Self-constrained diffusion bonding nickel-tungsten alloy composite base band billet and preparation method thereof

Abstract

The invention discloses a self-constrained diffusion bonding nickel-tungsten alloy composite base band billet and a preparation method thereof, and belongs to the technical field of preparation of metal base band billets for high-temperature coating superconductors. According to the method, a high-tungsten alloy bar with an interference size is pressed into a hollow low-tungsten alloy pipe, and the tubular structure restrains displacement, so that contact interfaces extrude each other to generate plastic deformation. And the deformation amount of the alloy interface is larger than the critical deformation amount, recrystallization occurs at the high temperature to accelerate diffusion of atoms, metallurgical bonding is achieved, and the nickel-tungsten alloy composite base band billet of the three-layer sandwich structure is obtained. Plastic deformation generated between layers through self-constraint drives recrystallization and promotes element diffusion to form metallurgical bonding in the thermal activation process, and the probability of the cracking phenomenon of the cold-rolled nickel-tungsten alloy composite base band can be remarkably reduced; the preparation method is a preparation mode for realizing the ultra-long metal base band billet with a sharp cubic texture surface, high strength and low magnetism; and the surface texture content, the magnetism and the strength of the composite base band can be flexibly regulated and controlled by matching nickel-tungsten alloy bars with different components, shapes and sizes.

Description

Technical Field

[0001] The invention belongs to the technical field of preparation of metal substrate billets for high-temperature coated superconductors, and in particular relates to a self-constrained diffusion-connected nickel-tungsten alloy composite substrate billet and a preparation method thereof. Background Art

[0002] High-temperature superconducting materials have a high critical temperature and can produce superconductivity in a liquid nitrogen environment, which reduces the operating costs of equipment in electric transportation, energy information, military and magnet technology, and has broad application prospects. Yttrium barium copper oxide (YBCO) has attracted much attention as the most promising second-generation high-temperature superconducting tape. In order to solve the disadvantage of high brittleness in engineering applications, Oak Ridge National Laboratory has developed a rolling assisted biaxial textured substrate (RABiTS) method to prepare high-temperature superconducting tape. The cubic texture on the surface of the metal substrate can be used as a template for epitaxial growth of superconducting materials and provide mechanical strength. The RABiTS method has simple equipment, low production cost and high efficiency. Compared with other preparation methods, it is suitable for industrial preparation of long metal strips. The surface of metal nickel treated by large deformation recrystallization process has a high-strength cubic texture, but its ferromagnetism and insufficient strength have hindered its further development. Alloying can significantly reduce the ferromagnetism of nickel-based tape and improve its mechanical properties. Elements such as W, Cr, V, Mo, and Cu can improve the performance of nickel-based tape to varying degrees. Among them, W not only improves the strength of nickel alloys through solid solution strengthening and grain refinement mechanisms, but also effectively reduces the magnetic permeability of the metal substrate, so it has received widespread attention. Nickel-tungsten alloy substrates are divided into low-tungsten alloys and high-tungsten alloys according to the W content. Low-tungsten alloys have a W atomic percentage of less than or equal to 5%, and high-tungsten alloys have a W atomic percentage of more than 5%. Low-tungsten alloys have high stacking fault energy and are easy to form a strong biaxial cubic texture. Ni5W (5at.%) has been used to prepare YBCO coated conductors. However, its ferromagnetism and low strength hinder the expansion of YBCO to a wider range of applications. The stacking fault energy (SFE) of nickel-tungsten alloys gradually decreases with the increase of W content. Although it will lead to a reduction in cubic texture after recrystallization annealing, it can significantly improve the mechanical properties of the alloy and reduce magnetism.

