NiW layered composite metal matrix strip based on hot extrusion process and preparation method thereof

Abstract

The application discloses a NiW layered composite metal base strip based on a hot extrusion process and a preparation method thereof, and belongs to the technical field of high-temperature coating superconductor metal base strip preparation. In the process of preparing the layered composite billet, the outer layer of the low-W-content NiW alloy and the inner layer of the high-W-content NiW alloy are subjected to synergistic plastic deformation and dynamic recrystallization under the joint action of a stress field and a temperature field, the oxidation film and the impurity layer at the interface are crushed and extruded, the fresh metal surfaces are fully contacted and atom interdiffusion and new grain interembedding are realized, and thus a dense and continuous metallurgical bonding interface is formed. In the subsequent multi-pass cold rolling process, the good interlayer interface bonding can continuously transmit the interlayer stress and is not prone to cracking. The application can simultaneously complete the compounding and densification of the NiW composite billet in a one-time forming process, significantly improves the production efficiency and reduces the interface defect rate, and will help to promote the large-scale preparation and industrial application of the ultra-long metal base strip.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of high-temperature coating superconductor metal-based tape preparation, and relates to a NiW layered composite metal-based tape and a preparation method thereof, in particular to a NiW layered composite metal-based tape based on a hot extrusion process and a preparation method thereof. BACKGROUND

[0002] With the rapid development of high-temperature superconducting technology in the fields of energy transmission, magnetic confinement fusion, magnetic resonance imaging and high-field magnets, higher and higher requirements are put forward for the performance and reliability of superconducting tapes. Although rare earth barium copper oxide (REBCO) high-temperature superconducting materials exhibit excellent performance in current carrying capacity and critical temperature, their inherent ceramic brittleness seriously restricts their popularization in practical applications. In order to overcome the intrinsic brittleness of REBCO and fully exert its superconducting performance, the strategy of preparing it into a thin film and depositing it on a metal-based tape with excellent mechanical properties is adopted to form a coated conductor. As a key component of the second generation of high-temperature superconducting tapes, the metal-based tape plays a crucial role in bearing mechanical stress, maintaining the orientation of the superconducting layer and ensuring the overall electrical performance.

[0003] The metal-based tapes widely used at present mainly include pure nickel, NiCr, NiW alloy and non-magnetic high-strength alloy (such as Hastelloy, Inconel, etc.). Among them, NiW alloy has become one of the preferred materials for the preparation of REBCO superconducting tapes due to its excellent controllability of cubic texture, good chemical stability and moderate mechanical properties. However, the anti-fatigue performance of traditional single-layer low-W-content NiW-based tapes is low and they are ferromagnetic, which has several deficiencies in high-field and complex stress environments. Increasing the W content can improve the mechanical properties of NiW alloy through solid solution strengthening and reduce the magnetism. When the W content exceeds 9at.% or more, not only the yield strength is greatly improved, but also the magnetism almost completely disappears at 77K temperature. However, the increase of W content will make the stacking fault energy of NiW alloy decrease seriously and it is difficult to form concentrated cubic texture.

