Fiber preform for producing a component made of a composite material with a ceramic matrix and method

Abstract

The invention relates to a fibrous preform (1) for producing a part (10) made of a ceramic matrix composite material, comprising: a fibrous reinforcement (2) comprising fibers (20) based on silicon carbide; an intermediate layer (3) extending around the surface of each of said silicon carbide-based fibers, preferably boron nitride-based; a pre-densified layer (4) comprising silicon carbide, located on the intermediate layer and having a columnar microstructure, said pre-densified layer having a thickness of between 3 [mu] m and 20 [mu] m; and a sacrificial layer (7) on the pre-densified layer, the sacrificial layer comprising silicon carbide having an average particle size of between 0.1 [mu] m and 0.5 [mu] m.

Description

Technical Field

[0001] The present invention relates to the general field of manufacturing components made of composite materials having a ceramic matrix, in particular based on silicon carbide. More specifically, the present invention relates to fiber preforms for producing components made of composite materials having a ceramic matrix. The present invention also relates to a method for manufacturing such fiber preforms and a method for manufacturing components made of composite materials having a ceramic matrix. Background Art

[0002] The prior art particularly includes the documents US-A1-2016 / 107940, US-A1-2014 / 363663, US-A1-2016 / 159702, US-B2-8039053 and EP-A1-3957619.

[0003] Ceramic matrix composites (CMCs) have good thermo-structural properties, namely high mechanical energy, making them suitable for structural components, and the ability to maintain these properties at high temperatures (especially up to 1200 °C and even higher) and in an oxidizing environment.

[0004] In the aviation field, for example, it is advantageous to use CMC materials instead of metallic materials in aircraft turbines. In fact, compared to metallic materials, these CMC materials are relatively light and are suitable for use at higher temperatures compared to metallic materials.

[0005] Generally, CMC materials are ceramic matrices in which ceramic fibers (or filaments) are embedded. CMC materials can be based on carbides, for example, silicon carbide (SiC) fibers or carbon (C) fibers reinforced with a silicon carbide matrix, or any other non-oxide ceramic fiber reinforcement reinforced with a non-oxide ceramic matrix.

[0006] A method for manufacturing CMC materials, in particular CMC materials reinforced with silicon carbide-based fibers, includes producing a fiber preform having a shape close to the shape of the component to be manufactured, and subsequently densifying the fiber preform with a matrix.

[0007] Figure 1 An example of a method for manufacturing a component made of a CMC material is shown. To achieve this, the method includes the following steps:

[0008] (a) Producing a fiber reinforcement 2, which includes silicon carbide fibers 20,

[0009] (b) Covering the fibers 20 of the fiber reinforcement with an intermediate layer 3,

[0010] (c) A so-called pre-densified silicon carbide layer 4 is formed on the intermediate layer 3 by chemical vapour infiltration (CVI) to form the fibre preform 1.

[0011] (e) Silicon carbide powder is incorporated into the pores of the fibre preform 1.

[0012] (f) The fibre preform 1 obtained in step (e) is densified by molten infiltration (MI) of the ceramic matrix 6, in particular with liquid silicon, to form a component made of CMC material.

[0013] Thus, the fibre preform 1 formed in step (c) comprises:

[0014] A fibre reinforcement 2, which comprises silicon carbide-based fibres 20.

[0015] An intermediate layer 3 surrounding the surface 22 of the fibres 20.

[0016] A pre-densified layer 4, which at least partially encapsulates the intermediate layer 3.

[0017] The intermediate layer 3 can be based on boron nitride (BN). The intermediate layer 3 covering the fibres 20 optimizes the bond between the fibres 20 and the matrix 6 of the component made of CMC material. In fact, this intermediate layer 3 provides sufficient bonding to ensure that the mechanical stresses to which the component made of CMC material is subjected are transmitted to the fibre reinforcement. Thus, the intermediate layer 3 deflects cracks generated within the matrix 6.

[0018] The silicon carbide in the pre-densified layer 4 has a microstructure consisting of grains, which grow along a preferred direction during CVI deposition to form a columnar microstructure of silicon carbide. In such a columnar microstructure, the maximum size of the grains is their radial size, i.e. the size extending between the fibres 20 and the outer surface of the pre-densified layer 4. The pre-densified layer 4 also protects the fibres 20 and the intermediate layer 3 by consolidating them into a predetermined shape by a first stage of densification.

[0019] The incorporation of the silicon carbide powder 5 limits the reactivity of the liquid silicon on the pre-densified layer 4 during step (f). The powder mixture 5 also enables the porosity of the fibre preform 1 to be fractionated to promote the capillary rise of the liquid silicon in the fibre preform 1 during step (f).

[0020] Finally, the melt infiltration technique provides a second stage of densification to fill the pores of the fibre preform 1. Step (f) allows densification and the formation of a component made of CMC material while also protecting the fibres 20 and the matrix 6.