[0003] The contradiction between the strength, magnetism and texture of the nickel-tungsten base tape shows that a single component cannot meet the demand, and the development of composite materials with high strength, low magnetism and sharp cubic texture on the surface has become an urgent problem to be solved. Figure 1As shown, the high-tungsten alloy is in the middle, and the low-tungsten alloy is located on the upper and lower sides of the plate. Common preparation methods for composite materials include hot forging, hot rolling, deformation, and annealing of composite billets, explosion welding in which two pieces of metal are melted by the energy provided by the explosion of explosives, and continuous solid-liquid bonding in which molten metal is poured onto a metal plate. Suo (IEEE Transactions on Applied Superconductivity, 17 (2), 3420-3423.) first rolled Ni5W and Ni9W ingots to a thickness of 2.5 mm, and stacked and pressed Ni5W / Cu / Ag / Cu / Ni9W / Cu / Ag / Cu / Ni5W in sequence, and then sintered in argon at 850°C for 4 hours. The thin Ag and Cu layers embedded between Ni5W and Ni9W acted as bonding layers to form a chemical interface connection. Wu (Adv. Eng. Mater., 22: 2000735.) loaded the Ni-W powder after proportional ball milling into a graphite mold according to the structure of Ni8W / Ni12W / Ni8W, and obtained a metal ingot by spark plasma sintering (SPS) and then homogenization annealing. Cui (J. Mater. Res. 34, 3141–3150 (2019)) adopted a solid-liquid coating method to prepare Ni9.3W alloy by vacuum induction melting, hot forging into a cuboid and vertically placed in a graphite matrix, leaving a cavity of the same size around it, pouring Ni5W melt into the cavity, and obtaining a Ni5W-Ni9.3W-Ni5W composite ingot after cooling. Good bonding at the interface of the nickel-tungsten composite ingot is the key factor to ensure rolling. The uneven deformation of different layers of the composite material during rolling leads to uneven stress on the base strip, which is prone to cracking. Therefore, it is of great significance to enhance the connection strength at the interface of the ingot.

[0004] In summary, low-W-NiW alloys can form a cubic texture on the surface after multiple rolling deformation and recrystallization, which is easy for the growth of second-generation high-temperature coated superconductors, but their poor mechanical properties and strong magnetism limit their wide application; high-W-NiW alloys can meet the requirements of mechanical properties and magnetism, but the introduction of higher W content reduces the stacking fault energy of the alloy and affects the formation of surface cubic texture. Single-component NiW alloys can no longer meet the comprehensive performance requirements of metal substrates for coated superconductors. In order to solve this problem, it is of great significance to develop a preparation process for NiW composite substrate billets. Summary of the invention

[0005] The technical problem to be solved by the present invention is to solve the cracking caused by weak connection at the interface of the nickel-tungsten alloy composite ingot during the rolling process, and propose a method for applying stress by structural self-constraint to obtain good contact and plastic deformation at the interface, induce interface recrystallization and promote atomic diffusion to obtain a metallurgically bonded nickel-tungsten composite material. The outer layer of the nickel-tungsten composite ingot is a low-tungsten alloy that is easy to form a sharp cubic texture, and the core is a high-tungsten alloy that provides strength and reduces overall magnetism. The increase of the W element can increase the strength of the material. The low-tungsten alloy of the outer layer is easier to deform than the core. The difference in strength will cause the interface to be susceptible to complex stress and cracking during the subsequent rolling process. The high-tungsten alloy with a size difference greater than the critical deformation amount is inserted into the tube sleeve to cause a large deformation of the low-tungsten alloy at the interface, so as to achieve metallurgical bonding of the interface in the subsequent diffusion annealing heat treatment.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for preparing a self-constrained diffusion-bonded nickel-tungsten alloy composite base strip ingot, the preparation method comprising pressing a high-tungsten alloy rod with an interference fit into a hollow low-tungsten alloy tube, wherein the tubular structure constrains the displacement, causing the contact interfaces to squeeze each other and produce plastic deformation. In addition to the stress required for diffusion bonding provided by the structural self-constraint, the deformation at the alloy interface is greater than the critical deformation, and recrystallization occurs at high temperatures to accelerate the diffusion of atoms, making it easier to connect the interface between the high- and low-tungsten alloys, achieving metallurgical bonding, and significantly reducing the probability of cracking in the cold-rolled nickel-tungsten alloy composite base strip. Specifically, the following steps are included:

[0008] S1 melts high tungsten alloy ingots and low tungsten alloy ingots;

[0009] The low-tungsten alloy and the high-tungsten alloy are melted separately, and the high-tungsten alloy is processed into a series of solid bars with different sizes and one end chamfered to obtain the high-tungsten alloy billet; the low-tungsten alloy is processed into a series of hollow tubes with different sizes and one end chamfered to obtain the low-tungsten alloy billet. The solid bars and hollow tubes are processed in the same number and size, and the outer diameter of the high-tungsten alloy is slightly larger than the inner diameter of the low-tungsten alloy; the chamfers of the high-tungsten alloy and the low-tungsten alloy are used to achieve composite processing of the two.

