Tooling for shaping a fibrous texture

Abstract

Tooling for shaping a fibrous texture. The present invention relates to a tooling (1) for shaping a fibrous texture for gas-assisted consolidation, comprising a plurality of shaping blocks (10) having a plurality of gas supply orifices and intended to bear against the fibrous texture so as to shape it into the form of a part to be obtained, characterized in that the shaping blocks are made of ceramic and comprise at least silica in a mass content greater than or equal to 30%. Figure for the abstract: Fig. 3.

Description

Title of the invention: Tool for shaping a fibrous texture Technical field

[0001] The present invention relates to a tool for shaping a fibrous texture for gas consolidation, and associated methods for manufacturing a part made of composite material. A particular field of application of the invention is the manufacture of parts made of ceramic matrix composite material ("Ceramic Matrix Composite"; "CMC"), for example with a silicon carbide matrix. Prior art

[0002] Ceramic matrix composite materials withstand temperatures ranging from 600°C to 1400°C. Due to their better resistance to high temperatures, CMCs require less cooling. This cooling traditionally comes from a sample in the compressor which impacts the efficiency of the turbomachine, CMC materials therefore make it possible to improve engine efficiency which reduces fuel consumption. Furthermore, their use contributes to optimizing the performance of turbomachines, in particular by reducing the overall mass of the turbomachine which further contributes to a reduction in fuel consumption and therefore to a significant reduction in pollutant emissions.

[0003] The manufacture of such parts may include obtaining a reinforcing texture, in particular by three-dimensional weaving, which is then shaped in a shaping tool in order to obtain a preform of the part to be obtained. The shaping tool is usually made of graphite and is multi-perforated so as to allow the infiltration of a gaseous phase containing one or more precursors to carry out a step, called consolidation, in which material is deposited in a porosity of the texture shaped in the shaping tool from the gaseous precursor(s). The thickness of the material thus deposited is sufficient to bind the fibers of the preform together so that it can be handled while retaining its shape without assistance from the shaping tool.The manufacturing of the part can then be continued after demolding the consolidated preform by gas pre-densification of the residual porosity of the consolidated preform, then by densification by slip injection and infiltration with molten silicon. According to an example of a possible manufacturing range of a composite material part, it is possible to carry out consolidation by boron nitride (BN) and silicon carbide (SiC). The demolding operation which allows the consolidated preform to be removed from the tooling can nevertheless be delicate and lead to non- . conformities in production if it is not carried out correctly. More specifically, we can see adhesion of the preform to the mold following a significant gas deposition, which can pose a problem in particular in thin areas with complex geometry and large radii of curvature (blade veil, trailing edge of a distributor). There is therefore an interest in facilitating the natural detachment of the part in these cases. The risk is to damage the part by trying to detach it from the mold after consolidation. It is, therefore, desirable to facilitate this operation. Statement of the invention

[0004] The present invention relates to a tool for shaping a fibrous texture for consolidation by gas, comprising a plurality of shaping blocks having a plurality of gas supply orifices and intended to bear on the fibrous texture so as to shape it into the form of a part to be obtained, characterized in that the shaping blocks are made of ceramic and comprise at least silica (SiO2) in a mass content greater than or equal to 30%.

[0005] The invention proposes the use of conformation blocks which are dimensionally stable under conditions typical of the first step of consolidation by boron nitride by chemical vapor infiltration ("CVI") which involve a moderate temperature. The blocks thus make it possible to guarantee the desired dimension and shape for the fiber preform. However, the significant silica content of the conformation blocks gives them the ability to undergo significant dimensional shrinkage under conditions typical of the second step of consolidation by silicon carbide by chemical vapor infiltration which involve a reducing atmosphere, for example based on dihydrogen, and a higher temperature.Thus, once the dimensions and shape of the part have been fixed by the first stage of consolidation, the blocks undergo a volumetric contraction during the second stage of consolidation in a reducing atmosphere carried out after this first stage, which facilitates the demolding of the consolidated preform. The composition of the conformation blocks is cleverly chosen to only present the dimensional shrinkage during the consolidation by silicon carbide carried out after the consolidation by boron nitride, that is to say after the dimensions and shape of the part have been fixed.

