A method for preparing sulfur-doped Ni-based thin strip for coated conductor

Abstract

The invention discloses a method for preparing a sulfur-doped Ni-based thin strip for a coated conductor. Firstly, high-purity Ni powder and W powder are fully ground and mixed according to a specific atomic ratio, and a NiW-based strip is prepared through pre-pressing, sintering, rolling and other steps. Then, H2S mixed gas is introduced to perform a sulfur-doping recrystallization operation on the NiW-based strip. Under the conditions of a specific temperature and a specific amount of hydrogen sulfide mixed gas introduced, the formation of grain boundary grooves on the surface of the NiW-based strip is effectively prevented by sulfur doping. Moreover, the method does not require intermediate heat treatment during rolling, has simple process steps, shortens the preparation time, and is easy to control process parameters. The method is suitable for industrial-scale production and continuous production.

Description

Technical Field

[0001] The invention belongs to the technical field of high-temperature superconducting metal base strips, and in particular relates to a method for preparing a sulfur-doped Ni-based thin strip for a coating conductor. Background Art

[0002] Rolling Assisted Biaxially Textured Substrate (RABiTS) is a very promising technology route for preparing superconducting tapes, with simple equipment and low cost. In the RABiTS route, the metal substrate needs to provide texture and withstand stress and strain, which requires the metal substrate to have sharp texture, high yield strength, high oxidation resistance, small surface roughness, high conductivity, and low AC loss. Therefore, the preparation of the metal substrate is one of the most critical links in the RABiTS route.

[0003] As an ideal material for substrates, NiW substrates have been widely studied by domestic and foreign researchers. For example, the hot isostatic pressing method disclosed in the invention patent with the authorization announcement number [CN101850422B] is used to prepare Ni-based alloy composite substrates, which are generally prepared through pre-pressing-sintering-rolling and other steps. However, during the high-temperature recrystallization process of NiW substrates, grain boundary grooves will be formed, resulting in a decrease in critical current density, which seriously restricts the development of RABiTS technology.

[0004] In the existing technology, the base strip produced by the RABiTS technology route is mostly polished as a whole to eliminate the grain boundary grooves in the market. However, a large amount of polishing also causes a waste of materials and energy, and cannot fundamentally prevent the formation of grain boundary grooves. Summary of the invention

[0005] Aiming at the problem that grain boundary grooves are formed in a NiW-based strip during high-temperature recrystallization, the present invention proposes a method for preparing a sulfur-doped Ni-based thin strip capable of effectively reducing the formation of grain boundary grooves.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is: a method for preparing a sulfur-doped Ni-based thin strip for a coated conductor, comprising the following steps:

[0007] Step A: Preparation of NiW baseband:

[0008] (1) grinding and mixing Ni powder and W powder in an atomic ratio of 91:9-85:15 to obtain NiW powder;

[0009] (2) pre-pressing the mixed NiW powder to obtain NiW blocks of a specific size, and sintering the pressed NiW blocks to obtain NiW ingots;

[0010] (3) grinding the sintered NiW ingot to remove the oxidized part and defective part of the surface layer, and rolling the NiW ingot to obtain a NiW base strip;

[0011] Step B: Preparation of sulfur-doped Ni-based thin strip:

[0012] The NiW substrate is placed in a tubular furnace, and a H2S-H2-Ar mixed gas is introduced, wherein the H2S content is 0.01%-1.00%, the H2 content is 1%-5%, and the rest is Ar gas, and it is recrystallized at 1250°C-1450°C for 5-10 hours.

[0013] Furthermore, in step B, the H2S-H2-Ar mixed gas introduction rate is 30L / h-120L / h.

[0014] Furthermore, the content of H2S gas in step B is 0.1%.

[0015] Furthermore, the purity of the Ni powder and the W powder in step A is greater than 99.99%, which is sufficient to avoid stress concentration on the base tape and prevent the base tape from breaking.

[0016] Furthermore, in step A, when sintering the NiW block, the NiW block is placed in a tubular furnace, an inert gas is introduced into the tubular furnace to exhaust the internal air, and then the temperature is raised to 1250° C.-1450° C. and sintered for 5-10 hours.

[0017] Furthermore, in step A, the heating rate is 7°C / min-9°C / min.

[0018] Furthermore, in step A, the sintering temperature is 1350°C.

[0019] Furthermore, in the step A, the NiW powder is placed in a powder briquetting machine for pre-compression to form a dense long strip shape with a size of 50 mm*40 mm.

[0020] Furthermore, in step A, the thickness of the obtained NiW base tape is 40 μm-60 μm.