[0004] To overcome the above problems, researchers have proposed the design idea of layered NiW alloy composite baseband in recent years. This kind of composite structure is usually composed of multiple layers of NiW alloy: the outer layer of NiW usually adopts a lower W content (3-5at.%), in order to maintain excellent cubic texture, providing an ideal template for the epitaxial growth of buffer layer and superconducting layer; the inner layer adopts a high W layer (7-10at.%), in order to significantly improve the overall mechanical strength, creep resistance, thermal stability and reduce the magnetic permeability; this layered structure not only can realize the comprehensive optimization of texture, magnetism and mechanical properties, but also can effectively reduce the thermal stress concentration, thereby improving the reliability and service life of the superconducting layer. The performance of the layered NiW alloy composite baseband not only depends on the organization and composition of each single layer material, but more importantly, the bonding strength of the interlayer interface. The interface bonding state directly affects the deformation coordination and overall mechanical stability of the material during the subsequent multi-pass cold rolling process. In view of the above problems, scholars at home and abroad have carried out a lot of research and put forward some solutions, such as Chinese invention patent (application number 200610080876.7) which uses Cu foil-Ag foil-Cu foil as an intermediate connecting layer, which is placed between the inner and outer layers of NiW alloy with different W contents, and a reaction layer is formed at the interface through chemical sintering process, thereby realizing the metallurgical bonding between the heterogeneous interlayers. This method not only helps to reduce the overall sintering temperature of the composite baseband, but also can enhance the bonding strength between the inner and outer layers through chemical reaction at the interface. However, the introduction of multiple intermediate layers increases the complexity of the preparation process, such as the need to accurately control the thickness, element ratio and bonding parameters of each layer. Chinese invention patent (application number 201310453121.7) prepares a NiW alloy composite baseband ingot by melting method, puts the NiW alloy with high W content into the mold as the inner layer, then pours the melted NiW alloy with low W content around the high W alloy in a protective atmosphere to form a NiW composite ingot, and finally obtains a NiW composite ingot after homogenization annealing, high temperature hot forging and hot rolling process. The interface of the NiW composite ingot prepared by this method is tightly bonded, and the proportion of the inner and outer layers is easy to control, but it involves multiple steps, from melting, pouring, homogenization to hot forging and hot rolling, each step needs to be accurately controlled, and multiple steps may cause long production cycle, high energy consumption and other problems.

[0005] Therefore, it is of great significance to develop a production scheme of NiW layered composite metal baseband with high composite interface bonding strength, simple and controllable process, and high production efficiency. SUMMARY

[0006] The technical problem to be solved by the present application is the interlayer interface cracking problem of the laminated composite material in the rolling deformation process due to the uneven stress deformation caused by the difference in material properties, and a NiW laminated composite metal-based strip based on a hot extrusion process and a preparation method thereof are provided. In the process of preparing the laminated composite material, the high temperature and high pressure applied in the hot extrusion process causes severe plastic deformation and atomic diffusion between the metal layers. The extrusion stress promotes the crushing or extrusion of the oxide film and impurity layer between the interfaces, so that the fresh metal surfaces are directly contacted to form a stable metallurgical bonding interface. The present application aims to use the hot extrusion technology to provide a high temperature environment and severe plastic deformation conditions for the composite billet, so that the materials in each layer occur synchronous plastic flow and dynamic recrystallization under the joint action of stress field and temperature field. Through the process, the atomic interdiffusion and mutual embedding of new grains in the interface region are realized, so as to enhance the interlayer metallurgical bonding strength of the composite billet and solve the interlayer cracking problem caused by the weak bonding force between the layers in the existing composite base strip preparation process.

[0007] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is:

[0008] A preparation method of a NiW laminated composite metal-based strip based on a hot extrusion process, comprising the following steps:

[0009] S1, designing a composite metal billet structure;

[0010] The composite metal billet is a double-layered H-shaped structure, the outer layer is a low-W-content NiW alloy, and the inner layer is a high-W-content NiW alloy; the W content in the outer layer is 3-5at.%, and the rest is Ni, and the W content in the inner layer is 9-13at.%, and the rest is Ni.

[0011] S2, preparing a NiW composite billet;

[0012] S21, processing the NiW alloy of the inner layer into a cylindrical rod with a diameter of 10-20mm, and processing the NiW alloy of the outer layer into a circular tube with an outer diameter of 25-35mm and an inner diameter of 10-20mm. The outer diameter of the cylindrical rod matches the inner diameter of the circular tube; the length of the cylindrical rod and the circular tube is 70-150mm, and the length of the two is the same.

[0013] S22, placing the size-matched cylindrical rod into the circular tube, and sealing a stainless steel outer sleeve on the outermost layer of the circular tube to prevent high-temperature oxidation, to obtain an assembled sample.

