Method for producing a metal-matrix composite powder

Abstract

The invention relates to a method for producing a metal-matrix composite powder, in which method a metal-matrix composite material is produced by introducing ceramic particles into a molten metal matrix and stirring and a semi-finished product in the form of a melt is formed therefrom, which melt is sprayed or atomized, wherein the metal-matrix composite material is brought into a container in a flowable state or is melted in a container, in which the metal-matrix composite material remains for a dwell time until a molding compound or a molding body having a lower and an upper region forms therein, wherein, because of gravity and / or because of an electromagnetic field applied to or around the container, the lower region has a different proportion of the ceramic particles than the upper region, and wherein either the lower or the upper region has a ceramic particle proportion of at least 30 wt.%, and subsequently the upper region is separated from the region, and wherein the region having the ceramic particle proportion of at least 30 wt.% forms the semi-finished product or is molded or remolded to form the semi-finished product.

Description

[0001] Process for producing a metal matrix composite powder

[0002] The present invention relates to a method for producing a metal matrix composite powder, in which a metal matrix composite material is produced by introducing ceramic particles into a molten metal matrix and stirring the resulting metal matrix ceramic mass, and a semi-finished product is formed from the metal matrix composite material, which is a melt or from which a melt is formed which is atomized or atomized to form the metal matrix composite powder.

[0003] Monolithic metal powders are known in the prior art. For example, EP 3 216 545 A1 describes a precious metal powder produced by an atomization process. The starting material can be melted, for example, inductively and then gas-atomized. In gas atomization, the starting material is melted under an air or protective gas bell, or in a vacuum. The molten metal is then conveyed through a nozzle, where an atomization gas impacts the flowing molten metal at high speed, breaking it up. This creates spherical metal droplets that then quickly solidify into spherical metal particles. Alternatively, plasma atomization or centrifugal atomization can be used.Furthermore, it is possible to gradually melt the free end of a rotating metal rod using an electron beam, an arc, or a plasma. The resulting molten droplets are ejected and solidify into spherical metal particles. The resulting precious metal powder can be used, for example, to produce components in an additive manufacturing process. However, the conventional precious metal powder is not suitable for applications requiring a particularly hard powder.

[0004] A powder that is significantly more mechanically resilient can be produced using the process proposed in DE 10 2011 120 540 A1. This process describes the production of a sintered powder from a metal matrix composite material that can be used, for example, to manufacture a brake disc for a motor vehicle. First, a metal alloy is melted. A gas jet directed at this melt is then used to generate a directed melt droplet jet. At the same time, ceramic particles are discharged as a directed particle jet. The melt droplet jet and the particle jet are discharged in such a way that they collide at an angle in an impact zone, with the particles of the particle jet entraining melt droplets from the melt droplet jet, resulting in the ceramic particles being coated with the molten metal alloy.

[0005] The problem with the process known from DE 10 2011 120 540 A1 is that aluminum, for example, adheres very poorly to or wets ceramic particles, such as SiC. A certain degree of frictional connection between the ceramic particle and the metal coating only occurs at the ceramic particle surface due to the particle surface roughness.

[0006] EP 0 529 993 A1 discloses a process for producing an aluminum matrix composite powder comprising ceramic particles uniformly distributed in an aluminum or aluminum alloy matrix. To produce this powder, a melt of aluminum or an aluminum alloy is uniformly mixed with ceramic particles by mechanical stirring and then atomized by compressed air, the resulting droplets freezing very quickly, at a solidification rate of at least 10 2K / s cooled.

[0007] The powder known from EP 0 529 993 A1 is intended, for example, to be used as a grinding powder. To provide a suitable grinding powder, it must contain a high proportion of hard ceramic particles in addition to the comparatively very soft aluminum content. Although this document generally refers to a ceramic content in the powder in the range of 1 to 40 wt.%, the exemplary embodiments indicate ceramic contents of up to 25% in the aluminum matrix composite materials used, which is why the ceramic content in the produced powder cannot be higher than 25 wt.%.

