Refractory metal powder for additive manufacturing and method for producing same

Abstract

The invention relates to refractory metal powders for additive manufacturing, to a method for the production thereof and to the use thereof in additive manufacturing.

Description

[0001] The invention relates to refractory metal powder for additive manufacturing, a preparation method thereof and use thereof in additive manufacturing. Background Art

[0002] The name "additive manufacturing" summarizes all manufacturing processes, in contrast to subtractive processes, in which a workpiece is built up by adding volume elements or layers directly from digital 3D data in an automated manner, or by applying other volume elements to an existing workpiece, thereby generating a three-dimensional object. The layer-by-layer construction is usually carried out by computer control from one or more liquid or solid materials. The construction of the three-dimensional object is achieved by different physical and chemical solidification and melting processes, making it possible to produce a specific product without a specific tool in which the corresponding geometry of the product is already stored.

[0003] Although the processing of plastics, synthetic resins and ceramics for the production of complex models, samples and prototypes is widely used in industry and research, the number of suitable metals is still limited. Among other reasons, this is because metals must meet certain properties to be able to be used in additive manufacturing processes. Metals can be in solid form, such as rods or wires, or in powder form.

[0004] All manufacturing processes starting with metal in powder form involve numerous requirements that the metal to be processed must meet. These requirements include, among others, high flowability and a high bulk and tap density, in order to achieve uniform and well-defined application in the manufacturing process on the one hand and to obtain compact workpieces on the other.

[0005] Metal powders that meet the above requirements usually have a high degree of sphericity, which can currently only be achieved through high-energy melting and nozzle spraying methods.

[0006] Thus, WO 2020 / 220143 describes a metal powder for additive manufacturing processes produced by plasma treatment, which comprises spherical particles with a particle size distribution of 0 μm to 1000 μm and has a flowability of up to 20 s.

[0007] US 2022 / 0023941 discloses a metal powder for 3D printing, comprising a metal selected from tantalum, titanium, niobium and an alloy of tantalum, titanium and niobium, wherein the average aspect ratio of the particles of the metal powder is A is between 0.7 and 1, where ψ A =x 最小费雷特直径 / x 最大费雷特直径 .

[0008] DE 10 2019 130 941 relates to a method for processing metal powders for additive manufacturing, comprising the following steps: a) providing at least two metal powders with different physical properties, at least one of which is a residual powder from additive manufacturing and at least one of which is a new powder; b) proportioning the at least two powders and subsequently mixing them to form a powder mixture; c) subsequently drying the powder mixture and thereafter separating it into fractions, wherein in a first step, an ultrafine fraction is separated from the residual fraction by sieving, a coarse particle fraction is separated from the residual fraction by sieving, or a coarse particle fraction and at least one fine particle fraction are separated by sieving in a sieving device, wherein the residual fraction is a processed metal powder for additive manufacturing, wherein the processed powder is homogenized by the previous method steps and can be further used.

[0009] YY Sun et al. described spherical Ti powder for additive manufacturing obtained from precursor powders in their article “Manipulation and characterization of novel titanium powder precursor for additive manufacturing applications” published in The Minerals, Metals & Materials Society, 2015, Vol. 67, No. 3, which is not suitable for additive manufacturing due to its large particle size and other morphologies.

[0010] Technical issues

[0011] Melting metals with very high melting temperatures, such as typical refractory metals, results in very high specific energy requirements and, therefore, high manufacturing costs. Although the prior art has mastered some methods for lower melting point refractory metals such as titanium, niobium and tantalum, there is still a need for satisfactory solutions for higher melting point refractory metals, among which tungsten has the highest melting point and is additionally characterized by its unusual strength, which makes mechanical processing more difficult but at the same time makes it an attractive material.

[0012] In view of the above, it is an object of the present invention to provide a refractory metal powder, in particular tungsten, which is suitable for additive manufacturing on the one hand. A further object of the present invention is to provide a method for producing such a powder which is more sustainable than the methods known from the prior art.

