WO2014044433A1

WO2014044433A1 - Production of a refractory metal component

Info

Publication number: WO2014044433A1
Application number: PCT/EP2013/065213
Authority: WO
Inventors: Mathias Sommerer; Hubertus VON DEWITZ
Original assignee: Siemens Aktiengesellschaft
Priority date: 2012-09-24
Filing date: 2013-07-18
Publication date: 2014-03-27
Also published as: DE102012217182A1

Abstract

The invention relates to a method (S1-S15) for the production of a refractory metal component, said method having the following steps: provision (S4) of a feed stock (M) which contains a refractory metal powder consisting of at least one refractory metal and/or a compound thereof, in addition to at least one binding agent; and primary shaping (S5-S7) of the feed stock (M) to form at least one green body (4), said feed stock (M) containing ceramic powder. A refractory metal component was produced by means of this method (S1-S15). The invention can be used in particular on X-ray tubes or fusion reactors, in particular for a surface of an X-ray anode, or a wall of a fusion reactor.

Description

description

The invention relates to a method for producing a refractory metal component, the method comprising the following steps: providing a starting material comprising a refractory metal powder of at least one refractory metal and / or a compound thereof and at least one binder ; and prototyping the starting material to at least one green body. The invention also relates to a refractory metal component produced by the method. The invention is particularly applicable to X-ray tubes or fusion reactors, in particular for a surface of an X-ray anode, accelerator targets or the wall and structural component of a fusion reactor.

The plasma-facing surfaces of a wall of a fusion reactor or the surface of an X-ray anode in addition to high temperatures also high mechanical, thermocyclic loads that can lead to cracking or melting of the materials. In both applications, refractory metals, in particular tungsten, are used. For the production of planar components in tungsten heavy metal alloys, the film casting process for refractory metals is known from WO 2007/147792 A1. WO 2007/147792 A1 discloses a process for the production of planar, shaped articles from a tungsten or molybdenum heavy metal alloy, from which a slurry for film casting is produced, from which slurry a film is poured and the film is debinded after drying and sintered to to obtain the molded article. Within the meaning of WO 2007/147792 A1, the term tungsten or molybdenum heavy metal alloy is to be understood as meaning materials selected from the group consisting of tungsten heavy metal alloys, tungsten, tungsten alloys, molybdenum and molybdenum alloys. Tungsten heavy metal alloys consist of about 90% to about 97% by weight. made of tungsten or tungsten alloys. The remainder is binder metal. As metallic binder, the elements Fe, Ni and / or Cu in proportions greater than 1% by mass are preferred. The metallic binders provide simplified manufacturing processes through lower sintering temperatures, improved mechanical properties, in particular ductility, and improved machinability, such as better machinability. These materials are intended for use in radiation shielding applications, with a high density of alloys in the foreground.

GB 928 626 A discloses a method for producing a dense, substantially crack-free and distortion-free refractory metal component by means of cold rolling and sintering. For this purpose, pure tungsten powder can be mixed with organic binder and water and subsequently extruded under heat to provide a starting material for cold rolling. The cold rolled stock was subsequently air dried and then sintered.

There are known components with a tungsten matrix in which long fibers of tungsten are embedded. As a result, it is achieved under mechanical stress that cracks propagate along the long fibers, resulting in a considerably longer crack length than with a tungsten solid material without long fibers. Of influence here is also the interface structure between matrix and fiber. This in turn results in a pseudoplasticity on component level of otherwise very brittle tungsten in practice. For such components, a large fiber length is advantageous. A disadvantage of the large fiber length, however, is the incompatibility of production by means of many original molding processes. For example, long fibers make production by extrusion more difficult because the fibers in the extruder screw can be arranged irregularly or can not be conveyed at all. Even a foil casting is insufficient with long fibers, since the alignment of long fibers is difficult and possibly a direction-dependent shrinkage is generated. It is the object of the present invention to overcome the disadvantages of the prior art, at least in part, and in particular to provide a heat-exchanging improved, behaving, in particular longer-life, refractory metal component, which is relatively easy to produce.

