Spherical powder for three-dimensional object manufacturing

Abstract

The present invention relates to a spherical alloy powder of at least two refractory metals, the alloy powder having a homogeneous microstructure and at least two distinct crystalline phases, and to a method for producing the powder. The invention also relates to the use of the powder in the production of three-dimensional parts, and to parts produced from the powder.

Description

[Technical Field]

[0001] The present invention relates to a spherical alloy powder of at least two refractory metals, the alloy powder having a homogeneous microstructure and at least two distinct crystalline phases, and to a method for producing the powder. The invention also relates to the use of the powder in the production of three-dimensional parts, and to parts produced from the powder.

[0002] There are various methods for producing metal parts with complex geometries. One method for producing such parts is additive manufacturing, also known as 3D printing. The term "additive manufacturing" refers to a general manufacturing process that produces three-dimensional objects by applying material layer by layer under computer control, typically bonding the layers together through physical and chemical hardening or melting processes. Additive manufacturing processes, in particular, are characterized by high precision and geometric accuracy, making it possible to produce prototypes and samples quickly and cost-effectively. Another method for producing metal parts is metal injection molding (MIM), which originated from plastic injection molding technology. In MIM, fine metal powder is mixed with an organic binder and introduced into a mold using an injection molding machine. The binder is then removed, and the part is sintered. This combines the mechanical advantages of sintered parts with the wide molding versatility of injection molding. Another advantage of this method is the potential to produce parts with demanding geometries in one piece, which would otherwise require multiple parts in traditional processes.

[0003] Common materials used in additive manufacturing and injection molding processes are plastics, resins, ceramics, and metals. Currently, a wide range of plastic materials are routinely used in these processes, but in the metal sector there is also a need for suitable powders with particularly good flowability and sintering activity to be processed into stable and durable objects.

[0004] WO 2011 / 070475 describes a method for producing an alloy containing at least two refractory metals, in which the two refractory metals are melted and mixed in a melting crucible by application of an electron beam, and the molten material is solidified, during which the molten metals are heated to 200 Ks. -1 ~2000Ks -1 The two metals are rapidly cooled and solidified at a cooling rate in the range of 100 to 1500°C. It is recommended to provide the two metals in powder form and mix them together before melting to completely dissolve the two metals in each other. In this case, it is particularly important that the two metals form a solid solution in any composition and prevent the formation of a second phase. However, this method has the disadvantage that the use of a melting crucible and the high temperatures required result in a large amount of impurities being mixed into the powder.

[0005] U.S. Patent Application Publication No. 2019 / 084048 discloses a method for producing atomized spherical β-Ti / Ta alloy powder for additive manufacturing, which includes: a) mixing elemental Ti and Ta powders to form a Ti-Ta powder composition; b) hot isostatically pressing the powder composition to form a Ti / Ta electrode; and c) subjecting the Ti / Ta electrode to EIGA to obtain atomized spherical Ti / Ta alloy powder. However, this method has the disadvantage that the resulting powder has a non-uniform microstructure, which may be undesirable for some applications.

[0006] Chinese Patent No. 108296490 provides a method for producing spherical tungsten-tantalum alloy powder, using amorphous tungsten-tantalum mixed powder produced using a high-energy spherical milling process as raw material. The raw powder is then formed into the desired alloy powder by plasma spheroidization. The milling process used is known to have the disadvantage of introducing undesirable wear to the milling balls.

[0007] The methods described in the prior art for producing alloy powders suffer in part from the drawback that a high proportion of foreign particles is introduced into the powder during the production process, resulting in powders with dendritic element distributions, which in turn can adversely affect the quality of parts produced from these powders, since the parts must be sintered for long periods of time, and usually at high temperatures, to achieve the desired mechanical strength. It is therefore an object of the present invention to overcome the drawbacks of the prior art and to provide a powder that can be used to produce porosity-free, mechanically stable parts, especially parts with complex shapes suitable for high-temperature applications.

[0008] Surprisingly, it has now been found that this problem is solved by a powder consisting of an alloy of at least two refractory metals and having a homogeneous microstructure and at least two different crystalline phases.

[0009] A first subject of the present invention is therefore a spherical powder for the production of three-dimensional parts, said powder being an alloy powder of at least two refractory metals, said alloy powder having a homogeneous microstructure and at least two different crystalline phases.

[0010] The powders according to the invention are characterized by good flowability and high sintering activity, which allows the production of pore-free and mechanically stable parts using additive manufacturing and / or injection molding.