[0013] Technical Solutions

[0014] Within the scope of the present invention, it has surprisingly been found that powders can be used in additive manufacturing processes even if they do not show the sphericity that was considered indispensable in the prior art. Thus, it has surprisingly been found that powders are suitable for additive manufacturing even if their particle shape deviates from the ideal spherical shape that is usually sought. Summary of the invention

[0015] Unless otherwise stated, the particle size distribution determined by laser diffraction relates to the mass distribution of the particles. The following applies:

[0016] D10: 10% by mass of the powder has a particle size smaller than a specified value, or 90% by mass of the powder has a particle size larger than a specified value.

[0017] D50: 50% by mass of the powder has a particle size smaller than a specified value, or 50% by mass of the powder has a particle size larger than a specified value.

[0018] D90: 90% by mass of the powder has a particle size smaller than a specified value, or 10% by mass of the powder has a particle size larger than a specified value.

[0019] Within the scope of this application, the terms "grain" and "particle" are used interchangeably, as are the terms "grain size" and "particle size".

[0020] Specifically, "non-spherical particles" used in the present invention refer to those particles having a cylindrical or ellipsoidal shape.

[0021] The term "fraction" as used in the present invention refers to a separated portion of a powder obtained by a separation process, wherein at least two fractions are formed in each separation process. This separation may be affected by characteristics such as mass, density, size, color or shape. DETAILED DESCRIPTION

[0022] In a first aspect, the present invention relates to a non-spherical refractory metal powder selected from vanadium, chromium, molybdenum and tungsten and alloys thereof for additive manufacturing of three-dimensional workpieces, wherein the powder consists of non-spherical particles and wherein each particle has a dimension A n , where at least 2 of the dimensions A n Different from each other. For example, the dimensions of the particles can be determined by optical methods using scanning electron microscopy.

[0023] The term "dimension" as used in the present invention refers to any distance between two points on the surface of a particle whose connecting line passes through the center of gravity of the particle. Although spherical particles have the same distance from the surface to the center in all spatial dimensions, any number of dimensions can be determined in all particles of the refractory metal powder according to the invention, of which at least two, preferably at least 3, more preferably at least 4 dimensions are different from each other. Although in spherical particles A1=A2, the powder according to the invention is characterized in that, in particular, it has at least two distances for which A1≠A2. For further explanation, refer to Figure 1 In a particularly preferred embodiment of the refractory metal powder according to the invention, the smallest dimension A of the particles is 最小 and the maximum dimension A 最大 The particle size is determined by the factor f(A), wherein the value of f(A) is >1.001 to 5. In other preferred embodiments, the maximum dimension A of the particle is 最大 With the minimum dimension A 最小 The ratio (A 最大 / A 最小 )<5.

[0024] In the context of the present invention, it has surprisingly been found that powders consisting of non-spherical particles are characterized by a particular particle size distribution function, since the model of spheres with equal volumes, on which the particle size distribution is usually based, does not apply here.

[0025] In a preferred embodiment, the refractory metal powder of the present invention is characterized by a particle size distribution as determined by:

[0026] Screening a refractory metal powder using n sieves, where n ≥ 2, and where the sieves have different mesh sizes;

[0027] Get F(x i ) = n + 1 fractions, which include the coarse particle fraction F(x i +1), where F(x i +1)>x i ; Medium particle fraction F(x i ), where F(x i )=x i , and the fine particle fraction F(x i -1), where F(x i -1) <x i , where x i represents the mesh size of the sieve, and where x i+1 / x i =a i , where 1.1≤a i ≤1.5;

[0028] The medium particle fraction F(x i ) particle size distribution,

[0029] The fraction F(x i ) has a particle size distribution D90 value greater than the mesh size x i +1, where x i +1>x i .

[0030] Sieving can be carried out in accordance with DIN 66165, wherein, for example, sieve towers with standardized test sieves as described in DIN ISO 3310 or ASTM B214 can be used.

[0031] The determination by laser diffraction can be carried out in accordance with DIN ISO 13320.

[0032] In a preferred embodiment, for all ratios x i+1 / x i , a i Essentially the same, wherein the deviation between these values ​​is preferably less than 5%, more preferably less than 3%.

