Slip composition for manufacturing a ceramic matrix composite part

Abstract

The invention relates to a slip composition for manufacturing a ceramic matrix composite part, the slip composition comprising: - a carrier liquid; - silicon carbide powder suspended in the carrier liquid, the silicon carbide powder representing between 50% and 77.5% by volume of powder; - carbon powder suspended in the carrier liquid, the carbon powder representing between 7.5% and 40% by volume of powder; - boron-containing species powder suspended in the carrier liquid, the boron-containing species powder representing between 5% and 20% by volume of powder, preferably between 5% and 15% by volume of powder; - the total of the percentages by volume of silicon carbide powder, carbon powder and boron-containing species powder being equal to 100%.

Description

DESCRIPTION TITLE: SLUDGE COMPOSITION FOR THE MANUFACTURE OF A PART IN CERAMIC MATRIX COMPOSITE MATERIAL

[0001] The present invention relates to a slip composition for the manufacture of a part made of ceramic matrix composite material.

[0002] The invention finds a particularly advantageous application in the manufacture of ceramic matrix composite (CMC) parts integrated into the hot sections of an aircraft turbomachine, such as combustion chamber walls, turbine blades, or distributors. The invention can be applied in other fields, for example, in the field of industrial gas turbines.

[0003] Indeed, CMC materials are known to possess both good mechanical properties allowing their use for structural elements and the ability to retain these properties at high temperatures.

[0004] CMC materials include a fibrous preform made of refractory fibers, notably carbon or ceramic, which is densified by a ceramic matrix, for example based on silicon carbide SiC.

[0005] A known process for manufacturing parts from CMC material is described in document US2019337859. This process includes a step of creating a fibrous preform from carbon fibers or silicon carbide (SiC).

[0006] The process then includes a step of consolidating the fibrous preform by chemical gas infiltration (CVI) of silicon carbide. The fibrous preform is held in the forming tooling during CVI. The reactive gases decompose on the surface of the fibers to produce silicon carbide. The silicon carbide thus obtained (SiC / CVI) consolidates the fibrous preform.

[0007] The process includes a step of impregnating the fibrous preform with a slurry containing a suspended silicon carbide (SiC) powder ("Slurry Cast" or "Slurry Transfer Molding" according to Anglo-Saxon terminology). The impregnation step is carried out by injecting a loaded slurry into the fibrous preform under pressure. The slurries used are lightly loaded in order to exhibit stable viscosity (rheo-thinning index > 0.7) and low viscosity (< 100 mPa·s) for the transport of fillers within the volume of the fibrous preform.

[0008] The process also includes a step of infiltrating the fibrous preform with a molten silicon-based composition to form a ceramic matrix. This densification process is known as the Ml process ("Melt Infiltration" in Anglo-Saxon terminology).

[0009] The fabrication of CMC material is conventionally carried out using a slurry of submicron silicon carbide powders to generate the granular matrix during the slurry cast process. The slurry produces a granular network with characteristics compatible with the Ml densification cycle. However, the formulation of this slurry is difficult to repeat and unstable over time due to the rapid evolution (within a few hours) of the slurry's particle size and rheological characteristics.

[0010] Furthermore, the use of most silicon carbide powders in the slip increases the level of reactivity during the liquid silicon infiltration step. This is because the liquid silicon tends to react with the carbon in the SiC / CVI layer, which deteriorates the SiC / CVI layer and thus increases the scrap rate of parts made from CMC material.

[0011] Figure 1 shows the fibers 1 of the fibrous preform covered by a SiC / CVI layer 2, as well as the granular matrix 3 of SiC powder obtained during the Slurry Cast process. This figure highlights a zone 4 of the SiC / CVI layer attacked by liquid silicon during the densification step M1.

[0012] It is known to add carbon to the slip composition to limit the reactivity of liquid silicon with the carbon in the SiC / CVI layer. However, such a solution is not satisfactory, since the reactivity of liquid silicon with carbon leads to the creation of large particles that prevent good filling of the granular matrix during the M1 densification step.

