Infiltration of a fibrous structure comprising a liquid silicon reactive layer.

Abstract

INFILTRATION OF A FIBROUS STRUCTURE COMPRISING A LIQUID SILICON REACTIVE LAYER. The invention relates to a method for manufacturing a part made of a ceramic matrix composite material, comprising: - infiltrating a pre-densified fibrous structure (10) 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 (13), a reactive layer (14) comprising a reactive material comprising carbon and capable of reacting with the silicon of the infiltration composition, the reactive layer covering the first layer, and a molten silicon wetting layer of silicon carbide or carbon (15) covering the reactive layer. Figure for abstract: Fig. 1

Description

Title of the invention: Infiltration of a fibrous structure comprising a liquid silicon reactive layer. 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 in the molten state ("Melt-Infiltration"; "MI") of a silicon-based composition. The part made of composite material thus obtained can find an application as a hot 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 formed 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 zone of the material. It is desirable to propose a solution to address this drawback. Statement of the invention

[0004] The invention aims precisely to meet this need.

[0005] To this end, it proposes a method for manufacturing a part made of ceramic matrix composite material, comprising:

[0006] - the infiltration of a pre-densified fibrous structure by a composition molten infiltration 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, a reactive layer comprising a reactive material comprising carbon and capable of reacting with the silicon of the infiltration composition, the reactive layer covering the first layer, and a molten silicon wetting layer of silicon carbide or carbon, covering the reactive layer.

[0007] In the application, the expression "wetting" must be understood in the usual sense of physical wetting between a surface and a liquid, the surface here being the surface of the wetting layer and the liquid the infiltration composition. Wetting can be measured by the contact angle as it is usually defined, that is to say by the tangent to the liquid at the air / liquid / surface interface point. The wetting is all the better the smaller the contact angle.

[0008] A layer will be said to be “wetting” if the contact angle is less than 50°.

[0009] For example, the contact angle for quantifying wetting can be measured using a fixed drop method, a hanging drop method using a goniometer, the Wilhelmy method or even capillary rise.

[0010] In the method of the invention, the particular composition of the layers of the pre-densification matrix makes it possible to solve the technical problem.

[0011] In fact, the liquid silicon first reacts with the molten silicon wetting layer which it passes through to reach the reactive layer.

[0012] Once the reactive layer is reached, the liquid silicon reacts preferentially with this layer, and therefore does not penetrate into the first layer of silicon carbide.

[0013] From the reactive layer, the flow of molten silicon is diverted so as to be diverted away from the first layer and the underlying fibers, thereby protecting the material.

[0014] Deflecting the progression of the silicon ensures that the liquid silicon from the infiltration does not damage the pre-densified fibrous structures as it might do to prior art fibrous structures. This results in composite material parts with less variable properties from one part to another.

[0015] In one embodiment, the reactive material may be selected from pyrocarbon or boron-doped carbon.

[0016] These materials are preferred for the invention because they are easily deposited by chemical vapor infiltration processes. They therefore represent good alternatives to reactive materials if the remainder of the pre-densification of the fibrous structure is carried out by chemical vapor infiltration.

[0017] In one embodiment, the molten silicon wetting layer has a thickness greater than or equal to 0.2 μm, for example between 0.2 μm and 10.0 μm, or even between 1.0 μm and 10.0 μm.

[0018] In one embodiment, the fused silicon wetting layer has a columnar microstructure.

[0019] This embodiment can be obtained when the pre-densification of the fibrous structure is carried out by chemical vapor infiltration.

[0020] The columnar microstructure is then oriented with the grain boundaries along a direction transverse to a surface of the fibers. The columnar microstructure makes it possible to limit the liquid silicon reaching the reactive material due to the need for infiltration between the columns and therefore to offer good protection even with a thin layer of reactive material.

[0021] The reactive layer then allows the reorientation of the direction of the attack of the molten silicon, and prevents it from continuing its propagation towards the fibers.

[0022] In one embodiment, the thickness of the reactive layer may be less than or equal to 1000 nm.

[0023] Having the smallest possible reactive layer ensures that the reactive layer does not affect the mechanical properties of the fiber structure.

[0024] In one embodiment, the thickness of the reactive layer may be greater than or equal to 20 nm.

[0025] Having a sufficiently thick reactive layer ensures that the latter is not crossed by the liquid silicon during impregnation.

[0026] In one embodiment, the thickness of the reactive layer is between 20 nm and 1000 nm, or even between 200 nm and 500 nm.