[0008] It is therefore the object of the present invention to provide a process for producing a metal matrix composite powder comprising a metal matrix and ceramic particles, in which there is good adhesion of the metal matrix to the ceramic particles and whose ceramic particle content can be reliably adjusted to at least 30 wt.%.

[0009] This object is achieved by a method for producing a metal matrix composite powder, in which a metal matrix composite material is produced by introducing ceramic particles into a molten metal matrix and stirring the resulting metal matrix ceramic mass, and a semi-finished product is formed from the metal matrix composite material, which is a melt or from which a melt is formed which is atomized or atomized, wherein the metal matrix composite material is brought into a container in a flowable state or is melted in a container, wherein the metal matrix composite material remains in the container for a residence time until a molding compound or a molded body with a lower region and an upper region is formed in the container,wherein the lower region has a different proportion of ceramic particles than the upper region due to gravity and / or due to an electromagnetic field applied to or around the container, and wherein either the lower region or the upper region has a proportion of ceramic particles of at least 30 wt.%, and subsequently the upper region is separated from the lower region, wherein the one of the upper or lower region which has the proportion of ceramic particles of at least 30 wt.% forms the semi-finished product or is formed or primary formed into the semi-finished product.

[0010] In the present invention, the term "ceramic" refers to a variety of materials. Typical ceramic particles that can be used in the present invention are, for example, oxides such as Al2O3 or SiO2, silicates or germanates such as mullite, carbides such as SiC or TiC, nitrides such as Si3N4, AlN or BN, and borides such as TiB2. The ceramic particles are typically produced by grinding a starting ceramic material and thus have a spherical shape with a rugged surface. The ceramic particles preferably have an average diameter of 3 to 150 pm, preferably 5 to 60 pm, particularly preferably 20 to 50 pm. The material used to form the metal matrix in the present invention is preferably aluminum or an aluminum alloy. In principle, however, other metals or metal alloys are also suitable as a metal matrix.Alloy components of the respective metal alloy can be, for example, Al, Si, Mg, Fe, Ni, Cr and / or Mn.

[0011] In addition to the metal matrix and the ceramic particles, the metal matrix composite material used in the present invention may also contain impurities, which, however, should not exceed a total of 0.1 wt.%.

[0012] In the present invention, the term “container” is understood to mean, for example, a casting mold or a crucible, such as a melting pot.

[0013] In the present invention, the semi-finished product can be solid or liquid.

[0014] If, in the present invention, a melt is formed from the semi-finished product, the melting of the semi-finished product, which may be present, for example, as at least one ingot, can be carried out completely, for example in a crucible, or locally, for example by means of induction, arc or plasma.

[0015] If the melt is atomized in the present invention, this is preferably done by means of gas atomization. If the melt is atomized in the present invention, droplets of the melt can be atomized, for example, using ultrasound.

[0016] The process according to the invention produces a metal matrix composite powder with an average powder particle diameter of 10 pm to 80 pm. However, the metal matrix composite powder can also contain powder particles with a powder particle diameter of less than 10 pm. Furthermore, the particle diameter of individual powder particles in the metal matrix composite powder can be up to 250 pm.

[0017] The metal matrix composite powder produced according to the invention contains

[0018] Powder particles are essentially spherical or flimsy. In the metal matrix composite powder, any ceramic particles contained within each powder particle are enclosed within the metal matrix.

[0019] Preferably, in the metal matrix composite powder produced according to the invention, the ceramic particles are uniformly encased by the metal matrix. However, it is also possible for at least one ceramic particle to be located in an edge region of the respective powder particle. Furthermore, it is possible for more than one ceramic particle to be enclosed by the metal matrix in each of the powder particles.

[0020] Due to the production of the metal matrix composite material used in the process according to the invention by introducing the ceramic particles into the molten metal matrix and stirring the resulting metal matrix-ceramic mass, a force-fit and form-fit connection is achieved between the ceramic particles and the metal matrix. The force-fit connection arises from the ceramic particles being "clamped" by the larger thermal expansion coefficient of the metal matrix, while the material bond results from the ceramic particles being completely encased by the metal matrix. This results in particularly good adhesion of the metal matrix to the ceramic particles in the metal matrix composite material, which is maintained in the metal matrix composite powder.

