METHOD FOR COMPACTING A FIBROGENIC TEXTURE BY INJECTION OF A SCHLICKER

Description

Technical Field

[0001] The present invention relates to the general field of manufacturing parts in ceramic matrix composite (CMC) material, and more particularly to a process for densifying a fibrous texture in ceramic material comprising a ceramic matrix. Previous technique

[0002] The densification of a fibrous texture, i.e. the formation of a ceramic matrix in the fibrous texture, includes a slip injection step which consists of impregnating the fibrous texture with a suspension of ceramic particles or slip which penetrates the porosity of the fibrous texture and allows the obtaining of a ceramic matrix in the fibrous texture.

[0003] To improve the aerodynamic properties of the final part, a densified fibrous texture with a smooth surface is required. Generally, a smooth surface is achieved by machining the densified fibrous texture or by adding material (thickening). However, this incurs additional costs, can reduce the material's thermomechanical strength, and, most importantly, complicates the manufacturing process of the ceramic matrix composite.

[0004] It is therefore desirable to have a new process for densifying a fibrous texture that allows obtaining a densified fibrous preform with a smooth surface without generating excess thickness and without an additional surface machining step.

[0005] Document WO 2018 / 234669 describes a method for manufacturing a ceramic part with local variations in thickness using a tool for impregnating a fibrous texture to form the future part. The tool includes an impermeable membrane having a portion shaped to correspond to the local thicknesses of the fibrous texture, in order to distribute the impregnation solution homogeneously within the fibrous texture. Description of the invention

[0006] The invention relates to a method for densifying a fibrous texture in ceramic matrix material implemented in an injection mold comprising: a molding cavity defined between a mold and a counter-mold, the molding cavity defining an internal volume, and a membrane comprising a stiffened zone, the membrane being intended to be placed between a fibrous texture present in the molding cavity and the counter-mold and the stiffened zone of the membrane having a Young's modulus greater than 200 GPa, the process comprising: the placement of a pre-densified fibrous texture in the molding cavity, the pre-densified fibrous texture having undulations on its surface and the placement of the membrane on the pre-densified fibrous texture so that the stiffened area of ​​the membrane is in contact with the crest of the undulations of the pre-densified fibrous texture, the closing of the injection tooling by placing the counter-mold on the membrane and the application of compaction pressure on the membrane so as to maintain the stiffened area of ​​the membrane in contact with the crest of the undulations of the pre-densified fibrous texture, and the densification of the pre-densified fibrous texture by infiltrating a slurry into the porosity of the pre-densified fibrous texture, the slurry being injected into the molding chamber laterally to the stiffened area of ​​the membrane under injection pressure,such that the pressure difference between the compaction pressure and the injection pressure is between 0.5 x 10⁵ Pa and 6 x 10⁵ Pa.

[0007] The fact that the stiffened zone has a Young's modulus greater than 200 GPa allows for a stiffened zone that is sufficiently rigid so that it does not deform during the application of compaction pressure on the membrane and the densification of the fibrous texture.

[0008] Thanks to the process of the invention, particularly the placement of the rigidified zone of the membrane at the crest of the undulations of the fibrous texture and the fact that this rigidified zone has a Young's modulus greater than 200 GPa, the surface of the fibrous texture can be smoothed during its densification while avoiding the creation of excess thickness (the excess thickness generated by matrix growth is very limited, reaching a maximum of 0.05 mm). Indeed, matrix growth, i.e., the densification of the fibrous texture, stops at the rigidified zone of the membrane, thus preventing the formation of excess thickness on the surface of the fibrous texture. The volume of the matrix thus formed is therefore limited up to the highest undulations of the pre-densified fibrous texture.

[0009] Furthermore, maintaining a pressure difference between the compaction and injection pressures of between 0.5 bar and 6 bar (i.e., between 0.5 x 10⁵ Pa and 6 x 10⁵ Pa) allows the rigidified zone of the membrane to remain in contact only with the crests of the fibrous texture's undulations. Thus, this rigidified zone does not conform to the texture's contours and does not deform during matrix growth within the fibrous texture's porosity. This pressure differential range makes it possible to obtain a fibrous preform, that is, a densified fibrous texture with a smooth surface.

