Production of a refractory metal component

Abstract

The embodiments relate to a method for the production of a refractory metal component by casting. The method includes providing a slip that contains a powder including at least one refractory metal or a compound thereof, in addition to at least one binding agent. The method further includes processing the slip by casting, (e.g., film casting or slip casting), to form at least one slip coating, the slip being devoid of a metal binding agent. A component was produced by this method. The embodiments may be used, in particular, on X-ray tubes, accelerator targets, or fusion reactors, such as for a surface of an X-ray anode, or a wall of a fusion reactor.

Claims

1. A process for producing a surface of an X-ray anode or a wall of a fusion reactor by casting, wherein the process comprises: providing a slip comprising a powder of at least one refractory metal or a compound thereof and also at least one binder, wherein a proportion of the refractory metal in the slip is 70% by weight to 99% by weight; and tape casting or slip casting the slip to provide a plurality of slip layers having individual slip layers stacked on top of one another, wherein the slip is free of a metal binder.

2. The process as claimed in claim 1, wherein the slip further comprises ceramic particles.

3. The process as claimed in claim 2, wherein the ceramic particles comprise one or more of the following: La.sub.2O.sub.3, Y.sub.2O.sub.3, TiC, or HfC.

4. The process as claimed in claim 2, wherein a median of a particle size of the powder is less than two microns.

5. The process as claimed in claim 1, wherein the powder is a powder of pure tungsten, WRe, or WTa.

6. The process as claimed in claim 1, wherein the binder comprises at least one organic binder.

7. The process as claimed in claim 1, wherein a layer thickness of a slip layer of the plurality of slip layers is 20 microns to 3 millimeters.

8. A process for producing a surface of an X-ray anode or a wall of a fusion reactor by casting, wherein the process comprises: providing a slip comprising a powder of at least one refractory metal or a compound thereof and also at least one binder, wherein a proportion of the refractory metal in the slip is 70% by weight to 99% by weight; and tape casting the slip to a carrier tape to provide at least one flexible slip layer, wherein the slip is free of a metal binder.

9. The process as claimed in claim 1, wherein at least two slip layers of the plurality of slip layers differ in terms of their respective properties.

10. The process as claimed in claim 1, wherein the processing of the slip is followed by heat-treating the plurality of slip layers.

11. The process as claimed in claim 10, wherein the heat-treating comprises sintering below a maximum sintering temperature to a density below a maximum density and subsequently a further heat-treating of further densification.

12. The process as claimed in claim 10, wherein the plurality of slip layers becomes at least closed-pored as a result of the heat-treating.

13. The process as claimed in claim 1, wherein the plurality of slip layers comprises green sheets.

14. The process as claimed in claim 10, wherein the heat-treating comprises sintering of the plurality of slip layers.

15. The process as claimed in claim 1, wherein the plurality of slip layers is a gradient structure achieved by layering tungsten sheets with tungsten-rhenium sheets.

16. The process as claimed in claim 1, wherein the plurality of slip layers is a gradient structure achieved by layering alternating dense tungsten sheets and porous tungsten sheets.

17. The process as claimed in claim 1, wherein the slip further comprises a plasticizer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above-described properties, features, and advantages, and also the way in which they are achieved, will be made clearer and more understandable in connection with the following schematic description of an example that will be explained in connection with the drawings. In the interest of clarity, identical elements or elements having the same effect will be provided with the same reference symbols.

(2) FIG. 1 depicts an embodiment of the course of a process in a number of variants.

(3) FIG. 2 depicts an embodiment of an apparatus for tape casting in order to carry out the process.

DETAILED DESCRIPTION

(4) FIG. 1 depicts the course of a process for producing a refractory metal component by tape casting in a number of variants.

(5) Act S1 includes providing a powder mixture composed of refractory metal powder in the form of two tungsten powders. The two tungsten powders differ in terms of their average particle size, D50, namely in one case 0.7 microns and in one case 1.7 microns.

(6) Act S2 includes provision of additives such as a dispersant (Hypermer KD1), solvents in the form of ethanol and toluene and also a binder in the form of polyvinyl butyral (Pioloform BR 18) and a plasticizer in the form of dibutyl phthalate.

(7) To produce the slip, the constituents of the slip S (see also FIG. 2) are mixed in act S3 and thereby provided. For this purpose, the refractory metal powders, the dispersant, and the liquids are firstly mixed in a speed mixer for three minutes at 1400 l/min. The binder, to which ethanol has already been added, and the plasticizer are subsequently added and the mixture is mixed in the speed mixer at 1500 l/min for ten minutes.

