CN1312301C - Prepn process of high temperature superconductive Ni-W alloy - Google Patents

Abstract

The present invention belongs to the field of coating a tough base band with high temperature superconductivity and the preparation of a superconductive film thereof. The smelting easily causes the non-uniform distribution of W, and the casting easily forms holes with low-density; thus, the density needs to be improved by subsequent hot forging which causes the oxidization of the surface of materials. Powder metallurgy has the defects of long cycle, high temperature, coarse and large crystal grains and low-density. The present invention comprises the following steps: Ni powder and W powder are uniformly mixed, wherein the purity is more than 99.9%, the granularity is from 3 to 6 micrometers, and the atomic percent of W of the alloy components is from 3 to 7%; the mixed powder is filled in a mould and is treated by spark plasma sintering at a temperature of 800 to 1200 DEG C and a pressure of 30 to 80MPa, and is treated by heat preservation for 0 to 10 minutes; a Ni-W plate is treated by cold rolling at a room temperature, wherein the deflection per pass is from 5 to 15%, and the total deflection is more than 97%; Ar is mixed with H2 atmosphere, and treated with recrystallization anneal, wherein H2 accounts for 4 vol%, the temperature is from 900 to 1300 DEG C, and the anneal is carried out for 0.5 to 3 hours. The present invention has the advantage of simple and rapid production process, and can prepare alloy blocks with uniform components and fine crystal particles, and a crystal Ni-W base band containing strong recrystallization texture with an individual component {100}; thus, the present invention can be used for depositing a YBCO high-temperature superconductive film.

Description

Preparation method of Ni-W alloy for high temperature superconductivity

technical field

The invention relates to a method for preparing a polycrystalline textured Ni-W baseband, which belongs to the technical field of high-temperature superconducting coating tough baseband and superconducting thin film preparation.

Background technique

Compared with Bi-based superconducting strips, YBa ₂ Cu ₃ O _7-δ (YBCO) superconductors have the ability to carry a larger current in a magnetic field, and their application prospects are very broad. Making brittle high-temperature superconducting materials into wires and strips is an important link to realize their practical applications. In recent years, great progress has been made in the preparation of wires and strips by depositing superconducting films on polycrystalline ductile metal substrates, and high-performance YBCO coated conductors have been successfully prepared. However, the texture state of the baseband directly affects the texture state of the superconducting film epitaxially grown on it, and affects the electrical properties of the superconductor, so the texture state is very important for the baseband material.

Pure nickel is a widely used baseband material. This is because pure nickel has good working performance, and it is very easy to form a strong cubic texture {100}<100> after severe deformation and annealing (that is, most of the nickel grains are parallel to the rolling surface of the base strip with the {100} plane, and parallel to the rolling direction of the base strip in the <100> direction). However, the strength of pure nickel is not high, and its mechanical properties are poor; it is ferromagnetic at room temperature (Curie temperature is 627K), which makes the application of YBCO coated conductors in high magnetic fields difficult (such as nuclear magnetic resonance imaging, etc.); and Pure nickel basebands cause energy losses in AC applications due to hysteresis losses.

Nickel alloying is an effective way to solve the problem of low strength of pure nickel and the removal of ferromagnetism, among which nickel-tungsten alloy has received extensive attention. The Ni-W alloy base strip has four advantages: (1) A strong cubic texture appears after severe cold rolling and recrystallization annealing; (2) The material strength is improved and the mechanical properties are better; (3) Compared with other Ni alloys, it has Better oxidation resistance, such as Ni-Cr, Ni-V, Ni-Fe; (4) The magnetism is very small. Therefore, the Ni-W base tape is easier to commercially produce high-temperature superconducting YBCO tapes that can carry large currents at liquid nitrogen temperature (77K) and in a magnetic field.

However, since the melting point of W is as high as 3410°C and the atomic radius is large, it is difficult to alloy with Ni, and it is easy to cause uneven distribution of W in the alloy material, which affects the performance of the baseband and reduces the strength of the biaxial texture. and concentration. In the past, Ni-W alloy blocks were prepared by smelting or common powder metallurgy sintering. The method of smelting is firstly to prepare Ni-W master alloy, then make proportioning according to the required alloy components, and then smelt and cast to obtain the alloy blank. However, since the melting point difference between W and Ni is about 2000°C, and the atomic radius of W is large, it is easy to cause uneven distribution of W in the alloy material, thereby affecting the performance of the baseband and reducing the strength and concentration of the biaxial texture; Moreover, casting is easy to form cavities, and the density is low, which affects the uniformity and texture distribution of the base band. Therefore, subsequent hot forging is required to increase the density, but hot forging will cause oxidation on the surface of the material. However, the ordinary powder metallurgy method has a long preparation period, high sintering temperature, coarse grains after sintering, and it is difficult to achieve high density.

