Method for producing a composite component having different resistivity in the longitudinal direction

Abstract

The present invention relates to a method for manufacturing a composite component (21) having different resistivities along the longitudinal direction of the component. A first slurry (10a) having at least a first composition and a second slurry (10b) having at least a second composition are prepared. The slurry is transferred to a supply chamber (35) of a processing device (31), such as an extruder. A green body (20) is formed by forcing the slurry from the supply chamber through a mold (32), and then sintering or oxidizing the green body to form a composite component. The slurry may contain metal powder, ceramic powder and a binder. The different resistivities may be caused by changes in one or more of the following parameters: the volume ratio between the metal powder and the ceramic powder, the size of the ceramic particles and the type of ceramic material.

Description

Technical Field

[0001] The present invention relates to a method of manufacturing a composite component, and in particular to a method involving sintering or oxidation of a powder-based material and manufacturing a composite component having different resistivities along the longitudinal direction of the component. Background Art

[0002] In many areas of technology, it is well known to exploit the electrical properties of metal components to conduct electricity. It may, for example, be in order to transmit electricity from a power source to another unit driven by the electricity, such as in an electrical cable. Due to the resistivity of metals, it is also possible to use electricity to heat a conductive component and then use the heated metal to heat another medium, such as a fluid flowing along the metal. However, since electricity follows the shortest conduction path through a metal component, this may result in certain areas of it becoming too hot while other areas are at a significantly lower temperature. This may both cause damage to the component and result in an underutilized utilization of the amount of material available in the component.

[0003] Therefore, improved methods of manufacturing composite components would be advantageous, particularly in relation to composite components made from metal-based materials and used to transmit electrical energy.

[0004] Purpose of the Invention

[0005] It is therefore an object of the present invention to provide a method for producing a composite component with which the electrical properties of the component can be adapted to a given application of the component.

[0006] Another object of the invention is to provide a method for producing a composite component, with which a composite component having non-constant electrical properties in the longitudinal direction can be obtained.

[0007] It is an object of some embodiments of the present invention to provide a method of manufacturing a metal composite part comprising sintering or oxidizing a powder-based material.

[0008] Another object of the present invention is to provide an alternative to the prior art.

[0009] In particular, one object of the present invention may be seen as providing a method for manufacturing a composite component which solves the above-mentioned problems of the prior art. SUMMARY OF THE INVENTION

[0011] Therefore, a first aspect of the present invention aims to achieve the above and several other objects by providing a method for manufacturing a composite component having different resistivity along the longitudinal direction, the method comprising the following steps:

[0012] -Preparing a plurality of slurries, comprising:

[0013] - at least a first slurry having a first composition, and,

[0014] - at least a second slurry having a second composition,

[0015] - Transfer multiple slurries into the supply chamber of the processing equipment,

[0016] - forming a green body from a plurality of slurries by forcing the slurry from a supply chamber through a mold of a processing device, and,

[0017] - Sintering or oxidizing the green body to obtain a composite part having a different resistivity along a longitudinal direction corresponding to the direction of movement of the slurry through the mould and the variation in resistivity being caused by the first composition being different from the second composition.

[0018] "Composite" generally means composed of different parts or elements. For the present invention, it refers to a composite part made from multiple slurries with different compositions. For some embodiments, each slurry itself can constitute a composite material, for example by including metal and ceramic materials, as described below.

[0019] The different resistivity can be said to be predetermined because it is determined as part of the design process based on the expected non-constant electrical properties required for a given application of the component. Or in other words, the resistivity is the parameter that determines the selection of the first and second paste compositions.

[0020] The step of preparing the slurry may be performed by kneading the materials in a kneader such as a Z-blade kneader or a sigma blade kneader.

