Method for generating a component by a power-bed-based additive manufacturing method and powder for use in such a method

Abstract

The disclosure relates to a powder and a method for generating a component by a powder-bed-based additive manufacturing method, such as laser melting. The powder includes particles having a core and a shell. The particles have an alloy composition of the component. The concentration of higher-melting alloy elements is greater in the shell and the concentration of lower-melting alloy elements is greater in the core, wherein the surface of the particles is higher in comparison with particles with a constant alloy composition. This advantageously prevents the particles from caking together in the powder bed during the production of the component, and so the powder bed may also be subjected to high preheating temperatures of up to 1000° C.

Claims

1. A method for generating a component by powder-bed-based additive production, the method comprising: providing a powder having a plurality of particles, wherein each particle of the powder comprises a core and shell, wherein the core of each particle comprises a first metallic alloy composition having at least 50 mass % nickel, wherein the shell comprises a second metallic alloy composition having a different composition than the first metallic alloy composition, wherein the second metallic alloy composition comprises cobalt, iron, chromium, molybdenum, tantalum, tungsten, or combinations thereof, and wherein a melting temperature of the first metallic alloy composition is lower than a melting temperature of the second metallic alloy composition; forming a layer of a powder bed by melting or sintering a portion of the particles of the powder with an energy beam; heating the powder bed to a temperature below a melting temperature of the particles; and repeating the forming of at least one additional layer of the powder bed by melting at least one additional portion of the particles of the powder to form the component.

2. The method of claim 1, wherein the shell of the particles has a thickness of at least 0.1 μm and at most 3 μm.

3. The method of claim 1, wherein the particles have a particle size of at least 10 μm and at most 100 μm.

4. The method of claim 1, wherein the melting or sintering of the portion of the particles of the powder and the melting of the at least one additional portion of the particles of the powder comprises electron beam melting.

5. The method of claim 1, wherein the first metallic alloy composition is a superalloy.

6. The method of claim 5, wherein the heating of the powder bed comprises heating the powder bed to a temperature of at least 800° C. and at most 1200° C.

7. The method of claim 6, further comprising: cooling the temperature of the powder bed down at a rate of at most 1° C./s following formation of the component.

8. The method of claim 1, wherein the particles have an average particle size in a range of 25 μm to 30 μm.

9. The method of claim 1, wherein the shell of the particles comprises tungsten or chromium.

10. The method of claim 1, wherein the shell comprises more than 99 mass % of an element that has a highest melting temperature of elements within the first metallic alloy composition and the second metallic alloy composition of the particle.

11. The method of claim 10, wherein the element is tungsten.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further details of the disclosure are described below with reference to the drawing. Identical or corresponding elements in the drawing are each provided with the same reference symbols and are explained more than once only insofar as there are differences between the individual figures.

(2) FIG. 1 depicts, in section, a laser melting unit in which an exemplary embodiment of the method is carried out.

(3) FIGS. 2 to 4 depict selected acts in the implementation of the method according to FIG. 1, with a small detail of the component under production being shown in section.

(4) FIG. 5 depict a detail of an exemplary embodiment of the component produced in accordance with FIGS. 2 to 4.

DETAILED DESCRIPTION

(5) Represented schematically in FIG. 1 is a unit 11 for laser melting. This unit has a process chamber 12 in which a powder bed 13 may be produced. To produce, respectively, one layer of a powder bed 13, a spreader in the form of a doctor blade 14 moves over a powder store 15 and subsequently over the powder bed 13, so forming a thin layer of powder in the powder bed 13. A laser 16 then generates a laser beam 17, which is moved by an optical deflection apparatus with mirror 18 over the surface of the powder bed 13. At the point of impingement of the laser beam 17, the powder is melted, to form a component 19.

(6) The powder bed 13 comes about on a building platform 20, which may be lowered step by step, by the thickness of one powder layer in each case, in a pot-shaped housing 22 by an actuator 21. In the housing 22 and also in the building platform 20, heating devices 23 are provided in the form of electrical resistance heaters (induction coils are an alternative option), which are able to preheat the component 19 being formed and also the particles of the powder bed 13. To permit the energy required for preheating, on the outside of the housing 22 there is insulation 24 of low thermal conductivity.

