Composite material with embedded carbide

Abstract

The invention relates to a composite material comprising a metal matrix that consists of iron and / or nickel, and comprising embedded carbide, for specifically changing the mechanical and technical properties in relation to the metal matrix. The composite material has a mixed carbide proportion of less than 0.5 vol.-%.

Description

[0001] Composite material with embedded carbide

[0002] The invention relates to a composite material with a metallic matrix of iron and / or nickel, which has embedded carbides, for the targeted modification of the mechanical and technical properties compared to the metallic matrix.

[0003] Components made of composite materials with enclosed hard materials, such as carbides, can be produced by casting into a mold or by sintering a compact.

[0004] Hard materials are materials characterized by particularly high hardness. They are usually formations of intermetallic phases, often metal carbides, and less frequently ceramics, which contain a high proportion of metallic bonding. Hard materials are practically impossible to process in their pure form and are therefore usually used as additives in metal matrix composites. These composite materials are then classified as hard metals or cermets.

[0005] Chilled cast iron is metastable cast iron with a high carbide content. Metastable solidification leads to the formation of ledeburite, which is particularly hard and wear-resistant. Depending on the cooling rate or wall thickness of a component, stable solidification can also occur, leading to the formation of graphite in a matrix of ferrite and pearlite. In thick components, this results in the surface layer consisting of ledeburite and pearlite, while the core consists of graphite, pearlite, and ferrite. This chilled cast iron, also called chilled mold cast iron, has a ductile core and a hard shell. For solid chilled cast iron, the maximum cross-section may be no more than 100 mm to ensure that the component consists predominantly of hard ledeburite.

[0006] DE 195 12 044 A1 describes a corrosion- and wear-resistant chilled casting which has the following composition in weight%: Cr = 36 - 46, Ni = 5 - 12, Mo = 2 - 6, Cu < 3, N < 0.2, Si < 1.5, Mn < 1.5, C = 1.4 - 1.9, remainder Fe and melting-related impurities; the following composition in volume%: austenite 20 - 40, ferrite 20 - 40, carbides 20 - 40, whereby the carbides have a net-like structure.

[0007] Hard metals are metal matrix composites in which hard materials, present as small particles, are held together by a metal matrix and can be produced by sintering a compact. The materials are first prepared in a defined particle size distribution, mixed according to a recipe, and pressed with a binder into a green compact. Subsequently, fine-grained ceramic and / or metallic materials are usually heated under elevated pressure, but the temperatures remain below the melting point of the main components, so that the shape of the component is retained. This typically results in shrinkage because the particles of the starting material become denser and pore spaces are filled.

[0008] DE 10 2016 207 028 A1 discloses a hard metal comprising a phase of hard material grains and a phase of a heterogeneously distributed binder metal, wherein the hard material grains have an average grain size in the range from 1 nm to 1000 nm, preferably 50 nm to 500 nm, and the heterogeneously distributed binder metal is present in the hard metal in the form of binder islands which have an average size of 0.1 pm to 10.0 pm, preferably 0.2 pm to 5.0 pm, and an average distance between the binder islands of 1.0 pm to 7.0 pm, preferably 2.0 pm to 5.0 pm, and particularly preferably 1.0 pm to 4.0 pm. In both known processes, the shaping of components made of composite material with embedded hard materials and in particular the finishing of the surfaces is severely limited due to the properties of the hard materials.In addition, it is difficult to specifically influence the toughness, brittleness, hardness as well as the chemical and mechanical resistance of the composite component.

[0009] The object of the invention is to provide a composite material that can be specifically modified with respect to its mechanical and technical properties compared to the metallic matrix, while simultaneously allowing for flexible shaping. Furthermore, the composite material should exhibit improved tensile strength and optimized hardness without exhibiting particularly brittle properties. The composite material should be easy and cost-effective to produce.

[0010] This object is achieved according to the invention by a composite material according to the features of claim 1. Preferred variants can be found in the independent main claims, the subclaims, the description and the drawings.

[0011] According to the invention, the composite material has a proportion of mixed carbides of less than 0.5 vol.%.

[0012] In a particularly advantageous variant of the invention, the composite material does not contain any mixed carbides.

[0013] In conventional processes for producing a composite material with carbides, carbides are usually formed from the melt, particularly from carbon dissolved in the melt matrix, with one or more elements from the melt. These elements can enter the melt, for example, through the addition of scrap, recycled material, or other impurities. As a result, the formation of carbides, especially mixed carbides, from the melt cannot be precisely controlled. Thus, when producing a composite material from the melt, mixed carbides are usually formed, which are referred to as "impure" in the sense of a defined, mechanical-technological creation of a composite material.