[0011] In the present invention, the term "alloy powder" is considered to be synonymous with the powder according to the invention, unless otherwise specified.

[0012] Refractory metals within the meaning of the present invention are refractory base metals of subgroups 3, 4, 5 and 6 of the periodic table of the elements, which, in addition to having a high melting point, are characterized by having a passivation layer at room temperature.

[0013] In the present invention, the term "alloy powder" refers to a powder in which refractory metals are in the form of an alloy and form a macroscopically homogeneous powder, as opposed to a mixed powder in which the components are present in the form of a mixture and the distribution of elements is macroscopically non-uniform.

[0014] By "homogeneous microstructure" in the sense of the present invention is understood a uniform distribution of the elements, i.e. a uniform space-filling distribution of the alloying constituents in the individual powder particles without any macroscopic variations from place to place.

[0015] As used herein, the term particle size refers to the longest linear dimension of a powder particle from one edge to the other.

[0016] By agglomerates, within the meaning of the present invention, is meant a solidified collection of previously loose powder particles. Previously loose particles that have become agglomerates, for example by sintering, are called primary particles.

[0017] Additive manufacturing, or MIM, is used in almost every industrial sector. The properties of the manufactured parts can be influenced by the powders used, allowing the mechanical properties of the part to be tailored, as well as other properties, such as optical or electronic properties.

[0018] Therefore, in a preferred embodiment of the powder according to the present invention, the refractory metal is selected from the group consisting of tantalum, niobium, vanadium, yttrium, titanium, zirconium, hafnium, tungsten, and molybdenum. In a particularly preferred embodiment, the at least two refractory metals are tantalum and tungsten. In a particularly preferred embodiment, the alloy powder according to the present invention does not contain Ti. In this case, it is particularly preferred that the proportion of titanium in the alloy powder according to the present invention is less than 1.5 wt.%, particularly preferably less than 1.0 wt.%, in particular less than 0.5 wt.%, and especially less than 0.1 wt.%, based on the total weight of the alloy powder.

[0019] The powder according to the invention is characterized in that the alloy powder contains at least two different crystalline phases. It has been found to be particularly advantageous if one of these crystalline phases is a metastable crystalline phase. Metastable crystalline phase here means a phase that is thermodynamically unstable at room temperature. The crystalline phases occurring in the alloy powder according to the invention can be determined, for example, by X-ray diffraction analysis (XRD) and distinguished based on the reflections in the X-ray diffraction pattern. The distribution of different crystalline phases in the powder can vary. A preferred embodiment of the invention is characterized in that one crystalline phase is present in a greater proportion than the other crystalline phases. The most prevalent phase is called the main crystalline phase, and the less prevalent phase is called the secondary or minor crystalline phase. Preferably, the powder according to the invention has a main crystalline phase and at least one secondary crystalline phase. Surprisingly, it has been found that the ratio of these phases influences the mechanical properties of the resulting component, and that the ratio of these phases can be determined by the reflection intensity (expressed as the number of pulses per angle [2θ°]) in the X-ray diffraction pattern. In a particularly preferred embodiment, the ratio of the reflection with the highest intensity of at least one minor phase (I(P2)100) to the reflection with the highest intensity of the main crystalline phase (I(P1)100), i.e., the ratio expressed as I(P2)100 / I(P1)100, is less than 0.75, particularly preferably 0.05 to 0.55, and in particular 0.07 to 0.4, when measured by X-ray diffraction.

[0020] Another characteristic feature of the powders according to the present invention is their homogeneous microstructure. Typically, alloy powders, especially refractory metal powders, suffer from a non-uniform distribution of the various alloying elements within the individual powder particles due to the manufacturing process, which typically involves a short particle residence time and insufficient mixing and diffusion of the elements. This non-uniform distribution is particularly detrimental to the mechanical properties of the components produced from these powders. This can only be compensated for by using significantly higher energy input during the manufacturing process, e.g., by significantly higher laser power or lower laser scanning speed in SLM processes. However, in the present invention, it has surprisingly been found that the powder itself already exhibits a homogeneous distribution of the alloying elements. Therefore, preferred embodiments of the powders according to the present invention are those in which the content of the alloying elements, expressed as a percentage by weight within the particles, varies by less than 8%, preferably 0.05-6%, and particularly preferably 0.05-3%, as measured by EDX (energy dispersive X-ray spectroscopy) in at least 95%, preferably at least 97%, and particularly preferably at least 99% of all powder particles.

