EP1922426B1 - Method for producing and using a nickel-based semi-finished product having a recrystallisation cube structure - Google Patents

Description

Technical area

The invention relates to a process for the production of nickel-based semi-finished products in strip or flat wire form with a recrystallization cube texture and the use of the semifinished product produced.

The semifinished product can be used in particular as a substrate for physico-chemical coatings with a high degree of microstructural alignment. Such supports are suitable, for example, as substrates for ceramic coatings as used in the field of high temperature superconductivity. In this case, they are used in superconducting magnets, transformers, motors, tomographs or superconducting current paths.

State of the art

It is known that polycrystalline metals with face-centered cubic lattice, such as nickel, copper and aluminum, after pronounced cold forming by rolling in the subsequent recrystallization form a pronounced texture with cube layer ( G. Wassermann: Textures of Metallic Materials, Springer, Berlin, 1939 ). Metal strips, in particular nickel tapes, textured in this manner are also used as a support for metallic coatings, ceramic buffer layers and ceramic superconductor layers (US Pat. US 5,741,377 ). The suitability of such metal strips as a substrate material largely depends on the achievable degree of texturing and the stability of the texture in the range of temperatures at which the coating processes work.

There are already textured semi-finished products known for the production of high-temperature superconductors, which consist of Ni-Cr, Ni-Cr-V, Ni-Cu and similar alloys ( US 5,964,966 ; US 6,106,615 ).

Also known for these purposes, Ni alloys with Mo and W ( DE 100 05 861 C1 ). It has also been proposed to add to such Ni alloys up to a maximum of 0.3 atom% Ag ( DE 103 42 965.4 ).

All such known metal bands with a cube texture, which is formed by recrystallization, have a structure with equiaxed grains, that is, based on the band level, they are about the same length and width. For theoretical reasons, however, a grain extension in the longitudinal direction should be advantageous for the current transport in superconductivity and lead to higher transferable currents ( Hammerl, H. et al., Eur. Phys. Journ. B (2002) 299-301 ). However, it has not yet been possible to produce substrate tapes with cube texture with simultaneously greatly extended grain structure.

• Rekristallisiertes Nickel oder dessen Legierungen mit Würfeltextur weisen Körner auf, die in Längsrichtung etwa die gleiche Ausdehnung haben wie in Querrichtung,
• Nickel neigt nach Kaltumformung und Rekristallisationsglühung stark zur Ausbildung einer groben Kornstruktur, die zur Erzielung der hochgradigen Würfeltextur nachteilig ist,
• kaltumgeformte Ni-Bänder neigen bei der Rekristallisations-Wärmebehandlung, insbesondere bei höheren Temperaturen (800 bis 1150°C) stark zur Bildung von Korngrenzengräben,
• Substratmaterial mit Korngrenzengräben ist wenig geeignet als Unterlage für epitaktische Schichtabscheidungen, zum Beispiel für Pufferschichten und Supraleiterschichten.

The known semi-finished products have the following disadvantages:

• Recrystallized nickel or its cubic texture alloys have grains which are approximately the same lengthwise in the longitudinal direction as in the transverse direction,
• Nickel, after cold working and recrystallization annealing, has a strong tendency to form a coarse grain structure, which is detrimental to achieving the high grade cube texture.
• Cold-formed Ni strips tend to form grain boundary trenches during recrystallization heat treatment, especially at higher temperatures (800 to 1150 ° C.).
• Grain trench substrate material is poorly suited as a substrate for epitaxial layer depositions, for example, for buffer layers and superconductor layers.

Disclosure of the invention

It is an object of the present invention to provide a process for producing nickel-based semifinished product which has improved performance for use as a substrate for high chemical microstructural alignment physical-chemical coatings. In particular, the semi-finished product should have an elongated grain shape with stable cube texture, and the expanded grain should remain intact even after further thermal treatment at high temperatures for the purpose of oxide layer growth.

This object is achieved with the features characterized in the claims.

The method according to the invention is characterized in that initially a starting semi-finished product is produced by fusion metallurgy or powder metallurgy involving mechanical alloying, which consists of technically pure Ni or a Ni alloy, wherein an Ag addition in the microalloying range of at least 10 atomic ppm and a maximum of 1000 atomic ppm is contained. This starting semifinished product is processed by means of a hot forming with subsequent cold working of> 50% thickness reduction to tape or flat wire with an intermediate dimension. In this intermediate dimension, the semi-finished product is annealed in the temperature range between 500 ° C and 850 ° C annealed, the higher temperatures are used for the higher Ag contents, and then quenched. Subsequently, this intermediate is highly> 80% cold formed. Finally, a recrystallizing annealing treatment to achieve a complete cube texture is performed.

The final recrystallization annealing treatment is carried out at temperatures of 500 ° C to 1200 ° C, preferably at 850 ° C, depending on the alloy content in the nickel.

