WO2019058069A1

WO2019058069A1 - Method for manufacturing a part using cmc

Info

Publication number: WO2019058069A1
Application number: PCT/FR2018/052316
Authority: WO
Inventors: Thierry Guy Xavier TESSON; Maxime François Roger CARLIN; Nicolas Eberling-Fux; Eddy GOULLIANNE
Original assignee: Safran Ceramics
Priority date: 2017-09-21
Filing date: 2018-09-21
Publication date: 2019-03-28
Also published as: FR3071246B1; FR3071246A1

Abstract

The invention relates to a method for manufacturing a part using CMC, i.e. a ceramic matrix composite material, as well as such a part made of CMC, the method comprising the following steps: providing (E1) a fibrous reinforcement (10); injecting (E3) a slurry comprising at least one ceramic powder and a solvent, the slurry being injected so as to impregnate the fibrous reinforcement (10) and to fill a volume located on the surface of at least one portion of the fibrous reinforcement (10); drying (E4) the assembly obtained; and densifying (E6) by infiltrating a liquid densification material and solidifying said densification material.

Description

PROCESS FOR MANUFACTURING A CMC PIECE

FIELD OF THE INVENTION

The present disclosure relates to a method of manufacturing a CMC part, that is to say of ceramic matrix composite material, and such a piece CMC.

Such a manufacturing process can in particular be used in the field of aeronautics to manufacture parts capable of withstanding high temperatures. Such parts can thus be used to construct a combustion chamber or turbine of a turbomachine, such as an aircraft turbojet, to name only these examples.

STATE OF THE PRIOR ART

A known method for manufacturing a CMC part is as follows:

- weaving a fibrous reinforcement;

depositing an interphase, that is to say a sheath, around the fibers of the fibrous reinforcement in order to consolidate the fibrous reinforcement and freeze its shape;

injecting a slip comprising a ceramic powder and a solvent onto the fibrous reinforcement, the ceramic powder then penetrating into the pores of the fibrous reinforcement and sedimenting into the fibrous reinforcement,

drying to remove the solvent;

- Densification by infiltration of a liquid material which fills the remaining voids by capillarity within the fibrous reinforcement and solidification of said liquid material;

- Machining of the blank thus obtained.

Such a method allows good densification of the part within the fibrous reinforcement; on the other hand, the densification obtained on the surface is rather poor. In particular, with such a method, it is customary for the blank to have an irregular surface condition, directly printed by the texture of the underlying fibrous reinforcement: thus, the surface of the piece has a relief pattern corresponding to the texture fibrous reinforcement. Depending on the nature of the room, such a state of irregular surface can raise aesthetic and / or functional issues.

Moreover, with such a method, the machining of the surface of the part necessarily leads to the fibers fiber reinforcement bare, which can cause corrosion problems and / or oxidation of the workpiece.

There is therefore a real need for a method of manufacturing a CMC part and such a CMC part which are lacking, at least in part, the disadvantages inherent in the aforementioned known method.

PRESENTATION OF THE INVENTION

The present disclosure relates to a method of manufacturing a CMC part, comprising the following steps:

- supply of a fibrous reinforcement,

injecting a slip comprising at least one ceramic powder and a solvent, the slip being injected so as to impregnate the fibrous reinforcement and to fill a free volume located on the surface of at least a portion of the fibrous reinforcement,

drying of the assembly obtained,

densification by infiltration of a liquid densification material and solidification of said densification material.

Thus, in such a method, the slip is injected into both the fibrous reinforcement and the free volume located outside the fibrous reinforcement, on the surface thereof. Consequently, after drying of the assembly, a green part is obtained having a first portion formed by the fibrous reinforcement embedded in the ceramic matrix and a second portion formed by the ceramic matrix without reinforcement.

