Metal molded body with gradient in the alloy

Abstract

Process for producing a shaped body containing metal which has a varying composition across a spatial direction, in which a) forms a layer containing a metal powder on a substrate, b) at least one strengthening composition is applied to the aforementioned layer on at least a part thereof, c) steps a) and b) are repeated at least once, and d) the unbound metal powder is removed, exposing the molded body, wherein the strengthening composition contains a binder, and wherein the strengthening composition contains 0.01 to 99.99 wt.% of an organoelement compound, and wherein the metallic powders form new phases with the organoelement compounds introduced by the solidification composition by diffusion and / or formation of melts.

Description

[0001] The present invention relates to a method for producing a metallic shaped body and to the metallic shaped body itself.

[0002] To date, there are several printing processes for molded bodies (for example, known from DE 10 2012 219 989 A1).

[0003] The development effort required to develop new components can be significantly reduced through the rapid provision of prototypes. Design changes can be immediately implemented into components based on CAD data, for example, without having to change tools.

[0004] The term rapid prototyping refers to the rapid production of prototypes and a technology that has been suitable for additive manufacturing processes since the early 1990s through continuous development with powerful, computer-aided control technology. Terms such as "rapid tooling" and "rapid manufacturing" are subordinate to the term rapid prototyping. These are further developments of the actual process that describe specific areas of application and use. The term rapid prototyping generally refers to the technology itself, while "rapid tooling" refers to additive toolmaking as an application, and "rapid manufacturing" refers to additive series production.

[0005] Rapid prototyping is a state-of-the-art process, particularly in the plastics industry. This typically makes it possible to manufacture components directly from 3D CAD data. Highly complex and intricate structures can be realized cost-effectively within a few hours. This significantly reduces development times and costs, as well as the time to market for new components.

[0006] All additive manufacturing processes share a basic process chain: The component to be manufactured is designed as a CAD model and then sliced ​​into superimposed layers. The contours and the surfaces they enclose are generated layer by layer in an additive process, building up the component layer by layer. These layers are always visible in the final component. Even at very high resolution, i.e., minimal layer thickness and the highest contour precision, they remain recognizable and give the components a rough surface that can be reworked if necessary.

[0007] The technological foundations of 3D printing date back to developments at MIT, Boston; the first patents (e.g., EP 0 644 809 B1) date back to 1993. In 3D printing, an organic binder is applied to a powder bed using a print head. The binder locally bonds individual powder particles together. The printed powder layer is lowered by a defined amount, for example, 100 µm, and covered with a new layer of powder. The printed binder also ensures that the layers are bonded together. In this way, the three-dimensional body is created layer by layer, which can be freed of loose powder after the binder has hardened.

[0008] One of the advantages of the process is that the areas solidified by the printed binder are surrounded by loose powder, eliminating the need for support structures, such as overhangs. This also allows for virtually no restrictions on geometric design freedom.

[0009] The density of the particles in the powder bed roughly corresponds to the bulk density of the powder. Therefore, the density of the green compacts is well below 50%, resulting in high porosity even after sintering. This can be used positively when it comes to the production of kiln furniture. Even high-purity Al2O3 parts exhibit excellent thermal shock resistance. In glasses and glass-ceramics, however, the sintering process succeeds in creating a dense microstructure – with comparatively high shrinkage. In metals, porosity can be slightly reduced but not completely eliminated.

[0010] Due to the geometric freedom of 3D printing, macroscopic porosity can also be used as a structural element. This allows mass to be reduced in areas of a component where there is little or no stress. This is achieved using a bionic approach, similar to that used in bone structures, for example.

[0011] DE 103 06 887 A1 describes a method for producing a ceramic molded body, wherein particles of ceramic powder can be provided with a coating containing different nanoparticles.

[0012] DE 10 2006 029 298 A1 describes a material system for 3D printing, whereby the described process can also lead to a metallic molded body.

[0013] DE 20 2005 020 596 U1 describes a powder for rapid prototyping, whereby a molded body is created by laser sintering.

