Method for manufacturing a component using hot isostatic pressing

Abstract

Method for manufacturing a component by means of hot isostatic pressing, comprising the steps: • Coating a surface (7) of a workpiece (2) with at least one first reactant and one second reactant, • Forming a container (8) for hot isostatic pressing on the surface (7) of the workpiece (2) without melting or powder metallurgical processes of the first and second reactants by means of a solid-state diffusion reaction between the first reactant and the second reactant, wherein a temperature is applied for the solid-state diffusion reaction which is below the melting temperature of the first and the second reactants, wherein the container (8) formed by the solid-state diffusion reaction of the first reactant and the second reactant has a melting temperature which is higher than the temperature during hot isostatic pressing and • hot isostatic pressing of the workpiece (2), wherein either the first reactant is aluminium and the second reactant is iron or the first reactant is copper and the second reactant is nickel.

Description

[0001] The invention relates to a method for manufacturing a component using hot isostatic pressing.

[0002] Methods for manufacturing components using hot isostatic pressing (HIP) are known in the art. For example, DE 10 2016 206 105 A1 describes the production of a three-dimensional workpiece by HIP. In this method, a container, a so-called capsule or wall, is formed in preparation for the HIP process through a powder metallurgy process followed by irradiation with high-energy radiation. However, these powder metallurgy processes are very complex and expensive. Furthermore, they are not well suited for manufacturing components with intricate shapes. Other methods for producing containers for hot isostatic pressing are also known, such as laser cladding of a material layer, such as a steel layer, onto the workpiece. However, this method is very complex, relatively expensive, and unsuitable for material combinations with different coefficients of thermal expansion.Furthermore, the following documents can be mentioned in this context: EP 2551040 A1, DE 10 2019 110 400 A1, US 6,089,444 A1, EP 2 113 583 A1 and CA 2 572 699 C. In addition, DE 690 06 874 T2 describes a process for producing a cladding metal by forming a layer of dissimilar metal powder on the surface of a base metal by cold-fixing the powder to the surface under pressure, compacting only the surface and an area below the surface of the layer of dissimilar metal powder by melting and immediate solidification in a vacuum, and fusing the layer of dissimilar metal powder together with the base metal at a temperature not higher than the solidus line temperature of the two dissimilar metals under a pressure of not less than 300 kgf / cm². 2(or 29.4 MPa) is compressed using a hot isostatic press and the layer of dissimilar metal powder is hot-processed together with the base metal.

[0003] Based on this state of the art, an object of the invention is to provide a method for manufacturing a component by means of hot isostatic pressing that is easy to apply and cost-effective to implement and enables the production of complex components with complicated structures.

[0004] This problem is solved by the features of the independent claim. The dependent claims contain advantageous embodiments of the invention.

[0005] Thus, the inventive method for manufacturing a component by means of hot isostatic pressing comprises a step of coating a workpiece surface with at least a first reactant and a second reactant. The workpiece is not specifically limited. The workpiece is transformed into the desired component by hot isostatic pressing.

[0006] This requires the formation of a container, serving as a capsule or wall, for hot isostatic pressing on the surface of the workpiece. According to the invention, this container is formed by a solid-state diffusion reaction between the first and second reactants. The container is thus formed virtually in situ, not by conventional alloying through the melting of metals or other powder metallurgy processes, but by diffusion of one of the reactants into the corresponding other reactant, with both reactants being in the solid phase. This solid-state diffusion reaction is carried out at a temperature below the melting point of both the first and second reactants. Preferably, the temperature is approximately 350 °C to 600 °C.The solid-state diffusion reaction forms a phase characterized by high impermeability to gas, even at high process temperatures, high thermal and mechanical resistance, and yet a very simple structure. The vessel formed by the solid-state diffusion reaction of the first and second reactants has a melting point higher than the temperature during hot isostatic pressing. Advantageously, the temperature for hot isostatic pressing can be in the range of approximately 950 to 1150 °C, and a pressure of at least approximately 1000 bar up to over 200 bar can be applied. The temperature during hot isostatic pressing is always below the melting point of the materials of the workpiece being manufactured.

[0007] Following the formation of the container, the workpiece undergoes hot isostatic pressing. This hot isostatic pressing is performed using standard parameters. The high melting temperature of the container prevents it from melting during the hot isostatic pressing process, ensuring that the component is formed with high precision and without defects.

[0008] The process is easy to implement without high technical effort and is also cost-effective.