[0006] In an exemplary embodiment, the conformation blocks comprise at least silica in a mass content greater than or equal to 70%.

[0007] Such a characteristic helps to increase the dimensional shrinkage in a reducing atmosphere and therefore to further facilitate the demolding of the preform.

[0008] In particular, the conformation blocks may further comprise alumina (A12O3) in a mass content of less than or equal to 15%, for example in a content mass less than or equal to 10%, or even less than or equal to 5%.

[0009] A reduced alumina content helps to increase dimensional shrinkage in a reducing atmosphere and therefore to further facilitate demolding of the preform.

[0010] The present invention also relates to a method for manufacturing a part made of composite material using shaping tools as described above, comprising: - shaping a fibrous texture in the tooling so as to obtain a fibrous preform of the part to be obtained, - consolidation by chemical vapor infiltration comprising a first step at a temperature less than or equal to 900°C, comprising the deposition of a first material in a porosity of the fiber preform maintained in the shaping tool, and a second step by chemical vapor infiltration at a temperature of at least 1000°C under a reducing atmosphere carried out after the first step, comprising the deposition of a second material different from the first material in a residual porosity of the fiber preform.

[0011] In an exemplary embodiment, the fiber preform is a turbine blade preform.

[0012] In an exemplary embodiment, the first material is boron nitride and the second material is silicon carbide.

[0013] In an exemplary embodiment, the reducing atmosphere comprises dihydrogen.

[0014] In an exemplary embodiment, the method further comprises removing the consolidated fibrous preform of the tool followed by densification of the latter.

[0015] In an exemplary embodiment, the densification is carried out by infiltration in the melt state.

[0016] The part may be a turbomachine part, for example an aeronautical turbomachine. The part may in particular be a turbine part, such as a turbine blade, a distributor sector or a ring sector. Brief description of the drawings

[0017] [Fig-1] [Fig.l] is a flowchart representing a succession of steps of a example of a method according to the invention.

[0018] [Fig.2] [Fig.2] represents, in a schematic and partial manner, an example shaping tool according to the invention containing the preform before consolidation.

[0019] [Fig.3] [Fig.3] schematically and partially represents the shaping tool containing the consolidated preform in which the shaping blocks have undergone volumetric shrinkage following consolidation. Description of the embodiments

[0020] A fibrous texture is initially manufactured by implementing one or more textile operations, for example by three-dimensional weaving, in a manner known per se (step E10). The texture may be formed from ceramic threads, for example made of silicon carbide, or carbon. The texture is intended to form the fibrous reinforcement of the composite material part to be obtained. The fibrous texture is then shaped in a shaping tool so as to obtain a fibrous preform which has the shape of the part to be obtained (step E20). [Fig. 2] represents an example of shaping tool 1 according to the invention adapted to the shaping of a fibrous texture intended to form the fibrous reinforcement of a turbine blade for an aeronautical turbomachine, it being understood that the invention is not limited to this application.The tool 1 comprises a frame 3, typically made of graphite, which positions and holds a plurality of shaping blocks 10 which define a mold for the texture. The texture is positioned inside a volume defined by the blocks 10 so as to be held in shape by the latter and to obtain the preform 12 which has the shape of the part to be obtained. The blocks 10 come to bear on the preform 12, the latter being located between the latter. The blocks 10 can also compact the preform 12 to a target thickness according to the zone considered so as to guarantee obtaining the desired fiber content. In the example illustrated, the blocks 10 define the shape of an external surface of the preform 12, in particular of an aerodynamic profile PA of the part to be obtained, as well as of a fixing portion PF.The frame 3 and the blocks 10 have gas supply orifices (not shown) through which a gaseous phase, comprising one or more precursors of a consolidation phase, is intended to flow to reach the preform 12 and deposit material in its porosity. The frame 3 and the blocks 10 have a degree of permeability suitable for ensuring the diffusion of the gases and the good consolidation of the part. This degree of permeability is determined by a person skilled in the art depending on the intended application. The gas supply orifices can be formed by machining, or by focusing an energy beam. The blocks 10 can be obtained by different techniques, such as powder injection molding. Formation of the blocks 10 by additive manufacturing can also be envisaged for the production of complex opening patterns.The frame 3 and the blocks 10 are held in place by a plurality of locking elements (not shown) allowing the tool 1 to be closed and ensuring the preform 12 is held in place before being placed in the CVI furnace. Those skilled in the art will recognize that arrangements other than those illustrated in Figures 2 and 3 are possible depending on the geometry of the part to be obtained.