[0021] Although the chemical interaction between the liquid silicon and the pre-densification layer 4 is limited (especially by steps (c) and (e)), the above method is not entirely satisfactory. Even in the presence of the silicon carbide powder 5, corrosion of the pre-densification layer by the liquid silicon can be randomly observed on the pre-densification layer. This corrosion is mainly observed at the grain boundaries of the pre-densification layer and propagates along the grain boundaries. Due to the columnar microstructure of the pre-densification layer and the preferential propagation along the grain boundaries, the corrosion can lead to the formation of cracks extending radially along the fibers, i.e., from the free surface of the pre-densification layer to the fibers of the fiber reinforcement. The presence of such cracks will adversely affect the mechanical properties and service life of the components made of CMC materials.

[0022] These cracks are indicated by arrows in Figure 2 They explain the deterioration of the pre-densification layer up to the depth of the intermediate layer. The liquid silicon can penetrate between the columns of the pre-densification layer. Therefore, depositing the pre-densification layer on the intermediate layer may have limited effectiveness in protecting the intermediate layer from the penetration of liquid or molten silicon.

[0023] Therefore, it is necessary to optimize the manufacturing of components of CMC materials by restricting the reactivity of liquid silicon relative to the silicon carbide deposited by CVI before adopting the MI densification operation. Summary of the Invention

[0024] In view of the above-mentioned drawbacks of the prior art, the present invention provides a simple, effective and economical solution.

[0025] To this end, the present invention relates to a fiber preform for producing a component made of a ceramic matrix composite material, the fiber preform comprising:

[0026] A fiber reinforcement comprising silicon carbide-based fibers,

[0027] An intermediate layer extending around the surface of each of the silicon carbide-based fibers, preferably, the intermediate layer is based on boron nitride,

[0028] A pre-densification layer comprising silicon carbide, located on the intermediate layer and having a columnar microstructure, the pre-densification layer having a thickness between 3 μm and 20 μm.

[0029] According to the present invention, the fiber preform further comprises a sacrificial layer located on the pre-densification layer, the sacrificial layer comprising silicon carbide having grains with an average size between 0.1 μm and 0.5 μm.

[0030] The fiber preform is an intermediate component for producing a component made of CMC material. Such a fiber preform can be said to be "pre-densified" because it has a first stage of densification. In fact, the fiber preform comprises a layer pre-densified by a pre-densification phase of silicon carbide deposited by CVI.

[0031] The main advantage of the fiber preform according to the invention is that it significantly enhances the protection of the pre-densification layer, the intermediate layer and the fiber reinforcement during the production of the fiber preform against the erosion by liquid silicon.

[0032] To this end, the fiber preform includes a silicon carbide sacrificial layer on the pre-densification layer, so that the sacrificial layer forming the outer surface of the fiber preform prevents the degradation of the pre-densification layer (as well as the intermediate layer and the fibers) by liquid silicon.

[0033] The term "sacrificial" means that a part (or region) of the sacrificial layer is non-functional and is thus configured to be degraded by liquid silicon first.

[0034] In particular, the silicon carbide grain size of the sacrificial layer is smaller than the size of the columnar microstructure of the pre-densification layer. Compared with the columnar microstructure of the pre-densification layer, this allows the formation of a fine-grained microstructure of the sacrificial layer. Therefore, the sacrificial layer is rich in carbon (compared with the pre-densification layer). In fact, the small grain size of the sacrificial layer enables an increase in the grain boundary surface in the sacrificial layer, where the carbon can react with liquid silicon, and thus the sacrificial layer protects the underlying layer (i.e., the pre-densification layer) from the liquid silicon reaction. In addition, the fine-grained microstructure of silicon carbide in the sacrificial layer creates tortuosity (i.e., a zigzag / meandering, labyrinthine path) to limit the penetration and propagation of liquid silicon to the layer below the sacrificial layer. Therefore, the fiber preform according to the invention has a very good resistance to the chemical reactivity of liquid silicon and improves the mechanical properties of the CMC material component made from the fiber preform.

[0035] The sacrificial layer and the pre-densification layer can be distinguished by the shape and / or average size of the silicon carbide grains. In fact, the pre-densification layer has a columnar microstructure (i.e., having a columnar shape, such as SiC grains that are substantially cylindrical or frustoconical), and the maximum size of each SiC grain is greater than or equal to 3 μm, while the grain size of the sacrificial layer is between 0.1 and 0.5 μm (i.e., SiC grains having a more or less spherical and / or fine or flat shape, and the maximum size of each SiC grain is less than or equal to 0.5 μm). As a result, the grain size of the sacrificial layer is smaller than the columnar grain size of the pre-densification layer.