This object is achieved according to the features of the independent claims. Preferred embodiments are in particular the dependent claims.

The object is achieved by a method for producing a component (hereinafter also referred to as "refractory metal composite component"), the method comprising (at least) the following steps: providing a starting material (molding compound) which is a refractory metal powder of at least one refractory metal and or a compound thereof ("refractory metal powder") and at least one binder; and prototyping the starting material to at least one green body. The starting material additionally has short fibers.

Among other things, such a method has the advantage that the admixture of the short fibers makes the starting material also formable by methods which are virtually closed to starting material with long fibers. Nevertheless, the short fibers may still cause pseudoplasticity in the refractory metal composite component if they are significantly longer than the microstructural sizes (eg, grain size, pore size, etc.) of the refractory metal matrix in the final product. In this case, the pseudoplasticity may come into play. The more one approximates the fiber geometry to a spherical geometry of the reinforcement phase (eg, through coated tungsten fibers or particles), the sooner the conventional heterogeneous properties of composites come into play. For even shorter short fibers, especially nanofibers less than one micron in length, the effect is that they also affect the microstructure. They can bring about a change in the grain boundary stability, in particular with regard to a recrystallization behavior and / or a grain boundary sliding.

By means of the above effects (pseudo-plasticity, heterogeneous material properties (matrix / particles) and change of the grain boundary stability), a stress distribution and the crack profile in the refractory metal composite component and a stability of the microstructure can be set in a targeted manner, whereby in the use of the polymer, for example. critical load conditions can be reduced or excluded.

It is also possible to produce homogeneous, isotropic and low-stress microstructures (in particular by the addition of nanoparticles) of the final refractory metal component with a narrowly distributed and fine particle size distribution. This may in particular also be associated with an isotropic crystal orientation. It may also be a setting e.g. a bimodal particle size distribution in terms of mechanical properties desired and achievable. In addition, the grain boundary property and, in total, the fracture behavior under pointy, thermocyclic loading are influenced by setting the grain structure (distribution / size). In addition, the method makes it possible to produce large-area refractory metal components. Basically everyone likes a refractory metal component

Body or workpiece to be understood, which has been produced by means of the method.

Under a starting material, any solids-containing, viscous suspension with the refractory metal powder and the

Short fibers are understood as a solid which is suitable for carrying out the cold forming (eg film casting, extrusion, etc.), optionally also with heat support. The The starting material may in particular be a refractory metal powder / short fiber / liquid mixture of defined viscosity, in particular with an anhydrous liquid. One or more powders of one or more pure refractory metals (eg tungsten and / or molybdenum), alloys thereof (eg tungsten-rhenium, WRe), may be in particular a (refractory metal) powder of at least one refractory metal and / or a compound thereof. and / or compounding thereof. The refractory metal powder may include, for example, tungsten, molybdenum, rhenium and / or tantalum and / or alloys thereof and / or compounds thereof. Under archetypes can be understood in particular a manufacture of a first shape of powder-containing molding composition to molding material (in particular semi-finished). By prototyping a solid body can be made in particular from a formless material. Archetypes are used, for example, to produce a first form of a geometrically determined, solid body and / or to create the substance together.

It is a development that thermal processing of the at least one refractory metal powder takes place in the absence of oxygen, e.g. under a protective gas atmosphere, reducing atmosphere or under vacuum. This prevents oxidation of the refractory metal powder.

The binder can in principle have any organic and / or non-organic binder or binder. The binder binds the refractory metal powder functionally similar to an adhesive. Preference is given to organic binders, for example Polvvenylbutyral. It is a development that the starting material has additional additives such as dispersants, plasticizers, solvents, etc. In particular, a viscosity of the starting material and the properties of the original shaped green body (eg its strength and / or deformation capacity) influence.