[0014] Due to its special manufacturing process, the composite material according to the invention contains less than 0.5 vol.% or no mixed carbides, and thus exclusively "pure" carbides and a quantity of monocarbide adjusted by targeted addition. The targeted embedding and uniform arrangement of defined carbides creates a composite material with improved mechanical and technological properties.

[0015] In a particularly preferred variant of the invention, the composite material comprises exclusively monocarbides. These are precisely the carbides that were previously mixed with the alloy particles of the metallic matrix and then generated into a composite material using a powder bed process. The special production of the composite material ensures the defined and targeted incorporation of the carbides into the composite material, thus achieving the desired mechanical and technological properties.

[0016] In an advantageous variant of the invention, the carbides are embedded in the form of particles in the metallic matrix of an iron-based or nickel-based alloy.

[0017] The carbide particles are preferably well bonded into or to the metallic matrix by the special additive manufacturing process, particularly the powder bed process or laser powder deposition welding. This is evident, for example, in fracture patterns, especially on tensile test specimens, where a fracture caused by the carbide particle is evident. The melting or melting zone around each carbide particle firmly bonds the particles into the metallic matrix. A matrix, particularly a metal matrix composite, consists of a coherent metal matrix with a discontinuous ceramic or organic reinforcement within it, often in the form of fibers, particles, or whiskers.

[0018] For example, individual carbide particles can be integrated uniformly and / or finely distributed in a matrix in the form of a coherent surface structure and / or network structure.

[0019] Carbides are generally a group of binary chemical compounds consisting of one element and carbon. This group includes salt-like, preferably metallic compounds such as tantalum carbide, tungsten carbide, chromium carbide, and titanium carbide.

[0020] In additive manufacturing, particularly selective laser melting, a composite material is produced using a process in which a layer of powdered particles is first applied to a substrate. The application-specific mixture of powdered particles consisting of a metallic matrix and one or more carbides is applied in powder form in a thin layer to a plate. The powdered material is then completely melted locally at the desired locations using radiation, and after solidification, a solid layer of material consisting of embedded carbide in a metallic matrix forms. The substrate is then lowered by the amount of one layer thickness, and more powder is applied and melted using radiation, after which the new layer thickness solidifies again.

[0021] This advantageous process, combined with an application-specific blend, results in a metallic matrix that, due to the very local energy input, does not dissolve any significant portions of the carbide and does not form solid solutions or segregated phases upon solidification. This allows for previously unattainable material properties to be combined, for example, the ductility of the metallic matrix combined with the wear and / or corrosion resistance of the carbide.

[0022] Ideally, this would allow a composite material to be shaped and formed in a way that is not possible with the known forming methods for sintered hard materials and / or chilled castings.

[0023] The application-specific mixture of powder particles, and thus the carbide content, can preferably be varied. For example, for a composite material that is required to have a higher hardness, for example, according to the Vickers hardness test, a higher proportion of carbide can be added to the application-specific mixture. The intensive mixture of powder particles is thus uniformly, continuously, and homogeneously integrated into the metallic matrix during selective laser melting.

[0024] Basically, the term “particle” refers to a part of a body or a form of a composite material that is small compared to the scale of the system under consideration.

[0025] Advantageously, the carbide is embedded in the metallic matrix in the form of particles. Since the radiation energy in selective laser melting melts one powdered particle at a time, and the carbide does not melt completely with the applied energy, a structure is created in which the carbide is embedded in the matrix in its initial particle form.

[0026] Ideally, the additive process and the properties of the carbides allow for the embedding of many different particle shapes into the matrix. These can be round, polygonal, elongated, rod-shaped, and even needle-shaped particles, for example, which thus particularly advantageously shape the properties of the composite material. The embedded carbide is preferably in a crystalline form. A carbide is called crystalline if individual crystals are no longer recognizable in its particle shape, but the carbide exhibits a regular arrangement.

[0027] In a particularly preferred variant of the invention, the embedded carbide has a homogeneous arrangement in the metallic matrix. This corresponds to an arrangement that cannot be achieved by producing a chilled or sintered cast iron.

[0028] Homogeneity refers to the equality of a property across the entire extent of a system or the similarity of elements of a system.