[0036] The fiber preform may include one or more of the following features, either alone or in combination with each other:

[0037] The at least one sacrificial layer has a grain density that is 20 to 40 times greater than the grain density of the pre-densification layer;

[0038] The at least one sacrificial layer has a thickness between 1 μm and 4 μm;

[0039] A plurality of sacrificial layers are stacked on top of each other and extend over the pre-densification layer, and the number of these sacrificial layers is at most five;

[0040] The columnar microstructure of the pre-densification layer has cylindrical SiC grains, preferably having a height greater than or equal to 3 μm and / or a width between 0.2 μm and 1 μm;

[0041] The columnar microstructure of the pre-densification layer has SiC grains in a columnar form (such as cylindrical, truncated conical or trapezoidal, etc.), preferably having a height greater than or equal to 3 μm and / or a width between 0.2 μm and 1 μm;

[0042] The shape factor of the silicon carbide grains in the columnar microstructure of the pre-densification layer is strictly greater than the shape factor of the silicon carbide grains in the sacrificial layer;

[0043] The shape factor of the SiC grains in the pre-densification layer is greater than or equal to 10, preferably greater than or equal to 20;

[0044] The shape factor of the SiC grains in the sacrificial layer is less than or equal to 5, preferably less than or equal to 2;

[0045] The thickness of the pre-densification layer is between 10 μm and 20 μm;

[0046] The thickness of the sacrificial layer is 5% to 20% of the thickness of the pre-densification layer;

[0047] The thickness of the intermediate layer is 100 nm to 700 nm, preferably 250 nm to 500 nm;

[0048] The size of the SiC grains can be the grain diameter;

[0049] The thicknesses of the intermediate layer, the pre-densification layer and the sacrificial layer are measured by transmission electron microscopy or scanning electron microscopy;

[0050] The sizes of the SiC grains in the pre-densification layer and the sacrificial layer are measured by transmission electron microscopy;

[0051] The crystal orientation and general structure (or structural differences) of the SiC grains in the pre-densification layer and the sacrificial layer are determined by transmission electron microscopy or Raman spectroscopy;

[0052] The density of the SiC grains in the pre-densification layer and the sacrificial layer is measured by transmission electron microscopy TEM or Raman spectroscopy.

[0053] The shape factor of the silicon carbide grains is the ratio of its maximum size to its minimum size.

[0054] The present invention also relates to a ceramic matrix composite component, which comprises a fiber preform according to any one of the foregoing claims and a densified ceramic matrix, and the ceramic matrix is preferably based on silicon carbide.

[0055] The component made of CMC material can be a component of a turbine, especially a component of an aircraft. For example, the turbine component is a turbine or a blade of a compressor of the turbine, an annular wall of a combustion chamber of the turbine, etc.

[0056] The present invention also relates to a method for manufacturing a fiber preform according to one of the features of the present invention. The fiber preform is used to manufacture a ceramic matrix composite component according to the present invention. The method includes the following steps:

[0057] (a) Obtaining a fiber reinforcement including silicon carbide-based fibers,

[0058] (b) Forming an intermediate layer on each surface of the silicon carbide-based fibers,

[0059] (c) Forming a pre-densification layer on the intermediate layer by chemical vapor infiltration (CVI) to obtain the fiber preform, and

[0060] (d) Depositing at least one silicon carbide-based sacrificial layer on the pre-densification layer obtained in step (c) by chemical vapor infiltration (CVI).

[0061] As described above, the sacrificial layer encapsulating the pre-densification layer of the fiber preform prevents the deterioration of the pre-densification layer by liquid silicon. To achieve this, one or more parameters of the CVI silicon carbide deposition can be changed from the columnar microstructure of the silicon carbide grains in the pre-densification layer to the crystalline microstructure of the silicon carbide grains in the sacrificial layer. In particular, by changing at least one parameter among the duration of the CVI deposition, the volume ratio of methyltrichlorosilane (MTS) and hydrogen (H2) in the gas mixture, the pressure, the temperature, the number of cycles, and the duration of each cycle, the shape, size, and / or density of the SiC grains are changed. The aim is to generate an excess of carbon in the sacrificial layer compared to the carbon level in the pre-densification layer. Therefore, the method for obtaining the fiber preform of the present invention enables the above object to be achieved by changing the parameters of the existing CVI deposition step in the method for manufacturing a CMC material component.

[0062] At the end of steps (c) and (d), the fiber preform can be called "pre-densified" because the first-stage densification or pre-densification is achieved by the silicon carbide deposited by CVI.

