CN1546717A - Preparation method of biaxially textured polycrystalline silver base tape - Google Patents

Abstract

The invention discloses a method for preparing a polycrystalline textured silver base band, which belongs to the field of preparation of high-temperature superconducting coating tough base bands and superconducting thin films. The preparation method of the present invention is characterized in that it comprises the following steps: using the existing vacuum smelting method to reduce the oxygen content in the silver raw material, then casting it into a silver billet, and cutting it into silver plates with a thickness of 3.5mm-4.5mm; The plate is cold-rolled, the deformation of each pass is 10-40%, and the total deformation is 90-97%; 700℃～920℃ in the mixed atmosphere of air, argon, oxygen or argon and 2-15% air by volume Annealing in any one of the atmospheres is optional for 0.5 to 10 hours. After research, it is found that a strong single-component {110}<110> biaxial texture can be prepared repeatedly; annealing in a mixed atmosphere of argon and 2-15% air by volume can also obtain a silver-based band with a flat surface. After surface treatment of the prepared silver ribbon, a superconducting thin film is prepared by thermal decomposition of trifluoroacetate, and a thin film with single composition, high c-axis orientation and good in-plane orientation is prepared.

Description

Preparation method of biaxially textured polycrystalline silver base tape

technical field

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

Background technique

Making high-temperature superconducting materials with ceramic brittleness into wires and strips is an important link to realize their practical applications. In recent years, people have made great progress in the preparation of high-temperature superconducting long strips by depositing superconducting films on polycrystalline ductile metal substrates. Yttrium barium copper oxide ( _YBa2Cu ) with a length of 10 meters has been prepared. ₃ O _7-δ ) superconducting tape, which is expected to be used in strong electric applications. Silver is the only baseband metal that does not require an isolation layer when preparing superconducting materials. If the texture of polycrystalline silver ribbons can be controlled, it is expected to directly prepare high-performance high-temperature superconducting films on polycrystalline silver ribbons. Therefore, the process can be simplified and the cost can be reduced.

At present, many research groups at home and abroad use polycrystalline silver substrates to study coated high-temperature superconducting films. Studies have shown that {110} biaxially textured silver substrates are conducive to the formation of YBa ₂ Cu ₃ O _7-δ high-performance superconducting films. In the {110} biaxial texture, the {110}<110> biaxial texture is favored due to its high symmetry and absence of twinning. Therefore, how to control the silver texture and obtain a single-oriented {110}<110> biaxial texture is the key to the practical application of silver-based tapes to prepare YBa ₂ Cu ₃ O _7-δ superconducting films. At present, foreign research groups have obtained silver basebands with {110}<110> biaxial texture, but the texture in the baseband is not single enough, and there are still weak other orientations.

In addition, due to the low mechanical strength of silver, mechanical polishing cannot be used for surface treatment, and chemical polishing can easily cause grain boundaries to deepen during surface polishing, which is not conducive to the preparation of high-performance superconducting films. Therefore, it is very important for the direct deposition of the subsequent superconducting film to adopt an appropriate atmosphere for annealing to make the silver-based strip have a flat surface. At present, foreign research groups have obtained silver substrates with {110}<110> biaxial texture, using the method of annealing in air or vacuum, and experiments have proved that: annealing at temperatures above 800°C in air, The corrosion of the grain boundary is very severe, which deepens and widens the grain boundary; while annealing in vacuum cannot eliminate the surface rolling marks. Therefore, although the silver-based strips obtained in the two annealing atmospheres have a good texture, they do not have a good surface state.

Contents of the invention

The present invention obtains a certain deformation texture by controlling the deformation and recrystallization annealing process of silver, adopting the method of cold rolling and recrystallization annealing, and controlling the oxygen content in the raw material, the deformation amount of each pass and the total deformation amount during deformation, Then, a certain recrystallization annealing method, annealing temperature, annealing atmosphere and annealing time are used to obtain a strong single component {110}<110> biaxially textured polycrystalline silver base band, which can be used for deposition after surface treatment YBa ₂ Cu ₃ O _7-δ high temperature superconducting film.

In the present invention, recrystallization annealing is adopted in a mixed atmosphere of argon and a small amount of air to obtain a polycrystalline silver base band with a strong single-component {110}<110> biaxial texture and a flat surface. A small amount of air can eliminate surface rolling marks during annealing, and the protection of argon can avoid corrosion of grain boundaries. The superconducting film with high critical current value can be directly prepared by using the silver base tape.

