EP4373796A1

EP4373796A1 - Method for manufacturing a hollow part made of metal matrix or ceramic matrix composite reinforced with short fibers

Info

Publication number: EP4373796A1
Application number: EP21810068.3A
Authority: EP
Inventors: Arnaud DELEHOUZE; Eric Bouillon
Original assignee: Safran Ceramics SA
Current assignee: Safran Ceramics SA
Priority date: 2020-10-20
Filing date: 2021-10-12
Publication date: 2024-05-29
Also published as: WO2022084602A1; FR3115280A1; CN116547253A; US20230382813A1; FR3115280B1

Abstract

The invention relates to a method for manufacturing a hollow part made of metal matrix or ceramic matrix composite, comprising the following steps: • - preparing a raw material (30) comprising at least short fibers and a ceramic matrix or metal matrix precursor charge, • - positioning a sacrificial core (10) in a molding cavity (23) of injection-molding equipment (20), the molding cavity having dimensions larger than the dimensions of the sacrificial core, • - shaping the raw material (30) by injection molding said raw material into the free space (230) between the sacrificial core (10) and an internal wall of the molding cavity so as to obtain a green part comprising the sacrificial core and the shaped raw material, • - extracting the green part from the injection-molding equipment (20), • - densifying the raw material (30) by flash sintering of the green part so as to transform the charge into a ceramic matrix or into a metal matrix, • - removing or eliminating the sacrificial core (10) so as to obtain a hollow part made of ceramic matrix or metal matrix composite, • wherein the sacrificial core is coated with a flexible graphite sheet, with a graphite layer deposited by spraying or with a boron nitride paint layer before the step of injecting the raw material.

Description

Title of the invention: Process for manufacturing a hollow part in composite material with a metal or ceramic matrix reinforced with short fibers

Technical area

The present invention relates to the general field of the manufacture of hollow parts made of composite material with a metal or ceramic matrix.

Prior technique

Ceramic (CMC) or metallic (CMM) matrix composite materials are materials consisting of a fibrous reinforcement densified by a ceramic or metallic matrix. These materials have a high level of performance in terms of stiffness and resistance at high temperature.

A field of application of the invention is the manufacture of hollow parts used in the hot parts of a turbomachine, for example parts of the turbine, rear body or secondary nozzles of the turbomachine. More specifically, the invention can be used for producing distributors or hollow turbine blades.

A turbine stage consists of a fixed blade or distributor belonging to a stator, followed by a mobile blade belonging to a rotor. The first stages of the distributor are generally hollow in order to route air radially from the outside to the inside of the turbine, so as to supply the hub with air to ensure its pressurization and purging as well as its possible cooling. . Part of this air can be intended for cooling the distributor.

In addition, the moving blades can also be hollow so that cooling air can pass through them. The use of hollow parts also makes it possible to reduce the mass of the turbomachine.

Document US2020270180 discloses a process for manufacturing hollow CMC parts which consists of forming a fibrous preform around a core, consolidating the preform and eliminating the core. In document US2020270180, the fibrous preform is formed with continuous fibers by draping fibrous textures around the core or by weaving a preform comprising a hollow zone intended for the insertion of the core.

The solution described in the document US2020270180 uses strata or woven structures with continuous fibers which intrinsically have a hold or cohesion which allows them to be shaped around a core before consolidation.

The solution disclosed in document US2020270180 cannot be transposed to the manufacture of a hollow CMC part from short fibers which are by definition discontinuous and cannot be woven together to form a coherent fibrous structure.

Short fibers make it possible to obtain small parts. Short fibers also allow the manufacture of composite material parts directly in their final shape (“net shape”) or near final shape (“near net shape”).

It would therefore be desirable to have a solution allowing the manufacture of hollow parts in CMC or CMM with short fibers.

