Method for densifying a fiber structure by injecting a slurry

Abstract

The present invention relates to a method for densifying a fibrous structure made of a ceramic material used in an injection device, the injection device comprising: - a cavity defined between a mold and an opposing mold, the cavity defining an internal space; and - a film comprising a reinforcing zone, the film being disposed between the fibrous structure placed in the cavity and the opposing mold, the reinforcing zone of the film having a Young's modulus greater than 200 GPa, the method comprising: - placing (110) a pre-densified fibrous structure in the cavity, the pre-densified fibrous structure having corrugations on its surface, and placing the film on the pre-densified fibrous structure such that the reinforcing zone of the film contacts the peaks of the corrugations of the pre-densified fibrous structure; - closing (120) the injection device by placing the opposing mold on the film and applying a pressing pressure (P 压紧 ) to keep the reinforcing zone of the film in contact with the peaks of the corrugations of the pre-densified fibrous structure; and - densifying (130) the pre-densified fibrous structure by infiltrating a slurry into the pores of the pre-densified fibrous structure, the slurry being injected laterally into the cavity under an injection pressure (P 注射 ) with respect to the film, such that the pressure difference between the pressing pressure and the injection pressure is between 0.5 x 10 5 Pa and 6 x 10 5 Pa.

Description

Technical Field

[0001] The present invention relates to the general field of manufacturing components made of ceramic matrix composite (CMC) materials, and more particularly, to a method for densifying a fibrous structure made of ceramic materials comprising a ceramic matrix. Background Art

[0002] The densification of a fibrous structure - i.e., the formation of a ceramic matrix in the fibrous structure - includes a slurry injection step, which consists of impregnating the fibrous structure with a slurry or a suspension of ceramic particles, the slurry or suspension of ceramic particles penetrating into the pores of the fibrous structure and allowing a ceramic matrix to be obtained in the fibrous structure.

[0003] In order to improve the aerodynamic performance of the final component, it is necessary for the densified fibrous structure to have a smooth surface. Generally, in order to obtain a smooth surface, the surface of the densified fibrous structure is smoothed by machining or by adding material (extra thickness). However, this results in additional costs, reduces the thermomechanical resistance of the material, and most importantly complicates the manufacturing method of the ceramic matrix composite.

[0004] Therefore, there is a desire to provide a new method for densifying a fibrous structure so as to obtain a densified fibrous preform having a smooth surface without generating an excessive thickness and without the need for an additional surface machining step. Summary of the Invention

[0005] The present invention relates to a method for densifying a fibrous structure made of ceramic materials having a ceramic matrix for use in an injection device, the injection device comprising:

[0006] - a cavity defined between a mold and a counter mold, the cavity defining an internal space; and

[0007] - a membrane including a reinforcing zone, the membrane being placed between the fibrous structure present in the cavity and the counter mold, and the Young's modulus of the reinforcing zone of the membrane being greater than 200 GPa;

[0008] The method comprises:

[0009] - placing a pre-densified fibrous structure in the cavity, the surface of the pre-densified fibrous structure having corrugations, and placing the membrane on the pre-densified fibrous structure in such a way that the reinforcing zone of the membrane is in contact with the peaks of the corrugations of the pre-densified fibrous structure

[0010] ;

[0011] - closing the injection device by placing the counter mold on the membrane and applying a pressing pressure to the membrane to maintain contact between the reinforcing zone of the membrane and the peaks of the corrugations of the pre-densified fibrous structure; and

[0012] - Densifying a pre-densified fibrous structure by infiltrating a slurry into the pores of the pre-densified fibrous structure, the slurry being injected into the membrane cavity laterally to the reinforcement zone of the membrane under an injection pressure such that the pressure difference between the pressing pressure and the injection pressure is between 0.5 x 10 5 Pa and 6 x 10 5 Pa.

[0013] The Young's modulus of the reinforcement zone is greater than 200 GPa, which gives the reinforcement zone sufficient rigidity so that it does not deform during the application of the pressing pressure to the membrane and the densification of the fibrous structure.