[0033] While for spherical particles it is not important where the particle falls through the mesh of the sieve, this is not the case for non-spherical particles. In this case, there is a longitudinal dimension that is larger than the mesh size of the sieve. Without being bound by theory, it is assumed that this effect results in a fraction F(x i ) contains a relatively coarse mesh x i+1 The particle size distribution of the fractions is determined by laser diffraction.

[0034] Sieving the powder according to the invention within the determined range of its particle size distribution is preferably achieved using a series of sieves, wherein the mesh size x i Different constant factors, especially when using x i+1 =ai*x i The sieve is realized, of which 1.38 i <1.43. In particular for powders designed for additive manufacturing, sieves with mesh sizes of up to 125 μm have proven to be particularly suitable. Therefore, sieves with mesh sizes x i The embodiments of the screen are preferred:

[0035] x i :32µm(±5µm);

[0036] x i+1 :45µm(±5µm); preferably a1=1.40​

[0037] x i+2 :63µm(±8µm); a2=1.40 is preferred

[0038] x i+3 :90µm(±12µm); a3=1.42 is preferred

[0039] x i+4 :125µm (±20µm); among which a4=1.38 is preferred.

[0040] The value in brackets is the tolerance, which describes the permissible deviation from the nominal mesh size.

[0041] The particle size distribution of spherical particles generally follows a Gaussian normal distribution. In contrast, it has been unexpectedly found that the particle size distribution of the refractory metal powder according to the present invention deviates from this distribution. Therefore, embodiments in which the powder has a particle size distribution that conforms to a log-normal distribution are preferred.

[0042] The present invention relates to refractory metals which have been shown to have a high corrosion resistance due to their passivation effect. The refractory metal powder according to the present invention is selected from vanadium, chromium, molybdenum and tungsten and their alloys. More preferably, the refractory metal is tungsten and / or a tungsten alloy. Even more preferably, the refractory metal is tungsten, which is preferably obtained by reduction from tungsten oxide.

[0043] In particular, the refractory metal powders according to the invention are suitable for the requirements of additive manufacturing, wherein a flowability of not more than 9 s has proven to be suitable, in particular within the scope of powder printing methods. Within the scope of the present invention, it has been surprisingly found that the refractory metal powders according to the invention also meet this requirement despite their non-spherical shape, which has previously been considered disadvantageous for their use in additive manufacturing. Therefore, embodiments are preferred in which the flowability of the refractory metal powders according to the invention, as determined by ASTM B213, is not more than 9 s, preferably not more than 6 s.

[0044] Other properties that are critical to the suitability of metal powders in additive manufacturing include bulk density and tap density. It has been surprisingly found that these properties are achieved by the refractory metal powders according to the invention, which are unexpected due to the non-spherical shape of their particles, a deviation from the actually advantageous spherical particle form.

[0045] In a preferred embodiment, the bulk density of the refractory metal powder according to the present invention, as measured according to ASTM B329, is at least 40%, preferably greater than 45%, more preferably greater than 50% of the theoretical density of the refractory metal.

[0046] It is also preferred that the tap density of the refractory metal powder according to the present invention, measured according to ASTM B527, is at least 45%, preferably greater than 50%, more preferably greater than 56% of the theoretical density of the refractory metal. Thus, the powder according to the present invention has a bulk density and a tap density comparable to those of conventional powders having spherical particles.

[0047] The bulk density and tap density are expressed as a ratio to the theoretical density of the refractory metal. For the exemplary case where the refractory metal is tungsten, a density of 19.25 g / cm³ is taken as a reference of 100%. The theoretical density of refractory metals is known to a person skilled in the art and can be obtained from the corresponding reference works.