Spark Plasma Sintering (SPS for short) is a fast, low-temperature, energy-saving and environmentally friendly material preparation and processing technology. This technology is a new technology that directly injects pulsed electric energy between the pressurized powder particles, heats the plasma generated instantaneously by spark discharge, and uses thermal effects, field effects, etc. to sinter at low temperature for a short time. Its power consumption is only 1/5 to 1/3 of the traditional sintering process (pressureless sintering PLS, hot pressing sintering HP, hot isostatic pressing HIP). SPS technology has the incomparable advantages of hot pressing and hot isostatic pressing technology:

In the initial stage of sintering, due to the action of the pulse current, a discharge phenomenon is generated between the powder particles, and the high temperature of the generated particles and the discharge shock pressure can not only effectively remove the adsorbed gas and impurities on the surface of the powder particles, but also cause the discharge. Rapid diffusion facilitates the particle densification process. Therefore, SPS can obtain homogeneous and dense materials. So far, no Ni-W alloy material has been prepared by spark plasma sintering.

Contents of the invention

The invention is for the first time at home and abroad to prepare Ni-W alloy material by spark plasma sintering method (SPS), obtain Ni-W alloy block with uniform composition and fine grain, and simultaneously simplify and speed up the preparation process.

Afterwards, by controlling the deformation and recrystallization annealing process of Ni-W alloy, including controlling the total rolling deformation and each pass deformation to obtain a certain deformation texture, and then adopting a certain recrystallization annealing temperature, annealing atmosphere and annealing Over time, a polycrystalline Ni-W substrate with a strong single component {100}<100> recrystallization texture was obtained, which can be used to deposit YBCO high-temperature superconducting films.

The invention provides a method for preparing a Ni-W alloy for high-temperature superconductivity, which is characterized in that it comprises the following steps:

(1) The raw materials used are Ni powder and W powder, the purity is more than 99.9% by weight, the particle size is 3 to 6 microns, and the atomic percentage of the alloy composition W is 3 to 7%; the nickel powder and the tungsten powder are mixed evenly, Then put it into the mold for spark plasma sintering; the sintering temperature is 800°C-1200°C, the sintering holding time is 0-10 minutes; the sintering pressure is 30-80Mpa;

(2) Cold-rolling the Ni-W plate at room temperature, the deformation of each pass is 5-15%, and the total deformation is 97% or more;

(3) Recrystallization annealing is carried out by using Ar mixed with H ₂ atmosphere, wherein the volume percentage of H ₂ is 4%, the annealing temperature is 900-1300° C., and the annealing time is 0.5-3 hours.

The above-mentioned step (2) if the pass deformation is too large, it is easy to form twins in the Ni-W belt, which is not conducive to the acquisition of a single orientation texture; after our research, the pass deformation is 5-15% suitable; the total deformation Less than 97%, the texture is not concentrated enough.

The invention obtains a Ni-W alloy block with uniform composition and fine crystal grains, and simultaneously simplifies and speeds up the preparation process. The invention obtains a polycrystalline Ni-W base band with strong single component {100}<100> recrystallization texture, which can be used for depositing YBCO high-temperature superconducting film.

Description of drawings:

Fig. 1: the backscattered electron diffraction pattern of Ni-3%W blank in embodiment 1;

Fig. 2: the grain distribution data graph of Ni-3%W billet in embodiment 1;

Fig. 3: (111) and (200) pole figure of Ni-3%W thin strip among the embodiment 1;

Fig. 4: the backscattered electron diffraction pattern of Ni-5%W blank in embodiment 2;

Fig. 5: the grain distribution data graph of Ni-5%W billet in embodiment 2;

Fig. 6: (111) and (200) pole figure of Ni-5%W thin strip among the embodiment 2;

Figure 7: PHI scanning diagram of (111) crystal plane (right) and ω rocking curve diagram of (200) crystal plane (left) of Ni-5%W thin ribbon in Example 2.

Fig. 8: the backscattered electron diffraction pattern of Ni-7%W blank in embodiment 3;

Fig. 9: the grain distribution data graph of Ni-7%W billet in embodiment 3;

Figure 10: (111) and (200) pole figures of the Ni-7%W ribbons in Example 3.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings and embodiments.

Example 1. adopt Ni powder and W powder as raw materials, the purity is 99.9% by weight, the particle size of Ni powder is 4～6 microns, the particle size of W powder is 3～4 microns, and W accounts for 3% by atomic percentage in the alloy. After mixing evenly, put it into a mold for SPS sintering. The sintering temperature is 800° C., and the sintering holding time is 10 minutes. The sintering pressure is 80MPa. A Ni-3%W block with a density of 98% was obtained. Figure 1 is its backscattered electron diffraction (EBSD) diagram, which shows that the grain size is relatively uniform. Figure 2 is the grain distribution data calculated from the EBSD results, the data shows that the average grain size of the sample is about 10 microns, and the grains are fine. The results of energy spectrum test show that the distribution of W in the alloy is very uniform.