[0021] "Slurry" refers to a heavy, soft, viscous substance made by mixing a liquid with a powder. In other words, a slurry generally consists of a suspension of a granular material in a background fluid. In the context of the present invention, the viscosity of the slurry should be such that it allows the necessary handling of the slurry during transfer from the device used to prepare the slurry to the processing equipment. Subsequent process steps should also be taken into account; that is, the viscosity of the slurry should be low enough to allow it to be formed by a mold, and high enough to ensure that the formed green body retains the desired geometry. The viscosity of a given slurry can be determined by equipment and methods designed accordingly, for example by using a capillary rheometer that is commonly used to measure shear viscosity and other rheological properties. However, since viscosity is related to the hardness of the material, this parameter can also be used to determine whether a given slurry is suitable for the manufacturing method. A related measurement that may be used is the Shore hardness, which can be determined according to ISO 868 / ASTM D2240. Another option is to use a special tool designed for clay; this has been used during the development of the present invention. The tool is similar to a Shore tester, but has been adapted for the characterization of clay; such an instrument may also be called a clay hardness tester. The working principle is based on the force applied by the sample material on the instrument's calibrated spring penetration when the tool's pin is pressed into the material being tested until the pin reaches the holder. In this way, a steady force with a steady stroke is always applied to the instrument. It has a scale from 0 to 20, used as a relative hardness reference parameter, as well as a scale in grams of the applied force. With this tool, the penetration point is pressed into the slurry as it comes out of the kneader. The maximum value indicated when the penetration point is inside the slurry is then measured. The maximum value is used rather than waiting for it to stabilize, as it will eventually show a much lower value, possibly close to 0, as the penetration point will be forced through the slurry. Using this method, it has been found that, at least for the geometries tested, values ​​greater than 12 Shore are required to obtain satisfactory results.

[0022] By the method according to the invention, the step of shaping the green body by forcing the slurry through a mold preferably thereby directly provides the green body with a shape corresponding to the desired final shape of the composite part obtained after the sintering or oxidation step. "Corresponding to" means that the dimensions usually change slightly due to the chemical reactions that occur during the sintering or oxidation process. For certain geometries, this may also lead to small changes in shape. But the overall final shape is caused by the slurry being forced through the mold, so that the green body obtains a shape that matches the shape of the mold. This will be illustrated in the figures. This shaping method is different from, for example, 3D printing, in which the shape of the part is obtained by moving the mold (also called nozzle) and / or a work platform, which fixes the manufactured part relative to each other and builds the part layer by layer.

[0023] The resistivity difference between areas of a sintered or oxidized component made from different pastes is typically between 2 and 20. However, other factors are also included in the protection range. The value used will be determined by the expected non-constant electrical characteristics required for a given application of the component.

[0024] With respect to the present invention and its description, the focus will be on the resistivity that varies along the composite part, since this is the parameter used to determine the slurry composition. However, since the variation in resistivity is due to the different compositions of the different slurries, other parameters will typically also vary. These parameters may be mechanical properties, such as stiffness and fracture strength. Examples of possible design parameters for obtaining different compositions are given below. If preliminary studies for a given application indicate that the slurry composition determined to obtain the desired different resistivities results in unsatisfactory mechanical properties of the composite part, then compromises may need to be made in the composition, as long as all design requirements are still met.

[0025] As mentioned above, the resistivity that varies along the longitudinal direction of the component is due to the first composition being different from the second composition. This is typically due to the first and second compositions having different resistivities, which may be referred to as the "initial resistivity," which results in what may be referred to as the "final resistivity" after sintering or oxidation. The initial resistivity on the green body is typically several orders of magnitude higher than the resistivity of the sintered or oxidized component.

[0026] The first aspect of the invention as described above may alternatively be expressed as a method of manufacturing a composite component, the method comprising the following steps:

[0027] -Preparing a plurality of slurries, comprising:

[0028] - a first slurry having at least a first composition, the first composition having a first resistivity when sintered or oxidized, and,

[0029] - a second paste having at least a second composition, the second composition having a second resistivity when sintered or oxidized,

[0030] - transferring the plurality of slurries into a supply chamber of a processing device, shaping the green body by longitudinally changing the slurry type while forcing the slurries from the supply chamber through a mold of the processing device, and

[0031] - sintering or oxidizing the green body to obtain a composite component having different resistivity along the longitudinal direction of the component, the longitudinal direction corresponding to the direction of movement of the slurry through the mold, and the change in resistivity is caused by the first resistivity being different from the second resistivity after sintering or oxidation.

[0032] Throughout the description, the expression "sintering or oxidation" is used, but this does not mean to exclude that both sintering and oxidation occur.

[0033] In a currently preferred embodiment of the invention, there are more than two different slurries, and they may all have different compositions.