[0010] Furthermore, the inner diameter of the low tungsten alloy is Lmm, and the outer diameter of the high tungsten alloy is 1.02-1.04Lmm.

[0011] S2 treats the alloy surface of the high tungsten alloy ingot and the low tungsten alloy ingot;

[0012] The axial outer side surface of the high-tungsten alloy ingot and the inner surface of the hole of the low-tungsten alloy ingot are processed by mechanical, chemical, laser and other methods to obtain a smooth surface.

[0013] S3 assembles nickel-tungsten alloy composite ingot;

[0014] A series of high-tungsten alloy solid bars of different sizes are inserted into low-tungsten alloy hollow tubes with the same inner diameter by applying a pressure of 10-15kN, and the insertion rate is 0.3-0.6mm / min. During the insertion of the high-tungsten alloy solid bars, pressure and shear stress are applied to the inner side of the aperture of the low-tungsten alloy hollow tube, causing the low-tungsten alloy at the interface between the outer surface of the solid bar and the inner surface of the hollow tube to deform, thereby obtaining a composite metal bar.

[0015] S4 nickel-tungsten alloy composite rod recrystallization annealing;

[0016] The composite metal rod assembled by S3 is subjected to diffusion annealing treatment under vacuum or Ar-4% H2 mixed gas protection, and annealed at 1000-1400°C for 12-48h, so that the interface along the axial side of the high-tungsten alloy and the inner surface of the low-tungsten alloy hole is fully annealed and recrystallized.

[0017] S5 observed the scanning electron microscope and energy spectrum surface scanning images at the interface of the nickel-tungsten alloy after recrystallization annealing. There was no void at the interface in the scanning electron microscope image and the energy spectrum surface scanning image showed that the elements diffused, and a self-constrained diffusion-connected nickel-tungsten alloy composite base strip ingot was obtained.

[0018] Furthermore, the W content of the low tungsten alloy mentioned in step S1 includes 3-5 at.%, and the rest is nickel. The W content of the high tungsten alloy includes 7-11 at.%, and the rest is nickel.

[0019] Furthermore, the high-tungsten alloy rods and low-tungsten alloy hollow tubes mentioned in step S1 include round rods, rectangular rods, hollow rod-shaped tubes, and hollow rectangular tubes obtained by casting, hot forging, drilling, turning, etc.

[0020] A self-constrained diffusion-bonded nickel-tungsten alloy composite base strip billet is prepared by the above method. The nickel-tungsten alloy composite base strip billet is a three-layer sandwich structure from the outside to the inside in the radial direction, the outermost layer is a low-tungsten alloy, the middle layer is a transition layer, and the innermost layer is a high-tungsten alloy. The plastic deformation between the layers generated by self-constraint drives recrystallization and promotes element diffusion to form a metallurgical bond during the thermal activation process, effectively reducing the probability of cracking during the rolling of the composite billet. It is a method for preparing an ultra-long metal base strip billet with a sharp cubic texture surface, high strength, and low magnetism. In addition, the present invention can flexibly achieve the regulation of the surface texture content, magnetism, and strength of the composite base strip by matching nickel-tungsten alloy rods of different compositions and shapes and sizes.

[0021] Effects and benefits of the present invention:

[0022] (1) The present invention provides a method for obtaining a nickel-tungsten alloy composite ingot by self-constrained diffusion connection of a low-tungsten alloy and a high-tungsten alloy. Due to the circular ring structure of the tube, the circular tube is constrained to move during the process of pressing the rod into the tube, so that the interface between the high-tungsten alloy and the low-tungsten alloy undergoes plastic deformation, which drives recrystallization and promotes element diffusion during the thermal activation process, thereby achieving metallurgical bonding between metal layers with different tungsten contents, reducing the probability of rolling cracking, and providing reliable support for subsequent cold deformation.

[0023] (2) The present invention provides a metal base strip ingot required for a superconducting strip, wherein the outer layer is a low-tungsten alloy that is easy to form a strong biaxial texture, and the core layer is a high-tungsten alloy that provides high strength and low magnetism. The components and content can be designed to flexibly adjust the required cubic texture content, base strip strength and magnetic permeability.

