EP4337405A1

EP4337405A1 - Process for producing a porous metallic or ceramic component and a component produced with the process

Info

Publication number: EP4337405A1
Application number: EP22729448.5A
Authority: EP
Inventors: Alexander Füssel; Gisela Standke; Daniela Haase; Jörg ADLER; Ulf Waag
Original assignee: Hollomet GmbH; Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Current assignee: Hollomet GmbH; Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Priority date: 2021-05-11
Filing date: 2022-05-10
Publication date: 2024-03-20
Also published as: WO2022238399A1; JP2024518981A; KR20240007239A; CN117295571A; DE102021204741A1; CA3217583A1

Abstract

In the process an open-cell polymeric foam body is provided with a metallic coating or coating at the surfaces of cell walls of the foam body. At the surface regions of the semifinished product a suspension formed with metallic or ceramic particles and which additionally contains gas bubbles is brought into contact with the surface of the foam body and into a predetermined shape. A portion of this suspension penetrates into open cells of the foam body. This is followed by a thermal treatment in which the liquid is driven out, polymeric components are removed and a sintering is subsequently performed. A first volume region comprising the metal or the ceramic deriving from the suspension and having a lower porosity is formed. A second volume region which is likewise porous and has been formed with the metal or the ceramic from the coating of the cell walls of the semifinished product with the metal or ceramic of the suspension is formed adjacent to this first volume region. The second volume region is joined to the third volume region obtained from the coated foam body.

Description

1

FRAUNHOFER-GESELLSCHAFT...e.V., hollomet GmbH

Process for the production of a porous metallic or ceramic construction part and a component produced with the process

The invention relates to a method for producing a porous metallic or ceramic component and one produced using the method

component. Porous components are used in a wide variety of technical areas. They are used for filtering or absorbing solid or liquid media, but also as heat exchangers. They often also serve as an isolator or damping element. In many applications an open porous structure is desirable. However, the open porosity leads to losses in strength and stability, so that for many applications it is necessary to use separate supporting frame structures which, although they ensure greater strength, are difficult or impossible to combine with an open-porous foam body with sufficient permanent strength - get tied.

It is also problematic to connect to open-porous bodies To create 2 per, with which, for example, an electrical contact for the supply of electrical energy or a supply and / or removal of a Me medium, in particular a fluid is possible, as is required for example with electrical heating elements or heat exchangers.

It is known to positively connect an open-pored foam body to a frame or other elements. In this case, however, problems arise with a permanent connection, since webs in the connection area can break as a result of mechanical stress. However, these problems cannot be adequately taken into account even with a sole or additional material-locking connection. Welding, soldering or gluing causes weak points or interfaces at the connection points that can lead to the connection breaking.

It is therefore the object of the invention to specify options with which the stability of open-pored components can be increased and/or to offer connection options to an open-pored structure with which media or energy can be supplied or removed safely and permanently.

According to the invention, this object is achieved with a method having the features of claim 1. Claim 10 defines a correspondingly manufactured component. Advantageous refinements and developments of the invention can be implemented with features identified in the dependent claims.

In the manufacture of the open-pored metallic and/or ceramic components in question, which have at least three adjacent volume areas with different porosity, the procedure is such that a semi-finished product is first prepared in a manner known per se, which has an open-pored structure , which with an open-cell foam body, which is formed from a polymeric material. The polymeric material has been provided with a metallic coating or a coating formed with metallic or ceramic particles on the surfaces of webs of the foam body in such a way that an open-pored basic structure has been retained. This can be done, for example, with a known CVD or PVD process, galvanically or by the so-called 3 named Schwartzwalder method, in which the webs have been provided with a coating containing metallic or ceramic particles. A semi-finished product obtained using the Schwartzwalder process should be dried before further processing to the extent that sufficient green strength has been achieved. The corresponding known procedure is described, for example, in US Pat. No. S 0,900,94 B or US Pat. No. 3,111,396 B.

