DE1241999B - Process for the manufacture of wires and tapes from zirconium-niobium alloys for hard superconductors - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. CL:

C22f

German class: 4Od-1/18

Number: 1241999

File number: M 52625 VI a / 40 d

Filing date: April 25, 1962

Open date: June 8, 1967

It is known that wires and tapes made of so-called hard superconductors, i.e. those superconductors whose maximum current strength in the area of superconductivity is only slightly influenced by an external magnetic field up to high field strengths, can be produced from niobium-zirconium alloys by cold forming. The subject of an earlier patent, which is to be regarded as an earlier right here, is a method for improving the superconducting properties of a binary niobium alloy with 10 to 90 atomic percent zirconium. According to this older process, the alloy present in the homogeneous / 3-phase is _{annealed at at least 300 ° C. for V 2} to 10 hours and then rapidly cooled. Strong cold deformation results in cross-section reductions of at least 60%. As far as the critical current density could be increased by the heat treatment, this was attributed to the phase dissociation and the induction of local stresses. However, the earlier patent does not reveal how optimal properties can be achieved with alloys of different compositions. It has finally been assumed that superconductors consisting of the intermetallic compound Nb ₃ Sn can then absorb a higher current intensity if they have a lamellar structure, a so-called filament structure. The diameter of the lamellae should be smaller than the penetration depth and noticeably smaller than 100 Å.

The invention is based on the knowledge that wires and tapes made of hard superconductors, which are deformable Niobium-zirconium alloys, then have optimal superconductivity properties, when alloys with a niobium content of 30 to 90%. The rest of the zirconium in addition to the usual impurities, intermediate annealing in a temperature range between the individual deformation steps, in the niobium-zirconium mixed crystals in at least two phases of different concentration, 4 » but have the same structure, are subjected to such a temperature and for such a long time, until a fine lamellar structure of the structure with an average lamellar thickness of 0.01 to 1 μ, preferably about 0.1 μ, largely parallel to the surface achieved wild.

The heat treatment varies in temperature and duration depending on the composition of the alloy. However, it can easily be determined by experiments at which annealing temperatures and Annealing times and what degree of deformation must be worked to achieve the lamellar structure.

Method of making wires

and zirconium-niobium alloy ribbons

for hard superconductors

Applicant:

Metallgesellschaft Aktiengesellschaft,

Frankfurt / M., Reuterweg 14

Named as inventor:

Dipl.-Chem. Dr. Ulrich Zwicker, Aalen (Württ.)

The degree of deformation is only important insofar as it is over 40% if possible. should lie, while the annealing temperature and duration from alloy to alloy exactly in the way must be coordinated that no Phase granularly molded. For this reason, it is above all important to ensure that the annealing temperature is not too high, because then there is a greater risk of granular denting. When the annealing temperature is kept too low, a longer glow time is required, which is for practical reasons is generally not desirable, but this is inferior to achieving the desired lamellar Structure after cold working generally not in the way. The minimum temperature must, however be so high that the softening required for further processing after the heat treatment entry.

The intermediate annealing should be adjusted according to temperature and duration so that the Lamellar structure extends in the longitudinal direction of the wires and bands and also parallel to the Surface runs in such a way that it is interrupted as little as possible. So the slats should be embedded parallel to the surface slate-like and, if possible, without any noticeable interruption get lost. This is z. B. achieved in such a way that the temperature of the annealing treatment is chosen so high that any existing grain structure, which leads to the formation of long plate-shaped lamellae suitable, does not disintegrate into individual round grains. The phases are said to be after the heat treatment be as flat as possible. To the hostel tour The alloys to be treated according to the invention, the mixed crystals, are suitable for such a structure contained in