[0021] Preferably, the process according to the invention for producing the metal matrix composite material uses a process as described in WO 2022 / 214890 A1. This process results in excellent wetting of the ceramic particles with the metal matrix, with stable adhesion of the metal matrix material to the ceramic particles, which is maintained even after atomization or atomization of the melt in the metal matrix composite powder.

[0022] The process according to the invention is characterized by the fact that the concentration of the ceramic particles reliably coated with the metal matrix material in the melt is increased prior to atomization or spraying compared to other processes. This is achieved according to the invention by introducing the stirred melt containing the ceramic particles into the container, in which a specific distribution of the ceramic particles results depending on the density of the ceramic particles and / or the influence of an electromagnetic field applied to or around the container.

[0023] If the ceramic particles are heavier than the metal matrix, a majority of the ceramic particles sink to the bottom of the container during the residence time. This applies, for example, if the metal matrix material is aluminum, which has a density of approximately 2.7 g / cm 3and as ceramic particles silicon carbide particles with a density of 3.21 g / cm 3 and / or aluminum nitride particles with a density of 3.26 g / cm 3 and / or silicon nitride particles with a density of 3.17 g / cm 3 and / or aluminum oxide particles with a density of 3.95 g / cm 3 be used.

[0024] If the ceramic particles are lighter than the metal matrix material, as is the case with aluminum as a metal matrix material and ceramic particles made of boron nitride, which have a density of 2.1 g / cm 3 the ceramic particles will primarily accumulate in the upper area of ​​the container during the residence time.

[0025] This sinking or rising of the respective material in the container can be further enhanced by the influence of an electromagnetic field. The electromagnetic field can be used to control the particle movement of the metal matrix particles in the container, allowing the metal matrix particles to be moved in a preferred direction, such as toward the bottom of the container. For this purpose, it is advisable to construct the container from an electrically and / or magnetically conductive material, such as graphite.

[0026] By subsequently separating the upper region from the lower region of the molded body formed in the container or the molding compound formed in the mold, the region from the upper region and the lower region that has a ceramic particle content of at least 30 wt.%, i.e., the region with the increased ceramic particle concentration, can be selected as the semi-finished product and used for further processing. During this further processing, either the upper region or the lower region is used directly as the semi-finished product for the subsequent atomization or spraying, or it is reshaped or pre-shaped into the semi-finished product, provided that the ceramic particles sink into a container designed as a casting mold.If the ceramic particles have settled in a container designed as a crucible and the material with a higher concentration of ceramic particles is still molten, it can be poured into a mold to solidify.

[0027] For example, the metal matrix composite powder produced using the method according to the invention can be used for additive manufacturing processes. A component can be built up layer by layer using the metal matrix composite powder.

[0028] However, the metal matrix composite powder produced according to the invention is also suitable for other applications. For example, the metal matrix composite powder can be used for coatings, e.g., in laser-, arc-, or plasma-assisted coating processes. In particular, the metal matrix composite powder produced according to the invention is suitable for at least partially coating engines that are essentially made of aluminum. Since the metal matrix composite powder is significantly more wear-resistant than conventional aluminum due to the ceramic particles it contains, the metal matrix composite powder coating results in less wear, for example, at points where the engine is suspended from body parts, compared to a stainless steel coating of the engine.In addition, aluminum engines coated with the metal matrix composite powder produced according to the invention are much better recyclable than aluminum engines coated with stainless steel due to the similarity of the materials.

[0029] The complete coating of the ceramic particles by the metal matrix material achieved by the process according to the invention results in the powder particles of the metal matrix composite powder being mechanically highly stable due to the internal ceramic particles, but relatively soft on the outside. This makes the metal matrix composite powder according to the invention also well-suited as a grinding or cutting powder. Due to the relatively soft coating of the ceramic particles, for example, a nozzle used to spray the grinding or cutting powder is not damaged. While the coating wears away quickly when the metal matrix composite powder comes into contact with the material to be ground or cut, the excellent grinding and cutting properties of the ceramic particles can be fully utilized.Based on the molded body(s) / molding compound formed in the container, the separated molded body region with the larger ceramic particle content can, for example, be melted again during subsequent processing once a molded body has been formed in the container. The resulting melt serves as a semi-finished product and is atomized or atomized to form the metal matrix composite powder. Alternatively, the liquid molding compound with the higher ceramic particle content can be poured off to solidify into a molded body, whereby no subsequent division of the semi-finished product is necessary.

