EP3253513A1 - Method for producing a component from a superalloy by way of a powder-bed-based additive production method and component made from a superalloy - Google Patents

Abstract

The invention relates to a method for producing a component by means for example of laser melting. Here, the component (19) is produced in a powder bed (13), wherein the powder is melted by a laser beam (17). If the component (19) is intended to be produced for example from a nickel-based superalloy, the microstructure with γ'-precipitates that is typical for this alloy can only be created when, according to the invention, the cooling rate of the solidifying and cooling material (shortly after the melt pool created by the laser beam (17)) is kept at less than 1°C per second. To this end, the invention provides for the powder bed to be preheated by means of heating devices (23). Preheating the powder into temperature ranges of about 1000°C is possible according to the invention only in that the powder made from the nickel-based superalloy is coated with a thin layer made for example from aluminium oxide. As a result, caking of those particles in the powder bed which are not involved in the formation of the component (19) is prevented. Therefore, after a production process has been completed, the powder can advantageously be easily removed and used multiple times.

Description

description

A method of producing a superalloy member having a powder bed-based additive manufacturing method and superalloy member

The invention relates to a method for producing a component from a superalloy with a powder bed-based additive manufacturing method. In this method, the component is layer by layer in a powder bed by melting the powder bed forming particles with an energy beam such. B. an electron beam or a laser beam. Here, the powder bed is preheated to a temperature below the melting temperature of the particles before and while the particles are melted. Furthermore, the invention relates to a component made of a superalloy, which may have been produced, for example, by the said method. A method of the type described above is known for example from EP 1 355 760 Bl. The selective laser melting method discussed in this document is intended to be suitable for processing refractory materials. Since there is an interest in producing components from high-melting materials which have a low level of residual stresses, it is proposed according to this document that pre-heating of the material powder to a temperature of at least 500 ° C. be preceded by melting of the powder. However, this temperature must still be clearly below the melting point of the material of the powder.

Furthermore, according to Y.-C. Hagedorn al "Processing of Nickel based super alloy MAR M-247 in Means of High Temperature Selective Laser Melting (HT-SLM)" High Value Manufacturing, pages 291 to 295, London 2014, desire, also materials superalloys as powders by means of the selective to process laser melting. However, there is a problem that the manufactured products are subjected to high residual stresses, and because of this, cracks may occur. The authors therefore suggest a more intensive preheating of the powder.

On the other hand, it is known that the powder, which is strongly preheated, according to the mechanism of sintering with each other

baked. In selective laser melting, this results in the problem that the powder bed solidifies and also can cake with the surface of the manufactured component. A clean separation of the manufactured component from the powder bed is then no longer possible. In addition, the powder can not be used again if the particles cake together. This increases the cost of the process because regular raw material has to be discarded. The caking of the powder bed can additionally lead to the surface of the powder bed not remaining level. The application of new powder layers is thus made more difficult and geometric errors can occur in the surface of the powder bed. As a result, the quality of the components to be produced is impaired.

It is therefore an object of the invention to provide a method for producing a component from a superalloy with a powder bed-based additive manufacturing method, with which components can be produced from superalloys that meet the requirements placed on the components. In addition, it is an object of the invention to specify such a component, which can be produced inexpensively with high reliability.

This object is achieved by the method given above according to the invention that a powder is used, the particles are coated with a ceramic layer.

The coating of the particles has the advantage that they can be preheated to a higher temperature without having to to cook adjacent particles. This is explained by the fact that ceramic materials can be heated to higher temperatures without caking of the particles. The use according to the invention of a powder which is enveloped merely with a ceramic layer therefore has the advantage that the core of the particles has the material properties which are required on account of the material selection. The ceramic layer acts, so to speak, as a masking of these particles, which behave with regard to the problem of caking by powder preheating, such as ceramic particles. Although constituents of the layer located on the particles can be incorporated into the constituent component, this proportion is extremely low, since the layer on the particles is a very thin layer. The layer may, for example, have a thickness of at least 1 nm and at most 20 nm. This is advantageously sufficient already so that caking on adjacent particles is effectively prevented. With advantageously selected particle sizes of at least 10 μm and at most 50 μm, preferably an average particle size of 25 μm to 30 μm, it is then ensured that the proportion of the ceramic with respect to the entire particle material turns out to be very small. Assuming, for example, particles with a diameter of 30 μm, which are provided with a coating of 3 nm, the volume fraction of the ceramic is only 0.06% (3 × 3 nm / 15 μm). Thus, the impurities in the alloy that result from melting the powder by incorporating the material of the cladding into the component can be minimized. Incidentally, it has been shown that the very thin

Ceramic layer from the powder flakes off when it is heated to melting. This is due to the fact that the metallic alloy forming the core of the particles expands more strongly during heating than the ceramic layers. It is advantageous that the ceramic layers prevent caking of adjacent particles, even if these are due to the Heating the particles from the core of the Particles peel off. In the areas in which the particles touch, the residual layers remain even after a release of the core surface between the respective particles and thus prevent caking.

