METHOD FOR DEPOSITING A METAL MATERIAL ON A CERAMIC OR MINERAL SUBSTRATE USING AN APPLICATION DEVICE

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application is a national stage application, filed under 35 U.S.C. § 371, of International Patent Application PCT/EP 2023/071085, filed on Jul. 28, 2023, which claims the benefit of Luxembourg Patent Application LU502912, filed on Oct. 17, 2022.

BACKGROUND

Laser cladding is an established process for depositing or applying a metal material to the surface of a metal substrate for processing workpieces. In the conventional process, an application device with a laser unit is used for this purpose. The surface of the metal substrate is melted locally at the point of impact by a laser beam emitted by the laser device and directed at the surface. A fine-grained metal material is fed into the resulting localised melt. The feed takes place by transport using an inert carrier gas. The metal powder fed to the localised melt in this way is also melted by the laser beam or the heat of the existing melt of the substrate. Once the molten metal material has solidified, an integral bond is formed between the metal material and the metal substrate. This process can be repeated by moving the metal substrate and/or the application device relative to one another at different points on the metal substrate or can also be carried out over a continuous area of the surface.

However, this conventional process has disadvantages when applying a metal material to a non-metal substrate such as a ceramic substrate or a mineral substrate. Due to the different chemical and physical properties inherent in the material classes, it is challenging to create a bond between metal and ceramic using a laser beam, for example. Due to the generally high melting points of the ceramics, which can lie in a range between 2000 and 3000° C., melting is complex, especially as the required temperatures are sometimes above the boiling point of the metal materials used. As a result, vaporisation of the metal material applied would not be possible. Furthermore, ceramics and metal materials have different expansion coefficients, which are in the range of 4 to 13 10⁻⁶K⁻¹ for ceramics and between 1 and 30 10⁻⁶K⁻¹ for metal materials. This results in the problem of crack and fracture formation in the ceramic substrate during heating due to the brittle fracture tendency of the ceramic, especially during rapid heating and cooling processes, as is the case when using laser radiation. As a result of the high and rapid induced heat and the low thermal conductivity of the ceramic, stresses arise in the ceramic. As ceramics only have a very low deformability even at higher temperatures, it is difficult to relieve these thermal stresses, unlike metal materials. If these stresses exceed the hardness of the material, they lead to breakage. These effects lead to the failure of the component and are irreparable. Another problem is the poor wettability of the ceramic with molten metals due to the so-called “balling effect”.

Various processes are known from the prior art to overcome the problems mentioned. On the one hand, application via physical vapour deposition (PVD) is the most commonly used process. In this process, an active metal such as a metal alloy or a pure metal is transferred into the gas phase and then deposited on the ceramic surface as an adhesion promoter, creating a thin metal layer. The actual metal material can then be applied to this thin metal layer, which acts as an adhesion promoter. This process takes place under vacuum or inert gas conditions. Furthermore, the surface of the ceramic substrate must be thoroughly cleaned before application in order to enable a suitable bond to the ceramic substrate. Metallisation using PVD processes is subject to other limiting factors in addition to cleaning the surface. For example, the size of the substrate to be coated also depends on the size of the available process chamber.

Aerosol jet printing (AJP) is also well known. In this process, the metal material is applied as an aerosol. The aerosol is generated in an ultrasonic or pneumatic atomiser and applied to the substrate at high pressure together with a carrier gas. The disadvantage here is that only layers in the micrometre range can be applied and it is not yet possible to produce layer thicknesses in the millimetre range.

SUMMARY

The disclosure relates to a method for depositing a metal material on a ceramic or mineral substrate using an application device, wherein a high-energy beam from an energy source arranged on the application device is directed onto a surface of the ceramic or mineral substrate, wherein, with the aid of the application device, the metal material is applied to a region of the surface of the ceramic or mineral substrate, wherein the metal material is melted, at least in portions, by the high-energy beam, and therefore, after the metal material has solidified, the metal material is deposited in the form of a material application on the surface of the ceramic or mineral substrate, wherein the high-energy beam impinging on the surface of the ceramic or mineral substrate defines a working region, wherein the position of the working region on the surface can be modified by a relative displacement of the surface of the ceramic or mineral substrate and the energy source.

The method provides an alternative to known processes and offers significant economic and technical advantages.

These advantages are achieved by creating an indentation in the working region on the surface of the ceramic or mineral substrate, wherein the material is applied into the indentation.

By applying the metal material in the indentation, reliable adhesion of the metal material to the ceramic or mineral substrate can be achieved. Advantageously, the method enables freedom of geometry, which also allows 3D geometries to be coated. In addition, isolated, individual areas can be selectively coated without the need for masking or other preliminary work, as is known in prior art methods.