[0030] In the process according to the invention, the semi-finished product can be completely or partially melted again before atomizing or spraying.

[0031] The remelting of the semi-finished product and the immediately subsequent atomization or spraying can be carried out gradually. In such a case, it is advantageous if the semi-finished product is rod- or wire-shaped. This can be achieved in the process according to the invention by appropriate reshaping or primary forming of the semi-finished product.

[0032] Alternatively, during further processing, the flowable molding compound from the container can be kept in the melt state and at least partially sprayed or atomized immediately as a semi-finished product.

[0033] In an advantageous embodiment of the present invention, the separation of the upper region from the lower region of a shaped body formed in the container can be carried out mechanically, for example by breaking off or cutting.

[0034] If the molding compound in the container has not yet solidified, in another advantageous embodiment of the present invention the upper region can be separated from the lower region of the molding compound by casting technology. For example, a drain can be provided at the bottom of the container through which the lower region of the molding compound can drain. If the lower region has a higher ceramic particle content than the upper region, the molding compound draining out at the bottom can be kept hot and immediately atomized to form the metal matrix composite powder. However, the draining lower region can also run into a rod-shaped casting mold, for example, solidify therein to form the semi-finished product, and then the semi-finished product can be atomized or atomized to form the metal matrix composite powder.

[0035] Alternatively, the upper area can be skimmed off from the lower area.

[0036] Despite the high proportion of ceramic particle reinforcement, the metal matrix composite powder produced in the process according to the invention can also contain powder particles that contain no ceramic particles, i.e., are formed solely from the metal matrix. These metal powder particles are therefore unreinforced. However, the proportion of such unreinforced metal powder particles can be adjusted in the process according to the invention by appropriately adjusting the process parameters. Furthermore, such unreinforced metal powder particles can be filtered out of the metal matrix composite powder, for example, by subsequently passing the metal matrix composite powder through an air stream and / or thermally using infrared and camera technology.

[0037] Preferred embodiments of the present invention are explained in more detail below with reference to figures, wherein Figures 1a to 1f schematically show steps of an embodiment of the method according to the invention with mechanical separation of regions of a molded body produced in a container; Figures 2a to 2e schematically show steps of a further embodiment of the method according to the invention with casting-technical separation of regions of a molding compound produced in a container; and Figures 3a to 3d schematically show steps of yet another embodiment of the method according to the invention with casting-technical separation of regions of a molding compound produced in a container and powder particle filtration.

[0038] Figures 1a to 1f schematically show steps of an embodiment of the method according to the invention. In step 1a, a metal matrix composite material 1 is first produced. In a device 1, ceramic particles 3 are introduced into a metal matrix 2 in the form of a melt, which in the illustrated embodiment is an aluminum or aluminum alloy matrix, by stirring using at least one stirrer 4. As shown in Figure 1a, the melt can flow in an inclined channel 5. As further shown in Figure 1a, at least one basin 6 can be formed in the channel 5, into which basin the metal matrix 2, in the form of a melt, flows with the ceramic particles 3 introduced therein and into which the respective stirrer 4 is immersed for stirring.At the end of the groove 5 there is a metal matrix composite material 7 in which the ceramic particles 3 are homogeneously incorporated into the metal matrix 2 and are surrounded on all sides by the metal matrix 2.

[0039] In the embodiment shown, the metal matrix composite material 7 is still flowable at the end of the channel 5, i.e., in the illustrated embodiment, it is a so-called AMC (aluminum matrix composite) melt. In another embodiment of the invention, the metal matrix composite material 7 has cooled to one or more ingots, which are subsequently remelted.

[0040] The flowable metal matrix composite material 7 is poured into a preferably heatable and / or insulated container 8, as shown schematically in Figure 1b. If the metal matrix composite material 7 is in the form of at least one ingot, it is melted in a heated container 8.