[0021] The powder according to the invention is characterized in particular by its sphericity, which makes it particularly suitable for use in additive manufacturing and injection molding processes. Thus, the powder particles have an average aspect ratio Ψ of 0.7 to 1, preferably 0.8 to 1, particularly preferably 0.9 to 1, in particular 0.95 to 1. A Preferred is an embodiment having A is defined as the ratio of the minimum ferret diameter to the maximum ferret diameter, which is A =x Ferret min / x Ferret max Here, the Ferret diameter is the distance between two tangents at any angle to the particle. Maximum Ferret diameter x Ferret max90can be determined by first determining the maximum ferret diameter and then determining the ferret diameter offset by an angle of 90° relative to this maximum ferret diameter. The same applies to determining the minimum ferret diameter. The ferret diameter of a particle can be determined, for example, by image evaluation procedures from scanning electron microscope images (SEM images) (see also Figure 9).

[0022] In addition to sphericity, the flowability of a powder is also a criterion for its suitability for use in additive manufacturing processes in particular. The powders according to the invention are characterized by a flowability that is adapted to the requirements of these manufacturing processes. Therefore, preferred embodiments of the powders according to the invention are those in which the powders have a flowability of less than 25 s / 50 g, preferably less than 20 s / 50 g, in particular less than 15 s / 50 g, measured according to ASTM B213, respectively.

[0023] Furthermore, the powders according to the invention are characterized by a high tap density, which is another criterion to be considered when selecting powders for use in such manufacturing processes. In a preferred embodiment, the powders according to the invention have a tap density of 40 to 80% of their theoretical density, preferably 60 to 80% of their theoretical density, respectively, as measured according to ASTM B527.

[0024] It is known that the mechanical properties and porosity of parts produced by such manufacturing processes can be controlled, inter alia, by the particle size of the powder used, which should be selected depending on the respective manufacturing process, with a particularly narrow particle size distribution proving to be advantageous. In a preferred embodiment of the invention, the powder according to the invention has a particle size distribution, measured according to ASTM B822, with a D10 value of more than 2 μm, preferably more than 5 μm, a D90 value of less than 80 μm, preferably less than 70 μm, and a D50 value of 20 to 50 μm, preferably 25 to 50 μm. This particle size distribution has proven to be particularly advantageous for selective laser melting (SLM) processes.

[0025] In a further preferred embodiment, the particle size distribution of the powder according to the invention has a D10 value of more than 20 μm, preferably more than 50 μm, a D90 value of less than 150 μm, preferably less than 120 μm, and a D50 value of 40 to 90 μm, preferably 60 to 85 μm, when measured according to ASTM B822. In particular in the field of electron beam melting (EBM) processes, particle size distributions as indicated have proven to be particularly advantageous.

[0026] In a further preferred embodiment, the powder according to the invention has a particle size distribution with a D10 value of more than 50 μm, preferably more than 80 μm, a D90 value of less than 240 μm, preferably 210 μm, and a D50 value of 60 to 150 μm, preferably 100 to 150 μm, respectively, as measured according to ASTM B 822. Powders with such particle size distribution have been found to be particularly advantageous for use in laser cladding (CL) processes.

[0027] In a further preferred embodiment, the powder according to the invention has a particle size distribution with a D10 value of more than 1 μm, preferably more than 2 μm, a D90 value of less than 45 μm, preferably less than 40 μm, and a D50 value of 6 to 30 μm, preferably 8 to 20 μm, respectively, as measured in accordance with ASTM B 822. Particle size distributions in the indicated ranges have proven advantageous, in particular when such powders are used in injection molding processes, such as metal injection molding (MIM).

[0028] In the present invention, the D50 value is understood to be the average particle size for which 50% of the particles are smaller than the indicated value. The same applies to the D10, D90 and D99 values.

[0029] A further subject of the invention is a method for producing the alloy powder according to the invention, which method comprises the steps of: a) providing a starting powder mixture comprising at least two refractory metals, wherein the starting powder mixture has a particle size with a D99 value of less than 100 μm and at least one of the refractory metals has a particle size with a D99 value of less than 10 μm, each measured according to ASTM B822; b) producing a powder from the starting powder mixture by cold isostatic pressing (CIP); c) sintering the pressed body at a temperature between 400 and 1150°C, preferably between 700 and 1050°C, lower than the lowest melting point of the components of the starting powder mixture; d) melting the sintered body by electrode induction melting (EIGA); e) atomizing and simultaneously cooling the melt to obtain spherical alloy powder; Includes.