[0048] The powder according to the invention differs from the powders of the prior art, in particular by the non-spherical shape of its particles. The sphericity of a solid is defined as the ratio of the surface of a sphere of equal volume to the surface of the solid, wherein a sphericity of 1 describes a sphere. Therefore, embodiments in which the sphericity factor of the refractory metal powder is <0.95, preferably 0.65 to 0.9, are preferred. The sphericity can be determined statically according to ISO 13322-1 or dynamically according to ISO 13322-2. Within the scope of the present invention, particles having a "sub-circular" or "rounded" shape have been demonstrated according to the classification of Power in Power, MC, Journal of Sedimentary Petrology, 1953, Volume 23, page 118 (see Figure 2 ) are particularly advantageous.

[0049] Refractory metal powders have a natural oxide passivation on the surface, which, although making them relatively corrosion resistant, can lead to defects in workpieces produced by additive manufacturing due to the incorporation of foreign elements. Therefore, embodiments are preferred in which the refractory metal powder has an oxygen content of at most 1000 ppm, preferably at most 500 ppm, as determined by the LECO method.

[0050] As described in the prior art, refractory metal powders for additive manufacturing characterized by a high degree of sphericity have the disadvantage that they can only be produced by plasma spheroidization or other energy-intensive atomization methods, in which the metal is melted or partially melted and sprayed, which involves a large amount of energy consumption, mainly due to the high melting point of the refractory metal. On the contrary, it has been surprisingly found that the powders according to the invention can be produced by simple mechanical methods. In particular, these methods have the advantage that the metal does not need to be heated above its melting point. Therefore, the present invention also relates to a method for producing a powder according to the invention, which comprises the following steps:

[0051] i) providing a starting refractory metal powder selected from vanadium, chromium, molybdenum and tungsten and alloys thereof, having a particle size distribution as measured by laser diffraction of at least 10 μm D10 and less than 1000 μm D90;

[0052] ii) Mechanically treating the starting refractory metal powder to obtain the refractory metal powder according to the present invention.

[0053] In additive manufacturing, a general requirement for metal powders is a minimum particle size of 10 μm. It has been demonstrated herein that it is advantageous if the starting powder already has a corresponding particle size distribution so that the first step of the method according to the invention provides a starting refractory metal powder with a particle size distribution with a D10 of at least 10 μm, wherein the D90 should be below 1000 μm.

[0054] Preferably, in addition to the particle size distribution, the particles of the starting refractory metal powder have a dense, non-porous structure. Therefore, in a preferred embodiment, the density of the starting refractory metal powder is preferably at least 80% of the theoretical density of the refractory metal, more preferably at least 90%, in particular at least 95% of the theoretical density of the refractory metal. The theoretical density of the material is known to those skilled in the art and can be obtained from a corresponding set of tables.

[0055] Within the scope of the method according to the invention, the starting refractory metal powder is subjected to a mechanical treatment. This mechanical treatment surprisingly makes it possible to provide the powder with the properties necessary for additive manufacturing, such as bulk density and tap density, with a low energy consumption compared to the energy consumption of melt spheroidization. Without being bound by theory, it is assumed that the mechanical treatment of the starting powder leads to a smoothing of the particle surface, thereby obtaining advantageous properties. Therefore, it is preferred to choose a mechanical treatment without the presence of comminuting the particles.

[0056] In this respect, mechanical treatment in a ball mill or jet mill has proven to be particularly advantageous.

[0057] Therefore, the embodiment of the method according to the present invention in which the mechanical treatment of the starting refractory metal powder is carried out in a ball mill is preferred. In order to limit the formation of flakes by compressing particles, it has been shown that it is advantageous to select the size and quantity of the grinding balls accordingly. Therefore, the embodiment in which the size of the grinding balls is at most 8mm, preferably 4mm or less than 4mm is preferred, wherein the value represents the diameter of the grinding balls. In addition, the mass of the grinding balls should be in a suitable proportion to the mass of the powder to be processed. In this regard, the embodiment of the method according to the present invention in which the weight ratio of the starting refractory metal powder and the grinding balls is 1:1 to 1:5 is preferred. Both methods are used to limit the energy input, thereby obtaining powder particles with a shape suitable for additive manufacturing. The grinding balls can be made of iron-based materials, steel, Fe-Co, Ni alloys, ceramics or carbides. The mechanical treatment in the ball mill is preferably carried out for a period of 3 hours to 7 hours, preferably 4 hours to 6 hours, particularly 4.5 hours to 5.5 hours. After this period of time, the powder particles have a suitable shape so that the powder can be used for additive manufacturing. In mechanical treatment, the rpm of the ball mill is preferably selected to be below the critical rpm. The critical rpm of the ball mill depends on its diameter and is calculated according to the following formula:

[0058] .