[0027] Such a thickness of the reactive layer represents an optimum between the two effects described above.

[0028] In one embodiment, the ratio between the thickness of the molten silicon wetting layer and the thickness of the first silicon carbide layer is between 40 / 60 and 10 / 90.

[0029] This ratio fixes the positioning of the reactive layer within the predensification matrix.

[0030] A ratio between the values ​​proposed above ensures a sufficient thickness of the first layer of silicon carbide so that the pre-densified fibrous structure has the expected properties. The ratio also ensures that the reactive layer is sufficiently far from the external surface of the pre-densification matrix (surface furthest from the fibers) so that the molten silicon wetting layer prevents the liquid silicon from directly reacting with the reactive layer, which is not desirable.

[0031] The invention has just been described with a single reactive layer.

[0032] In other embodiments, the pre-densification matrix may comprise above the fused silicon wetting layer between one and eight structures additional protective structures, each additional structure comprising an additional reactive layer comprising a reactive material comprising carbon and capable of reacting with the silicon of the infiltration composition and an additional molten silicon wetting layer covering the additional reactive layer.

[0033] In the case where several additional protection structures are present, they can be placed in succession and in contact with each other.

[0034] This results in an alternation of reactive layers and wetting layers with molten silicon, which ensures that even in the case where the silicon crosses a reactive layer, it will be diverted to the next reactive layer.

[0035] Furthermore, an alternating structure in which there is more than one reactive layer allows the fibrous structure to better accommodate the heat generated by the chemical reaction between the silicon and one of the reactive layers.

[0036] Indeed, the reaction between the silicon and the reactive layer can then take place on several reactive layers rather than on just one, which ensures better distribution of the heat produced, thus avoiding hot spots which can harm the integrity of the fibrous structure.

[0037] In one embodiment, the pre-densified fibrous structure further comprises a boron nitride interphase between a fibrous reinforcement and the pre-densification matrix.

[0038] The presence of a boron nitride interphase advantageously makes it possible to deflect cracks that may appear in the matrix of the composite part during operation so as to preserve the fiber reinforcement.

[0039] In one embodiment, the pre-densified fibrous structure comprises a fibrous reinforcement formed by three-dimensional weaving or from a plurality of two-dimensional fibrous layers.

[0040] The particular choice of the weaving structure makes it possible to give the pre-densified fibrous structure and consequently the part obtained particular mechanical properties.

[0041] In particular, such structures are particularly suitable for parts used in the aeronautical field.

[0042] In one embodiment, the part may be a turbomachine part. Brief description of the drawings

[0043] [Fig.l] [Fig.l] schematically represents a pre-densified structure useful for the invention.

[0044] [Fig.2] [Fig.2] schematically represents the behavior of molten silicon on a pre-densified structure when carrying out the method of the invention. Description of the embodiments

[0045] The invention is now described by means of figures, present for descriptive purposes to illustrate certain embodiments of the invention and which should not be interpreted as limiting the latter.

[0046] Furthermore, the figures are represented with non-realistic scales which allow easy understanding, and which should not be interpreted as the real scales between the different elements.

[0047] [Fig.l] represents a pre-densified fibrous structure useful for carrying out a method of the invention.

[0048] Such a pre-densified structure 10 may comprise a fibrous reinforcement 11, a boron nitride interphase 12, a first layer of silicon carbide 13, a reactive layer of a material comprising carbon 14 and a molten silicon wetting layer 15.

[0049] [Fig.l] is a projection in a plane perpendicular to the direction in which the greatest direction of a fibrous reinforcement 11 of the structure 10 extends.

[0050] [Fig.l] further represents the thickness el of the molten silicon wetting layer 15, the thickness e2 of the reactive layer 14 and the thickness e3 of the first silicon carbide layer 13.

[0051] In one embodiment, the pre-densified fibrous structure does not comprise any elements other than the fibrous reinforcement 11 and the layers 12, 13, 14 and 15 which have just been described.

[0052] In one embodiment, the interphase layer 12 is in contact with the fibrous reinforcement 11, and in contact with the first layer of silicon carbide 13.

[0053] In one embodiment, the first silicon carbide layer is in contact with the boron nitride interphase layer 12, and in contact with the reactive layer 14.

[0054] In one embodiment, the reactive layer 14 is in contact with the first layer of silicon carbide 13, and in contact with the molten silicon wetting layer 15.