[0030] It has surprisingly been found that the method according to the invention allows for the production of spherical powders with narrow particle size distribution and high sintering activity, enabling the production of porosity-free and mechanically stable parts by additive manufacturing processes or MIM. The powders produced by the method according to the invention are further characterized by a homogeneous distribution of the alloying elements and the presence of at least two crystalline phases.

[0031] The cold inert powder pressing (CIP) is preferably at least 1.7 x 10 8 Pa (1700 bar), particularly preferably at least 1.9 × 10 8 The compression pressure is 1900 bar.

[0032] In a preferred embodiment, the process according to the invention further comprises a classification step, preferably sieving, in which way the desired particle size distribution can be adjusted and set.

[0033] In a further preferred embodiment, the starting powder mixture has a particle size with a D99 value of less than 100 μm, preferably less than 80 μm, respectively, as measured according to ASTM B822.

[0034] In a preferred embodiment, at least one of the refractory metals in the starting powder mixture has a particle size with a D99 value, measured in accordance with ASTM B822, of less than 10 μm, preferably less than 5 μm, particularly preferably less than 2 μm, whereby this is preferably the refractory metal with the highest melting point.

[0035] It has proven advantageous to use in the starting powder mixture refractory metals whose primary particles have been sintered into porous agglomerates, in particular refractory metals having a primary particle size of less than 10 μm, preferably less than 3 μm, and particularly preferably less than 1 μm, as determined by image evaluation from scanning electron microscope (SEM) images. Preferred embodiments are therefore those in which at least one refractory metal of the starting powder mixture is in the form of a sintered porous agglomerate having a particle size with a D99 value of less than 100 μm, preferably less than 80 μm, as measured in accordance with ASTM B822, and a primary particle size of less than 10 μm, preferably less than 3 μm, and particularly preferably less than 1 μm, as determined by SEM images.

[0036] The sintering in step c) of the method according to the invention is carried out at a temperature 400-1150°C, preferably 700-1050°C, lower than the melting point of the alloy component having the lowest melting point, which is known to those skilled in the art or can be found in the literature. The duration of the sintering process can be adapted depending on the required powder properties, but is preferably 0.5-6 hours, particularly preferably 1-5 hours.

[0037] In the present invention, it is preferred to use a refractory metal with a high melting point, and therefore sintering is preferably carried out at a temperature of at least 1400°C.

[0038] In some applications, high oxygen concentrations in the alloy powder have been found to be detrimental to its use in certain manufacturing processes. Therefore, embodiments of the method according to the invention preferably further subject the alloy powder to a deoxidation step in the presence of a reducing agent, preferably magnesium or calcium, particularly in vapor form. Those skilled in the art will find detailed descriptions of suitable deoxidation processes, for example, in EP 1 144 147 B1.

[0039] In order to keep the oxygen content of the powder according to the invention as low as possible during the production process, it has already proven advantageous if the cooling takes place in an oxygen-depleted environment, and therefore an embodiment in which the cooling during atomization takes place with a cooled inert gas is preferred.

[0040] However, for special applications, it is desirable to tailor the oxygen content, and therefore in a preferred embodiment, oxygen-containing components of refractory metals, such as their oxides or suboxides, are added to the starting powder mixture in order to tailor the desired oxygen content in the powder according to the invention.

[0041] It has surprisingly been found that the powder according to the invention can be used not only in additive manufacturing processes but also in the production of three-dimensional parts by metal powder injection molding (MIM). Therefore, a further subject of the invention is the use of the powder according to the invention or the powder obtained according to the method according to the invention in additive manufacturing processes and / or metal powder injection molding processes. Preferably, the additive manufacturing process is one selected from the group consisting of selective laser melting (SLM), electron beam melting (EBM) and laser cladding (LC).