[0041] The container 8 is shown only schematically in the figures and, in reality, preferably has a significantly greater depth t than width b. For example, the width b can be 10 mm and the depth 1,700 mm.

[0042] The molten metal matrix composite material 7 remains in the container 8 for a residence time. The metal matrix composite material 7 can be kept in the molten state in the container 8 at a temperature above the solidus temperature. Since, as shown in the exemplary embodiment shown, the ceramic particles 3 have a greater mass than the metal matrix 2, they settle in a lower region 81 within the container 8 during the residence time. This means that they sink toward the bottom of the container 8. Within an upper region 82 within the container 8, the proportion of ceramic particles 3 is then correspondingly lower than in the lower region 81. The lower region 81 forms a highly particle-reinforced metal matrix composite material melt, while in the upper region 82 an almost unreinforced to unreinforced metal matrix or metal matrix alloy forms.In the lower region 81, the proportion of ceramic particles 3 is at least 30 wt.%. In other, not shown, embodiments of the present invention, in which the ceramic particles 3 are lighter than the metal matrix 2, the proportion of ceramic particles 3 in the upper region 82 is higher, in this case at least 30 wt.%.

[0043] In the process step shown in Figure 1b, the metal matrix composite material 7 remains in the container 8 until it has solidified into a shaped body 10. The shaped body 10 is then removed from the container 8, as shown schematically in Figure 1c. The shaped body 10 can, for example, have the shape of a cylinder or a rod.

[0044] As schematically illustrated in Figure 1d, the upper region 82 is subsequently mechanically separated from the lower region 81 of the molded body 10. The mechanical separation can be achieved by a suitable separation method, for example by breaking the molded body 10, e.g., by cracking the lower region 81 from the upper region 82, or by means of a tool.

[0045] The separated region which has a proportion of ceramic particles 3 of at least 30% by weight, ie in the exemplary embodiment shown the separated lower region 81, is then processed, as schematically shown in Figure 1e, into a semi-finished product 811 in the form of a rod or wire. For this purpose, forming, such as rolling, rotary swaging or extrusion, or also primary forming, such as casting, can be used. The rod or wire produced has, for example, a diameter in a range from 1 mm to 5 cm, preferably in a range from 1 mm to 2 cm, more preferably in a range from 1 mm to 1 cm, particularly preferably in a range from 1 mm to 3.6 mm, for example in a range from 1 mm to 2 mm.Since a rod or wire of limited length is produced during forming, it is advantageous for the continuous execution of the subsequent process steps if several such rods or wires are joined, for example by friction welding or by means of a laser, to form a longer rod or wire, which is then used as semi-finished product 811.

[0046] The semi-finished product 811 has the advantage that the concentration of the ceramic particles 3 is precisely defined. In the illustrated embodiment, the proportion of the ceramic particles 3 in the semi-finished product 811 is at least 30 wt.%.

[0047] The semifinished product 811 is atomized in a subsequent process step, which is shown schematically in Figure 1f. A rod or wire feeding process is used for this purpose. A beginning of the semifinished product 811, in this case a rod or wire beginning, is fed continuously or in pulsed fashion to a melting device 11, which can be, for example, an induction coil or a plasma torch. The melting device 11 melts the respective rod or wire beginning. The rod- or wire-shaped semifinished product 811 is thus only melted locally and fed (semi-)continuously. This melting of the semifinished product 811 can be carried out in a protective gas atmosphere.

[0048] The resulting semi-finished product melt 811' is atomized immediately after melting in an atomizer 12, such as a cyclone separator, assisted by a compressed gas or pressurized water jet. In the atomizer 12, which is also referred to as an atomizer, the melt is atomized with compressed gas or pressurized water.

[0049] Alternatively, the semi-finished product melt 811 ' can be atomized.