Therefore, the surface of the fiber reinforcement at the interface between the first and second parts is no longer on an edge of the green part but is now deep in the green part: consequently, the subsequent densification infiltration of the densification material will be effected effectively at this periphery of the fibrous reinforcement, without undergoing the edge effect usually found in the state of the art. In addition, thanks to this method, once the densification performed and the blank obtained, it will be possible to machine the blank to remove the second portion without the fiber reinforcement to obtain a final part in CMC whose dimensions are closest to the fibrous reinforcement without its surface state being altered by the underlying presence of the fibrous reinforcement. The aesthetic and functional qualities of the final piece are thus improved. In particular, an improved surface condition, i.e. roughness and / or lower waviness, improves the aerodynamic performance of the part and facilitates its cooling in case of impact cooling.

Alternatively, this also makes it possible to keep part portions completely free of fibers in order to perform machining, such as the production of grooves or bores, for example, without exposing fibers. This reduces the risk of corrosion and / or oxidation of the part, which increases its life and reduces the need for maintenance. In addition, the material is more homogeneous and isotropic, it is possible to obtain lower roughness after machining.

In some embodiments, the fiber reinforcement is made by weaving, preferably by 3D weaving. 3D weaving makes it possible to obtain fibrous reinforcements having complex geometries in a single piece, thus ensuring very good mechanical resistance to the final piece.

In some embodiments, the fibrous reinforcement comprises SiC fibers, preferably at least 50% SiC fibers, more preferably at least 95% SiC fibers. However, any type of ceramic fiber could also be used including carbon fibers.

In some embodiments, the second part of the green part has a constant thickness. This thickness is measured relative to the outer surface of the fibrous reinforcement, that is to say the area passing through the tops of the fibers of the fibrous reinforcement. This makes it possible to obtain a continuous surface devoid of ripples

In some embodiments, the second part of the green part, devoid of reinforcement, has a thickness less than 1mm. Its thickness is preferably less than 0.6 mm. This thickness is sufficient to allow subsequent machining. Of more preferably, its thickness is between 0.1 and 0.3 mm. Such a thickness range is sufficient to allow the texture of the underlying fibrous reinforcement to be erased in order to obtain a satisfactory surface condition for the final piece.

In some embodiments, the ceramic powder of the slurry comprises SiC, preferably at least 50% SiC, more preferably at least 95% SiC. However, any type of ceramic powder could also be used and especially B, BC, TiC, ZrC, BN, Si ₃ N ₄ , or TiSi ₂ .

In certain embodiments, the average particle diameter of the ceramic powder of the slip is between 0.1 μm and 10 μm, preferably between 0.5 μm and 5 μm. The production of a green part part formed exclusively of ceramic matrix, out of the fibrous reinforcement, is delicate because of the high porosity rate left in this part of the green part after the removal of the solvent. Thus, before its densification, this second part of the green part is very fragile and can easily crumble, crack or even fall completely away from the first part provided with the fibrous reinforcement. Several parameters make it possible to reinforce this second part of the green part in order to reduce the risks of damage mentioned above: among these, the particle diameter of the ceramic powder. Thus, the inventors have found that the diameter ranges proposed above facilitated the implementation of the present method.

In some embodiments, the diameter D50 of the particles of the ceramic powder of the slip is between 0.5 and 2pm. The distribution of the powder particles may be monomodal or bimodal.

In certain embodiments, the diameter d10 of the particles of the ceramic powder of the slip is greater than 0.1 μm.

In some embodiments, the d90 diameter of the particles of the ceramic powder of the slip is less than 4 .mu.m.

In some embodiments, the solvent of the slip is an aqueous solvent.

In some embodiments, the slip includes an organic binder. This binder allows a better holding of the slip then the second part of the green part obtained after the drying of the slip: this facilitates in particular the release of the green part and its handling without damage.

In some embodiments, said organic binder comprises at least one of the following compounds: polyvinyl alcohol; polyvinylpyrrolidone; polyethylene imine and polyethylene glycol. These different compounds substantially increase the holding of the green part.

In some embodiments, the mass concentration of said organic binder relative to the mass of powder is between 0.5 and 10%, preferably between 1 and 5%. Such concentrations provide good effectiveness to the binder and therefore a good performance of the green part.

