal sub-component wires from Step 2 to length, insert them into a silver-magnesium alloy tube to obtain a secondary composite. Then, perform drawing processing to obtain pre-textured Bi-2212 wires.

[0007] To address the issues of traditionally prepared Bi-2212 wires where the core wire is typically circular, the Bi-2212 grains exhibit a weak a-axis orientation, high mismatch angles between grains, and weak connections leading to high-angle grain boundaries that hinder current transmission along the copper-oxide surface and reduce the wire's current-carrying capacity, this invention combines a single-core flat strip with a multi-core circular structure through a pre-texturing method. This introduces a c-axis orientation along the rolling direction into the traditional a-axis orientation of Bi-2212, enhancing the texture of the Bi-2212 wire in both the a and c directions. This promotes orderly grain arrangement, sharpens the biaxial orientation of the Bi-2212 grains, reduces the mismatch angles of the Bi-2212 grains, decreases weak connections, and ultimately improves the current-carrying capacity of the Bi-2212 wire.

[0008] Typically, in step two of this invention, the cut and sized flat strips are arranged and fixed according to their size before being inserted into the silver tube. Alternatively, the wider flat strips are inserted first, followed by the narrower ones, to ensure that the core wires remain flat strips after insertion, thus achieving the best possible filling rate.

[0009] The above-mentioned method for preparing a pre-woven Bi-2212 wire is characterized in that the width of the flat strip in step one is 1.0mm~4.6mm and the thickness is 0.2mm~0.7mm.

[0010] The above-mentioned method for preparing a pre-textured Bi-2212 wire is characterized in that the sub-component wire in step two contains 12, 16 or 32 flat strips.

[0011] The above-mentioned method for preparing a pre-textured Bi-2212 wire is characterized in that the secondary composite in step three comprises 7, 18 or 36 sub-component wires, and the central component is a silver insert rod.

[0012] Compared with the prior art, the present invention has the following advantages: 1. This invention combines strip and wire structures, introducing a flat strip core wire structure while maintaining isotropic circular wire, forming preferentially oriented grains arranged along the a and c axes; this not only improves the texture orientation of the core wire in the a and c directions, but also reduces the anisotropy of the circular wire structure to a greater extent, reduces the mismatch angle of Bi-2212 grains, reduces weak connections, and improves the current carrying capacity of Bi-2212 wire.

[0013] 2. By adjusting the thickness and width of the strip, this invention can achieve better filling, so that the core wire of the strip can maintain the optimal structure. During the processing, the core wire deformation is more uniform, maintaining the strip structure and reducing the breakage and fusion of the core wire. This uniformly distributed strip structure can better induce the growth of Bi-2212 and sharpen the grain texture orientation, which is conducive to obtaining high-performance Bi-2212 wire.

[0014] 3. To address the problem of uneven stress distribution during wire processing, which often leads to inconsistent deformation of the silver layer and powder, and easy cracking of the central barrier silver layer, this invention achieves uniform deformation of the silver layer and powder in the single-core strip by appropriately increasing the thickness of the sub-component central strip. This greatly reduces the cracking of the barrier silver layer, reduces the residual impurities and destructive bridging during melting growth, and further improves the current carrying capacity of Bi-2212 wire. Moreover, this method is simple and easy to operate and has good application prospects.

[0015] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0016] Figure 1 This is a cross-sectional schematic diagram of a primary composite containing a flat strip in Embodiment 1 of the present invention.

[0017] Figure 2 This is a schematic cross-sectional view of the pre-textured Bi-2212 wire in Embodiment 1 of the present invention.

[0018] Figure 3 This is a cross-sectional schematic diagram of a primary composite containing a flat strip in Embodiment 2 of the present invention.

[0019] Figure 4 This is a schematic cross-sectional view of the pre-textured Bi-2212 wire in Embodiment 2 of the present invention.

[0020] Figure 5 This is a cross-sectional schematic diagram of a primary composite containing a flat strip in Embodiment 3 of the present invention.

[0021] Figure 6 This is a schematic cross-sectional view of the pre-textured Bi-2212 wire in Embodiment 3 of the present invention. Detailed Implementation

[0022] Example 1 This embodiment includes the following steps: Step 1: The Bi-2212 precursor powder is loaded into a silver tube and drawn into wire. The wire is then rolled into flat strips of four different sizes. The thicknesses of the flat strips are 0.35mm, 0.45mm, 0.55mm, and 0.65mm, and the widths are 1.4mm, 1.7mm, 2.0mm, and 2.3mm, respectively. Step 2: After the flat strip from Step 1 is cut to length and placed into a silver tube, it is drawn to obtain a primary composite containing the flat strip. Then, the primary composite is processed into a hexagonal sub-component wire; the sub-component wire contains 16 flat strips. Step 3: After the hexagonal sub-component wires from Step 2 are cut to length and then inserted into a silver-magnesium alloy tube, a secondary composite is obtained. Then, the composite is drawn to obtain a pre-woven Bi-2212 wire. The secondary composite contains 18 sub-component wires, and the central component is a silver insert rod. The pre-woven Bi-2212 wire contains 288 flat strip core wires.

[0023] Testing revealed that the pre-textured Bi-2212 wire prepared in this embodiment has a good microstructure. After heat treatment, the grains in the core wire have good a- and c-axis orientations. Under liquid helium temperature self-field, the critical current of the wire is 1200A, indicating good performance.