[0059] Alternatively, the mechanical treatment can also be carried out in a jet mill.Therefore, the alternative embodiment of the method according to the invention in which the mechanical treatment of the starting refractory metal is carried out in a jet mill is preferred.

[0060] According to the principle of the jet mill, the particles are ground in a gas stream without the use of mechanical tools such as high-speed rotors. The grinding gas is introduced into the grinding chamber through a nozzle and is highly accelerated so that the individual particles are carried away and collide with each other. Since the processing of the particles is mainly spontaneous, this method is particularly suitable for the comminution of very hard materials. Surprisingly, it has been found that within the scope of the present invention, conventional jet mills can be used to produce suitable particles for additive manufacturing.

[0061] According to the invention, the mechanical treatment is preferably carried out at a grinding pressure of less than 8 bar. Preferably, a grinding gas with a grinding gas temperature of 10° C. to 40° C. is used, wherein the temperature relates to the gas at the grinding pressure. Surprisingly, it has been found that by using a jet mill, its grinding time can be shortened compared to the grinding time of a ball mill. Therefore, an embodiment in which the mechanical treatment is carried out for a period of 0.5 to 3 hours, preferably 0.5 to 1.5 hours, is preferred.

[0062] Mechanical processing of powders according to the present invention has been shown to produce refractory metal powders having a variety of properties required for additive manufacturing, particularly with respect to bulk density and tap density.

[0063] In a preferred embodiment, for example, the obtained refractory metal powder may be further classified to obtain a desired particle size range.Thus, in a preferred embodiment, the method according to the present invention provides a step of classifying the refractory metal powder.

[0064] The classification of the material to be ground is preferably carried out by screening, in particular by screening with a sieve tower. Alternatively, the classification can also be achieved by using other mechanical classification methods. For this purpose, devices such as gravity screeners, fluidized beds, zigzag sifters, cyclones, centrifugal separators, spiral screeners or dynamic wind screeners, or variations of these basic principles can be used.

[0065] If the mechanical treatment of the starting refractory metal is carried out in a jet mill, it can advantageously be combined with classification by sieving. In this case, an embodiment in which the jet mill has a dynamic wind sifter is preferred. Preferably, a conventional sieve wheel is used, the revolutions per minute of which are set so high that the separation boundary established by itself is finer than the minimum particle size of the particles to be treated. Although in this case the grinding gas can leave the mill, the particles still remain in the grinding space. Only the very fine fraction is discharged from the mill together with the grinding gas flow and can be separated out as a by-product in a filter.

[0066] Jet mills are usually operated in a continuous mode. However, within the scope of the present invention, it has been found that it is advantageous for the jet mill to be operated in an intermittent mode in this case. The mill can be filled automatically and the powder can be processed for the above-mentioned time and removed from the device in another step. Then, the device can be filled again and another treatment can be started. The discharge of the treated particles from the grinding space can be achieved by different variants. In a preferred embodiment, the ground material is blown through a baffle or valve that opens after a predetermined time and flows from the grinding space into a separate filter together with the grinding gas. In an alternative preferred embodiment, the treated refractory metal powder is separated by reducing the revolutions per minute of the sifter and cyclone separator placed between the grinding device and the filter. After the discharge process is completed, the revolutions per minute of the sifter can be reset to the original high value. Thereafter, the process can be restarted and repeated several times until the desired amount is completely processed.

[0067] The method according to the invention offers the advantage that the particle size distribution of the metal powder to be processed can be adjusted according to the requirements and the desired processing method.

