EP3572539A1 - Method for generating a nbti alloy - Google Patents

Abstract

The invention relates to a method for producing a NbTi alloy (24) from metallic Nb and metallic Ti, characterized by the steps
A) Arc melting, vacuum induction melting or Skull melting of the metallic Nb and the metallic Ti, so that the Nb and the Ti mix together and alloy a mixture, and solidification of the mixture, wherein upon solidification at least one alloyed body (14) of a NbTi material is created
B) producing a melt (22) by subsequent electron beam melting of the at least one alloyed body (14) of the NbTi material in a vacuum and solidifying the melt (22) produced with the electron beam melt, wherein upon solidification after the electron beam melting the NbTi alloy (24) arises. The invention also relates to an NbTi alloy (24) produced by such a method.

Description

The invention relates to a method for producing a niobium-titanium alloy (NbTi alloy) from niobium (Nb) and titanium (Ti).

Currently, NbTi alloys for use as Type II superconductors are typically made by at least three times vacuum arc melting to achieve the necessary homogeneity and quality of the alloy. Such methods are known from JP H04-131 332 A and the JP H03-281 746 A known. The vapor pressure of Ti is about 0.05 mbar at 1900 ° C. and about 1 mbar at 2500 ° C. This results in a loss of Ti by evaporation of the Ti in a processing of the starting metals.

From the patent EP 0 595 877 B1 For example, a method of manufacturing a type II superconductor from a composite material is known. However, these materials have the disadvantage that they are subsequently difficult to process than a homogeneous material that can be produced for example as rods and wires. The US Pat. No. 3,268,373 A. proposes to improve the alloying of the elements Nb and Ti by vacuum annealing and rolling. However, these methods are very expensive and time-consuming. The DE 35 18 855 C2 discloses a method of making an Nb and Ti electrode to produce an NbTi alloy alloyed by multiple vacuum arc melting. The JP S06-220 844A suggests the use of a wound electrode in which the Nb is wound into the Ti and multiple melting. However, the multiple melting and the production of the wound electrode are very expensive.

The object of the invention is therefore to overcome the disadvantages of the prior art. In particular, an efficient and simple and inexpensive to implement method for the production of NbTi alloys is to be found, which enables the production of superconducting NbTi wires in high quality.

1. A) Lichtbogenschmelzen, Vakuuminduktionsschmelzen oder Skull-Schmelzen des metallischen Nb und des metallischen Ti, so dass sich das Nb und das Ti miteinander zu einem Gemisch mischen und legieren, und Erstarren des Gemischs, wobei beim Erstarren zumindest ein legierter Körper aus einem NbTi-Material entsteht, insbesondere zumindest ein Stab aus dem NbTi-Material entsteht,
2. B) Erzeugen einer Schmelze durch nachfolgendes Elektronenstrahlschmelzen des zumindest einen legierten Körpers aus dem NbTi-Material in einem Vakuum, insbesondere des zumindest einen Stabs, und Erstarren der mit dem Elektronenstrahlschmelzen erzeugten Schmelze, wobei bei dem Erstarren nach dem Elektronenstrahlschmelzen die NbTi-Legierung entsteht.

The objects of the invention are achieved by a method for producing a niobium-titanium alloy (NbTi alloy) from metallic niobium (Nb) and metallic titanium (Ti), in particular for producing a superconducting NbTi alloy of metallic Nb and metallic Ti, characterized by the steps

1. A) Arc melting, vacuum induction melting or skull melting of the metallic Nb and the metallic Ti, so that the Nb and the Ti together to form a mixture mix and alloy, and solidification of the mixture, wherein upon solidification at least one alloyed body is formed from a NbTi material, in particular at least one rod is formed from the NbTi material,
2. B) producing a melt by subsequent electron beam melting of the at least one alloyed body of the NbTi material in a vacuum, in particular the at least one rod, and solidification of the melt produced by the electron beam melting, wherein upon solidification after the electron beam melting, the NbTi alloy is formed.

The vacuum during electron beam melting in step B) has a maximum pressure of 10-3 mbar. Preferably, the electron beam melting takes place in a high vacuum at a pressure of at most 10-4 mbar.

The NbTi material is completely melted by electron beam melting, thereby completely alloying the Nb and Ti homogeneously with a maximum percentage deviation of the alloy composition of not more than +/- 1.5% nominal.

The skull melting according to step A) is preferably realized by electron beam skull melting, induction skull melting or arc-skull melting.

