Methods for the production of sintered metallic and / or ceramic components, as well as components produced using the method

Abstract

In this process, at least one first component (1, 4) containing particles of a material is formed into a first predetermined shape, resulting in a green body. At least one second component (3, 6) containing particles of a material is then formed into a second predetermined shape, such that at least one surface area has a complementary surface contour and geometry with respect to at least one surface area of ​​the green body for the first component (1, 4). The green bodies thus obtained are positioned relative to each other such that the complementary surface areas face each other.The gap between the complementary surface contours and geometries of the green bodies is filled or coated with a closed-cell foam (2, 5) formed with at least one organic binder and metallic or ceramic particles, and containing gas bubbles with a volume fraction of at least 15% and at most 80%, such that the gap(s) is / are filled with the closed-cell foam. The green bodies and the foam (2, 5) are then subjected together to a thermal treatment in which the organic components are removed, joint sintering is achieved, and the individual parts (1, 4, 3, 6) are metallurgically bonded together.

Description

[0001] The invention relates to a method for producing sintered metallic and / or ceramic components which consist of several materially bonded individual parts, as well as to components produced by the method.

[0002] These are therefore components that consist of several individual parts, which are first provided in the form of semi-finished products and as green bodies, as is usual in the production of sintered components, and are then bonded together by sintering in a material-locking and, if necessary, additionally form-fitting manner.

[0003] The joint sintering of differently manufactured structures made of metallic or ceramic powders can be advantageous in terms of functionality, material savings, manufacturability and / or sinterability.

[0004] For example, material savings can be achieved by combining pressed structures with additively manufactured structures. For example, a gear with a pressed rim can be manufactured as a single component, and another component with a delicate design that achieves sufficient strength can be manufactured as an additively manufactured internal geometry, providing a complete gear as an example of a component in a specific shape. These components are then bonded together by sintering.

[0005] This also allows for reduced manufacturing costs by combining a dense pressed body with an open-cell foam structure. Heatable open-cell foam bodies with a pressed outer ring for contact and mechanical fixation can be produced.

[0006] The powders used for the respective processes for producing the individual parts to be joined often differ in particle size distribution and / or particle shape, which means that the final shrinkage as well as the shrinkage rate of both individual parts can differ depending on the temperature.

[0007] Different manufacturing processes for individual parts to be joined together often result in different green densities of the resulting green bodies, even when using similar powders with the same particle size distribution. This can also influence the nominal shrinkage and shrinkage rate. Contact zones between individual parts with different shrinkage properties (nominal shrinkage and / or shrinkage rate) can warp or become separated locally or globally.

[0008] Form-fitting joints of individual parts with different shrinkage properties (nominal shrinkage and / or shrinkage rate) can suffer local or global damage (cracking, breakage, unwanted deformation in the joined component caused by the different shrinkage behavior). In any case, internal mechanical stresses arise in the finished component, which at the very least leads to a reduction in the component's service life.

[0009] It is therefore an object of the invention to provide possibilities with which internal mechanical stresses, delaminations, cracks or other defects due to different shrinkage behavior during sintering can be avoided in components made up of several individual parts joined to form a component by sintering.

[0010] According to the invention, this object is achieved by a method according to claim 1. Claim 7 defines components produced in this way. Advantageous embodiments and further developments of the invention can be realized with features defined in the dependent claims.

[0011] In the method according to the invention, at least one first individual part with particles of a material is brought into a first predetermined shape, so that a green body is obtained therefrom as a semi-finished product.

[0012] In addition, at least one second individual part is formed into a second predetermined shape with particles of the first or a second material, so that at least one surface area is provided with a complementary surface contour and geometry in relation to at least one surface area of ​​the green body with which the first individual part was obtained.

[0013] The green body thus obtained as a semi-finished product for the second individual part is positioned with the first component in such a way that the complementary surface areas are arranged facing each other.