[0013] The invention aims to effectively remedy the aforementioned drawbacks by proposing a slip composition for the manufacture of a ceramic matrix composite part comprising: - a carrier liquid, - a silicon carbide powder suspended in the carrier liquid, comprising between 50% and 77.5% by volume of powder, preferably between 72.5% and 77.5% by volume of powder, - a carbon powder suspended in the carrier liquid comprising between 7.5% and 40% by volume of powder, preferably between 7.5% and 22.5% by volume of powder, and - a boron-based powder suspended in the carrier liquid, comprising between 5% and 20% by volume of powder, preferably between 5% and 15% by volume of powder, - the total of the percentages by volume of silicon carbide powder, carbon powder and borate species powder being equal to 100%.

[0014] The invention thus makes it possible, through the addition of boron-containing powder and carbon powder, to obtain a stable composition while significantly reducing the action of liquid silicon on the SiC / CVI layer due to the carbon saturation of the liquid silicon and also the formation of SiBx species, which slows the attack of the liquid silicon on the SiC / CVI layer. Furthermore, the choice of powder particle characteristics (size and distribution) and organic additives (dispersant, binder, plasticizer, antiwetting agent) allows control of the pore size of the granular network and the packing ratio in order to optimize the filling of the silicon carbide matrix during the molten silicon infiltration step.

[0015] According to one embodiment of the invention, silicon carbide powder, carbon powder and boron species powder each exhibit a unimodal distribution.

[0016] According to one embodiment of the invention, a ratio between a median size of carbon and boron particles (d50C / B) divided by a median size of silicon carbide particles (d50SiC) is less than 1.5.

[0017] According to one embodiment of the invention, a particle size range of silicon carbide powder, carbon powder and boron species powder is as follows: 0.1 < d10 < 0.5 pm, 0.5 < d50 < 1.5 pm, preferably 0.5 < d50 < 1 pm, and d90 < 2 pm preferably d90<1.5 pm.

[0018] According to one embodiment of the invention, the carrier liquid is water. Alternatively, the carrier liquid is a mixture of water and alcohol, for example ethanol or alcohol alone.

[0019] According to one embodiment of the invention, the slip composition comprises a polyelectrolyte type dispersant having a mass average molar mass Mw greater than or equal to 20000 g / mol.

[0020] According to one embodiment of the invention, the slip composition comprises an organic binder chosen for example from the following products: polyvinyl alcohol (PVA), polyethylene glycol (PEG), glycerol, polyvinylpyrrolidone (PvP).

[0021] According to one embodiment of the invention, the slip composition comprises a plasticizer having a mass average molar mass (Mw) less than or equal to 1000 g / mol.

[0022] According to one embodiment of the invention, the slip composition comprises a wetting agent based on a solution of alkyl ammonium salt of a polyfunctional polymer.

[0023] According to one embodiment of the invention, the filler content is between 15% and 25% by volume of slip.

[0024] The invention also relates to a method for manufacturing a ceramic matrix composite part comprising: - a step in creating a fibrous preform from carbon fibers or silicon carbide, - a consolidation step of a fibrous preform carried out by gas-phase chemical infiltration of silicon carbide, - a step of impregnating the fibrous preform with a slip having a composition as previously defined, and - a step of infiltrating the fibrous preform with a molten silicon-based composition in order to form a ceramic matrix.

[0025] The present invention will be better understood and other features and advantages will become apparent upon reading the following detailed description, which includes embodiments given by way of illustration with reference to the accompanying figures, presented by way of non-limiting examples, which may serve to complete the understanding of the present invention and the explanation of its implementation and, where appropriate, contribute to its definition, on which:

[0026] [Fig. 1] Figure 1, already described, is a microscopic view of a section of a CMC part obtained by a prior art process highlighting the attack of the SiC / CVI layer by liquid silicon during the densification step M1;

[0027] [Fig. 2] Figure 2 is a diagram of the different stages of a manufacturing process for a CMC part;

[0028] [Fig. 3a] Figure 3a shows graphical representations, as a function of a shear rate, of an upper limit, a lower limit and an average viscosity of a first embodiment of the slip composition according to the invention,