[0034] In some embodiments of the present invention,

[0035] - a first slurry comprises a metal powder having a first alloy composition, a ceramic powder and a first binder,

[0036] - the second slurry comprises a metal powder having a second alloy composition and a second binder, and

[0037] wherein the first alloy composition and the second alloy composition each consist of at least one chemical element, and wherein the chemical elements are selected such that for each chemical element present in an amount greater than 0.5 weight percent of each alloy composition, the chemical element is contained in both the first and second alloy compositions, and

[0038] - for a chemical element present in an amount up to 5.0 wt. % in the first alloy composition, the amount of the chemical element differs by at most 1 percentage point between the first and second alloy compositions, and

[0039] - For a chemical element present in the first alloy composition in an amount greater than 5.0 wt. %, the amount of this chemical element differs by at most 3 percentage points between the first and second alloy compositions.

[0040] It can be obtained that the metal powder forms a coherent structure after sintering or oxidation, without any abrupt interfaces between materials originating from two adjacent pastes. Weak points (for example due to defects) that could lead to fracture can therefore be avoided. A further advantage of having the first and second compositions just described is that the metal structure has substantially the same properties throughout the component; these properties are, for example, mechanical properties, corrosion resistance and creep resistance. In addition, the metal parts of the composite component will have substantially the same thermal expansion and contraction during sintering or oxidation and during use of the component, so that the risk of thermal stresses can be minimized.

[0041] The word "alloy" is used throughout the specification and claims because it is most common for the first and second alloy compositions to each contain at least two chemical elements that form the alloy. For embodiments that include using at least one slurry having only one chemical element, this is also included in the wording "alloy", even though it may also be simply referred to as a "metal composition" rather than an "alloy composition". This means that the different compositions of two or more different slurries may include one or more slurries having only one chemical element, such as iron or copper.

[0042] Binder or binder (binder / binding agent) is any material or substance that mechanically, chemically holds or pulls other materials together to form a cohesive unit by adhesion or cohesion. Binders are preferably organic, such as cellulose ethers, agarose or polyoxymethylene. Examples of binders are: methylcellulose, 25 poly (ethylene oxide), polyvinyl alcohol, sodium carboxymethylcellulose (cellulose gum), alginate, ethyl cellulose and asphalt.

[0043] The first binder and the second binder may have similar or identical solvabilities to ensure that the extruded material has identical flow characteristics during the extrusion process.

[0044] In some embodiments of the invention, the slurry typically comprises a binder in an amount of 2 to 8% by weight of the slurry, such as 2 to 6% by weight of the slurry, or such as 3 to 5% by weight of the slurry. The slurry typically further comprises a liquid, such as water, in an amount of 5 to 25% by weight of the slurry, such as 5 to 15% by weight of the slurry, such as 5 to 10% by weight of the slurry, or it may be in an amount of 10-20% by weight of the slurry, such as 12-18% by weight of the slurry.

[0045] In the embodiments described above, the second slurry may further include ceramic powder. In any embodiment, the metal powder and the ceramic powder may have the same average particle size, which may result in easier and more uniform mixing. In alternative embodiments, they have different particle sizes. By using different particle sizes, better powder packing may be obtained, making it easier to avoid the appearance of pores in the sintered or oxidized composite part.

[0046] In embodiments including ceramic powders, different resistivities may be obtained by varying one or more of the following parameters:

[0047] - volume ratio between metal powder and ceramic powder,

[0048] - the size of the ceramic particles,

[0049] - the shape of the ceramic particles, and

[0050] - Type of ceramic material.

[0051] "Size" refers to any metric commonly used to describe powder-related parameters. It usually includes consideration of the average size and size distribution of the particles.

[0052] The different resistivities are obtained because the resistivity of ceramic materials is several orders of magnitude higher than that of metallic materials. The resistivity of the metallic materials used in the present invention is generally between 10 -5 Up to 10 -8The resistivity of ceramic materials at 20°C is usually above 10Ω·m, for example, 9 Up to 10 25 Which design parameter to use may depend on the requirements for other properties of the component, such as mechanical stiffness or impact strength. The actual choice for a given component can be determined, for example, by experimentation and / or computer simulation.

[0053] In addition to the above parameters, the final resistivity may also be influenced by different process parameters, such as sintering temperature, sintering duration and sintering atmosphere. Which parameters are selected for a given material combination can be determined, for example, by experiments and / or computer simulations.