[0014] S23, put the assembled sample in a muffle furnace and heat to 1000-1200℃, and keep for 30-60min. In this step, high temperature can significantly improve the plasticity and fluidity of the alloy, ensuring the forming of the workpiece during extrusion; appropriate holding at high temperature can ensure the uniformity of the temperature inside and outside the alloy, eliminating thermal stress caused by temperature gradient.

[0015] S24, apply lubricant in the extrusion sleeve, and put the heated sample into the extrusion sleeve for extrusion, extruding the circular bar into a square to obtain a square NiW composite billet; wherein the extrusion ratio is 5-12, and the extrusion speed is 15-40mm / s. The extrusion ratio refers to the ratio of the cross-sectional area of the sample before extrusion to the cross-sectional area of the NiW composite billet after extrusion, and the cross-sectional area after extrusion decreases. In this step, high pressure extrusion is applied to the assembled sample under high temperature conditions, so that the material forms a NiW composite billet with a square cross section through the die hole. Under the combined action of extrusion stress and thermal activation, the outer alloy and the inner alloy are tightly mechanically combined, accompanied by element diffusion and migration, realizing metallurgical bonding, so as to form a composite structure with firm interface bonding.

[0016] S25, remove the stainless steel outer sleeve of the NiW composite billet and polish the surface of the NiW composite billet.

[0017] S3, rolling of the metal-based strip and recrystallization annealing;

[0018] S31, roll the NiW composite billet in single pass with 3-5% deformation and multi-pass, to obtain a cold-rolled strip, and the total deformation is 90-95%, and the strip is a NiW layered composite metal-based strip. In this step, plastic deformation makes a large number of dislocations and distortion energy accumulate in the alloy.

[0019] S32, recrystallization annealing of the cold-rolled strip in a vacuum tube furnace; the recrystallization annealing temperature is 900-1200℃, and the time is 30-90min. In this step, the stored energy generated by plastic deformation drives recrystallization nucleation and growth; with the progress of recrystallization, new grains with {001} <100> orientation grow preferentially due to their lower interface energy and orientation advantage, finally making the outer alloy of the NiW layered composite metal-based strip form a cubic texture.

[0020] Further, in the cubic texture, the volume fraction of the outer alloy is greater than 95%.

[0021] A NiW layered composite metal-based strip based on hot extrusion process, which is prepared by the above method.

[0022] Effects and benefits of the present application:

[0023] (1) The interlayer interface of the NiW layered composite metal base strip provided by the application is a metallurgical bond, and different alloy layers form a firm bonding structure at the interface. This bonding mode effectively improves the bonding strength and structural stability between the layers, ensuring the overall coordinated deformation performance of the material during subsequent rolling deformation. Thus, the risk of defects such as stress concentration, micro-cracks, and even cracking in the interface area due to inconsistent deformation of the alloy materials in each layer can be significantly reduced;

[0024] (2) The outer layer of the NiW layered composite metal base strip provided by the application is a low-W-content NiW alloy, which can obtain strong cubic texture through subsequent rolling and recrystallization annealing;

[0025] (3) The inner layer of the NiW layered composite metal base strip provided by the application is a high-W-content NiW alloy, which can provide high strength to the metal composite base strip and reduce magnetic loss;

[0026] (4) The interface connection of the NiW layered composite metal base strip provided by the application is reliable, the process is simple, and can meet the needs of ultra-long metal base strip preparation. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The cross section of the NiW layered composite metal billet (including a stainless steel jacket) obtained in Example 1;

[0028] Figure 2 The backscattered electron image of the interface of the NiW layered composite metal billet obtained in Example 1;

[0029] Figure 3 The cross-section metallograph of the NiW layered composite metal base strip obtained in Example 1;

[0030] Figure 4 The inverse pole figure of the outer layer alloy in the NiW layered composite metal base strip obtained in Example 1;

[0031] Figure 5 The cubic texture distribution diagram of the outer layer alloy in the NiW layered composite metal base strip obtained in Example 1.