As an open-pored foam body formed from a polymeric material, a blank made from a reticulated open-cell polyurethane foam is preferably used. The entire range of commercially classified reticulated foams according to pores per inch (according to ASTM D3576-77) from 8 ppi to 100 ppi can be used as cell size for this purpose, but it is advantageous if coarser foams in the range 8 ppi -30 ppi are used . The ppi values can easily be converted into pore sizes in mm using light-optical or computer tomographic methods.

However, other open-pore structures formed from polymers can also be used, e.g. non-woven fabrics or grids manufactured using additive processes.

A suspension formed with metallic or ceramic particles, a liquid and a polymeric binder, which additionally contains gas bubbles that have previously been formed in the suspension, with a surface, is then applied to predetermined surface areas of a semi-finished product obtained in this way of the foamed body and formed into a predetermined shape. A part of this suspension penetrates into open pores of the foam body as a semi-finished product in a surface layer area.

Drying with a thermal treatment is then carried out, in which liquid contained in the suspension is first expelled, then or simultaneously polymeric components, in particular polymeric components of the binder and the polymeric material of the foam body, are removed and sintering is then carried out on this.

During sintering, a first volume area with the metal or the 4 ceramic material that comes from the suspension, which has a smaller porosity than the porosity of the semi-finished product, which has been obtained exclusively as a result of the gas bubbles contained in the suspension, and adjacent to this first volume area, a second volume area is formed, the is or can also be porous, and the second volume area with the metal or ceramic has been formed from the coating of the webs of the semi-finished product and the metal or ceramic of the suspension, these metals and/or ceramics being materially and positively bonded within the second Volume area are connected to each other. As a result, the second volume area connects the first volume area with the metallic or ceramic open-pored structure of the open-pored third volume area obtained from the coated foam body, which has a greater porosity than the first volume area, in an edge layer area of the third volume area, which forms the second volume area .

The suspension with which the first and second volume areas of the component are formed can be produced in a manner known per se. A suitable liquid with at least one polymeric binder and a proportion of metallic or ceramic powdered solid can be used for this purpose. Gas bubbles can be incorporated into the suspension by mechanical stirring or by another method, for example a procedure as is known from DE 102010039 322 A1. In addition to air, other gases or gas mixtures can also be used, which can also have an inert effect, so that there is no adverse effect on the respective metal or the respective ceramic with which the component was ultimately formed.

Binders already used for such suspensions, e.g. polyvinyl alcohols, can be used as polymeric binders. Defoamers should be avoided in any case. Water can preferably be used as the liquid. However, other liquids are also suitable, which Kings preferably have a lower boiling point than water.

A suspension should preferably be used to form the first and second 5 lumen range are used, which has a viscosity of at least 0.1 mPas. The suspension should preferably also have a shear-thinning flow behavior with a pronounced yield point. The suspension should contain gas bubbles alone or in addition, with a volume fraction of at least 5% and at most 50% of the total volume of the suspension.

Advantageously, the webs of the semi-finished product should be coated with the same metal or the same ceramic that was used to form the suspension for forming the first and second volume areas. It can be a pure metal of a chemical element, but it can also be an alloy. When using alloys, the alloy composition of the coating of the semi-finished product can differ from the alloy composition of the particles used for the suspension.

However, it is also possible for different materials to be used for the coating of the webs of the semi-finished product and for the suspension to form the first and second volume areas. The expansion coefficients of the materials should be in a similar range and the thermal behavior should be similar depending on the sintering temperature. This is the case, for example, when using stainless steel and zirconium oxide ceramics. In this context, similar should be understood to mean deviations of less than 10% from one another. A second volume area can be formed with metal and ceramic material in the composite if the sintering temperatures and thermal expansion coefficients of the different materials allow this.

