Method for producing a coating of a base body and functional element having a base body with a coating

Abstract

In a method for coating a base body, a first target and a second target are arranged in a vacuum chamber. A base body to be coated is arranged in the vacuum chamber is heated to a coating temperature of less than 600° C. During sputtering with sputter gas ions, first target particles are liberated from the first target and second target particles are liberated from the second target and are deposited as coating particles on the base body. A first sputter rate is specified for the first target and a second sputter rate is specified for the second target such that, during the sputtering process, the coating is generated as an A15 phase with an intended stoichiometric ratio of the first target particles to the second target particles. A functional element has a base body and a coating of Nb.sub.3Sn applied directly on the surface of the base body.

Claims

1.-19. (canceled)

20. A method for coating a base body (2) with a coating (18) of a first material and of a second material, comprising: arranging a first target (4) made of the first material and a second target (5) made of the second material in a vacuum chamber; arranging the base body (2) to be coated in the vacuum chamber; introducing a sputter gas into the vacuum chamber; liberating, during a sputtering process with sputter gas ions (16), first target particles (10) from the first target (4) and depositing the first target particles (10) as coating particles on the base body (2); liberating second target particles (11) from the second target (5) and depositing the second target particles (11) as coating particles on the base body (2); specifying, during the sputtering process, a first sputter rate for the first target (4) and specifying a second sputter rate for the second target (5) such that, during the sputtering process, the coating (18) is generated with an intended stoichiometric ratio of the first target particles (10) to the second target particles (11); and heating the base body (2), during the sputtering process, by a heating device (8) to a coating temperature of less than 600° C.

21. The method according to claim 20, wherein the first material is a first metal and that the second material is a second metal or a metal mix.

22. The method according to claim 20, wherein the first target particles (10) of the first material and the second target particles (11) of the second material form an A15 phase.

23. The method according to claim 20, wherein, during the sputtering process, at least one further, third target is arranged in the vacuum chamber, and wherein for each further, third target a third sputter rate for the deposition of third target particles in the coating is specified such that the coating is generated with an intended stoichiometric ratio of the third target particles to the first and second target particles (10, 11).

24. The method according to claim 20, wherein the base body (2) is heated, during the sputtering process, to a coating temperature of between 400° C. and 500° C.

25. The method according to claim 20, wherein magnetron sputtering is carried out during the sputtering process.

26. The method according to claim 20, wherein the base body (2) is treated in an adhesion-enhancing step preceding the sputtering process in order to strengthen adhesion of the coating (18) to a surface (6) of the base body (2) to be coated.

27. The method according to claim 20, wherein a specified sputter performance ratio is specified for the first sputter rate and the second sputter rate.

28. The method according to claim 20, wherein the first material is niobium and the second material is tin or a mixture of two or more elements with more than 50 mole percent of tin.

29. The method according to claim 28, wherein the sputter rate of niobium corresponds to 5.25 times the sputter rate of the second material.

30. The method according to claim 20, wherein the coating (18) is produced with a layer sequence of at least two layers (20, 21) of a coating material, wherein arranged between adjacent layers (20, 21) of a superconductive coating material in each case is a separating layer (22) of another, non-superconductive material.

31. The method according to claim 30, wherein a ceramic layer is applied as a separating layer (22).

32. The method according to claim 20, wherein the first target (4) and the second target (5) are arranged in a recess or in a hollow space (23) of the base body (2) that is accessible from outside and wherein an inner wall (24) of the base body (2) delimiting the recess or the hollow space (23) is coated in the sputtering process.

33. The method according to claim 32, wherein the base body (2) on the one hand and the first and second target (4, 5) on the other hand are displaced relative to one another during the sputtering process.

34. A functional element (17) having a base body (2) with a coating (18) of an A15 phase, wherein the coating (18) is produced directly on a surface (6) of the base body (2) using the method according to claim 20.

35. The functional element (17) according to claim 34, wherein the base body (2) is made of copper.

36. The functional element (17) according to claim 34, wherein the base body (2) has a recess or a hollow space (23) and the coating (18) covers an inner wall (24) of the recess or the hollow space (23) partially or completely.

37. The functional element (17) according to claim 34, wherein the functional element (17) is a cavity for an accelerator.

