Method for producing a capsule for hot isostatic pressing

Abstract

The present invention relates to a method for producing a capsule for hot isostatic pressing, comprising the steps of: providing a powder starting material which contains alloy constituents of a nickel alloy; constructing a wall of the capsule layer-by-layer by selectively solidifying some regions of the powder starting material, wherein a part of the powder starting material that has not been solidified in a particular layer remains within the wall; testing the part of the powder starting material remaining in the particular layer within the wall for impurities.

Description

[0001] Method for producing a capsule for hot isostatic pressing

[0002] DESCRIPTION

[0003] Technical area

[0004] The present invention relates to a method for producing a capsule for hot isostatic pressing.

[0005] State of the art

[0006] In powder metallurgical production, a component is consolidated from a powdered starting material into a raw body by hot isostatic pressing. For this purpose, the powdered starting material is kept in a so-called capsule, which holds the powder together for and during pressing. Conventionally, such a capsule can be produced, for example, by assembling and welding sheets, which allows a three-dimensional structure. However, evenly filling the capsule with the powder can be complex and entails the risk of uneven shrinkage or warping. Another critical factor can be the defect density in the powder, whereby the type and frequency of the defects can determine the subsequent process steps. Contaminated powder particles or occupied prior particle boundaries (PPBs), for example, can lead to defects in the powder.After hot isostatic pressing, further steps may be necessary, such as extrusion and forging.

[0007] Extrusion can, for example, break up former powder particle boundaries by stretching them beyond 6 / 1 (no longer having closed seams), whereby the resulting strong texture (microstructure, coorientation and properties) can be reduced again by subsequent isothermal forging and recrystallization. However, both during extrusion and forging, the initial microstructure can be exposed to comparatively high temperatures, which can result in the microstructure coarsening. Even if the microstructure can be partially refined and formed again through appropriate thermoprocessing consisting of cooling rates, forging and subsequent heat treatments through recrystallization, these steps at least involve effort and the fine-grained initial microstructure can usually no longer be achieved. This coarsening can, for example,be disadvantageous in that the coarsest remaining grains can be decisive for the fatigue strength (with regard to creep stability and thus tolerance, an overall coarser structure can also offer advantages, at least if the grain boundaries are interlocked).

[0008] Description of the invention

[0009] The present invention is based on the technical problem of providing an advantageous method for producing a capsule for hot isostatic pressing.

[0010] This is achieved with the method according to claim 1, in which the powdered starting material is first provided with alloying components, a nickel alloy (step i). A wall of the capsule is then built up layer by layer by selectively solidifying the powdered starting material in certain areas (step ii). The unsolidified portion of the powdered starting material in each layer remains within the wall, thus forming the powder filling of the capsule. Furthermore, the remaining portion of the powdered starting material within each layer is tested for impurities, thus testing the powder in situ for impurities before the next powder layer is applied.

[0011] As explained at the beginning, the type and frequency of defects or impurities in the powdered starting material can depend on the material. By building up the capsule layer by layer, i.e. the powdered material is applied layer by layer and locally solidified to produce the wall, the powder can be checked during "filling", thus reducing or preventing the introduction of impurities. This makes higher γ'solvus temperatures and γ'solvus phase proportions possible, for example because fewer or no subsequent extrusion or forging processes are necessary. In this case, the powdered starting material contains the alloying constituents of a nickel alloy, in particular a high-temperature-resistant nickel-based alloy. This, in turn, can enable the production of high-temperature-resistant engine components, e.g. rotor disks used in turbines.

[0012] Preferred embodiments can be found throughout the disclosure and in particular in the dependent claims, whereby the description of the features does not always distinguish in detail between process, use, or device aspects; in any case, the disclosure is implicitly to be read with regard to all claim categories. If steps for producing a capsule for hot isostatic pressing (HIPing) are described, this is also to be read as referring to the production of a component by HIPing with a corresponding prior capsule production. Furthermore, the production process is always also directed to a corresponding certificate, i.e., a correspondingly produced capsule or a correspondingly produced component.

[0013] The layer-by-layer build-up can take place in a generative manufacturing station, e.g., using a powder bed process. The powdered starting material is applied layer by layer, e.g., using a doctor blade. Within each layer, the powder is selectively solidified in the wall area before the next layer is applied. For this purpose, the respective layer is irradiated in the corresponding area with a beam source. This can generally be a laser source, for example, so that the area to be solidified is scanned with a laser beam. Preferably, however, an electron beam source can be provided, i.e., the area to be solidified is irradiated with an electron beam.