[0024] Figure 1 This is a cross-sectional schematic diagram of the primary composite containing the flat strip in this embodiment. Figure 1 It can be seen that the central core filament of this primary composite has a flat ribbon structure; Figure 2 This is a schematic cross-sectional view of the pre-woven Bi-2212 wire in this embodiment. Figure 2 It can be seen that the structure of the Bi-2212 wire is 16×18+1, that is, the central component is a silver insert bar, and the silver insert bar is surrounded by 288 flat strip core wires.

[0025] Example 2 This embodiment includes the following steps: Step 1: The Bi-2212 precursor powder is loaded into a silver tube and drawn into wire. The wire is then rolled into flat strips of eight different sizes. The thicknesses of the flat strips are 0.35mm, 0.45mm, 0.55mm, 0.65mm, 0.45mm, 0.5mm, 0.55mm, and 0.6mm, respectively, and the widths are 1.4mm, 1.7mm, 2.0mm, 2.3mm, 2.0mm, 3.5mm, 4.0mm, and 4.5mm, respectively. Step 2: After the flat strip from Step 1 is cut to length and placed into a silver tube, it is drawn to obtain a primary composite containing the flat strip. Then, the primary composite is processed into a hexagonal sub-component wire; the sub-component wire contains 12 flat strips. Step 3: After the hexagonal sub-component wires from Step 2 are cut to length and then inserted into a silver-magnesium alloy tube, a secondary composite is obtained. Then, the composite is drawn to obtain a pre-woven Bi-2212 wire. The secondary composite contains 7 sub-component wires, and the pre-woven Bi-2212 wire contains 84 flat strip core wires without a silver insert bar in the center.

[0026] Testing revealed that the pre-textured Bi-2212 wire prepared in this embodiment has a good microstructure. After heat treatment, the grains in the core wire have good a- and c-axis orientations. Under liquid helium temperature self-field, the critical current of the wire is 1100A, indicating good performance.

[0027] Figure 3 This is a cross-sectional schematic diagram of the primary composite containing the flat strip in this embodiment. Figure 3 It can be seen that the central core filament of this primary composite has a flat ribbon structure; Figure 4 This is a schematic cross-sectional view of the pre-woven Bi-2212 wire in this embodiment. Figure 4 It can be seen that the Bi-2212 wire contains 84 flat strip core wires.

[0028] Example 3 This embodiment includes the following steps: Step 1: The Bi-2212 precursor powder is loaded into a silver tube and drawn into wire. The wire is then rolled into flat strips of eight different sizes. The thicknesses of the flat strips are 0.20mm, 0.21mm, 0.22mm, 0.23mm, 0.24mm, 0.25mm, 0.26mm, and 0.27mm, and the widths are 1.0mm, 1.2mm, 1.4mm, 1.6mm, 1.7mm, 1.8mm, 1.9mm, and 2.0mm, respectively. Step 2: After the flat strip from Step 1 is cut to length and inserted into the silver tube, it is drawn to obtain a primary composite containing flat strips, which is similar to the primary composite structure in Example 1. Then, the primary composite is processed into hexagonal sub-component wires; the sub-component wires contain 32 flat strips. Step 3: After the hexagonal sub-component wires from Step 2 are cut to length and then inserted into a silver-magnesium alloy tube, a secondary composite is obtained. Then, a drawing process is performed to obtain a pre-woven Bi-2212 wire. The secondary composite contains 18 sub-component wires, and the central component is a silver insert rod. The pre-woven Bi-2212 wire contains 576 flat strip core wires.

[0029] Testing revealed that the pre-textured Bi-2212 wire prepared in this embodiment has a good microstructure, and the critical current of the wire under liquid helium temperature self-field is 1250A, indicating good performance.

[0030] Figure 5 This is a cross-sectional schematic diagram of the primary composite containing the flat strip in this embodiment. Figure 5 It can be seen that the core wire of this primary composite is a structure of 32 flat strips. Figure 6 This is a schematic cross-sectional view of the pre-woven Bi-2212 wire in this embodiment. Figure 6 It can be seen that the structure of the Bi-2212 wire is 32×18+1, that is, the central component is a silver insert bar, and there are 576 flat strip core wires surrounding the silver insert bar.

[0031] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing pre-textured Bi-2212 wire, characterized in that, The method includes the following steps: Step 1: Load Bi-2212 precursor powder into a silver tube, draw it into wire, and roll the wire into flat strips of different sizes. Step 2: After the flat strip from Step 1 is cut to length and placed into a silver tube, it is drawn to obtain a primary composite containing the flat strip. Then, the primary composite is processed into hexagonal sub-component wires. Step 3: After cutting the hexagonal sub-component wires from Step 2 to length, insert them into a silver-magnesium alloy tube to obtain a secondary composite. Then, perform drawing processing to obtain pre-textured Bi-2212 wires.

2. The method for preparing a pre-textured Bi-2212 wire according to claim 1, characterized in that, The width of the flat strip mentioned in step one is 1.0mm~4.6mm, and the thickness is 0.2mm~0.7mm.

3. The method for preparing a pre-textured Bi-2212 wire according to claim 1, characterized in that, The sub-component wires described in step two contain 12, 16, or 32 flat strips.

4. The method for preparing a pre-textured Bi-2212 wire according to claim 1, characterized in that, The secondary composite described in step three contains 7, 18, or 36 sub-component wires, and the central component is a silver insert.

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