[0024] (3) The present invention provides a method for preparing a nickel-tungsten alloy composite ingot with simple process and low equipment cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the nickel-tungsten alloy substrate of Example 1;

[0026] Figure 2 This is a schematic diagram of the nickel-tungsten alloy recrystallization connection of Example 1;

[0027] Figure 3 Figures 1 and 2 are diagrams of the NiW alloy composite rod of Example 1 before and after heat treatment, wherein: Figure (a) is the SEM image of the interface before heat treatment; Figure (b) is the Ni element distribution of the interface before heat treatment; Figure (c) is the W element distribution of the interface before heat treatment; Figure (d) is the SEM image of the interface after heat treatment; Figure (e) is the Ni element distribution of the interface after heat treatment; Figure (f) is the W element distribution of the interface after heat treatment; Figure (g) is the EBSD of the interface after heat treatment.

[0028] Figure 4 Figure 2 is a diagram of the NiW alloy composite rod after heat treatment of Example 2, wherein: a) is a SEM image of the interface after heat treatment; Figure (b) is the Ni element distribution of the interface after heat treatment; Figure (c) is the W element distribution of the interface after heat treatment;

[0029] Figure 5 These are pictures of the NiW alloy composite rod of Example 3 after heat treatment, where: a) is the SEM picture of the interface after heat treatment; Figure (b) is the Ni element distribution of the interface after heat treatment; Figure (c) is the W element distribution of the interface after heat treatment. DETAILED DESCRIPTION

[0030] The specific implementation of the present invention is described in detail below in conjunction with the technical solution (and drawings).

[0031] Example 1

[0032] The hollow cylindrical tube of low tungsten alloy with W content of 3at.% and the solid rod of high tungsten alloy with W content of 11at.% were melted and processed. The diameter of the low tungsten alloy is 24mm, the diameter of the center hole is 16mm, and the diameter of the high tungsten alloy rod is 16.56mm. The oxide layer on the surface of the nickel-tungsten alloy was turned off. The high tungsten alloy rod was pressed into the low tungsten alloy tube with a pressure of 13kN and a pressing rate of 0.3mm / min to deform the low tungsten alloy at the interface. Recrystallization heat treatment was performed at 1000℃ in a vacuum and Ar-4%H2 mixed gas for 24h to fully recrystallize the alloy at the interface. After heat treatment, the boundary line of the elements at the NiW alloy composite interface became blurred than before heat treatment and recrystallized grains appeared.

[0033] Figure 3 These are pictures of the NiW alloy composite rod of Example 1 before and after heat treatment. It can be seen from the picture that the interface between the low-tungsten alloy and the high-tungsten alloy is obvious before heat treatment, and after heat treatment, the elements on both sides of the interface diffuse, the interface becomes blurred, and recrystallized grains appear at the interface.

[0034] Example 2

[0035] Melt and process low tungsten alloy hollow cylindrical tubes with a W content of 4at.% and solid rods of high tungsten alloy with a W content of 8at.%. The diameter of the low tungsten alloy is 24mm, the center hole diameter is 16mm, and the diameter of the high tungsten alloy rod is 16.48mm. Turn off the oxide layer on the surface of the nickel-tungsten alloy. Apply a pressure of 12kN and a pressing rate of 0.4mm / min to press the high tungsten alloy rod into the low tungsten alloy tube to deform the low tungsten alloy at the interface. Recrystallization heat treatment is performed at 1100℃ for 12h in a vacuum and Ar-4%H2 mixed gas to fully recrystallize the alloy at the interface.

[0036] Figure 4 This is a picture of the NiW alloy composite rod of Example 2 after heat treatment. It can be seen from the picture that after heat treatment, the elements at the NiW alloy composite interface diffuse significantly, achieving the combination of the high tungsten alloy and the low tungsten alloy interface.

[0037] Example 3

[0038] Melt and process low tungsten alloy hollow cylindrical tubes with a W content of 5at.% and solid rods of high tungsten alloy with a W content of 10at.%. The diameter of the low tungsten alloy is 24mm, the center hole diameter is 16mm, and the diameter of the high tungsten alloy rod is 16.40mm. Turn off the oxide layer on the surface of the nickel-tungsten alloy. Apply a pressure of 13kN and a pressing rate of 0.5mm / min to press the high tungsten alloy rod into the low tungsten alloy tube to deform the low tungsten alloy at the interface. Recrystallization heat treatment is performed at 1200℃ for 24h in a vacuum and Ar-4%H2 mixed gas to fully recrystallize the alloy at the interface.