[0063] The method for manufacturing a fiber preform may include one or more of the following features, either alone or in combination with each other:

[0064] The chemical vapor infiltration of step (c) is carried out for a first time of 10 hours to 30 hours at a first pressure between 70 mbar and 150 mbar with a first gas mixture containing methyltrichlorosilane (MTS) and hydrogen (H2), wherein the volume ratio of hydrogen to methyltrichlorosilane is 5 to 15 (i.e., correspondingly, the volume proportion of H2 is 83% to 94%, and the volume proportion of MTS is 17% to 6%), and

[0065] The chemical vapor infiltration of step (d) is carried out for a second duration of 30 minutes to 3 hours at a second pressure equal to the first pressure with a second gas mixture containing methyltrichlorosilane (MTS) and hydrogen (H2);

[0066] Step (c) comprises a single cycle;

[0067] Step (d) comprises at least two consecutive cycles, preferably 2 to 10 cycles, each cycle having a duration of 3 minutes to 18 minutes;

[0068] In step (d), the second gas mixture comprises a higher proportion of methyltrichlorosilane (MTS) than hydrogen (H2), preferably the volume ratio of methyltrichlorosilane (MTS or CH3Cl3Si) and hydrogen (H2) is 70 / 30 to 85 / 15 by volume, and wherein the first predetermined pressure and the second predetermined pressure are the same;

[0069] The method comprises: step (e), incorporating a mixture of ceramic powder, preferably silicon carbide, into the fiber preform obtained in step (d).

[0070] The present invention also relates to a method for manufacturing a component made of a composite material having a ceramic matrix according to the present invention. The method comprises steps (a) to (e) of the method for manufacturing the above-mentioned fiber preform, and step (f), which is to densify the fiber preform obtained in step (e) by infiltrating a molten ceramic matrix to form the component made of the composite material having a ceramic matrix.

[0071] Preferably, the ceramic matrix is based on liquid silicon.

[0072] At the end of step (f), the fiber preform can be said to be "densified" by the ceramic matrix because the secondary densification of silicon is achieved by MI infiltration. Description of the Drawings

[0073] The present invention will be better understood by the following description, which is by way of non-limiting examples and with reference to the drawings, and other details, features and advantages of the present invention will become more apparent, wherein:

[0074] Figure 1Schematically shows a method for manufacturing CMC materials according to the prior art,

[0075] Figure 2 shows the reactivity of liquid silicon on the pre-densified layer of silicon carbide of the CMC material obtained by the Figure 1 method shown,

[0076] Figure 3 is a partial schematic view of a pre-densified fiber preform according to the present invention,

[0077] Figure 4 is Figure 3 an enlarged view of

[0078] Figure 5 shows the reactivity of liquid silicon on the sacrificial layer of the Figure 3 pre-densified fiber preform,

[0079] Figure 6 shows a schematic block diagram of the steps in a method for manufacturing a CMC material component according to the present invention.

[0080] Elements having the same function in different embodiments have the same reference numerals in the figures. Detailed Description

[0081] Figure 1 and Figure 2 have been described in the background art of the present invention and show a fiber preform for manufacturing a component made of a ceramic matrix composite (CMC), in particular a ceramic matrix composite (CMC) reinforced with silicon carbide (SiC), and its manufacturing method according to the prior art.

[0082] Figure 3 and Figure 4 show a fiber preform 1 for producing a component 10 made of CMC material.

[0083] The fiber preform 1 according to the present invention comprises:

[0084] a fiber reinforcement 2,

[0085] at least one intermediate layer 3,

[0086] at least one pre-densified layer 4, and

[0087] at least one sacrificial layer 7.

[0088] The fiber reinforcement 2 may comprise ceramic fibers 20. For example, the fibers 20 may mainly comprise silicon carbide (hereinafter referred to as SiC) or non-oxide ceramic fibers. SiC fibers sold under the trade name "Hi-Nicalon S" may be used. Alternatively, carbon fibers may be used.

[0089] The fiber reinforcement 2 can be in the form of a unidirectional (1D) texture, such as a thread or a roving, or a bidirectional (2D) texture, such as a unidirectional or multi-directional fabric or mesh, or even a three-dimensional (3D) texture, such as felt, fabric or knitted fabric; or even a 3D texture formed by winding or covering a 1D or 2D texture. Preferably, the fiber reinforcement has a deformable structure. The intermediate layer 3 extends around the surface 22 of each fiber 20. In other words, the intermediate layer 3 wraps each fiber 20 of the fiber reinforcement. As previously mentioned, this intermediate layer optimizes the bond between the fiber 20 and the matrix 6 of the component made of CMC material and deflects the cracks (which can be generated within the matrix 6) that will propagate towards the fiber 20.

[0090] Preferably, the intermediate layer 3 is based on boron nitride (BN). Boron nitride has good oxidation resistance and can be easily implemented.

[0091] Advantageously, the thickness of the intermediate layer 3 is from 100 nm to 700 nm, preferably from 250 nm to 500 nm.