A dispersing agent ensures that the wetting behavior of the particles of the refractory metal powder and possibly of the (in particular coated) short fibers is improved and agglomeration is prevented. The solvent, e.g. Ethanol and / or toluene, dissolves organic components, in particular the binder. About an admixture of a plasticizer, the flexibility and strength of the green body and thus its handling can be adjusted. Various mixing and grinding processes produce a virtually homogeneous starting material. It may be necessary to degas the feedstock prior to primary forming to avoid blistering in the feedstock.

For the preparation of the starting material, for example, a mixture of the individual powders and optionally the short fibers in a tumble mixer, in ball mills, etc. take place. Care must be taken that the grinding and mixing process does not destroy the fiber or particle geometry

It is an embodiment that a length of the short fibers is at least ten times the microstructural sizes of the refractory metal or the refractory metal matrix, e.g. at least ten times the mean grain size of the refractory metal or the refractory metal matrix. This can cause a pseudoplasticity and at the same time even with large grain sizes of e.g. 200 to 500 microns, a short enough length for use with the master mold.

A grain size may, in particular, be understood as meaning a median diameter or equivalent diameter, D50, which is exceeded or undershot by 50 percent of the grains.

It is still an embodiment that a length of the short fibers at least five microns, in particular at least 20 Micrometer, is. Thus, a pseudoplasticity even at very small grain sizes of the refractory metal powder, for example, of 500 nm, caused and processing is particularly simplified.

It is yet another embodiment that a length of the short fibers does not exceed five millimeters. This provides the advantage that the length does not hinder the prototyping and this length in particular also maximum typical layer thicknesses, e.g. of green films, does not exceed. In turn, an embedding and relatively free orientation of the short fibers can be achieved even for thin components, which in turn suppresses a directional dependence of the orientation of the short fibers and thus a direction-dependent shrinkage.

It is particularly preferred that a length of the short fibers does not exceed three millimeters, in particular two millimeters.

It is a further development that at least some short fibers (also referred to below as "nanofibers"), in particular all short fibers, do not exceed a length of one micron ("nanofibers"). In particular, nanofibers can bring about a change in the grain boundary stability, in particular with regard to a recrystallization behavior and / or a grain boundary sliding.

It is furthermore an embodiment that the short fibers have the material of at least one of the refractory metal powders. As a result, a deterioration of the properties of the finished refractory metal composite component with regard to its temperature resistance can be excluded. Even so unwanted chemical reactions can be excluded. In addition, a thermo-mechanical mismatch due to expansion coefficients, etc. can be suppressed, but this may also be desirable in composite materials. It is a development that the fiber or a fiber coating is a ceramic (eg oxide or carbide) fiber or fiber coating, which in particular affects the crack profile in the interface with the matrix.

For example, both the refractory metal powder and the short fibers may be made of high purity tungsten. Also, the starting material may include both high purity tungsten powder and tungsten rhenium powder, and the short fibers may be e.g. consist of pure tungsten and / or tungsten rhodium.

In particular, the fiber has a coating to achieve or enhance pseudoplasticity. It is also an embodiment that the short fibers are or have carbon nanotubes. The carbon nanotubes may be single tubes or form a fibrous tissue. It is also an embodiment that the short fibers are coated in order to adjust their shear strength against the Refrak- tärmetall- particles, in turn, to influence the mechanical properties, in particular the crack profile, the refractory metal composite component.

It is still an embodiment that the starting material comprises ceramic powder. This provides the advantage that a recrystallization behavior and / or a strength of the subsequently produced refractory metal composite component can be influenced. The presence of ceramics stabilizes the grain boundaries of the refractory metal, in particular in the context of dispersion hardening, and in particular can suppress grain boundary growth. This in turn gives the refractory metal composite component increased resistance to thermal shock (eg triggered by a punctual thermal cycling). It is a development that the ceramic particles La ₂ 0 ₃ , Y ₂ 0 ₃ , Tic and / or HfC have or consist of.