[0014] DE 10 2005 058 118 A1 describes a process for manufacturing components, whereby the metallic components are produced by laser sintering.

[0015] DE 10 2005 058 116 A1 describes a method for producing metallic implants, which are locally cured with a laser.

[0016] DE 10 2006 015 014 A1 describes a method and a device for three-dimensional shaped bodies, wherein a suspension of metallic particles is printed with an inkjet printer.

[0017] DE 10 2005 058 121 A1 describes a method for manufacturing components, whereby the green body can be cured locally with a laser.

[0018] DE 602 07 204 T2 describes three-dimensional structured printing for the production of polymer bodies. Nanoparticles can also be incorporated into these polymer bodies.

[0019] DE 10 2004 008 122 A1 describes coated powder particles for the production of three-dimensional bodies by means of layer-building processes, whereby the powder particles can be coated.

[0020] EP 0 431 924 A2 describes a process in which binders are applied to ceramic powder.

[0021] DE 10 2008 022 664 A1 describes a printing process for ceramic components.

[0022] The article “Production of ceramic-metallic molded bodies by 3D printing” (Melcher et al., Ceramic Materials, January 2007, 3.4.2.4.) describes printed aluminum oxide-dextrin molded bodies and the resulting ceramic molded bodies.

[0023] WO 2013 / 112 217 A2 describes a process for producing articles from gradient alloys with multifunctional properties and applications for the use of such gradient alloys.

[0024] The processes known to date have various disadvantages. In some processes, the material that will later become the molded article is printed in a suspension. This requires a high solids concentration in the suspension to be printed, which clogs the printing nozzles. With the processes mentioned above, the properties of the resulting molded article cannot be varied across the spatial extent of the molded article. It is already known to add additional particles to the metallic powder. However, this has so far been done, for example, by coating the metallic articles and then printing them to produce the molded article. This can impart properties to the molded article that cannot be produced by the powder originally used. However, these properties cannot be produced in such a way that they are differently pronounced at different points on the molded article.In addition, a complex coating process for the particles is currently necessary.

[0025] Previous metallic molded bodies have a fixed, uniform composition.

[0026] The object of the present invention is therefore to provide a technology with which a metallic molded body with a flexible composition can be obtained.

[0027] It is a further object of the present invention to provide a method by which the material composition of a metallic shaped body can be varied at the microscopic level and thereby its properties can be adjusted in a spatially resolved manner.

[0028] There is a shaped body containing metal, characterized in that the shaped body has a varying composition across a spatial direction.

[0029] The shaped body preferably contains at least 90% metal by weight. Most preferably, the shaped body is made of metal.

[0030] The metal is preferably an alloy whose composition varies within the shaped body.

[0031] The shaped body preferably contains metals from the group of transition metals, aluminum, magnesium or mixtures thereof.

[0032] The molded body is preferably self-supporting. The molded body preferably has an aspect ratio of the largest spatial dimension to the smallest spatial dimension of up to 10:1. In particular, the molded body is not a coating. If a gradient exists in the molded body based on the composition, the gradient preferably does not extend from layer to layer.

[0033] In a first embodiment, the object underlying the invention is achieved by a method for producing a shaped body containing metal which has a varying composition across a spatial direction, in which a) forms a layer containing a metal powder on a substrate, b) at least one strengthening composition is applied to the aforementioned layer on at least a part thereof, c) steps a) and b) are repeated at least once, and d) the unbound metal powder is removed, exposing the molded body, wherein the strengthening composition contains a binder, and wherein the strengthening composition contains 0.01 to 99.99 wt.% of an organoelement compound, and wherein the metallic powders form new phases with the organoelement compounds introduced by the solidification composition by diffusion and / or formation of melts.

[0034] Preferably, the layer in a) also contains binders.

[0035] The composition of the layer in a) can also be spatially non-uniform. For example, it may be preferable for the layer to have a different composition of the metal powder at one location than at another location.

[0036] The solidifying composition preferably contains a dispersant or solvent. Water or an organic dispersant is most preferably selected as the dispersant or solvent. The dispersant is preferably present in the solidifying composition in an amount of 0.01 to 99.9 wt.%.