[0092] The pre-densification layer 4 extends over the intermediate layer 3. The intermediate layer is interposed between the fiber 20 and the pre-densification layer 4. The pre-densification layer 4 can be made of a ceramic, such as SiC, especially when the fiber 20 is made of SiC or carbon.

[0093] The pre-densification layer 4 has a columnar microstructure particularly composed of SiC grains.

[0094] In the usual sense in the field of crystallography, a columnar microstructure is a microstructure in which the grains have an elongated columnar shape (such as a cylindrical shape or any other non-cylindrical shape, such as a truncated conical shape or a trapezoidal shape), that is, one direction is greater than the other two directions. In the present application, the maximum grain direction of the columnar microstructure extends in the radial direction from the fiber 20 towards the pre-densification layer 4.

[0095] Such a columnar microstructure can be the result of the CVI method, which will be described below, and in particular the result of the grains growing along a preferred crystallographic direction.

[0096] To ensure that the microstructure can be columnar, it is preferred that the pre-densification layer 4 has a thickness of 3 μm or more.

[0097] Thus, the columnar (e.g., cylindrical) SiC grains in the pre-densification layer 4 can have a height (in the radial direction) of greater than or equal to 3 μm. The width of these cylindrical SiC grains can be between 0.2 μm and 1 μm.

[0098] In the present application, a "columnar" shape can be defined as an elongated shape that extends mainly in one direction. The columnar shape can have two opposite bases, which can be parallel or non-parallel to each other, and each base has a circular, elliptical, prismatic, and / or other cross-sectional shape. The columnar shape can have a constant or variable cross-section between its two bases. For example, a tubular shape can be cylindrical (especially a straight cylinder), frustoconical, trapezoidal, prismatic, etc.

[0099] A "cylindrical" shape can be a straight cylinder with two opposite bases that are parallel to each other, and each base has a circular, elliptical, prismatic, or other cross-sectional shape. The straight cylinder can have a constant cross-section between its two bases. For example, a straight cylinder is a rotating cylinder with a constant diameter between its two bases.

[0100] Advantageously, the thickness of the pre-densification layer 4 is from 3 μm to 20 μm. This numerical range allows for obtaining a pre-densification layer with a columnar microstructure. Preferably, the thickness of the pre-densification layer is from 10 μm to 20 μm.

[0101] The sacrificial layer 7 is located on the pre-densification layer 4 and preferably in direct contact therewith. The sacrificial layer 7 can be made of a ceramic, such as SiC, especially when the pre-densification layer 4 is made of SiC.

[0102] The sacrificial layer 7 comprising SiC has grains with an average size of from 0.1 μm to 0.5 μm.

[0103] The sacrificial layer 7 has a (SiC) grain density greater than that of the pre-densification layer 4. For example, the grain density of the sacrificial layer 7 is 20 to 40 times greater than that of the pre-densification layer 4. In particular, compared with the columnar microstructure of the pre-densification layer 4, this allows for obtaining a fine-grained microstructure of the sacrificial layer 7.

[0104] Furthermore, compared with the columnar SiC grains 42 in the pre-densification layer 4, the density of the SiC grains in the sacrificial layer 7 is greater than that of the SiC grains in the pre-densification layer 4, enabling the formation of microstructured SiC grains 70 in the sacrificial layer 7, as Figure 4 schematically shown. Thus, the sacrificial layer 7 has a larger fine grain boundary surface area than the pre-densification layer, such that liquid silicon preferentially reacts with the sacrificial layer 7 and thus protects the pre-densification layer 4 from erosion by liquid silicon.

[0105] The thickness of the sacrificial layer 7 can be 5% to 20% of the thickness of the pre-densification layer 4;

[0106] Advantageously, the thickness of the sacrificial layer 7 is from 1 μm to 4 μm. Preferably, the thickness of the sacrificial layer is from 1 μm to 2 μm. This allows enhancing the fine-grained bonding surface such that the liquid silicon reacts with the carbon in the sacrificial layer 7.

[0107] For example, the thickness of each layer of the fiber preform 1, such as the intermediate layer 3, the pre-densification layer 4, and the sacrificial layer 7, can be measured by TEM or scanning electron microscopy. The grain size, particularly the grain size of the sacrificial layer 7 and the pre-densification layer 4, can be measured by transmission electron microscopy. The density of the grains, particularly the density of the sacrificial layer 7 and the pre-densification layer 4, can also be measured by transmission electron microscopy or Raman spectroscopy. The crystal orientation and general structure (or structural differences) of the SiC grains in the pre-densification layer 4 and the sacrificial layer 7 can be determined by transmission electron microscopy or Raman spectroscopy.

[0108] The columnar microstructure of the pre-densification layer 4 can have columnar silicon carbide grains with a first shape factor (e.g., generally cylindrical or frustoconical). The first shape factor of the SiC grains can be greater than or equal to 10. Preferably, the first shape factor can be greater than or equal to 20.