[0014] Due to the method of the present invention, in particular due to placing the reinforcement zone of the membrane at the peaks of the corrugations of the fibrous structure and having the Young's modulus of the reinforcement zone greater than 200 GPa, the surface of the fibrous structure can be smoothed during its densification while avoiding the generation of an excessive thickness (the excess thickness due to matrix growth is very limited, at most reaching 0.05 mm). In fact, the matrix growth - i.e., the densification of the fibrous structure - stops at the reinforcement zone of the membrane, which avoids the formation of an excessive thickness on the surface of the fibrous structure. Thus, the volume of the matrix thus formed is limited to the highest corrugations of the pre-densified fibrous structure.

[0015] In addition, having the pressure difference between the pressing pressure and the injection pressure between 0.5 bar and 6 bar (i.e., between 0.5 x 10 5 Pa and 6 x 10 5 Pa) allows the reinforcement zone of the membrane to remain in contact only with the peaks of the corrugations of the fibrous structure. Thus, the reinforcement zone does not match the contour of the structure and does not deform during the growth of the matrix in the pores of the fibrous structure. This difference in the pressure range allows the obtaining of a fibrous preform - i.e., a densified fibrous structure - with a smooth surface.

[0016] In addition, when the fibrous structure is pre-densified when placed in the mold cavity so that it no longer deforms. In other words, the fibrous structure is consolidated before being introduced into the mold cavity. This increases its mechanical strength to prevent its deformation. This also extends the pressing pressure range and provides a pressing pressure between 0.5 bar and 6 bar, which is not possible for a deformable reinforcement.

[0017] The slurry can be injected into the mold cavity laterally to the reinforcement zone of the membrane and into the pores of the pre-densified fibrous structure at the applied flow rate or under the applied pressure such that the pressure difference between the pressing pressure and the injection pressure remains constant throughout the injection process. When injecting at the applied flow rate, the pressure distribution can be monitored, especially during matrix growth, where the pressure rises with the increase in flow resistance to demonstrate that the pressure difference between the pressing pressure and the injection pressure remains constant.

[0018] According to a specific feature of the present invention, the reinforcement zone of the membrane is formed by a metal foil placed on the surface of the membrane opposite to the fibrous structure.

[0019] According to another specific feature of the present invention, the metal foil is made of molybdenum.

[0020] According to another specific feature of the present invention, the metal foil includes an anti-stick coating on the surface facing the fibrous structure.

[0021] According to another specific feature of the present invention, the method further includes: before placing the metal foil, treating the metal foil with an anti-stick coating in the form of a spray or a self-adhesive film.

[0022] The anti-stick coating is, for example, a polytetrafluoroethylene (PTFE) film.

[0023] The presence of the anti-stick coating on the metal foil helps to limit material tearing.

[0024] According to another specific feature of the present invention, the reinforcement zone of the membrane is formed by a fabric or a metal insert inside the membrane. In other words, there is a metal insert or a fabric between the inner surface and the outer surface of the membrane. The fabric is, for example, a consolidated fabric formed by woven fibers, such as a fine two-dimensional fabric made of carbon or glass, which can be integrally formed during the casting process of the membrane. The metal insert is, for example, an insert made of molybdenum or steel.

[0025] According to another specific feature of the present invention, the pressure difference between the pressing pressure and the injection pressure is between 0.5 x 10 5 Pa and 1.5 x 10 5 Pa (i.e., between 0.5 bar and 1.5 bar).

[0026] This allows to improve the smoothness of the surface of the fibrous structure after densification.

[0027] According to another specific feature of the present invention, the thickness of the reinforcement zone of the membrane is between 50 μm and 100 μm.

[0028] According to another specific feature of the present invention, the thickness of the reinforcement zone of the membrane is greater than 50 μm, for example, between 0.05 mm and 0.5 mm, especially between 0.05 mm and 0.1 mm. This is especially the case during the densification of a fibrous structure with a flat surface. These thickness ranges and / or these materials for the reinforcement zone allow to have a zone that is rigid enough so that the zone does not deform when pressed against the fibrous structure and when the matrix grows in the fibrous structure, and is flexible enough so that it can match the geometric singularities of the part and maintain contact with the peaks of the corrugations of the fibrous structure at all points.

