Manufacturing process for a part made of ceramic matrix composite material

Abstract

Method for manufacturing a part made of ceramic matrix composite material The present invention relates to a method for manufacturing a part made of ceramic matrix composite material, comprising: - infiltrating (S60) a pre-densified fibrous structure with a molten infiltration composition comprising silicon in order to form a ceramic matrix in a residual porosity of said pre-densified fibrous structure, said pre-densified fibrous structure comprising a pre-densification matrix comprising a first layer of silicon carbide and a second protective layer covering the first layer and capable of protecting the latter from attack by the silicon of the infiltration composition, the second protective layer being formed by a binary BC system or by a ternary Si-BC system. Figure for abstract: Fig. 1.

Description

Title of the invention: Method for manufacturing a part made of ceramic matrix composite material Technical field

[0001] The invention relates to the manufacture of a part made of ceramic matrix composite material ("Ceramic Matrix Composite"; "CMC") during which the ceramic matrix is formed by infiltration of a molten silicon-based composition ("Melt-Infiltration"; "MI"). The invention proposes the presence of a protective layer making it possible to protect the underlying pre-densification silicon carbide from attack by the molten silicon. The part made of composite material thus obtained can find an application as a hot end part of a turbomachine, in particular an aeronautical turbomachine, such as a turbine part. 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] CMC parts can be densified by melt infiltration. In this technique, a molten silicon composition can be introduced into the porosity of a fibrous structure pre-densified by a silicon carbide deposit and loaded with silicon carbide particles. This method makes it possible to obtain a fully dense Si-SiC matrix of high modulus and a composite with a high linearity limit. The resulting composites have good mechanical properties but the inventors have observed a certain variability in the elongation at break which reduces the damage tolerance of the material. It is desirable to propose a solution to address this drawback. Statement of the invention

[0004] The invention relates to a method for manufacturing a part made of ceramic matrix composite material, comprising: - the infiltration of a pre-densified fibrous structure by a molten infiltration composition comprising silicon in order to form a matrix ceramic in a residual porosity of said pre-densified fibrous structure, said pre-densified fibrous structure comprising a pre-densification matrix comprising a first layer of silicon carbide and a second protective layer covering the first layer and capable of protecting the latter from attack by the silicon of the infiltration composition, the second protective layer being formed by a binary BC system or by a ternary Si-BC system.

[0005] The inventors found that the variability of the fracture behavior was linked to an uncontrolled attack of the silicon carbide of the pre-densification matrix by the molten silicon in the solution of the prior art. This phenomenon can go as far as the degradation of the fiber reinforcement and the interphase resulting in a reduction of the structural character of the composite. The invention proposes a functionalization of the pre-densification matrix so as to integrate therein a protective layer as described above which makes it possible to reduce the attack of the silicon carbide of the pre-densification matrix. The protective layer, forming an integral part of the pre-densification matrix, is distributed homogeneously in the pre-densified fiber structure to provide protection throughout its volume and throughout the infiltration. Composite materials are thus obtained with a much more efficient fracture behavior.

[0006] In an exemplary embodiment, the pre-densification matrix further comprises an additional protective layer of pyrocarbon covering the second layer.

[0007] Such a characteristic advantageously makes it possible to provide an additional source of carbon making it possible to further reduce the risk of attack on the silicon carbide of the pre-densification matrix.

[0008] In an exemplary embodiment, the infiltration composition comprises boron.

[0009] Such a characteristic advantageously makes it possible to further protect the underlying silicon carbide.

[0010] In an exemplary embodiment, the second protective layer is made of boron carbide, with the possible presence of excess free carbon, or of boron-doped carbon with boron in an atomic proportion of between 5% and 20%.

[0011] Such a protective layer has the advantage of being relatively simple to form.

[0012] Alternatively, the second protective layer is formed by a Si-BC ternary system having, in atomic percentage, a boron content of between 56% and 79%, a carbon content of between 17% and 39% and a silicon content of between 3% and 6%.

[0013] The use of a Si-BC ternary system is advantageous insofar as it does not require the addition of a carbon precursor, making the effluent treatment system of a SiC-CVI furnace compatible with the formation of this system.