[0037] The strengthening composition also contains at least one organoelement compound, which preferably contains at least one atom that is not C, H, O, or N, and this atom is bonded to at least one organic radical. The organoelement compound is present in an amount of 0.01 to 99.9 wt.%.

[0038] The strengthening composition may preferably also contain inorganic particles. The inorganic particles may be metallic or ceramic particles. The organic particles may preferably be present in an amount of 0.01 to 70 wt.%.

[0039] The solidifying composition also contains a binder. The binder can be an adhesive, starch, or sugar. The binder can preferably be present in an amount of 0.01 to 25 wt.%.

[0040] The solidification composition particularly preferably contains 10 to 99.9 wt.% dispersant.

[0041] The strengthening composition particularly preferably contains 0.01 to 25 wt.% of an organic binder.

[0042] The solidification composition particularly preferably contains 0.01 to 70 wt.% of inorganic particles, most preferably with an average diameter in a range of 5 to 10,000 nm.

[0043] The solidification composition particularly preferably contains 0.01 to 99.99 wt.% of an organoelement compound.

[0044] Before or after step d), the dispersant or solvent can preferably be removed. This can be done, for example, by heating or by applying a vacuum.

[0045] Preferably, a layer thickness of the metallic powder and optionally of the binder is selected in a range of 10 to 300 µm, in particular in a range of 50 to 120 µm.

[0046] Preferably, a metallic powder selected from the group of transition metals, aluminum, magnesium or mixtures thereof is used.

[0047] Preferably, the molded body is subsequently heated after step d). This preferably removes the organic components. Heating allows the metallic powder to form material bridges, for example, through diffusion.

[0048] The metallic powders with the particles and / or organoelement compounds introduced by the solidification composition form new phases by diffusion and / or formation of melts.

[0049] The process according to the invention is an additive process in which material is not processed, but new shaped bodies are created.

[0050] If thermal treatment is applied, the organic compound is converted into inorganic metallic or non-metallic compounds. This makes it possible to spatially influence properties such as color, strength, hardness, electrical conductivity, thermal conductivity, thermal expansion, magnetic properties, piezoelectric properties, inductive properties, capacitive properties, or optical properties.

[0051] Further advantages are that in this way, desired property gradients, jumps or gradations can be realized in any way for aesthetic or technical reasons.

[0052] The layer in a) may preferably also contain binders.

[0053] The solidifying composition may also contain 0.1 to 99.9 wt.% dispersant and, for example, organoelement compound.

[0054] After step c) and / or d), it may be preferable to at least partially or completely remove any dispersant or solvent to form a shaped body.

[0055] The solidifying composition may also contain 0.1 to 99 wt.% of a colloidal dispersion with an average diameter of the dispersed phases in a range of less than 5 nm, as well as a dispersant. The dispersant may be identical to the solvent.

[0056] Dispersant in the sense of the invention is the liquid phase of the dispersion of the colloid.

[0057] The organoelement compound can preferably be an organometallic compound. Irrespective of this, the organometallic compound comprises at least one metal atom selected from the following elements: Ag, Al, Au, B, Ba, Be, Bi, Ca, Cd, Ce, Cr, Cs, Co, Cu, Fe, Ga, Ge, Hf, In, Ir, K, La, Li, Mg, Mn, Mo, Na, Ni, Nb, Os, P, Pb, Pd, Po, Pt, Re, Rb, Ru, Rh, S, Se, Si, Sb, Sn, Sr, Ta, Te, Ti, Ti, V, W, Y, Zn, and / or Zr. The organometallic compound preferably comprises Fe, Pd, V, Mo, or Y.

[0058] In 3D printing, binders and metallic or ceramic powders can be matched. The binder must ensure that the powder particles "bond" together and that the green compact achieves sufficient strength. When applying the strengthening compound, which is applied, for example, using a push button, it must not run but must precisely match the contour. To achieve this, it must react quickly with a small number of particles in the powder bed. The proportion of organic additives should ideally be so low that no separate debinding process is necessary. The goal is to be able to sinter the "printed" green compact immediately after removal from the powder bed.

