Discontinuous-fiber ceramic matrix composite material

Abstract

The invention relates to a method for manufacturing a part made of composite material, the method comprising at least the following steps: - a step (E1) of preparing a feedstock comprising ceramic material fibers and a binder; - a step (E2) of preparing a preform having the shape of the part to be obtained by additive manufacturing of the prepared feedstock; - a step (E3) of consolidating debinding of the preform; - a step (E4) of forming an interphase by chemical vapor infiltration of the debindered preform; then - a step (E7) of forming a ceramic matrix in the porosity of the preform.

Description

Description Title of the invention: Staple fiber composite material and ceramic matrix Technical Field

[0001] The invention relates to the field of composite materials and more specifically to the manufacturing processes of such materials. Previous technique

[0002] Ceramic matrix composite (CMC) materials can withstand maximum temperatures ranging from 600°C to 1400°C.

[0003] Due to their superior resistance to high temperatures, CMC materials require less cooling. Since this cooling is traditionally drawn from the compressor, impacting turbomachine efficiency, CMC materials improve engine efficiency, thereby reducing fuel consumption.

[0004] Furthermore, their use helps to optimize the performance of turbomachines, particularly by reducing the overall mass of the turbomachine, which further contributes to a decrease in fuel consumption and therefore to a significant reduction in polluting emissions.

[0005] These advantages explain the industrial interest in developing such ceramic matrix composite materials.

[0006] A composite material is understood to be a material that comprises fibers bonded by a matrix.

[0007] The properties of composite materials are influenced by many factors, including the nature of the fibers and the nature of the matrix.

[0008] In particular, the nature of the fibers includes both their chemical composition, the length of the fibers, and whether or not they are woven together.

[0009] Since the properties depend on many factors, many composite materials have been developed with properties particularly suited for specific applications.

[0010] Usually, for aeronautical applications, woven fibrous armors are proposed, in particular by three-dimensional weaving, the armor then being infiltrated by the matrix.

[0011] However, the use of such a three-dimensional weave implies a loss of fibers of around 50%, due in particular to the complexity of the weaving and shaping stages.

[0012] Furthermore, when the part includes a fibrous preform, the process requires a consolidation step before infiltration. This step is very costly in terms of time and resources. Graphite conformers are indeed very expensive yet fragile parts that also require a high number of manual operations, which negatively impacts the process time.

[0013] Therefore, it has been proposed to manufacture the preforms not by weaving but by so-called "staple fiber" processes. In these processes, the fibers are mixed with a binder allowing them to be shaped directly into the form of the part to be obtained.

[0014] Unfortunately, it has been observed that current processes using such discontinuous fibers do not give complete satisfaction, at least for the following reasons.

[0015] Firstly, the fibers have very particular shape factors which makes the fluidization step necessary for a uniform application of an interphase on the fibers delicate.

[0016] The application of the fluidized bed interphase limits the maximum permissible fiber size and ultimately the thermomechanical behavior of the resulting part.

[0017] On the other hand, the preparation of the load before shaping requires mixing the fibers with a polymeric binder which can damage the interphase present around the fibers which is essential to give the fibers sufficient strength.

[0018] It is therefore necessary to propose processes free from the two disadvantages listed above in order to consider using parts made of composite material, whose preform is made of discontinuous fibers, meeting the quality requirements of the aeronautical field. Description of the invention

[0019] The invention aims precisely to propose such a method of manufacturing a part in composite material using a filler of discontinuous fibers and nevertheless allowing to achieve parts of a quality similar to that achieved by the processes of the prior art.

[0020] Accordingly, the invention relates, in one of its aspects, to a method for manufacturing a part made of composite material comprising at least the following steps: - a preparation step for a load comprising ceramic material fibers and a binder; - a step of preparing a preform having the shape of the part to be obtained by additive manufacturing of the prepared load; - a consolidating debinding step of the preform, consisting of leaving a carbon skeleton in the preform after debinding, allowing the preform to become self-supporting; - a step of forming an interphase by a chemical vapor-phase infiltration operation of the debound preform; then - a step of forming a ceramic matrix in the porosity of the preform.