[0029] Ideally, the arrangement of the carbide is uniform and / or even and / or uniform and / or similar and / or homogeneous in the metallic matrix.

[0030] Such an arrangement or distribution of carbides in the metallic matrix cannot be generated from the melt, especially by supersaturating the metallic matrix with carbide. Furthermore, this homogeneous arrangement of carbides in the metallic matrix cannot be achieved by precipitation at grain boundaries.

[0031] Ideally, the melting temperature of the embedded carbide is at least 1.2 times higher, preferably 1.4 times higher, and in particular 1.6 times higher, than the melting temperature of the metallic matrix. As a result, the carbide does not melt, or only partially melts, while the metallic matrix is ​​briefly molten due to the energy supplied by the radiation. This allows the shape of the carbide particles to be embedded in the metallic matrix, while at the same time allowing a particularly homogeneous distribution of the carbides in the metallic matrix to be achieved. In a favorable variant of the invention, the embedded carbide has a distribution in the metallic matrix that corresponds to a microstructure with regular inclusions.

[0032] Ideally, the embedded carbide is a tungsten carbide and / or a titanium carbide and / or a mixture thereof.

[0033] Tungsten carbide is very hard (Mohs hardness = 9.5) and melts at 2785 °C. Tungsten carbide has a tensile strength of more than 3500 MPa and a compressive strength of up to 6000 MPa.

[0034] Titanium carbide is characterized by a particularly high hardness of up to 4000 HV.

[0035] The flexural strength is 240 - 400 MPa and the elastic modulus is 550 - 570 GPa.

[0036] Advantageously, the carbide is formed from a powdered mixture of various carbide particles. The components can be weighed by mass, and a uniform distribution can be achieved through intensive mixing.

[0037] Furthermore, the proportion of carbide and / or carbide mixture can also be adjusted by mass-specific weighing into the powdered metallic matrix and the starting mixture for the selective laser melting can be produced by intensive mixing of the powdered particles.

[0038] In a favorable variant of the invention, the particle size is 10 - 40 pm and can be adjusted depending on the requirements in the powder mixture.

[0039] To produce bodies or components from the composite material with particularly stressed geometric regions, a powder mixture adapted to the load can also be created, for example, by adding a higher proportion of carbide to the powder mixture. Using boundary layers, modified powder can then be applied and melted in specific areas during selective laser melting, creating a component with geometric regions adapted to the load.

[0040] In a variant of the invention, the metallic matrix can be virtually carbon-free. Such a matrix can be formed, for example, by a stainless steel, preferably 1.4401, 1.4404, and / or 1.4435, which belong to the V4A group and, thanks to the addition of 2-2.5% molybdenum, exhibit good corrosion resistance even in the presence of chlorides.

[0041] Alternatively and / or additionally, the metallic powder particles can also be based on Alloy 718, 2.4668. Alloy 718 is a precipitation-hardenable nickel-chromium alloy with additions of niobium, molybdenum, aluminum, and titanium for improved corrosion resistance combined with extremely high strength.

[0042] In a favorable variant, the carbide content in the powder mixture is more than 4%, preferably more than 8%, especially more than 12%, tungsten carbide. This significantly increases the wear protection of the composite material in contact with abrasive media such as sand and solids, for example, in a corrosive environment.

[0043] In a favorable embodiment of the invention of the composite material compared to a chilled cast iron, the hardness increases from 290 to 410 HBW and the yield strength R P O,2 from 638 MPa to 933 MPa. The composite material according to the invention, which is produced using selective laser melting, achieves significantly improved material properties compared to known materials.

[0044] For example, the composite material has a bonding zone between the metallic matrix and the carbide particles.

[0045] In an advantageous variant of the invention, the carbide particles are embedded in the metallic matrix. The carbide particles are preferably bonded firmly into or to the metallic matrix, for example, an iron-based or nickel-based alloy, by means of the special additive manufacturing process, in particular the powder bed process or laser powder deposition welding. This is evident, for example, in fracture patterns, particularly from tensile test specimens, where a fracture caused by a carbide particle is evident. The melting or melting zone around each carbide particle firmly bonds the particles into the metallic matrix.

[0046] For example, thanks to the special additive manufacturing process, the composite material features a material bond between the metallic matrix and the carbide particles. This material bond significantly increases the strength of the composite material.

[0047] The alloy powder particles are melted and / or melted during the additive manufacturing process of the composite material, allowing diffusion processes, for example, to occur in the liquid phase. Optionally, tungsten or titanium can diffuse into the metallic matrix and contribute to the strengthening of the bonding zone.