In a preferred method it can be provided that the arc melting, the vacuum induction melting or the Skull melting is performed only once and the electron beam melting is performed only once.

This has the advantage that the NbTi alloy is produced in only two steps. As a result, the necessary time and cost is reduced.

Furthermore, it can be provided that in step A) the metallic Ti is over-alloyed with an excess of between 1% by weight and 5% by weight compared to the desired NbTi alloy.

As a result, the weight losses can be compensated for by evaporation of Ti during electron beam melting and optionally also during arc melting, vacuum induction melting or skull melting.

Furthermore, it can be provided that the arc melting, the vacuum induction melting or the skull melting in step A) is carried out in an inert gas, in particular in helium (He) or argon (Ar).

In this way, the evaporation losses of Ti that occur in arc melting, vacuum induction melting or skull melting can be reduced.

It can be provided that the arc melting, vacuum induction melting or Skull melting in step A) is carried out at a partial pressure between 20 mbar and 300 mbar of the inert gas.

Hereby, the evaporation losses of Ti that occur in arc melting, vacuum induction melting or skull melting can be further reduced.

According to a particularly preferred variant of the method can be provided that in step A) arc melting is used and that the arc melting in step A) an electrode of Nb is used and Ti is supplied as granules or sponge or an electrode of plates welded together Nb and Ti or a compressed rod of Nb coated with Ti, or a rod of Ti covered with Nb or an electrode of a compressed mixture of particulate Nb and particulate Ti.

In this way, the arc melting can be carried out inexpensively on a large scale.

It can be provided that the electrode and optionally the granules or sponge is melted with the arc and the mixture solidifies in a cooled arc melting crucible as the at least one alloyed body, in particular the at least one rod.

This measure also causes the process can be applied on an industrial scale. Preferably, the cooled arc melting crucible is a water-cooled copper arc melting crucible.

According to a preferred refinement, it can be provided that during electron beam melting, the at least one alloyed body, in particular the at least one rod, is melted with at least one electron beam from at least one electron beam gun and the melt is collected in a cooled electron beam melting crucible and solidifies.

This also makes a cost-effective industrial implementation possible. In addition, it can be ensured that existing Nb clusters and other inhomogeneities melted and alloyed with the Ti. Preferably, the cooled electron beam melting crucible is a water-cooled copper electron beam melting crucible. The cooled electron beam melting crucible preferably has a lowerable bottom.

It may also be provided that the NbTi alloy contains between 40% by weight and 60% by weight of Ti, preferably between 45% by weight and 50% by weight of Ti.

It may also be particularly preferable that an NbTi47 alloy is produced.

These alloys are particularly well applicable as type II superconductors. At the same time, the process according to the invention can be used particularly well for these alloys because of the almost equal proportions of Ti and Nb.

According to a particularly preferred embodiment it can be provided that in electron beam melting in step B) residual clusters of Nb contained in the at least one alloyed body, in particular in the at least one rod, are homogeneously alloyed with the Ti with a maximum percentage Deviation of the alloy composition from the nominal value of maximum +/- 1.5%.

Namely, the chosen sequence makes it possible to homogenize the at least one alloyed body, in particular the at least one rod, strongly and to homogenize the melt produced in a melting process with the large but temporally short energy input during electron beam melting. The resulting unavoidable Ti evaporations are compensated by a superalloy.

Furthermore, it can be provided that in electron beam melting in step B) the NbTi alloy solidifies in a cylindrical form.

Such cylindrical shapes, in particular rods or rods, can be processed very well, for example, in connection to pull wires.

It can be provided that the cylindrical shape has a diameter between 100 mm and 500 mm. Alternatively or additionally, it may be provided that the cylindrical shape has a length between 750 mm and 4000 mm.

Cylindrical molds of such dimensions, especially such rods or rods, are also very well suited for further processing, for example to subsequently produce wires or rod material from the cylindrical molds.

Furthermore, it may be provided that the arc melting, the vacuum induction melting or the Skull melting and the solidification of the mixture after the arc melting, the vacuum induction melting or the Skull melting continuously takes place, so that continuously new material is melted and the mixture on already solidified NbTi Material is frozen. Alternatively or additionally, it can be provided that the electron beam melting and the solidification of the melt take place continuously after the electron beam melting, so that melt continuously generated by the electron beam melting is solidified on already solidified NbTi alloy.