[0054] In embodiments of the invention, where the component comprises metal powder and ceramic powder, and where the final component is obtained by sintering the green body, the sintering is generally carried out at a sufficiently high temperature to sinter the metals together, rather than the ceramics. Which sintering temperature is used depends on the material composition, but the sintering temperature is generally 1000-1450° C. The amount of metal powder should preferably be such that a coherent metal structure is obtained.

[0055] Metal powders can be in the form of spherical or substantially spherical particles. Spherical powders help increase powder loading, allowing for the use of less binder, reducing debinding and shrinkage during sintering. Spherical powders also have better flow characteristics during processing (such as extrusion). Ceramic powders can also be in the form of spherical particles.

[0056] In any embodiment of the present invention comprising metal powder, the metal powder of each of the first slurry and the second slurry may comprise one or more of the following chemical elements: iron, copper, chromium, aluminum, cobalt, nickel, manganese, molybdenum, vanadium, yttrium, and silicon.

[0057] In any embodiment comprising a ceramic powder, the ceramic powder may comprise one or more of: alumina, zirconia, boron nitride, cordierite, and silicon nitride.

[0058] The step of preparing a plurality of slurries may include supplying materials from at least two feed chambers in different amounts into a mixing chamber, and preparing a plurality of slurries in the mixing chamber. Each supply of material may be pre-mixed, for example in an extruder. Examples of such embodiments will be described in conjunction with the accompanying drawings. The different quantities are typically obtained by varying the speed of the worm in the feed chamber.

[0059] The processing equipment used in any of the embodiments described above may be, for example, an extruder or a casting machine.

[0060] The predetermined order in which the multiple slurries are transferred to the supply chamber may correspond to the longitudinal direction of the manufactured component. Depending on the desired design for a given application, the order of the different slurries can be selected such that one region of the composite component has a higher or lower resistivity compared to other parts of the component. In the drawings, an example will be shown where the resistivity of the middle region of the composite component is the highest compared to the end regions, and the resistivity of one end region of the composite component is higher than that of the other end region of the composite component.

[0061] The multiple slurries can be transferred to the supply chamber before the start of the shaping step. This may be related, for example, to a piston extruder or to manufacturing components whose length does not exceed the volume of the extruder supply chamber. Thus, it is easier to control the alignment of the slurries as desired before extrusion.

[0062] Alternatively, the shaping step can start before all the multiple slurries are transferred to the supply chamber. For example, this may be related to long components where there is not enough space in the supply chamber to accommodate all the slurries simultaneously.

[0063] The step of shaping the green body can be performed by continuously forcing the slurry through a die. Alternatively, the shaping can be temporarily suspended, for example, to add more slurry to the supply chamber.

[0064] In some embodiments of the present invention, the die has an exit pattern, resulting in the green body having at least one longitudinally extending internal channel. For example, the die can have an exit pattern such that the green body has multiple longitudinally extending internal channels arranged in regular patterns, such as having a honeycomb structure. An example of such a component is shown in the figure. The scope of protection includes manufacturing components of any shape that can be made by forcing a slurry through a die. The external geometry of the component can be a simple geometry, such as a rod or a plate, or a more complex geometry.

[0065] In any of the embodiments described above, the debinding step can precede the sintering or oxidation step. The debinding step preferably includes heating the green body to a temperature at which at least part (e.g., all) of the binder is burned off. Debinding is the process of removing the binder from the green body to ensure that there is no residual carbon in the component during the sintering process. This debinding is typically done by heating the green body to a temperature between 200 and 750 degrees Celsius and allowing the binder to burn off. Different binders require different debinding temperatures. In embodiments using methylcellulose, the debinding is carried out in an oxidizing atmosphere, usually in air, but can also be partially carried out in the same atmosphere as the sintering atmosphere if the final components are not damaged by the additional carbon content. To ensure that the debound green body can still be handled, the powder may need to be slightly oxidized together; these oxides will be removed during the sintering process.

[0066] A second aspect of the invention relates to a composite component whose resistivity varies along the longitudinal direction of the composite component, wherein the composite component is manufactured by the method according to the first aspect of the invention, so that the longitudinal direction corresponds to the direction of movement of the slurry through the forming die during the manufacture of the composite component.