38. The functional element (17) according to claim 34, wherein the functional element (17) is a superconductive cable or a superconductive conduction element for solenoids.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] FIG. 1 shows a schematic layout of a device with which the method for producing a coating can be carried out.

[0039] FIG. 2 shows a schematic representation of measurement results of X-ray diffractometry measurement of a coating produced at a coating temperature of four hundred and thirty-five degrees Celsius with Nb.sub.3Sn, wherein the intensity of the scattered X-ray radiation is depicted over the diffraction angle 2-theta.

[0040] FIG. 3 shows measured values of the electrical resistance of the coating measured in FIG. 2 in a temperature range between twelve degrees Kelvin and twenty degrees Kelvin, standardised to the electrical resistance at twenty degrees Kelvin.

[0041] FIG. 4 shows a schematic representation of a partial region of a functional element having a base body and a coating arranged directly on a surface of the base body.

[0042] FIG. 5 shows a schematic sectional view of a partial region of the coated base body as in FIG. 4, wherein a region of the base body adjacent to the surface was treated and changed in an adhesion-enhancing step in order to increase the bonding effect for the coating applied thereto.

[0043] FIG. 6 shows a schematic sectional view of a partial region of the coated base body as in FIGS. 4 and 5, wherein the coating consists of a layer sequence.

[0044] FIG. 7 shows a schematic sectional view through a hollow space of a base body in which two targets are arranged during carrying out of the sputtering process.

DETAILED DESCRIPTION

[0045] In FIG. 1, a device 1 is depicted by way of example with which a method for coating a base body 2 with a coating of an A15 phase can be carried out. In a coating chamber 3, in which a vacuum can be created, a first target 4 made of a first target material and a second target 5 made of a second target material are arranged adjacent to one another. The target material of the first target 4 is a first metal, namely niobium (Nb). The target material of the second target 5 is a second metal, namely tin (Sn).

[0046] Arranged opposite the two targets 4, 5 is the base body 2 made of copper, wherein a surface 6 of the base body 2 facing the two targets 4, 5 is to be coated. The base body 2 can be heated during a sputtering process from a rear side 7 by a heating device 8 to a specifiable coating temperature. In the exemplary embodiments reproduced below, the coating temperature specified for the coating process in question is 435° C.

[0047] The coating chamber 3 has an inlet 9 for a suitable sputter gas, which can be a noble gas, for example, and preferably argon. The sputter gas can already have been ionised in advance or can be ionised in the coating chamber 3. The two targets 4, 5 and the base body 2 can each be brought to an individually specifiable electric potential so that an electrical field is formed in the coating chamber 3 that accelerates positively charged sputter gas ions 16 in the direction of the two targets 4, 5. By specification of a sufficiently high potential difference, the sputter gas ions 16 can be accelerated sufficiently on the way to the first target 4 or to the second target 5 to liberate first target particles 10 when they strike the first target 4 and to liberate second target particles 11 when they strike the second target 5. By suitable specification of the respective electric potentials and thus of the potential differences that the sputter gas ions 16 pass through on the way to the first and second target 4, 5, the respective sputter rates of the first target 4 and the second target 5 can be influenced and specified. The first and second target particles 10, 11 liberated by the bombardment with sputter gas ions 16 are deposited inter alia on the surface 6 of the base body 2. Sputter gas ions 16, used sputter gas particles or target particles 10, 11 which were liberated from the first target 4 or from the second target 5 and not deposited on a surface can be removed from the coating chamber 3 through an outlet 12.

[0048] Using a suitable magnetic field generating device 13, a magnetic field is generated respectively in a region between the two targets 4, 5 and the base body 2 in the immediate environment of the two targets 4, 5, due to which field free electrons are concentrated in a region over a respective surface 14, 15 of the two targets 4, 5. The density of the sputter gas ions 16 striking the respective target 4, 5 and thus the sputter rates for the first target 4 and for the second target 5 can be influenced thereby.

[0049] The first target particles 10 liberated from the first target 4 and second target particles 11 liberated from the second target 5 by the sputter gas ions 16 are deposited on the surface 6 of the base body 2 heated by the heating device 8. Due to the thermal energy of the heated base body 2, sufficient energy is transmitted to the target particles 10, 11 being deposited so that these migrate along the surface 6 and can react to give the desired A15 phase. In the exemplary embodiment depicted as an example, the first target particles 10 of niobium deposited on the surface 6 react with the second target particles 11 of tin to form the intermetallic phase Nb.sub.3Sn. In this case a highly homogeneous coating with a phase-pure crystal lattice is generated.