[0014] Each layer can, for example, have a thickness of no more than 200 μm, preferably no more than 100 μm. Possible lower limits can be, for example, 40 μm or 50 μm. Regardless of the layer thickness taken in the build direction, a wall thickness (thickness of the wall) taken perpendicular to the build direction can be in the millimeter range, e.g. at least 1 mm or 1.5 mm (with exemplary upper limits of, for example, 10 mm or 5 mm). After hot isostatic pressing, the part of the component that previously formed the capsule can be removed by material removal, e.g., turning. Homogeneous and reproducible powder filling of the capsule during its production can also be advantageous, for example, with regard to consistent shrinkage and reduced warpage of the component, whereby HIPing can take place closer to the final contour and thus reduce material requirements.

[0015] In a preferred embodiment, the powdered starting material is atomized into powder without the use of ceramics before the layer-by-layer buildup. This can be achieved, for example, with high-purity electrodes through Electrode Inert Gas Atomization (EIGA), whereby the melt jet has no contact with the nozzle and, for example, the copper coil and the entire atomization system are designed without ceramics. This preferably takes place in an argon atmosphere. To produce the electrodes, the starting material, i.e., the raw material for powder production, can be melted in a cold-wall crucible, for example, using Plasma Arc Melting (PAM), and drawn off into thin electrodes, e.g., using an inductively heated cold-wall mold system.

[0016] An electrode diameter can be a maximum of 150 mm, preferably a maximum of 100 mm (with a possible lower limit of 80 mm). These smaller diameters can, for example, enable higher solidification rates and thus reduce segregation. Ceramic-free atomization, for example, can reduce impurities, thus providing a high-quality starting material for additive manufacturing and HIPing (less scrap, etc.).

[0017] According to a preferred embodiment, a target fraction of the powdered starting material is adjusted by sieving and / or classifying prior to additive manufacturing, preferably to a range of at least 5 pm and at most 65 pm. This is preferably carried out on the unventilated powder, i.e., in a vacuum or under a protective gas atmosphere (e.g., with helium or argon). In a preferred embodiment, the powdered starting material is kept under vacuum during additive manufacturing and in-situ testing, for example, at a pressure of at most 10' 3 mbar, preferably not more than 10' 4 mbar (technically determined lower limits can be e.g. at 10' 6 mbar or 10' 5 mbar). Preferably, the capsule is sealed with layer-by-layer construction under vacuum conditions, so that the vacuum is maintained or "preserved" in the then hermetically sealed capsule.

[0018] In a preferred embodiment, the powdered starting material, after being atomized to powder, preferably using ceramic-free atomization (see above), is kept in a protective gas atmosphere until the additive manufacturing of the capsule. In the additive manufacturing station, the protective gas atmosphere, e.g., argon or helium, can be replaced by a vacuum, thus allowing the powder to be transferred from the protective gas to the vacuum without contact with air.

[0019] In a preferred embodiment, the powdered starting material is preheated during layer-by-layer construction such that the powder particles adhere slightly to one another at their surfaces. This can achieve a certain cohesion of the unsolidified part of the powdered material, which can, for example, prevent later demixing. Shocks or vibrations during transport of the capsule (see below for details) could otherwise lead to an accumulation of coarser particles at the top and finer particles at the bottom. Preheating can, for example, also prevent organic impurities and reduce powder contamination. The specific preheating temperature can depend on the material; it can, for example, be at least 500 °C, 700 °C, or 900 °C (with possible upper limits of, for example, 1200 °C or 1100 °C).

[0020] In a preferred embodiment, the testing according to step iii.) takes place after the application of each layer, i.e. the powdered starting material is applied layer by layer in the generative manufacturing station and each layer is tested for impurities before and / or after solidification. After the test, the subsequent layer is applied and in turn selectively solidified (and tested). The testing is preferably carried out using an electron beam process, which can be advantageous, for example, with regard to resolution and integration into the generative manufacturing station. The electron beam process can be, for example, electron optical imaging (ELO), which can be used, for example, to detect foreign inclusions with a composition different from the alloy components by evaluating backscattered electrons (BSE) (different elements have different electron contrast).In addition to elemental contrast, topography contrast can be used, for example, to detect irregularities or foreign particles > 100 pm. Energy-dispersive X-ray spectroscopy (EDX) detects the X-rays emitted upon electron beam excitation.