[0067] In some embodiments of the invention, such composite parts are made from a slurry comprising metal powder and ceramic powder.

[0068] As described above in relation to the first aspect of the invention, the different resistivities may be due to changes in one or more of the following parameters:

[0069] - volume ratio between metal powder and ceramic powder,

[0070] - the size of the ceramic particles,

[0071] - the shape of the ceramic particles, and

[0072] - Type of ceramic material.

[0073] The resistivity may be substantially constant in a cross section perpendicular to the longitudinal direction of the composite component. This may be achieved, for example, by ensuring that the slurries have the same or substantially the same flow characteristics (e.g., the same viscosity), thereby limiting mixing of materials from two subsequently arranged slurries during forming. The viscosity of a given slurry may be determined by apparatus and methods designed for this purpose, for example using the method described above.

[0074] The composite component may have at least one longitudinally extending internal channel. The composite component may have a plurality of longitudinally extending internal channels, for example having a honeycomb structure.

[0075] The first and second aspects of the invention may be combined.These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0076] BRIEF DESCRIPTION OF THE DRAWINGS

[0077] The method of manufacturing a composite part according to the invention will now be described in more detail with reference to the accompanying drawings. The drawings illustrate one way of implementing the invention and should not be interpreted as limiting other possible embodiments falling within the scope of the appended claims.

[0078] Figure 1 The general concept of a composite component having different resistivities along the length of the composite component is schematically shown.

[0079] Figure 2 Schematic showing how two pastes are extruded into a composite part with regions of different resistivity.

[0080] FIG. 3 schematically shows a cross section of a composite component, the two cross sections containing different amounts of ceramic particles.

[0081] Figure 4 A graph showing how the resistivity varies as a function of the alumina content of the ceramic.

[0082] Figure 5 .a and 5.b schematically show two examples of component shapes that can be manufactured using the method according to the invention. Figure 5 .c schematically shows an example of a mold that can be used to manufacture a part having an array of longitudinally extending internal channels.

[0083] Figure 6 A processing apparatus which can be used in the method according to the invention is schematically shown.

[0084] Figure 7 A flow chart of a method according to the invention is shown. DETAILED DESCRIPTION

[0085] A first aspect of the present invention relates to producing a composite component 21 having different resistivities along the longitudinal direction of the composite component 21 . Figure 1 .a schematically shows an example of such a composite component 21, which has four regions 21a, 21b, 21c, 21d with different resistivities along the longitudinal direction corresponding to the direction in which the slurry passes through the forming die 32 (see FIG. Figure 2 )'s moving direction. Figure 1 .b shows the resistivity ρ as Figure 1 .a is a graph showing a function of the position of the length X of the component 21 in FIG. In this illustrated embodiment, the resistivity changes stepwise in a narrow region around the boundaries between the different regions 21a, 21b, 21c, 21d and has a constant rate of increase. However, the protection range also covers non-constant rate of increase. Figure 1 .c shows schematically an example of what might be a desirable curve for a given application, where a smooth variation of the resistivity ρ is desired. Figure 1 .d shows an actual curve example of a component to be used in an application with Figure 1 .c The ideal curve shown.

[0086] Figure 2 All steps in the method are shown schematically. Figure 2.a shows the steps of preparing a first slurry 10a having a first composition and a second slurry 10b having a second composition. The steps of preparing the slurries can be carried out by kneading the materials in a kneader, such as a Z-blade kneader or a sigma blade kneader. This type of mixer has a high torque and a specific geometry of the mixing blades, which has been found to be suitable for obtaining a homogeneous mixture of the above-mentioned slurry types, which usually have a high viscosity. The first and second slurries 10a, 10b are then transferred to a supply chamber 35 of a processing device 31, which is located at Figure 2 .b schematically shows a piston extruder. The slurries 10a, 10b are forced from the supply chamber 35 through the die 32 of the processing device 31 to produce Figure 2 .c shows a green body sample 20. The green body 20 is formed by continuously forcing the slurries 10a, 10b through the die 32 by moving the piston 36 toward the die 32, usually at a constant speed. As shown for this embodiment, the order in which the slurries 10a, 10b are transferred to the supply chamber 35 corresponds to the longitudinal direction of the part 21 being manufactured. In a currently preferred embodiment, the forming step is performed by an extruder, and the extrusion is performed at room temperature, and the slurry has a temperature of at most 50 degrees Celsius, such as at most 40 degrees Celsius, preferably at most 30 degrees Celsius. Therefore, the properties of the slurry may be easier to control over time because the large amount of water or other liquid present in the slurry will not evaporate at these temperatures, and the binder will not reach its gelling temperature.