[0014] In an exemplary embodiment, the pre-densified fibrous structure comprises a fibrous reinforcement partially densified by the pre-densification matrix, and the second protective layer, or the possible additional protective layer, forms the layer of the pre-densification matrix furthest from the fibrous reinforcement.

[0015] In an exemplary embodiment, a thickness of the second layer is between 0.1 μm and 4 μm.

[0016] Such a characteristic makes it possible to obtain a good compromise between effective protection of the pre-densification silicon carbide during infiltration, without penalizing the manufacturing time of the part by controlling the thickness of the protective layer.

[0017] In an exemplary embodiment, the pre-densified fibrous structure further comprises a boron nitride interphase between a fibrous reinforcement and the pre-densification matrix.

[0018] The presence of a boron nitride interphase advantageously makes it possible to deflect cracks which may appear in the matrix of the composite part during operation so as to preserve the fiber reinforcement, and to provide resistance to oxidation.

[0019] In an exemplary embodiment, the pre-densified fibrous structure comprises a fibrous reinforcement formed by three-dimensional weaving or from a plurality of two-dimensional fibrous layers.

[0020] In an exemplary embodiment, the part is a turbomachine part.

[0021] The part may be a turbine part, for example an aircraft engine turbine part. The part may for example be a turbomachine blade, a turbine ring sector or a distributor. Brief description of the drawings

[0022] [Fig-1] [Fig.l] is a flowchart showing a succession of steps of a example of a method according to the invention.

[0023] [Fig.2] [Fig.2] schematically and partially represents an example of a pre-densified fibrous structure that can be implemented within the framework of the invention.

[0024] [Fig.3] [Fig.3] schematically and partially represents another example of a pre-densified fibrous structure that can be implemented within the framework of the invention. Description of the embodiments

[0025] An example of a method for manufacturing a part made of CMC material according to the invention will now be described in connection with the flowchart of [Fig. 1] and the architectures illustrated in Figures 2 and 3.

[0026] A first step S10 of the method may consist of forming the fibrous structure by implementing one or more textile operations such as three-dimensional weaving. mental. The fibrous structure may be formed of ceramic threads, for example silicon carbide threads. The fibrous structure may constitute the fibrous reinforcement 10 of the composite material part to be obtained. Examples of usable silicon carbide threads may be threads marketed under the reference “Nicalon”, “Hi-Nicalon”, “Hi-Nicalon-S” or Tyranno SA3 from the company UBE Industries. The ceramic threads of the fibrous structure may have an oxygen content of less than or equal to 1% in atomic percentage. The “Hi-Nicalon-S” threads, for example, have such a characteristic. By “three-dimensional weaving” or “3D weaving”, it is meant a weaving method by which at least some of the warp threads bind weft threads over several weft layers. A reversal of roles between warp and weft is possible in the present text and must be considered as also covered by the claims.The fiber structure may, for example, have an interlock weave. By "interlock weave or fabric" is meant a 3D weave in which each layer of warp yarns binds together several layers of weft yarns with all the yarns in the same warp column having the same movement in the plane of the weave. It is also possible to start with fiber textures such as two-dimensional fabrics or unidirectional webs, and to obtain the fiber structure by draping such fiber textures over a form. These textures may optionally be bound together, for example, by sewing or implantation of yarns to form the fiber structure.

[0027] In a step S20, a chemical vapor infiltration weakening interphase 20 can be formed on the threads of the fibrous structure. The fibrous structure can be positioned in a shaping tool allowing it to be shaped to the part to be obtained during the deposition of the interphase. The thickness e20 of the interphase can for example be between 10 nm and 1000 nm, and for example between 200 nm and 500 nm. After formation of the interphase, the fibrous structure remains porous, the initial accessible porosity being filled only for a minor part by the interphase. The interphase can be single-layer or multi-layer.The interphase may comprise at least one layer of pyrolytic carbon (PyC), boron nitride (BN), silicon-doped boron nitride (BN(Si), with silicon in a mass proportion of between 5% and 40%, the remainder being boron nitride) or boron-doped carbon (BC, with boron in an atomic proportion of between 5% and 20%, the remainder being carbon). The interphase here has a function of weakening the composite material which promotes the deflection of any cracks reaching the interphase after having propagated in the matrix, preventing or delaying the breakage of fibers by such cracks. Alternatively, it will be noted that it is possible to form the interphase on the yarns before the formation of the fiber structure, i.e. before implementation of step S10.