(7) Represented in FIG. 2 is an edge of the component 19 to be produced, which may be produced, for example, in a unit according to FIG. 1. This component is located in the powder bed 13, the borders of which are indicated by a dash-dotted line. Selected particles 25 from the powder bed 13 are also shown, including the material of a nickel-based alloy. The component to be produced may be, for example, a turbine blade.

(8) The particles 25 include in each case of a core 26 and a shell 27. The core 26 primarily includes nickel and further includes the nickel-based alloy. The shell 27 includes, for example, tungsten and otherwise of elemental alloy impurities to a technically irrelevant extent. Accordingly, the surface of the particles 25 has a melting temperature of above 3400° C. This allows the powder bed to be preheated at up to 1000° C. without adjacent particles 25 becoming caked together.

(9) Represented schematically in FIG. 2 (as also in FIGS. 3 and 4) are the particles 25; the size proportions between the core 26 and the shell 27 are not true to scale. Additionally, a discrete transition between core 26 and shell 27, as shown in FIG. 2, is not absolutely necessary. Gradient layers are also conceivable, in which a transition between core 26 and shell 27 is not abrupt but instead occurs with a concentration gradient (not shown). This advantageously supports the diffusion processes which lead, by melting of the particles, to the formation of alloy in the composition intended for the component. For the melting temperature at the surface of the particles 25, all that is necessary is that the shell 27 there has the composition required to achieve the melting temperature present there.

(10) Gradient layers may also be formed during the production of the particles themselves, if that process is accompanied by certain diffusion events of alloy elements in the core 26 and/or in the shell 27. Possible production methods for the particles include, for example, galvanic or electroless electrochemical coating processes, of the kind already described in German Patent Publication No. DE 198 23 341 A1. Another possibility is that of production by atomic layer deposition (ALD) processes as known in the art. In this case, layers of atoms are applied to the particles so as to form, e.g., very thin layers. To generate the required layer thickness, a number of coating acts may be necessary in the ALD process.

(11) FIG. 3 shows how one part of the powder bed 13 is melted by the laser beam 17, specifically the part which lies at the edge of the component 19. In this case, the cores 26 of the particles 25 are melted. The shells 27 around the cores 26 have a higher melting point and initially still remain in the melt bath, and form shell fragments 28 which remain in the molten material, where they dissolve (alloy formation with the desired alloy composition of the particles). This process may proceed very quickly and is represented here only in model form.

(12) It can be seen in FIG. 4 how the laser 17 is moved over the powder bed 13, with the melt bath, as shown in FIG. 4, traveling from left to right. As it does so, a layer of the component 19 to be produced corresponding to the layer thickness d of the powder bed is formed. If the laser beam 17 travels further, the material solidifies, with formation of the volume of the component at the same time. The effect of the heating indicated in FIG. 1 is that the cooling rate of the material of the component 19 under production is less than 1° C. per second and the formation of alloy is not disrupted by an excessive cooling rate.

(13) In FIG. 5, the completed component can be seen. It is represented schematically as a ground section. The material of which the component 19 is made is a nickel-based superalloy. The controlled cooling rate has successfully had the effect of achieving a high proportion of so-called γ′ precipitates 30 composed of intermetallic phases. They are embedded in a matrix 31 of the component. Consequently, by selective laser melting, it is possible to achieve a component microstructure of a kind hitherto generatable, according to the prior art, only by casting, of turbine blades, for example. The microstructure therefore differs from the microstructure of the particles processed.

(14) Although the disclosure has been illustrated and described in detail by the exemplary embodiments, the disclosure is not restricted by the disclosed examples and the person skilled in the art may derive other variations from this without departing from the scope of protection of the disclosure. It is therefore intended that the foregoing description be regarded as illustrative rather than limiting, and that it be understood that all equivalents and/or combinations of embodiments are intended to be included in this description.

(15) It is to be understood that the elements and features recited in the appended claims may be combined in different ways to produce new claims that likewise fall within the scope of the present disclosure. Thus, whereas the dependent claims appended below depend from only a single independent or dependent claim, it is to be understood that these dependent claims may, alternatively, be made to depend in the alternative from any preceding or following claim, whether independent or dependent, and that such new combinations are to be understood as forming a part of the present specification.