[0021] The nickel alloy contains nickel, and in a preferred embodiment it can additionally comprise: 2-5.5 wt% Al, 0.02-0.04 wt% C, 10-25 wt% Co, 8-18 wt% Cr, 0.2-1.5 wt% Hf, 0.5-5 wt% Mo, 0.1-6 wt% Nb, 0-3.5 wt% Ta, 0.3-3.5 wt% Ti, 0-10 wt% W, 0.02-0.04 wt% Zr, 0.01-0.03 wt% B.

[0022] The application also relates to a method for producing a component from a nickel alloy, wherein the capsule filled with the powdered starting material is first produced in a manner disclosed herein. This capsule is then pressed in a hot isostatic pressing station under a pressure of at least 100 MPa, preferably under a protective gas atmosphere (e.g., argon). A possible upper limit of the applied pressure can be, for example, 200 MPa. Pressing is carried out in combination with a heat treatment, whereby a temperature T > 1100 °C or T > the y-solvus temperature of the alloy can be applied (solution heat treatment). The heat treatment can, in particular, be multi-stage, for example, with holding times in the range of 0.2–5 hours.From the highest heat treatment temperature (solution heat treatment) down to temperatures below 600 °C, quenching can occur at one or more different rates of 20-500 K / min, with aging in the hot isostatic pressing station under a residual pressure of 750 °C to 900 °C for 1-5 hours, followed by cooling below 20 °C at, for example, a rate of 15-30 K / min. Optionally, after HIPing, breakdown forging and / or extrusion of the capsule to a stretch ratio of over 5 / 1 can be performed at a pressure of 100 MPa to 200 MPa and T > 1100 °C for 2-3 hours, e.g., in combination with subsequent near-net-shape forging to a disc contour (isothermal or conventional). A heat treatment can then be carried out (T > 1100 °C or T > y'solvus temperature of the alloy), whereby this heat treatment can in particular be carried out in several stages with the temperatures, rates and holding times mentioned in the previous paragraph.Regardless of whether the optional forging / extrusion step is available or not, a second aging treatment can optionally be performed following the multi-stage heat treatment, for example, at 650 °C to 850 °C for a duration of 5-24 hours. This can be done, for example, with air cooling in a separate furnace.

[0023] Following hot isostatic pressing, the capsule can be removed from the component by machining, for example, by turning. The component can be machined to a near net shape (NNS), with non-destructive testing, for example, using ultrasound and / or eddy current, possible before further processing.

[0024] In a preferred embodiment, the capsule is transported shock- and vibration-free before hot isostatic pressing, namely after capsule production and before HIPing. This applies to the path between the additive manufacturing station and the hot isostatic pressing station. Shocks and vibrations are reduced or avoided, for example, by appropriately supporting the capsule during transport. This can prevent segregation; the powdered starting material also adheres slightly to one another due to the preheating in the capsule (see above).

[0025] The invention also relates to a component which is produced using a capsule for hot isostatic pressing according to the inventive method described here. Thus, the invention extends to all components produced using the inventive method described here. In a preferred embodiment, the component is a component for a turbomachine, in particular for an aircraft engine, for example a disk, such as a rotor disk for the turbine sector. Following the steps described above, recesses for receiving blade roots, for example contoured recesses for positively holding the blade roots, can be introduced into the outer circumference of the disk.

[0026] Short description of the drawings

[0027] In the following, the invention is explained in more detail using an exemplary embodiment, whereby the individual features can also be essential in other combinations and no distinction is made in detail between the different claim categories.

[0028] In detail,

[0029] Figure 1 shows a schematic view of a generative capsule production for hot isostatic pressing;

[0030] Figure 2 shows some process steps in a flow chart;

[0031] Figure 3 shows a schematic longitudinal section of a turbofan engine to illustrate the application environment.

[0032] Preferred embodiment of the invention

[0033] Fig. 1 schematically illustrates a generative manufacturing station 1 in which a capsule 10 is produced and then fed to a hot isostatic pressing station 2. In the present example, the capsule 10 is produced using a so-called powder bed process from a powdered starting material 11, which is successively applied to a build platform 13 in layers 12.1-12.3. Using an electron beam 17 emitted by an electron beam source 16, a respective region 15.1-15.3 in a respective layer 12.1-12.3 is solidified by irradiation to produce a wall 15 of the capsule 10. Within the wall 15, an unsolidified portion 11.1-11.3 of the powdered starting material 11 remains, which forms the filling of the capsule 10.