A ceramic powder may, in particular, be present as nanopowder or micropowder. In particular, among a nanopowder, a powder having an average grain size (for example, expressed by an equivalent diameter) in the nanometer range, i. of a micrometer or less. In particular, a powder having a mean grain size (for example, expressed by an equivalent diameter) in the micrometer range, that is, a powder under a nanopowder may be used. of a millimeter or less, but more than a micron, be understood. A mixing of ceramic powders and / or metallic

Powders can be made along with other components of the feedstock or can be achieved by an optional prefixed mixing and milling process (e.g., in a ball mill, tumbler or attritor, etc.). Among other things, a particle size distribution can be adjusted.

It is a further development that the starting material has no metal binder, ie no low-melting metallic binder. The absence of the metal as a binder can be realized in particular by a lack of metal, mixtures or alloys thereof as an independent powder in the starting material. Such a configuration has the advantage that the material properties of the finished refractory metal composite component, in particular its high melting point and its breaking strength under thermal cycling, are not degraded by the metal or metals in the binder (which would otherwise be the case). As a result, in turn, a refractory metal composite component produced in this way can withstand higher temperatures without destruction and / or have a longer service life. The process is not or not essential to perform more complicated than in the presence of a metallic binder.

It is still a further embodiment that the starting material is extrusion compound (often also called "feedstock") and the primary molding comprises extrusion of the extrusion composition. An extrusion composition may generally be understood to mean a solids-containing, viscous suspension comprising the refractory metal powder and the short fibers as a solid, which is suitable for carrying out the extrusion. This is made possible only by the short length of the short fibers. The technique of extrusion is generally well known and need not be further explained here. In principle, all suitable extrusion processes are applicable.

It is a development that extrusion comprises extruding a (composite) green sheet. As a result, large-area semi-finished products or components can be produced without further aftertreatment (for example rolling). For example, an extruder die may be appropriately shaped and e.g. have a slot or gap-like discharge opening.

It is an alternative embodiment that the starting material is slip, the primary forms a casting, in particular film pouring or Schlickergießen, the slip comprises and the green body is formed as a slip layer. Slip can generally be understood to mean a solids-containing, viscous suspension with the refractory metal powder and the short fibers as a solid, which is suitable for carrying out the casting.

It is a development that the casting comprises a foil casting or a foil casting process. The technique of film casting is basically well known and need not be further explained here. In principle, all suitable film casting methods are applicable. The result is a (composite) slip layer, which is also referred to as "green film". The green foil can be an independent workpiece. It is still a development that the casting comprises a slip casting or a slip casting process. In this case, a carrier is pulled once or several times through the slurry or sprayed with it. The deposited as a green body, deposited slurry layer can then be thermally treated together with the carrier. The result is a refractory metal composite component with the carrier as the main body and at least one refractory metal layer.

The slip layer may in particular be in the form of a thin layer of the slip, ie in particular still contain the binder. The slip layer, in particular green film, may be dimensionally stable, in particular for further processing.

It is also a development that a thickness of the (individual) slip layer is about fifty micrometers to about five millimeters, preferably about three millimeters. Thereby, a sufficiently high layer thickness for accommodating a plurality of grains of the refractory metal powder can be provided. In addition, a sufficient homogeneity of the individual Schuickerbestandteile can be ensured across the thickness. It is a further development that a layer thickness corresponds to at least approximately five times to ten times the largest particle of the at least one refractory metal powder and / or ceramic powder (if present). This avoids that a film is built on its thickness or height only by a few grains.