[0039] Figure 5 This is a picture of the NiW alloy composite rod of Example 3 after heat treatment. It can be seen from the picture that after heat treatment, the elements at the NiW alloy composite interface diffuse significantly, achieving the combination of the high tungsten alloy and the low tungsten alloy interface.

[0040] The above-described embodiments merely express the implementation methods of the present invention, but they cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A method for preparing a self-constrained diffusion bonded nickel-tungsten alloy composite base strip ingot, characterized in that: The preparation method comprises the following steps: S1 melts high tungsten alloy ingots and low tungsten alloy ingots; The low-tungsten alloy and the high-tungsten alloy are melted separately, and the high-tungsten alloy is processed into a series of solid bars with different sizes and one end chamfered to obtain the high-tungsten alloy ingot; the low-tungsten alloy is processed into a series of hollow tubes with different sizes and one end chamfered to obtain the low-tungsten alloy ingot; the solid bars and the hollow tubes are processed in the same number and size, and the outer diameter of the high-tungsten alloy is slightly larger than the inner diameter of the low-tungsten alloy; the chamfers of the high-tungsten alloy and the low-tungsten alloy are used to achieve composite processing of the two; S2 treats the alloy surface of the high tungsten alloy ingot and the low tungsten alloy ingot; S3 assembles nickel-tungsten alloy composite ingot; Apply pressure to press the high tungsten alloy solid rod into the low tungsten alloy hollow tube. During the insertion of the high tungsten alloy solid rod, pressure and shear stress are applied to the inner side of the aperture of the low tungsten alloy hollow tube, so that the low tungsten alloy at the interface between the outer surface of the solid rod and the inner surface of the hollow tube is deformed to obtain a nickel-tungsten alloy composite rod. S4 is to perform recrystallization annealing on the nickel-tungsten alloy composite rod to obtain a self-constrained diffusion bonded nickel-tungsten alloy composite base strip ingot.

2. The method for preparing a self-constrained diffusion bonded nickel-tungsten alloy composite base strip ingot according to claim 1, characterized in that: The W content of the low tungsten alloy mentioned in S1 includes 3-5 at.%, and the rest is nickel; the W content of the high tungsten alloy includes 7-11 at.%, and the rest is nickel.

3. The method for preparing a self-constrained diffusion bonded nickel-tungsten alloy composite base strip ingot according to claim 1, characterized in that: In the above-mentioned S1, the inner diameter of the low-tungsten alloy is Lmm, and the outer diameter of the high-tungsten alloy is 1.02-1.04Lmm.

4. The method for preparing a self-constrained diffusion bonded nickel-tungsten alloy composite base strip ingot according to claim 1, characterized in that: In the above-mentioned S3, the applied pressure ranges from 10 to 15 kN, and the pressing rate is from 0.3 to 0.6 mm / min.

5. The method for preparing a self-constrained diffusion bonded nickel-tungsten alloy composite base strip ingot according to claim 1, characterized in that: The S4 is specifically: the composite metal rod assembled by S3 is subjected to diffusion annealing treatment under vacuum or Ar-4% H2 mixed gas protection, and annealed at 1000-1400°C for 12-48h, so that the interface along the axial side of the high tungsten alloy and the inner surface of the low tungsten alloy hole is fully annealed and recrystallized.

6. The method for preparing a self-constrained diffusion bonded nickel-tungsten alloy composite base strip ingot according to claim 1, characterized in that: In the above S1, the high tungsten alloy rod and the low tungsten alloy hollow tube include round rods, rectangular rods, hollow rod-shaped tubes, hollow rectangular tubes or other structural tubes.

7. The method for preparing a self-constrained diffusion bonded nickel-tungsten alloy composite base strip ingot according to claim 1, characterized in that: In the above-mentioned S2, the axial outer side surface of the high-tungsten alloy ingot and the inner surface of the hole of the low-tungsten alloy ingot are processed by mechanical, chemical or laser methods to obtain a smooth surface.

8. A self-constrained diffusion bonded nickel-tungsten alloy composite base strip ingot, characterized in that: The nickel-tungsten alloy composite base strip ingot is prepared by the preparation method described in any one of claims 1 to 7. The nickel-tungsten alloy composite base strip ingot is a three-layer sandwich structure from the outside to the inside in the radial direction, the outermost layer is a low-tungsten alloy, the middle layer is a transition layer, and the innermost layer is a high-tungsten alloy.

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