[0034] To apply layers 12.1-12.3, the powdered starting material 11 is stored in a container 18. This container can be moved across the build platform 13 to apply each layer, with a squeegee 19 provided for scraping and thus setting a defined layer thickness. After each layer has been applied, the build platform 13 can be lowered, which is not shown in the schematic representation of Figure 1.

[0035] The generative build-up takes place in a processing chamber 20, which is pressurized to a pressure of approximately 10' 5mbar. The capsule 10 is sealed under these vacuum conditions, so that the powdered starting material 11 is enclosed therein under vacuum. Furthermore, the portion 11.1-11.3 of the powdered starting material 11 remaining within the wall 15 is examined for impurities before the subsequent layer is applied. This is carried out using an electron beam method 21, for which an electron beam source 22 is provided for emitting an electron beam 23. In detail, the electron beam method can be, for example, electron-optical imaging or energy-dispersive X-ray spectroscopy.

[0036] The data obtained with the electron beam method, for example, regarding defect sizes or frequencies, can be compared with non-destructive measurements taken later (e.g., ultrasound or X-ray measurements), e.g., in an equal-or-better comparison. This can be used for quality control; the results can then be used, for example, to reliably detect and exclude components with foreign inclusions above critical sizes, or to achieve a higher defect resolution limit than with conventional non-destructive testing methods.

[0037] Before the capsule production shown in Figure 1, the powdered material can be obtained through ceramic-free atomization, for example, from high-purity electrodes using Electrode Inert Gas Atomization (EIGA). See the introduction to the description for details. The powdered starting material 11 is then introduced into the processing chamber 20 under an argon atmosphere, thus avoiding any air contact. The powdered starting material contains the alloying constituents of a nickel alloy, with some possible alloy compositions listed as examples in the table below.

[0038]

[0039] During the layer-by-layer buildup, the powdered starting material 11 is preheated after the application of each layer 12.1-12.3 so that the powder particles adhere slightly to one another and demixing can be prevented. Furthermore, the capsule 10 is transported shock- and vibration-free from the additive manufacturing station 1 to the hot isostatic pressing station 2. There, the capsule 10 is then pressed into the component 100 under a pressure of 100 MPa-200 MPa at a temperature T >1100 °C. During this process, the capsule 10 undergoes shrinkage, whereby the previously constructed wall 15 and thus the capsule contour take this into account; namely, a suitable capsule contour taking the shrinkage into account was numerically determined in advance through simulations.

[0040] Fig. 2 summarizes several process steps in a flowchart. Electrode production 30 for EIGA can be achieved by plasma arc melting (PAM) or vacuum induction melting (VIM). The subsequent powder production takes place by ceramic-free atomization 31 from the electrodes, e.g., via EIGA or new VIGA-CC. The powdered starting material is then sieved and / or classified 32 to a target fraction of 5 pm to 65 pm. The capsule is then produced by layer-by-layer construction 33 and filled and tested in situ; see above for details.

[0041] Furthermore, different processing routes are possible. On the one hand, after hot isostatic pressing 34 with heat treatment, the resulting component can be directly subjected to non-destructive testing 35. During subsequent machining 36 of the component, for example, the capsule, i.e., the wall, can be turned off and further processing steps can be performed on the component before it is again subjected to non-destructive testing 37.

[0042] In the alternative route, hot isostatic pressing 34 is followed by breakdown forging 40. After subsequent non-destructive testing 41, further forging 42 can be performed to increase strength (e.g., isothermal forging or conventional T / oZ-t / zc drop forging). After heat treatment 43, further non-destructive testing 44 can be performed. Following this, the component is machined 36 and subjected to further non-destructive testing 37.