[0009] According to an advantageous embodiment, the first and second reactants are applied to the workpiece surface in the form of separate layers. This can mean that the first reactant is applied to the workpiece surface first, and the second reactant is applied onto the layer of the first reactant. It is also possible that the second reactant is applied to the workpiece surface first, and subsequently the first reactant is applied onto the layer of the second reactant. This would each result in a complete overlap of the layers of the first and second reactants. However, it is also possible that only a partial overlap is achieved by applying the respective layers. A complete overlap is advantageous, however, due to the expected shorter diffusion time of the solid-state diffusion reaction.Furthermore, multiple layers of the first and second reactants can be applied alternately on top of each other. This can be advantageous for improving the mechanical stability of the container. The respective layer thickness of the first and second reactant layers is typically in the range of a few nanometers up to 100 µm. A lower limit of 5 µm is advantageous.

[0010] A further advantageous development involves applying the first and second reactants as a mixture. In other words, a mixture of the first and second reactants is first prepared and then applied to the surface of the workpiece. The mixture contains the first and second reactants homogeneously, ensuring that the diffusion reaction in the solid phase occurs particularly quickly and uniformly. Application methods for this mixture of first and second reactants include CVD, PVD, chemical coating, thermal spraying, and electroplating.

[0011] Furthermore, it is advantageous in terms of a simple and cost-effective process if at least one of the reactants has a melting point below 700 °C. For a solid-state diffusion reaction, the activation temperature is approximately 80% of the melting point of one of the reactants. Thus, if one reactant has a melting point below 700 °C, the solid-state diffusion reaction can be carried out faster and at a lower temperature.

[0012] Diffusion in solids is characterized by the microscopic relative motion of particles, the migration of individual crystal building blocks, which in two- or multiphase systems is referred to as extraneous diffusion. The necessary thermal activation is defined by the Arrhenius law, allowing for the straightforward selection of suitable reactants. Due to its excellent availability and high diffusivity, aluminum is a particularly suitable first reactant.

[0013] According to the present invention, a particularly stable and cost-effective container with high gas tightness and low toxicity can be produced by using aluminium as the first reactant and iron as the second reactant.

[0014] For the reasons stated above, an alternative container according to the invention is formed from copper as the first reactant and nickel as the second reactant.

[0015] To promote the most uniform and rapid formation of the container with good layer thickness, and thus high gas impermeability, the initial pressure applied during container formation is lower than the second pressure applied during hot isostatic pressing. This allows solid diffusion to proceed unhindered and completely. To further facilitate this, the initial pressure for the solid diffusion reaction is kept constant. The solid diffusion reaction is carried out over a period of up to 3 hours. This means that the initial pressure, which is below 1000 bar, is preferably kept constant for a period of up to approximately 3 hours. A pressure of 10 bar may already be sufficient and can, if necessary, be increased to a first pressure that is lower than the second pressure applied during hot isostatic pressing.

[0016] To form particularly stable components with very good mechanical and functional properties, it is advantageous if the workpiece consists of materials with different coefficients of thermal expansion.

[0017] The costs of the process can be further reduced by additively manufacturing at least part of the workpiece. This saves on material scrap. Additive manufacturing of the workpiece is understood as a manufacturing process characterized by the targeted building up of structures within the workpiece.

[0018] Due to the excellent ability to produce components with complex and intricate shapes and structures, at least part of the workpiece is advantageously manufactured using thermal spraying. Thermal spraying is an example of an additive manufacturing process.

[0019] Also described, but not part of the present invention, is an arrangement for manufacturing a component by means of hot isostatic pressing. This arrangement comprises a workpiece and a container arranged or formed on a surface of the workpiece. The arrangement can be transformed into the desired component by hot isostatic pressing. The container is formed by a solid-state diffusion reaction between the first and second reactants, wherein the container formed by the solid-state diffusion reaction of the first and second reactants has a melting temperature that is higher than the temperature to be applied during hot isostatic pressing.

[0020] The container formed on the surface of the workpiece comprises at least a first reactant and a second reactant that have undergone a solid-state diffusion reaction. This means that the first reactant and the second reactant, both present in the solid phase, have formed a phase through diffusion that is characterized by high gas impermeability as well as high mechanical and thermal stability, making the container suitable for forming highly complex components without defects or flaws.

[0021] The arrangement is characterized by a simple and cost-effective structure while offering high functionality.

[0022] The arrangement described above is suitable for use in the method according to the invention.