[0109] The SiC grains in the sacrificial layer 7 can have a second shape factor. The second shape factor of the SiC grains can be less than or equal to 5. Preferably, the second shape factor can be less than or equal to 2.

[0110] The first shape factor of the SiC grains is greater than the second shape factor of the SiC grains.

[0111] As previously described, the shape factor of the SiC grains is defined as the ratio of its maximum dimension to its minimum dimension. In the case of a columnar microstructure with rotationally cylindrical SiC grains, the maximum dimension of the SiC grains corresponds to the height of the cylinder, and its minimum dimension corresponds to its diameter. In the present application, the first shape factor and the second shape factor of the SiC grains can represent the average shape factor of the SiC grains that respectively constitute the pre-densification layer 4 and the sacrificial layer 7.

[0112] The fiber preform 1 can include a plurality of sacrificial layers 7 that are stacked on top of each other and extend over the pre-densification layer 4. The number of sacrificial layers 7 can be up to five. This increases the surface area of the sacrificial layer and further prevents the erosion of the pre-densification layer by the liquid silicon. In Figure 3 and Figure 4 the illustrated embodiment, a single sacrificial layer 7 covers the pre-densification layer 4.

[0113] Figure 5 An embodiment of the fiber preform 1 according to the present invention is shown, in which it can be seen that the sacrificial layer 7 has been deteriorated while the pre-densification layer 4 (as well as the intermediate layer 3 and the fiber 20) remains intact. The etching of this sacrificial layer 7 by the liquid silicon is in Figure 5is indicated by the arrow. Different from the cracks in the prior art ( Figure 2 ), since Figure 5 it is shown that there is no crack propagation in the pre-densified layer 4, it can be concluded that during the method of manufacturing a component from CMC material, the sacrificial layer 7 protects the pre-densified layer 4 from the erosion of liquid silicon.

[0114] The present invention also relates to a component 10 made of CMC material, which comprises the fiber preform 1 and the densified ceramic matrix 6 described above with reference to Figures 3 to 5 .

[0115] The component 10 can be a component of a turbine, in particular a component of an aircraft. For example, the turbine component is a turbine or compressor blade of a turbine, an annular wall of a combustion chamber of a turbine, etc.

[0116] Advantageously, the matrix 6 is based on silicon carbide, especially when the fibers 20 are made of SiC or carbon.

[0117] With reference to Figure 6 , the present application will now describe embodiments of the method for manufacturing the fiber preform 1 and for manufacturing the CMC material component 10.

[0118] The method for manufacturing the fiber preform 1 comprises the following steps:

[0119] (a) obtaining a fiber reinforcement 2, which comprises SiC-based fibers 20,

[0120] (b) forming an intermediate layer 3 on each surface 22 of the SiC-based fibers 20,

[0121] (c) forming a SiC-based pre-densified layer 4 on the intermediate layer 3 by chemical vapor infiltration (CVI), and

[0122] (d) depositing at least one SiC-based sacrificial layer 7 on the pre-densified layer 4 of step (c) by chemical vapor infiltration (CVI) to obtain, in particular, a partially pre-densified fiber preform 1.

[0123] The fiber reinforcement 2 in step (a) can have a shape approaching the shape of the component to be manufactured. As described above, the fiber reinforcement 2 can be obtained by multi-layer or 3D weaving from wires or rovings. It is also possible to start from a 2D texture, such as a fabric or a sheet of wires or rovings, to form layers, which will then cover the shaped object and may be connected together, for example, by stitching or implanting wires.

[0124] For example, the intermediate layer 3 can also be deposited by chemical vapor infiltration (CVI).

[0125] The CVI deposition technique is well known. For example, reference can be made to document FR-A1-2742433.

[0126] The CVI deposition in step (c) can be carried out using a first gas mixture containing methyltrichlorosilane (MTS) and hydrogen (H2) as reactants. The volume ratio of hydrogen to methyltrichlorosilane can be between 5 and 15. In other words, the volume fraction of H2 can be between 83% and 94%, and the volume fraction of MTS can be between 17% and 6%. In particular, this allows for the formation of SiC columnar (or in other words, substantially cylindrical or frustoconical) grains in the pre-densification layer 4.

[0127] For the CVI deposition of the pre-densification layer 4, at least one of the following parameters can be selected from:

[0128] The number of deposition cycles is equal to 1,

[0129] The first pressure of the first gas mixture is between 70 mbar and 150 mbar,

[0130] The first temperature of the first gas mixture is between 900 °C and 1100 °C, and

[0131] The initial time is between 10 and 30 hours.

[0132] The CVI deposit in step (d) can be produced by a second gas mixture containing methyltrichlorosilane (MTS) and hydrogen (H2). The volume fraction of H2 can be between 15% and 30%, and the volume fraction of MTS can be between 85% and 70%. In particular, this allows for the formation of microstructured SiC grains (or in other words, generally granular or spherical) in the sacrificial layer 7.

