Particle mixtures for additive manufacturing

Abstract

The invention relates to a particle mixture for additive manufacturing, to the use thereof in the production of three-dimensional parts by additive manufacturing and to a kit for the production of three-dimensional parts by additive manufacturing.

Description

Technical Field

[0001] The invention relates to a carbide particle mixture for additive manufacturing, its use in producing three-dimensional components by additive manufacturing, and a kit for producing three-dimensional components by additive manufacturing. Background Art

[0002] As part of the traditional production of ceramic and carbide components, a green body with a density of up to 55% of the theoretical density is usually first produced and then densely sintered under vacuum or protective atmosphere. The most common forming process for simple components is uniaxial pressing. Cylindrical components can be manufactured by extrusion, while processes such as powder injection molding can be used to manufacture more complex components.

[0003] While this already makes it possible to provide components with internal structures such as cooling channels, the production of components with more complex geometries is simply not possible using conventional processes or can only be achieved with a high degree of reworking.

[0004] Additive manufacturing processes offer an alternative to conventional manufacturing, where three-dimensional workpieces are created by applying material layer by layer. Compared to conventional abrasive processes, layer-by-layer additive construction offers a high degree of flexibility and design freedom, for example in prototype production and series production. Additive manufacturing processes offer the possibility to produce components with all their properties directly from the additive structure, or to produce a green body first and then sinter it into the desired component in further process steps, similar to conventional powder metallurgy processes.

[0005] Binder jetting is of particular interest due to its similarities to existing carbide production processes. In binder jetting, powdered starting materials are applied in layers and bonded with a liquid binder at selected locations to produce a component. However, binder jetting requires free-flowing powders to produce a uniform powder bed.

[0006] The prior art proposes various methods, such as by using spheroidized particles, to provide free-flowing carbide powders that are easy to agglomerate, especially free-flowing carbide powders that are easy to agglomerate in a small particle size range.

[0007] Thus, for example, US 2016 / 0375493 describes a method for producing a component, wherein a sintered carbide powder comprising tungsten carbide and a metallic binder phase is provided, the powder is formed into a green body by one or more additive manufacturing methods, and the green body is sintered to obtain a component having a density greater than 90% of the theoretical density, the density of the green body before sintering being less than 50% of the theoretical density.

[0008] US 11,065,863 describes a carbide powder for additive manufacturing processes, the density of the sintered carbide particles being at least 6 g / cm³ and having a bimodal or multimodal particle size distribution.

[0009] WO 2015 / 162206 describes a method for producing a powder from dense and spherical cermet or cemented carbide particles, the method comprising the following steps: (a) preparing spherical particles containing metal, hard components and an organic binder, (b) mixing the spherical particles with a sintering inhibitor powder to form a mixture of spherical particles and sintering inhibitor powder, (c) charging the mixture of spherical particles and sintering inhibitor powder into an oven, (d) heat treating the mixture obtained in step (b) in a furnace at a sintering temperature to remove the organic binder from the spherical particles and sinter the hard components in each spherical particle with the metal, thereby forming a mixture of sintered dense spherical particles and sintering inhibitor powder, (e) discharging the sintered dense spherical particles and sintering inhibitor powder from the furnace, and (f) separating the sintering inhibitor powder from the sintered dense spherical particles, thereby forming a powder of dense spherical cermet or cemented carbide particles.

[0010] WO 2017 / 178319 discloses a powder mixture for three-dimensional printing of carbide or metal ceramic bodies, the powder mixture containing 65% to 85% by weight of porous carbide and / or metal ceramic particles having an average size D50 of 10µm to 35µm, and 15% to 35% by weight of dense carbide and / or metal ceramic particles having an average size D50 of 3µm to 10µm.

[0011] WO 2021 / 072173 describes the production of carbide objects using a powder bed process, using a powder obtained by compacting spherical particles containing tungsten carbide and a metallic binder phase.

[0012] US 2020 / 0346365 describes a powder mixture for a method for additive manufacturing of components, which consists of sintered carbide particles having at least a bimodal particle size distribution, some of which have a D50 value of 25µm to 50µm and another portion of which has a D50 value of less than 10µm. The bulk density of the powder mixture is 3.5g / cm 3 Up to 8g / cm 3 .

[0013] US 2005 / 126334 describes a hybrid carbide composite material consisting of dispersed and continuous carbide phases, wherein the continuous ratio of the dispersed phase is less than or equal to 0.48.