[0021] It is to the credit of the inventors that they determined that such a process made it possible to obtain a part made of composite material with thermomechanical properties close to those obtained for parts whose preform is woven, but whose process of obtaining it is simplified, in particular since it does not include a weaving step or a shaping step.

[0022] Consolidating debinding is a particular debinding method which allows a carbon skeleton to remain in the preform after debinding, enabling the preform to become self-supporting.

[0023] A preform is said to be "self-supporting" when it has taken the shape of the part to be obtained and is no longer subject to variations in shape due to its own weight.

[0024] Without wanting to be bound by theory, the inventors are of the opinion that consolidating debinding makes it possible to create a residual carbon layer which gives the whole preform sufficient properties for it to be self-supporting, that is to say that it can be manipulated while retaining the shape acquired in the preform preparation stage.

[0025] Consolidating unbinding is enabled by the method chosen for unbinding, the nature of the binder and the temperature applied during unbinding.

[0026] In one embodiment, the consolidating unbinding can be carried out by thermal unbinding, by unbinding with a solvent, by capillary unbinding or by unbinding with supercritical fluids.

[0027] To ensure that the debinding is consolidating, the inventors determined that it was advantageous to use debinding carried out on a powder bed.

[0028] The preform is coated with a bed of powder, for example a porous ceramic powder, which allows the binder to be extracted when the preform is heated.

[0029] In addition, the presence of the powder bed can also play a role since it ensures that the preform retains its shape during debinding.

[0030] In one embodiment, the consolidating debinding can be carried out by a powder bed debinding step performed jointly with a heat treatment step carried out at a temperature between 450°C and 800°C, and preferably between 450°C and 650°C.

[0031] In one embodiment, the consolidating unbinding can also be carried out under a neutral atmosphere, for example under an atmosphere of nitrogen or argon.

[0032] In an embodiment where the consolidating debinding is carried out by a powder bed debinding step, the process includes a powder bed removal step after debinding and preferably before any subsequent step.

[0033] In one embodiment, the ceramic material fibers can be silicon carbide fibers.

[0034] In one embodiment, the binder can be chosen from polyesters, polyamides, elastomers, polyethylenes.

[0035] The described process eliminates the need for the consolidation step required by prior art methods. This avoids a time-consuming and materially expensive, yet essential, step in prior art processes.

[0036] In one embodiment, the preform obtained after consolidating debinding comprises a residual carbon content greater than or equal to 0.5% by mass, for example between 0.5% by mass and 2.0% by mass.

[0037] In one embodiment, the preform obtained after consolidating debinding comprises a porosity rate of between 50% by volume and 65% by volume, or even between 55% by volume and 65% by volume.

[0038] The "porosity ratio" characterizes the void volume within a fibrous preform. It is defined as the void volume in a unit elementary volume divided by that elementary volume.

[0039] In one embodiment, the preform obtained after debinding comprises an average pore size of between 10 and 20 pm, or even between 13 and 17 pm.

[0040] Pore ​​size and / or pore volume can be determined by mercury intrusion porosimetry.

[0041] In one embodiment, the additive manufacturing process used to prepare the preform into the shape of the part to be obtained can be chosen from among fused filament fabrication (FFF), fused granulate fabrication (FGF), and automated fiber deposition (AFP). automatic fiber placement), binder jetting and other indirect additive manufacturing methods including polymer mold additive manufacturing such as gel casting, polymer mold injection, and ceramic injection molding (CIM).

[0042] In a preferred embodiment, the additive manufacturing process used for the preparation of the preform is the deposition of molten granules.

[0043] The inventors are indeed of the opinion that this process makes it possible to obtain a preform in the shape of the part to be obtained, while guaranteeing a porosity rate after debinding which is excellent for the needs of the process and the mechanical properties of the part finally obtained.

[0044] In one embodiment, the preform obtained at the end of the additive manufacturing step may comprise a binder volume percentage between 40% and 70%, preferably between 50% and 65%.

[0045] In one embodiment, the preform obtained at the end of the additive manufacturing step may comprise a fiber volume percentage of between 30% and 60%, preferably between 35% and 45%.