[0042] A further subject of the invention is a part manufactured using the alloy powder according to the invention or the powder obtained by the method according to the invention, which is preferably a part used in high-temperature applications such as engines or high-temperature furnaces, or preferably a medical implant or device. [Brief explanation of the drawings]

[0043] [Figure 1] FIG. 1 shows an X-ray diffraction pattern of powder Ta2.5W according to the present invention. [Figure 2] FIG. 1 shows an X-ray diffraction pattern of powder Ta13W according to the present invention. [Figure 3] FIG. 1 shows an EDX image of a crushed sample of powdered Ta13W according to the present invention. [Figure 4] FIG. 1 is a diagram showing the spherical shape of powder particles of powder Ta13W according to the present invention. [Figure 5a] FIG. 1 shows the X-ray diffraction pattern of comparative powder Vg1. [Figure 5b] FIG. 1 shows an SEM image of comparative powder Vg1. [Figure 6a] FIG. 10 shows an SEM image of comparative powder Vg3. [Figure 6b] FIG. 1 shows the X-ray diffraction pattern of comparative powder Vg3. [Figure 7] FIG. 10 shows an SEM image of a milled sample of part D3 produced with powder E2b according to the invention. [Figure 8] FIG. 10 shows an SEM image of a milled sample of part D1 produced using comparative powder V3b. [Figure 9] FIG. 1 shows the Ferret diameter of particles.

[0044] Working Example: The present invention will now be described in more detail with reference to the following examples, which should not be construed as limiting the scope of the invention in any way.

[0045] Powders Ta2.5W (E1) and Ta13W (E2) according to the present invention were produced using starting powder mixtures in which the tantalum powder had a particle size D99 of 49 μm and the tungsten powder had a particle size D99 of 1.9 μm, respectively, as measured according to ASTM B822. These powders were compacted by cold isostatic pressing (CIP) at a pressure of 2000 bar into pressed bodies, which were then sintered at 1950 °C for 2 hours. The resulting sintered bodies were melted by electrode induction melting (EIGA), and the melt was atomized while simultaneously cooling. The resulting atomized powder was sieved into two fractions (<63 μm, 63-100 μm), and the resulting <63 μm alloy powder was deoxidized in the presence of Mg at 1000 °C for 2 hours. The composition and properties of the resulting powders are summarized in Table 1, where the parameters were determined according to the respective standards.

[0046] The oxygen and nitrogen contents of the powders were measured by hot carrier gas extraction (Leco TCH600), and particle size was measured by laser diffraction (ASTM B822, MasterSizer S, dispersion in water, and Daxad 11, 5 min sonication). Trace analysis of metal impurities was performed by ICP-OES using the following analyzers: PQ 9000 (Analytik Jena) or Ultima 2 (Horiba). Crystalline phases were measured by X-ray diffraction (XRD) using a Malvern-PANalytical X'Pert-MPD with a semiconductor detector, a 40 kV / 40 mA X-ray tube, a Cu LFF, and a Ni filter.

[0047] [Table 1-1] [Table 1-2]

[0048] In the case of the powders according to the invention, two distinct crystalline phases, a cubic main phase and a tetragonal minor phase, could be distinguished in the X-ray diffraction patterns, as can be seen in Figures 1 and 2, which show images of the powders Ta2.5W (Figure 1) and Ta13W (Figure 2) according to the invention. The ratios of the reflection intensities of the most intense reflections are shown in Table 1.

[0049] Furthermore, the image of the Ta13W powder from Test E2b shows that, unlike conventional powders, the powder particles are spherical and lack dendritic structures. Figure 3 shows an EDX image of a ground sample of Ta13W powder, and Figure 4 shows the spherical shape of the Ta13W powder particles based on an SEM image of a scattering slide.

[0050] For comparison, powdered Ta2.5W(Vg1) was produced according to a conventional process by first producing a molten ingot with an electron beam. This was then embrittled with hydrogen and crushed. The hydrogen was removed under high vacuum, and the material was sieved to a particle size of less than 63 μm. The corresponding results are summarized in Table 2.

[0051] As shown by X-ray diffraction analysis and SEM images, the resulting powder did not have two distinct crystalline phases or a spherical morphology (see Figures 5a and 5b).

[0052] [Table 2]

[0053] For further comparison, powder Ta2.5W(Vg2) was produced by pressing the corresponding starting powders and sintering them at 1200 °C to form metal bodies, which were then atomized. The particle diameters D99 of the starting metals Ta and W were 150 μm and 125 μm, respectively. The results are also summarized in Table 2.

[0054] A third comparative powder was prepared similar to Comparative 2, but using 13 wt % W (Vg3, see Table 2).

[0055] As can be clearly seen in Figure 6a, the powder from Vg3 has a dendritic microstructure, with the tantalum and tungsten content varying in different shades, reaching up to 15 wt% in the region marked 1 to 4. No secondary crystalline phase was identifiable (see Figure 6b).

[0056] Comparative tests show that powders with a homogeneous microstructure or element distribution and at the same time with two different crystalline phases are not obtainable by known methods.