[0010] Furthermore, the fibrous texture is pre-densified when placed in the mold cavity to prevent deformation. In other words, the fibrous texture is consolidated before being introduced into the mold cavity. This increases its mechanical strength and prevents deformation. It also allows for a wider compaction pressure range, enabling compaction pressures between 0.5 bar and 6 bar, which is not possible with a deformable reinforcement.

[0011] The injection of the slip laterally to the stiffened zone of the membrane in the molding chamber and into the porosity of the pre-densified fibrous texture can be carried out at a controlled flow rate or pressure such that the pressure difference between the compaction pressure and the injection pressure is kept constant throughout the injection. When injection is carried out at a controlled flow rate, the pressure profile, particularly its rise with increasing flow resistance during matrix growth, can be monitored to verify that the pressure difference between the compaction pressure and the injection pressure remains constant.

[0012] According to a particular feature of the invention, the rigidified area of ​​the membrane is formed by a metallic foil placed on a surface of the membrane opposite the fibrous texture.

[0013] According to another particular feature of the invention, the metallic shim is made of molybdenum or Inconel ®< .

[0014] According to another particular feature of the invention, the metallic shim comprises an anti-stick coating on a surface opposite the fibrous texture.

[0015] According to another particular feature of the invention, the process also includes, before placement, the treatment of the metallic foil with an anti-adhesive in the form of a spray or self-adhesive film.

[0016] The anti-stick coating is, for example, a polytetrafluoroethylene (PTFE) film.

[0017] The presence of a non-stick coating on the metallic foil helps to limit material tearing.

[0018] According to another particular feature of the invention, the stiffened zone of the membrane is formed by a metallic insert or a textile internal to the membrane. In other words, a metallic insert or a textile is present between the internal and external surfaces of the membrane. The textile is, for example, a consolidated textile made of woven fibers, such as a thin, two-dimensional textile, made of carbon or glass, which can be integrated during the casting of the membrane. The metallic insert is, for example, an insert made of Inconel®, molybdenum, or steel.

[0019] According to another particular feature of the invention, the pressure difference between the compaction pressure and the injection pressure is between 0.5 x 10⁵ Pa and 1.5 x 10⁵ Pa (i.e. between 0.5 bars and 1.5 bars).

[0020] This helps to improve the smoothness of the surface of the fibrous texture after its densification.

[0021] According to another particular feature of the invention, the stiffened area of ​​the membrane has a thickness between 50 µm and 100 µm.

[0022] According to another particular feature of the invention, the thickness of the stiffened zone of the membrane is greater than 50 µm, for example, between 0.05 mm and 0.5 mm, and in particular between 0.05 mm and 0.1 mm. This is especially relevant when densifying a fibrous texture with a flat surface. These materials and / or thickness ranges for the stiffened zone make it possible to have a zone that is sufficiently rigid so that it does not deform when it is pressed onto the fibrous texture and during the growth of the matrix within the fibrous texture, and sufficiently flexible so that it can conform to the geometric irregularities of the parts and remain in contact with the crest of the undulations of the fibrous texture at every point.

[0023] According to another particular feature of the invention, outside its stiffened area, the membrane has a thickness between 1.5 mm and 4 mm and a hardness between 30 Shore A and 60 Shore A.

[0024] This allows the membrane to apply compaction pressure homogeneously over its stiffened area without hindering the injection of slurry.

[0025] According to another particular feature of the invention, the process also includes drying the densified fibrous texture and demolding the densified fibrous texture after densification.

[0026] According to another particular feature of the invention, drying is carried out in the mold before demolding or outside the mold after demolding in an oven, in a climatic chamber or by freeze-drying (or "Freeze Drying" in English).