It is still an embodiment that the slurry is applied by means of a film casting (as a green sheet) on a carrier film. This facilitates handling of the green sheet, for example its shaping and / or stacking. The carrier film can then be removed again, for example stripped off, for example before a heat treatment of the green film. It is also an embodiment that several (two or more) slurry layers, in particular green sheets, are stacked on top of one another (eg laminated, isostatically pressed, cast or extruded). By means of the resulting layer stack, in particular large-area articles with a high layer thickness can be sintered in one operation. In addition, a high (basically unlimited) thickness of the refractory metal composite component can be achieved with a constant material density.

Alignment of fibers in the slurry layer may result in undesirable directional shrinkage for longer lengths. A refractory metal composite component may therefore alternatively be produced by stacking (possibly fiber-free) green sheets, in particular green sheet, and (optionally oriented) fiber layers. For example, a layer of oriented fibers may be laminated to a green sheet. In particular, a layer of oriented fibers may be pressed between two green sheets.

It is yet a further embodiment that at least two (stacked) slip layers, in particular green sheets, of the layer stack differ in their properties. In particular, the thermo-mechanical properties and the fracture behavior of the layer stack can be adapted constructively. Furthermore, such a layer stack enables the production of connection zones which allow attachment of refractory metal to external components, such as an anode support or a carrier of plasma chamber components in the fusion reactor. Also, stresses can be influenced by different thermal expansion coefficients of the components or the reaction behavior at the interfaces. In particular, a content of refractory metal, a type and / or composition of the refractory metal or a compound thereof (eg a content of W; Ta; Re; Mo, etc.), a presence, a type (material, countries ge etc.) and / or a content of short fibers, a microscopic structure (eg a particle size distribution), and / or a macroscopic structure (eg a size of the powder particles, a porosity, etc.). By way of example, the layer stack can be constructed by layering W layers with W / Re layers, or dense tungsten layers alternate with porous tungsten layers. The porosity can be adjusted, for example, via the sintering activity of the refractory metal powders.

It is a development that the slurry layers of the layer stack have a gradient structure. About a gradient structure is a crack-optimized and practically safe trained component produced. The gradient material may in particular by a gradual (in particular stepwise) change at least one property of

Mark slip layers over the stack thickness of the layer stack. Also by means of the slip casting process can several

Slip layers (e.g., analogous to several green sheets) may be applied to the support, e.g. as gradient layers.

By means other than casting, e.g. greensheets produced by extrusion, can be designed and combined in an analogous manner, e.g. to a gradient layer stack. The films or components can be applied to components in the "green state" and passed together through the heat treatment.

It is yet another embodiment that a median grain size of the particles of the refractory metal powder, D50, is less than two microns. These small grain sizes suppress grain growth at high sintering temperatures because the use of such fine powder fractions enables high sintering reactivity and therefore lower final sintering temperatures. It is also an embodiment that the refractory metal powder is a powder of pure tungsten, tungsten-rhenium, WRe, or tungsten-tantalum, WTa. It is also an embodiment that the proportion of the refractory metal or the compound thereof to the starting material is 50% by weight to 99% by weight.

It is a further development that the step of the original form is followed by a step of shaping the (composite) green body. The green body, e.g. a green sheet, for example, can be cut to a desired geometry by means of a knife, bent, rolled, etc. The green body can also be brought into various geometries (for example in the form of a tube). The method therefore not only permits the production of planar green bodies, but also the production of complex three-dimensionally shaped green bodies or refractory metal composite components. It is also an embodiment that is followed by a step of heat treatment of the at least one (composite) green body to the step of the primary forming and optionally shaping. Thereby, from the starting material, e.g. Green film, a solid, close to the shape refractory metal composite component are produced containing the short fibers.

The heat treatment may include a step of debinding the at least one green body. In this case, the at least one green body can be heated so much that the binder is removed (thermal debinding). Alternatively or additionally, debinding may be carried out by chemical debinding, in which the organic constituents of the binder are generally dissolved by solvents from the green body. The heat treatment may also include a step of sintering the at least one green body. Thereby, a compacted refractory metal composite member containing the short fibers is obtained. Sintering can be applied in particular to Binder follow. The sintering may in particular be a pressureless sintering.