[0055] In one embodiment, the molten silicon wetting layer 15 is in contact with the reactive layer 14.

[0056] The fibrous structure may be formed by carrying out one or more textile operations such as three-dimensional weaving. The fibrous structure may be formed from ceramic yarns, for example silicon carbide yarns.

[0057] In one embodiment, the fibrous reinforcements 11 of the pre-densified fibrous structure 10 may be formed from ceramic threads, for example silicon carbide threads. The fibrous structure may constitute the fibrous reinforcement of the composite material part to be obtained. Examples of usable silicon carbide threads may be threads marketed under the reference “Nicalon”, “Hi-Nicalon” or “Hi-Nicalon-S”. The ceramic threads of the fibrous structure may have a content in oxygen less than or equal to 1% in atomic percentage. “Hi-Nicalon-S” wires, for example, have such a characteristic.

[0058] By "three-dimensional weaving" or "3D weaving" 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 fibrous structure may for example have an interlock weave. By "interlock weave or fabric" is meant a 3D weave weave in which each layer of warp threads binds several layers of weft threads with all the threads of the same warp column having the same movement in the plane of the weave. It is also possible to start from fibrous textures such as two-dimensional fabrics or unidirectional sheets, and to obtain the fibrous structure by draping such fibrous textures over a form.These textures can possibly be linked together, for example by sewing or implantation of threads to form the fibrous structure.

[0059] In one embodiment, the interphase layer 12 may be formed by chemical vapor infiltration on the fiber reinforcements 11 of the fiber structure. The fiber structure may 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 of the interphase may for example be between 10 nm and 1000 nm, and for example between 10 nm and 100 nm. After formation of the interphase, the fiber structure remains porous, the initial accessible porosity being filled only for a minor part by the interphase. The interphase may 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 threads before the formation of the fibrous structure.

[0060] In one embodiment, the pre-densification of the fibrous structure may be carried out by a chemical vapor infiltration process.

[0061] For example, the first silicon carbide layer 13 may be formed from a gas phase comprising methyltrichlorosilane (MTS) and hydrogen (H2).

[0062] In one embodiment, the thickness e3 of the first layer of silicon carbide 13 may be between 0.2 μm and 10 μm.

[0063] For example, the first layer of silicon carbide 13 can be obtained in two successive phases of chemical vapor infiltration.

[0064] For example, during a first phase, the fibrous structure is still positioned in the shaping tool and a first part of the first layer of silicon carbide 13, called the consolidation layer, is deposited on the interphase 12 and the fibrous reinforcement 10. This consolidation layer can be deposited in contact with the interphase 12. 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). For example, the thickness of the consolidation layer can be greater than or equal to 0.1 μm, for example between 0.1 μm and 5.0 μm.

[0065] During the second phase, the consolidated fibrous structure shaped into the part to be obtained can be removed from the tool and the formation of the pre-densification matrix can resume by depositing a second part of the first layer of silicon carbide 13 on the consolidation layer.

[0066] 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 subsequent infiltration.

[0067] In one embodiment, and according to the variant illustrated in [Fig.l], the consolidation layer may not be the subject of a particular deposition, and the first layer of silicon carbide 13 of the predensification matrix could be directly formed on the interphase 12.

[0068] The formation of the first layer of silicon carbide 13 can be followed by a deposition of a reactive layer 14.

[0069] The reactive layer 14 can be deposited by chemical vapor infiltration.

[0070] The chemical vapor infiltration can be carried out in the same reactor as the chemical vapor infiltration allowing the first layer of silicon carbide 13 to be obtained.

[0071] This makes it possible in particular to reduce the number of operations for moving the fibrous reinforcement to be impregnated.

[0072] For example, the first layer of silicon carbide 13 may be deposited by a chemical vapor infiltration process. For example, a reactor is fed with silicon carbide precursors, the reactor being maintained at a temperature between 950°C and 1080°C and at a pressure between 10 and 40 mbar.

[0073] To move from a silicon carbide deposit 13 to a reactive layer deposit 14, the supply of silicon carbide precursors is cut off, and precursors of the reactive layer are then introduced, possibly after purging the reactor.

[0074] The pressure and temperature of the reactor may or may not be changed.

[0075] For example, the reactive layer 14 may be formed from pyrocarbon.

[0076] This embodiment makes it possible to avoid the use of boron in the process, except possibly for the interphase layer 12, which simplifies the chemical vapor infiltration process.