[0032] In the figure: 1 inner layer; 2 outer layer; 3 stainless steel jacket. DETAILED DESCRIPTION

[0033] The specific embodiments of the application will be described in detail below in combination with the technical solutions (and the drawings), but the application is not limited to the following examples.

[0034] Example 1

[0035] S1, design the structure of the composite metal billet;

[0036] The composite metal billet designed in the embodiment is a double-layered Hui-zi structure, the outer layer 2 is a low W content NiW alloy, and the inner layer 1 is a high W content NiW alloy; the W content in the outer layer 2 is 3at.%, and the rest is Ni, and the embodiment adopts a Ni3W alloy; the W content in the inner layer 1 is 9at.%, and the rest is Ni, and the embodiment adopts a Ni9W alloy.

[0037] S2, preparing a NiW composite billet;

[0038] S21, processing the vacuum induction melted NiW alloy ingot, specifically: processing the Ni9W alloy in the inner layer 2 into a cylindrical rod with a diameter of 10 mm, and processing the Ni3W alloy in the outer layer 2 into a circular tube with an outer diameter of 25 mm and an inner diameter of 10 mm. The length of both is 70 mm.

[0039] S22, assembling the alloy, putting the cylindrical rod with matched size into the circular tube, and sealing the outermost layer of the circular tube with a stainless steel jacket 3 to prevent high-temperature oxidation, to obtain an assembled sample.

[0040] S23, placing the assembled sample in a muffle furnace and heating to 1000℃, and keeping for 60 min.

[0041] S24, smearing a lubricant in the extrusion sleeve, and placing the heated sample in the extrusion sleeve for extrusion, to extrude the circular rod into a square, to obtain a square NiW composite billet; wherein the extrusion ratio is 5, and the extrusion speed is 15 mm / s. The cross section of the NiW composite billet is shown in Figure 1 The outermost layer is a stainless steel layer formed by the stainless steel jacket 3, and the cross section of the NiW composite billet shows a double-layered Hui-zi structure through corrosion by a corrosion liquid.

[0042] S25, cutting and removing the stainless steel jacket 3 in the outermost layer of the NiW composite billet, and polishing the outer surface of the NiW composite billet. Figure 2 The backscattered electron image of the connection interface of the NiW composite billet shows that the interface connection is tight, and there is no obvious hole or other defects.

[0043] S3, rolling and recrystallization annealing of the metal-based strip;

[0044] S31, rolling the NiW composite billet in a single pass with a deformation of 3% and in multiple passes, to obtain a cold-rolled strip, and the total deformation is 90%, and the strip is a NiW layered composite metal-based strip. The metallographic structure of the cross section of the NiW layered composite metal-based strip after cold rolling is shown in Figure 3 The grains present as long strips along the rolling direction, and no cracks are generated in the interlayer interface, proving that the connection between different layers is good.

[0045] S32, recrystallization annealing the cold-rolled strip in a vacuum tube furnace; the recrystallization annealing temperature is 900℃, and the time is 90min. After the recrystallization annealing, the inverse pole figure of the outer layer alloy is as shown in Figure 4 , and the cube texture distribution map is as shown in Figure 5 , which indicates that the cube texture with a volume fraction of greater than 95% is formed.

[0046] Example 2

[0047] S1, designing a composite metal billet structure;

[0048] The composite metal billet designed in the embodiment is a double-layered H-shaped structure, the outer layer 2 is a low-W-content NiW alloy, and the inner layer 1 is a high-W-content NiW alloy; the W content in the outer layer 2 is 4at.%, and the rest is Ni, and Ni4W alloy is used in the embodiment; the W content in the inner layer 1 is 10at.%, and the rest is Ni, and Ni10W alloy is used in the embodiment.

[0049] S2, preparing a NiW composite billet;

[0050] S21, processing the vacuum induction melted NiW alloy ingot, specifically: processing the Ni10W alloy in the inner layer 2 into a cylindrical rod with a diameter of 15mm, and processing the Ni4W alloy in the outer layer 2 into a circular tube with an outer diameter of 28mm and an inner diameter of 15mm. The length of both is 100mm.