[0046] The "fiber volume percentage" characterizes the volume of the preform actually occupied by the fibers. This can be determined by a simple measurement of the density of the preform compared to the density of the preform's constituent elements.

[0047] Without wishing to be bound by theory, the inventors are of the opinion that these characteristics for the preform ensure that the preform is in conditions optimal for the deposition of the interphase and then the formation of the ceramic matrix in the porosity of the preform.

[0048] The fiber content has two opposing effects. The higher the fiber content, the easier it is to control the part's dimensions after debinding. However, the higher the fiber content, the more difficult it is to extrude the raw material because the mixture's viscosity increases. Furthermore, with a high fiber content, there is a significant risk that the interphase deposition will cause bridging between the fibers, which can hinder the formation of the ceramic matrix within the preform's porosity because the pore size is then greatly reduced.

[0049] Thus, the proposed volumetric loading rate represents an excellent optimum between these two effects, namely that it allows for a porosity level and pore size that permit the formation of the ceramic matrix within the preform's porosity. Furthermore, it ensures that the loading is compatible, in terms of viscosity, with known additive manufacturing methods.

[0050] In one embodiment, the length of the ceramic material fibers introduced into the loading can be between 150 pm and 1000 pm, or even between 500 pm and 1000 pm.

[0051] This fiber length is found in the preform obtained at the end of the additive manufacturing step.

[0052] It is advantageous that a process described here allows the use of longer fibers than those accessible to prior art processes, which is permitted by the process as a whole.

[0053] Indeed, the proposed process differs from prior art processes in that the interphase deposition is carried out after the shaping of the preform, and not before the preparation of the loading as is proposed in prior art processes.

[0054] The ability to use longer fibers ensures a finer choice of the mechanical properties of the part that the process makes possible compared to a process that only allows the use of shorter fibers.

[0055] In one embodiment, the loading enabling the manufacture of the fibrous preform includes a binder volume percentage between 40% and 70%, preferably between 50% and 65%.

[0056] In one embodiment, the loading enabling the manufacture of the fibrous preform comprises a volume fraction of fibers between 30% and 60%, preferably between 35% and 45%.

[0057] In one embodiment, the loading enabling the manufacture of the fibrous preform comprises a mass content of between 5% and 10% of a powder of silicon carbide particles SiC.

[0058] The addition of SiC powder prevents shrinkage during debinding. This allows for better control of the accuracy and reproducibility of the finished part's dimensions, as well as the fiber content after binder removal.

[0059] Furthermore, a maximum rate of 10% must not be exceeded. Indeed, if the powders are introduced into the fibrous reinforcement to limit shrinkage and control the volumetric fiber content after debinding, an excess may impair infiltration during the chemical vapor phase infiltration stage, leading to discontinuities in the coating and the appearance of uncoated areas.

[0060] In one embodiment, such a particle powder can have a median particle size distribution in number, called D50, between 0.5 pm and 10 pm or even between 2.0 and 7.0 pm.

[0061] The presence of this particle powder ensures a more determined geometric evolution of the preform during the different stages of the process.

[0062] In addition, the presence of the powder ensures a certain spacing of the fibers in the loading which makes fiber bridging even more unlikely, which will ultimately help to facilitate a uniform deposition of the interphase around the fiber.

[0063] In a process described here, the interphase formation step is carried out by chemical vapor-phase infiltration.

[0064] In one embodiment, such a step can be carried out by introducing a reactive gaseous phase into the chamber of a furnace, under temperature and pressure conditions permitting the chemical decomposition of said reactive phase.

[0065] In one embodiment, the interphase can be a boron nitride BN interphase.

[0066] For example, the interphase can be in boron nitride BN and be made by chemical vapor phase infiltration.

[0067] In such an embodiment, the reactive gaseous phase may include or even consist of boron trichloride BCh and ammonia NH3.

[0068] It is noteworthy that the process of the invention proposes the formation of the interphase layer after the preparation of the loading which allows the additive manufacturing of the fibrous preform and even after the shaping of this loading.

[0069] In this way, it is intrinsically ensured that the interphase layer is not damaged by the loading preparation or the additive manufacturing step as can be observed with prior art processes.