[0029] [Fig. 3b] Figure 3b is a micro-tomographic cross-sectional view of the CMC object after the step of impregnating the fibrous preform with the slip composition according to the first embodiment of the invention;

[0030] [Fig. 3c] Figure 3c is a micro-tomographic cross-sectional view of the CMC object after densification Ml by liquid silicon of the granular network obtained with the slip composition according to the first embodiment of the invention;

[0031] [Fig. 3d] [Fig. 3e] Figures 3d and 3e show cross-sectional views of a CMC part obtained with the slip composition according to the first embodiment of the invention, respectively opposite the feed and liquid silicon feed side during the densification step M1;

[0032] [Fig. 4a] Figure 4a shows graphical representations, as a function of shear rate, of an upper limit, a lower limit and an average viscosity of a second embodiment of the slip composition according to the invention,

[0033] [Fig. 4b] Figure 4b is a micro-tomographic cross-sectional view of the CMC object after the step of impregnating the fibrous preform with the slip composition according to the second embodiment of the invention;

[0034] [Fig. 4c] Figure 4c is a micro-tomographic cross-sectional view of the CMC object after densification Ml by liquid silicon of the granular network obtained with the slip composition according to the second embodiment of the invention;

[0035] [Fig. 4d] [Fig. 4e] Figures 4d and 4e show cross-sectional views of a CMC part obtained with the slip composition according to the second embodiment of the invention, respectively opposite the feed and liquid silicon feed side following the densification step Ml.

[0036] It should be noted that identical, similar, or analogous elements retain the same reference from one figure to another.

[0037] Figure 2 shows the different stages of a manufacturing process for parts made of CMC material including a stage 100 of making a fibrous preform from carbon fibers or silicon carbide (SiC).

[0038] The process then includes a step 101 of consolidation of the fibrous preform carried out by chemical gas infiltration (CVI) of SiC. The fibrous preform is held in the shaping tooling during the CVI.

[0039] The process includes a step 102 of impregnating the fibrous preform with a slurry containing a suspended silicon carbide (SiC) powder ("Slurry Cast" or "Slurry Transfer Molding"). The impregnation step is carried out by injecting the loaded slurry under pressure into the fibrous preform.

[0040] The process also includes a step 103 of infiltrating the fibrous preform with a molten silicon-based composition to form a ceramic matrix. This densification process is known as the Ml process ("Melt Infiltration").

[0041] The slip composition used in the "Slurry Cast" process includes: - a carrier liquid, - a silicon carbide powder suspended in the carrier liquid, comprising between 50% and 77.5% by volume of powder, preferably between 72.5% and 77.5% by volume of powder, - a carbon powder suspended in the carrier liquid comprising between 7.5% and 40% by volume of powder, preferably between 7.5% and 22.5% by volume of powder, - a boron-containing powder suspended in the carrier liquid, comprising between 5% and 20% by volume of powder, preferably between 5% and 15% by volume of powder, - the total of the percentages by volume of silicon carbide powder, carbon powder and borate species powder being equal to 100%.

[0042] Preferably, the carrier liquid is water. Alternatively, the carrier liquid is a mixture of water and alcohol, for example ethanol or alcohol alone.

[0043] Carbon can be amorphous carbon, graphite, or diamond, alone or in mixtures.

[0044] The boron species can be boron, boron carbide B4C, or silicon boride (SiB3 or SiB6) alone or in mixture.

[0045] Advantageously, silicon carbide powder, carbon powder and borate species powder each exhibit a unimodal distribution, that is to say that the diameter distribution of each powder advantageously presents a single peak located at the median particle size (d50).

[0046] Carbon powder and boron powder also exhibit a particle size distribution equivalent to that of silicon carbide powder. The ratio of the median particle size of carbon and boron (d50C / B) to the median particle size of silicon carbide (d50SiC) is less than 1.5 (d50C / B / d50SiC ratio < 1.5). This particle size distribution helps to limit particle packing within the granular matrix.