The semifinished product may advantageously be heat treated after or during the recrystallizing annealing for the purpose of growing a cube-textured NiO layer having a texture content of> 90% in an oxidizing atmosphere.

It is also advantageous if a Ni alloy is used for the starting semi-finished product, which still contains Mo and / or W as alloying elements in addition to the Ag addition.

With the Ag addition according to the invention, the formation of a high-grade cube texture is favored. In addition, the expanded metal strip allows the growth of a highly cube textured NiO layer, which also has elongated grains.

According to the invention, the semifinished product can be used as a substrate for physico-chemical coatings with a high degree of microstructural orientation, in particular for producing wire-shaped or ribbon-shaped high-temperature superconductors.

The invention is explained below with reference to exemplary embodiments, with which the successful testing of the invention is demonstrated.

Brief description of the illustrations

Abb. 1

zeigt das gestrecktes Gefüge von Nickel mit 0,01 Atom-% Silber nach dem Warmwalzen bei 850°C und anschließendem Kaltwalzen mit einer Dickenreduktion von 85% und einer Anlassbehandlung mit Teilrekristallisation bei 550°C über 30 min (Längsschliff, geätzt).

Abb. 2

zeigt gestreckte Körner auf der Oberfläche eines 80 µm dicken Bandes von Nickel mit 0,025 Atom-% Silber, das bei 3 mm Dicke einer Zwischenglühung bei 650°C über 30 min unterzogen wurde, anschließend an 80 µm Dicke stark kalt umgeformt wurde und abschließend bei 550°C über 30 min geglüht wurde (Rasterelektronenaufnahme).

Abb. 3

zeigt gestreckte Körner mit Würfellage auf der Oberfläche eines 80 µm dicken Bandes von Nickel mit 0,025 Atom-% Silber nach einer Zwischenglühung bei 650°C über 30 min bei 3mm Dicke, anschließender starker Kaltumformung an 80 µm Dicke und der abschließenden Glühung bei 550°C über 30 min (Orientierungsmapping mit dem Rasterelektronenmikroskop).

Abb. 4

zeigt gestreckte Körner mit Würfellage des Nickeloxids auf der Oberfläche eines 80 µm dicken Bandes von Nickel mit 0,025 Atom-% Silber nach einer Zwischenglühung bei 650°C über 30 min bei 3 mm Dicke, anschließender starker Kaltumformung an 80 µm Dicke, der Texturglühung bei 550°C über 30 min und der Oxidation in Sauerstoff bei 1150°C über 2 min (Orientierungsmapping mit dem Rasterelektronenmikroskop).

The following explanations to the figures show the positive results of the application of the invention in the context of the described embodiments.

Fig. 1

shows the stretched structure of nickel with 0.01 atom% of silver after hot rolling at 850 ° C and then cold rolling with a thickness reduction of 85% and a tempering treatment with partial recrystallization at 550 ° C for 30 minutes (longitudinal grinding, etched).

Fig. 2

shows elongated grains on the surface of an 80 μm thick strip of nickel with 0.025 atom% of silver, which at 3 mm thickness was subjected to an intermediate annealing at 650 ° C for 30 minutes, then was strongly cold formed at 80 microns thick and was finally annealed at 550 ° C for 30 min (scanning electron micrograph).

Fig. 3

shows elongated grains with a dice layer on the surface of a 80 micron thick strip of nickel with 0.025 atom% of silver after an intermediate annealing at 650 ° C for 30 min at 3mm thickness, followed by strong cold forming at 80 microns thickness and the final annealing at 550 ° C. over 30 min (orientation mapping with the scanning electron microscope).

Fig. 4

shows elongated grains with cube layer of nickel oxide on the surface of a 80 micron thick band of nickel with 0.025 atom% of silver after an intermediate annealing at 650 ° C for 30 min at 3 mm thickness, followed by strong cold forming at 80 microns thickness, the texture annealing at 550 ° C for 30 min and the oxidation in oxygen at 1150 ° C for 2 min (orientation mapping with the scanning electron microscope).

example 1

Technically pure nickel, for example having a purity of 99.9 atomic percent nickel, is poured into a mold while admixing 0.025 atomic percent silver. The ingot is rolled at 850 ° C to the square dimension (22 x 22) mm ² , homogenizing annealed and quenched. Subsequently, the square material is machined to obtain a defect-free surface for subsequent cold working by rolling. The cold rolling is first carried out with a rolling degree of over 50 percent thickness reduction of 20 mm to 3 mm thickness, in this case, 85% thickness reduction. The subsequent tempering treatment at 650 ° C for 30 min followed by quenching in water causes a recrystallization with a proportion of elongated grains. Fig. 1 shows a typical micrograph (nickel with 0.01 atomic percent silver). This structure with elongated grains serves as a starting condition for further processing to the desired nickel ribbon with cube texture and with longitudinally stretched grains.