The method also makes it possible to produce a firmly adhering, electrically conductive metal coating without additional flux and with high application rates on ceramic or mineral substrates. In contrast to methods such as PVD, no process chamber that can be flooded with a protective gas or evacuated is required. Fields of application can include implants in medical technology as well as components in the automotive and aerospace sectors. Furthermore, circuit boards for high-performance LED installations, for example, can also be realised. The method can also be used in the production and development of energy storage devices.

The indentation can be created, for example, by removing substrate material from the surface of the substrate. The indentation is advantageously an area of the substrate of which the surface is concave and forms, for example, an elongate channel or is shaped like a spherical dome. The shape of the indentation can advantageously be very different, does not have to be symmetrical and can run in different directions over the surface and also have different cross-sectional areas. The indentation can advantageously also extend to the edge of the substrate, so that the indentation extends over a side edge of the substrate.

The metal material melted by the high-energy radiation can flow in liquid form into the indentation in the surface of the ceramic or mineral substrate, wherein it is bonded to the wall areas and the base area of the indentation by mechanical clamping after solidification and adheres there. As a result, the adhesion of the metal material to the ceramic or mineral substrate can be significantly improved and increased in contrast to the direct application of the metal material to a planar surface. The indentation made can also enable a stable integral bond between the metal material and the ceramic or mineral substrate through diffusion processes and ultimately through reactions at the atomic level—which lead to bonding.

It is possible for the metal material to be applied as a fine-grained powder based on classic laser cladding, or it can be applied as a wire fed via the application device or arranged in the indentation, which is melted by the energy applied.

A ceramic substrate is understood to be a substrate made of a ceramic material. A ceramic material is a material that is synthesised from non-metal inorganic substances at elevated temperatures, which gives it its characteristic properties such as its high melting point, its low electrical conductivity and its brittleness. These include, for example, oxides, nitrides and silicates. In this sense, glass ceramics that have both a polycrystalline and an amorphous phase are also considered to be ceramics in the broadest sense. Glasses can also be used.

A mineral substrate is generally understood to be crystalline substances of a wide range of chemical compositions, such as granite, formed by geological processes.

Advantageously, it is provided that the material application is formed exclusively from the metal material. In this way, the desired material properties of the material application can be predetermined by a suitable choice of metal material. The substrate is therefore not melted when the metal material is heated, or at most only melted superficially, so that no homogeneous melt is formed between the metal material and the substrate.

In an advantageous embodiment, it is provided that the energy source is a laser device emitting a laser beam, wherein the surface is selectively eroded by the laser beam directed onto the surface, so that the indentation is created on the surface by the eroded material. The use of a laser beam is an inexpensive and effective way of creating the indentation in the surface of the ceramic or mineral substrate. In particular, laser devices with high power such as solid-state lasers—including diodes or fibre lasers—but also classic CO₂ lasers can be used as laser device. Due to the high power of the laser radiation impinging on the surface, individual layers or particles can be detached from the surface and selectively eroded. The indentation can be formed as a result of the erosion.

Depending on the specific power and the cross-section of the laser beam, the desired geometric shape of the indentation can be controlled. The erosion and thus the removal of heated material from the ceramic or mineral substrate also prevents heat-induced stress, which could pass into the ceramic or mineral substrate and damage it.

Due to the relative movement of the ceramic or mineral substrate and the application device, the indentation can be repeated at different points on the ceramic or mineral substrate or can also be carried out over a continuous area of the surface. In this way, trench or furrow-like structures as well as any other geometric structure can be produced on the surface of the ceramic or mineral substrate.

In addition to using a laser device, the energy source can also be an electron source emitting an electron beam. This can be particularly advantageous if the metal material is introduced into the indentation as a wire, for example, and melted using an energy source such as an electron beam.

According to an advantageous realisation, it is envisaged that the indentation introduced into the surface of the ceramic or mineral substrate is a v-shaped indentation with an acute angle. Preferably, the indentation has a v-shaped geometry so that the molten metal material can flow easily into the indentation. After solidification, the metal material can be flush with the surface, resulting in a triangular indentation in cross-section. In an alternative embodiment, the metal material can also form an elevation on the surface, resulting in a substantially “cake-shaped” cross-section. In addition, the metal material can also only partially fill the indentation after solidification.

In addition to a v-shaped indentation, the indentation can also have configurations deviating from a v-shape and, in particular, a u-shaped configuration. Furthermore, embodiments of the indentation with a rectangular, trapezoidal or other polygonal cross-section are also possible. The indentation can also have undercuts.

The aforementioned indentation allows the molten metal material to flow into the indentation and at the same time optimises the wetting of the surface by the metal material.

It is advantageously provided that the molten metal material introduced into the indentation has a contact angle θ<90°. The contact angle refers here to the angle that a drop of liquid on the surface of a solid forms to this surface. This angle can be described by Young's equation. In the present case, the metal material applied and melted onto the surface of the ceramic or mineral substrate can be regarded as a liquid and the ceramic or mineral substrate as a solid.