[0070] Furthermore, it has also been observed that the formatting step could impair the integrity of the interface, which is also avoided here.

[0071] For example, the interphase can have a thickness between 0.1 pm and 1.0 pm.

[0072] In one embodiment, the interphase deposition step can be directly followed by a consolidation phase deposition.

[0073] In one embodiment, such a consolidation phase can be deposited by chemical vapor deposition.

[0074] For example, this consolidation phase may include, or even be made up of, silicon carbide (SiC).

[0075] In one embodiment, such a consolidation phase can be obtained by introducing into a chemical vapor infiltration furnace a reactive gaseous phase comprising methyltrichlorosilane (CHsSiCh).

[0076] The presence of such a consolidation phase ensures the protection of the interphase and reinforces the mechanical support of the preform after its coating by the interphase.

[0077] The process then includes a step of forming the ceramic matrix in the porosity of the preform.

[0078] In one embodiment, the matrix formation can be carried out by a chemical vapor phase infiltration step, by a polymer infiltration and pyrolysis step (known as "PIP" for the acronym "Polymer Infiltration and Pyrolysis"), by a melt infiltration step (known as "MI" for the English acronym "melt infiltration"), by a reactive melt infiltration step (known as "RMI" for the English acronym "Reactive Melt Infiltration"), or by a slurry transfer molding step (known as "STM" for the English acronym "Slurry Transfer Molding").

[0079] Preferably, the ceramic matrix formation step can be carried out by molten infiltration of an infiltration composition comprising molten silicon. This technique allows silicon to be delivered directly to the core of the porosity of the fibrous preform and the formation of a silicon carbide (SiC) matrix.

[0080] Alternatively, the infiltration composition can be a preceramic polymer, the pyrolysis of which allows the formation of a silicon carbide SiC and / or silicon nitride SisIXk matrix in the porosity of the preform.

[0081] Such a pre-ceramic polymer can be chosen from polycarbosilanes, polysilazanes, polyborosilazanes.

[0082] In one embodiment, the step of forming the ceramic matrix in the porosity of the preform is carried out by molten infiltration and may be preceded by a step of loading the porosity of the preform with particles of a precursor material, for example particles of a carbon precursor or silicon carbide particles.

[0083] In such an embodiment, the loading step allows the introduction into the porosity of the preform of fillers which will react with the matrix or matrix precursor which will be infiltrated during the subsequent matrix formation step.

[0084] In one embodiment such a precursor material may be particles of ceramic or preceramic material, for example particles of a carbon precursor or silicon carbide particles.

[0085] This step of loading the porosity of the preform allows to determine precisely the composition of the matrix finally obtained in the porosity of the fibrous preform.

[0086] For example, this step of loading the porosity of the preform can be carried out by a slurry comprising fillers of a carbon precursor or silicon carbide fillers allowing to reduce the residual silicon content in the final composite.

[0087] The process thus makes it possible to obtain a part made of composite material whose thermo-mechanical properties are satisfactory for aeronautical applications and close to those of a composite material obtained by a prior art process involving a complex weaving and shaping step.

[0088] The process allows for a significant reduction in its complexity compared to prior art processes.

[0089] In one embodiment, the part is an aeronautical part made of SiC / SiC composite material, for example chosen from a turbine blade, a distributor, a turbine ring. Brief description of the drawings

[0090] [Fig. 1] Figure 1 schematically represents the steps of a process in one embodiment of the invention. Description of the implementation methods

[0091] The invention is now described by means of a figure, presented for descriptive purposes to illustrate certain embodiments of the invention and which should not be interpreted as limiting the latter.

[0092] Figure 1 schematically represents the different stages of a process as described above.

[0093] Figure 1 shows mandatory steps in solid lines and optional steps in dotted lines.

[0094] The El stage is a preparation stage for a load comprising composite material fibers and a binder.

[0095] Preferably, the fibers are silicon carbide (SiC) fibers.

[0096] Composite material fibers can have a length between 150 pm and 1000 pm.

[0097] The binder can be chosen from polyesters, polyamides, elastomers, polyethylenes.