The suspension for forming the first and second volume area can be filled into at least one recess, depression, opening, which is formed on the semi-finished product, and/or into the interior of a mold that can be attached to the respective semi-finished product, before the thermal treatment is carried out which the component can ultimately be completed. For example, certain surface or edge layer areas of the respective component can be reinforced or connections formed there. A mold can be temporarily connected to the semi-finished product or the 6

Semi-finished product can be inserted into a frame-shaped mold, so that a suspension containing gas bubbles can be filled into at least one gap between the surface of the semi-finished product and the inner wall of the respective mold, in order to form a first volume area there and a second volume area directly next to it by penetration of the suspension into open pores of the semi-finished product to be able to

For this purpose, a mold can completely enclose the semi-finished product. However, it can also be sufficient to fix a molding tool to a partial area of the surface of a semi-finished product and then to fill the suspension there into the gap or a cavity between the surface of the semi-finished product and the inner wall of the molding tool. For example, hollow profiles with a round or square cross-section that can enclose a semi-finished product can be used as a mold. However, corresponding segments of such profiles, such as circular segments, can also be used as forming tools.

It is possible to demould before carrying out the thermal treatment or only after complete sintering.

The penetration depth of the suspension in the pores of the semi-finished product, starting from the surface of the semi-finished product, can be influenced by external forces, which in turn can selectively influence the thickness or width of an edge layer area that forms the second volume area. The thickness or width should be at least 3 mm, starting from the surface of the semi-finished product towards its interior. As already mentioned, this thickness or width can also be selected to be smaller or larger. However, it should be large enough that the three volume areas can be connected to one another sufficiently firmly and a sharp boundary surface between the first and third volume areas can be avoided as far as possible. The thickness or width required for this can be based on the cell width or pore size of the semi-finished product and should be at least a factor of 3 of the cell size or pore size of the semi-finished product.

For this purpose, a semi-finished product alone or a semi-finished product with a mold attached to it can be made to vibrate and/or pressure can be exerted on the suspension. A medium (gas or liquid) that is under pressure above the ambient pressure can be used. 7 zen, whereby the higher pressure acts on the surface of the suspension and the suspension is pressed into open pores of the semi-finished product. In order to use vibrations for this, you can use a vibrating table on which you can place the semi-finished product with suspension and, if necessary, at least one mold.

5 Depending on the amplitude of the oscillations and the duration, the width or thickness of the second volume area can be influenced. This can also be achieved with at least one vibrator attacking a mold or a semi-finished product.

A semi-finished product can be used that has a porosity in the range of 60% to 95% and/or a first and/or second volume area on the component with a porosity in the range of 0% to 55% can be formed with the suspension.

15 A corrosion-resistant FeCrAl alloy can advantageously be used as the metal. Both oxidic and non-oxidic ceramics can be used as ceramic materials.

A component produced according to the invention has a first volume region

20, which is formed with the metal or the ceramic that comes from the suspension. The first volume region has a smaller porosity than the third volume region, which is formed with the open-porous structure of the metallic or ceramic struts of the semi-finished product, the first volume region exclusively with the metal or the ceramic that / from

25 of the suspension contained in the gas bubbles has been obtained, is formed det. The porosity is determined by the number and size of the gas bubbles contained in the suspension. Adjacent to this first volume area, a second volume area is formed, which can also be porous but also impermeable. The second volume range is associated with the Me

BO tall and / or ceramic formed from the coating of the webs of the semi-finished product and the metal or the ceramic of the suspension, these metals and / or ceramics are materially and positively connected to each other. As a result, the second volume area with the metallic or ceramic rule open-porous structure of the open-porous from the coated half

35 tool obtained third volume region having a greater porosity than the first volume region connected. 8th

The third volume area should have a porosity of at least 65% and the porosity in the second volume area, which is arranged between the first and the third volume area, should be smaller than in the first and the third volume area of the component.

A plurality of first and second volume regions, which are arranged at a distance from one another, can be present on a component.

At least one externally accessible connection for electrical energy or the supply and/or removal of a medium from and/or into the component can be formed at least with the first volume region. It can represent a connection as an electrical contact for an electrical resistance heating element. In the case of an electrical resistance heating element, it is advantageous for a first volume region to have sufficient strength. The first volume area can be positively and materially connected to the third volume area via the second volume area and the third volume area can enable an improved heating effect, in particular because of its large specific surface area.