Debinding and sintering can be carried out in one work step, for example by guiding the at least one green body through the same furnace or the same installation. This avoids relocating and shortens a process time. Especially in the case of a green body of pure tungsten as a refractory metal, a continuous process in a reducing and carbon-free atmosphere is preferred in order to keep the carbon and oxygen content low. For this purpose, the process may be carried out under vacuum or hydrogen atmosphere.

It is still a development that sintering is not performed at maximum sintering temperature, but at lower sintering temperatures. Thus, grain growth can be inhibited, which supports a homogeneous and isotropic microstructure. It may be sufficient in particular that sets in the refractory metal composite piece a closed porosity and no maximum possible density. Sintering in which the composite piece has a non-negligible (closed) porosity and which is followed by another heat treatment step may also be referred to as pre-sintering.

In particular to achieve an even higher density at low operating temperatures of previously presintered

Workpieces, it is also a development that the step of, in particular unpressurized, (pre-) sintering followed by a further (high-temperature) heat treatment step, e.g. an isostatic hot pressing.

The step of heat treatment can thus be a step of hot pressing, in particular hot isostatic pressing, of the at least one (pre) sintered refractory metal composite workpiece.

The step of heat treatment may alternatively or additionally comprise a step of so-called "spark plasma" sintering. The unbound and pre-sintered at comparatively low temperatures refractory metal workpiece (a closed porosity is not necessary here) is thereby flowed under high pressure of electric current and so brought in a short time and at relatively low temperatures to the final density.

The step of heat treatment may alternatively or additionally comprise a step of microwave sintering. In this case, the debinded and pre-sintered at comparatively low temperatures refractory metal workpiece is irradiated with microwaves to bring it to the final density at low temperatures. It is therefore an embodiment that the step of heat treatment has a step of sintering below a maximum sintering temperature to a density below the maximum density and, following, a heat treatment step of further compacting.

It is a preferred embodiment for producing a particularly stable, in particular thermal shock resistant, refractory metal composite component, that at least one green body is at least closed-pored by the heat treatment. By "at least closed-pored", a closed-pored or dense (in particular, maximum, dense) state can be understood. This suppresses formation or propagation of surface cracks, e.g. by thermally induced stresses, thus improving longevity.

The refractory metal composite components (plates or structures, eg tubes) with short fibers produced by the above process may already be the final product or as Semi-finished over conventional joining techniques, such as soldering, are applied to surfaces. Alternatively, green bodies, in particular green sheets or green sheets, can be applied to components before oven processes. In this case, these components must undergo the temperature treatment of the green body in a manner similar to the slip casting process.

The object is also achieved by a component (refractory metal composite component) or body, which has been produced by means of the method as described above. The component may in particular be designed analogously to the method and have the same advantages. Thus, the refractory metal composite component has short fibers as described above.

It is also a development that the refractory metal composite component consists of several (two or more) layers, which may differ in particular in their properties. In particular, the layers may have a gradient structure.

It is also a development that the refractory metal composite component is a three-dimensional component.

It is still a further development that the refractory metal composite component is a closed-pored component or a dense component.

It is a development that the component for X-ray tubes or fusion reactors is applicable, in particular as a surface of an X-ray anode or as a wall of a fusion reactor. For example, for temperature stability in these applications, the use of a low melting metallic binder would be very disadvantageous. The above-described characteristics, features and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more clearly understood in connection with the following schematic description of an embodiment which will be described in detail in conjunction with the drawings. In this case, the same or equivalent elements can be provided with the same reference numerals for clarity Fig.l shows a sequence of a method according to the invention in several variants;

Fig. 2 shows an apparatus for film casting for carrying out the method; and

3 shows an apparatus for extruding to carry out the method.

Fig.l shows a sequence of a method for producing a refractory metal composite component by primary forming in several variants.