[0068] The refractory metal powder used as starting powder has a particle size distribution D10 of at least 10 μm D10. In a preferred embodiment, the starting refractory metal powder has a particle size distribution determined by laser diffraction within the limits of 10 to 250 μm, preferably 10 to 150 μm.

[0069] A refractory metal powder according to the invention is provided, in particular for use as a material in additive manufacturing. Therefore, the invention also relates to the use of the refractory metal powder according to the invention in additive manufacturing.

[0070] The advantages of the present invention will be further illustrated by means of the accompanying drawings and the following embodiments, which should not be construed as limiting the concept of the present invention.

[0071] Examples / Figures

[0072] Tungsten metal powder having a starting particle size distribution of D10 of 39.2 μm and D90 of 151 μm was processed as described in Example 1 (ball mill) and Example 2 (jet mill).

[0073] The obtained powder was separated into individual fractions by passing through the sieves described in Table 1.

[0074] Table 1:

[0075]

[0076] Measure the obtained fractions

[0077] F1: <45µm >32µm

[0078] F2: <63µm >45µm

[0079] F3: <90µm >63µm

[0080] F4: <125µm >90µm

[0081] The D10, D50, D90 and D95 ​​values ​​of their particle size distribution were determined, each of which was performed by using laser diffraction on a Mastersizer 3000 from Malvern Panalytical.

[0082] 1. Ball mill

[0083] 20 kg of tungsten metal powder was ground in a ball mill (outer diameter = 26 cm, length = 45 cm) equipped with 40 kg of 4 mm carbide balls. The mill was operated at 40 rpm for 5 hours. Subsequently, the material was sieved to < 63 µm. The results are summarized in Table 2.

[0084] Table 2:

[0085]

[0086] 2. Jet mill

[0087] In a second embodiment, tungsten metal powder is processed in a jet mill. For this purpose, an AFG 100 jet mill from Alpine is used. The grinding pressure of the grinding gas (nitrogen (20°C)) is set to 5 bar. The grinder is equipped with 2 lateral nozzles with an aperture of 1.9 mm and a bottom nozzle with an aperture of 3 mm. During the rounding process, the number of revolutions of the sieve wheel is 3000 rpm, and it is set in such a way that only the extremely fine fraction formed (based on the starting amount, about 1% to 2% of fine powder) can leave the grinding space. The rounding process is carried out with 7.5 kg of tungsten metal powder over a duration of 1 hour. The powder is then classified by sieving. The results are summarized in Table 3.

[0088] Table 3:

[0089]

[0090] Figure 3 The frequency distribution measured by laser diffraction is shown, wherein the dotted lines represent the mesh size of the used sieve respectively. It can be seen that the particle size distribution of the fractions produced due to screening is significantly wider than the expected particle size distribution. Therefore, each particle size distribution established by laser diffraction obviously extends beyond the mesh size of the coarser sieve. In the case of spherical particles with the same volume, each distribution should be just between the dotted lines. Therefore, the deviation is attributed to the non-spherical shape of the powder particles according to the present invention. It can also be seen that the translation of the distribution curve is caused by a series of selected sieves (see factor a).

[0091] Figure 4a and Figure 4b The particle size distribution of a conventional tungsten metal powder having spherical particles is shown compared to the particle size distribution of a tungsten metal powder according to the present invention. Figure 4a The particle size distribution of conventional spherical particles fractionated through a 32 μm fine sieve and a 45 μm coarse sieve is shown. Figure 4b The particle size distribution of the non-spherical particles according to the present invention classified by a 32 μm fine sieve and a 45 μm coarse sieve is shown.

[0092] Figure 5 A scanning electron micrograph of a tungsten metal powder according to the present invention is shown. The non-spherical shape of the particles can be clearly seen.

[0093] Figure 6 Tungsten metal powder prepared in a ball mill according to Example 1 is shown.

[0094] Figure 7Tungsten metal powder prepared in a jet mill according to Example 2 is shown.

[0095] In the context of the sustainability discussion, the issue of energy consumption plays a key role. Table 4 gives an overview of the specific energy consumption of electrical energy for the method according to the invention compared to melt spheroidization of tungsten metal powder.