[0087] After this shaping and possible further drying steps, the green body is sintered or oxidized to obtain a composite part 21 having different resistivities along the longitudinal direction of the composite part 21. Sintering can be carried out in a reducing atmosphere, a vacuum or an inert atmosphere. Sintering is usually carried out in a furnace at a temperature of 950 to 1430 degrees Celsius. As described in more detail above, a debinding step can be carried out before the sintering or oxidation step, and the debinding step usually includes heating the green body to a temperature at which at least a portion (e.g., all) of the binder is burned off.

[0088] from Figure 2 As can be seen in FIG. 1 , the longitudinal direction of the green body 20 and thus the longitudinal direction of the composite component 21 corresponds to the movement direction of the slurry 10a, 10b through the mold 32, and the different resistivity p is caused by the first composition being different from the second composition. Figure 2 As shown, the green body 20 acquires a shape that matches the shape of the mold 32. This shape corresponds to the shape of the final composite part 21, except for minor variations that may be caused by the following processing steps.

[0089] In a preferred embodiment of the present invention, the first slurry 10a includes a metal powder having a first alloy composition, a ceramic powder and a first binder. The second slurry 10b includes a metal powder having a second alloy composition and a second binder. The first alloy composition and the second alloy composition are both composed of a plurality of chemical elements. The metal powders of each of the first slurry 10a and the second slurry 10b may include one or more of the following chemical elements: iron, copper, chromium, aluminum, cobalt, nickel, manganese, molybdenum, vanadium, yttrium and silicon. Examples of alloys that have been used in the development work leading to the present invention are FeCrAl, TWIP, 316L and 17-4PH. However, the present invention can be used for many other alloys.

[0090] The second slurry 10b typically also includes ceramic powder. The ceramic powder used for the first and second compositions typically includes one or more of the following: alumina, zirconia, boron nitride, cordierite, and silicon nitride.

[0091] Different resistivities p in the slurries 10a, 10b are typically obtained by varying one or more of the following parameters:

[0092] - volume ratio between metal powder and ceramic powder,

[0093] - the size of the ceramic particles,

[0094] - the shape of the ceramic particles, and

[0095] - Type of ceramic material.

[0096] FIG3 schematically shows two examples of cross-sections of a component with different volume fractions of ceramic 14. In FIG3 , the ceramic particles are shown in black, even though they are white in the actual component. Due to the significant difference in resistivity between metal and ceramic materials, the different volume fraction examples shown in FIG3 result in different resistivities. The material properties associated with the ceramic particles, such as the above parameters as well as the distribution, can be analyzed, for example, by microscopy of a polished cross-section of the component.

[0097] Figure 4The results obtained during the development of the present invention are shown. It shows how the resistivity ρ of the composite part varies as a function of the ceramic content in the form of aluminum oxide. The figure is based on experiments in which the resistivity of composite parts manufactured following the method described above was measured. The resistivity was measured by applying a known current to the part and measuring the voltage drop with two probes, which were in contact with the part with a fixed distance between them. The experiments were carried out at room temperature and at a higher temperature, both showing different resistivities. For some materials used to develop the present invention, the resistivity is almost constant over the relevant temperature range. The composite part can, for example, be used in heating systems in which electricity is used to heat a conductive part due to the resistivity of the metal, and the heated metal is then used to heat another medium, such as a fluid flowing along the metal. In such applications, the resistivity that is almost independent of temperature makes the heating process stable and controllable, and hot spots may be more easily avoided. An example of a material with an almost constant resistivity is the FeCrAl alloy, which is used in a wide range of electrical resistance and high temperature applications. They have a resistivity of about 1.4 μΩ·m and a temperature coefficient of +49ppm / K (i.e. +49×10 -6 K -1 ).

