METHOD FOR PRODUCE A PART FROM A COMPOSITE MATRIX WITH A CERAMIC MATRIX

Description

Technical Field

[0001] The invention relates to the manufacture of a ceramic matrix composite (CMC) component in which the ceramic matrix is ​​formed by infiltration of a molten silicon-based composition (MI). The invention incorporates a functionalized powder composition to protect the pre-densified silicon carbide from attack by the molten silicon. The resulting composite component can be used as a hot section component in turbomachinery, particularly in aeronautical turbomachinery, such as a turbine component. Previous technique

[0002] Ceramic matrix composite materials (CMCs) can withstand temperatures ranging from 600°C to 1400°C. Thanks to their superior high-temperature resistance, CMCs require less cooling. Since this cooling is traditionally drawn from the compressor, impacting turbomachine efficiency, CMCs improve engine efficiency, thereby reducing fuel consumption. Furthermore, their use helps optimize turbomachine performance, notably by reducing the overall mass of the turbomachine, which further contributes to lower fuel consumption and thus significantly reduces pollutant emissions.

[0003] CMC parts can be formed by melt infiltration. In this technique, a molten silicon composition is introduced into the porosity of a fibrous structure pre-densified by a silicon carbide deposit and loaded with silicon carbide particles. This method yields a fully dense, high-modulus Si-SiC matrix and a high linearity limit composite.

[0004] The thesis "DEVELOPMENT OF FLUIDIZED BED CVD TECHNOLOGY FOR COATING CERAMIC POWDERS WITH PYROCARBON" by Amine El Mansouri, defended on February 26, 2021, describes the coating of SiC particles with a PyC layer deposited by fluidized bed CVD and discloses their use in forming ceramic matrices for composite materials. It also mentions a "hybrid route" combining liquid and gaseous processes, i.e., "slurry cast / MI" and CVD. This document also mentions aerospace applications.

[0005] US 2004 / 191411 A1 describes the fabrication of composites for turbomachinery parts and discloses the infiltration of a consolidated SiC fiber preform with a C-coated SiC particle slurry before infiltration with molten Si. The core-shell structure is obtained via a liquid process, not by fluidized bed CVI.

[0006] The resulting composites exhibit good mechanical properties, but the inventors observed some variability in elongation at break, which reduces the material's damage tolerance range. It is desirable to propose a solution to address this drawback. Description of the invention

[0007] 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 comprising a powder composition by a molten infiltration composition comprising silicon in order to form a ceramic matrix in a residual porosity of the pre-densified fibrous structure, the pre-densified fibrous structure comprising a pre-densification matrix comprising silicon carbide and the powder composition comprising core-shell particles comprising a silicon carbide core and a shell comprising at least one boron-doped carbon layer with boron in an atomic proportion between 5% and 20%.

[0008] The inventors observed that the variability in fracture behavior was linked to uncontrolled attack on the silicon carbide of the pre-densification matrix by the silicon molten in the prior art solution. This phenomenon can lead to the degradation of the fibrous reinforcement and the interphase, resulting in a reduction of the composite's structural integrity. The invention addresses this drawback by functionalizing the powder composition using core-shell particles, as described above, which reduce the attack on the silicon carbide of the pre-densification matrix. The powder composition is homogeneously distributed throughout the pre-densified fibrous structure to provide protection across its entire volume and along the entire penetration path. This results in composite materials with significantly improved fracture behavior.

[0009] In one embodiment example, the process further includes the manufacture of core-shell particles, prior to infiltration, by forming the shell around the core by chemical vapor deposition in a fluidized bed.

[0010] The shell formation conditions implemented during chemical vapor deposition advantageously allow for the deoxidation of the silicon carbide core surface through reduction without significant crystallite size growth. This leads to improved wetting by the molten silicon without promoting the attack of the pre-densified silicon carbide. Following the consumption of the shell carbon, capillary rise will not be hindered by poor wettability, due to the prior deoxidation of the silicon carbide cores.

[0011] According to the invention, the bark of the particles comprises a boron-doped carbon layer with boron in an atomic proportion of between 5% and 20%.

[0012] This characteristic allows for even greater protection of the underlying silicon carbide and provides protection throughout the volume of the pre-densified structure and throughout the infiltration, further improving the fracture behavior of the resulting composite material.

[0013] In particular, the particle shell may comprise a first layer of boron-doped carbon containing boron in an atomic proportion of between 5% and 20%, and a second carbon layer that may cover the first layer. However, this does not depart from the scope of the invention when the shell is a single layer of boron-doped carbon containing boron in an atomic proportion of between 5% and 20%.

[0014] In one embodiment example, the infiltration composition includes boron.

[0015] This characteristic offers an advantage in further protecting the underlying silicon carbide.

[0016] In one embodiment, the particle shell has a thickness between 5 nm and 300 nm, for example between 100 nm and 150 nm. This characteristic allows for a good compromise between effective protection of the pre-densified silicon carbide during infiltration, without compromising particle size so as not to affect their ability to penetrate the porosity of the fibrous structure.