[0014] Subsequently, the gap between the surface areas with the complementary surface contours and geometries of the first and the second green body is filled with a suspension which is formed with at least one organic binder and metallic or ceramic particles and in which gas bubbles with a volume fraction of at least 15% and a maximum of 80% are contained, forming a closed-pore foam, or at least one of these surface areas is coated therewith, so that the gap(s) between the at least two green bodies is / are filled with the closed-pore foam.

[0015] Afterwards, the at least two green bodies with the foam are subjected to a thermal treatment together, during which the organic components are removed, then a joint sintering is achieved and the first and thus the second individual part(s) are materially bonded to each other.

[0016] The surface areas, which exhibit complementary surface contours and geometries, should be curved radii, sawtooth-shaped, or meander-shaped. The process is therefore particularly suitable for the production of components with circular or elliptical outer surfaces. However, such surface areas can also exhibit elevations and complementary depressions, in which forces leading to mechanical stresses can occur due to different shrinkage behavior of the individual joined parts. These forces can be avoided or at least significantly reduced with the invention.

[0017] For the process, the first and second individual parts and the foam can be made from the same powdered material.

[0018] Alternatively, first and second individual parts can be made from the same powdered material and the foam with a further different powdered material or first individual parts, second individual parts and the foam can each be made from a different powdered material and / or first and second individual parts and the foam can each be made with different average particle sizes of the particles.

[0019] If different materials are used, at least for the various individual parts, the thermal expansion coefficients of the materials should differ only slightly. The difference should be within a maximum of 10%.

[0020] It is advantageous if the green bodies for the first individual parts are formed using a different forming or manufacturing process than the second individual parts. This allows for the individual component areas to be adapted to the respective application. For example, areas with different compressive and tensile strengths, hardness, thermal or electrical conductivity, density, or porosity can be obtained on a component.

[0021] The shaping of the first and / or second individual parts can be carried out by means of uniaxial pressing, hot isostatic pressing, injection molding, with molding tools, casting processes (for example slip casting or gel casting) and / or an additive manufacturing process by layer-by-layer construction in order to be able to provide corresponding green bodies as semi-finished products.

[0022] A layer of closed-cell foam with a thickness between 0.5 mm and 20 mm should be formed between complementary outer wall areas of the first and second individual parts. The layer thickness should be as constant as possible.

[0023] The bond between the sintered individual parts can be achieved by applying a liquid or flowable closed-cell foam, which is formed from a suspension containing metal or ceramic particles, preferably made of the same metallic or ceramic material as the individual parts to be joined. The closed-cell foam is thus a suspension consisting of metallic or ceramic particles, a liquid, at least one organic binder, and preformed gas bubbles held in the suspension.

[0024] The volume fraction of gas bubbles in the foam formed from a suspension should preferably be between 20% and 70% of the suspension. The suspension with which the first and second volume regions of the component are formed can be produced in a manner known per se. For this purpose, a suitable liquid with at least one polymeric binder and a proportion of metallic or ceramic powdered solid can be used. Gas bubbles can be incorporated into the suspension by mechanical stirring or by another method, for example a procedure as known from DE 10 2010 039 322 A1. In addition to air, other gases or gas mixtures can also be used, which can also have an inert effect, so that no adverse effects on the respective metal or ceramic with which the component is ultimately formed are observed.

[0025] Polymeric binders commonly used for such suspensions, such as polyvinyl alcohols, can be used as binders. Defoamers should be avoided. Water is the preferred liquid. However, other liquids are also suitable, preferably those with a lower boiling point than water.

[0026] Preferably, a suspension should be used to form the first and second volume ranges that has a viscosity of at least 0.1 mPas. The suspension should also preferably exhibit shear-thinning flow behavior with a pronounced yield point.

[0027] By means of the closed-cell foam, a compensation of different shrinkage states (stress relaxation) of the joining partners during the heat treatment (heating, debinding, sintering, cooling) can be achieved through a possible plastic deformation in the component area that has been manufactured with the closed-cell foam.