[0059] In order to ensure the dimensional accuracy of the component, it is important to know the shrinkage exactly and to take this into account as an allowance in the CAD model for the printing process.

[0060] A key objective is to ensure that the manufactured components exhibit material properties that would be expected in series production. This particularly includes density. To achieve densification, it is possible to infiltrate the molded body in a further step, thus achieving a closed surface.

[0061] Compliance with tolerances and geometric reproducibility are essential for manufacturing. Components manufactured using 3D printing exhibit a reproducibility of ± 50 µm. The process-related formation of steps on curved surfaces is also within this range.

[0062] The invention aims to precisely place dispersions containing organic compounds, inorganic particles, or colloids at the microscopic level into a component generated from a powder in such a way that, after heating or sintering, a metallic structure is created that exhibits different properties in precisely defined areas with regard to chemical composition, phase composition, and / or grain size. This makes it possible to give a metallic component a structure with local property differences that is adapted to the respective load case.

[0063] Alternatively, no binder can be used. This has the advantage that the resulting metallic molded article contains fewer organic contaminants, provided organic dispersants are used, and it exhibits lower porosity.

[0064] The preferred dispersant or solvent is water or an organic dispersant, or a mixture thereof. Examples of organic dispersants used include alcohols, ketones, or polyethers.

[0065] Preferably, a powder of the elements Ag, Al, Au, B, Ba, Be, Bi, Ca, Cd, Ce, Cr, Cs, Co, Cu, Fe, Ga, Ge, Hf, In, Ir, K, La, Li, Mg, Mn, Mo, Na, Ni, Nb, Os, P, Pb, Pd, Po, Pt, Re, Rb, Ru, Rh, S, Se, Si, Sb, Sn, Sr, Ta, Te, Ti, Ti, V, W, Y, Zn, Zr or mixtures thereof is used. Very particular preference is given to using Ti, Fe, Mo, Ni, Si, Al, Cu as the powder. These metallic materials have proven to be particularly suitable for the process according to the invention.

[0066] The metallic powder preferably has a grain size in the range of 0.1 to 100 µm, especially in the range of 10 to 50 µm. This prevents excessive surface roughness in the final molded body and also prevents contamination due to absorption at the high BET surface area of ​​excessively small grains.

[0067] The metallic powder is preferably used in an amount of 85 to 100 wt.%. This ensures a sufficiently high metal particle content while still allowing sufficient room for, for example, any binding agents present.

[0068] The binders, in turn, are advantageously selected from saccharides, gum arabic, resin, cellulose linen, wax, casein, epoxy resin, polyurethane, or mixtures thereof. In particular, the binder is selected from the group consisting of starch, sugar, and / or dextrin. These binders have been found to exhibit high compatibility with metallic materials and, at the same time, to produce the least amount of undesirable ceramic contamination in the resulting molded bodies.

[0069] The binder is preferably used in an amount of 1 to 15 wt.%. Below 1 wt.%, it loses its effectiveness. Above 15 wt.%, undesirable organic contamination occurs in the molded body.

[0070] The binder has, for example, a grain size in the range of 0.1 to 100 µm, in particular in a range of 20 to 80 µm.

[0071] If the process according to the invention is to be used to produce articles which have an overhang compared to the wetted part of the first layer (for example a sphere), the layer dimension of the first layer is preferably selected so that it has the maximum extension of the resulting shaped body.

[0072] The base within the meaning of the invention is not part of the molded body for the first layer, and the previous layer for the subsequent layers. The base on which the first layer is formed is preferably selected from plastic and / or metal. The layer is formed, for example, by applying the powder to the base or the previously formed layer and then leveling the applied powder, for example by moving a straight object over the applied powder at a distance from the previous layer or the base corresponding to the desired layer thickness, thus removing excess powder.

[0073] The solidifying composition is advantageously applied using an inkjet printer print head, a microdispenser, a microdoser, a piezo print head, or a freely programmable dispensing system. This allows standard components from other application areas to be used, significantly simplifying the process.