[0098] Figure 5 5a and 5.b schematically show two examples of the overall shape of a composite component 21 which can be manufactured using the method according to the invention. Figure 5 .a shows a component 21 having an internal passage 22 extending longitudinally. Figure 5 .b shows a component having a plurality of longitudinally extending internal channels arranged in a regular pattern and separated by walls 23. These geometries are obtained by using a mould 32 having a shape and arrangement corresponding to the cross-sectional shape of the component. Figure 5 .c shows an example of a possible design of a mold 32 that can be used to manufacture a component 21 having an array of longitudinally extending internal channels.

[0099] Figure 6 An example of a processing device with two extruders 21a, 21b is schematically shown, each extruder supplies material (possibly in different amounts) in the form of a manifold into a mixing chamber 37 so that a plurality of slurries for final extrusion into a green body 20 are prepared in the mixing chamber 37. "Preparation" preferably means mixing them into a homogeneous material. The mixing chamber may include a mixer to perform at least partial kneading. The continuous flow of the slurry is transferred from the mixing chamber 37 to the supply chamber 35, from which the slurry is forced through the die 32 to form the green body 20. The supply chamber 35 can be a separate chamber, but it can also be a part of the mixing chamber 37 close to the die 32. Figure 6The processing equipment shown has a single worm extruder 31b and a twin worm extruder 31a, but it can also be two extruders of the same type. By changing the speed of the worm 38, the composition of the slurry prepared by the materials supplied by the two extruders can be controlled. For example, one extruder can be used to supply a material containing ceramic powder and the other extruder can be used to supply a material without ceramic. The amount of ceramic in the prepared slurry then depends on the relationship between the speeds of the two extruders.

[0100] Figure 7 A flow chart of an embodiment of the method according to the present invention is shown. First, a plurality of slurries 10a, 10b are prepared as described above. Figure 7 Two slurries are shown, but there may be more. The preparation can be carried out by kneading the material in a kneader, such as a Z-blade kneader or a sigma blade kneader. The slurries 10a, 10b are then transferred to a supply chamber 35 of a processing device 31. Figure 6 This transfer into the supply chamber 35 will cause some mixing in the corresponding step in the process 31, so that there are no sharp boundaries between the slurries. The processing device 31 is used to form a green body 20 from a plurality of slurries 10a, 10b by forcing the slurries 10a, 10b from the supply chamber 35 through a mold 32 of the processing device 31, such as Figure 2 As shown. Figure 7 In an embodiment, a step of debonding the green body is then performed; this step may be preceded by a drying step not shown. Such a debonding step is optional, and whether it will be included will depend on the materials used. The debonding step typically includes heating the green body 20 to a temperature at which at least some of the binder is burned off. Different binders require different debonding temperatures, with typical debonding temperatures being between 200 and 750 degrees Celsius. Finally, the green body 20 is sintered or oxidized to obtain a composite component 21 having different resistivities ρ along the longitudinal direction of the composite component 21. The drying step is typically carried out in a controlled atmosphere, including controlling the temperature and humidity at the location of the green body. It may also include passing a gas stream, such as air, along the green body, and then the speed of the gas stream may also be controlled.

[0101] Although the present invention has been described in conjunction with specific embodiments, it should not be interpreted as being limited in any way to the examples presented. The scope of the present invention is defined by the appended claims. In the context of the claims, the terms "comprise" or "comprising" do not exclude other possible elements or steps. Furthermore, references such as "one" or "an" should not be interpreted as excluding pluralities. The use of reference signs in the claims with respect to elements indicated in the drawings should also not be interpreted as limiting the scope of the present invention. Furthermore, individual features mentioned in different claims may be advantageously combined, and the mention of these features in different claims does not exclude that a combination of features is impossible and advantageous.