[0021] The tool 1 is remarkable in that the blocks 10 have a particular composition which allows them to exhibit dimensional stability during the first stage of consolidation by boron nitride by CVI at a temperature below 900°C (step E30), and a reduction in their dimensions during the second consolidation step by silicon carbide by CVI under a reducing atmosphere and at a higher temperature, for example greater than or equal to 1000°C (step E40). More particularly, the blocks 10 comprise a significant mass fraction of silica, at a rate of at least 30% by mass, preferably at a rate of at least 70% by mass, for example at a rate of at least 85% by mass. Unless otherwise stated, the composition of the blocks 10 is taken before contact with the reducing atmosphere imposed during the second consolidation step (step E40). Whatever the embodiment considered, the blocks 10 may comprise silica in the proportions indicated above and alumina at a rate of at most 15% by mass, for example at a rate of at most 5% by mass.For example, blocks 10 formed from a mixture of silica present at a rate of 90% by mass, and alumina present at a rate of 10% by mass can be used. According to a variant, the blocks 10 can be substantially free of alumina, and for example be constituted essentially by silica. It is also possible to use blocks 10 having a higher alumina content, for example composed of 30% by mass of silica and 70% by mass of alumina. The blocks 10 are not necessarily of binary composition and it is also possible to use blocks 10 of ternary composition, for example having the following composition: silica at a rate of 50% to 96% by mass, zircon at a rate of 1% to 30% by mass and alumina at a rate of 1% to 5% by mass.

[0022] The tool 1 holding the preform 12 in the desired shape is placed in a chemical vapor infiltration furnace for successive performance of the first consolidation step (step E30) and the second consolidation step (step E40). These two steps will now be described.

[0023] Consolidation makes it possible to obtain a preform, called consolidated, which can be handled while retaining its shape without assistance from the shaping tooling. Consolidation is a technique known per se. The first consolidation step (step E30) can be carried out by depositing boron nitride in a porosity of the preform 12. The boron nitride has a function of weakening the composite material which promotes the deflection of any cracks which have propagated in the matrix, preventing or delaying the breakage of wires by such cracks. The conditions implemented during this step are known per se. It is thus possible to form a boron nitride consolidation from a mixture of boron trichloride (BC13) and ammonia (NH3), for example in a neutral atmosphere, comprising for example dinitrogen or argon or even in dihydrogen.Alternatively, only the mixture of boron trichloride and ammonia can be used without diluent gas. The temperature during the formation of boron nitride can be limited, typically . less than or equal to 900°C, for example between 650°C and 900°C or between 650°C and 800°C. The dimensions of the blocks 10 and of the frame 3 are not modified during the first consolidation step E30, which makes it possible to maintain the dimensions of the preform 12 imposed by the tooling 1 during this step E30. The first consolidation step sufficiently binds the wires of the preform 12 so that it retains its shape and dimensions in the tooling 1 during the second gas consolidation step using silicon carbide (step E40) despite the reduction in the dimensions of the blocks 10 produced during this second step. Thus, the thickness of the boron nitride consolidation phase may be greater than or equal to 50 nm, for example between 50 nm and 600 nm.

[0024] If desired, it is possible to carry out, after step E30 and before the second consolidation step E40, a heat treatment to stabilize the boron nitride at a temperature above 1300°C, for example between 1300°C and 1450°C, under a neutral atmosphere. The duration of this treatment may be between 0.25 hours and 4 hours, more preferably between 0.5 hours and 2 hours. Such a treatment is described in application WO 2014049221A1. The purpose of this treatment is to chemically stabilize the boron nitride by causing the degassing of volatile species originating from the reaction gas phase and present in the boron nitride deposit, and by eliminating the presence of active sites onto which oxygen could be grafted if the boron nitride were to be exposed to an oxidizing environment during use of the CMC part. It is not outside the scope of the invention if this stabilization treatment is omitted.