[0014] CN 107 557 639 describes a carbide having a three-phase structure, characterised in that it consists of three components with different proportions of a binder phase.

[0015] US 2010 / 044115 describes carbide materials consisting of dispersed and continuous carbide phases and forming mixed carbides.

[0016] T. Rieger et al. describe their research on photopolymerization of photosensitive resin using photosensitive WC-12 Co (weight percent) sheets in the article "Photopolymerization of cemented carbide samples" published in Materials 2021, 14, 7631.

[0017] Conventional particles, such as those obtained by spray drying, often have a morphology that is too porous to compact sufficiently during the subsequent sintering process after additive manufacturing using binder jetting, making it difficult or impossible to obtain high-density parts.

[0018] Therefore, there remains a need for producing dense components using carbide particles in an additive manufacturing process, preferably in a binder jetting or similar process. Summary of the invention

[0019] Against this background, the present inventors have surprisingly found that this need can be met by a carbide-based particle mixture.

[0020] Therefore, the present invention firstly relates to a particle mixture for additive manufacturing, which comprises at least one first particle component A and at least one second particle component B, wherein the first particle component A and the second particle component B each comprise at least one hard material, wherein at least one of the particle components A or B further comprises at least one binder metal, and wherein the particle components each have a different hard material content.

[0021] For the purposes of the present invention, a "particulate component" is understood to mean an agglomerated solid consisting of a plurality of primary particles.

[0022] The present invention relates in particular to the production of three-dimensional components made of carbides. The hard material contained in the particle mixture of the present invention is preferably selected from carbides of the metals Ta, Ti, Nb, Cr, Hf, V, Mo, Zr and W and mixtures thereof. More preferably, tungsten carbide (WC) is used as the hard material.

[0023] The particle mixture according to the invention allows the content of binder metal to be adjusted individually, thereby achieving a favorable sintering behavior. Therefore, a preferred embodiment is that the at least one first particle component A and the at least one second particle component B both have binder metal, and the content of binder metal in the particle components is different. Without being bound by theory, it is assumed that due to the different contents of hard material and binder metal, the distribution of binder metal in the particle mixture is uneven, which can be used to close the cavities in the component during the sintering process.

[0024] The particle mixture according to the invention is characterized in particular by different contents of hard material in the particle parts of the mixture. In a preferred embodiment, the carbide content differs between the particle parts by at least 1%, preferably at least 5%, more preferably at least 10%.

[0025] The binder metal is preferably selected from the group consisting of Cr, Mo, Fe, Co and Ni and mixtures and alloys thereof, wherein Co is particularly preferred as the binder metal.

[0026] The proportions of the particle components in the mixture according to the invention can be adjusted as desired, in particular according to the desired content of binder metal in the particle mixture. A preferred embodiment of the invention is characterized in that the mass ratio of the at least one first particle component A to the at least one second particle component B is 1:99 to 99:1, preferably 10:90 to 90:10, in particular 1:5 to 5:1.

[0027] Preferred embodiments of the invention include particle mixtures in which only one of the particle components also contains a binder metal, i.e. one of the particle components has only hard material, and particle mixtures in which both particle components contain hard material and binder metal. A preferred embodiment is therefore that the hard material content in the at least one first particle component A is 75% to 95% by mass, preferably 80% to 90% by mass, based on the total mass of the particle components A in each case.

[0028] In a further preferred embodiment, the hard material content in the at least one second particle component B is 90 to 100% by mass, preferably 93 to 97% by mass, based on the total mass of the particle component B in each case.

[0029] At least one particle component of the particle mixture according to the invention contains at least one binder metal in addition to the hard material. The binder metal content is preferably 5 to 25 mass %, more preferably 10 to 20 mass %, based on the total mass of the particle component.

[0030] In a particularly preferred embodiment, the particle mixture according to the invention comprises a first particle component having a hard material content of 75 to 95 mass %, preferably 80 to 90 mass %, and a binder metal content of 5 to 25 mass %, preferably 10 to 20 mass %, and a second particle component having a hard material content of 90 to 100 mass %, preferably 93 to 97 mass %, and a binder metal content of 0 to 10 mass %, preferably 3 to 7 mass %, wherein the mass ratios refer to the total mass of the particle components, but the hard material content of the individual particle components is different. Without being bound by theory, it is assumed that the different contents of hard material and binder metal in the particle components lead to an uneven distribution of the binder metal in the particle mixture, which leads to a movement of the molten metal during sintering, which in turn leads to the cavities in the component being closed.