Hereby, the process can be used well for larger quantities on an industrial scale, without requiring large amounts of the mixture or the melt liquid or must be kept warm. This also avoids further evaporation of Ti and thus a change in the composition of the NbTi alloy.

The objects underlying the invention are also achieved by a NbTi alloy prepared by a method according to the invention.

The invention is based on the surprising finding that it is possible by arc melting, vacuum induction melting or skull melting and subsequent electron beam melting to produce high-quality NbTi alloys in only a few steps, which meets the requirements for producing superconducting wires and other components , By avoiding additional steps, a cost effective NbTi alloy can be provided. Two remelting processes suffice, where up to now more remelting processes have been used. In the process control according to the invention, the amount of evaporated Ti is very accurately predictable. The known evaporating titanium amount can thus be overcompensated or weighed out beforehand, and thus the losses of the Ti can be compensated well. As a result, an NbTi alloy can be produced with a relatively accurately predictable and readily adjustable composition. The micro-element distribution of such a molten block is equal to or even more homogeneous than that of a four-time vacuum arc-melted block.

• Figur 1: eine schematische Darstellung einer Lichtbogenschmelzanlage im Querschnitt, die zum Durchführen eines ersten Teils eines erfindungsgemäßen Verfahrens geeignet ist;
• Figur 2: eine schematische Darstellung einer Elektronenstrahlschmelzanlage im Querschnitt, die zum Durchführen eines zweiten Teils des erfindungsgemäßen Verfahrens geeignet ist;
• Figur 3: eine energiedispersive Röntgenanalyse (EDX) erzeugt mit einem Rasterelektronenmikroskop (ESM) einer mit einem erfindungsgemäßen Verfahren hergestellten NbTi-Legierung; und
• Figur 4: eine energiedispersive Röntgenanalyse (EDX) erzeugt mit einem Rasterelektronenmikroskop (ESM) einer mit einem herkömmlichen, 4-fach durchgeführten Vakuumlichtbogenschmelzen hergestellten NbTi-Legierung zum Vergleich mit Figur 3.

In the following, embodiments of the invention will be explained with reference to four schematically illustrated figures, without, however, limiting the invention. Showing:

• FIG. 1 a schematic representation of an arc melting plant in cross-section, which is suitable for carrying out a first part of a method according to the invention;
• FIG. 2 a schematic representation of an electron beam melting plant in cross-section, which is suitable for carrying out a second part of the method according to the invention;
• FIG. 3 : an energy dispersive X-ray analysis (EDX) produced by means of a scanning electron microscope (ESM) of an NbTi alloy produced by a method according to the invention; and
• FIG. 4 : An energy dispersive X-ray analysis (EDX) generates with a scanning electron microscope (ESM) an NbTi alloy made with a conventional 4-fold vacuum arc melting for comparison FIG. 3 ,

The FIG. 1 shows a schematic representation of an arc melting plant 1 in cross section, which is suitable for performing a first part of a method according to the invention. Alternatively, a vacuum induction smelting plant or a Skull smelting plant may also be used. The arc melting is carried out in a pressure-tight and evacuatable chamber 2. Thus, the process can be carried out by evacuating and purging with a noble gas such as argon or helium, and then filling with an inert gas such as helium or argon in a protective gas atmosphere. Preferably, the first part of the process according to the invention can also be carried out in the protective gas under a partial pressure of between 20 and 300 mbar.

An electrode 4 is attached to a holder 6, which also serves the power supply. The electrode 4 is made of a core of Nb with two outer layers of Ti or coaxial of a core of Nb with an outer sheath of Ti. The electrode 4 can also be pressed from Nb and Ti particles. It is also possible to use an Nb electrode and continuously add the Ti in particulate form via a lateral access (not shown). The Ti in particulate form may be present, for example, as a Ti sponge.

Between the electrode 4 and a cooled arc-melting crucible 8, an electric voltage of about 28 V is applied and an arc is drawn or generated with an electric current between 4 kA and 6 kA, the electrode 4 (and optionally the separately supplied Ti particles ) melts.