[0028] A step S30 of forming a silicon carbide deposit is then carried out. This step S30 can be separated into two phases. During the first phase, the fibrous structure is still in the shaping tool and a silicon carbide consolidation layer 301 is deposited on the interphase 20 and the fibrous reinforcement 10. The consolidation layer 301 can be deposited in contact with the interphase 20. This layer has a sufficient thickness to sufficiently bond the fibers so that the structure retains its shape without assistance from the holding tool. This layer provides protection to the interphase against oxidation and can be formed by chemical vapor infiltration in a manner known per se, for example from a gas phase comprising methyltrichlorosilane (MTS) and hydrogen (H2). The thickness e30i of the consolidation layer 301 may be greater than or equal to 0.1 pm, for example between 0.1 pm and 5 pm.During the second phase, the consolidated and shaped fibrous structure of the part to be obtained can be removed from the tooling and the formation of the pre-densification matrix 35 can be initiated by depositing a first layer 302 thereof made of silicon carbide. The first layer 302 can be deposited in contact with the consolidation layer 301. The thickness e302 of the first layer 302 can be greater than the thickness e30i of the consolidation layer 301. This first layer of silicon carbide makes a large contribution to the mechanical performance of the composite material and provides protection against the molten silicon used during the subsequent infiltration. The thickness e302 of the first layer 302 can be greater than or equal to 1 μm, for example between 1 μm and 20 μm.As for the consolidation layer, the first layer of the pre-densification matrix can be formed by chemical vapor infiltration in a manner known per se. Generally, the pre-densification matrix can be formed by chemical vapor infiltration. According to a variant not illustrated, the layer 301 could be omitted and the first layer 302 of the pre-densification matrix could be formed directly on the interphase 20. The formation of the pre-densification matrix can be continued by forming the protective deposit on the first layer (step S40). As indicated above, this deposit makes it possible to protect the underlying silicon carbide from attack by the molten silicon. Different structures are possible for this deposit, as illustrated in Figures 2 and 3.

[0029] In the example of [Fig.2], the pre-densification matrix 35 comprises a single protective layer 40 formed by a binary BC or ternary Si-BC system. The protective layer 40 is here in contact with the first layer 302. In the example illustrated, the layer 40 defines an external surface Sext of the pre-densification matrix, that is to say that it forms the layer furthest from the fibrous reinforcement 10 during infiltration. Thus, during infiltration, no other layer is interposed between layer 40 and the infiltration composition in the example illustrated in [Fig.2]. In the example illustrated, the pre-densification matrix, covering the consolidation layer 301, comprises only the first layer 302 and the layer 40. The thickness e40 of the layer 40 may be greater than or equal to 0.1 pm, for example between 0.1 pm and 4 pm. Several compositions may be envisaged for the layer 40. The layer 40 may be made of boron carbide, with the possible presence of excess free carbon, or of boron-doped carbon with boron in an atomic proportion of between 5% and 20%. According to a variant, the layer 40 may be formed by a Si-BC ternary system having, in atomic percentage, a boron content of between 56% and 79%, a carbon content of between 17% and 39% and a silicon content of between 3% and 6%.These compositions are known per se in the field of CMCs and can be deposited by chemical vapor infiltration. The conditions for deposition of the materials capable of forming the protective layer are detailed in particular in WO 96 / 30317 and FR 2 668 477. In particular, a deposit of boron carbide, with possibly excess free carbon, can be obtained from a gas phase comprising boron trichloride (BC13) and a hydrocarbon such as methane (CH4). A deposit of a ternary Si-BC system can be obtained from a gas phase comprising a mixture of MTS, BC13 and H2. Generally, a temperature of between 850°C and 1000°C and a pressure of between 50 mbar and 150 mbar can be imposed during the deposition of the layer 40 by chemical vapor infiltration. The duration of the deposition of this layer is adjusted according to the desired thickness and is for example between 1 hour and 20 hours.