In some embodiments, the slip further comprises a plasticizer and / or a dispersant. It may especially be a plasticizer, or a binder, of the PVA, PEG or PvP type. A plasticizer increases the mechanical strength of the ceramic pot after injection: it lowers the viscosity of the slip and provides flexibility to the raw material. As regards the dispersants, they may be bases with a pH of between 8 and 12, preferably between 9 and 11, for example of the type of tetraethylammonium hydroxide (TEAH), tetraemethylammonium hydroxide (TMAH), or hydroxide sodium (NaOH), or electrosteric systems, for example of the polyethylene imine type (PEI). These dispersants make it possible to keep the particles in suspension by electrostatic dispersion.

In some embodiments, at least one consumable is put in place in the tooling containing the fibrous reinforcement during the injection step of the slip. Such a consumable makes it possible to obtain a predetermined surface state in the zone where it is placed. Various consumables can be used including fabrics, elastomers and / or metal foils. Depending on the area of the tool, the consumable may be porous, or not. In particular, it is possible to implement in the tooling at least one tearing tissue within the free volume located on the surface of the fibrous reinforcement. In such a case, after injection and drying, the second part of the green part contains the tearing tissue: the tearing of this fabric then makes it possible to remove part of the second part of the green part in order to obtain a residual thickness and a controlled surface condition. Thanks to such a tear-off fabric, it is possible in particular to obtain a roughness Ra of less than 15 μm.

In some embodiments, the slip injection step is of the injection-filtration type. In other words, it uses an evacuation vent and a filter passing the solvent of the slip but retaining the ceramic particles of the slip. An example of filtration-injection is described in particular in application FR 3030505. Such an injection-filtration makes it possible to obtain a concentration of ceramic particles in the green part that is greater than the concentration of the slip: this gives a piece of raw material more dense, and therefore more solid, especially in the second part devoid of fibrous reinforcement.

In some embodiments, the drying step comprises a lyophilization step. Such a lyophilization step reduces the risk of cracking of the second part of the green part during the drying step. It also ensures good cohesion between the first and second parts of the green part.

In some embodiments, the drying step comprises a controlled evaporation step with a ramp of increasing temperatures. Such controlled evaporation makes it possible to control the removal of the solvent, thereby reducing the risk of cracking during the drying step.

In some embodiments, the drying step comprises a drying step of the Deliquoring type during which the piece is dried by applying a pressure gradient, preferably often under vacuum.

In some embodiments, the slope of the temperature ramp of the controlled evaporation step is between 1 and 5 ° C / min.

In some embodiments, the temperature ramp of the controlled evaporation step is completed with a final temperature of between 100 and 140 ° C, preferably between 115 and 125 ° C. In some embodiments, the temperature ramp of the controlled evaporation step starts at an initial temperature of between 30 and 70 ° C, preferably between 45 and 65 ° C.

In some embodiments, the second portion of the green part has a constant thickness. This thickness is measured relative to the outer surface of the fibrous reinforcement, that is to say the area passing through the tops of the fibers of the fibrous reinforcement. This makes it possible to obtain a continuous surface devoid of ripples

In some embodiments, the second part of the green part, without reinforcement, has a thickness less than 1mm. Its thickness is preferably less than 0.6 mm. This thickness is sufficient to allow subsequent machining. More preferably, its thickness is between 0.1 and 0.3 mm. Such a thickness range is sufficient to allow the texture of the underlying fibrous reinforcement to be erased in order to obtain a satisfactory surface condition for the final piece.

In some embodiments, the compaction rate of the ceramic powder in the second part of the green part is greater than 45%, preferably greater than 50%. The compaction rate corresponds to the material content relative to the volume of the part considered: it reflects in particular the porosity rate of the part. Such a compaction rate ensures sufficient hold in the second part of the green part.

In certain embodiments, the densification material comprises Si, preferably at least 50% by weight of Si, more preferably at least 95% by weight of Si.

In some embodiments, the method further comprises a step of annealing and pre-sintering of the ceramic powder after the step of injecting the slip and before the densification step. This makes it possible to reinforce the behavior of the green part by creating connections between the particles of ceramic powder.