[0133] For the CVI deposition of one or more sacrificial layers 7, at least one of the following parameters can be selected from:

[0134] The number of deposition cycles is from 1 to 10,

[0135] The second pressure is between 70 mbar and 150 mbar,

[0136] The second temperature is between 900 °C and 1100 °C, and

[0137] The second duration is between 30 minutes and 3 hours.

[0138] Advantageously, the first parameter that can be used to distinguish the formation of the pre-densification layer 4 and the sacrificial layer 7 is the volume ratio of the reactants MTS and H2. As described above, the volume ratio of H2 can be between 83% and 94%, and the volume ratio of MTS can be between 17% and 6% to form the pre-densification layer 4, and the volume ratio of H2 can be between 15% and 30%, and the volume ratio of MTS can be between 85% and 70% to form the sacrificial layer 7.

[0139] When the volume ratio of MTS to H2 is the same and the temperature, flow rate, and pressure conditions are the same, the second parameter that can distinguish the formation of the pre-densification layer 4 and the sacrificial layer 7 is related to the environmental conditions during the regrowth of SiC grains. Local supersaturation promotes the germination of SiC grains during the CVI deposition process. For example, this local supersaturation is observed after the deposition cycle is interrupted. Therefore, the length of the CVI deposition cycle affects the structure of the deposit. A short cycle is favorable for the formation of SiC grains (and thus for the formation of the sacrificial layer 7), while a long cycle is favorable for the formation of columnar SiC grains (and thus for the formation of the pre-densification layer 4).

[0140] In the first embodiment, the CVI deposition in step (d) is carried out in a conventional mode. To achieve this, the CVI deposition can be carried out by actively stopping the supply of the reactive gas stream (i.e., MTS) and then re-supplying the reactive gas, for example, for a period between 30 minutes and 3 hours.

[0141] The second gas mixture includes a higher proportion of methyltrichlorosilane than hydrogen. Preferably, the ratio of methyltrichlorosilane to hydrogen is 70 / 30 to 85 / 15 by volume. In particular, this ratio allows obtaining the aforementioned SiC grain size and / or density of the sacrificial layer 7. Advantageously, these ratios allow an excess of carbon to be produced in the sacrificial layer.

[0142] The first pressure and the second pressure can be the same.

[0143] According to the second embodiment, the CVI deposition in step (d) is carried out in a pulsed mode. The pulsed mode can be achieved by multiple stops and returns of the reactant gas within a predetermined time interval (e.g., 30 minutes to 3 hours) to produce the sacrificial layer. In particular, this pulsed mode increases the concentration of the SiC fine grain microstructure in the sacrificial layer 7. In addition, the pulsed mode allows precise control of the microstructure of the formed sacrificial layer deposit. For this purpose, and in a non-limiting manner, the fiber reinforcement 1 is placed in a housing (not shown in the figure) where the above temperature and pressure conditions are established. A certain volume of the reactant gas phase for depositing the sacrificial layer 7 enters the housing and remains therein for the above time, and then the gaseous substances are discharged from the housing and a new certain volume of the gas phase is introduced. The cycle including introducing the gas phase into the housing, retaining the gas phase in the housing, and discharging the gaseous substances from the housing is repeated the required number of times to achieve the desired sacrificial layer deposition thickness.

[0144] Step (d), in particular the second duration of this step (d), may include at least two consecutive cycles, preferably 2 to 10 cycles. Each cycle can last from 3 to 18 minutes. Then, the second duration of step (d) corresponds to the cumulative duration of the various cycles of chemically vapor infiltrating the second gas mixture.

[0145] The methyltrichlorosilane content of the second gas mixture may be from 70% to 85% by volume, and the hydrogen content may be from 15% to 30% by volume. The methyltrichlorosilane content of the first gas mixture may be from 6% to 17% by volume, and the hydrogen content may be from 94% to 83% by volume.

[0146] The first pressure and the second pressure may be the same.

[0147] Reference Figure 6 , the method may include a step (e) of incorporating the powder 5 into the fiber preform 1 obtained in step (d). Preferably, the powder 5 may be silicon carbide SiC powder.

[0148] The partially densified and porous fiber preform 1 from step (d) or step (e) may be further densified by an MI-type process. To this end, the step (f) of consolidating the fiber preform 1 may be carried out by impregnating the consolidated fiber preform 1 with a liquid or molten ceramic matrix 6 to form a component made of CMC material 10. Preferably, the matrix 6 is silicon carbide-based.