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

[0018] The presence of a boron nitride interphase advantageously allows for the deflection of cracks that may appear in the matrix of the composite part during operation, thus preserving the fibrous reinforcement.

[0019] In one embodiment, the fibrous structure includes a fibrous reinforcement formed by three-dimensional weaving or from a plurality of two-dimensional fibrous layers.

[0020] In one example of implementation, the part is a turbomachine component.

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

[0022] [ Fig. 1 ] There figure 1 is a flowchart showing a sequence of steps in an example of a process according to the invention. Fig. 2 ] There figure 2 represents, schematically and partially, a core-shell particle usable within the framework of the invention. Fig. 3 ] There figure 3 provides images obtained by transmission electron microscopy of particles before and after bark formation. Fig. 4 ] There figure 4 represents, schematically and partially, a variant of core-shell particle usable within the framework of the invention. Description of the implementation methods

[0023] An example of a manufacturing process for a part made of CMC material according to the invention will now be described in relation to the flowchart of the figure 1 .

[0024] A first step, S10, of the process may consist of forming the fibrous structure by implementing one or more textile operations, such as three-dimensional weaving. The fibrous structure may be formed from ceramic yarns, for example, silicon carbide yarns. The fibrous structure can constitute the fibrous reinforcement of the composite part to be obtained. Examples of usable silicon carbide yarns include "Nicalon," "Hi-Nicalon," "Hi-Nicalon-S," or Tyranno SA3 yarns from UBE Industries. The ceramic yarns of the fibrous structure may have an oxygen content of 1% or less as an atomic percentage. "Hi-Nicalon-S" yarns, for example, exhibit this characteristic. "Three-dimensional weaving" or "3D weaving" refers to a weaving method in which at least some of the warp yarns interlace weft yarns across multiple weft layers.A reversal of roles between warp and weft is possible in this text and should be considered as also covered by the claims. The fibrous structure may, for example, exhibit an interlock weave. By "interlock weave or fabric," we mean a 3D weave in which each layer of warp yarns connects several layers of weft yarns, with all yarns in the same warp column having the same movement within the plane of the weave. It is also possible to start with fibrous textures such as two-dimensional fabrics or unidirectional sheets and obtain the fibrous structure by draping such fibrous textures over a form. These textures may optionally be joined together, for example, by stitching or yarn implantation, to form the fibrous structure.

[0025] In an S20 step, a chemical vapor infiltration (CVI) interphase can be formed on the fibers of the fibrous structure. The fibrous structure can be positioned in a shaping tool to conform it to the shape of the desired part during the interphase deposition. The interphase thickness can range, for example, from 10 nm to 1000 nm, or from 200 nm to 500 nm. After interphase formation, the fibrous structure remains porous, with only a small portion of the initial accessible porosity being filled by the interphase. The interphase can be single-layered or multi-layered.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 5% to 40%, the remainder being boron nitride), or boron-doped carbon (BC, with boron in an atomic proportion of 5% to 20%, the remainder being carbon). The interphase here serves to weaken the composite material by deflecting any cracks that may reach the interphase after propagating through the matrix, thus preventing or delaying fiber breakage due to such cracks. Alternatively, it should be noted that the interphase can be formed on the fibers before the formation of the fibrous structure, i.e., before the implementation of step S10.

[0026] Next, a silicon carbide deposit formation step (S30) is performed. This step can be divided into two phases. In the first phase, the fibrous structure remains in the forming tooling, and a silicon carbide consolidation layer is deposited over the interphase and the fibrous reinforcement. The consolidation layer can be deposited in contact with the interphase. This layer has sufficient thickness to bind the fibers adequately so that the structure retains its shape without support from the holding tooling. This layer provides protection to the interphase against oxidation and can be formed by chemical vapor infiltration in a known manner, for example, from a gaseous phase comprising methyltrichlorosilane (MTS) and hydrogen (H₂). The thickness of the consolidation layer can be greater than or equal to 0.1 µm, for example, between 0.1 µm and 5 µm.During the second phase, the consolidated and shaped fibrous structure of the desired part can be removed from the tooling, and the pre-densification matrix can be formed by depositing a layer of silicon carbide. This layer can be deposited in contact with the consolidation layer. Its thickness can be greater than that of the consolidation layer. This silicon carbide layer significantly improves the mechanical performance of the composite material and provides protection against the molten silicon used during subsequent infiltration. The thickness of this layer can be greater than or equal to 1 µm, for example, between 1 µm and 20 µm. As with the consolidation layer, the pre-densification matrix layer can be formed by chemical vapor infiltration using a method known per se.According to an unillustrated variant, the consolidation layer could be omitted and the pre-densification matrix could be formed directly on the interphase.

[0027] Le taux volumique The residual porosity of the pre-densified fibrous structure obtained following step S30 can be between 20% and 40%, for example between 30% and 35%.