[0050] Alternatively, metal matrix composite material ingots can be melted in the container 8, whereupon the molten metal matrix composite material 7 formed therefrom is left to stand in the container 8 for a residence time and then - insofar as the ceramic particles 3 have a greater mass than the metal matrix 2 - is skimmed off from the top of the container 8. The skimmed melt corresponds to the upper region 82 described above. The melt remaining in the container 8, which is more highly concentrated with the ceramic particles 3 than the skimmed melt and corresponds to the lower region 81 described above, is then poured into an unheated mold, in which this melt solidifies. After a certain residence time in the container 8, a maximum concentration of the ceramic particles 3 is reached in the melt more highly concentrated with the ceramic particles 3.Accordingly, the mold into which this melt is poured contains a material highly reinforced with ceramic particles 3, which can then be remelted and then atomized or sprayed. Alternatively, the flowable molding compound with the high ceramic particle content can also be directly atomized or sprayed.

[0051] The metal matrix composite powder 14 resulting from atomization or spraying contains a high proportion of at least 30 wt.% of ceramic particles 3 coated with the metal matrix 2. One metal matrix composite powder particle can contain one or more of the ceramic particles 3. However, the metal matrix composite powder 14 can also contain metal powder particles consisting only of the metal matrix 2. The metal matrix composite powder 14 is collected, for example, in a powder collection canister 13.

[0052] Figures 2a to 2e schematically show steps of a further embodiment of the method according to the invention. As in the method step shown in Figure 1a, in the method step shown in Figure 2a, a metal matrix composite material 1 is first produced. In a device 1, ceramic particles 3 are introduced into a metal matrix 2 in the form of a melt by stirring using at least one stirrer 4. As shown in Figure 2a, the melt can flow in an inclined channel 5. As further shown in Figure 2a, at least one basin 6 can be formed in the channel 5, into which basin the melt from the metal matrix 2 with the ceramic particles 3 introduced therein flows and into which the respective stirrer 4 is immersed for stirring. At the end of the groove 5 there is a metal matrix composite material 7 in which the ceramic particles 3 are homogeneously incorporated into the metal matrix 2 and are surrounded on all sides by the metal matrix 2.

[0053] In the process step shown in Figure 2b, the flowable metal matrix composite material 7 is fed into a container 8', in which it is kept flowable by continuous heating and / or by delaying cooling in the container 8'. Particularly preferably, the molding compound is even superheated in the container 8'. The metal matrix composite material 7 remains in the container 8' for a residence time. If the ceramic particles 3 have a greater mass than the metal matrix 2, the ceramic particles 3 sink into a lower region 81' of a molding compound formed in the container 8'. This results in a sedimentation of the ceramic particles 3 coated with the metal matrix material in the lower region 81. In the lower region 81', the proportion of ceramic particles 3 is thus higher than the proportion of ceramic particles 3 in an upper region 82' of the molding compound in the container 8', which upper region 82' lies above the lower region 81'.In the lower region 81' the proportion of the ceramic particles 3 is at least 30 wt.%.

[0054] Calculations and tests on the sedimentation of the ceramic particles 3 coated with the metal matrix 2 allow a calculation of the proportion of the ceramic particles 3 as a function of a height h within the molding compound in the container 8' and the residence time of the metal matrix composite material 7 in the container 8'. This makes it possible, for example, to determine the size of the lower region 81' and the size of the upper region 82', i.e., in this case, how much of the melt can be drained downwards or how much of the melt must be removed at the top.

[0055] The lower region 81' can, for example, be half, one-third, or one-quarter of the total molding compound contained in the container 8'. In the lower region 81', the proportion of ceramic particles 3 can be almost twice as high as in the upper region 82'.

[0056] In a subsequent process step, schematically illustrated in Figure 2c, the lower region 81' is drained from the container 8'. In the embodiment shown, the melt of the upper region 82', which is only weakly reinforced with the ceramic particles 3, is retained in the container 8'. The drained lower region 81' of the molding compound flows, as shown in Figure 2d, into a crucible 15 of a continuous casting device 16.

[0057] Alternatively, the upper portion 82' can also be skimmed off from the container 8' before the lower portion 8T is drained into the crucible 15.

[0058] The material discharged from the container 8' is reheated in the crucible 15. The reheated material then exits an outlet of the crucible 15. This exit occurs so slowly that the discharged molding compound solidifies upon exiting the crucible 15.

