METHOD FOR PRODUCING TURBOMACHINE DISKS

Abstract

A method for manufacturing turbomachine disks is provided. The method includes: providing a nickel alloy powder; and shaping the powder to obtain a disk. Providing a powder can include: manufacturing a nickel alloy electrode by PAM-CHR; atomizing a nickel alloy by EIGA from the nickel alloy electrode, leading to a raw powder; and sifting the raw powder under inert atmosphere or under vacuum with a granulometric cut-off between 150 ?m and 50 ?m, leading to the nickel-based alloy powder. In some examples, the granulometric cut-off can be between 125 ?m or 75 ?m.

Claims

1. A method for manufacturing turbomachine disks, comprising: providing a nickel alloy powder; shaping the powder to obtain a disk; a wherein providing the powder comprises: manufacturing a nickel alloy electrode by plasma arc melting cold hearth refining, PAM-CHR; atomizing a nickel alloy by electrode induction melting gas atomization, EIGA, from the nickel alloy electrode, leading to a raw powder; and sifting the raw powder under inert atmosphere or under vacuum with a granulometric cut-off between 150 ?m and 50 ?m, leading to the nickel alloy powder.

2. The method of claim 1, wherein during PAM-CHR, the nickel alloy is melted in a water-cooled copper crucible before being melted in a copper molder ring crucible.

3. The method of claim 1, wherein EIGA comprises: arranging the electrode having a longitudinal axis such that the longitudinal axis of the electrode is vertical; contactlessly heating the lowest end of the electrode leading to a thin stream of molten alloy flowing by gravity through a nozzle; and injecting, at the outlet of the nozzle, an inert gas directed towards and around the thin stream of molten alloy resulting in the atomization of the thin stream of alloy.

4. The method of claim 3, wherein the inert gas is argon.

5. The method of claim 1, wherein the sifting is carried out with a granulometric cut-off between 140 ?m and 60 ?m, between 130 ?m and 70 ?m, or between 125 ?m and 75 ?m.

6. The method of claim 1, wherein shaping comprises: hot densifying the powder into a forging blank; manufacturing the disk by isothermally forging, heat treating, and machining the blank.

7. The method of claim 6: wherein hot densifying comprises placing the powder under vacuum in a hermetically sealed container; hot compacting of the container; extruding the compacted container resulting in a cylindrical bar having an outer layer made of the material of the container and a cylindrical core made of nickel-based alloy; and eliminating of the outer layer; and cutting of the cylindrical core into forging blank.

Description

DESCRIPTION OF THE DRAWINGS

[0058] The foregoing aspects and many of the attendant advantages of the claimed subject matter will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:

[0059] FIG. 1A is a drawing of a VIGA atomization tower.

[0060] FIG. 1B is an enlargement at the crucible of the VIGA atomization tower of FIG. 1A.

[0061] FIG. 2 is a graph showing the lifetime (LT) of the test specimen of nickel alloy prepared from a powder obtained by VIGA as a function of the stress (a) applied during testing. The average LCF curve and the minimum LCF curve are shown.

[0062] FIG. 3 is a graph showing the lifetime (LT) of the test specimen of nickel alloy prepared from a powder obtained by VIGA with sifting as a function of the stress (a) applied during testing. The average LCF curve and the minimum LCF curve are given for two granulometric cut-offs used, <53 ?m and <75 ?m.

[0063] FIG. 4 is a chart schematically showing an exemplary method for manufacturing turbomachine disks according to the present disclosure.

[0064] FIG. 5 is a drawing of an upper part of an EIGA atomization tower where an electrode is melted, before the electrode melts.

[0065] FIG. 6 is the same drawing as FIG. 5 during melting of the electrode.

[0066] FIG. 7 is a chart schematically showing the steps for providing the powder according to an exemplary method for manufacturing turbomachine disks according to the present disclosure.

[0067] FIG. 8 is a chart schematically showing the steps for atomizing a nickel alloy according to an exemplary method for manufacturing turbomachine disks according to the present disclosure.

[0068] FIG. 9 is a chart schematically showing the steps of shaping the powder according to an exemplary method for manufacturing turbomachine disks according to the present disclosure.

[0069] FIG. 10 is a chart schematically showing the steps for densifying the powder according to an exemplary method for manufacturing turbomachine disks according to the present disclosure.

[0070] FIG. 11 is a chart schematically showing the steps for manufacturing a disk from a forging blank according to an exemplary method for manufacturing turbomachine disks according to the present disclosure.

DETAILED DESCRIPTION

[0071] The detailed description set forth above in connection with the appended drawings, where like numerals reference like elements, are intended as a description of various embodiments of the present disclosure and are not intended to represent the only embodiments. Each embodiment described in this disclosure is provided merely as an example or illustration and should not be construed as preferred or advantageous over other embodiments. The illustrative examples provided herein are not intended to be exhaustive or to limit the disclosure to the precise forms disclosed.

[0072] A method for manufacturing turbomachine disks according to the present disclosure is described below with reference to FIGS. 4 to 11.

[0073] Such a method comprises providing S100 a powder of nickel alloy and shaping S200 the powder into a disk (FIG. 4).