[0031] One prior art method of improving the flowability of carbide powders is to use powders with a bimodal or multimodal particle size distribution. In contrast, within the scope of the present invention, it has surprisingly been found that good flowability and sintering behavior can also be achieved if the particle size distribution is as uniform as possible. Therefore, in a preferred embodiment, the size distribution of the particle components of the particle mixture according to the invention differs from each other by no more than 35%, preferably by no more than 20%, based on the D50 value of the particle size distribution.

[0032] In the present invention, the grain size can be determined, for example, by laser diffraction in accordance with DIN ISO 13320:2020. Unless otherwise stated, the particle size distribution determined by laser diffraction relates to the mass distribution of the particle components. The following applies:

[0033] 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.

[0034] D50: 50% by mass of the powder has a particle size smaller than a specified value, or 5% by mass of the powder has a particle size larger than a specified value.

[0035] 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.

[0036] In a preferred embodiment, the particle mixture according to the invention is characterized in that the D50 values ​​of the hard material particle size distribution in the individual particle components preferably differ by no more than 20%. The particle size distribution can be determined, for example, using chord length analysis according to ISO 4499-2 / 3 or EBSD (electron backscatter diffraction) measurements on a scanning electron microscope.

[0037] In order to achieve a high green body density from the outset, it has proven to be advantageous to use suitable starting powders. In the context of the present invention, it has surprisingly been found that the green body density can be further increased by using pretreated granular components. It has proven to be particularly advantageous to obtain granular components with a low porosity by hot compression of spray-dried granules. Therefore, in a preferred embodiment, the granular components of the granular mixture according to the invention are spray-dried hot-pressed granules. Hot compression is preferably carried out by sintering, microwave or plasma treatment.

[0038] In a preferred embodiment, the particle components of the particle mixture according to the invention are obtained by spray drying, hot pressing and subsequent fractionation, wherein the fractionation is preferably carried out in such a way that particle components having a particle size distribution D50 of 10 µm to 35 µm, preferably 15 µm to 25 µm and / or a particle size distribution D90 of 25 µm to 50 µm, preferably ≤ 50 µm are obtained.

[0039] More preferably, particulate components are used which have a porosity of 0% to 40% by volume, preferably 20% to 35% by volume, wherein the porosity can be determined, for example, by gas adsorption measurements in accordance with DIN ISO 9277:2014.

[0040] The BET surface area of ​​the particle components used in the particle mixture according to the invention is preferably from 0.01 m2 / g to 1 m2 / g, more preferably from 0.1 m2 / g to 0.5 m2 / g.

[0041] In a further preferred embodiment, the bulk density of the particle mixture is between 30% and 50% of the theoretical density, determined according to ASTM B329, wherein the theoretical density can be found in the corresponding table. Preferably, the tap density of the particle mixture is at least 35%, preferably greater than 40%, more preferably greater than 46% of the theoretical density determined according to ASTM B527. Within the scope of the present invention, it has been found that particle components having such a distribution of properties can be used to produce high-density components.

[0042] "Particles" generally refer to macroscopic particles consisting of many small primary particles (also called grains). The primary particles are held together by bonding forces, for example those generated by sintering bridges. These bonding forces can be broken down again, and when using such particles, a certain particle strength has proven to be advantageous, since this strength can have a positive effect on the properties of subsequent components. Therefore, in a preferred embodiment of the present invention, the particles of the particle component according to the present invention have a compressive strength of more than 400 MPa. For example, the strength of the particles can be determined by compression tests.

[0043] As required, other components can be added to the particle mixture according to the invention, particularly preferred other components are carbides of metals of Groups 4 to 6 of the Periodic Table of Elements. The remaining components can be in the form of particles or powders. For example, other components can be used to favorably influence the sintering behavior of the particle mixture according to the invention.

[0044] The particle mixture according to the invention was developed especially for use in additive manufacturing techniques. The invention therefore also relates to the use of the particle mixture according to the invention for producing three-dimensional components by additive manufacturing techniques, preferably using binder jetting or powder bed fusion. Surprisingly, we have found that the use according to the invention results in components having a high density.

[0045] The present invention also relates to a method for producing a three-dimensional component using the particle mixture of the present invention. The process comprises the following steps:

[0046] a) providing a particle mixture according to the invention;

[0047] b) printing the particle mixture to form a three-dimensional body; and

[0048] c) Sintering the green body to obtain a three-dimensional component.

[0049] The printout is preferably performed by binder jetting.