Disclosure of Invention

The object of the present invention is therefore to overcome the aforementioned drawbacks by proposing a method for manufacturing a hollow part made of composite material with a ceramic or metallic matrix comprising the following steps: preparation of a raw material comprising at least short fibers and a ceramic matrix or metal matrix precursor loading, positioning of a sacrificial core in a molding cavity of an injection tool, the molding cavity having dimensions greater than the dimensions of the sacrificial core, shaping of the raw material by injection molding said raw material into the free space between the sacrificial core and an internal wall of the molding cavity so as to obtain a green part comprising the sacrificial core and the shaped raw material , extraction of the green part from the injection tooling, densification of the raw material by flash sintering of the green part so as to transform the charge into a ceramic matrix or a metal matrix, removal or elimination of the sacrificial core so as to obtain a hollow part made of composite material with a ceramic or metal matrix.

The manufacturing method of the invention advantageously combines the use of a sacrificial core with the techniques of injection molding and densification by flash sintering. Indeed, the sacrificial core serves both as a counter-mold during the shaping step to define the shape and dimensions of the cavity to be formed and of the final part ("net shape") and as a conductor which participates in the sintering of the particles of the matrix precursor filler.

The method of the invention makes it possible to manufacture hollow parts in CMC or CMM composite material with short fiber reinforcement, even for parts of small dimensions and/or having a complex geometry.

According to a first aspect of the method of the invention, the sacrificial core has a geometry capable of being unmolded from the densified raw material after the densification step. In this case, the sacrificial core can be coated with a sheet of flexible graphite, a layer of graphite deposited by spraying or a layer of boron nitride paint before the step of injecting the raw material in order to facilitate its mechanical removal.

According to a second aspect of the method of the invention, the sacrificial core is eliminated by chemical treatment. This makes it possible to use cores that have complex geometries that cannot be demolded (undercuts) and to form parts with any shape of cavity.

According to a third aspect of the process of the invention, the sacrificial core is made with one of the following materials: graphite, zirconia and alumina.

According to a fourth aspect of the process of the invention, the raw material comprises a ceramic matrix precursor filler and short fibers made of a material chosen from one of the following materials: carbon, silicon carbide and alumina.

According to a fifth aspect of the process of the invention, the raw material comprises a metal matrix precursor filler and short fibers made of a material chosen from one of the following materials: silicon carbide and alumina. A load metal, typically silicon, can also be added to the raw material to promote final densification.

According to a sixth aspect of the process of the invention, at least one diffusion barrier layer is deposited on the sacrificial core before the injection of the raw material. This avoids possible chemical interactions between the sacrificial core material and the material(s) used in the raw material to form the matrix.

According to a seventh aspect of the process of the invention, the raw material further comprises a binder, the process further comprising a step of debinding the raw material before or during the densification of the raw material. This eliminates the presence of organic matter in the composite material of the final part.

Brief description of the drawings

[Fig. 1] Figure 1 is a flowchart showing the steps of a method of manufacturing a hollow part made of composite material with a ceramic or metal matrix with short fiber reinforcement according to the invention,

[Fig. 2] Figure 2 is a schematic perspective view of a sacrificial core in accordance with one embodiment of the invention,

[Fig. 3] Figure 3 is a schematic exploded perspective view showing the positioning of a sacrificial core in an injection molding tool according to one embodiment of the invention,

[Fig. 4] Figure 4 is a sectional view of the tooling of figure 3 once closed,

[Fig. 5] Figure 5 is another sectional view of the tooling of figure 3 once closed,

[Fig. 6] Figure 6 is a schematic exploded perspective view showing the extraction of a green part of the tooling of Figures 3, 4 and 5,

[Fig. 7] Figure 7 is a schematic sectional view of a flash sintering tool in which the green part of Figure 6 is placed, [Fig. 8] Figure 8 is a schematic perspective view of a hollow part made of composite material with a ceramic or metal matrix with short fiber reinforcement after removal of the sacrificial core.