[0074] Obtaining S100 the powder comprises atomizing S120 a nickel alloy through Electrode Induction-Melting Gas Atomization (also called EIGA) and sifting S130 the raw powder under vacuum or under neutral atmosphere with a granulometric cut-off of between 150 ?m and 50 ?m (FIGS. 4 and 7). The neutral atmosphere may be an argon atmosphere.

[0075] EIGA (FIG. 8) is performed with a nickel alloy electrode 2 with a longitudinal axis. EIGA results in a raw powder. Atomizing S120 may comprise placing S121 the electrode 2 such that the longitudinal axis of the electrode is vertical, contactlessly heating S122 the lowest end of the electrode 2 resulting in a thin stream of molten alloy flowing by gravity through a nozzle and injecting S123, at the outlet of the nozzle, an inert gas directed towards and around the thin stream of molten alloy resulting in the atomization of the thin stream of alloy. Thus, there is no contact between the electrode and any other element during heating.

[0076] Contactlessly heating S122 may be carried out through induction. Heating S122 is performed until the electrode material melts and a thin stream of molten alloy flows from the lower end of the electrode.

[0077] Injecting S123 the inert gas towards the thin stream of molten alloy cuts the thin stream of molten alloy into molten alloy particles Pm. The injected inert gas may be argon.

[0078] Atomizing S120 may comprise cooling S124 the molten alloy particles Pm to obtain solid particles Ps. Cooling S124 may be performed passively, meaning by contacting the molten alloy particles Pm with the surrounding atmosphere, the molten alloy particles Pm exchanging heat with this atmosphere. Cooling S124 may also be active, for example by injecting an inert gas with a temperature lower than the melting temperature of the alloy. Active cooling S124 may also be performed by cooling the atomization tower in which particles are produced, for example using a cooling circuit surrounding the atomization tower.

[0079] FIG. 5 shows the upper part of an EIGA atomization tower. The remainder of the tower (lower part) is similar to the VIGA atomization tower of FIG. 1A. Thus, this lower part will not be described in more detail here.

[0080] EIGA requires an electrode 2 of the desired nickel alloy, a contactless heater, for example an induction heater 3, and an inert gas injector 4. The contactless heater comprises a space for receiving the lower end of the electrode 2. In the case of an induction heater 3, this latter comprises coils around a receiving space. The injector 4 comprises a central orifice 41 serving as a nozzle with an inlet at its upper part and an outlet at its lower part. The injector 4 also comprises an injection crown 42 and a convergence crown 43 for bringing the gas towards the outlet of the injector 4. Further, the injector 4 may be conFIGUREd to generate a swirling flow of the inert gas. During contactless heating, the lower end of the electrode 2 is induction heated by the coils of the induction heater 3 until the electrode material melts. From this moment (see FIG. 6), a thin stream of molten alloy flows through the orifice 41 of the injector 4. Inert gas is injected by the injection crown 42 and redirected towards the outlet by the convergence crown 43. The inert gas jet cuts the thin stream of molten alloy and atomizes it to form molten particles Pm which solidify into falling solid particles Ps. It is worth observing once again that the bottom end of the electrode 2 is heated without contact with another element and that the thin stream of molten alloy also flows through the orifice 41 of the injector 4 without contact with the walls of the orifice 41. Thus, unlike VIGA, there is no risk of pulling ceramic particles free with EIGA.

[0081] Replacement of VIGA by EIGA is not an obvious choice. In fact, VIGA allows a very precise control of the temperature to which the alloy is heated and in particular allows overheating this alloy because this latter is contained in a crucible during heating. The overheating of the alloy has the advantage of allowing production of powders that are very fine compared to a heating temperature equal to the melting temperature. This overheating is not as easily controllable with EIGA because the alloy flows in the form of a thin stream as soon as it reaches its melting temperature. Further, VIGA makes it possible to control the thickness of the stream flowing from the crucible by controlling the opening of the crucible nozzle. This control is not possible with EIGA.

[0082] Also, EIGA uses an electrode which must be fabricated. This then adds an additional step in the manufacturing process of the powder, whereas VIGA simply makes it possible to gather the ingredients in the crucible before heating.

[0083] The electrode used in EIGA is made by plasma arc melting with cold hearth refining(also known under the acronym PAM-CHR).

[0084] PAM-CHR may be carried out in a cold-crucible refining furnace. In that kind of furnace, the metal is first melted in a water-cooled copper crucible before flowing into a copper molder ring. Copper is not reactive with nickel alloys; this eliminates any contamination of the electrode by ceramic inclusions.

[0085] Thus, providing S100 the powder comprises manufacturing S110 an electrode 2 such as described above (FIG. 7).

[0086] The granulometric cut-off may be comprised between 140 ?m and 60 ?m or even between 130 ?m 70 ?m, for example 125 ?m, 75 ?m or 53 ?m. Sifting S130 results in a nickel alloy powder which will be used for shaping S200.