With first and second volume areas, areas can also be formed on a component that can fulfill a dowel function for anchoring elements, e.g. screws.

If a first and a second volume area are formed circumferentially or at least partially circumferentially around the outer edge of a third volume area, a frame can be formed in which the open-pored structure can be held and protected in a form-fitting and material-locking manner.

In addition, the invention can also be used for the production of components that are to be used in lightweight construction, automobile construction, electrical engineering and aerospace.

The invention is to be explained in more detail below using examples.

example 1 9

A metal foam plate with two compact, rectangular direct foam contacts was manufactured as a component as follows. To produce the component, a plate was used as a rough, rectangular metal foam with the dimensions 125 mm x 75 mm x 20 mm as a semi-finished product. In this case, two first volume areas should be formed on two sides arranged opposite one another, so that a square overall shape of the finished component of 125 mm×125 mm×20 mm can be obtained. The coarse foam as a semi-finished product had a cell width of approx. 4.5 mm and a density of around 10% of the metal density of the semi-finished material. The two first volume areas formed solely with the suspension achieved a sinter density of approx. 50% and there an average pore size of between 100 μm and 1500 μm and a porosity of 50% were obtained.

The production of the coarse foam as a semi-finished product was carried out according to the molding process by coating an open-cell polymer foam with the appropriate cell size using the squeeze-rolling process (Schwartzwalder process). preparation that is commercially available from Zschimmer&Schwarz) and additives (e.g. a fatty alcohol preparation, from Zschimmer&Schwarz) to defoam and adjust the rheological properties with water to form a suspension with a solid metal content of about 86% The foam was impregnated with the suspension and squeezed out over the rollers until the desired loading quantity was set on the web surfaces of the foam structure.The coated and dried foam formed the semi-finished product and was then inserted in the middle of a divisible mold so that s a margin of 25 mm width remained on both sides between the inner wall of the mold and the surface of the semi-finished product in areas in which an additional first volume area was to be formed. The mold and the semi-finished product were placed on a te Rüttelplat.

The suspension with which the first and second volume areas are to be formed was produced separately in a batch process. The basis is formed by the same suspension composition of metal powder, organic 10

Binders and rheological additives, but this time without defoamers.

Instead, up to 5% by mass of surfactant (e.g. a fatty alcohol sulphate preparation from Zschimmer & Schwarz) was added as a foaming agent. The mixture was foamed in a glass beaker at a speed of 1000 rpm for 10 minutes, the aim being to increase the volume by about 50%.

The foamed suspension, in which gas bubbles were distributed as homogeneously as possible in the suspension, was then filled with a spatula into the free edge areas between the inner wall of the mold and the surface of the semi-finished product. The flow behavior of the suspension foamed in this way was adjusted in such a way that it becomes flowable when the mold is gently vibrated by the vibrating plate, but remains motionless without the application of external force. In this way, the penetration of the suspension containing gas bubbles into the pores of the coarse metal foam that forms the semi-finished product can be controlled and a composite area of 1 to 2 cell levels (approx. 4.5 mm - 9 mm) can be set as the second volume area . After filling the edge areas of the semi-finished product in which the second volume areas are to be formed, drying took place over a period of approx. 24 hours at approx. 40° C. and the mold could then be removed. For this purpose, it is advisable to use a molding tool that consists of several divisible individual parts, with divided molding tools generally being preferred. After drying, the binder was removed to remove the organic components and the metal was then sintered. It was possible to produce a component that has a first volume area pointing outwards on two opposite sides, the porosity of which is smaller than the porosity of the third volume area, which was predetermined by the porosity of the semi-finished product. Between the first and third volume areas, the second volume area has been formed, to which the first and third volume areas have been connected in a form-fitting and material-locking manner, and the second volume area has no porosity or a smaller porosity than the first volume area. Connections for electrical contacting could be formed with the first volume areas. All three volume ranges have been formed with the same metal 11

example 2

As an alternative to metal components, a ceramic component is to be manufactured using the same principle. For this purpose, a ceramic suspension based on water is prepared. This contains a bimodal SiC grain distribution, produced by mixing SiC powders with an average grain diameter of 0.8 μm and 3.0 μm in a ratio of 70:30; also 0.6% boron (carbide) and 11% of a water-soluble polysaccharide (corresponds to 4% carbon after pyrolysis) as a sintering additive. The suspension is adjusted to a solids content of 78%.