Cold rolling and recrystallization annealing are carried out to the Ni-3%W block at room temperature, the pass deformation of cold rolling is 5-10%, and the total deformation is 97%; Ar mixed with H2 (the volume percentage of H2 is 4% ) atmosphere for recrystallization annealing, the annealing temperature is 900°C, and the annealing time is 0.5 hours. A thin ribbon with a strong, single-oriented {100}<100> texture was obtained, and Figure 3 shows its (111) and (200) pole figures. A very good cubic texture Ni-3%W baseband material is obtained, which can be used for the preparation of subsequent YBCO-coated superconducting materials.

Example 2. Adopting Ni powder and W powder as raw materials, the purity is 99.99% by weight, the particle size of Ni powder is 3～5 microns, the particle size of W powder is 3～5 microns, and W accounts for 5% by atom in the alloy. After mixing evenly, put it into a mold for SPS sintering. The sintering temperature is 1000° C., and the sintering holding time is 5 minutes. The sintering pressure is 50MPa. A Ni-5%W block with a density of 98.5% was obtained. Figure 4 is its backscattered electron diffraction (EBSD) diagram, which shows that the grain size is uniform. Fig. 5 is the grain distribution data calculated from the EBSD results, and the data shows that the average grain size of the sample is about 10 microns, and the grains are fine. The results of energy spectrum test show that the distribution of W in the alloy is very uniform.

Cold rolling and recrystallization annealing are carried out on the Ni-5%W block at room temperature, the deformation of each pass of cold rolling is 10-15%, and the total deformation is 98%; Ar mixed with H ₂ (the volume percentage of H ₂ is 4%) atmosphere for recrystallization annealing, the annealing temperature is 1100° C., and the annealing time is 2 hours. A thin ribbon with a strong, single-oriented {100}<100> texture was obtained, and Figure 6 shows its (111) and (200) pole figures. Figure 7 is the PHI scanning diagram (right) of the (111) crystal plane and the ω rocking curve diagram (left) of the (200) crystal plane. It can be seen from the figure that the full width at half maximum (HWFM) of the PHI scan of the (111) crystal plane and the half maximum width of the ω rocking curve of the (200) crystal plane are only 7.01° and 4.73° (HWFM), respectively, and a very good cubic The textured Ni-5%W base band material can be used in the preparation of subsequent YBCO coated superconducting materials.

Example 3. adopt Ni powder and W powder as raw materials, the purity is 99.9% by weight, the particle size of Ni powder is 4～6 microns, the particle size of W powder is 3～4 microns, and W accounts for 7% of atomic percentage in the alloy. After mixing evenly, put it into a mold for SPS sintering. The sintering temperature was 1200°C, and no sintering heat preservation was carried out. The sintering pressure is 30MPa. A Ni-7%W block with a density of 97.7% was obtained. Figure 8 is its backscattered electron diffraction (EBSD) diagram, which shows that the grain size is uniform. Fig. 9 is the grain distribution data calculated from the EBSD results, and the data shows that the average grain size of the sample is about 6.6 microns, and the grains are fine. The results of energy spectrum test show that the distribution of W in the alloy is very uniform.

Cold rolling and recrystallization annealing are carried out on the Ni-7%W block at room temperature, the deformation of each pass of cold rolling is 5-10%, and the total deformation is 97%; Ar mixed with H ₂ (the volume percentage of H ₂ is 4%) atmosphere for recrystallization annealing, the annealing temperature is 1300° C., and the annealing time is 3 hours. A thin ribbon with {100}<100> texture with a certain intensity was obtained, and Fig. 10 is its (111) and (200) pole figures.

Claims (1)

1. A method for preparing a Ni-W alloy for high-temperature superconductivity, comprising the following steps: 1) The raw materials used are Ni powder and W powder, the purity is more than 99.9% by weight, the particle size is 3-6 microns, and the atomic percentage of alloy composition W is 3-7%; the nickel powder and tungsten powder are mixed evenly, and then Put it into the mold for discharge plasma sintering; the sintering temperature is 800°C-1200°C, the sintering holding time is 0-10 minutes; the sintering pressure is 30-80Mpa; 2) Cold-rolling the Ni-W plate at room temperature, the deformation of each pass is 5-15%, and the total deformation is 97% or more; 3) Recrystallization annealing is carried out by using Ar mixed with H ₂ atmosphere, wherein the volume percentage of H ₂ is 4%, the annealing temperature is 900-1300° C., and the annealing time is 0.5-3 hours.

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