[0028] The closed porosity reduces mechanical stiffness and increases plastic deformability, allowing deformation to be largely confined to the foam. Forces can be absorbed and compensated for by plastic deformation of the foam.

[0029] This allows both compressive and tensile or bending stresses to be compensated.

[0030] The foam used to connect the different individual parts can also be used to improve the damping properties of a component manufactured in this way.

[0031] The invention will be explained in more detail below by way of example.

[0032] Showing: Fig. 1 an example of a component manufactured according to the invention, in which two individual parts, one with a rotationally symmetrical inner surface and the other with a rotationally symmetrical outer surface, are integrally bonded with sintered foam and Fig. 2 a gear as an example of a component produced according to the invention, in which two individual parts are materially connected with sintered foam and one individual part has an external toothing and the second individual part forms a filigree support structure.

[0033] The Fig. The example shown in Figure 1 is a green body as a semi-finished product in a circular shape, which is hollow on the inside, for a first individual part 1, which has been shaped and made green-strengthened. The green body for the second individual part 3 here is cylindrical with a rotationally symmetrical outer surface, and has been made green-strengthened. The green body for the second individual part 3 was inserted into the cavity of the green body for the first individual part 1, and then the gap between the inner outer wall of the green body for the first individual part 1 and the outward-facing surface of the green body for the second individual part 3 was filled with a suspension which had been formed with a liquid, at least one organic binder, and metallic or ceramic particles.

[0034] Before filling the gap, glass bubbles were formed in the suspension, occupying a volume of at least 50% of the total volume of the suspension. This formed a liquid foam.

[0035] After filling the gap, a thermal treatment was performed in which all organic components were removed from both the green bodies and the suspension. A joint sintering process was then carried out, during which the metallic or ceramic particles were sintered together, as well as the individual parts and foam 2. The two individual parts 1 and 3 were bonded together using foam 2. Due to the residual gas in foam 2, this area of ​​the component has greater plastic deformability, which allows the aforementioned disadvantages to be taken into account.

[0036] For the production of a Fig.For the production of the green body for the first individual part 4, i.e., the gear rim shown in Figure 2, uniaxial pressing for shaping can be carried out using so-called ready-to-press granules or by using pure powder without organic components. The rotationally symmetrical surface of the green body for the first individual part 4, which faces inward, i.e., toward a second individual part 6, has an inner diameter that is larger than the outward-facing surface of the green body for the second individual part 6.

[0037] For the production of the geometrically complex second component 6, which is intended to form the internal volume of the gear as a component, a corresponding green body can be produced using additive manufacturing while remaining in the powder route. The outer diameter of the green body is smaller than the inner diameter of the green body for the first individual part 4.

[0038] The green body for the second individual part 6 can be produced, for example, by means of thermoplastic 3D printing, powder jetting or binder jetting.

[0039] This is followed by positioning for coaxial arrangement of the two individual parts 4 and 6. The gap between the individual parts 4 and 6 is then filled with flowable closed-cell foam 5.

[0040] This is followed by thermal treatment to remove the organic components and joint sintering.

[0041] To produce a gear for high-temperature lightweight applications from a FeCrAl alloy for the production of a component, you can proceed as follows: The production of a green body for a first individual part 4, which forms the outer gear ring of the component, can be achieved by uniaxial pressing. For this purpose, the metal powder can have an average particle size d 50 in the range 20 µm to 50 µm.

[0042] The inner diameter of the green body for the first individual part 4 was 60 mm. The green body for the second individual part 6 with a geometrically complex internal volume was manufactured using additive manufacturing via binder jetting. The metal powder used had an average particle size of d 50 in the range 20 µm to 50 µm.

[0043] The outer diameter of the green body for the second individual part 6, which represents the complementary surface to the inner diameter of the green body for the first individual part 4, had a value of 55 mm.

[0044] The two green bodies were positioned in a coaxial arrangement to each other.

[0045] To fill the gap between the outer diameter of the green body for the second individual part 6 and the inner diameter of the green body for the first individual part 4, flowable closed-cell foam was used.