[0059] If ceramic particles 3 having a lower mass than the metal matrix 2 are used in the process according to the invention, more ceramic particles 3 are present in an upper region 82' within the container 8' after the residence time. In this case, first the lower region 81' with the lower ceramic particle concentration is drained from the container 8', and then the upper region 82' is drained into the crucible 15.

[0060] The outlet of the crucible 15 is connected to an optionally cooled mold 23. With the continuous casting device 16, a shaped body produced from the lower region 8T of the molding compound after cooling is formed into a rod-shaped or other specially shaped semi-finished product 812 with a cross-section in a range of 1 mm to 5 cm, preferably in a range of 1 mm to 2 cm, preferably in a range of 1 mm to 1 cm, particularly preferably in a range of 1 mm to 3.6 mm, for example in a range of 1 mm to 2 mm. The semi-finished product 812 is withdrawn mechanically via rollers 24 in a withdrawal direction Z.

[0061] The semifinished product 812 is atomized in a subsequent process step, shown schematically in Figure 2e. For this purpose, one end of the semifinished product 812 is continuously melted locally in a melting device 11, which can be, for example, an induction coil or a plasma torch. The resulting semifinished product melt 812' is atomized in an atomizer 12, such as a cyclone separator, assisted by a compressed gas or pressurized water jet.

[0062] Alternatively, the semi-finished melt 812' can be atomized drop by drop, for example.

[0063] The resulting metal matrix composite powder 14 contains a high proportion of at least 30 wt.% of the ceramic particles 3. The proportion of ceramic particles 3 in the metal matrix composite powder 14 can also be at least 35 wt.%, at least 40 wt.%, or at least 45 wt.%. One or more of the ceramic particles 3 can be contained in one metal matrix composite powder particle. Almost every, i.e., at least 90% of the powder particles of the metal matrix composite powder 14 contains at least one ceramic particle 3. The metal matrix composite powder 14 can also contain metal powder particles consisting solely of the metal of the metal matrix 2.

[0064] The metal matrix composite powder 14 is collected in a powder collection canister 13.

[0065] Figures 3a to 3d schematically show steps of yet another embodiment of the method according to the invention. As in the method steps of Figures 1a and 2a, in the method step shown in Figure 3a, a metal matrix composite material 1 is first produced. In a device 1, ceramic particles 3 are introduced into a metal matrix 2 in the form of a melt by stirring using at least one stirrer 4. As shown in Figure 3a, the melt can flow in an inclined channel 5. As further shown in Figure 3a, at least one basin 6 can be formed in the channel 5, into which basin the metal matrix material in the form of a melt flows with the ceramic particles 3 introduced therein and into which the respective stirrer 4 is immersed for stirring.At the end of the groove 5 there is a metal matrix composite material 7 in which the ceramic particles 3 are homogeneously incorporated into the metal matrix 2 and are surrounded on all sides by the metal matrix 2.

[0066] In the process step shown in Figure 3b, the flowable metal matrix composite material 7 is fed into a container 8', in which it is kept flowable by continuously heating the container 8'. The metal matrix composite material 7 remains in the container 8' for a residence time. If the ceramic particles 3 have a greater mass than the metal matrix material, the ceramic particles 3 sink into a lower region 81' of a molding compound formed in the container 8'. In the lower region 81', the proportion of ceramic particles 3 is thus higher than the proportion of ceramic particles 3 in an upper region 82' of the molding compound in the container 8', which upper region 82' lies above the lower region 81'. In the lower region 81', the proportion of ceramic particles 3 is at least 30 wt.%.As schematically shown in Figure 3c, the still-flowable metal matrix composite material 7 is poured directly into a cold-wall crucible 17 via an outlet of the container 8'. The cold-wall crucible 17 is, for example, a water-cooled copper crucible. In the cold-wall crucible 17, the metal matrix composite material 7 is kept liquid by induction heating or a plasma torch. Due to the water cooling of the wall of the cold-wall crucible 17, a so-called "skull" forms on the surface of the metal matrix composite material 7, which protects the metal matrix composite material 7 from contamination by dissolved copper.