[0043] To illustrate the field of application, Fig. 3 shows a turbomachine 50, specifically an aircraft engine 60. This is functionally divided into a compressor 52, a combustion chamber 53, and a turbine 54. Air drawn in the compressor 52 is compressed and combusted with added fuel in the downstream turbine 54. The resulting hot gas is expanded in the turbine 54 and drives its rotors 55 (only a few are referenced here as examples). Each rotor 55 comprises a respective rotor disk 55.1, which can be manufactured as a component 100 by hot isostatic pressing from a capsule 10; see also the illustration in Figure 1. LIST OF REFERENCE SYMBOLS

[0044] Additive Manufacturing Station 1

[0045] Hot isostatic pressing station 2

[0046] Capsule 10

[0047] Powdered starting material 11

[0048] Unconsolidated part 11.1-11.3

[0049] Layers 12.1-12.3

[0050] Construction platform 13

[0051] Wall 15

[0052] Area 15.1-15.3

[0053] Electron beam source 16

[0054] Electron beam 17, 23

[0055] Container 18

[0056] Squeegee 19

[0057] Processing chamber 20

[0058] Electron beam process 21

[0059] Electron beam source 22

[0060] Electrode position 30

[0061] Atomization 31

[0062] Sieving / Sifting 32

[0063] Layered construction 33

[0064] Hot isostatic pressing 34

[0065] Exam 35, 37, 41, 44

[0066] Component processing 36

[0067] Breakdown- Forging 40

[0068] Forging 42

[0069] Heat treatment 43

[0070] Turbomachine 50

[0071] Compressor 52

[0072] Combustion chamber 53

[0073] Turbine 54 Rotor 55

[0074] Rotor disc 55.1

[0075] Aircraft engine 60

[0076] Component 100

Claims

CLAIMS 1. A method for producing a capsule (10) for hot isostatic pressing, comprising the steps of: i.) providing a powdered starting material (10) which contains alloy components of a nickel alloy; ii.) building up (33) a wall (15) of the capsule (10) layer by layer by selectively solidifying the powdered starting material in certain areas, wherein a portion (11.1-11.3) of the powdered starting material (11) which is not solidified in a respective layer (12.1-12.3) remains within the wall (15); iii.) testing the portion (11.1-11.3) of the powdered starting material (11) which remains in the respective layer (12.1-12.3) within the wall (15) for impurities.

2. The method according to claim 1, wherein the powdered starting material (11) is atomized (31) to powder in step i.) without ceramics.

3. Method according to claim 2, wherein the powdered starting material (11) is sieved and / or classified (32) after the ceramic-free atomization (31) to a target fraction of at least 5 pm and at most 65 pm.

4. A method according to any one of the preceding claims, wherein the powdered starting material (11) is kept under a vacuum condition during steps ii.) and iii.).

5. The method according to claim 4, wherein the capsule (10) is sealed by layering under vacuum conditions.

6. Method according to one of the preceding claims, in which the powdered starting material (11) after atomization (31) to powder and before layer-by-layer construction (33) according to step ii.) is kept in a protective gas atmosphere.

7. A method according to any one of the preceding claims, wherein the powdered starting material (11) is preheated in step ii) to adhere the unsolidified part of the powdered starting material (11).

8. Method according to one of the preceding claims, in which steps ii.) and iii.) are repeated several times, i.e. in each case a layer (12.1-12.3) of the powdered starting material (11) is applied and in each layer (12.1-12.3) the respective non-solidified part (11.1-11.3) of the powdered starting material (11) is tested before a subsequent Layer (12.1-12.3) is applied.

9. Method according to one of the preceding claims, wherein the testing according to step iii.) is carried out in an electron beam method (21).

10. The method according to claim 9, wherein the electron beam method (21) is an electron optical imaging (ELO) or an energy dispersive X-ray spectroscopy (EDX).

11. A method according to any one of the preceding claims, wherein the alloying constituents comprise, in addition to Ni, at least one of Al, C, Co, Cr, Hf, Mo, Nb, Ta, Ti, W, Zr and B.

12. A method for producing a component (100) from a nickel alloy, in which a capsule (10) is produced in a method according to one of the preceding claims; the capsule (10) is hot isostatically pressed (34) under a pressure of at least 100 MPa.

13. The method according to claim 12, wherein the fully assembled capsule (10) is transported from a generative manufacturing station (1) to a hot isostatic pressing station (2) without shock or vibration.

14. Method according to one of claims 12 to 13, wherein the component (100) is a component (100) for a turbomachine (50), in particular a disk (55.1) for an aircraft engine (60).

15. Component (100), in particular a component (100) for a turbomachine (50), manufactured via a capsule (10) for hot isostatic pressing according to one of claims 1 to 14.

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