[0050] FIG. 2 depicts the measurement result of X-ray diffractometry measurement of a coating of Nb.sub.3Sn produced using the method described previously in the device 1 depicted as an example. Here the intensity I of the X-ray radiation scattered on the coating is depicted in an arbitrary unit as a function of the respective diffraction angle 2θ over a range of the diffraction angle 2θ between 30° and 90°. Exclusively characteristic diffraction peaks of Nb.sub.3Sn could be detected by the measurement, which peaks occurred at the diffraction angles 2θ indicated in each case by a dashed line with a concluding triangle. Other likewise possible compounds of niobium and tin such as NbSn.sub.2 or Nb.sub.2Sn.sub.5, for example, could not be detected, on the other hand, likewise pure niobium or pure tin. The measurement result accordingly confirms that the desired coating of the base body 2 with the superconductive material Nb.sub.3Sn with a highly phase-pure crystal lattice could be generated using the method according to the disclosure.

[0051] In FIG. 3, the electrical resistance R for the coating of Nb.sub.3Sn measured in FIG. 2 by X-ray diffractometry is shown as a function of the temperature T, wherein the electrical resistance R is standardised to the measured resistance value R(20K) at a temperature T of 20 K. It appears that the coating has superconductive properties and an infinitesimally low standardised resistance R/R (20K) at a temperature T of below roughly 15.3 K. The transition temperature above which the superconductive property disappears is roughly 16.3 K and is close to the highest transition temperature of 18.3 K for this coating material that has ever been established for a bulk material or for a solid with comparatively large dimensions. This measurement also proves that a high-quality coating of Nb.sub.3Sn with a phase-pure crystal lattice could be produced using the method according to the disclosure.

[0052] A section of a functional element 17 is depicted by way of example in FIG. 4. A coating 18 of Nb.sub.3Sn is applied directly on the surface 6 of the base body 2, which consists of copper in the exemplary embodiment shown. In contrast to the functional elements with such a coating that are produced using conventional methods, no separate diffusion barrier is arranged between the surface 6 of the base body 2 and the coating 18. Highly effective heat transmission from the base body 2 into the coating 18 and vice versa is supported thereby, which is advantageous for numerous applications of such functional elements 17.

[0053] In the exemplary embodiment depicted in FIG. 5, the surface 6 to be coated of the base body 2 was treated by an etching process in an adhesion-enhancing step preceding the sputtering process and a region 19 of the base body 2 adjacent to the surface 6 was changed such that the coating 18 subsequently applied to the surface 6 adheres more strongly.

[0054] In the exemplary embodiment depicted in FIG. 6, the coating 18 has a layer sequence consisting of two layers 20, 21 of a superconductive coating material, between which layers a separating layer 22 of a non-superconductive metal is arranged. The two layers 20, 21 have each been applied using the sputtering method. The separating layer 22 can likewise be applied using a sputtering method or also using any conventional coating method. Here the surfaces lying externally in each case and then covered by a layer 20, 21, 22 applied thereto can each be treated in an adhesion-enhancing step and the bonding effect for the subsequently applied layer 20, 21, 22 improved thereby.

[0055] In FIG. 7, an exemplary embodiment of a base body 2 with a hollow space 23 is depicted merely schematically, wherein an inner wall 24 of the hollow space 23 in the base body 2 is provided with the coating 18 during the sputtering process. For this purpose, the first target 4 and the second target 5 as well as the associated components of the magnetic field generating device 13 are arranged in the hollow space 23 of the base body 2 during the sputtering process. In addition, a relative movement, indicated only by way of example by an arrow 25, between the base body 2 and the first and second target 4, 5 arranged in the hollow space 23 of the base body 2 can be brought about during the sputtering process. Thus the base body 2, for example, can rotate about the first and second target 4, 5, which are fixed stationarily in each case on a target holder, which is not shown and which projects into the hollow space 23 of the base body 2, in order to generate as quickly as possible a coating 18 of the inner wall 24 of the hollow space 23 in the base body 2 that is as uniform as possible.