[0096] Table 4:

[0097]

[0098] The specific energy consumption represents a fundamental factor for manufacturing costs and ecologically sustainable production. The main disadvantage of conventional melt spheroidization methods is obviously the very high energy consumption. Especially in the processing of tungsten, a metal with a very high melting temperature, a large amount of energy is required to produce a well-flowing powder as required in additive manufacturing. In contrast, the method according to the invention represents a simple and energy-saving alternative.

Claims

1. A non-spherical refractory metal powder selected from vanadium, chromium, molybdenum and tungsten and alloys thereof for additive manufacturing of three-dimensional workpieces, characterized in that The powder consists of non-spherical particles, each of which has a dimension A n , where at least 2 of the dimensions A n Different from each other.

2. The refractory metal powder according to claim 1, characterized in that The powder has a particle size distribution determined as follows: sieving the refractory metal powder using i sieves, where i ≥ 2, and wherein the sieves have different mesh sizes; Get F(x i ) = i + 1 fractions, which include the coarse particle fraction F(x i +1), where F(x i +1)>x i ; Medium particle fraction F(x i ), where F(x i )=x i , and the fine particle fraction F(x i -1), where F(x i -1) <x i , where x i represents the mesh size of the sieve, and where x i+1 / x i =a i , where 1.1≤a i ≤1.5; The medium particle fraction F(x i ) particle size distribution, The fraction F(x i ) has a particle size distribution D90 value greater than the mesh size x i +1, where x i +1>x i .

3. The refractory metal powder according to claim 2, characterized in that A series of sieves are used, where the mesh size of the sieve is x i Different constant factors, especially when using x i+1 =a i *x i The screen, of which 1.38 i <1.43.​ 4. Refractory metal powder according to at least one of claims 2 or 3, characterized in that will have the following mesh size x i The sieves are used for grading: x i :32µm±5µm; x i+1 :45µm±8µm; x i+2 :63µm±12µm; x i+3 :90µm±20µm; x i+4 :125µm±20µm。 5. Refractory metal powder according to at least one of the preceding claims, characterized in that The particle size distribution of the powder conforms to the log-normal distribution.

6. Refractory metal powder according to at least one of the preceding claims, characterized in that The flowability of the powder measured by ASTM B213 is not more than 9 s, preferably not more than 6 s.

7. Refractory metal powder according to at least one of the preceding claims, characterised in that The bulk density of the powder measured according to ASTM B329 is at least 40%, preferably greater than 45%, and more preferably greater than 50% of the theoretical density of the refractory metal.

8. Refractory metal powder according to at least one of the preceding claims, characterised in that The tap density of the powder measured according to ASTM B527 is at least 45%, preferably greater than 50%, and more preferably greater than 56% of the theoretical density of the refractory metal.

9. Refractory metal powder according to at least one of the preceding claims, characterized in that The sphericity factor of the powder, determined by image analysis, is <0.95, preferably 0.65 to 0.

9.

10. A method for preparing a refractory metal powder according to at least one of claims 1 to 9, comprising the following steps: i) providing a starting refractory metal powder selected from vanadium, chromium, molybdenum and tungsten and alloys thereof, having a particle size distribution of at least 10 μm D10 and less than 1000 μm D90 as measured by laser diffraction; ii) mechanically treating a starting refractory metal powder to obtain said refractory metal powder.

11. The method according to claim 10, characterized in that Step b) is carried out in a ball mill, wherein the diameter of the grinding balls preferably does not exceed at most 8 mm, more preferably 4 mm, and / or the weight ratio of refractory metal powder to grinding balls is preferably from 1:1 to 1:

5.

12. The method according to claim 10, characterized in that Step b) is carried out in a jet mill, wherein the pressure of the grinding gas preferably does not exceed 8 bar.

13. The method according to claim 10, characterized in that The particle size distribution of the starting refractory metal powder measured by laser diffraction is 10 μm to 250 μm, preferably 10 μm to 150 μm.

14. Use of a refractory metal powder according to at least one of claims 1 to 9 in additive manufacturing.

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