[0029] According to another specific feature of the present invention, outside its reinforcement zone, the thickness of the membrane is between 1.5 mm and 4 mm, and the hardness is between 30 Shore A and 60 Shore A.

[0030] This enables a membrane such that the pressing pressure is uniformly applied to its reinforcement zone without hindering the injection of the slurry.

[0031] According to another specific feature of the present invention, the method further comprises drying the densified fibrous structure and demolding the densified fibrous structure after densification.

[0032] According to another specific feature of the present invention, the drying is carried out in the mold before demolding, or outside the mold in an oven, in a climate chamber or by freeze-drying after demolding.

[0033] For example, the drying temperature in the oven or climate chamber is between 40 °C and 80 °C. In addition, the oven or climate chamber preferably has a relative humidity between 40% and 90% to limit cracking.

[0034] According to another specific feature of the present invention, the slurry comprises a ceramic filler, a binder and a plasticizer, the volume ratio of the ceramic filler is 5% to 50%, for example 15% to 25% by volume, the mass ratio of the binder is 0% to 20%, and the mass ratio of the plasticizer is 0% - 20%.

[0035] For example, the ceramic filler comprises silicon carbide SiC particles with a d50 of less than 2 μm. The binder is, for example, polyvinyl alcohol (PVA), polyethylene glycol (PEG) or glycerol. The plasticizer is, for example, polyethylene glycol 200 (PEG 200). Description of the Drawings

[0036] Other features and advantages of the present invention will become apparent from the following description with reference to the drawings, which show exemplary embodiments of the present invention without any limiting characteristics.

[0037] Figure 1 Schematically shows a method for densifying a fibrous structure made of a ceramic material and having a ceramic matrix according to an embodiment of the present invention.

[0038] Figure 2A Schematically and partially shows an exploded view of an injection device for implementing a densification method according to an embodiment of the present invention.

[0039] Figure 2B Schematically and partially shows Figure 2A a part of the injection device.

[0040] Figure 3Schematically and partially shows a metal foil in contact with the peaks of the corrugations of a pre-compacted fibrous structure present in an injection device for implementing the present invention. Detailed Description

[0041] Figure 1 Schematically shows a method 100 for densifying a fibrous structure made of a ceramic material and having a ceramic matrix according to an embodiment of the present invention.

[0042] Figure 2A 、 Figure 2B and Figure 3 Schematically and partially shows an injection device 260 including a fibrous structure 210 for implementing Figure 1 the method 100 shown.

[0043] The injection device 260 includes a mold cavity 263 defined between a mold 261 and an opposing mold 262. Thus, the mold cavity 263 defines an internal space. The injection device 260 further includes a membrane 240, which is intended to be placed between the fibrous structure 210 present in the mold cavity 263 and the opposing mold 262. The membrane 240 includes a reinforcement zone 220. In this exemplary embodiment, the reinforcement zone 220 is formed by a metal foil present on the surface of the membrane 240 facing the fibrous structure 210. Thus, in the remaining description of these figures, the reinforcement zone 220 of the membrane 240 will be simply referred to as the "metal foil".

[0044] Except for the region including the metal foil, the thickness of the membrane 240 can be between 1.5 mm and 4 mm. Its hardness can be between 30 Shore A and 60 Shore A. The membrane 240 has a hardness of, for example, 50 Shore A and a thickness of 4 mm in order to facilitate good management of the seal between the opposing mold 262 / mold 261 and the membrane 240.

[0045] The device 260 further includes two ports 251 for injecting a slurry into the mold cavity 263 and an outlet port 252 configured to eliminate the liquid phase from the injected slurry. It may also include an injection wedge 250, which allows the membrane 240 and the fibrous structure 210 to be wedged so as not to impede the injection of the slurry and its impregnation into the structure 210.

[0046] The injection device 260 further includes a filter element 230 present in the mold cavity 263 below the fibrous structure 210. The filter element 230 is configured to filter the liquid phase of the slurry injected into the mold cavity 263. The liquid phase filtered by the filter element 230 can be excluded through the outlet port 252.