The present invention provides a kind of preparation method of biaxial textured polycrystalline silver substrate, it is characterized in that, it comprises the following steps:

(1) adopt existing vacuum smelting method to reduce the oxygen content in the silver raw material, cast into silver ingot then, be cut into the thick silver plate of 3.5mm-4.5mm;

(2) Cold-rolling the silver plate at room temperature, the deformation of each pass is 10-40%, and the total deformation is 90-97%;

(3) Annealing at 700° C. to 920° C. for 0.5 to 10 hours in an atmosphere of air, argon, oxygen or a mixed atmosphere of argon and 2 to 15% air by volume.

The silver raw material used is commercial silver ingot with a purity of 99.9-99.99wt%. For the first time, the existing vacuum smelting method is used to reduce the oxygen content in the high-purity silver material. When the silver is in a liquid state, a high vacuum of 3 to 8×10 ^-3 Pa is maintained for 3 to 10 minutes, and then cast into silver blanks, cut Form a silver plate with a thickness of 3.5mm-4.5mm, the oxygen content before degassing is 120-230ppm, and the oxygen content after degassing is reduced to 10-50ppm. The previous technology to reduce the oxygen content in the high-purity silver material is to cut the commercial silver ingot into a certain thickness, and directly keep it in high vacuum for degassing, which takes a long time and the distribution of oxygen content on the surface and middle of the silver plate is uneven all. The vacuum smelting method we adopt reduces the oxygen content in the high-purity silver material, and the time is short and the effect is good.

In the rolling process of the silver strip, if the pass deformation is too small, the texture uniformity of the material will be affected. If the pass deformation is too large, twins will easily form in the silver strip, which is not conducive to the acquisition of a single orientation texture. After our research, the pass deformation is suitable for 10-40%. The total deformation is less than 90% or greater than 97%, and the texture is not concentrated enough. It is found that the total deformation is 90-97%.

After research, it is found that recrystallization annealing can be carried out in three atmospheres of air, argon or oxygen to obtain the desired textured silver ribbon, the annealing temperature is 700°C-920°C, and the annealing time is 0.5-10 hours.

Annealing is carried out in a mixed atmosphere of argon and 2-15% air by volume for 0.5-10 hours. It is found that silver-based strips with flat surfaces can be obtained in a mixed atmosphere of argon and 2-15% air. The experiment proves that polycrystalline silver-based tapes with a strong single-component {110}<110> biaxial texture and flat surface can be repeatedly prepared, and superconducting films with high critical current values can be directly prepared with this silver-based tape.

Description of drawings

Fig. 1: the recrystallization texture orientation distribution function (ODF) sectional view ( ₂ =0° section) and (111) pole figure of the silver ribbon in embodiment 1;

Fig. 2: the recrystallization texture orientation distribution function (ODF) sectional view ( ₂ =0° section) and (111) pole figure of silver ribbon in embodiment 2;

Fig. 3: the recrystallization texture orientation distribution function (ODF) sectional view ( ₂ =0° section) and (111) pole figure of the silver ribbon in embodiment 3;

Fig. 4: the recrystallization texture orientation distribution function (ODF) sectional view ( ₂ =0° section) and (111) pole figure and metallographic photograph (500 times) of silver ribbon in embodiment 4;

Fig. 5: Recrystallization texture orientation distribution function (ODF) section diagram ( ₂ =0° section), (111) pole figure and metallographic photograph (500 times) of the silver ribbon in Example 5.

Detailed ways

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

Example 1. Grinding and polishing the rolls of a rolling mill. The low-oxygen-content silver ingot with a purity of 99.99% and vacuum smelting is used, and cut into 3.5mm thick silver plates; then cold-rolled at room temperature. The amount of deformation in the first pass is 35%, the amount of deformation in subsequent passes is 15-20%, and the total amount of deformation is 90%. The rolled silver strip was placed in an air annealing furnace, slowly heated to 700°C, and then kept for 30 minutes to form a {110}<110> silver texture, as shown in Figure 1. In Fig. 1, the intensive intensity distribution area of  ₁ =90°, φ=45°, and  ₂ =0° represents the {110}<110> texture, which has strong strength and single composition.