The size of the contact angle between the liquid and the solid is a function, among other things, of the interaction between the two phases at their contact surface. The wetting of the surface by the drop of liquid can be described as a function of the cohesive forces within the drop and the adhesive forces of the drop of liquid against the surface. If the cohesive forces within the drop of liquid outweigh the adhesive forces between the drop of liquid and the surface, the drop of liquid will assume the shape of a sphere and only touch the surface at a small contact area.

In the case of a liquid metal on a ceramic or mineral substrate surface, the cohesive forces far outweigh the adhesive forces, so that a sphere with a contact angle θ>90° forms on a planar surface. The following is true here: the smaller the contact angle, the larger the contact area.

The contact angle θ should preferably be >90° in order to achieve the best possible connection and thus the largest possible contact surface of the drop of liquid to the ceramic or mineral substrate.

The indentation forms a geometric shape on the surface of the substrate. The design of this indentation, for example with a v-shaped design with an acute angle, reduces the contact angle of the metal material flowing into the indentation or melted there to below 90°, thereby optimising the wettability of the surface of the indentation. Thus, by artificially reducing the contact angle through the geometric design of the indentation, an optimum bond between the metal material and the ceramic or mineral substrate can be achieved. As already mentioned, the indentation can also have other configurations that deviate from a V-shape, as long as the selected configuration creates a suitable angle between the opposing surfaces in an upper region of the groove.

The small contact angle and thus the largest possible surface connection between the two phases is maintained even after the metal material has hardened, which means that a continuous connection can be achieved with as few bubbles or cavities as possible.

It is also possible that an adhesion promoter is used to improve the adhesion between the applied metal material and the ceramic or mineral substrate. An adhesion promoter can, for example, be a metal or a metal alloy that is applied directly to the surface of the ceramic or mineral substrate. Preferably, its properties are selected in such a way that it has an optimum bond to the ceramic or mineral substrate on the one hand and to the metal material applied to the adhesion promoter on the other. In this way, the bonding of the metal material to the ceramic or mineral substrate can be improved. The adhesion promoter is also applied in the indentation.

To this end, the adhesion promoter preferably has a low contact angle so that an optimum bond can be achieved. In the case of metal adhesion promoters, the bond between the adhesion promoter and the metal material applied to it can also be strengthened by a form-fit connection in the form of a metal bond and, in particular, by the formation of an alloy at the interface of the two metals.

The adhesion promoter can also be adapted to the low coefficient of thermal expansion of the ceramic or mineral substrate to favour the bonding process. Ductile alloy elements can be used for this purpose, which can compensate for the thermally induced stresses due to the different coefficients of thermal expansion in the boundary layer.

Copper or titanium, for example, can be used as an adhesion promoter.

It is preferable that the erosion of an area of the surface by the laser beam and the application of the metal material are carried out simultaneously. This makes it possible for the process chain for applying the metal material—and possibly the prior application of the adhesion promoter—to be carried out in a single process step. For this purpose, a mixture of an inert carrier gas and a fine-grained metal material can be supplied, similarly to laser cladding. The metal material melted by the laser beam, for example, can also be melted by the laser beam or the heat of the ceramic or mineral substrate and can flow into the indentation before solidification.

Furthermore, it is possible and provided for the indentation to be produced in a separate step before the metal material is applied. For this purpose, the indentation can be carved out in a separate process step by means of the laser radiation directed onto the surface, while the metal material is introduced into the indentation and melted in a second subsequent process step. For this purpose, a device with a laser device can be used to create the indentation, or it can be created using the application device

The indentation can also be produced by an etching process with an etching compound or by other mechanical processes. Furthermore, the ceramic or mineral substrate can also be provided with the desired indentations during production, for example by using suitable moulds.

In an advantageous embodiment, it is envisaged that the laser beam generates a working region of between 0.2 and 3 mm. This makes it possible to form indentations with an application of metal structures over a large area. The dimensions of the indentation are substantially determined by the area of the working region and thus by the cross-section of the laser beam and the power of the laser beam.

In an advantageous realisation, it is envisaged that an application device with a powder nozzle is used to generate a coaxial continuous powder gas jet. The powder nozzle can have a circumferential annular gap surrounding the emitted laser beam, or multi-jet nozzles can also be used, which have several discrete powder nozzles arranged in such a way that the injected metal powder meets at a common focus.

Advantageously, a metal oxide and/or a nitride and/or a silicate is used as the ceramic substrate. Preferably, aluminium oxide Al₂O₃ can be used as the ceramic substrate.