[0074] The solidifying composition may also contain, for example, conventional additives such as surfactants, dispersants, pH adjusters, emulsifiers, extenders, defoamers, preservatives, drying retarders, rheology control additives, wetting agents, antioxidants, UV absorbers, light stabilizers, or a combination thereof. For example, these additives are included in an amount ranging from 0.05 to 10 wt.%.

[0075] Advantageously, the viscosity of the solidifying composition is at most 105 mPas xs, preferably at most 50 mPa xs at 20 °C and 1 bar. The viscosity can be measured using a Brookfield CAP 1000+ viscometer with the CAP-S-01 spindle at a rotation speed of 750 rpm.

[0076] In step c), steps a) and b) are preferably repeated at least 50 times, in particular at least 100 times, so that the staircase effects on the surface which are always inherent in these processes are minimized as much as possible.

[0077] The dispersant, in particular the water, is removed, for example, by drying. The removal time of the dispersant can be, for example, in a range of 8 to 48 hours. The temperature is, for example, in a range of 15 to 150 °C, in particular in a range of 30 to 80 °C. The atmosphere in which the dispersant is removed is, for example, air. During removal of the dispersant, a flow of the atmosphere can be induced by a fan, by applying a vacuum, or by convection. Depending on the metallic powder used, a hydration shell or other compounds form with the dispersant, making it difficult to completely remove the dispersant.For the purposes of the invention, the removal of the dispersant is therefore preferably to be considered complete when, towards the end of the drying process, no further loss of dispersant can be observed, i.e. the weight remains substantially constant.

[0078] The unbound metallic powder is removed, for example, by shaking or blowing it out.

[0079] When applying the strengthening composition, for example, a nozzle opening in the range of 10 to 1000 µm is selected, and independently of this, a droplet size in the range of 5 to 500 µm. The droplet size according to the invention allows the surface of the metallic powder to be wetted particularly evenly.

[0080] The additional solidifying composition is mixed with the first solidifying composition immediately before application, for example, in the print head of an inkjet printer.

[0081] The method according to the invention is therefore suitable for creating a 3D microstructure design of a metallic molded body that can be designed very flexibly. This allows the metallic molded bodies to be provided with a wide variety of properties in a spatially resolved manner. This is made possible by the fact that any concentration of the most diverse materials can be positioned very precisely within the metallic molded body. A wide variety of element distributions can thus be placed in a targeted manner. In the method according to the invention, these different elemental compounds can be applied to the layer containing the metallic powder in the same work step, for example, from different tanks using the same print head or from different print heads.

[0082] Furthermore, the method according to the invention is not only suitable for the creation of prototypes, but can also be used in series production.

[0083] In the method according to the invention, for example, a 3D model of the molded body can first be created on a computer. This can then be divided into slices in the computer, the thickness of which corresponds to the desired layer thickness of the metallic powder. In this case, it is possible, for example, to use color gradients to control which of the possibly different tanks containing the solidifying composition delivers this composition to the print head. For example, a solidifying composition containing a titanium tetrachloride solution can be introduced into the tank that contains blue ink in a conventional inkjet printer. A solution of copper citrate can be introduced into another tank as the solidifying composition, which usually contains yellow ink. With the help of a computer, one can now define, for example, a gradient from blue to yellow across the molded body in the 3D model.If this data is now transferred to the printer, the result is a molded body that is, for example, photocatalytically active on one side of the gradient, is particularly thermally conductive on the other side of the gradient, and has a smooth transition of these properties in between.

[0084] For example, a powder prepared by spray granulation is mixed with an organic binder, such as potato starch, and fed into a Z-Printer 510 (Z-Corporation, USA). Using the water-based binder solution (ZB54, Z-Corporation), which is applied via an inkjet printer, the component to be manufactured can be built up layer by layer according to the CAD data. After the printing process, the parts are dried and blown clean, followed by a final sintering firing.