[0028] The process continues by introducing a powder composition into a residual porosity of the pre-densified structure (step S40). This powder composition can be introduced into the fibrous structure by slurry-casting in a manner known per se. The powder composition is notable in that it comprises core-shell particles 1, which will now be described. Particle 1 comprises a silicon carbide core 3 and a shell formed by a layer 5, distinct from the core 3, which surrounds it. The shell 5 is made of boron-doped carbon with boron in an atomic proportion between 5% and 20%. The shell 5 defines an external surface Sext of particle 1. The shell 5 is a single layer. In the illustrated example, the shell 5 extends from the surface Sext to the core 3. The bark 5 completely encloses the core 3. The particle 1 can have a size less than or equal to 5 µm, for example less than or equal to 1 µm.The size d of the core 3 of the particles 1 can be between 0.5 µm and 4 µm. The thickness e of the shell 5 can be between 5 nm and 300 nm, for example between 100 nm and 150 nm. The particle 1 can have a granular shape, for example a substantially spherical or ellipsoidal shape. The . figure 2 This illustrates the case of a bi-material particle 1 where the particle 1 consists essentially of a silicon carbide core 3 and a boron-doped carbon region 5 in contact with the core 3. As mentioned above, the particle 1 can be obtained by forming the shell 5 on the core 3 through fluidized bed chemical vapor deposition. The inventors have implemented the operating conditions described below to manufacture such particles 1, which are provided as examples.

[0029] A 250-gram charge of silicon carbide powder was fluidized at 400 mbar with a nitrogen flow rate of 1000 standard cubic centimeters per minute (sccm). The fluidized bed was heated to 1000°C and then exposed to a propane flow rate of 200 standard cubic centimeters per minute for 5 hours. High-resolution TEM analyses (see figure 3 ) show that the powder grains are initially coated with a thin, nanometric, amorphous layer, presumably silica. After the treatment described above, the SiC grains are individually coated with a thin layer of sp2 carbon. The carbon is in direct contact with the SiC surface, and the amorphous layer has disappeared.

[0030] The volumetric residual porosity rate of the pre-densified fibrous structure loaded by the powder composition can be less than or equal to 25%, for example between 15% and 25%.

[0031] There figure 2 illustrates a particle 11 with a single-layered shell 5, but alternatively, a particle with a two-layered shell can be used, comprising, for example, a first layer 51 of boron-doped carbon surrounding the core 3 and a second layer 52 of carbon surrounding the first layer, as illustrated in the figure 4 .

[0032] Once the powder composition is introduced, step S50 is carried out, during which the residual porosity is infiltrated with a molten infiltration composition containing at least silicon, in order to form a ceramic matrix within the porosity of the fibrous structure. The formation of this ceramic matrix can finalize the densification of the part. This infiltration step corresponds to a molten infiltration step. The infiltration composition can 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 can be predominantly silicon by mass, i.e., have a silicon content greater than or equal to 50% by mass. For example, the infiltration composition can have a silicon content greater than or equal to 75% by mass.The constituent(s) present in the silicon alloy can be chosen from B, Al, Mo, Ti, Ge, and mixtures thereof. When the powder composition includes carbon particles in addition to the core-shell particles, a chemical reaction can occur between the infiltration composition and these carbon particles during infiltration, resulting in the formation of silicon carbide. A reaction also occurs with the carbon in the shell.

[0033] After step S50, a part made of CMC material is obtained. Such a CMC part can be a static or rotating turbomachine component. Examples of turbomachine components were mentioned earlier. This part can also be coated with an environmental or thermal barrier coating before use.

[0034] The expression "between ... and ..." should be understood as including the boundaries.

Claims

1. A process for manufacturing a ceramic matrix composite part, comprising: - infiltrating (S50) a pre-densified fibrous structure comprising a powder composition with a molten infiltration composition comprising silicon, in order to form a ceramic matrix in a residual porosity of the pre-densified fibrous structure, the pre-densified fibrous structure comprising a pre-densification matrix comprising silicon carbide, and the powder composition comprising core-shell particles (1; 11) having a silicon carbide core (3) and a shell having at least one layer (5; 51; 52) of boron-doped carbon containing boron at an atomic proportion of between 5% and 20%.

2. The process according to claim 1, wherein the process further comprises the manufacturing of core-shell particles (1), before the infiltration, by forming the shell around the core (3) by fluidised bed chemical vapour deposition.

3. The process according to claim 1 or 2, wherein the shell of the particles comprises a first layer (51) made of boron-doped carbon containing boron at an atomic proportion of between 5% and 20%, and a second layer (52) made of carbon covering the first layer.

4. The process according to any one of claims 1 to 3, wherein the infiltration composition comprises boron.

5. The process according to any one of claims 1 to 4, wherein the pre-densified fibrous structure further comprises an interphase of boron nitride between a fibrous reinforcement and the pre-densification matrix.

6. The process according to any one of claims 1 to 5, wherein the fibrous structure comprises a fibrous reinforcement formed by three-dimensional weaving or from a plurality of two-dimensional fibrous strata.

7. The process according to any one of claims 1 to 6, wherein the part is a turbomachine part.