Description of embodiments

As represented in FIG. 1, the process for manufacturing a part made of ceramic matrix composite material (CMC) or of metal matrix composite material (CMM) according to the invention begins with the production of a sacrificial core 10 (step S1 , Figure 2). In accordance with the invention, the sacrificial core is made of a material compatible with the manufacturing steps of the method of the invention and of the desired final material, the material of the core preferably having thermochemical compatibilities with the composite material of the part. The constituent material of the sacrificial core also has mechanical and thermal properties allowing it to withstand the pressures and temperatures used during the manufacture of the part as described below. The sacrificial core can also be electrically conductive to participate in the heating of the green part during the SPS flash sintering step. The sacrificial core material must also be easily removable or removable without damaging the final part. For this purpose and in a non-limiting way, the sacrificial core can be made of graphite, alumina or zirconia.

As illustrated in FIG. 2, the sacrificial core 10 comprises a body 11 which has a geometry and dimensions corresponding to those of the hollow or the cavity which it is desired to form in the final CMC or CMM part. The core 10 further comprises positioning pins or extra lengths 12 which extend from the body 11 and which are intended to facilitate holding the sacrificial core in position in an injection tool as explained below. The sacrificial core can be obtained by machining or any other means known to those skilled in the art.

The next step consists in preparing a raw material (also called “feedstock” in English) comprising (step S2) at least short fibers and a precursor filler of ceramic matrix or metal matrix. The raw material may further comprise a binder, which is the case in the example described here. The short fibers here have a length of between 50 mm and 100 mm.

Short fibers allow the manufacture of CMC or CMM parts directly in their final shape ("net shape") or near final shape ("near net shape"). In the case of a CMM part, the short fibers provide isotropic or transverse isotropic reinforcement which improves the creep resistance of the metal matrix of the part. This improves the rigidity of the CMM part at high temperature while reducing its density, which makes it possible to increase the specific mechanical properties.

In the case of the manufacture of a hollow CMC part, the raw material comprises a ceramic matrix precursor filler and short fibers made of a material chosen from one of the following materials: carbon, silicon carbide, alumina, mullite and magnesia. The ceramic matrix precursor filler consists of a powder of refractory ceramic particles, for example particles of silicon carbide, boron nitride (Si ₃ N ₄ ) or any mixture of ceramic powders.

In the case of the manufacture of a CMM hollow part, the raw material comprises a metal matrix precursor filler and short fibers in a material chosen from one of the following materials: silicon carbide and alumina. The metal matrix precursor filler consists of a powder of metal particles, in particular particles of titanium alloy, nickel alloy or aluminum alloy.

The binder consists of at least one polymeric binder such as polyethylene glycol (PEG), stearic acid, polypropylene, or even a formulation based on polyoxymethylene (POM).

The method continues with the positioning of the sacrificial core 10 in a molding cavity 23 of an injection tool 20 as illustrated in FIG. 4 (step S3). More specifically, the injection tool 20 comprises a first half-shell 21 comprising an imprint 210 and a second half-shell 22 comprising an imprint 220. When the tool 20 is closed by joining the two half-shells 21 and 22 (FIGS. 4 and 5), the cavities 210 and 220 delimit a molding cavity 23 having dimensions greater than the dimensions of the sacrificial core 10 in order to provide an injection space between the external surface of the core and the wall of the mold cavity. Housings 211 and 221 also extend respectively from cavities 210 and 220. Housings 211 and 221 are intended to cooperate with overlengths 12 of sacrificial core 10 so as to hold the core in position in the cavity of molding to form an injection space 230 between the core and the wall of the cavities 210 and 220 for the raw material (FIGS. 4 and 5). The injection space 230 is sized as a function of the final thickness of the material of the target part, taking account in particular of the influence of sintering and of any debinding on the geometric variation of the part.