[0048] The carbide particles within the composite material, for example, significantly improve the wear behavior of the composite material. The blasting wear when the composite is damaged by a 30 g / L quartz sand suspension with a quartz sand particle size of 100 pm, a beam speed of 20 m / s, and a beam angle of 45° is 0.71 mm. 3 / kJ. In comparison to an Alloy718 without attached and / or embedded carbide particles, the jet wear is 2.18 mm 3 / kJ.

[0049] For example, the carbide particles have a round and / or angular particle shape. Regardless of the particle shape, the particles are excellently integrated into the metallic matrix. According to the invention, the composite material is produced using an additive or generative manufacturing process. For this purpose, a powder mixture of alloy and carbide powder is produced, the powder mixture is applied to a substrate, and by selectively exposing a layered powder mixture to radiation, it is melted and solidified into a composite material. Using a three-dimensional data set, a complete component, preferably a flow-guiding component, for example, a pump impeller, can be formed from the composite material according to the invention.

[0050] In the powder bed process or selective laser melting, the powder of the composite material is applied in a thin layer to the build platform using a coater. The layers are gradually melted into the powder bed by precisely controlling the laser beam according to the layer contour of a component. Upon re-solidification, they fuse with the underlying and neighboring structures. The build platform is then lowered slightly, and a new layer is applied.

[0051] A composite material is created using an additive manufacturing process. This involves computer-controlled layer-by-layer construction from one or more solid, powdered materials according to specified dimensions and shapes. Physical or chemical curing or melting processes take place during the construction process.

[0052] In selective laser melting, the composite material is produced with the appropriate component dimensions using a process in which a layer of a powdered mixture of composite particles is first applied to a substrate. The powdered composite material is then completely melted locally at the desired locations using radiation, and after solidification, a solid layer of material forms. The substrate is then lowered by the amount of one layer thickness, and more powder is applied. This cycle is repeated until all layers have been produced and the finished composite material or composite component has been created. A laser beam, for example, can be used as the radiation, which generates the composite material from the individual powder layers. The data for guiding the laser beam is generated using software based on a 3D CAD body.As an alternative to selective laser melting, an electron beam (EBN) can also be used.

[0053] In a particularly advantageous variant of the invention, a composite material is produced from powdered particles by successively melting and solidifying layers using radiation. Different properties of the composite material can be generated by varying the radiation. By specifically controlling the local heat input, the material properties are modified during the construction of the composite material. This makes it possible to create zones and structures with different material states and thus different properties within a single area of ​​the composite material.

[0054] Ideally, the carbide is uniformly distributed in the metallic matrix of the composite through selective laser melting. This leads to a significant increase in the hardness and strength of the composite.

[0055] In a favorable variant of the invention, the proportion of carbide in the powder mixture can be adjusted to specifically increase the tensile strength during the powder mixture production process. For example, the proportion of carbide can be increased partially or generally to increase the hardness of particularly mechanically compromised surfaces of the composite material.

[0056] In principle, a component made of the composite material can be produced by selective laser melting, comprising regions melted with different mixtures of the powdered particles. For example, the proportion of tungsten and / or titanium carbide can be adapted to the load situation of the composite material components. This can preferably be achieved with a higher carbide content and / or varied radiation energy. In one variant of the invention, for example, damaged components can be repaired using a composite material powder mixture according to the invention and the use of selective laser melting, and can be consistently adapted to the existing load situation by a modified proportion of carbide.

[0057] Optionally, the composite material is produced using laser powder deposition welding.

[0058] For example, the composite material is produced in which directed radiation from an energy source, preferably a directed laser beam, melts and / or melts a surface and a powdery material mixture is introduced into the melt of the composite material body via a powder dispensing device with at least one powder channel.

[0059] Ideally, the process for producing a composite material is carried out as laser cladding (also known as laser metal deposition (LMD), direct metal deposition (DMD) or direct energy deposition (DED)).

[0060] Preferably, a molten pool is created on the surface of a composite material using a laser, or a base material forming the surface is heated. The molten pool can also generally be referred to as the process zone, which contains the heated or molten material of the body. The molten pool can, for example, be several hundred micrometers thick. The powder mixture of the composite material is automatically introduced using a powder dispensing device, usually in the form of a nozzle. Welded beads or flat material layers are created, which form the body of the composite material.