Example 2. Grinding and polishing the rolls of a rolling mill. The vacuum smelted low-oxygen silver ingot with a purity of 99.99% is used to cut into 4.5mm thick silver plates; and then cold-rolled at room temperature. The amount of deformation in the first pass is 30%, the amount of deformation in subsequent passes is 30-40%, and the total amount of deformation is 97%. The rolled silver strip was placed in an annealing furnace in an argon atmosphere, slowly heated to 920°C, and then kept for 3 hours to form a {110}<110> silver texture, as shown in Figure 2. A single-oriented {110}<110> silver texture is formed, with high texture strength and single composition.

Example 3. Grinding and polishing the rolls of a rolling mill. The low-oxygen-content silver ingot with a purity of 99.9% and vacuum smelting is used to cut into 3.96mm-thick silver plates; and then cold-rolled at room temperature. The amount of deformation in the first pass is 15%, the amount of deformation in subsequent passes is 10-40%, and the total amount of deformation is 94%. The rolled silver strip was placed in an annealing furnace in an oxygen atmosphere, slowly heated to 800°C, and then kept for 10 hours to form a {110}<110> silver texture, as shown in Figure 3. A single-oriented {110}<110> silver texture is formed, with high texture strength and single composition.

Example 4. Grinding and polishing the rolls of a rolling mill. The vacuum smelted low-oxygen silver ingot with a purity of 99.99% is used to cut into 3.87mm thick silver plates; and then cold rolled at room temperature. The deformation amount of the first pass is 20%, the deformation amount of subsequent passes is about 15%, and the total deformation amount is 94%. The rolled silver strip was placed in an annealing furnace, fed with argon gas and 2% air by volume, slowly heated to 850°C, and then kept for 5 hours, forming a single-oriented {110}<110> silver texture, texture High structural strength and single composition. Metallographic analysis shows that it has a flat surface and very shallow grain boundaries, as shown in Figure 4.

Example 5. Grinding and polishing the rolls of a rolling mill. The vacuum smelted low-oxygen silver ingot with a purity of 99.99% is used to cut into 4.2mm thick silver plates; and then cold-rolled at room temperature. The amount of deformation in the first pass is 22%, the amount of deformation in subsequent passes is 20%, and the total amount of deformation is 96%. The rolled silver strip was slowly heated to 850°C in a mixed atmosphere of argon and 15% air by volume, and then kept for 1 hour to form a strong {110}<110> silver texture. Metallographic analysis shows that it has a flat surface and very shallow grain boundaries, as shown in Figure 5.

Using the above-mentioned silver tape as the base tape, YBa ₂ Cu ₃ O _7-δ superconducting thin film is prepared by using the existing trifluoroacetate thermal decomposition (TFA-MOD) method. The compound is dissolved in an appropriate solvent to form a sol, which is then coated on the substrate by a homogenizing method. After preheating, the organic components are decomposed and volatilized, and then sintered at a high temperature to form the desired YBCO film. This method does not require high vacuum, the composition is easy to control, additives can be added or subtracted at will, and long superconducting tapes can be produced.

Taking the silver tape prepared in Example 1 as the base tape to prepare the yttrium barium copper oxide superconducting thin film as an example, after surface treatment, YBa ₂ Cu ₃ O _{7- The δ} superconductor is thin, and the YBa ₂ Cu ₃ O _7-δ film with single composition, high c-axis orientation and good in-plane orientation has been prepared. The critical current Jc value is about 10000A/cm ² (77K, self-field).

Taking the silver tape prepared in Example 5 as the base tape to prepare the yttrium-barium-copper-oxygen superconducting thin film as an example, after cleaning the surface, prepare YBa ₂ Cu ₃ O _{7- The δ} superconductor is thin, and the YBa ₂ Cu ₃ O _7-δ film with single composition, high c-axis orientation and good in-plane orientation has been prepared. The critical current Jc value is 15000A/cm ² (77K, self-field), which is For the first time at home and abroad, this method is used to prepare YBa ₂ Cu ₃ O _7-δ high temperature superconducting film on polycrystalline textured silver substrate.

Claims (1)

1, a kind of preparation method of biaxial texture polycrystalline silver based belt is characterized in that it may further comprise the steps:

(1) the existing vacuum smelting method of employing reduces the oxygen level in the silver-colored starting material, is cast into silver-colored base then, is cut into the thick silver plate of 3.5mm-4.5mm;

(2) at room temperature silver plate is carried out cold rollingly, pass deformation is 10～40%, and total deformation is 90～97%;

(3) in 700 ℃～920 ℃ atmosphere that adopt air, argon gas, oxygen or argon gas and volume percent 2～15% Air mixing atmosphere to choose one wantonly, annealed 0.5～10 hour.

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