According to a particular embodiment of the invention it is provided that the ceramic contains metals, which also represents an alloying constituent of the superalloy. These metals advantageously interfere with the alloy composition much less than non-alloyed metals, since these only insignificantly shift the alloying proportions in the alloy of the manufactured component. On the other hand, non-alloy alloy components can have a greater share in the fact that the property profile of the material of the component changes.

It can be provided particularly advantageously that the alloy content of that alloying constituent of the superalloy in the core of the particles, which, as mentioned, is also contained in the ceramic, is reduced in comparison to the desired alloy composition of the superalloy. The reduction is carried out according to the invention to an extent that this alloying component based on the entire particle (including the layer) reaches or exceeds the alloy content of the target alloy composition of the superalloy. In other words, a compensation of a possible change in the alloy composition is counteracted here by the fact that this is already taken into account in the production of the component.

The material of the layer is then incorporated in the melting of the particles in the material of the forming component and there replaces the missing alloy content in the particles, which was deliberately omitted taking into account this effect. Prerequisite for this measure is a sufficient diffusibility of the alloy component in question, said diffusivity by the on Reason the preheating reduced cooling rate of the component is given.

Another development of the invention provides that the ceramic is oxidic or nitridic. Oxygen and nitrogen as an alloying component in superalloys can be advantageously taken to some extent without the alloy changing its property profile too much.

Advantageously, a nickel-base superalloy is used as the superalloy. From these superalloys, for example, the blades of gas turbines can be produced. The powder is advantageously preheated in this material to a temperature of at least 800 ° C and at most 1000 ° C. In addition, it is ensured by means of the device, which enters the heat for the purpose of preheating in the powder bed, that the cooling is cooled after the manufacture of the component at a rate of at most 1 ° C per second. Advantageously, it is thus possible for γ ^λ precipitates of intermetallic phases to form in the nickel-base superalloy component that characterize the typical microstructure of the nickel-base superalloy. For the formation of these excretions, it is well known that the growth of cuboid γ ^λ precipitates is suppressed by too rapid cooling. If the component is cooled at a slower rate than 1 ° C. per second, however, the precipitations mentioned are produced when the temperature falls below the γ ^λ solid temperature. The

Solidus temperature is 1150 ° C. To ensure a slow cooling from this temperature level, the temperature of the powder bed must be slightly lower. A temperature level between 900 ° C and at most 1000 ° C has proven to be advantageous.

If oxidic or nitridic ceramics are used as a layer on the particles (advantageous are aluminum oxide, titanium). tanoxide, silicon oxide, zirconium oxide, yttrium oxide and aluminum nitride), then a structure is formed in the component which contains oxygen or nitrogen or both alloying components. Such a component advantageously solves the problem stated at the outset that this can be produced by selective laser melting, the powders described being used.

According to an advantageous embodiment of the component, it is provided that the proportion of oxygen or the proportion of nitrogen does not exceed 0.3% by volume, preferably 0.1% by volume. In this way, it is advantageously ensured that, on the one hand, the layer on the particles can have a sufficient thickness in order to develop its effect. On the other hand, the resulting proportion of nitrogen or oxygen is nevertheless so low that this does not adversely affect the alloy of the component.

On the other hand, it is provided that the proportion of oxygen or the proportion of nitrogen is at least 0.03 vol%, so that the ceramic layer on the particles can have a sufficient thickness.

Further details of the invention are described below with reference to the drawing. Identical or corresponding drawing elements are each provided with the same reference numerals and will only be explained several times as far as there are differences between the individual figures. Show it :

1 shows a laser melting system in which an embodiment of the method according to the invention is carried out, cut,

 Fig. 2 to 4 selected steps in the implementation of

 Process according to Figure 1, wherein a smaller

Section of the component being produced is shown in section, and Figure 5 shows a detail of an embodiment of the component according to the invention, which has been prepared according to the figures 2 to 4.

FIG. 1 schematically shows a system 11 for laser melting. This has a process chamber 12, in which a powder bed 13 can be produced. To produce a respective layer of the powder bed 13, a distribution device in the form of a doctor blade 14 is moved over a powder supply 15 and then over the powder bed 13, whereby a thin layer of powder in the powder bed 13 is formed. A laser 16 then generates a laser beam 17, which is moved by means of an optical deflection device with mirror 18 over the surface of the powder bed 13. The powder is melted at the point of impact of the laser beam 17, whereby a component 19 is formed.