[0061] Laser cladding enables, for example, the application of three-dimensional structures to existing or new, possibly even uneven, body surfaces.

[0062] Complex body geometries can be created additively, and changes in powder composition can be easily adapted. Laser cladding typically uses a material deposition unit with a laser unit that directs the laser beam onto a body, while the powder dispensing device delivers powder to the body in a directed manner.

[0063] The powder dispensing device is typically designed to dispense the material powder toward the workpiece or body via a nozzle or multiple powder dispensing units, which can be configured, for example, as powder outlet openings. This results in one or more powder jets. These powder jets are centered in a material focus zone.

[0064] The powder dispensing units have multiple powder channels. The number of powder channels corresponds to the number of powder dispensing units. For example, seven powder dispensing units provide seven powder channels. The powder distribution unit can thus provide homogeneous or heterogeneous material flows of alloy powder and / or carbide powder in varying proportions. Furthermore, different powdery components of carbide powder can also be mixed together to form a layer of the composite material.

[0065] According to the invention, an additively manufactured composite material is used to improve the mechanical-technological material properties.

[0066] Further features and advantages of the invention will become apparent from the description of embodiments with reference to the drawings and from the drawings themselves.

[0067] It shows:

[0068] Fig. 1 shows a microstructure of a composite material according to the invention,

[0069] Fig. 2 shows another, enlarged micrograph. Fig. 1 shows a micrograph of the composite treated with V2A pickling at 200x magnification. The metallic matrix is ​​based on Alloy 718, 2.4668, with a tungsten carbide content of 12%. The metallic matrix exhibits a well-fused, coherent structure, while the tungsten particles are embedded in the metallic matrix in a nearly round or circular shape. The average size of the tungsten carbide particles is 10–40 μm. The tungsten carbide particles are evenly distributed and exhibit a homogeneous arrangement. At a 12% tungsten carbide content, the average number of particles per mm is 2 200 - 250.

[0070] Fig. 2 shows a microscopic image of the composite treated with V2A pickling at 500x magnification. The metallic matrix is ​​based on Alloy 718, 2.4668, with a tungsten carbide content of 12%. The tungsten carbide particles are nearly circular in shape and have a size of 20-30 pm. The spacing between the tungsten carbide particles is approximately 30-60 pm and exhibits a uniform distribution and homogeneous arrangement.

[0071] The tungsten carbide particles shown in Fig. 2 each have a melting zone arranged in the form of an annular strip around the round tungsten carbide particles. These melting zones are formed during the formation of the composite material in the powder bed process, with tungsten also diffusing into the metallic matrix in detectable quantities. This melting zone demonstrates excellent bonding of the tungsten carbide particles in and to the metallic matrix.

Claims

Patent claims Composite material with embedded carbide 1. Composite material with a metallic matrix of iron and / or nickel, which has embedded carbides, for the targeted modification of the mechanical and technical properties compared to the metallic matrix, characterized in that the composite material has a proportion of mixed carbides of less than 0.5 vol.%.

2. Composite material according to claim 1, characterized in that the composite material does not contain mixed carbides.

3. Composite material according to claim 1 or 2, characterized in that the carbide is embedded as particles in the metallic matrix.

4. Composite material according to one of claims 1 to 3, characterized in that the embedded carbide has a homogeneous arrangement in the metallic matrix.

5. Composite material according to one of claims 1 to 4, characterized in that the melting temperature of the incorporated carbide is at least by a factor of 1.2, preferably by a factor of 1.4, in particular by a factor of 1.6, higher than the melting temperature of the metallic matrix.

6. Composite material according to one of claims 1 to 5, characterized in that the embedded carbide in the metallic matrix has a distribution which corresponds to a microstructure with regular inclusions.

7. Composite material according to one of claims 1 to 6, characterized in that the composite material comprises different monocarbides.

8. Process for the additive manufacturing of a composite material for a component, comprising the following steps: - Production of a powder mixture of alloy and monocarbide powder - Selective exposure of radiation to a layered powder mixture - Manufacturing a component from a composite material 9. A method according to claim 8, characterized in that the composite material is produced using the powder bed process.

10. Method according to claim 8, characterized in that the composite material is produced by laser deposition welding.

11. Method according to one of claims 8 to 10, characterized in that the carbides are incorporated in the metallic matrix of the composite material in a uniform distribution.

12. Use of an additively manufactured composite material according to one of claims 1 to 8 for improving the mechanical-technological material properties.

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