[0050] Within the scope of the method according to the invention, the particle mixture according to the invention can be printed together with a binder. Therefore, the method preferably includes a step of removing the binder from the green body before sintering.

[0051] The present invention also relates to a kit for preparing three-dimensional parts by additive manufacturing, which comprises at least one first particle component A and at least one second particle component B, wherein the first particle component A and the second particle component B each comprise at least one hard material, wherein at least one of the particle components A or B further comprises at least one binder metal, and wherein the particle components each have a different hard material content. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 A scanning electron micrograph of a WC / Co particle mixture according to the invention is shown, where the binder metal (dark grey) is not uniformly distributed.

[0053] Figure 2 A cross-section of a test sample prepared by sintering or with the addition of the particle mixture of the present invention is shown. The high density of the test sample can be clearly seen. DETAILED DESCRIPTION

[0054] The present invention is described in detail by the following examples and figures, which however should not be understood as limiting the concept of the present invention.

[0055] Example

[0056] The spray-dried WC / Co powder was sintered at 1000 to 1200°C and then sieved to achieve a particle size distribution of D50 of 20 μm. In this way, two particle components A and B were produced and processed into the particle mixture of the present invention. Its composition is shown in Table 1:

[0057]

[0058] The particle mixture is sprayed through a binder into a test specimen, which is then released and sintered. The density of the test specimen prepared in this way is greater than 99% of its theoretical density.

Claims

1. A particle mixture for additive manufacturing of a carbide component, comprising at least one first particle component A and at least one second particle component B, wherein each of the first particle component A and the second particle component B comprises at least one hard material, wherein: At least one of the particle components A or B further comprises at least one binder metal, and wherein the particle components each have a different hard material content.

2. The particle mixture according to claim 1, characterized in that The hard material contained in the particle mixture is selected from the group consisting of carbides of metals Ta, Ti, Nb, Cr, Hf, V, Mo, Zr and W, and mixtures thereof.

3. The particle mixture according to at least one of the preceding claims, characterized in that The at least one first particle component A and the at least one second particle component B have a binder metal, and the contents of the binder metal in the particle components are different.

4. The particle mixture according to at least one of the preceding claims, characterized in that The binder metal is selected from the group consisting of Cr, Mo, Fe, Co and Ni, and mixtures and alloys thereof.

5. The particle mixture according to at least one of the preceding claims, characterized in that The hard material content in the at least one first particle component A is 75% to 95% by mass, preferably 80% to 90% by mass, based on the total mass of the particle component A in each case.

6. The particle mixture according to at least one of the preceding claims, characterized in that The hard material content in the at least one second particle component B is 90% to 100% by mass, preferably 93% to 97% by mass, based on the total mass of the particle component B in each case.

7. The particle mixture according to at least one of the preceding claims, characterized in that Based on the D50 value of the particle size distribution determined in accordance with DIN ISO 13320:2020, the particle size distributions of the particle components differ from one another by no more than 35%, preferably by no more than 20%.

8. The particle mixture according to at least one of the preceding claims, characterized in that The granular components are spray-dried hot-pressed granules.

9. The particle mixture according to at least one of the preceding claims, characterized in that The porosity of the particle component is 0% to 40% by volume, preferably 20% to 35% by volume.

10. The particle mixture according to claim 1, characterized in that According to DIN ISO9277:2014, the particle component has a particle size of 0.01 m 2 / g to 1m 2 / g, more preferably 0.1m 2 / g to 0.5m 2 / g BET specific surface area.

11. The particle mixture according to at least one of the preceding claims, characterized in that The bulk density of the particle mixture is 30% to 50% of the theoretical density as determined according to ASTM B329.

12. The particle mixture according to at least one of the preceding claims, characterized in that The particle mixture has a tap density of at least 35%, preferably greater than 40%, and more preferably greater than 46% of the theoretical density as determined according to ASTM B527.

13. Use of the particle mixture according to at least one of claims 1 to 12 for producing three-dimensional components by additive manufacturing techniques, preferably by binder jetting.

14. A process for producing a three-dimensional component, comprising the steps of: a) providing a particle mixture according to at least one of claims 1 to 12; b) printing the particle mixture to form a three-dimensional body; and c) Sintering the green body to obtain a three-dimensional component.

15. A kit for preparing a three-dimensional component by additive manufacturing, comprising at least one first particle component A and at least one second particle component B, wherein the first particle component A and the second particle component B each comprise at least one hard material, wherein: At least one of the particle components A or B further comprises at least one binder metal, and wherein the particle components each have a different hard material content.

Images