[0030] In the example of [Fig.3], the architecture is similar but includes a layer 42 of pyrocarbon which defines the external surface Sext of the predensification matrix 35a. The pyrocarbon forms in this example the layer of the predensification matrix furthest from the fiber reinforcement. The thickness e42 of the layer 42 may be greater than or equal to 0.1 μm, for example between 0.1 μm and 2 μm.

[0031] The residual porosity volume rate of the pre-densified fibrous structure obtained following step S40 may be greater than or equal to 20%, for example between 20% and 40%, for example between 30% and 35%.

[0032] The method continues by introducing a powdery composition into a residual porosity of the pre-densified structure (step S50). This powdery composition may be introduced into the fibrous structure by slurry-casting in a manner known per se. The powdery composition may comprise a silicon carbide powder and / or a carbon powder and / or a boron carbide powder. The volumetric rate of residual porosity of the pre-densified fibrous structure loaded with the powdery composition may be less than or equal to 25%, for example between 15% and 25%. If desired, the silicon carbide powder can be deoxidized before infiltration by applying a temperature greater than or equal to 1250°C for a period of at least 30 minutes under vacuum or a pressure less than or equal to 100 mbar of an inert gas.

[0033] Once the powdery composition has been introduced, step S60 is carried out during which the residual porosity is infiltrated with a molten infiltration composition comprising at least silicon so as to form a ceramic matrix in the porosity of the fibrous structure. The formation of this ceramic matrix can make it possible to finalize the densification of the part. This infiltration step corresponds to a molten infiltration step. The infiltration composition may consist of pure molten silicon or, alternatively, be in the form of a molten alloy of silicon and one or more other constituents. The infiltration composition may comprise predominantly silicon by mass, i.e. have a silicon content by mass greater than or equal to 50%. The infiltration composition may, for example, have a silicon content by mass greater than or equal to 75%.The constituent(s) present within the silicon alloy may be chosen from B, Al, Mo, Ti, Ge and mixtures thereof. When the powder composition comprises carbon particles, a chemical reaction may occur between the infiltration composition and these carbon particles during infiltration resulting in the formation of silicon carbide.

[0034] After step S60, a part made of CMC material is obtained. Such a part made of CMC material may be a static or rotating part of a turbomachine. Examples of turbomachine parts have been mentioned above. Such a part may further be coated with an environmental or thermal barrier coating before use.

[0035] The expression “between ... and ...” must be understood as including the limits.

Claims

Claims

1. A method of manufacturing a part made of ceramic matrix composite material, comprising: - infiltrating (S60) a pre-densified fibrous structure with a molten infiltration composition comprising silicon in order to form a ceramic matrix in a residual porosity of said pre-densified fibrous structure, said pre-densified fibrous structure comprising a pre-densification matrix (35; 35a) comprising a first layer (302) of silicon carbide and a second protective layer (40) covering the first layer and capable of protecting the latter from attack by the silicon of the infiltration composition, the second protective layer being formed by a Si-BC ternary system.

2. The method of claim 1, wherein the pre-densification matrix (35a) further comprises an additional protective layer (42) of pyrocarbon covering the second layer (40).

3. A method according to claim 1 or 2, wherein the infiltration composition comprises boron.

4. A method according to any one of claims 1 to 3, wherein the second protective layer (40) is formed by a Si-BC ternary system having, in atomic percentage, a boron content of between 56% and 79%, a carbon content of between 17% and 39% and a silicon content of between 3% and 6%.

5. Method according to any one of claims 1 to 4, in which the pre-densified fibrous structure comprises a fibrous reinforcement (10) partially densified by the pre-densification matrix (35; 35a), and in which the second protective layer (40), or the optional additional protective layer (42), forms the layer of the pre-densification matrix furthest from the fibrous reinforcement.

6. A method according to any one of claims 1 to 5, wherein a thickness (e40) of the second layer (40) is between 0.1 pm and 4 pm.

7. A method according to any one of claims 1 to 6, wherein the pre-densified fibrous structure further comprises a boron nitride interphase (20) between a fibrous reinforcement (10) and the pre-densification matrix (35; 35a).

8. A method according to any one of claims 1 to 7, wherein the

9. pre-densified fibrous structure comprises a fibrous reinforcement (10) formed by three-dimensional weaving or from a plurality of two-dimensional fibrous layers. A method according to any one of claims 1 to 8, wherein the part is a turbomachine part.

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