[0087] The use of a <53 ?m granulometric cut-off in VIGA was due to the intent to improve the mechanical properties of the manufactured parts which were reduced by the presence of ceramic inclusions in the material. The present authors, when looking for a solution for even further improving the mechanical properties, identified the combination of PAM-CHR and EIGA as a solution for manufacturing the nickel alloy powder with a greatly reduced or even nonexistent ceramic inclusion contamination level compared to VIGA. They next had the idea of raising the granulometric cut-off up to 75 ?m, even 125 ?m or even 150 ?m. The use of a higher granulometric cut-off leads to an improvement in the atomization yield; indeed, less raw powder needs to be discarded, or otherwise expressed, a larger portion of raw powder may be used for manufacturing the disks.

[0088] Another indirect advantage relates to the grain size of the finished parts. Now, it is well known that the creep properties increase with the grain size. During the manufacturing of the disks, the nickel alloy is treated at temperatures over ? solvus. At these temperatures, the primary ? grains, the role of which is to block the grain joints, are dissolved and the grains grow. However, in the case of powders, the growth of the grain remains limited to the size of the particles of the initial powder. In fact, the growth of the grains is blocked by the prior particle boundaries of the particles (also known as PPB) which are thin oxide layers at the surface of the powder particles and which limit the grain size to the initial size of the powder particles.

[0089] By increasing the granulometric cut-off, the powder particle size is increased which makes it possible to increase the grain size in the finished part thereby improving the creep properties thereof.

[0090] The absence of ceramic inclusions makes it possible to dispense with the probabilistic approach to the sizing of the parts and return to a conventional approach in which the sampled test specimen is representative of the material of the entire part.

[0091] Shaping S200 may comprise hot densifying S210 the sifted powder into a forging blank and manufacturing S220 the disk (FIG. 9).

[0092] Densifying S210 may comprise placing S211 the sifted powder under vacuum in a hermetically sealed container, hot compacting S212 the container, extruding S213 the compacted container resulting in a cylindrical bar having an outer layer made of the material of the container and a cylindrical core made of nickel alloy, and eliminating S214 the outer layer, for example by machining, and cutting S215 the cylindrical core into forging blanks (FIG. 10).

[0093] Manufacturing S220 the disk may comprise isothermally forging S221 the blank, heat treating S222 and machining S223 the disk (FIG. 11). Isothermally forging may comprise transforming the cylindrical blank into a disk, of more or less complex shape, by the use of matrices; the cylindrical blank and the matrices are at the same temperature. Isothermally forging, as long as the nickel alloys are concerned, makes it possible to avoid surface cracks which form during contact of the cylindrical blank with cold matrices.

[0094] Heat treating may comprise solution annealing at high temperature followed by controlled cooling and a tempering treatment at a lower temperature for a longer time. With a combination of temperature, time and cooling speeds, these treatments make it possible to guide the microstructure in terms of grain size and size distribution of the hardening ? phase to obtain the required mechanical properties.

[0095] Machining provides the part with its final geometry according to the plan.

[0096] In the foregoing description, specific details are set forth to provide a thorough understanding of exemplary embodiments of the present disclosure. It will be apparent to one skilled in the art, however, that the embodiments disclosed herein may be practiced without embodying all of the specific details. In some instances, well-known process steps have not been described in detail in order not to unnecessarily obscure various aspects of the present disclosure. Further, it will be appreciated that embodiments of the present disclosure may employ any combination of features described herein.

[0097] The present application may reference quantities and numbers. Unless specifically stated, such quantities and numbers are not to be considered restrictive, but exemplary of the possible quantities or numbers associated with the present application. Also in this regard, the present application may use the term plurality to reference a quantity or number. In this regard, the term plurality is meant to be any number that is more than one, for example, two, three, four, five, etc. The terms about, approximately, near, etc., mean plus or minus 10% of the stated value. For the purposes of the present disclosure, the phrase at least one of A and B is equivalent to A and/or B or vice versa, namely A alone, B alone or A and B.. Similarly, the phrase at least one of A, B, and C, for example, means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B, and C), including all further possible permutations when greater than three elements are listed.

[0098] It should be noted that for purposes of this disclosure, terminology such as upper, lower, vertical, horizontal, fore, aft, inner, outer, front, rear, etc., should be construed as descriptive and not limiting the scope of the claimed subject matter. Further, the use of including, comprising, or having and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless limited otherwise, the terms connected, coupled, and mounted and variations thereof herein are used broadly and encompass direct and indirect connections, couplings, and mountings.

[0099] Throughout this specification, terms of art may be used. These terms are to take on their ordinary meaning in the art from which they come, unless specifically defined herein or the context of their use would clearly suggest otherwise.

[0100] The principles, representative embodiments, and modes of operation of the present disclosure have been described in the foregoing description. However, aspects of the present disclosure, which are intended to be protected, are not to be construed as limited to the particular embodiments disclosed. Further, the embodiments described herein are to be regarded as illustrative rather than restrictive. It will be appreciated that variations and changes may be made by others, and equivalents employed, without departing from the spirit of the present disclosure. Accordingly, it is expressly intended that all such variations, changes, and equivalents fall within the spirit and scope of the present disclosure as claimed.