In some embodiments, the annealing and pre-sintering step is carried out at a temperature of between 1200 and 1600 ° C., preferably between 1300 ° C. and 1500 ° C., for a period of time of between 30 minutes. and 2h, preferably between 45 min and 1:30. In some embodiments, the annealing and pre-sintering step is conducted under a neutral gas, for example under Argon.

In some embodiments, the method further comprises, prior to the step of injecting the slip, an interphase deposition step provided for sheathing the fibers of the fiber reinforcement with an interphase material.

In some embodiments, the interphase deposition step is carried out by gaseous means.

In some embodiments, the interphase material comprises SiC and / or BN, preferably at least 50% SiC, more preferably at least 95% SiC.

In some embodiments, the method further comprises a preparation step. It may especially be a sandblasting step or any other step to locally increase the roughness of the surface of the room.

In some embodiments, the method further comprises a machining step performed on the blank obtained at the end of the densification step, the blank including a first part, resulting from the first part. of the green part, including the fibrous reinforcement and a second part, issued from the second part of the green part, devoid of the fibrous reinforcement, in which the first part of the blank including the fibrous reinforcement is left intact during the step machining.

In some embodiments, the CMC part obtained has a main part, formed by the fibrous reinforcement embedded in the ceramic matrix, and a surface layer, resulting from the second part of the green part, formed by the ceramic matrix. devoid of reinforcement.

In some embodiments, the surface layer is located on the surface of the final piece. In other words, this surface layer is not covered by any coating; she is in direct contact with her environment.

In other embodiments, a coating covers at least part of the surface layer.

In some embodiments, the surface layer of the CMC part has a constant thickness. This thickness is measured relative to the outer surface of the fibrous reinforcement, that is to say the area passing through the tops of the fibers of the fibrous reinforcement. This makes it possible to obtain a continuous surface devoid of undulations.

In some embodiments, the surface layer of the CMC part has a roughness Ra less than 40 μm, preferably less than 15 μm, more preferably less than 2 μm.

In some embodiments, the surface layer of the CMC part has a thickness of less than 1 mm, preferably less than 0.6 mm, more preferably between 0.1 and 0.3 mm. Such a thickness range is sufficient to allow the texture of the underlying fibrous reinforcement to be erased in order to obtain a satisfactory surface condition.

In some embodiments, said CMC part is an aeronautical part, for example a combustion chamber or turbine part.

The present disclosure also relates to a CMC part, obtained using a method according to any one of the preceding embodiments.

The present disclosure further relates to a turbomachine comprising at least one CMC part according to any one of the preceding embodiments.

The above-mentioned characteristics and advantages, as well as others, will appear on reading the following detailed description of embodiments of the proposed method. This detailed description refers to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are schematic and are intended primarily to illustrate the principles of the invention.

In these drawings, from one FIG (FIG) to the other, elements

(or parts of element) are identified by the same reference signs.

FIG. 1 illustrates the successive steps of an exemplary method according to the disclosure.

FIG. 2 illustrates the evolution of the part during this example of a process. DETAILED DESCRIPTION OF EXAMPLE (S) OF REALIZATION

In order to make the invention more concrete, an exemplary method is described in detail below, with reference to the accompanying drawings. It is recalled that the invention is not limited to this example.

FIGS. 1 and 2 illustrate the various steps of an exemplary method according to the disclosure for manufacturing a CMC part, that is to say in ceramic matrix composite material. This piece can be of any nature: it can be in particular a turbojet turbine ring sector.

The process begins with El weaving of a fibrous preform 10 which will act as a fibrous reinforcement of the CMC part. This preform 10 is preferably woven according to a 3D weaving technique, known moreover, for example with an armor of the interlock type. In this example, the preform 10 is woven with SiC silicon carbide fibers.

Once the preform 10 is complete, it is shaped and undergoes a step E2 interphase deposition, known for example, for example chemical vapor deposition type (also known as CVD for Chemical Vapor Deposition). ). In this example, the deposited interphase material is SiC silicon carbide. An SiC sheath is thus formed around the fibers of the preform 10, which consolidates the preform 10 and blocks the shape given during the shaping. At the end of this interphase deposition step E2, the fibers of the preform 10 are thus coated with an interphase sheath, but the preform 10 still remains very porous.