[0077] The reactive layer can be obtained from gaseous precursors chosen from hydrocarbons, in particular methane, propane or a mixture of these two elements.

[0078] In one embodiment, the reactive layer may be doped with boron.

[0079] The boron which dopes the reactive layer makes it possible to form SiBx elements allowing to protect the underlying silicon carbide.

[0080] To dope a reactive layer 14 with boron as indicated above, it is possible to use a BC13 precursor.

[0081] The reactive layer 14 deposited by a chemical vapor infiltration process makes it possible to obtain a uniform layer on the fiber reinforcements 11.

[0082] The thickness e2 of the reactive layer can be between 20 pm and 1000 pm.

[0083] As shown in [Fig. 1], the reactive layer 14 may be covered with a molten silicon wetting layer 15.

[0084] For example, the molten silicon wetting layer 15 may be deposited by chemical vapor infiltration, for example under the same conditions as the first silicon carbide layer 13.

[0085] In one embodiment, to move from a deposition of a reactive layer 14 to a deposition of the molten silicon wetting layer 15, the supply of reactive layer precursors is cut off, then silicon carbide precursors are introduced into the reactor, possibly after purging the reactor.

[0086] The pressure and temperature of the reactor may or may not be changed.

[0087] This makes it possible to simply move from a deposition of the reactive layer 14 to a deposition of the molten silicon wetting layer 15.

[0088] The thickness el of the molten silicon wetting layer 15 may be between 0.2 μm and 10 μm.

[0089] [Fig.2] illustrates the interest of the reactive layer during the infiltration of a fibrous structure.

[0090] Identical reference numerals indicate identical elements between [Fig.l] and 2.

[0091] [Fig.2] shows the infiltration of liquid silicon 21 into the molten silicon wetting layer 15.

[0092] The infiltration 21 is shown in [Fig. 2] in a very schematic manner. However, it should be seen that the silicon has a progression in the molten silicon wetting layer 15 aligned with the direction transverse to the fibers. In addition, the attack of the liquid silicon can take place in several places on the external surface of the fiber 10 as shown in [Fig. 2].

[0093] The molten silicon wetting layer 15, due to its columnar structure, nevertheless limits the access of the liquid silicon 21 to the reactive layer 14.

[0094] The liquid silicon 22 which has nevertheless passed through the molten silicon wetting layer 15 and which reaches the reactive layer 14 then changes direction of progression by reacting with the reactive layer 14.

[0095] The reactive layer 14 hinders the progression of the liquid silicon towards the fibrous reinforcement 11 and ensures that the first layer of silicon carbide 13, and especially the interphase 12 and the fibrous reinforcement 11 are protected from the liquid silicon 21, 22.

Claims

Claims

1. A method of manufacturing a part made of ceramic matrix composite material, comprising: - infiltrating a pre-densified fibrous structure (10) 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 (13), a reactive layer (14) comprising a reactive material comprising carbon and capable of reacting with the silicon of the infiltration composition, the reactive layer covering the first layer, and a molten silicon wetting layer of silicon carbide (15) covering the reactive layer, wherein the pre-densified fibrous structure (10) comprises a fibrous reinforcement (11) formed by three-dimensional weaving,the pre-densification matrix comprising above the molten silicon wetting layer between one and eight additional protective structures, each additional structure comprising an additional reactive layer comprising a reactive material comprising carbon and capable of reacting with the silicon of the infiltration composition and an additional molten silicon wetting layer of silicon carbide covering the additional reactive layer.,

2. The method of claim 1, wherein the reactive material is selected from pyrocarbon or boron-doped carbon.

3. The method of claim 1 or 2, wherein the molten silicon wetting layer (15) has a thickness of between 0.2 pm and 10.0 pm.

4. The method of claim 3, wherein the molten silicon wetting layer (15) has a columnar microstructure.

5. Method according to any one of claims 1 to 4, wherein the thickness (e2) of the reactive layer (14) is less than or equal to 1000 nm.

6. A method according to any one of claims 1 to 5, wherein the ratio of the thickness (el) of the silicon wetting layer 11 melted (15) and the thickness (e3) of the first layer of silicon carbide (13) is between 40 / 60 and 10 / 90.

7. A method according to any one of claims 1 to 6, wherein the pre-densified fibrous structure further comprises a boron nitride interphase (12) between a fibrous reinforcement (11) and the pre-densification matrix (13, 14, 15).

8. A method according to any one of claims 1 to 7, wherein the part is a turbomachine part.

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