Claims

1. A method for manufacturing a composite component (21) having different resistivities along a longitudinal direction, the method The following steps are involved: - Preparing a plurality of slurries (10a, 10b), comprising: - at least a first slurry (10a) having a first composition, and, - at least a second slurry (10b) having a second composition, wherein the first and second compositions are selected based on a predetermined varying resistivity, - transferring the plurality of slurries (10a, 10b) into a supply chamber (35) of a processing device (31), - forming a green body (20) from a plurality of slurries (10a, 10b) by forcing the slurries (10a, 10b) from a supply chamber (35) through a mold (32) of a processing device (31), and, - sintering or oxidizing the green body (20) to obtain a composite part (21) having a different resistivity (ρ) along a longitudinal direction, the longitudinal direction corresponding to the direction of movement of the slurry (10a, 10b) through the mold (32), and the variation in resistivity (ρ) is caused by the first composition being different from the second composition; The first slurry (10a) comprises a metal powder having a first alloy composition, a ceramic powder and a first binder, The second slurry (10b) comprises a metal powder having a second alloy composition and a second binder, wherein the first alloy composition and the second alloy composition each consist of at least one chemical element, and wherein the chemical elements are selected such that for each chemical element present in an amount greater than 0.5 weight percent of each alloy composition, the chemical element is contained in both the first and second alloy compositions, and - for a chemical element present in the first alloy composition in an amount up to 5.0 wt. %, the amount of this chemical element differs by at most 1 percentage point between the first and second alloy compositions, and - For a chemical element present in the first alloy composition in an amount greater than 5.0 wt. %, the amount of this chemical element differs by at most 3 percentage points between the first and second alloy compositions.

2. The method according to claim 1, in, The first binder and the second binder have similar or identical solubility.

3. The method according to claim 1 or 2, in, The second slurry (10b) further includes ceramic powder.

4. The method according to claim 1 or 2, in, Different resistivities (ρ) are obtained by varying one or more of the following parameters: - volume ratio between metal powder and ceramic powder, - the size of the ceramic particles, - the shape of the ceramic particles, and - Type of ceramic material.

5. The method according to claim 1 or 2, in, The metal powder of each of the first slurry (10a) and the second slurry (10b) includes one or more of the following chemical elements: iron, copper, chromium, aluminum, cobalt, nickel, manganese, molybdenum, vanadium, yttrium and silicon.

6. The method according to claim 1 or 2, in, The step of preparing a plurality of slurries (10a, 10b) includes supplying materials from at least two feed chambers in different amounts into a mixing chamber (37), and preparing a plurality of slurries (10a, 10b) in the mixing chamber (37).

7. The method according to claim 1 or 2, in, The predetermined order in which the plurality of slurries (10a, 10b) are transferred into the supply chamber (35) corresponds to the longitudinal direction of the composite component (21) being manufactured.

8. The method according to claim 1 or 2, in, The step of shaping the green body (20) is performed by continuously forcing the slurry (10a, 10b) through the mold (32).

9. The method according to claim 1 or 2, in, The die (32) has an exit pattern resulting in the green body (20) having at least one longitudinally extending internal channel (22).

10. The method according to claim 9, in, The die (32) has an outlet pattern resulting in the green body (20) having a plurality of longitudinally extending internal channels (22) arranged in a regular pattern.

11. A method according to claim 1 or 2, wherein the sintering or oxidation step is preceded by a debinding step.

12. The method according to claim 10, wherein the mold (32) has a honeycomb structure.

13. The method of claim 11, wherein the debinding step comprises heating the green body (20) to a temperature at which at least a portion of the binder is burned off.

14. The method of claim 11, wherein the debinding step comprises heating the green body (20) to a temperature at which all of the binder is burned off.

15. A composite component (21) whose resistivity (ρ) varies along the longitudinal direction of the composite component (21), wherein the composite component is manufactured by the method according to any one of claims 1 to 14, so that the longitudinal direction corresponds to the movement direction of the slurry (10a, 10b) through the forming die (32) during the manufacture of the composite component (21).

16. The composite component (21) according to claim 15, in, The composite component is made of a slurry containing metal powder and ceramic powder.

17. The composite component (21) according to claim 16, in, The changing resistivity (ρ) is caused by changes in one or more of the following parameters: - volume ratio between metal powder and ceramic powder, - the size of the ceramic particles, - the shape of the ceramic particles, and - Type of ceramic material.

18. The composite component (21) according to any one of claims 15 to 17, in, The resistivity (ρ) is substantially constant in a cross section perpendicular to the longitudinal direction of the composite member (21).

19. The composite component (21) according to any one of claims 15 to 17, in, The composite component (21) has at least one longitudinally extending inner channel (22).

20. The composite component (21) according to claim 19, in, The composite component (21) has a plurality of longitudinally extending internal channels (22).

21. The composite component (21) according to claim 19, in, The composite member (21) has a honeycomb structure.

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