[0023] Further details, advantages and features of the present invention will become apparent from the following description of exemplary embodiments with reference to the drawing. It shows: Fig. 1. A schematic representation of the process steps of a process for manufacturing a component. Fig. 2 a sectional view of a layer arrangement for the production of a component, Fig. 3 a sectional view of an arrangement for the manufacture of a component and Fig. 4. A light microscopic image of a component from Example 1. Fig. 3.

[0024] The figures only depict the essential aspects. All other aspects have been omitted for the sake of clarity. Furthermore, identical reference symbols number identical elements / components.

[0025] Fig. Figure 1 is a schematic representation of process steps of a method for manufacturing a component according to a first embodiment.

[0026] In process step 100, the surface of a workpiece is coated with at least one first reactant and one second reactant. The first and second reactants are preferably applied alternately in layers. One or more layers per reactant are possible. The layers of first and second reactants can be applied, for example, by CVD, PVD, chemical coating, thermal spraying, or electroplating.

[0027] In process step 200, a container for the hot isostatic pressing of the workpiece is formed during component formation. The container is formed by a solid-state diffusion reaction between the first and second reactants on the workpiece surface. Thus, the reactants do not melt to form an alloy. The reactants are selected such that the container formed by the solid-state diffusion reaction of the first and second reactants has a melting temperature higher than the temperature during hot isostatic pressing. This prevents the container formed by the solid-state diffusion reaction from melting during the hot isostatic pressing process.

[0028] The container formed in this way is characterized by very good thermal and mechanical stability, which simplifies the process control during hot isostatic pressing.

[0029] In process step 300, the workpiece is then hot isostatically pressed to form the component. The component can have a particularly complex three-dimensional structure and be made of materials with different coefficients of thermal expansion.

[0030] The process is cost-effective and easy to implement without high technical effort.

[0031] Fig. Figure 2 shows a layer arrangement 1 for manufacturing a component by hot isostatic pressing in cross-section. A workpiece 2 is shown in detail, onto which a first layer 3 of a second reactant is applied. A second layer 4 of the first reactant is applied to the first layer 3 of the second reactant, and a third layer 5 of the second reactant is applied to this second layer 4 of the first reactant. The first reactant is, for example, aluminum, and the second reactant is, for example, iron. Alternatively, the first reactant could also be, for example, copper and the second reactant nickel.

[0032] Through a solid-state diffusion reaction between the respective layers 3, 4, and 5 of the first and second reactants, the container 8 is formed directly on the surface 7 of the workpiece 2. The formed container 8 has a melting point higher than the temperature during the hot isostatic pressing process. No liquid phase of the reactants is formed during the solid-state diffusion reaction. Instead, crystallites diffuse from the second layer 4 of the first reactant into the first and third layers 3 and 5 of the second reactant. This is indicated by the two arrows. Thus, mixed phases of the first and second reactants are formed. Preferably, a complete reaction of the first reactant from the second layer 4 into the first and third layers 3 and 5 of the second reactant takes place.Thus, the resulting container 8 will have a homogeneous structure consisting of a single mixed phase of the first and second reactants. However, a thin layer of pure second reactant may remain on the surface 6 of the third layer 5 of the second reactant and on the surface 7 of the workpiece 2, which does not significantly impair the stability of the container 8. The container 8 has a layer thickness of up to 150 µm, resulting in very good gas impermeability, high thermal stability, and also very good mechanical stability.

[0033] Fig. Figure 3 shows an arrangement 10 for the production of a component in section.

[0034] The arrangement 10 comprises a workpiece 2 and a container 8 arranged on a surface 7 of the workpiece 2. The container 8 comprises at least a first reactant and a second reactant, wherein the container 8 is formed by a solid-state diffusion reaction between the first and the second reactant and thus exists in the form of a single homogeneous phase. The container 8 formed by the solid-state diffusion reaction of the first and second reactants has a melting point that is higher than the temperature applied during hot isostatic pressing. The resulting container 8, which completely surrounds the surface 7 of the workpiece 2, forms a gas-impermeable capsule with high thermal and mechanical resistance, which protects the workpiece 2 when subjected to the pressure and temperature applied during hot isostatic pressing.

[0035] The following are two examples that illustrate the production of a component using hot isostatic pressing by applying the arrangement. Example I:

[0036] A workpiece 2 made of a copper alloy (2a) with a cold gas sprayed functional layer of hot work steel (2b) was electroplated alternately with nickel (second reactant), copper (first reactant) and again nickel (second reactant) with a layer thickness of at least 50 µm per layer.

