US-12617733-B2 - Method for producing a porous metallic or ceramic component and component produced using the method

US12617733B2US 12617733 B2US12617733 B2US 12617733B2US-12617733-B2

Abstract

An open-pored polymeric foam body is provided with a metallic coating or a coating at the surfaces of struts of the foam body. At the semi-finished product, a suspension that is formed with metallic or ceramic particles, in which additionally gas bubbles are present, is brought in contact with the surface of the foam body in surface regions and is brought into a predefined shape. A portion of this suspension penetrates into open pores of the foam body. Thereafter, a thermal treatment is carried out, during which liquid is expelled, polymeric components are removed, and subsequently a sintering process is carried out. A first volume region is formed with the metal or the ceramic originating from the suspension, which has a smaller porosity. Adjoining this first volume region, a second volume region is created, which is likewise porous.

Inventors

Alexander Füssel
Gisela Standke
Daniela Haase
Jörg Adler
Ulf Waag

Assignees

Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
hollomet GmbH

Dates

Publication Date: 20260505
Application Date: 20220510
Priority Date: 20210511

Claims (14)

1 . A method for producing a porous metallic and/or ceramic component, which comprises at least three mutually adjoining volume regions having differing porosities, in which an open-pored foam body, which is formed of a polymeric material, is provided with a metallic coating or a coating formed with metallic or ceramic particles at the surfaces of struts of the foam body in such a way that an open-pored base structure is preserved to form a semi-finished product; and a suspension, which is formed with metallic or ceramic particles, a liquid, a polymeric binder and additionally previously formed gas bubbles is brought in contact with the surface of the semi-finished product, creating a predefined shape at predefined surface regions of the semi-finished product, with a portion of this suspension penetrating the open pores of the semi-finished product, in an edge layer region; and thereafter, a drying process using a thermal treatment is carried out, during which liquid contained in the suspension is expelled, the polymeric binder is removed, and subsequently a sintering process is carried out, wherein during sintering, a first volume region being formed with the metallic or ceramic particles originating from the suspension, which has a smaller porosity that was exclusively obtained as a result of the gas bubbles present in the suspension, and, adjoining this first volume region, a second volume region is created, which is likewise porous, and the second volume region has been formed with the metallic or ceramic particles from the coating of the struts of the semi-finished product and the metallic or ceramic particles of the suspension, these metallic or ceramic particles having been joined to one another integrally and in a form-fitting manner within the second volume region, and thereby the second volume region being joined to a metallic or ceramic open-pored structure of an open-pored third volume region that was obtained from the coated foam body and has a larger porosity than the first volume region.
2 . The method according to claim 1 , wherein the foam body formed with the polymeric material, for creating the semi-finished product, is coated at the struts thereof with metal by means of a CVD method, PVD method, galvanically or with a suspension containing metallic or ceramic particles, the semi-finished product obtained by coating with a suspension being dried prior to having the suspension applied thereto for creating the first and second volume regions so that sufficiently high green strength is achieved to ensure that the coated struts have sufficient strength to avoid damage when a surface region is brought in contact with the suspension containing gas bubbles.
3 . The method according to claim 1 , wherein the struts of the semi-finished product are coated with the same metallic or ceramic particles which were used to form the suspension for creating the first and second volume regions.
4 . The method according to claim 1 , wherein a suspension which has a viscosity of at least 0.1 mPas and/or in which gas bubbles are present, having a volume percentage of at least 5% up to a maximum of 50% of the total volume of the suspension, is used for creating the first and second volume regions.
5 . The method according to claim 1 , wherein the suspension is added into at least one recess, depression, or perforation that is formed on the semi-finished product, and/or into the interior of a molding tool that can be attached to the particular semi-finished product, for creating the first and second volume regions.
6 . The method according to claim 1 , wherein a penetration depth of the suspension in pores of the semi-finished product, proceeding from the semi-finished product surface, is influenced by forces acting from outside of the suspension.
7 . The method according to claim 1 , wherein the semi-finished product by itself, or a semi-finished product having a molding tool attached thereto, is caused to vibrate and/or a pressure is exerted on the suspension.
8 . The method according to claim 1 , wherein the semi-finished product is used, which has a porosity in the range of 60% to 95% and/or that a first and/or second volume region is created with the suspension at the component having a porosity in the range of 0% to 55%.
9 . The method according to claim 1 , wherein the metallic particles used are an FeCrAl alloy.
10 . The porous metallic and/or ceramic component, produced using a method according to claim 1 , wherein the first volume region is formed with the metallic or ceramic particles originating from the suspension, which has a smaller porosity that was exclusively obtained as a result of the gas bubbles present in the suspension, and, adjoining this first volume region, the second volume region is created, which is porous, and the second volume region is formed with the metallic and/or ceramic particles from the coating of the struts of the semi-finished product and the metallic and/or ceramic particles of the suspension, with these metallic and/or ceramic particles being joined to one another integrally and in a form-fitting manner, and thereby the second volume region being joined to the metallic or ceramic open-pored structure of the semi-finished product, which has a larger porosity than the first volume region.
11 . The component according to claim 10 , wherein the third volume region has a porosity of at least 65%, and the porosity in the second volume region, which is arranged between the first and third volume regions, is smaller than in the first and third volume regions.
12 . The component according to claim 10 , wherein at least with the first volume region, at least one connection for electrical energy, is created.
13 . The component according to claim 10 , wherein a plurality of first and second volume regions, which are arranged spaced apart from one another, are present.
14 . The component according to claim 10 , wherein the third volume region has a porosity in the range of 80% to 93%.