[0098] In one embodiment, the load can be prepared by extrusion.

[0099] This method of implementation is particularly preferred if additive manufacturing is a molten filament deposition step.

[0100] In one embodiment, the loading can be prepared by mixing and granulation.

[0101] This method of implementation is particularly preferred if additive manufacturing is a step involving the deposition of molten granules.

[0102] Additive manufacturing by molten pellet deposition is particularly preferred, as it ensures excellent mixing between the binder and the ceramic material fibers, and where applicable the powder, without being limited by the fragility of the filament required in the case of molten filament deposition.

[0103] In one embodiment, the loading may further include a powder of ceramic particles.

[0104] For example, such a powder may include particles of silicon carbide SiC, silicon nitride Si3N4 or boron carbide B4C.

[0105] In one embodiment, the particles of the particle powder may have a median number size, called D50, between 0.5 pm and 10 pm, or even between 2.0 pm and 7.0 pm.

[0106] Here and throughout the application, it is understood that the granulometry of a powder is meant to characterize the median size of the particles composing the powder, also noted as d50 or D50 in the field.

[0107] The median size of a particle distribution can be determined in a classical way in the field of powdered materials, for example by using a particle size analyzer, for example a particle size analyzer employing the Mie method.

[0108] In a known way, which is not explained in detail here, such a measurement relies on the detection of the angles of refraction of a laser beam sent onto a sample.

[0109] The loading preparation step El is followed by an additive manufacturing step E2 of a fibrous preform.

[0110] The specific choice of additive manufacturing method is not decisive for obtaining the technical effects described above.

[0111] In one embodiment, step E2 of additive manufacturing can be carried out by deposition of molten granules.

[0112] Indeed, this allows for a perfectly controlled volumetric fiber content, binder content, and geometric precision of the preform, enabling the manufacture of parts with improved properties compared to parts obtained by prior art processes.

[0113] In one embodiment, the preform can be a preform of an aeronautical part, for example of a turbomachine blade or distributor.

[0114] It is stated that the preform has the dimensions of the part to be obtained. This is intended to characterize the expression used in the field, "near net shape".

[0115] However, this does not mean that the preform must have the exact final dimensions of the part to be produced, as subsequent steps may slightly alter the preform's dimensions. It simply means that no complex machining or cutting steps are required once the preform is obtained.

[0116] Step E3 is a consolidating unbinding step.

[0117] This E3 consolidating debinding step can be carried out under a neutral atmosphere, in a powder bed with heat treatment and allows a carbon residue to be formed in the preform after removal of the binder, for example by carbonization of said binder.

[0118] Thus, the preform at stage E3 exhibits superior mechanical and structural resistance compared to that at the end of stage E2 due to the presence of the carbon residue in the preform.

[0119] This ensures in particular that the preform is self-supporting, that is to say that it retains the acquired shape and can be transported without losing the dimensions given to it in the E2 additive manufacturing step.

[0120] This E3 consolidating debinding step then allows us to have a preform that can be handled, without requiring a conforming step.

[0121] Having a process that does not require such a conforming step is a major economic gain for the process compared to prior art processes.

[0122] Preferably, step E3 is completed by removing the powder bed, which is not shown as a step in itself.

[0123] The E3 consolidating debinding step is then followed by an E4 interphase deposition step.

[0124] This step allows a thin layer of interphase to be deposited on the preform fibers and in its internal porosity.

[0125] For example, the interphase layer can have a thickness between 0.1 pm and 1.0 pm.

[0126] Preferably, the interphase layer is a boron nitride (BN) layer.

[0127] The execution of step E4 after debinding E3 and after the additive manufacturing step of the preform E2, ensures excellent integrity of the interphase layer.

[0128] Indeed, prior art processes generally perform additive manufacturing with ceramic material fibers on which the interface is already present.

[0129] It is to the credit of the inventors that they determined, on the one hand, that defects in parts obtained at the end of a process could originate from damage to the interphase and, on the other hand, that damage to the interphase could originate from the conditions of preparation of the load for additive manufacturing.

[0130] Thus, it is surprising to suggest depositing the interface after the additive manufacturing step, but this results in a part made of a much better quality composite material.