In addition, it is continuously cold-worked from a thickness of 3 mm to a thickness of 3 μm down to a thickness of 97.3% and finally annealed in a non-oxidizing gas atmosphere at 550 ° C. for 30 minutes. The result is grains on the surface of the strip which are several times longer than they are wide, such as Fig. 2 shows. At the same time results in an extremely sharp Rekristallisationswürfeltextur, as from Fig. 3 is apparent. The proportion of crystallites with dice position is 97.5 percent, and the proportion of small-angle grain boundaries is 92 percent.

Example 2

Technically pure nickel, for example having a purity of 99.9 atomic percent nickel, is melted while admixing 0.01 atomic percent silver in a vacuum induction furnace and poured into a mold. The ingot is rolled at 900 ° C to the square dimension (22 x 22) mm ² , homogenizing annealed and quenched. Subsequently, the square material is machined to obtain a defect-free surface for subsequent cold working by rolling. Cold rolling is carried out with a rolling degree of over 50 percent thickness reduction, in this case 85%. The resulting nickel strip has a thickness of 3 mm. It is subsequently tempered at 650 ° C for 30 minutes and quenched in water. The recrystallization produces a proportion of elongated grains. It is subsequently continuously cold formed with a thickness reduction of 97.3% from 3 mm to 80 μm thickness and finally annealed in a non-oxidizing gas atmosphere at 550 ° C. for 30 min. The result is an almost complete recrystallization cube texture in a stretched grain structure (cf. Fig. 3 ). Subsequently, the strip is exposed in pure oxygen gas at 1150 ° C a 2-minute oxidation.

The resulting nickel oxide layer has a structure with elongated grains, whose proportion with cube position is 97% ( Fig. 4 ). The proportion of small-angle grain boundaries is 96%. This texture is rotated 45 ° from the texture of the nickel strip.

Example 3

Technically pure nickel powder is powder metallurgically processed with the addition of 5.0 atomic percent tungsten powder and 0.1 atom% silver powder. After pressing, annealing and hot forming, a rod material of (22 x 22) mm ^{2 is} obtained. The surface is machined to obtain a defect free surface for subsequent cold working by rolling. The cold rolling is carried out from about (20 X 20) mm ² to a thickness of 3 mm.

It is subsequently tempered at 650 ° C for 30 minutes and quenched in water. Then cold rolled to the finished size of 80 microns thickness. The edge areas of the band are separated and discarded. The resulting nickel strip is then first subjected at 850 ° C a 30-minute annealing for recrystallization in a reducing atmosphere. Thereafter, the strip is treated in a second annealing for 8 minutes at 1150 ° C in a reducing atmosphere to set a thermally highly resilient cube layer.

Claims (7)

1. Method for the production of a nickel-based semifinished product having a recrystallization cube texture, characterised in that firstly a starting semifinished product is produced by a melt metallurgy or powder metallurgy process, with the inclusion of mechanical alloying, said starting semifinished product consisting of technically pure Ni or an Ni alloy, in which an Ag addition is present in the microalloying range of at least 10 atom ppm and at most 1000 atom ppm, in that this starting semifinished product is processed to form strip or flat wire having an intermediate dimension by means of hot-forming with subsequent cold-forming with a thickness reduction of > 50%, this strip or flat wire is softened by annealing in the temperature range of between 500°C and 850°C, with the hither temperatures being used for the hither Ag contents, in that consequently quenching is carried out, in that subsequently this intermediate product is subjected to cold-forming to a high degree of > 80%, and in that finally a recrystallizing annealing treatment is carried out to achieve a complete cube texture.
2. Method according to Claim 1, characterized in that the final recrystallization annealing treatment is carried out at temperatures of 500°C to 1200°C, depending on the alloy content in the nickel.
3. Method according to Claim 2, characterized in that the final recrystallization annealing treatment as carried out at a temperature of 850°C.
4. Method according to Claim 1, characterized in that the semifinished product is subjected to a heat treatment in an oxidizing atmosphere after or during the recrystallizing annealing for the purpose of growing a cube-textured NiO layer having a texture content of > 90%.
5. Semifinished product according to Claim 1, characterised in that an Ni alloy containing Mo and/or W and the Ag addiction is used for the starting semifinished product.
6. Use of the semifinished product produced according to Claims 1 to 5 in strip or flat wire form having a recrystallization cube texture and stretched grain shape as a substrate for physical-chemical coatings having a high degree of microstructural orientation.
7. Use of the semifinished product produced according to Claims 1 to 5 in strip or flat wire form having a recrystallization cube texture and stretched grain shape as a substrate for the production of wire-like or strip-like high-temperature superconductors.

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