Claims (4)

two types of superconducting crystals of different concentration but with the same structure decay. Assuming a cast structure in which the mixed crystals have concentration differences due to grain segregation, this lamellar structure can be formed particularly well by a corresponding annealing treatment. A lamellar structure in which the lamellas run parallel to the surface is best achieved in the manufacture of wires by performing as many deformations as possible on round calibres. As a result, the lamellae are deformed largely parallel to the surface and to the desired thickness. The thickness of the lamellae is 0.01 to 1 μ, preferably around 0.1 μ. For niobium-zirconium alloys with 75 atomic percent niobium, the remainder being zirconium, the intermediate annealing is best carried out at 850 to 95O0C for a period of about 30 minutes. In the case of niobium-zirconium alloys with 66 atomic percent ao niobium, the temperature is 750 to 85O0C with an annealing time of about 30 minutes. An increase in the annealing temperature above the specified upper limit would have the disadvantages that the annealing time must either be very short and therefore difficult to adhere to, or the undesired granular agglomerations mentioned above occur in the structure, which would make it much more difficult to achieve the desired lamellar structure . A reduction in the annealing temperature can be accepted, but the annealing time is then extended. The annealing temperature will expediently not be below 6000 ° C., because then the formation of zirconium makes it much more difficult to achieve the lamellar structure with the long annealing times required for the deformation. The number of deformations and the degree of deformation depend on the size of the casting. In the case of smaller castings it is actually possible to get by with an intermediate annealing before the final deformation. In general, however, several deformations with a respective intermediate anneal should be necessary. The invention is illustrated by the following examples. EXAMPLE 1 A casting made of an alloy with 66 atomic percent niobium, the remainder being zirconium, was cold-worked over 99% to a wire 0.2 mm thick and then showed a critical current density with an external magnetic field of 38,000 oersteds of 10,000 A / cm2 at 4, 2 ° K. In contrast, a sample which, after being deformed to a diameter of 0.3 mm, had been annealed for 1/2 hour at 850 ° C. and, after cooling, also cold-deformed into a wire 0.2 mm thick, had a critical current density that was 20% higher at the same temperature in the same magnetic field. This sample had a fine lamellar structure with a lamella thickness of about 0.1 μ, while the previously described sample had a much thicker lamella thickness. Example 2 A casting with the same alloy composition was annealed after deformation to 0.33 mm at 12000 ° C. and then further deformed to 0.2 mm. Even under a magnetic field of 5000 Oersted at 5.0 ° K, the critical current densities of the above-mentioned samples were no longer achieved. A lamellar structure was not formed in this case. In contrast, the same alloy, which was initially cold-worked to 0.4 mm, then annealed for half an hour at 800 ° C. and then cold-worked to 0.2 mm, showed a current density of 40,000 A / cma at 5 in an Oersted magnetic field, 0 ° K. In this case, too, a fine lamellar structure with an average diameter of 0.1 μ was formed. Patent claims: 1. Process for the production of wires and strips from deformable zirconium-niobium alloys for had superconductors with optimal superconductivity properties, characterized by that zirconium alloys with a niobium content of 30 to 90%, the remainder being zirconium in addition to the usual impurities, intermediate anneals between the individual deformation slides in a temperature range in which niobium-zirconium mixed crystals in at least two Phases of different concentration but the same structure exist at such a temperature and subjected to such a long time until a distant lamellar structure of the structure of a average lamellar thickness of 0.01 to 1μ, preferably about 0.1μ, largely parallel to the surface is achieved. 2. The method according to claim 1, characterized in that niobium-zirconium alloys with 75 atomic percent niobium, the remainder zirconium, intermediate annealing at 850 to 95O ⁰ C and each for a duration of about 30 minutes are subjected. 3. The method according to claim 1, characterized in that niobium-zirconium alloys with 66 atomic percent niobium, the remainder zirconium, intermediate annealing at 750 to 850 ⁰ C and each for a duration of about 30 minutes are subjected. 4. The method according to claims 1 to 3, characterized in that almost all deformations can be carried out on round calibers. Legacy Patents Considered:
German Patent No. 1180 955. 709589/30 * 5.67 © Bundesdruckerei Berlin