To produce the foamed ceramics, a polyurethane foam with a cell width of 30 ppi (pores per inch) is impregnated with the suspension and the excess suspension is then separated off using a centrifuge. A plate measuring 200 mm×250 mm×10 mm is mentioned as an example, which had two symmetrically arranged rectangular recesses measuring 20 mm×50 mm on the outer edge and was used as a semi-finished product. These recesses, which represent a cavity that at least resembles the interior of a molding tool, were filled with a foamed suspension to form tighter contact terminals. The recesses can be made in the foam body, for example, by laser or water jet cutting, and this should preferably be done before the polymer foam is coated, during which the semi-finished product is produced.

Otherwise, at least approximately the same procedure and consistencies of semi-finished product and suspension as in example 1 were observed. In contrast to the production of the suspension containing foamed gas bubbles, as was used in Example 1, air was introduced into the suspension in the form of gas bubbles using a device as described in DE 10 2010039 322 A1. The ceramic suspension used for impregnating the polymer foams was slightly modified and, in addition to the tenside, a plasticizer (e.g. high-polymer polysaccharide, Zschimmer & Schwarz) was added, which improves the processing properties of the suspension with the first and second volume 12 richly trained, improved. The device consists of a hollow steel cylinder with a length of 182 mm and an external diameter of 70 mm with a wall thickness of 2.9 mm. This cylinder has a connection for the controllable compressed air supply. At the end of the pipe there is a metal disc with a concentric nozzle, which can also be used as a hose connection. The back of the tube is also sealed with a metal disk that has a through-hole with a diameter of 10 mm. Inside the steel cylinder is a porous hollow cylinder with an outer diameter of approx. 25 mm and a wall thickness of approx. 2 mm, clamped between the two covers by sealing rings. The porosity of the stainless steel tube is around 43%.

A static mixer from the SMX series (from Sulzer Chemtech AG) with a diameter of approx. 20 mm is located in the core of the tube. The metal powder suspension is passed through this porous inner tube with the static mixer, while at the same time it is impinged by the compressed air at a pressure of approx. 0.3 MPa and an air volume flow of approx. 600 ml/min. This creates uniform air bubbles in the suspension.

The suspension foamed in this way can be filled into the recesses already formed in advance on the semi-finished product by switching the foaming device on and off. The edge area, which forms the second volume area, should be about 4 mm thick in order to achieve a form-fitting and cohesive bond between the second and third volume area after sintering.

Finally, gentle drying takes place in a drying cabinet at 40 °C for at least 12 hours. After drying, the polymer foam inside the webs of volume 1 is burned out to a temperature of 800° C. under an inert gas atmosphere. The remaining SiC powder structure is pressureless sintered under an argon atmosphere at a temperature of 2100° C., and a component made of SiC according to the invention is thus obtained.

Claims

13

FRAUNHOFER-GESELLSCHAFT...e.V., hollomet GmbH

patent claims

5

1. A method for producing a porous metallic and / or ceramic component that has at least three adjacent volume areas with differing porosity, in which

10 an open-pored foam body, which is formed from a polymeric material, is provided with a metallic coating or a coating formed with metallic or ceramic particles on the surfaces of webs of the foam body in such a way that an open-pored basic structure is retained and

15 on a semi-finished product obtained in this way at given surface areas is a suspension which is formed with metallic or ceramic particles, a liquid and a polymeric binder, in which additional gas bubbles are contained which have been formed in advance, with the surface of the foam body as Semi-finished product in contact and in