[0027] Drying in an oven or climate chamber, for example, is carried out at a temperature between 40°C and 80°C. Furthermore, ideally, the oven or climate chamber has a relative humidity between 40% and 90% to limit cracking.

[0028] According to another particular feature of the invention, the slip comprises ceramic fillers with a rate of between 5% and 50% by volume, for example between 15% and 25% by volume, a binder with a rate of between 0% and 20% by mass and a plasticizer with a rate of between 0% and 20% by mass.

[0029] The ceramic fillers include, for example, silicon carbide (SiC) particles 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). Brief description of the drawings

[0030] Other features and advantages of the present invention will become apparent from the description given below, with reference to the attached drawings which illustrate examples of embodiment without any limiting character. [ Fig. 1 ] There figure 1 represents, schematically, a process for densifying a fibrous texture in ceramic material and ceramic matrix according to an embodiment of the invention. Fig. 2A ] There figure 2A represents, schematically and partially, an exploded view of an injection mold for implementing the densification process according to an embodiment of the invention. Fig. 2B ] There figure 2B represents, schematically and partially, a cross-section of the injection molding tooling of the figure 2A . [ Fig. 3 ] There figure 3 represents, schematically and partially, a metallic shim in contact with the top of the undulations of a pre-densified fibrous texture present in an injection tool for the implementation of the invention. Description of the implementation methods

[0031] There figure 1 represents, schematically, a 100 process for densifying a fibrous texture in ceramic material and ceramic matrix according to an embodiment of the invention.

[0032] THE figures 2A , 2B et 3 schematically and partially represent the injection molding tooling 260 comprising a fibrous texture 210 for implementing the process 100 illustrated in figure 1 .

[0033] The injection mold 260 includes a mold cavity 263 defined between a mold 261 and a counter-mold 262. The mold cavity 263 thus defines an internal volume. The injection mold 260 also includes a membrane 240 intended to be placed between a fibrous texture 210 present in the mold cavity 263 and the counter-mold 262. The membrane 240 includes a stiffened zone 220. In this embodiment, the stiffened zone 220 is formed by a metallic shim on the surface of the membrane 240 opposite the fibrous texture 210. In the remainder of the description of these figures, the stiffened zone 220 of the membrane 240 will therefore simply be referred to as "metallic shim".

[0034] With the exception of the area containing the metallic flash 220, the membrane 240 can have a thickness between 1.5 mm and 4 mm. It can have a hardness between 30 shA and 60 shA. For example, membrane 240 has a hardness of 50 shA and a thickness of 4 mm to ensure proper sealing between the counter-mold 262 / mold 261 and membrane 240.

[0035] The tooling 260 also includes two injection ports 251 for injecting a slip into the mold cavity 263 and an outlet port 252 configured to remove a liquid phase from the injected slip. It may also include an injection wedge 250 that allows the membrane 240 and the fibrous texture 210 to be positioned correctly so as not to interfere with the injection of the slip and its impregnation into the texture 210.

[0036] The injection molding tooling 260 also includes a filter element 230 located in the molding cavity 263 beneath the fibrous texture 210. This filter element 230 is configured to filter a liquid phase from the slurry injected into the molding cavity 263. The liquid phase filtered by the filter element 230 can be removed through the outlet port 252.

[0037] The densification process 100 comprises placing 110 a pre-densified fibrous texture 210 in the mold cavity 263 of an injection mold 260, and placing the membrane 240 on the pre-densified fibrous texture 210. The pre-densified fibrous texture 210 has undulations 211, 212 on its surface (shown in figure 3For example, there can be up to a 0.3 mm difference between the crest of a corrugation 211, 212 and the lowest point of the corrugation. The metallic foil 220 of the membrane 240 is placed on the fibrous texture 210 so that it is in contact with the crest of the corrugations 211, 212 of the fibrous texture 210. The metallic foil 220 is in contact only with the crest of the corrugations and not with the lowest point located, for example, 0.3 mm from the crest.