[0046] The still liquid foam can be produced with a suspension as described in the general part of the description and as in DE 10 2021 204 741 A1.

[0047] For this purpose, FeCrAl metal powder with an average particle size d 50 A 7 µm diameter was first mixed with a polymeric binder (e.g., a polyvinyl preparation commercially available from Zschimmer & Schwarz) and additives (up to 5 mass% surfactant, e.g., a fatty alcohol sulfate preparation, Zschimmer & Schwarz) for foaming and adjusting the rheological properties. The mixture was then stirred with water to form a suspension with a metal solids content of approximately 86 vol.%. The mixture was foamed in a beaker for 10 minutes at a speed of 1000 rpm, with the aim of achieving a volume increase of approximately 50%.

[0048] The foam can be filled into the gap by extrusion from a commercially available cartridge syringe or by removing excess material using a squeegee.

[0049] Then, drying was carried out at 80 °C in air in an oven for 2 hours.

[0050] The green bodies with the foam were subjected to a thermal treatment to first remove the organic components and then sinter together. A maximum temperature of 1250 °C was reached and maintained for 1.5 hours. This was done in a hydrogen atmosphere.

[0051] The finished component consisted of the first individual part 4 and the second individual part 6, which were integrally bonded to the solidified foam 5. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2010 039 322 A1

[0024] DE 10 2021 204 741 A1

[0046]

Claims

[1] Process for the production of sintered metallic and / or ceramic components consisting of several materially bonded individual parts, in which at least one first individual part (1, 4) is brought into a first predetermined shape with particles of a material, so that a green body is obtained therefrom as a semi-finished product and at least one second individual part (3, 6) is brought into a second predetermined shape with particles of the first or a second material, so that at least one surface area has a complementary surface contour and geometry in relation to at least one surface area of ​​the green body with which the first individual part (1, 4) was obtained, and the green body thus obtained as a semi-finished product for the second component (3, 6) is positioned with the first component (1, 4) in such a way that the complementary surface areas are arranged facing each other and the gap between the surface areas with the complementary surface contours and geometries of the first and second green bodies is filled with a suspension formed with at least one organic binder and metallic or ceramic particles, and in which gas bubbles are contained with a volume fraction of at least 15% and a maximum of 80%, forming a closed-pore foam (2, 5), or at least one surface area is coated therewith, so that the gap(s) between the at least two green bodies is / are filled with the closed-pore foam and thereafter, the at least two green bodies with the foam (2, 5) are jointly subjected to a thermal treatment in which the organic components are removed, a joint sintering is achieved and the first and second individual parts (1, 4, 3, 6) are joined to one another in a material-to-material manner. [2] Method according to claim 1, characterized bythat the first and second individual parts (1, 3, 4, 6) and the foam (2, 5) are made of the same powdered material. [3] Method according to claim 1, characterized by that first and second individual parts (1, 3, 4, 6) are made of the same powdered material and the foam (2, 5) is made of a further different powdered material or first individual parts (1, 4), second individual parts (2, 6) and the foam (2, 5) are each made of a different powdered material and / or first and second individual parts (1, 3, 4, 6) and the foam (2, 5) are produced with different average particle sizes of the particles. [4] Method according to one of the preceding claims, characterized by that the shaping of the green bodies for first individual parts (1, 4) is carried out using a different shaping process or manufacturing process than for the shaping of second individual parts (2, 5). [5] Method according to one of the preceding claims, characterized by that the shaping of the first and / or second individual parts (1, 3, 4, 6) is carried out by means of uniaxial pressing, hot isostatic pressing, injection molding, with molding tools, casting processes (for example slip casting or gel casting) and / or an additive manufacturing process by layer-by-layer construction. [6] Method according to one of the preceding claims, characterized by that a layer with the closed-cell foam (2, 5) with a thickness of between 0.5 mm and 20 mm is formed between complementary outer wall regions of first and second individual parts (1, 3, 4, 6). [7] Component manufactured by a method according to one of the preceding claims.

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