[0037] From the binary phase diagram of copper and nickel, it is known that copper and nickel mix infinitely. This resulted in the formation of a container 8 from a solid solution across the entire phase width. The temperature during the production of container 8 was below the solidus line. The workpiece 2 was then hot isostatically pressed at 1060°C and a pressure of 1000 bar for 5 hours.

[0038] The heat treatment can also be carried out in stages at different temperatures. The crucial point is that neither the melting point of the copper alloy nor the solidus line of the binary system is exceeded. In this example, the steel layer was successfully hardened.

[0039] Fig. Figure 4 shows a light micrograph of the component formed in the example above after hot isostatic pressing. The solid solution of first and second reactants forming container 8 is clearly visible, extending across the entire phase width. A remnant of the nickel layer (second reactant), which served as mechanical protection, is still visible as the uppermost layer 9. Furthermore, another residual layer of nickel 11 (second reactant) is also visible on the component surface. It is also clearly evident that container 8 was impermeable to gas, as the copper alloy and the hot-work steel of workpiece 2 were successfully fused together. Example II:

[0040] Instead of forming a container from a solid solution as in Example I, the binary system of iron (second reactant) and aluminum (first reactant) was used here, resulting in the formation of defined intermetallic phases. To successfully carry out the process, the individual heating and pressure steps were followed as follows: First, a workpiece 2 was again coated alternately with iron (second reactant), aluminium (first reactant) and then again with iron (second reactant) with a layer thickness of at least 50 µm each.

[0041] The coated workpiece 2 was heated to 640°C without pressure and held at this temperature for 3 hours. This resulted in the formation of a container 8 consisting of the intermetallic phases FeAl2 and Fe2Al5. The two phases had melting points of 1160°C and 1169°C, respectively. Subsequently, the assembly was hot isostatically pressed at 1060°C and a pressure of 1000 bar for 5 hours.

[0042] The latter example enabled the production of a component using hot isostatic pressing at lower temperatures than in the first example, since the formation of the container 8 (phase formation) took place at lower temperatures (requiring less activation energy). Therefore, the container 8 formed here is also conceivable for light metal alloys.

[0043] In addition to the foregoing written description of the invention, explicit reference is hereby made to the graphic representation in the following for its supplementary disclosure. Fig. 1, Fig. 2, Fig. 3 to Fig. 4 referenced. Reference symbol list 1 Layer arrangement for manufacturing a component by means of hot isostatic pressing 2 workpieces 2a Copper alloy 2b cold gas sprayed functional layer made of hot work steel 3 first layer of a second reactant 4. Second layer of a first reactant 5. Third layer of a second reactant 6 Surface of the third layer of a second reactant 7. Surface of the workpiece 8 containers 9 top layer 10. Arrangement for manufacturing a component by means of hot isostatic pressing 11 Residual layer of nickel

Claims

[1] Method for manufacturing a component by hot isostatic pressing, comprising the steps: • Coating a surface (7) of a workpiece (2) with at least one first reactant and one second reactant, • Forming a container (8) for hot isostatic pressing on the surface (7) of the workpiece (2) without melting or powder metallurgical processes of the first and second reactants by means of a solid-state diffusion reaction between the first reactant and the second reactant, wherein a temperature is applied for the solid-state diffusion reaction which is below the melting temperature of the first and the second reactants, wherein the container (8) formed by the solid-state diffusion reaction of the first reactant and the second reactant has a melting temperature which is higher than the temperature during hot isostatic pressing and • hot isostatic pressing of the workpiece (2), wherein either the first reactant is aluminium and the second reactant is iron or the first reactant is copper and the second reactant is nickel. [2] Method according to claim 1, wherein the first reactant and the second reactant are applied in the form of separate layers (3, 4, 5). [3] Method according to claim 1, wherein the first reactant and the second reactant are applied as a mixture. [4] Method according to any of the preceding claims, wherein at least one of the reactants has a melting temperature below 700 °C. [5] Method according to any of the preceding claims, wherein a first pressure applied during the formation of the container (8) is less than a second pressure applied during the hot isostatic pressing and wherein the first pressure is kept constant to carry out the solid diffusion reaction. [6] Method according to one of the preceding claims, wherein the workpiece (2) consists of materials with different coefficients of thermal expansion. [7] Method according to any of the preceding claims, wherein at least a part of the workpiece (2) is additively manufactured. [8] Method according to one of the preceding claims, wherein at least a part of the workpiece (2) is manufactured by thermal spraying.

Images