[0021] Compared with the prior art, the advantages and positive effects of the present invention are:

[0022] This scheme uses H2S mixed gas to perform sulfur doping on NiW-based strips, combines the introduction ratio of H2S gas, and realizes the preparation of sulfur-doped Ni-based thin strips of coated conductors under specific H2S mixed gas introduction time and temperature conditions. Sulfur doping fundamentally prevents the formation of grain boundary grooves and avoids the reduction of critical current density of Ni-based thin strips. In addition, this method does not require intermediate heat treatment during rolling, has simple process steps, and shortens the preparation time. The process parameters are easy to control and are suitable for industrial-scale production and continuous production. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the preparation method according to an embodiment of the present invention;

[0024] Figure 2 This is an AFM image of a NiW substrate without H2S mixed gas doping according to an embodiment of the present invention;

[0025] Figure 3 This is an AFM image of a NiW substrate prepared by the method described in Example 1 of the embodiment of the present invention;

[0026] Figure 4 This is an AFM image of the NiW substrate prepared by the method described in Example 2 of the embodiment of the present invention. DETAILED DESCRIPTION

[0027] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described below in conjunction with the accompanying drawings and embodiments. In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention can also be implemented in other ways different from those described herein, and therefore, the present invention is not limited to the specific embodiments disclosed below.

[0028] In order to facilitate the understanding of the scheme of the present invention, it should be explained here that, in order to minimize the energy, the surface of the crystal is preferably a close-packed plane. However, due to the lattice matching with YBCO and the transition layer, the surface of the NiW base strip is generally required to be (100), but (100) does not belong to the most close-packed plane of the NiW base strip, and its surface energy is relatively high; in order to reduce its overall energy, the crystal tends to cut off the surrounding of the (100) to make it spherical, thereby reducing the energy, which also causes the formation of grain boundary grooves. Grain boundary grooves are one of the main obstacles to the development of RABiTs technology, and the problem of grain boundary grooves has not been effectively solved.

[0029] like Figure 2 As shown, this is an AFM image of a NiW substrate prepared by conventional pre-pressing-sintering-rolling steps without introducing H2S mixed gas for doping. Figure 2It can be seen that the grain boundary groove is deep. According to the above principle, if the energy of (100) can be reduced to make it the crystal plane with the lowest energy in the NiW substrate, it must be made the most densely packed plane. Therefore, if a suitable substance can be doped into the NiW substrate and it is ensured that it adsorbs more doping substances on the (100) plane, so that (100) has the largest number of atoms (including Ni, W, and doping atoms), then (100) can be made the crystal plane with the lowest energy, thus preventing the formation of grain boundary grooves.

[0030] In the prior art, although there are related literatures on optimizing the nucleation process of the oxidation buffer layer on the surface of the Ni substrate by chemical adsorption of sulfur on the Ni substrate, the principle of the method is mainly: first, sulfur is adsorbed on the Ni substrate (about The chemical adsorption of S on the plane of the Ni substrate (on the surface of the Ni substrate) will be due to the segregation of S, which will present a c(2×2) structure; secondly, the chemical properties of S are close to those of O, and their electronic valence states are often the same. Therefore, during the deposition of the seed layer, the cations in the seed layer can easily combine with S atoms, thereby causing the film to grow outward along (001), but its principle is substantially different from that of this scheme. In fact, the adsorption of S will not only occur above the Ni substrate, but will also segregate at the grain boundaries of the surface layer of the substrate, and this segregation has a great influence on the grain boundary grooves. Therefore, this scheme prepares the Ni-based thin strip through the steps of grinding and mixing-prepressing-sintering-rolling-sulfur doping and recrystallization, which fundamentally prevents the formation of grain boundary grooves. Sulfur doping is to increase the content of cubic texture and reduce grain boundary grooves. In order to more clearly understand the scheme of the present invention, the scheme is described in detail with specific examples below:

[0031] Example 1:

[0032] The Ni powder and W powder with a purity of 99.999% are fully ground and mixed according to the atomic ratio of 91:9. The mixed NiW powder is then placed in a powder briquetting machine for pre-pressing to a size of 50mm*40mm. The pressed NiW block is placed in a tubular furnace, pre-introduced with inert gas for cleaning, and then heated to 1350℃ for sintering for 6h at a heating rate of 8℃ / min. The sintered NiW ingot is ground to remove the oxidized and defective parts of the surface. The NiW ingot is then rolled with a large deformation amount to make its thickness 50μm. A 50μm thick NiW substrate was placed in a tube furnace, and a H2S-H2-Ar mixed gas was introduced, with the corresponding component contents of 0.1%, 4%, and 95.9%, respectively, and the gas flow rate was 50L / h, so that it was recrystallized at 1350℃ (while ensuring that the recrystallization temperature of the high-strain NiW thin strip is reached, ensuring that other random crystal orientations will not have a growth advantage in this process, which is conducive to the formation of cubic texture) for 6h (ensuring that the sulfide gas diffuses into the substrate and avoids the energy at the grain boundary groove from gradually volatilizing at high temperature). Subsequently, the surface roughness in the 50μm*50μm area was analyzed using AFM, and its 3D image is as follows Figure 3 As shown in the figure, its arithmetic average roughness (Ra) is 50.4nm and its root mean square roughness (Rq) is 63.2nm. Figure 2 By comparison (Ra is 62.0 nm, Rq is 79.1 nm), it can be seen that after the sulfur doping treatment according to the method of this embodiment, the grain boundary grooves on the surface of the NiW substrate are effectively weakened.