The preform 10 is then transferred into a mold to undergo a step E3 of injection of a ceramic slip. In this example, the slip comprises a solvent, here water, a ceramic powder, here silicon carbide SiC, and an organic binder, here polyvinyl alcohol.

In this example, the concentration of the SiC powder in the slip is about 20% by volume. The concentration of the binder is for its part 1% by weight relative to the mass of SiC powder in slip. The mold is provided for its part so as to match the shape of the preform 10 while leaving a free surface volume of at least some portions of the preform 10, for example along a main surface 19 of the preform 10. Thus, when the slip is injected into the mold, it impregnates on the one hand the preform 10 and on the other hand fills the free volume left in front of the main surface 19 of the preform 10.

[0065] Preferably, the injection is of the njection-filtration type. The slip is thus injected continuously, the solvent being drained by an evacuation vent while a filter retains the ceramic particles which sediment within the fibrous preform 10 and then within the free volume.

A drying step E4 is then conducted to remove the solvent from the slurry. In this example, it is a lyophilization step (also known by its English name of "freeze-drying"), during which the mold is abruptly brought to a negative temperature in order to solidify the solvent and then gradually warmed to very low pressure so as to cause the sublimation of the solvent substantially without altering the surrounding materials, the solvent in the gas phase is then removed using a cold trap for example.

According to one variant, the drying step E4 could comprise a step of controlled evaporation of the solvent during which the temperature of the chamber is progressively raised from 50 to 120 ° C. at the rate of an increase of 1 at 5 ° C / min, preferably 1 ° C / min.

According to yet another variant, the drying step E4 could comprise a Deliquoring step carried out under a pressure of between 50 and 100 mbar, for 1 to 2 hours or from 1 to 3 hours.

During the drying step E4, within the preform

10, the ceramic particles of the slip settle and settle on the fibers of the preform as the solvent is removed, thus filling a portion of the pores of the preform 10. In addition, within the free volume, the ceramic particles agglomerate and bind to each other under the effect of the organic binder. Thus, at the end of the drying step E4, there is obtained a green part 20 having a first part 21 provided with the reinforcement formed by the fibrous preform 10 and a second part 22, free of the fiber reinforcement 10 and constituted of agglomerated ceramic powder having a compaction rate greater than 45% vol, or even greater than 50%. The main surface 19 of the preform 10 is then found at the interface between these first and second parts 21, 22 of the green part 20.

The green part 20 thus obtained then undergoes a step E5 annealing and pre-sintering to strengthen the connections between the particles of the ceramic powder and thus enhance the holding of the green part 20, especially in its second part 21.

In this example, the annealing takes place under a neutral gas, for example argon, at a temperature of 1400 ° C for 1h.

Once this step E5 is complete, the green part 20 is demolded and transferred to undergo a densification step E6. During this densification step E6, a liquid densification material, here silicon Si, is poured on the green part 20: the densification material then penetrates by capillarity into the green part 20, whether in its first phase. part 21 or its second part 22, and fills the residual pores of the green part 20.

After cooling and solidification of the densification material, there is obtained a blank 30 having no longer, or substantially no longer, porosity. In a similar way to the green part, the blank 30 has a first portion 31, provided with the reinforcement formed by the fiber preform 10 and embedded in the matrix, and a second portion 32, devoid of the fiber reinforcement 10 and consisting exclusively of matrix.

In particular, since the main surface 19 of the preform 10 extended inside the green part 20, the densification at this main surface 19 could be complete and homogeneous, without edge effect.