[0047] The densification method 100 includes placing 110 a pre-densified fibrous structure 210 in a mold cavity 263 of an injection device 260, and placing a membrane 240 on the pre-densified fibrous structure 210. The pre-densified fibrous structure 210 has corrugations 211, 212 on its surface (as Figure 3 shown). For example, there is a difference of up to 0.3 mm between the peaks of the corrugations 211, 212 and the lowest points of the corrugations. The metal foil of the membrane 240 is placed on the fibrous structure 210 such that it contacts the peaks of the corrugations 211, 212 of the fibrous structure 210. The metal foil only contacts the peaks of the corrugations and does not contact the lowest points, for example, located 0.3 mm from the peaks.

[0048] The metal foil is made of, for example, molybdenum or steel. Its Young's modulus is greater than 200 GPa, and the thickness can be between 50 μm and 100 μm, for example, 100 μm. The metal foil may also include an anti-stick coating on its surface facing the fibrous structure 210.

[0049] Then, the method 100 includes closing 120 the injection device 260 by placing an opposing mold 262 on the membrane. A pressing pressure P 压紧 is applied to the membrane 240 such that the metal foil remains in contact with the peaks of the corrugations 211, 212 of the pre-densified fibrous structure 210.

[0050] For example, the pressing pressure P 压紧 is applied to the metal foil via the membrane 240 by air pressure or the pressure from another fluid (such as, for example, silicone oil).

[0051] Finally, the method 100 includes densifying 130 the pre-densified fibrous structure 210 by infiltrating a slurry into the pores of the pre-densified fibrous structure 210. At an injection pressure P 注射 , the slurry is injected into the mold cavity 263 laterally to the membrane 240 - in particular, laterally to the metal foil - through an injection port 251 of the injection device 260. Thus, a densified fibrous structure forms a fiber preform containing a matrix.

[0052] The injection pressure P 注射 and the pressing pressure P 压紧 are defined such that the pressure difference ΔP between the pressing pressure and the injection pressure (ΔP = P 压紧 – P 注射 ) is between 0.5 bar and 6 bar (that is, in pascals, between 0.5x10 5 Pa and 6x10 5 Pa). The pressure difference ΔP is, for example, between 0.5 bar and 1.5 bar, for example, 1 bar.

[0053] The injection pressure P 注射For example, it can be between 3 bar and 20 bar.

[0054] Compaction pressure P 压紧 For example, it can be between 0.5 bar and 6 bar.

[0055] During the injection 130 of the slurry, the compaction pressure P 压紧 and the injection pressure P 注射 may vary in value, and thus the method 100 can include monitoring the pressure difference ΔP throughout the injection 130 to keep the pressure difference ΔP within the range of 0.5 bar to 6 bar, or within a more limited range, for example, between 0.5 bar and 1.5 bar.

[0056] The method 100 can also include drying and demolding the densified fibrous structure 210. Drying can be carried out before or after demolding the densified fibrous structure. For example, drying is carried out inside the mold before demolding, or outside the mold after demolding. When drying is carried out outside the mold, it can be carried out in a climate chamber, an oven or by freeze-drying.

[0057] The method 100 can also include treating the metal foil with an anti-sticking coating before placing the film 240 on the fibrous structure 210. Treating the metal foil with an anti-sticking coating can be achieved by spraying the anti-sticking coating onto the metal foil or by bonding a self-adhesive film to the metal foil.

[0058] The pre-densified or consolidated fibrous structure includes, for example, silicon carbide fibers. The fibrous structure can be produced by stacking layers or pleated layers obtained by two-dimensional weaving. The structure can also be directly and integrally produced by three-dimensional weaving. Here, two-dimensional weaving refers to the traditional weaving method in which each weft yarn passes from one side of the yarns of a single warp yarn layer to the other side or vice versa. Here, three-dimensional weaving refers to the weaving in which the warp yarns pass through several weft yarn layers, or the weft yarns pass through several warp yarn layers.

[0059] The fibrous structure can also be realized by a unidirectional fibrous sheet, which can be obtained by automated fiber placement or fiber winding.

[0060] The fibrous structure can be pre-densified or consolidated by chemical vapor infiltration (CVI) by depositing a boron nitride or pyrolytic carbon interface phase and then depositing a layer of silicon carbide or silicon nitride or a mixture of both (gas-phase consolidation). Densification can also be carried out with silicon carbide outside the shaped part to protect the structure during the melt infiltration step.