[0057] The powder according to the invention E2b as well as the powder according to comparative example 3 (Vg3) were printed by SLM with the printing parameters shown in Table 3. The aim was to produce cubic parts with a side length of approximately 2.5 cm and a homogeneous microstructure that were as dense as possible. The density of the parts is given as the ratio (%) of the measured density to the theoretical density of the alloy. A density below 100% indicates the presence of undesired porosity, which may have a negative effect on the mechanical properties of the parts.

[0058] Parts manufactured using the powder according to the invention can already be obtained at the required density at low laser powers or volumetric energy densities, which leads, among other things, to increased process reliability, lower energy consumption, and reduced oxygen uptake in the remaining powder. It was also possible to increase the laser scanning speed, thereby achieving a higher throughput.

[0059] [Table 3]

[0060] FIG. 7 shows an SEM image of a milled sample of a part (D3) having a density of 99% of the theoretical density, produced using powder E2b according to the invention.

[0061] Figure 8 shows an SEM image of a milled sample of part D1 produced with comparative powder V3b. The low density of the part, less than 80% of the theoretical density, can be clearly seen.

Claims

1. 1. A spherical powder for manufacturing three-dimensional parts, the powder being an alloy powder of at least two refractory metals selected from the group consisting of tantalum, niobium, vanadium, yttrium, titanium, zirconium, hafnium, tungsten, and molybdenum, the alloy powder having a homogeneous microstructure and at least two different crystalline phases, the at least two different crystalline phases having a cubic primary crystalline phase and a tetragonal secondary crystalline phase, and the content of Ti in the alloy powder is less than 1.5 wt.%.

2. The powder of claim 1 wherein the refractory metals are tungsten and tantalum.

3. 3. The powder according to claim 1, wherein the content of Ti in the alloy powder is less than 1.0 wt. %.

4. 4. The powder according to claim 1, wherein the powder has a cubic major crystalline phase and at least one tetragonal minor crystalline phase, and the intensity ratio between the reflection in the X-ray diffraction pattern having the highest intensity of the at least one tetragonal minor crystalline phase (I(P2)100) and the reflection in the X-ray diffraction pattern having the highest intensity of the cubic major crystalline phase (I(P1)100), i.e., the intensity ratio expressed as I(P2)100 / I(P1)100, is less than 0.75 as measured by X-ray diffraction.

5. 5. The powder according to claim 1, wherein the content of alloying elements, expressed as % by weight within the particles, varies by less than 8% in at least 95% of all powder particles, as measured by EDX (energy dispersive X-ray spectroscopy).

6. 6. The powder of claim 1, wherein the powder has a flowability of less than 25 s / 50 g as measured according to ASTM B213.

7. 7. The powder of claim 1, wherein the powder has a tap density of 40 to 80% of its theoretical density, as measured according to ASTM B527.

8. A method for producing a spherical alloy powder according to any one of claims 1 to 7, a) providing a starting powder mixture comprising at least two refractory metals, each of which has a particle size with a D99 value of less than 100 μm, and at least one of the refractory metals has a particle size with a D99 value of less than 10 μm, as measured in accordance with ASTM B822; b) producing a pressed powder from the starting powder mixture by cold isostatic pressing (CIP); c) sintering the pressed powder at a temperature 400-1150°C lower than the lowest melting point of the refractory metal of the starting powder mixture; d) melting the sintered powder by electrode induction melting; e) atomizing and simultaneously cooling the melt to obtain spherical alloy powder; A method comprising:

9. 9. The method of claim 8, wherein one of the refractory metals of the starting powder mixture is in the form of porous aggregates having a particle size D99 of less than 100 μm as measured according to ASTM B822.

10. 10. The method of claim 8 or 9, wherein the sintering is carried out for 0.5 to 6 hours.

11. 11. The method according to any one of claims 8 to 10, wherein the alloy powder is further subjected to a deoxidation step in the presence of a reducing agent, the reducing agent being magnesium or calcium.

12. 12. The method according to claim 8, wherein the cooling during atomization is performed by means of a cooled inert gas.

13. 13. Use of an alloy powder according to any one of claims 1 to 7 or a powder obtainable by a method according to any one of claims 8 to 12 in additive manufacturing processes and / or metal powder injection molding processes (MIM).

14. 14. The use according to claim 13, wherein the additive manufacturing process is a process selected from the group consisting of selective laser melting (SLM), electron beam melting (EBM) and laser cladding (LC).

15. A method for producing a part produced using the alloy powder according to any one of claims 1 to 7.

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