The powder bed 13 is produced on a building platform 20, which can be lowered incrementally by one respective powder layer thickness via an actuator 21 in a cup-shaped housing 22. In the housing 22 and the building platform 20 heaters 23 are provided in the form of electrical resistance heaters, which can preheat the emerging component 19 and the particles of the powder bed 13. In order to limit the energy requirement for preheating, is located on the housing 22 outside an insulation 24 with low thermal conductivity.

FIG. 2 shows an edge of the component 19 to be produced, which could be produced, for example, in a system according to FIG. This component is located in the powder bed 13, whose edges are indicated by a dot-dash line. In addition, 13 selected particles 25 are shown from the powder bed, which consist of the material of a nickel-based alloy. The manufactured component can, for. B. be a turbine blade. The particles each consist of a core 26, which consists of the actual material of the component 19, in the present case a nickel-based alloy. In addition, the core 26 of the particles 19 is surrounded by a layer 27 which completely envelopes the core and consists of alumina. This allows a preheating of the powder bed to up to 1000 ° C without adjacent particles 25 caked together. FIG. 3 shows how a part of the powder bed 13 is melted by means of the laser beam 17, namely that part which lies on the edge of the component 19. During this process, the cores 26 of the particles 25 melt. Before it melts, however, the cores 26, which are made of a metallic material, expand. In this case, the layer 27 partially bursts from the cores 26, resulting from it layer fragments 28 remain in the molten material and dissolve there (alloy formation). However, part of the layer fragments 28 is blasted so far that they remain outside of the molten bath 29 formed by the laser beam 17.

FIG. 4 shows how the laser 17 is moved over the powder bed 13, wherein the molten bath, as shown in FIG. 4, travels from left to right. In this case, a position of the component 19 to be produced corresponding to the layer thickness d of the powder bed is formed. If the laser beam 17 continues to migrate, the material solidifies with simultaneous formation of the component volume. The heating indicated in FIG. 1 causes the cooling rate of the material of the component 19 being produced to be less than 1 ° C. per second.

In Figure 5, the finished component can be seen. This is shown schematically as a microsection. The material from which the component 19 is made is a nickel-base superalloy. Due to the controlled cooling speed It has been possible to achieve a high proportion of so-called γ ^λ precipitates 30 from intermetallic phases. These are embedded in a matrix 31 of the component. In this way, a component structure can be achieved by means of the selective laser melt according to the invention, as could hitherto only be produced by casting, for example, turbine blades according to the prior art.

Claims

claims 1. A method for producing a component (19) from a superalloy with a powder bed-based additive production method, in which the component (19) is built up in layers in a powder bed (13) by melting particles (25) forming the powder bed (13) with an energy beam (17), the powder bed (13) being at a temperature below that Melting temperature of the particles (25) is preheated before and while the particles (25) are melted, characterized, that a powder is used whose particles (25) are coated with a ceramic layer (27). 2. The method according to claim 1, characterized, that the ceramic contains metals which also constitute an alloying constituent of the superalloy. 3. The method according to claim 2, characterized, in that the alloy content of the alloying constituent of the superalloy which is also contained in the ceramic is reduced compared to the target alloy composition of the superalloy to the extent that this alloying constituent is calculated based on the amount of the metal contained in the layer (27) coated particles (25) reaches or exceeds the alloy content of the target alloy composition. 4. Method according to one of the preceding claims, characterized in that that the ceramic is oxidic or nitridic. 5. The method according to any one of the preceding claims, characterized the layer (27) on the particles (25) has a thickness of at least 1 nm and at most 20 nm. 6. The method according to one of the preceding claims, d a d u c h e c e n e c e n e, that particles (25) having a particle size of at least 10 μπι and at most 50 μπι, preferably with a mean Particle size of 25 μπι to 30 μπι be used. 7. Method according to one of the preceding claims, characterized in that that a nickel-base superalloy is used as the superalloy. 8. The method according to claim 7, characterized, that the powder bed (13) to a temperature of at least 800 ° C and at most 1000 ° C is preheated. 9. The method according to any one of claims 7 or 8, characterized, that the component (19) is cooled after its completion at a speed of at most 1 ° C / s. 10. The method according to one of the preceding claims, d a d u c h e c e n e c e n e, that the ceramic is selected from the group of the following materials: aluminum oxide, titanium oxide, silicon oxide, Zirconia, yttria, aluminum nitride and silica. 11. Component made of a superalloy characterized, in that the alloy composition of the superalloy contains an alloying fraction of oxygen or of nitrogen. 12. Component according to claim 11, characterized, the proportion of oxygen or the proportion of nitrogen does not exceed 0.3% by volume. 13. Component according to one of claims 11 or 12, characterized, that it is at least 0.03% by volume of oxygen or the proportion of nitrogen.