[0038] The 220 metallic foil is, for example, made of molybdenum, steel, or Inconel®. It has a Young's modulus greater than 200 GPa and can have a thickness between 50 µm and 100 µm, for example, 100 µm. The 220 metallic foil may also include a non-stick coating on its surface opposite the 210 fibrous texture.

[0039] Then, process 100 includes closing 120 the injection tooling 260 by placing the counter-mold 262 on the membrane. A compaction pressure P is applied to the membrane 240 so that the metallic foil 220 remains in contact with the crest of the undulations 211, 212 of the pre-densified fibrous texture 210.

[0040] The compaction pressure P compaction is for example applied to the metal shim 220 via the membrane 240 by air pressure or by pressure from another fluid, such as silicone oil.

[0041] Finally, the process 100 includes the densification 130 of the pre-densified fibrous texture 210 by infiltrating a slip into the porosity of the pre-densified fibrous texture 210. The slip is injected through the injection ports 251 of the injection tooling 260 into the mold cavity 263 laterally to the membrane 240, specifically laterally to the metal foil 220, under an injection pressure Pinjection. The densified fibrous texture thus forms a fibrous preform comprising a matrix.

[0042] The injection and compaction pressure values, Pinjection and Pcompaction, are defined such that the pressure difference ΔP between the compaction pressure and the injection pressure (ΔP = Pcompaction - Pinjection) is between 0.5 bar and 6 bar (i.e., in pascals, between 0.5 x 105 Pa and 6 x 105 Pa). For example, if the pressure difference ΔP is between 0.5 bar and 1.5 bar, it is 1 bar.

[0043] The injection pressure P injection can, for example, be between 3 bars and 20 bars.

[0044] The compaction pressure P compaction can for example be between 0.5 bar and 6 bar.

[0045] During the injection 130 of the slurry, the compaction pressure values ​​Pcompaction and injection pressure values ​​Pinjection may vary, so the process 100 may include monitoring the pressure difference ΔP throughout the injection 130 so as to maintain the pressure difference ΔP in the range of 0.5 bars to 6 bars, or in a narrower range, for example between 0.5 bars and 1.5 bars.

[0046] Process 100 may also include drying and demolding the densified fibrous texture 210. Drying may occur before or after demolding the densified fibrous texture. For example, drying may take place in the mold before demolding, or outside the mold after demolding. When drying occurs outside the mold, it may be carried out in a climate chamber, in an oven, or by freeze-drying.

[0047] The process 100 can also include the treatment of the metallic foil 220 with an anti-stick agent before the placement 110 of the membrane 240 on the fibrous texture 210. The treatment of the foil 220 with an anti-stick agent can be carried out by spraying the anti-stick agent onto the foil 220 or by sticking a self-adhesive film onto the foil 220.

[0048] Pre-densified or consolidated fibrous texture includes, for example, silicon carbide fibers. The fibrous texture can be created by stacking layers or plies obtained through two-dimensional weaving. The texture can also be produced directly in a single piece through three-dimensional weaving. Two-dimensional weaving refers to a conventional weaving method in which each weft yarn passes from one side of the warp yarns to the other, or vice versa. Three-dimensional weaving refers to a weave in which warp yarns pass through several layers of weft yarns, or weft yarns pass through several layers of warp yarns.

[0049] The fibrous texture can also be achieved by sheets of unidirectional fibers, which can be obtained by automatic fiber placement, or by filament winding.

[0050] The fibrous texture can be pre-densified or consolidated by chemical vapor infiltration (CVI) with the deposition of a boron nitride or pyrolytic carbon interphase, followed by the deposition of a silicon carbide or silicon nitride layer, or a mixture of the two (gas-phase consolidation). It can also be densified outside the conformer with silicon carbide to protect the texture during the melt infiltration step.