[0131] This is also made possible by the process steps ensuring a self-supporting preform without requiring consolidation and thus allowing the interphase to be deposited on an already self-supporting preform.

[0132] For example, the E4 interphase deposition step can be carried out by a chemical vapor phase infiltration process.

[0133] The process then includes an optional step E5, represented by dotted lines, in which the interphase is coated, for example with a layer of silicon carbide SiC.

[0134] In one embodiment, such a silicon carbide SiC layer can be disposed of by a chemical vapor phase infiltration process.

[0135] In particular, such a layer can be deposited in the same furnace as the one in which step E4 took place, by changing the reactive gaseous phase introduced.

[0136] For example, the reactive gas phase for silicon carbide deposition can be methyltrichlorosilane CHsSiCh.

[0137] Such a consolidation layer ensures the protection of the interphase and the mechanical support of the preform after its coating by the interphase.

[0138] In one embodiment, the formation step of the consolidation phase can be followed by an optional step E6 of loading the porosity of the fibrous preform.

[0139] Such a step allows for better control of the matrix formed in the internal porosity of the fibrous preform.

[0140] For example, porosity loading can be done with particles.

[0141] Such particles can be particles of a carbon precursor or silicon carbide particles (SiC).

[0142] These particles will be chosen according to the desired matrix.

[0143] Finally, the process includes an E7 step of forming a ceramic matrix in the internal porosity of the preform.

[0144] For example, this step can be achieved by capillary infiltration into the porosity of the preform of an infiltration composition comprising molten silicon.

[0145] This step, commonly called "MI" for the English acronym "melt infiltration", allows a silicon carbide ceramic matrix to be formed directly in the porosity of the preform.

[0146] This final step E7 allows the densification of the part in composite material.

[0147] In one embodiment, the part comprises, at the end of step E7, a residual porosity of less than or equal to 2%.

[0148] In one embodiment, the process may not include any steps other than those described in Figure 1, it being understood that steps E5 and E6 are optional.

Claims

Demands

1. A method for manufacturing a part made of composite material comprising at least the following steps: - a step (El) of preparing a load comprising ceramic material fibers and a binder; - a step (E2) of preparing a preform having the shape of the part to be obtained by additive manufacturing of the prepared load; - a step (E3) of consolidating debinding of the preform, consisting of leaving a carbon skeleton in the preform after debinding, allowing the preform to become self-supporting; - a step (E4) of forming an interphase by a chemical vapor-phase infiltration operation of the debound preform; then - a step (E7) of forming a ceramic matrix in the porosity of the preform.

2. A process according to claim 1, wherein the consolidating debinding step is carried out by a powder bed debinding step performed jointly with a heat treatment step carried out at a temperature between 450°C and 800°C.

3. A method according to claim 1 or 2, wherein the additive manufacturing process used for the preparation of the preform is the deposition of molten granules.

4. A method according to any one of claims 1 to 3, wherein the preform obtained at the end of the additive manufacturing step (E2) comprises a binder volume percentage of between 40% and 70%, preferably between 50% and 65%.

5. A method according to any one of claims 1 to 4, wherein the preform obtained at the end of the additive manufacturing step (E2) comprises a fiber volume percentage of between 30% and 60%, preferably between 35% and 45%.

6. A method according to any one of claims 1 to 5, wherein the length of the ceramic material fibers introduced into the feed is between 150 µm and 1000 µm.

7. A method according to any one of claims 1 to 6, wherein the loading of the step (El) comprises a mass content of between 5% and 10% of a silicon carbide particle powder SiC.

8. A method according to any one of claims 1 to 7, wherein the interphase formation step (E4) is carried out by chemical vapor-phase infiltration and wherein the interphase is a boron nitride interphase.

9. A method according to any one of claims 1 to 8, wherein the interphase deposition step (E4) is directly followed by a consolidation phase deposition step (E5).

10. A method according to any one of claims 1 to 9, wherein the infiltration step (E7) is carried out by infiltration in the molten state and is preceded by a step (E6) of loading the porosity of the preform with particles of a carbon precursor or silicon carbide particles.

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