The raw material is then shaped by the injection molding technique (step S4). More specifically, once the injection tool 20 is closed with the sacrificial core 10 positioned inside, a raw material 30 prepared in step S2 is injected into the free space 230 between the sacrificial core 10 and the wall. inside the mold cavity 23 via an injection port 30 (FIGS. 4 and 5).

Once the injection of the raw material is complete, a green part 40 is obtained, also called a “green body”, comprising the sacrificial core 10 coated on its outer surface with a layer of shaped raw material 30 (figure 6).

The green part 40 is then extracted (stripped) from the injection tooling (FIG. 6, step S5).

When the raw material comprises a binder, a step of debinding the raw material is carried out before the step of placing the green part in the flash sintering tool so as to eliminate the organic material from the composite material to be manufactured (step S6 ). The debinding step can be carried out by solvent route, thermal route under inert gas, a combination of these two routes, etc. Debinding can also be carried out directly in-situ in the flash sintering tooling by a suitable treatment carried out before the flash sintering.

The green part 40 is placed in a flash sintering tool or SPS (“Spark Plasma Sintering”) 50 (FIG. 7, step S7). The difference between conventional hot pressing and flash sintering is that the heat source is not external but an electric current (direct - pulsed direct - or alternating) applied via electrodes passes through a conductive mold. "Flash sintering" consists of heat treatment under mechanical stress using a tool to enclose the green part. The application of the heat is carried out by Joule effect as close as possible to the green part by the passage of an electric current, which makes it possible to quickly close the porosity and to very quickly reach a maximum rate of densification (formation of bonds between grains without total fusion of these). This weld, produced by diffusion of material, is accompanied by densification, that is to say a reduction in the level of porosity and hardening which confers cohesion on the shaped raw material. The flash sintering tool 50 makes it possible to subject the raw material 30 to pulses (3.3 ms) of direct electric current (typically 0-25 V, 1-20 kA) while applying a pressure of several tens of MPa ( up to 300 MPa) and this in a range of temperatures varying from ambient temperature to 2500°C. Flash sintering is generally carried out under vacuum but it is possible to work under an inert atmosphere (nitrogen, argon).

The flash sintering tool 50 comprises for this purpose a mold formed by two half-shells 51 and 52 made of an electrically conductive material such as graphite. The two half-shells 51 and 52 define between them a molding cavity, which may have a complex shape, the dimensions of which are defined according to the dimensions of the final part to be produced. The sacrificial core plays here the role of counter-mold to ensure the densification of the internal walls of the final part.

The tool 50 comprises first and second electrodes 55 and 56 connected, on the one hand, to a current generator 57 and, on the other hand, to the half-shells 51 and 52 of the mold respectively via a first piston 53 and a second piston 54. In the case of the formation of a part having a complex geometry, a key tool can be used. The generator 57 emits a current I which circulates through all the tooling 50, namely the electrodes 56 and 57, the pistons 53 and 54 and the half-shells 51 and 52, but also the charge of the raw material 30 and the sacrificial core 10. A mechanical stress P is also applied to the half-shells 51 and 52 by the pistons 53 and 54 during sintering.

The parameters of the densification cycle, namely mainly the intensity of the electric current, the value of the mechanical stress applied and the nature of the treatment atmosphere, are defined by the nature of the elements to be sintered of the raw material and are well known to those skilled in the art. The electric current is controlled according to the defined thermal cycles (temperature rise/fall ramps, stages, etc.). The mechanical constraint can also be controlled if necessary (release/application of constraint).

The molds used are preferably made of graphite and are separated from the powder by a sheet of graphite to avoid any sticking or by any other means known to those skilled in the art, such as in particular a layer of graphite deposited by spraying or a layer of paint of boron nitride.