[0051] S22, assembling the alloy, putting the cylindrical rod with matched size into the circular tube, and sealing the outermost layer of the circular tube with a stainless steel jacket 3 to prevent high-temperature oxidation, to obtain an assembled sample.

[0052] S23, placing the assembled sample in a muffle furnace and heating to 1100℃, and keeping the temperature for 50min.

[0053] S24, smearing a lubricant in the extrusion sleeve, and placing the heated sample in the extrusion sleeve for extrusion, to extrude the circular rod into a square, to obtain a square NiW composite billet; wherein the extrusion ratio is 8, and the extrusion speed is 25mm / s. The outermost layer of the NiW composite billet is a stainless steel layer formed by the stainless steel jacket 3, and the cross section of the NiW composite billet shows a double-layered H-shaped structure through etching by an etching liquid.

[0054] S25, cutting and removing the stainless steel jacket 3 in the outermost layer of the NiW composite billet, and polishing the outer surface of the NiW composite billet. The backscattered electron image of the interface of the NiW composite billet shows that the interface is tightly connected, and there is no obvious hole defect.

[0055] S3, rolling and recrystallization annealing of the metal-based strip;

[0056] S31, the NiW composite billet is rolled by single pass 4% deformation and multi-pass to obtain the cold-rolled strip, and the total deformation is 92%, and the strip is a NiW layered composite metal base strip. The metallographic cross section of the NiW layered composite metal base strip after cold rolling shows that the grains are in the form of long strips along the rolling direction, and no cracks are generated at the interface between the layers, which proves that the connection between different layers is good.

[0057] S32, the cold-rolled strip is recrystallized annealed in a vacuum tube furnace; the recrystallization annealing temperature is 1100℃, and the time is 60min. After recrystallization annealing, the inverse pole figure and the cubic texture distribution diagram of the outer layer alloy show that it forms a cubic texture with a volume fraction of more than 95%.

[0058] Example 3

[0059] S1, design the structure of the composite metal billet;

[0060] The composite metal billet designed in this embodiment is a double-layered H-shaped structure, the outer layer 2 is a low-W-content NiW alloy, and the inner layer 1 is a high-W-content NiW alloy; the W content in the outer layer 2 is 5at.%, and the rest is Ni, and Ni5W alloy is used in this embodiment; the W content in the inner layer 1 is 13at.%, and the rest is Ni, and Ni13W alloy is used in this embodiment.

[0061] S2, prepare the NiW composite billet;

[0062] S21, process the vacuum induction melted NiW alloy ingot, specifically: process the Ni13W alloy of the inner layer 2 into a cylindrical rod with a diameter of 20mm, and process the Ni5W alloy of the outer layer 2 into a circular tube with an outer diameter of 35mm and an inner diameter of 20mm. The length of both is 150mm.

[0063] S22, assemble the alloy, put the cylindrical rod with matched size into the circular tube, and seal the outermost layer of the circular tube with a stainless steel jacket 3 to prevent high-temperature oxidation, to obtain the assembled sample.

[0064] S23, place the assembled sample in a muffle furnace and heat it to 1200℃, and keep it for 30min.

[0065] S24, apply lubricant in the extrusion sleeve, and put the heated sample into the extrusion sleeve for extrusion, to extrude the circular rod into a square one, to obtain a square NiW composite billet; wherein the extrusion ratio is 12, and the extrusion speed is 40mm / s. The outermost layer of the cross section of the NiW composite billet is a stainless steel layer formed by the stainless steel jacket 3, and the cross section of the NiW composite billet shows a double-layered H-shaped structure by etching with an etching liquid.

[0066] S25, cutting and removing the outermost stainless steel sleeve 3 of the NiW composite billet, and polishing the outer surface of the NiW composite billet. The backscattered electron image of the interface connection of the NiW composite billet shows that the interface connection is tight and has no obvious hole defects.