[0067] The metal matrix composite material 7 contained in the cold-wall crucible 17 forms a semi-finished product 813 in the form of a melt. This semi-finished product 813 is fed directly into an atomizer 12, such as a cyclone separator, assisted by a compressed gas or pressurized water jet, and atomized by it. Alternatively, the semi-finished product 813 can be atomized.

[0068] The resulting metal matrix composite powder 14 contains a high proportion of at least 30 wt.% of ceramic particles 3 coated with the metal matrix 2. One metal matrix composite powder particle can contain one or more of the ceramic particles 3. However, the metal matrix composite powder 14 can also contain metal powder particles consisting only of the metal of the metal matrix 2.

[0069] The metal matrix composite powder 14 is preferably collected in a powder collection canister 13.

[0070] In a subsequent process step, shown schematically in Figure 3d, the produced metal matrix composite powder 14 is passed through an air stream 19 generated by an air nozzle 18 in a filter device 20. The filter device 20 further comprises an infrared camera 23. The air stream 19 swirls the powder particles of the metal matrix composite powder 14, with the lighter powder particles being swirled upwards, while the heavier powder particles fall downwards. If the ceramic particles 3 are heavier than the metal matrix material, the ceramic particles 3 coated with the metal matrix 2 are also heavier than pure metal powder particles, which may also be present in the metal matrix composite powder 14. The infrared camera 23 detects the thermal behavior of the powder particles, which differs for pure metal powder particles from the powder particles containing the ceramic particles 3.Depending on the density and thermal behavior of the powder particles, they are then separated from one another, for example by the pure metal powder particles 14' falling through a perforated bottom 21 of the filter device 20, being collected in a collecting container 22 located thereunder and thereby being separated from the ceramic-reinforced powder particles.

[0071] The method according to the invention may also have further embodiments. For example, individual method steps of the above-described embodiments may be adopted or replaced by one of the other embodiments.

Claims

AMENDED CLAIMS received by the International Bureau on 3 January 2025 (03.01.2025) 1. A method for producing a metal matrix composite powder (14), in which a metal matrix composite material (7) is produced by introducing ceramic particles (3) into a molten metal matrix (2) and stirring the resulting metal matrix ceramic mass, and a semi-finished product (811, 812, 813) is formed from the metal matrix composite material (7), which is a melt or from which a melt is formed which is atomized or atomized to form the metal matrix composite powder (14), in which the ceramic particles (3) are coated by the metal matrix (2), characterized in that the ceramic particles (3) have an average diameter of 3 to 150 pm, the metal matrix composite material (7) is brought into a container (8, 8') in a flowable state, or is melted in a container (8, 8'), wherein the metal matrix composite material (7) remains in the container (8, 8') for a residence time,until a molding compound or a molded body (10) having a lower region (81, 81') and an upper region (82, 82') is formed in the container (8), wherein the lower region (81, 81') has a different proportion of the ceramic particles (3) than the upper region (82, 82') due to gravity and / or due to an electromagnetic field applied to or around the container (8, 8'), and wherein either the lower region (81, 81') or the upper region (82, 82') has a proportion of the ceramic particles (3) of at least 30 wt.%, and subsequently the upper region (82, 82') is separated from the lower region (81, 81'), wherein that of the upper or lower region (82, 82'; 81, 81') which has the proportion of the ceramic particles of at least 30 wt.%, which forms the semi-finished product (811, 812, 813) or is formed or primary formed into the semi-finished product (811, 812, 813), which is atomized or sprayed into the metal matrix composite powder (14).

2. Method according to claim 1, characterized in that the upper region (82) is mechanically separated from the lower region (81) of the shaped body (10).

3. Method according to claim 1, characterized in that the upper region (82') is separated from the lower region (81 = ) of the molding compound (9) is separated by casting.

4. Method according to one of the preceding claims, characterized in that the metal matrix composite powder (14) is passed through an air stream in which unreinforced metal powder particles (14') are filtered out of the metal matrix composite powder (14), and / or unreinforced metal powder particles (14') are extracted from the metal matrix composite powder (14) using infrared and camera technology (23).

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