The selected current depends on the selected geometry of the electrode. For example, for the amperage between 4 kA and 6 kA given here by way of example, the electrode 4 can have a diameter of 100 mm which matches these current intensities and the arc melting crucible 8 has a diameter of 200 mm which matches these current intensities. As arc melting crucible 8, for example, a water-cooled copper crucible can be used. In the arc melting crucible 8, a mixture 10 of the raw materials Nb and Ti is collected. The mixture 10 solidifies at the bottom of the arc melting crucible 8 (in FIG FIG. 1 below) and forms an alloyed body 14 of NbTi material. While the mixture 10 already solidifies in the arc melting crucible 8 as an alloyed body 14, new mixture 10 is continuously generated with the arc from the electrode 4 until the starting materials Ti and Nb are completely or substantially exhausted. The melted parts of the electrode 4 dripping continuously on top of the mixture 10 and the underlying solidified alloy body 14. The NbTi material of the alloyed body 14 may include unfused Nb clusters. One or more alloyed bodies 14 can be produced, which are subsequently processed further with electron beam melts. The alloyed body 14 has a diameter of about 200 mm and a length of about 1600 mm and weighs about 300 kg.

In a second part of the process according to the invention, which in FIG. 2 1, which shows a schematic representation of an electron beam melting system 11 in cross section, the alloyed body 14 produced in the first part of the method according to the invention is again melted into a vacuum chamber 12 of the electron beam melting system 11. The vacuum chamber 12 can be evacuated via a vacuum connection 13. For this purpose, a vacuum pump (not shown) is connected to the vacuum connection 13. For melting the alloyed body 14, two electron guns 16 are arranged in the vacuum chamber 12, with which a conical region (referred to herein as electron beam 17) is scanned, as is the case with Brownian tubes The intensity of the electron beam 17 in the region of the cone can be regulated by a suitable guidance of the electron beam 17 in order to adapt the electron beam melting to the alloyed body 14.

The alloyed body 14 is inserted laterally horizontally. Likewise, with a suitable adaptation of the electron beams 17, it is possible to introduce the alloyed body 14 vertically from above, ie vertically. Below the alloyed body 14 is disposed a cooled electron beam melting crucible 18 made of copper with lowerable bottom 19 (preferably of inherent NbTi). The alloyed body 14 is melted with the electron beams 17, and the melt 20 dripping from the alloyed body 14 falls into the Electron beam melting crucible 18, where the melt 22 is collected and continuously solidified as the desired NbTi alloy 24 while the lowerable bottom 19 is driven down. The result is a rod made of NbTi. In this case, the alloyed body 14 is continuously advanced and optionally further alloyed body 14 are pushed. The Nb clusters still contained in the alloyed body 14 are completely melted during the electron beam melting, so that a homogeneous melt 22 and thus a homogeneous NbTi alloy 24 are produced after only one melting with the electron beams 17 of the alloyed body with arc melting.

The NbTi alloy 24 solidifies in the electron beam melting crucible 18 and is continuously drawn down to form a cylindrical body of about 305 mm in diameter, about 2200 mm in length. For this purpose, several of the alloyed bodies 14 must be melted with the electron beam melts and solidified in the electron beam melting crucible 18.

Our own experiments show that the 20 mm diameter NbTi alloy prepared by the described method has the same micro-homogeneity and element distribution quality as an NbTi alloy of the same diameter produced by four times arc melting of 20 mm. For this purpose, an NbTi alloy prepared by the above-described inventive method and a conventional NbTi alloy prepared by four times vacuum arc melting (VAR) were examined by means of a scanning electron microscope. In the cross-section image in the scanning electron microscope (ESM - electron scanning microscope) were no differences in the micro-homogeneity of the two NbTi alloys can be seen. Both cross sections show no contrasts with regard to the secondary electrons in the SEM image.

FIG. 3 shows an energy dispersive X-ray analysis (EDX) generated by the scanning electron microscope (ESM) of the NbTi alloy obtained by a method according to the invention and FIG. 4 Energy dispersive X-ray analysis (EDX) using the Scanning Electron Microscope (ESM) generates a NbTi alloy obtained by conventional vacuum arc melting four times for comparison FIG. 3 , In both samples, Nb and Ti are contained in equal amounts, that is, the ratio of the integrals of the intensities of the secondary electrons in the regions typical for Nb and Ti is the same for both samples (see Figures 3 and 4 ). Thus, the two NbTi alloys have the same or at least very similar compositions. The with the inventive Thus, the NbTi alloy produced in the simpler manufacturing process has the same composition and quality as the NbTi alloy produced by four-time vacuum arc melting.

The features of the invention disclosed in the foregoing description, as well as the claims, figures and embodiments may be essential both individually and in any combination for the realization of the invention in its various embodiments.