20 is brought into a predetermined shape, with part of this suspension penetrating into open pores of the foam body as a semi-finished product in an edge layer region, and subsequent drying with a thermal treatment is carried out in which the liquid contained in the suspension is drained

25 driven, polymeric components are removed and subsequently ei ne sintering is carried out, wherein during the sintering a first volume area with the metal or the ceramic, which comes from the suspension, is formed, which has a smaller porosity, which is exclusively due to the in the sus

BO pension contained gas bubbles has been obtained, and adjacent to this first volume region, a second volume region is formed, which is also porous, and the second volume region with the metal or ceramic from the coating of the webs of the semi-finished product and the metal or the ceramics of the suspension formed

35 has been det, these metals and / or ceramics material and 14 have been positively connected to one another, and thereby the second volume area is connected to the metallic or ceramic open-porous structure of the open-porous third volume area obtained from the coated foam body, which has a greater porosity than the first volume area.

Method according to Claim 1, characterized in that the foam body formed with the polymeric material is coated on its webs to form the semi-finished product with metal by means of a CVD, PVD process, electrolytically or with a suspension containing metallic or ceramic particles, the semi-finished product obtained by coating with a suspension is dried prior to application of the suspension to form the first and second volume area, so that a sufficiently high green strength is achieved to ensure that when a surface area is brought into contact with the gas bubbles-containing Suspension the coated webs have sufficient strength to avoid damage.

Method according to one of the preceding claims, characterized in that the webs of the semi-finished product are coated with the same metal or the same ceramic with which the suspension for forming the first and second volume region was formed.

Method according to one of the preceding claims, characterized in that a suspension is used to form the first and second volume region, which has a viscosity of at least 0.1 mPas and/or in which gas bubbles with a volume fraction of at least 5% up to a maximum of 50% of the total volume of the suspension is used.

Method according to one of the preceding claims, characterized in that the suspension for forming the first and second volume area in at least one recess, depression, opening, which is formed on the semi-finished product, and / or in the interior 15 re an attachable to the respective semi-finished mold is filled. Method according to one of the preceding claims, characterized in that the penetration depth of the suspension in the pores of the semi-finished product is influenced by external forces acting on the surface of the semi-finished product. Method according to the preceding claim, characterized in that the semi-finished product alone or a semi-finished product with a mold attached thereto is made to oscillate and/or pressure is exerted on the suspension. Method according to one of the preceding claims, characterized in that a semi-finished product is used which has a porosity in the range of 60% to 95% and/or with the suspension a first and/or second volume area on the component with a porosity in the range of 0% up to 55% is trained. Method according to one of the preceding claims, characterized in that an FeCrAl alloy is used as the metal. Component produced using a method according to one of the preceding claims, characterized in that the first volume area is formed with the metal or ceramic material which comes from the suspension and which has a smaller porosity, which is exclusively due to the contained in the suspension gas bubbles has been obtained, and a second volume area is formed adjacent to this first volume area, which is also porous or dense, and the second volume area with the metal and/or the ceramic from the coating of the webs of the semi-finished product and the metal and/or or the ceramic of the suspension is formed, these metals and/or ceramics being materially and positively connected to one another, and thereby the second volume area being connected to the metal or ceramic open-pored structure of the semi-finished product, which has a greater porosity than the first volume area - 16 den.

11. Component according to the preceding claim, characterized in that the third volume area has a porosity of at least 65% and the porosity in the second volume area, which is arranged between the first and the third volume area, is smaller than in the first and in the third volume area of the component is.

12. Component according to one of the two preceding claims, characterized in that at least one externally accessible connection for electrical energy or the supply and/or removal of a medium from and/or into the component is connected to at least the first volume region, is trained.

13. Component according to one of the three preceding claims, characterized in that a plurality of first and second volume areas, which are arranged at a distance from one another, are present on a component.

14. Component according to one of the four preceding claims, characterized in that the third volume region has a porosity in the region of 80% to 93%.