[0051] The slip injected during the densification step 130 may contain ceramic fillers at a concentration of between 10% and 50% by volume, for example, between 15% and 25% by volume, a binder at a concentration of between 0% and 20% by mass, and a plasticizer at a concentration of between 0% and 20% by mass. The ceramic fillers may be, for example, silicon carbide powder with a particle size d50 less than 2 µm. The binder may be, for example, polyvinyl alcohol (PVA), polyethylene glycol (PEG), or glycerol. The plasticizer may be, for example, polyethylene glycol 200 (PEG 200). The slip may also contain a dispersant, which may be electrostatic, such as tetraethylammonium (TEAH), electrosteric, such as polyetherimide (PEI), or steric, such as polyvinylpyrrolidone (PvP). It may also include a wetting agent.

[0052] According to another embodiment, the stiffened area of ​​the membrane can be formed by a metallic insert or a textile present between the two external surfaces of the membrane.

[0053] The metal insert can, for example, be made of Inconel®, molybdenum or steel.

[0054] Textiles can, for example, be consolidated textiles, such as two-dimensional textiles. They can be made of carbon or glass fibers and may include an epoxy matrix.

[0055] The expression "between ... and ..." should be understood as including the boundaries.

Claims

1. A method (100) for densifying a fibrous texture made of ceramic material with a ceramic matrix used in injection equipment (260) comprising: - a mold cavity (263) defined between a mold (261) and a counter-mold (262), the mold cavity defining an internal space, and - a membrane (240) comprising a stiffened zone (220), the membrane being intended to be placed between a fibrous texture (210) present in the mold cavity and the counter-mold, and the stiffened zone of the membrane having a Young's modulus greater than 200 GPa, the method comprising: - placing (110) a predensified fibrous texture in the mold cavity, the predensified fibrous texture having corrugations (211, 212) on the surface and placing the stiffened zone of the membrane on the predensified fibrous texture in such a way that the stiffened zone of the membrane is in contact with the peaks of the corrugations of the predensified fibrous texture; - closing (120) the injection equipment by placing the counter-mold on the membrane and applying a compaction pressure (Pcompaction) to the membrane so as to keep the stiffened zone of the membrane in contact with the peaks of the corrugations of the predensified fibrous texture; and - densifying (130) the predensified fibrous texture by infiltrating a slip into the porosity of the predensified fibrous texture, the slip being injected into the mold chamber laterally to the stiffened zone of the membrane at an injection pressure (Pinjection) such that the difference in pressure (ΔP) between the compaction pressure and the injection pressure is between 0.5 x 105 Pa and 6 x 105 Pa.

2. The densification method according to claim 1, wherein the difference in pressure between the compaction pressure and the injection pressure is between 0.5 x 105 Pa and 1.5 x 105 Pa.

3. The densification method according to any one of claims 1 or 2, wherein the stiffened zone of the membrane has a thickness of between 50 µm and 100 µm.

4. The densification method according to any one of claims 1 to 3, wherein the stiffened zone of the membrane is formed by a metal foil placed on a surface of the membrane opposite the fibrous texture.

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

6. The densification method according to any one of claims 4 or 5, wherein the metal foil comprises an anti-adhesive coating on a surface facing the fibrous texture.

7. The densification method according to any one of claims 4 to 6, also comprising treating the metal foil with an anti-adhesive coating in the form of a spray or self-adhesive film.

8. The densification method according to any one of claims 1 to 3, wherein the stiffened zone of the membrane is formed by a metal insert or a textile internal to the membrane.

9. The densification method according to any one of claims 1 to 8, wherein, outside its stiffened zone, the membrane has a thickness of between 1.5 mm and 4 mm and a hardness of between 30 Shore A and 60 Shore A.

10. The densification method according to any one of claims 1 to 9, also comprising drying and demolding the densified fibrous texture after densification.

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

12. The densification method according to any one of claims 1 to 11, wherein the slip comprises ceramic fillers with a rate of between 10% and 50% of the volume, a binder with a rate of between 0% and 20% by mass and a plasticizer with a rate of between 0% and 20% by mass.