[0025] The method continues with the second step of gaseous consolidation using silicon carbide (step E40). This step uses operating conditions that are known per se. It can use a gaseous phase comprising a SiC precursor, such as methyltrichlorosilane (MTS), as well as a reducing gas, such as dihydrogen (H2). A temperature greater than or equal to 1000°C, for example between 1000°C and 1400°C, can be imposed during this step. The mass flow rate of SiC precursor introduced into the CVI furnace relative to the volume of the preform can be greater than or equal to 0.2 kg / h / L (kilogram per hour of precursor per liter of preform), for example between 0.2 kg / h / L and 5 kg / h / L. The amount of reducing gas is determined based on the amount of precursor, the QR / QP ratio being between 1 and 30, where QR denotes the amount of reducing gas and QP the amount of precursor.During step E40, the preform 12 is subjected to a temperature higher than that imposed during the first consolidation step E30.

[0026] [Fig. 3] illustrates the volume contraction of the blocks 10 during step E40. The blocks 10 undergo, during this step, a chemical reduction in contact with the reducing atmosphere under the effect of the imposed temperature which leads to a reduction in their dimensions. A preform 14 is obtained consolidated by a boron nitride phase and by a silicon carbide phase, and the volume contraction of the blocks 10 causes a clearance J to appear between the blocks 10 and the consolidated preform 14 which allows easy removal of the blocks 10 and simple extraction of the CMC material (step E50). The volume of the blocks 10 may decrease during the second consolidation step (step E40) by at least 0.2%, for example by at least 0.5%, this decrease being for example between 0.2% and 5% or between 0.5% and 5%. The frame 3 does not undergo any dimensional variation during step E40.

[0027] Following removal of the consolidated preform 14 from the tool 1, densification (step E60) thereof may be carried out by forming a matrix phase in its residual porosity by implementing techniques known per se. It is thus possible to obtain a part made of composite material with a ceramic matrix, for example with a silicon carbide matrix. For example, the densification may be carried out by infiltration of silicon in the molten state (“Melt-Infiltration” process). In the latter case, a powder is introduced into the residual porosity of the consolidated preform, this powder possibly being a carbon powder, a ceramic powder, for example silicon carbide, or a mixture of such powders, and a metallic composition based on silicon in the molten state is then infiltrated to form a SiC or SiC-Si matrix.Those skilled in the art will recognize that other techniques can be implemented for densification, such as for example chemical vapor infiltration or polymer infiltration and pyrolysis (“Polymer Infiltration and Pyrolysis”; “PIP”). A first densification step can be carried out by chemical vapor infiltration and then a second densification step by introducing powder and infiltrating silicon in the molten state. Whatever the embodiment considered, the part obtained can have a matrix that is predominantly ceramic in volume, for example entirely ceramic.

[0028] The expression “between ... and ...” must be understood as including the limits.

Claims

Claims

1. Tool (1) for shaping a fibrous texture for gas consolidation, comprising a plurality of shaping blocks (10) having a plurality of gas supply orifices and intended to bear on the fibrous texture so as to shape it into the shape of a part to be obtained, characterized in that the shaping blocks are made of ceramic and comprise at least silica in a mass content greater than or equal to 70% and in addition alumina in a mass content less than or equal to 15%.

2. Method for manufacturing a part made of composite material using a shaping tool (1) according to claim 1, comprising: - shaping (E20) a fibrous texture in the tool so as to obtain a fibrous preform (12) of the part to be obtained, - consolidation (E30) by chemical vapor infiltration comprising a first step at a temperature less than or equal to 900°C, comprising the deposition of a first material in a porosity of the fibrous preform maintained in the shaping tool, and a second step by chemical vapor infiltration at a temperature of at least 1000°C under a reducing atmosphere carried out after the first step, comprising the deposition of a second material different from the first material in a residual porosity of the fibrous preform.

3. The method of claim 2, wherein the fibrous preform (12) is a turbine blade preform.

4. The method of claim 2 or 3, wherein the first material is boron nitride and the second material is silicon carbide.

5. A method according to any one of claims 2 to 4, wherein the reducing atmosphere comprises dihydrogen.

6. A method according to any one of claims 2 to 5, wherein the method further comprises removing (E50) the consolidated fibrous preform (14) from the tooling followed by densifying (E60) it.

7. A method according to claim 6, wherein the densification (E60) is carried out by melt infiltration.

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