[0033] Example 2:

[0034] The Ni powder and W powder with a purity of 99.999% were fully ground and mixed according to the atomic ratio of 90.5:9.5. The mixed NiW powder was then placed in a powder briquetting machine for pre-pressing to a size of 50mm*40mm. The pressed NiW block was placed in a tubular furnace, pre-introduced with inert gas for cleaning, and then heated to 1400℃ for sintering for 5h at a heating rate of 7℃ / min. The sintered NiW billet was ground to remove the oxidized and defective parts of the surface. The NiW billet was then rolled with a large deformation amount to a thickness of 50μm. A NiW base strip with a thickness of 50μm was placed in a tubular furnace, and a H2S-H2-Ar mixed gas was introduced, with the corresponding component contents of 0.5%, 5%, and 94.5%, respectively, and the gas flow rate was 40L / h, so that it was recrystallized at 1400℃ for 5h. Then AFM was used to analyze the surface roughness in the 50μm*50μm area, and the 3D image is as follows: Figure 4 As shown in the figure, its arithmetic average roughness (Ra) is 50.0nm and its root mean square roughness (Rq) is 65.8nm. Figure 2By comparison (Ra is 62.0 nm, Rq is 79.1 nm), it can be seen that after sulfur doping, the grain boundary grooves on the surface of the NiW substrate are effectively weakened.

[0035] In summary, the reason for the formation of grain boundary grooves is that the energy of the grain boundary is too high. By reducing the energy of (100) and making it the crystal plane with the lowest energy, the formation of grain boundary grooves during the recrystallization process can be reduced. In the high-temperature recrystallization process of this scheme, as the grains grow, when the grain size gradually becomes larger than the base strip thickness, the surface energy (generally 2-3 times the grain boundary energy) will replace the grain boundary energy as the main driving force for the movement of the grain boundary. During the high-temperature recrystallization process, H2S mixed gas is introduced to make it adsorbed to different degrees on each crystal plane of NiW, among which the adsorption degree of the (100) crystal plane is the largest, resulting in the (100) crystal plane replacing the (111) crystal plane as the crystal plane with the lowest surface energy. Therefore, the preparation method of sulfur-doped Ni-based thin strip for coated conductors described in this embodiment fundamentally prevents the formation of grain boundary grooves.

[0036] The above description is only a preferred embodiment of the present invention and does not limit the present invention in other forms. Any technician familiar with the profession may use the technical content disclosed above to change or modify it into an equivalent embodiment with equivalent changes and apply it to other fields. However, any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing a sulfur-doped Ni-based thin strip for a coated conductor, characterized in that: The steps include: Step A, preparing a NiW base tape; (1) grinding and mixing Ni powder and W powder with a purity greater than 99.99% in an atomic ratio of 91:9 to 85:15 to obtain NiW powder; (2) pre-pressing the mixed NiW powder to obtain NiW blocks of a specific size, and sintering the pressed NiW blocks to obtain NiW ingots; (3) grinding and rolling the sintered NiW ingot to obtain a NiW base strip; Step B: Preparation of sulfur-doped Ni-based thin strip: The NiW substrate is placed in a tubular furnace, and a H2S-H2-Ar mixed gas is introduced, wherein the H2S content is 0.01%-1.00%, and the H2 content is 1%-5%, and the NiW substrate is recrystallized at 1250°C-1450°C for 5-10h, and the H2S-H2-Ar mixed gas introduction rate is 30L / h-120L / h.

2. The method for preparing a sulfur-doped Ni-based thin strip for a coated conductor according to claim 1, characterized in that: The content of H2S gas in step B is 0.1%.

3. The method for preparing a sulfur-doped Ni-based thin strip for a coated conductor according to claim 1, characterized in that: In the step A, when the NiW block is sintered, the NiW block is placed in a tubular furnace, an inert gas is introduced into the tubular furnace to exhaust the internal air, and then the temperature is raised to 1250° C.-1450° C. for sintering.

4. The method for preparing a sulfur-doped Ni-based thin strip for a coated conductor according to claim 3, characterized in that: The heating rate in step A is 7°C / min-9°C / min.

5. The method for preparing the sulfur-doped Ni-based thin strip for coated conductor according to claim 3, characterized in that: In the step A, the sintering time is 5-10 hours.

6. The method for preparing a sulfur-doped Ni-based thin strip for a coated conductor according to claim 1, characterized in that: In the step A, NiW powder is placed in a powder briquetting machine for pre-compression to form a dense long strip shape with a size of 50 mm*40 mm.

7. The method for preparing a sulfur-doped Ni-based thin strip for a coated conductor according to claim 1, characterized in that: In the step A, the thickness of the obtained NiW base tape is 40 μm-60 μm.

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