LIST OF REFERENCE NUMBERS

1

Arc melting plant

2

Evacuable chamber

4

electrode

6

Power supply and holder

8th

Arc melting crucible

10

mixture

11

Electron beam furnace

12

vacuum chamber

13

vacuum connection

14

Alloy rod made of NbTi material

16

electron beam gun

17

electron beam

18

Electron beam melting crucible

19

Lowerable floor

20

Dripping melt

22

melt

24

NbTi alloy

Nb

niobium

Ti

titanium

Claims (15)

A method for producing a niobium-titanium alloy (24) (NbTi alloy) from metallic niobium (Nb) and metallic titanium (Ti), in particular for producing a superconducting NbTi alloy (24) of metallic Nb and metallic Ti, characterized by the steps A) Arc melting, vacuum induction melting or Skull melting of the metallic Nb and the metallic Ti, so that the Nb and the Ti mix and alloy together to form a mixture (10), and solidification of the mixture (10), wherein when solidified at least one alloyed Body (14) is formed from a NbTi material, in particular at least one rod (14) is formed from the NbTi material, B) producing a melt (22) by subsequent electron beam melting of the at least one alloyed body (14) of the NbTi material in a vacuum, in particular of the at least one rod (14), and solidifying the melt (22) produced by the electron beam melting, wherein upon solidification after electron beam melting, the NbTi alloy (24) is formed. A method according to claim 1, characterized in that the arc melting, the vacuum induction melting or Skull melting is performed only once and the electron beam melting is performed only once. A method according to claim 1 or 2, characterized in that in step A) the metallic Ti is over-alloyed with an excess of between 1% by weight and 5% by weight compared to the desired NbTi alloy (24). Method according to one of the preceding claims, characterized in that the arc melting, the vacuum induction melting or the Skull melting in step A) is carried out in an inert gas, in particular in He or Ar. A method according to claim 4, characterized in that the arc melting, the vacuum induction melting or Skull melting in step A) is carried out at a partial pressure between 20 mbar and 300 mbar of the inert gas. Method according to one of the preceding claims, characterized in that in step A) an arc melting is used and in the arc melting, an electrode of Nb is used and Ti is supplied as granules or sponge or an electrode (4) made of sheets of Nb and Nb welded together Ti or a compressed rod of Nb coated with Ti, or a rod of Ti coated with Nb or an electrode of a compressed mixture of particulate Nb and particulate Ti. A method according to claim 6, characterized in that the electrode (4) and optionally the granules or sponge is melted by the arc and the mixture (10) in a cooled arc melting crucible (8) than the at least one alloyed body (14). , in particular the at least one rod (14), solidifies. Method according to one of the preceding claims, characterized in that, during the electron beam melting, the at least one alloyed body (14), in particular the at least one rod (14), is melted with at least one electron beam from at least one electron beam gun (16) and the melt (22) is melted. is collected in a cooled electron beam melting crucible (18) and solidifies. Method according to one of the preceding claims, characterized in that the NbTi alloy (24) contains between 40 wt% and 60 wt% Ti, preferably between 45 wt% to 50 wt% Ti. Method according to one of the preceding claims, characterized in that an NbTi47 alloy (24) is produced. Method according to one of the preceding claims, characterized in that in the electron beam melting in step B) residual clusters of Nb, which are contained in the at least one alloyed body (14), in particular in the at least one rod (14), homogeneously with the Ti are alloyed with a maximum percentage deviation of the alloy composition from the nominal value of maximum +/- 1.5%. Method according to one of the preceding claims, characterized in that the electron beam melting in step B), the NbTi alloy (24) solidifies in a cylindrical shape. A method according to claim 12, characterized in that the cylindrical shape has a diameter between 100 mm and 500 mm and / or the cylindrical shape has a length between 750 mm and 4000 mm. Method according to one of the preceding claims, characterized in that the arc melting, the vacuum induction melting or Skull melting and the solidification of the mixture (10) after the arc melting, the vacuum induction melting or the Skull-melting continuously, so that continuously new material melted and the mixture (10) is solidified on already solidified NbTi material, and / or the electron beam melting and solidification of the melt (22) takes place continuously after the electron beam melting, so that continuously melt (22) produced by the electron beam melting on already solidified NbTi alloy (24) is frozen. NbTi alloy (24) prepared by a process according to any one of the preceding claims.

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