Advantageously, it is optionally provided that copper and/or titanium and/or aluminium and/or vanadium and/or silver and/or iron and/or gold and/or an alloy thereof is used as the metal material. Preferably, titanium or a titanium alloy such as Ti-6Al-4V can be used as the metal material.

Advantageously, it is provided that the metal material is electrically conductive and that the material application is electrically conductive, wherein an electrical resistance of the material application corresponds to an electrical resistance of the metal material. In this way, highly conductive conductor tracks can be applied to the non-conductive substrate.

Advantageously, it is provided that the ceramic or mineral substrate is electrically non-conductive. In this way, for example, circuit arrangements made of the metal material can be arranged on the substrate and are electrically insulated from each other by the substrate.

Advantageous embodiments of the method for depositing a metal material on a ceramic or mineral substrate using an application device are illustrated in the following drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a method for depositing a metal material on a ceramic or mineral substrate using an application device, wherein a laser beam is directed onto the surface of the ceramic or mineral substrate,

FIG. 2 shows the method from FIG. 1, wherein the surface of the ceramic or mineral substrate is selectively removed to create an indentation,

FIG. 3 shows the method from step 2, wherein a metal material is applied to the resulting indentation,

FIG. 4 shows a comparison of a contact angle between a drop of liquid on a planar surface and a drop of liquid in the indentation,

FIG. 5 shows a circuit board produced by the method with applied conductor tracks made of the metal material, and

FIG. 6 is a sectional drawing along line of section VI-VI from FIG. 5.

DETAILED DESCRIPTION

FIGS. 1 to 3 schematically illustrate a variant of the method for depositing a metal material on a ceramic or mineral substrate using an application device.

FIG. 1 shows an application device 1 with an energy source 2 in the form of a laser device 3. The laser device 3 is used to emit a laser beam 4 onto the surface 5 of a ceramic or mineral substrate 6 in the form of a plate. The laser beam 4 directed onto the surface 5 defines a working region 7 on the surface. The application device 1 also has a powder nozzle 8 arranged on the application device 1, with which a continuous powder gas jet 9 of a carrier gas and a finely distributed metal material is directed along a powder gas path 10 onto the surface 5 of the ceramic or mineral substrate 6 in the area of the working region 7. The laser beam 4 directed onto the surface 5 heats the ceramic or mineral substrate 6 within an effective range 11.

Due to the high power density of the laser beam 4, the surface 5 of the ceramic or mineral substrate 6 is eroded piece by piece in the working region 7 and removed from the surface 5. The removal of the material 12 prevents the formation of cracks caused by the heat, which could lead to the failure of the ceramic or mineral substrate 6. By removing the material 12, an indentation 13 is carved out on the surface 5 of the ceramic or mineral substrate 6. FIG. 2 shows the method step of forming the indentation 13.

Metal material 14 introduced into the indentation 13 through the powder nozzle 8 is melted by the incident laser radiation 4 and flows into the indentation 13, where it solidifies and forms a layer of material in the indentation 13. This method step is shown in FIG. 3.

FIG. 4 shows a schematic view of the advantage of the method. On the left-hand side, the application of a molten metal material 14 is shown as a drop of liquid on a planar ceramic or mineral substrate 6. The wetting of the surface 5 by the drop of liquid depends here on the cohesive forces within the drop of liquid and the adhesive forces of the drop of liquid against the surface. If, as in the case of a metal material 14, the cohesive forces within the drop of liquid outweigh the adhesive forces, the drop of liquid will assume the shape of a sphere and only touch the surface at a small contact area 15. In this case, the contact angle θ16—the angle that a drop of liquid on the surface of a solid forms with the surface—is greater than 90°.

Due to the v-shaped geometry of the indentation 13 with an acute angle, on the other hand, the contact angle θ16 of a drop of liquid in the indentation 14 is always less than 90° C., whereby complete wetting of the side areas and the base area of the indentation 13 is achieved. The contact angle θ16 of a drop of liquid in the indentation is shown on the right-hand side in FIG. 3.

FIG. 5 shows a circuit board 17 produced using the method with applied conductor tracks 18 made of the metal material 14, while FIG. 6 shows a sectional drawing of the circuit board 17 along the line of section VI-VI from FIG. 5. The v-shaped indentations 13 can be recognised.

LIST OF REFERENCE SIGNS

• • 1 application device
  • 2 energy source
  • 3 laser device
  • 4 laser beam
  • 5 surface of the ceramic or mineral substrate
  • 6 ceramic or mineral substrate
  • 7 working region
  • 8 powder nozzle
  • 9 powder gas jet
  • 11 powder gas path
  • 11 effective range
  • 12 material removed from the surface
  • 13 indentation
  • 14 metal material
  • 15 contact surface between metal material and the surface of the ceramic or mineral substrate
  • 16 contact angle
  • 17 circuit board
  • 18 conductor track