[0061] The slurry injected during the densification step 130 may include ceramic fillers in a volume ratio between 10% and 50% - for example, between 15% and 25% by volume - binders in a mass ratio between 0% and 20%, and plasticizers in a mass ratio between 0% - 20%. The ceramic filler is, for example, silicon carbide powder with a d50 size of less than 2 μm. The binder is, for example, polyvinyl alcohol (PVA), polyethylene glycol (PEG), or glycerol. The plasticizer is, for example, polyethylene glycol 200 (PEG 200). The slurry may also contain a dispersant, which may be electrostatic (such as tetraethylammonium hydroxide (TEAH)), or electrosteric (such as polyetherimide (PEI)), or steric (such as polyvinylpyrrolidone (PvP)). It may also include a wetting agent.

[0062] According to another embodiment, the reinforcement zone of the membrane may be formed by a metal insert or fabric present between the two outer surfaces of the membrane.

[0063] For example, the metal insert may be made of molybdenum or steel.

[0064] The fabric may be, for example, a consolidated fabric, such as a two-dimensional fabric. The fabric may be made of carbon or glass fibers and may include an epoxy resin matrix.

[0065] The expression "between... and..." should be understood to include the end point values.

Claims

1. A method of densifying a fiber structure made of a ceramic material with a ceramic matrix for use in an injection device, the injection device comprising: - a cavity defined between a mold and a counter mold, the cavity defining an internal space, and - a film including a reinforcing zone, the film to be placed between the fiber structure present in the cavity and the counter mold, and the reinforcing zone of the film having a Young's modulus greater than 200 GPa, The method includes: - placing a pre-densified fiber structure in the cavity, the pre-densified fiber structure having corrugations on its surface, and placing the reinforcing zone of the film on the pre-densified fiber structure in such a way that the reinforcing zone of the film contacts the peaks of the corrugations of the pre-densified fiber structure; - closing the injection device by placing the counter mold on the film and applying a pressing pressure to the film to maintain contact between the reinforcing zone of the film and the peaks of the corrugations of the pre-densified fiber structure; and - densifying the pre-densified fibrous structure by infiltrating a slurry into pores of the pre-densified fibrous structure, the slurry being injected into the mold cavity laterally of the reinforcement zone of the membrane under an injection pressure such that a pressure difference between the pressing pressure and the injection pressure is between 0.5 x 10 5 Pa and 6 x 10 5 Pa.

2. The densification method according to claim 1, wherein, The pressure difference between the pressing pressure and the injection pressure is between 0.5x10 5 Pa and 1.5x10 5 Pa.

3. The densification method according to claim 1, wherein The thickness of the reinforcing zone of the film is between 50 μm and 100 μm.

4. The densification method according to claim 1, wherein, The reinforcing zone of the film is formed by a metal foil provided on the surface of the film opposite to the fiber structure.

5. The densification method according to claim 4, wherein The metal foil is made of molybdenum.

6. The densification method according to claim 4, wherein, The metal foil includes an anti-stick coating on the surface facing the fiber structure.

7. The densifying method according to claim 4, further comprising treating the metal foil with an anti-stick coating in the form of a spray or a self-adhesive film.

8. The densification method according to claim 1, wherein The reinforcing zone of the film is formed by a fabric or a metal insert within the film.

9. The densification method according to claim 1, wherein, Outside the reinforcing zone of the film, the thickness of the film is between 1.5 mm and 4 mm, and the hardness is between 30 Shore A and 60 Shore A.

10. The densifying method according to claim 1, further comprising drying and demolding the densified fiber structure after densification.

11. The densification method according to claim 10, wherein, The drying of the fiber structure is carried out in the mold before demolding, or outside the mold in an oven, a climate chamber or by freeze-drying after demolding.

12. The densification method according to claim 1, wherein, The slurry contains a ceramic filler in a volume ratio between 10% and 50%, a binder in a mass ratio between 0% and 20%, and a plasticizer in a mass ratio between 0% and 20%.

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