Once the raw material has been densified by flash sintering around the sacrificial core 10 (step S8), the preform obtained is extracted from the tool 50. The next step consists in removing or eliminating the sacrificial core (step S9). If its geometry allows it, i.e. if the core has no undercut, the core can be removed mechanically. In order to facilitate mechanical removal, the sacrificial core may be wrapped or coated with a sheet of flexible graphite, a layer of spray-deposited graphite or a layer of boron nitride paint before the shaping step. raw material by injection molding.

The sacrificial core can also be removed by thermochemical treatment. In the case, for example, of a sacrificial graphite core, this can be eliminated by thermochemical oxidation treatment carried out, for example, in air at a temperature between 400° C. and 600° C. if the material of the part allows it. .

After the removal or elimination of the sacrificial core, a part 60 is obtained in composite material with a ceramic or metal matrix reinforced with short fibres, the part comprising an internal recess 61 whose shape and dimensions have been defined by the sacrificial core. 10.

In order to avoid possible chemical interactions between the matrix and the fibers (if these are not protected) of the part to be manufactured and the sacrificial core during the manufacturing process, a diffusion barrier layer can be formed on the outer surface of the core before the injection of the raw material. By way of non-limiting example, the diffusion barrier can consist of a layer of boron nitride. In the case of metallic bases, it is possible to deposit alumina or tungsten as a barrier layer). The method of the invention makes it possible to easily and reproducibly produce hollow parts made of composite material with a short fiber ceramic matrix (CMC-FC), the fibers being coated with an interphase and optionally with a protective layer of the interphase. or short fiber metal matrix material (CMM -FC), even for small parts, which is not possible with continuous fibers. The invention finds a particular but not exclusive application in the manufacture of hollow parts of small gas turbine dimensions such as, for example, outlet guide vanes or "OGV" (for "outlet guide vane") used in distributor stages turbine.

Claims

[Claim 1] Method for manufacturing a hollow part (60) made of composite material with a ceramic or metal matrix, comprising the following steps: preparing a raw material (30) comprising at least short fibers and a ceramic matrix precursor filler or metal matrix, positioning a sacrificial core (10) in a molding cavity (23) of an injection tool (20), the molding cavity having dimensions greater than the dimensions of the sacrificial core, shaping raw material (30) by injection molding said raw material into the free space (230) between the sacrificial core (10) and an internal wall of the molding cavity so as to obtain a green part (40) comprising the sacrificial core and the shaped raw material, extraction of the green part (40) from the injection tooling (20), densification of the raw material (30) by flash sintering of the green part (40) in such a way to transform the c load in ceramic matrix or in metal matrix, removal or elimination of the sacrificial core (10) so as to obtain a hollow part (60) in composite material with ceramic or metal matrix; wherein the sacrificial core is coated with a sheet of flexible graphite, a layer of spray-deposited graphite or a layer of boron nitride paint prior to the step of injecting the raw material.

[Claim 2] Process according to claim 1, in which the sacrificial core (10) has a geometry capable of being demolded from the densified raw material after the densification step.

[Claim 3] Method according to any one of Claims 1 to 2, in which the sacrificial core (10) is made of one of the following materials: graphite, zirconia and alumina.

[Claim 4] Process according to any one of Claims 1 to 3, in which the raw material (30) comprises a ceramic matrix precursor filler and short fibers made of a material chosen from one of the following materials: carbon, silicon carbide and alumina.

[Claim 5] A method according to any one of claims 1 to 3, wherein the raw material (30) comprises a metal matrix precursor filler and short fibers of a material selected from one of the following materials: silicon carbide and alumina .

[Claim 6] A method according to any one of claims 1 to 5, wherein at least one diffusion barrier layer is deposited on the sacrificial core (10) before the injection of the raw material (30).

[Claim 7] A method according to any one of claims 1 to 6, wherein the raw material further comprises a binder, the method further comprising a step of debinding the raw material (30) before or during the densification of the raw material.

[Claim 8] Method according to claim 7, in which the step of debinding the raw material (30) is carried out within a tool (50) used for the flash sintering of the green part (40).