A first preparation step S1 for producing a starting material M (see also FIGS. 2 and 3) comprises providing a powder mixture of refractory metal powder in the form of two tungsten powders. The two tungsten powders differ in their mean grain size, D50, namely once at 0.7 micrometers and once at 1.7 micrometers.

A second preparation step S2 comprises providing short fibers, e.g. of pure tungsten to achieve pseudoplasticity and / or as carbon nanotubes for altering grain boundary stability.

A third preparation step S3 comprises providing additives such as a dispersing agent (hypermer KD1), solvents in the form of ethanol and toluene, and a binder in the form of polvvenyl butyral (Pioloform BR 18) and a plasticizer in the form of dibutyl phthalate. For producing the starting material M, the constituents provided are mixed in a fourth step S4. For this purpose, first the refractory metal powders, the dispersing agent and the liquids are mixed in a speed mixer for 3 min at 1400 1 / min. Subsequently, the binder, to which ethanol has already been added, and the plasticizer are added and mixed for 10 minutes in the Speedmixer at 1500 1 / min. The short fibers can be mixed in one of these substeps or separately, for example in a last substep.

The dispersant ensures that the wetting behavior of the refractory metallic powder particles and the short fibers is improved and agglomeration is prevented. The solvents ethanol and toluene dissolve the organic components of the binder, in particular the binder Pioloform BR18. About the admixture of a plasticizer, the flexibility and strength of urformed green body 4, 17 (see also Figures 2 and 3) and thus its handling can be adjusted. Various homogeneous mixing and milling processes produce a homogeneous starting material M. In some cases, it may be necessary to degas the starting material M or molding compound prior to primary molding to avoid blistering in the reformed green body 4, 17. The aim is a weight fraction or volume fraction of 70% to 99% of refractory metallic powder in the starting material.

In a subsequent step S5, the starting material M is uroformed.

In one variant, the prototype S5 comprises the step S6 of a film casting. The starting material M is used as a slip to produce green bodies in the form of the short fibers having green sheet (s). For carrying out the step S6, namely, the film casting, the starting material M is filled into a storage chamber 2 of a film casting installation 1, as shown in FIG. The starting material M flows out of the storage chamber 2 and is by means of a Main doctor blade ("Doctor Blade") 3 as a green sheet 4 on a carrier sheet 5 stripped off. The carrier foil 5 lies on a flat base 6. A pre-doctor blade 7 upstream of the main doctor blade 3 can be used to set a hydrostatic pressure in front of the main doctor blade 3, which thus influences the thickness of the cast green foil 4. The viscosity of the starting material M or slip and the pulling speed (relative speed between carrier film 5 and main blade 3 in the direction of movement indicated by the arrow) likewise influence the thickness of the cast green film 4.

The minimum film thickness is particularly limited by the particle size of the starting powder and corresponds approximately to 5 to 10 times the largest refractory metal particles. With the above starting powders (especially D50 = 1.7 microns), the lower limit of the green cast film 4 is about 60 microns. The maximum thickness of the green sheet 4 is approximately 1.5 mm to 2.0 mm.

For example, a length of tungsten short fibers may range between 20 microns and 1.5 to 2 millimeters. In another variant, the prototyping S5 comprises the step S7 of an extrusion. The starting material M is now used as an extruder mass or feedstock to produce rod-like green bodies. For carrying out the step S7, the starting material M is introduced into a filling funnel 12 of an extrusion plant 11, as shown in FIG. 3 as a single-screw

Plasticizing extruder is shown filled. The starting material M passes from the hopper 12 into a cylinder 13, in which an extruder screw 14 is driven by a motor 15 rotates. The extruder screw 14 conveys the starting material M to a tip of the cylinder 13, on which an optionally heatable extrusion die 16 is located. From the extrusion die 16, the rod-like green body 17 is pushed out as an extrudate. Due to the short length of the short fibers promotion in the extruder screw 14 is not hindered. In a following step S8, the green body 4, 17 can be formed. For example, the green sheet 4 may be cut and / or shaped, in particular three-dimensionally shaped. The extrusion green body 17 may be cut off, cold rolled, etc., for example.