Claims

1. A fiber preform (1) for producing a component (10) made of a ceramic matrix composite material, the fiber preform (1) comprising: A fiber reinforcement (2), the fiber reinforcement comprising fibers (20) based on silicon carbide (SiC), An intermediate layer (3), the intermediate layer extending around the surface of each of the silicon carbide-based fibers, preferably, the intermediate layer (3) is based on boron nitride (BN), A pre-densification layer (4), the pre-densification layer comprising silicon carbide (SiC), located on the intermediate layer (3) and having a columnar microstructure, the pre-densification layer (4) having a thickness between 3 μm and 20 μm, The fiber preform (1) is characterized in that it further comprises a sacrificial layer (7) located on the pre-densification layer (4), the sacrificial layer (7) comprising silicon carbide having particles with an average size between 0.1 μm and 0.5 μm.

2. The fiber preform according to claim 1, characterized in that, The at least one sacrificial layer (7) has a grain density 20 to 40 times greater than that of the pre-densification layer (4).

3. The fiber preform according to claim 1 or 2, characterized in that, The at least one sacrificial layer (7) has a thickness between 1 μm and 4 μm.

4. The fiber preform according to any one of the preceding claims, characterized in that, A plurality of sacrificial layers (7) are stacked on top of each other and extend over the pre-densification layer (4), and the number of these sacrificial layers (7) is at most five.

5. The fiber preform according to any one of the preceding claims, characterized in that, The columnar microstructure of the pre-densification layer (4) has columnar-shaped silicon carbide grains, and the silicon carbide grains preferably have a height greater than or equal to 3 μm and / or a width between 0.2 μm and 1 μm.

6. The fiber preform according to any one of the preceding claims, characterized in that, The columnar microstructure of the pre-densification layer (4) has silicon carbide grains having a shape factor strictly greater than that of the silicon carbide grains of the sacrificial layer (7).

7. The fiber preform according to claim 6, wherein The shape factor of the silicon carbide grains of the pre-densification layer (4) is greater than or equal to 10, and the shape factor of the silicon carbide of the sacrificial layer (7) is less than or equal to 5.

8. The fiber preform according to any one of the preceding claims, characterized in that, The thickness of the sacrificial layer (7) is 5% to 20% of the thickness of the pre-densification layer (4).

9. A ceramic matrix composite component, comprising the fiber preform (1) according to any one of the preceding claims and a densified ceramic matrix (6), the ceramic matrix (6) being preferably based on silicon carbide (SiC).

10. A method for manufacturing the fiber preform (1) according to any one of claims 1 to 8, the fiber preform (1) being intended to produce the component (10) made of a ceramic matrix composite material according to claim 9, the method comprising the following steps: (a) Obtaining a fiber reinforcement (2) comprising fibers (20) based on silicon carbide; (b) Forming an intermediate layer (3) on each surface (22) of the silicon carbide-based fibers (20); (c) Forming a pre-densification layer (4) on the intermediate layer (3) by chemical vapor infiltration (CVI); and (d) Depositing at least one silicon carbide-based sacrificial layer (7) on the pre-densification layer (4) obtained in step (c) by chemical vapor infiltration (CVI) to obtain the fiber preform (1).

11. The method according to claim 10, wherein, The chemical vapor infiltration in step (c) is carried out at a first pressure of 70 mbar to 150 mbar for a first duration of 10 hours to 30 hours with a first gas mixture containing methyltrichlorosilane (MTS) and hydrogen (H2), wherein the volume ratio of hydrogen to methyltrichlorosilane is 5 to 15; the chemical vapor infiltration in step (d) is carried out at a second pressure equal to the first pressure for a second duration of 30 minutes to 3 hours with a second gas mixture containing methyltrichlorosilane (MTS) and hydrogen (H2).

12. The method according to claim 11, wherein In step (d), the second gas mixture comprises a higher proportion of methyltrichlorosilane (MTS) than hydrogen (H2). Preferably, the ratio of methyltrichlorosilane (CH3Cl3Si) to hydrogen (H2) is 70 / 30 to 85 / 15 by volume, and wherein the first predetermined pressure and the second predetermined pressure are the same.

13. The method according to claim 11 or 12, characterized in that, Step (d) includes at least two consecutive cycles, preferably 2 to 10 cycles, each cycle having a duration of 3 minutes to 18 minutes.

14. The method according to any one of claims 10 to 13, characterized in that, The method includes: step (e), incorporating a mixture of ceramic powder (4), preferably silicon carbide, into the fiber preform (1) obtained in step (d).

15. A method for manufacturing a component (10) made of a ceramic matrix composite according to claim 9, characterized in that the method includes steps (a) to (e) of the method for manufacturing a fiber preform (1) according to any one of claims 10 to 14, and step (f), wherein step (f) is to densify the fiber preform (1) obtained in step (e) by infiltrating a molten ceramic matrix (6), preferably a silicon-based ceramic matrix, to form the component (10) having a composite material with a ceramic matrix.

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