[0067] S3, rolling of the metal matrix strip and recrystallization annealing;

[0068] S31, rolling the NiW composite billet by single pass 5% deformation and multi-pass to obtain the cold-rolled strip, and the total deformation is 95%, and the strip is a NiW layered composite metal matrix strip. The metallographic cross section of the NiW layered composite metal matrix strip after cold rolling shows that the grains are in the form of long strips along the rolling direction, and no cracks are generated at the interlayer interface, which proves that the connection between different layers is good.

[0069] S32, recrystallization annealing of the cold-rolled strip in a vacuum tube furnace; the recrystallization annealing temperature is 1200℃, and the time is 30min. After recrystallization annealing, the inverse pole figure and the cubic texture distribution diagram of the outer layer alloy show that it forms a cubic texture with a volume fraction of more than 95%.

[0070] The above-mentioned embodiments only express the implementation of the present application, but cannot be interpreted as a limitation to the scope of the present application. It should be pointed out that for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are all within the protection scope of the present application.

Claims

1. A method for preparing NiW layered composite metal substrate strip based on hot extrusion process, characterized in that, The method for preparing the NiW layered composite metal substrate includes the following steps: S1. Design the structure of the composite metal billet; The composite metal ingot has a double-layer U-shaped structure, with the outer layer being a NiW alloy with low W content and the inner layer being a NiW alloy with high W content; the outer layer has a W content of 3-5 at.%, with the remainder being Ni, and the inner layer has a W content of 9-13 at.%, with the remainder being Ni; S2. Preparation of NiW composite billet; S21. The inner NiW alloy is processed into a cylindrical bar, and the outer NiW alloy is processed into a circular tube; the outer diameter of the cylindrical bar matches the inner diameter of the circular tube; the cylindrical bar and the circular tube have the same length. S22. Place the cylindrical rod into the circular tube, and seal the outermost layer of the circular tube with a stainless steel jacket to obtain the assembled sample. S23. The sample is subjected to high-temperature heating treatment; the temperature of the high-temperature heating treatment is 1000-1200℃, and the time is 30-60min; S24. The sample is placed in the extrusion sleeve for extrusion, and the round bar is extruded into a square shape to obtain a square NiW composite billet; the extrusion ratio is 5-12 and the extrusion speed is 15-40 mm / s; the extrusion ratio refers to the ratio of the cross-sectional area of ​​the sample before extrusion to the cross-sectional area of ​​the NiW composite billet after extrusion, and the cross-sectional area decreases after extrusion. S25. Remove the stainless steel outer layer of the NiW composite billet and grind the outer surface of the NiW composite billet; S3, Rolling and recrystallization annealing of metal base strip; S31. Roll the NiW composite billet in multiple passes with a single pass deformation of 3-5% to obtain a cold-rolled strip, wherein the strip is a NiW layered composite metal base strip. S32. The cold-rolled strip is recrystallized and annealed in a vacuum tube furnace to form a cubic texture in the outer alloy of the NiW layered composite metal substrate, wherein the volume fraction of the outer alloy in the cubic texture is greater than 95%.

2. The method for preparing NiW layered composite metal substrate based on hot extrusion process according to claim 1, characterized in that, In step S21, the diameter of the cylindrical rod is 10-20 mm, and the outer diameter of the circular tube is 25-35 mm, while the inner diameter is 10-20 mm.

3. The method for preparing NiW layered composite metal substrate based on hot extrusion process according to claim 1, characterized in that, In S21, the length of the cylindrical bar or circular tube is 70-150mm.

4. The method for preparing NiW layered composite metal substrate based on hot extrusion process according to claim 1, characterized in that, In S31, the total deformation is 90-95%.

5. The method for preparing NiW layered composite metal substrate based on hot extrusion process according to claim 1, characterized in that, In step S32, the recrystallization annealing temperature is 900-1200℃ and the time is 30-90min.

6. A NiW layered composite metal substrate strip based on hot extrusion process, characterized in that, It is prepared by any one of the preparation methods described in claims 1-5.

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