It is then possible during a machining step E7 to cut all or part of the second portion 32 of the blank 30 to obtain a final piece 40 having a main portion 41, resulting from the first part. 31 of the blank 30, formed by the fibrous reinforcement 10 embedded in the densified matrix, and a surface layer 42, derived from the second portion 32 of the blank 30, formed exclusively of densified matrix. The surface 49 of this surface layer 42, constituting an exposed surface of the final piece 40, is thus close to the sides of the main surface 19 of the fiber reinforcement 10 (exaggerated distance in FIG 2 for reasons of readability) while benefiting a state of controlled surface. In this case, a distance of about 0.2 mm separates this surface 49 from the final piece 40 of the main surface 19 of the fibrous reinforcement 10.

Of course, other machining is also possible in the second part 32 of the blank without exposing fibers of the fibrous reinforcement 10.

Although the present invention has been described with reference to specific exemplary embodiments, it is obvious that modifications and changes can be made to these examples without departing from the general scope of the invention as defined by the revendications. In particular, individual features of the various embodiments illustrated / mentioned can be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than restrictive sense.

It is also obvious that all the features described with reference to a method can be transposed, alone or in combination, to a device, and conversely, all the features described with reference to a device can be transposed, alone or in combination, to a method.

Claims

A method of manufacturing a CMC part, comprising the following steps:

providing (E1) fibrous reinforcement (10),

injection (E3) of a slip comprising at least one ceramic powder and a solvent, the slip being injected so as to impregnate the fibrous reinforcement (10) and to fill a free volume located on the surface of at least a portion of the reinforcement fibrous (10),

drying (E4) of the assembly obtained and obtaining a green part (20) having a first portion (21), formed by the fibrous reinforcement (10) embedded in a ceramic matrix, and a second portion (22), issue free volume, formed by the ceramic matrix devoid of reinforcement, and

densification (E6) by infiltration of a liquid densification material and solidification of said densification material,

wherein the resulting CMC piece (40) has a main portion (41), derived from the first portion (21) of the green piece (20), formed by the fibrous reinforcement (10) embedded in a ceramic matrix, and a layer surface (42), issuing from the second part (22) of the green part (20), formed by a ceramic matrix devoid of reinforcement,

wherein the surface layer (42) of the CMC part (40) has a thickness of less than 1 mm.

2. Method according to claim 1, wherein the fibrous reinforcement (10) is made by 3D weaving.

3. The method of claim 1 or 2, wherein the average particle diameter of the ceramic powder of the slip is between 0.1 pm and 10 pm, preferably between 0.5 pm and 5 pm.

4. A process according to any one of claims 1 to 3, wherein the slip comprises an organic binder.

The method of claim 4, wherein said organic binder comprises at least one of the following compounds: polyvinyl alcohol; polyvinylpyrrolidone; polyethylene imine and polyethylene glycol.

6. The method of claim 4 or 5, wherein the mass concentration of said organic binder relative to the mass of powder is between 0.5 and 10%.

7. Process according to claims 1 to 6, wherein the injection step (E3) is of the injection-filtration type.

The method of any one of claims 1 to 6, wherein the drying step (E4) comprises a lyophilization step.

The method of any one of claims 1 to 7, wherein the drying step (E4) comprises a controlled evaporation step with increasing temperature ramp.

10. A method according to any one of claims 1 to 8, further comprising a step of annealing and pre-sintering (E5) of the ceramic powder after the injection step (E3) of the slip and before the densification step (E6).

11. Method according to any one of claims 1 to 9, further comprising a machining step (E7) performed on the blank (30) obtained at the end of the densification step (E6), the piece crude (30) then comprising a first part (31), issuing from the first part (21) of the green part (20), including the fibrous reinforcement (10) and a second part (32), coming from the second part ( 22) of the green part (20), devoid of the fibrous reinforcement (10),

wherein the first portion (31) of the blank (30) including the fibrous reinforcement (10) is left intact during the machining step (E7).

The method of any one of claims 1 to 11, wherein the surface layer (42) of the CMC part (40) has a constant thickness.

13. Method according to any one of claims 1 to 12, wherein the surface layer (42) of the CMC part (40) has a roughness Ra less than 40 μιη, preferably less than 15 μητι, more preferably less than 2 pm.

14. CMC part obtained by a method according to any one of the preceding claims.

15. Turbomachine, comprising at least one CMC part (40) according to the preceding claim.