Description

FIELD The invention relates to a method for producing a porous metallic or ceramic component and to a method produced using the method. Porous components are employed in a wide variety of technical areas. They are used for filtering or for receiving solid or liquid media, but also as heat exchangers. Frequently, they are also used as insulators or damping elements. In many applications, an open-pored structure is desirable. The open porosity, however, results in losses of strength and stability, making it necessary for many applications to use supporting, separate frame structures that, even though these ensure greater strength, cannot be reconciled, or can only be reconciled with great difficulty, with sufficient lasting strength with an open-pored foam body. BACKGROUND In addition, it is problematic to create connection options to open-pored bodies which, for example, allow electrical contacting for supplying electrical energy or allow a medium, in particular a fluid, to be supplied and/or removed, as is necessary, for example, in the case of electrical heating elements or heat exchangers. It is known to connect an open-pored foam body to a frame or other elements in a form-locked manner. However, problems arise with a permanent joint since struts in the connecting region may break due to mechanical stresses. These problems, however, also cannot be sufficiently taken into consideration when using a single or additional integral joint. Weak spots or interfaces that may result in the breakage of the joint occur at the joining points as a result of welding, soldering or bonding. SUMMARY It is therefore the object of the invention to provide options by way of which the stability of open-pored components is increased and/or to provide connecting options to an open-pored structure by way of which a secure and permanent supply or removal of media or energy can be achieved. This object is achieved according to the invention by a method having the features of the claims. The claims define an accordingly produced component. Advantageous embodiments and refinements of the invention can be implemented with features set out in the dependent claims. DETAILED DESCRIPTION When the open-pored metallic and/or ceramic components in question are produced, comprising at least three mutually adjoining volume regions having differing porosities, the procedure is such that first a semi-finished product is prepared in the manner known per se, which has an open-pored structure that is with an open-pored foam body made of a polymeric material. At the surfaces of struts of the foam body, the polymeric material has been provided with a metallic coating or a coating formed with metallic or ceramic particles in such a way that an open-pored base structure has been preserved. This can be achieved, for example, by way of a CVD or PVD method, which is known per se, galvanically or according to the so-called Schwartzwalder process, in which the struts have been provided with a coating containing metallic or ceramic particles. A semi-finished product obtained by way of the Schwartzwalder process should be dried prior to further processing to such an extent that sufficient green strength has been achieved. The corresponding known procedure is described in U.S. Pat. No. 3,090,094 B or U.S. Pat. No. 3,111,396 B, for example. Preferably, a cut-out from a reticulated open-cell polyurethane foam is used as the open-pored foam body that is formed of a polymeric material. For this purpose, the cell size used can cover the entire range of reticulated foams commercially classified according to pores per inch (according to ASTM D3576-77) from 8 ppi to 100 ppi, but it is advantageous when coarser foams in the range of 8 ppi to 30 ppi are used. A conversion of the ppi values into pore sizes in mm is easily possibly using photooptical or computer tomography methods. However, it is also possible to use other open-pored structures that are formed of polymers, for example non-woven fabrics or lattice structures produced by means of additive processes. A suspension, which is formed with metallic or ceramic particles, a liquid and a polymeric binder and in which gas bubbles that were previously formed in the suspension are additionally present, is brought in contact with a surface of the foam body and is then brought into a predefined shape at predefined surface regions on a semi-finished product thus obtained. In the process, a portion of this suspension penetrates into open pores of the foam body, serving as the semi-finished product, in an edge layer region. Thereafter, a drying process using a thermal treatment is carried out, during which first liquid contained in the suspension is expelled, and thereafter or simultaneously polymeric components, in particular polymeric components of the binder and the polymeric material of the foam body, are removed, and subsequently a sintering process is carried out. During sintering, a first volume region is formed wi