(8) The dispersant provides that the wetting behavior of the refractory metal powder particles is improved and agglomerate formation is suppressed. The solvents ethanol and toluene dissolve the organic components, in particular, the Pioloform BR18 binder. Mixing-in of a plasticizer enables the cast sheet to be made flexible and strong and thus readily handleable. A homogeneous slip is produced by various further mixing and milling processes. In some cases, it may be necessary to degas the slip before tape casting in order to avoid bubble formation in the sheet. A proportion by weight of metallic powder of from 70% to 99% in the slip S is sought.

(9) The slip S is subsequently introduced into a stock tank 2 of a tape casting plant 1 as depicted in FIG. 2 for carrying out act S4 of tape casting. The slip S flows from the stock tank 2 and is spread by a doctor blade 3 as green sheet 4 on a carrier tape 5. The carrier tape 5 rests on a flat underlay 6 during this operation. A preliminary blade 7 preceding the doctor blade 3 makes it possible to set a hydrostatic pressure upstream of the doctor blade 3 that thus influences the thickness of the cast green sheet 4. The viscosity of the slip S and the drawing speed (relative velocity between carrier tape 5 and doctor blade 3 in the direction of motion indicated by the arrow) likewise influence the thickness of the cast green sheet 4.

(10) The minimum sheet thickness is limited, in particular, by the particle size of the starting powders and corresponds approximately to 5 to 10 times the largest particles. In the case of starting powders as above (in particular, D50=1.7 microns), the lower limit of the cast green sheet 4 is approximately 60 microns.

(11) The maximum thickness of the green sheet 4 is from about 1.5 mm to 2.0 mm.

(12) In act S5, the green sheet 4 may be cut to size and/or shaped, in particular given a three-dimensional shape.

(13) In an additional act, the carrier tape 5 is pulled off from the green sheet 4.

(14) In act S6, the cut-to-size/shaped green sheet 4 is heat treated in order to produce the finished refractory metal component.

(15) In act S7, the green sheet 4 is subjected to binder removal, in particular, by a heat treatment.

(16) In act S8, the green sheet 4 that has been subjected to binder removal and optionally shaped is sintered in a contiguous, in particular, atmospheric-pressure, sintering process at an appropriately high sintering temperature until a dense or virtually pore-free refractory metal component has been obtained.

(17) In an alternative to act S8, the green sheet 4 that has been subjected to binder removal and optionally shaped is firstly sintered at a comparatively lower sintering temperature (presintered) in act S9 in which it does not yet reach its dense state but remains porous (open-pored or closed-pored).

(18) In act S10, the presintered workpiece is densified, in particular, densified so as to be pore-free, in particular, to its maximum density, by hot isostatic pressing to give the refractory metal component. This has the advantage that the temperatures required for hot isostatic pressing are lower than the sintering temperature required in act S8 and grain growth (which increases with increasing temperature) is thus inhibited.

(19) As an alternative to or in addition to act S10, act S11 of spark plasma sintering and/or act S12 of microwave sintering may be carried out.

(20) Although the invention has been illustrated and described in detail by the example presented, the invention is not restricted thereto and other variations may be derived therefrom by a person skilled in the art without going outside the scope of protection of the invention.

(21) Thus, ceramic powder may also be added to the slip.

(22) In addition, it is possible, for example, for a further act of stacking (optionally including lamination and/or isostatic pressing) of green sheets 4 to give a stack of layers to be carried out between act S4 and act S5. Such a further act may also include stacking of green sheets 4 from different tape casting plants 1 or different batches from the tape casting plant 1, especially if these green sheets 4 differ.

(23) A layer structure or gradient structure may be obtained, in particular, by multilayer casting. Here, a plurality of slip layers are applied in succession (or simultaneously) in modified tape casting plants.

(24) It is to be understood that the elements and features recited in the appended claims may be combined in different ways to produce new claims that likewise fall within the scope of the present invention. Thus, whereas the dependent claims appended below depend from only a single independent or dependent claim, it is to be understood that these dependent claims may, alternatively, be made to depend in the alternative from any preceding or following claim, whether independent or dependent, and that such new combinations are to be understood as forming a part of the present specification.

(25) While the present invention has been described above by reference to various embodiments, it may be understood that many changes and modifications may be made to the described embodiments. It is therefore intended that the foregoing description be regarded as illustrative rather than limiting, and that it be understood that all equivalents and/or combinations of embodiments are intended to be included in this description.