In a following step S9, the cut / shaped green body 4, 17 is heat-treated to produce the finished refractory metal composite component. In a first sub-step S10 of step S9, the

Base body 4, 17 entbindert, in particular by a heat treatment.

In a second sub-step Sil, the debindered and possibly shaped main body 4, 17 is sintered, in a coherent, in particular pressureless, sintering process at a correspondingly high sintering temperature until a dense or practically nonporous refractory metal composite component is present.

In an alternative procedure to step Sil, the debinded and possibly shaped green body 4, 17 is first sintered ("pre-sintered") at a comparatively lower sintering temperature in step S 12, wherein it does not yet reach its dense state, but remains porous (closed-pored).

In a following step S13, the presintered refractory metal work piece is compacted by hot isostatic pressing to form the refractory metal composite component, in particular compressed without pores, in particular at least approximately to its maximum possible density. This has the advantage that the temperatures required for hot isostatic pressing are lower than the sintering temperature required in step S12 and thus a grain growth (which increases with increasing temperature) is inhibited.

Alternatively or in addition to step S13, a spark plasma sintering step S14 and / or a microwave sintering step S15 may be performed.

While the invention has been further illustrated and described in detail by the illustrated embodiment, the invention is not so limited and other variations can be derived therefrom by those skilled in the art without departing from the scope of the invention.

Claims

Method (S1-S15) for producing a refractory metal component, the method comprising the following steps:

Providing (S4) a starting material (M) comprising a refractory metal powder of at least one refractory metal and / or a compound thereof and at least one binder; and

Prototypes (S5-S7) of the starting material (M) to at least one green body (4; 17);

in which

the starting material (M) comprises short fibers.

The method (S1-S15) of claim 1, wherein a length of the short fibers is at least ten times the microstructural size of the refractory metal matrix.

A method (S1-S15) according to any one of the preceding claims, wherein a length of the short fibers is at least five microns.

Method (S1-S15) according to one of the preceding claims, wherein a length of the short fibers does not exceed 5 mm.

A method (S1-S15) according to any one of the preceding claims, wherein a length of the short fibers does not exceed one micron.

Method (S1-S15) according to any one of the preceding claims, wherein the short fibers comprise the material of at least one of the refractory metal powders.

Method (S1-S15) according to any one of the preceding claims, wherein the short fibers are or have carbon nanotubes. Method (S1-S15) according to any one of the preceding claims, wherein the short fibers are coated.

Method (S1-S15) according to one of the preceding claims, wherein the starting material (M) comprises ceramic powder.

Method (S1-S15) according to one of the preceding claims, wherein

the starting material (M) is extrusion compound and the master molding (S5) comprises extruding (S7) the starting material (M).

The method (S1-S15) according to claim 10, wherein said extruding (S7) comprises extruding a greensheet (17).

A method (S1-S15) according to any one of claims 1 to 9, wherein

the starting material (M) is slip,

the master molding (S5) comprises casting (S6), in particular film casting or slip casting, of the starting material (M) and

the green body (4) is formed as a green sheet.

Method (S1-S15) according to one of claims 11 or 12, wherein a plurality of green sheets (4) or green sheets are stacked on top of each other.

Method (S1-S15) according to any one of the preceding claims, wherein at the step _of, primary forming (S5-S7) of the starting material (M) is a step of heat-treating (S9), in particular debinding (S10) and / or sintering (Sil, S12), the at least one green body (4, 17) connects.

15. refractory metal component, which has been produced by the method (S1-S15) according to one of the preceding claims. 16. refractory metal component according to claim 15, wherein the

Refractory metal has an isotropic fine grain structure.