[0085] The Z-Printer 310 is typically offered for producing colored plaster models. Like an inkjet printer, it is equipped with four colors. Instead of a colored binder, it is conceivable, for example, to use dispersions with different organometallic compounds. This allows the base titanium powder to be sprayed with the various compositions in variable quantities. The printer typically has three ink chambers. By filling it with solutions of organometallic compounds or colloidal dispersions, the desired alloys can be printed in µm to mm scales. According to a technical specification, a coordinated mixture of aluminum nitrate and vanadium chloride, for example, can be sprayed onto highly stressed areas. A Ti-6Al-4V alloy forms in this area during sintering.

[0086] The object underlying the invention is achieved in a further embodiment by a shaped body which is produced by the process according to the invention.

[0087] In yet another embodiment, the object underlying the invention is achieved by a method for producing a metallic shaped body, wherein first the method according to the invention is carried out and then the shaped body is heated or sintered.

[0088] The temperature is selected, for example, in a range between 1000 and 2000 °C and, independently of this, the holding time is selected in a range of 0.5 to 10 h, in particular 1 to 4 h.

[0089] The shaped body has, for example, a porosity in the range of 0 to 60%, particularly preferably in the range of 0 to 20%. Example

[0090] A titanium powder -100 +45 µm (TLS Technik GmbH & Co. Spezialpulver KG; Postfach 1328; D-06733 Bitterfeld) was mixed with 7 mass% potato dextrin powder, grain size 115 µm (Superior yellow F, Südstärke, Schrobenhausen, Germany).

[0091] 10 wt% of vanadium chloride (CAS number 7718-98-1, Sigma-Aldrich Chemie, Taufkirchen, Germany) was added to the water-based binder solution (ZB54, Z-Corporation, USA). The components were mixed in a beaker using a magnetic stirrer for 5 minutes.

[0092] Rod-shaped bodies (1 cm x 1 cm x 5 cm) were designed using a CAD program for sample production. These were color-graded (yellow to blue) from one end of the bar to the other. The data set was converted by the 3D printer (Z-510, Z Corporation, USA). The layer thickness was set to 0.088 mm and the saturation was set to maximum.

[0093] A pure binder solution (ZB 54) was filled into one binder tank, and the second tank contained a mixture of the binder solution and vanadium chloride. Depending on the color gradation, the two binders were applied to the powder bed in different ratios during the printing process.

[0094] The printed samples were dried at room temperature in the powder bed of the 3D printer for 12 hours. The specimens were then removed and completely dried in a drying cabinet at 60 °C for another 12 hours. The specimens were then freed of unbound powder using a brush and compressed air.

[0095] The test specimens were heated at 1300 °C and held for 3 hours.

Claims

[1] A process for producing a shaped body containing metal which has a varying composition across a spatial direction, in which a) forms a layer containing a metal powder on a substrate, b) at least one strengthening composition is applied to the aforementioned layer on at least a part thereof, c) steps a) and b) are repeated at least once, and d) the unbound metal powder is removed, exposing the molded body, wherein the strengthening composition contains a binder, and wherein the strengthening composition contains 0.01 to 99.99 wt.% of an organoelement compound, and wherein the metallic powders form new phases with the organoelement compounds introduced by the solidification composition by diffusion and / or formation of melts. [2] Method according to claim 1, characterized bythat the strengthening composition contains a binder in an amount ranging from 0.01 to 25 wt.%. [3] Method according to one of claims 1 or 2, characterized by that the solidifying composition contains a dispersant, and water or organic dispersant is particularly preferably selected as the dispersant. [4] Method according to one of claims 1 to 3, characterized by that a layer thickness of the metallic powder is selected in a range of 10 to 300 µm, in particular in a range of 50 to 120 µm. [5] Method according to one of claims 1 to 4, characterized by that a metallic powder selected from the group of transition metals, aluminum, magnesium or mixtures thereof is used. [6] Method according to one of claims 1 to 5, characterized bythat the solidifying composition contains 0.01 to 70 wt.% inorganic particles, most preferably with an average diameter in a range of 5 to 10000 nm. [7] Method according to one of claims 1 to 6, characterized by that the molded body is then heated. [8] Method according to one of claims 2 to 7, characterized by that the binding agent is glue, starch or sugar.