[0047] A particle size range for silicon carbide powder, carbon powder, and boron species powder is advantageously as follows: 0.1 < d10 < 0.5 pm, 0.5 < d50 < 1.5 pm, preferably 0.5 < d50 < 1 pm and d90 < 2 pm, preferably d90 < 1.5 pm. - d10 being the cumulative distribution percentage of 10% of particles having a diameter less than a given value between 0.1 and 0.5 pm, - d90 being the cumulative distribution percentage of 90% of particles having a diameter less than a given value of 2 micrometers, and - d50 being a median particle size corresponding to a percentage of cumulative distribution of 50% of particles having a diameter less than a given value between 0.5 and 1 pm.

[0048] The organic additives in the slip (dispersant, binder, plasticizer) are chosen for their water-soluble properties. The dispersant / binder system is selected to ensure sufficient steric hindrance between the particles to limit granular packing, specifically to a packing ratio of 55% or less by volume, thus ensuring good aeration of the granular matrix.

[0049] Preferably, the slip composition includes a polyelectrolyte dispersant having a mass average molar mass Mw greater than or equal to 20000 g / mol. The dispersant is chosen for example from the following products: Polyethyleneimine (PEI) having a mass average molar mass Mw equal to 25000 g.mol-1, Dolapix PC 21 (trade name), PvP (polyvinylpyrrolidone), polyacrylate which may be Darvan 821A (trade name), Darvan CN (trade name), Dolapix A88 (trade name), Dolapix CE64 (trade name).

[0050] Furthermore, the organic binder is chosen for example from the following products: polyvinyl alcohol (PVA), polyethylene glycol (PEG), glycerol, polyvinylpyrrolidone (PvP).

[0051] The plasticizer has a mass average molar mass (Mw) less than or equal to 1000 g / mol. The plasticizer is, for example, polyethylene glycol (PEG) of the type PEG 200, having a mass average molar mass of 200 g.mol-1.

[0052] The slip composition also includes a wetting agent based on an alkyl ammonium salt solution of a polyfunctional polymer, such as DisperBYK 181 (trade name, see technical data sheet https: / / www.byk.com / en / products / additive-guide / disperbyk-181) or any other equivalent product.

[0053] The filler content is between 15% and 25% by volume of slip. The fillers consist of the active components (powders, binder, plasticizer, dispersant and wetting agent) of the slip.

[0054] Following a first example of embodiment, the slip composition having a filler content of 20% comprises a carrier liquid consisting of water, silicon carbide powder at a level of 75% by volume of powder, carbon powder at a level of 15% by volume of powder, and boron powder at a level of 10% by volume of powder.

[0055] The particle size range of silicon carbide powder, carbon powder and boron species powder is as follows: d10 = 0.40 pm, d50 = 0.86 pm, and d90 = 1.63 pm.

[0056] The binder is PEG10000, the weight of which is equal to 1% of the total weight of all the powders.

[0057] The plasticizer is PEG200, the weight of which is equal to 1% of the total weight of all the powders.

[0058] The dispersant is PEI, the weight of which is equal to 1.4% of the total weight of all the powders.

[0059] The wetting agent is DisperBYK 181, the weight of which is equal to 0.6% of the total weight of all the powders.

[0060] The jar-turning time (TJ) is 72 hours. TJ corresponds to the duration of the deagglomeration phase, which disperses the particles within the suspension. Specifically, a jar is used in which 33% slip, 33% silicon carbide (SiC) beads (for example, 10 mm in diameter), and 33% empty space are mixed by volume. The system is positioned on a rotating device (the jar turner) to ensure mixing at a speed between 20 and 100 rpm. This mixing process lasts 72 hours and allows the suspension to achieve the correct particle size distribution and viscosity.

[0061] Figure 3a shows graphical representations, as a function of a shear rate Te, of a viscosity V of the slurry having the aforementioned composition. The average viscosity curve C1 of the slurry composition according to the first embodiment lies between an upper limit (curve C2) and a lower limit (curve C3) of viscosity acceptable for the implementation of the "Slurry Cast" process.

[0062] The slip composition has a Shear Thinning Index of 0.73.

[0063] The rheological and granulometric characteristics are repeatable and compatible with good filling of the fibrous preform when implementing the "Slurry cast" process.

[0064] Thus, Figure 3b showing the CMC object after the step of impregnating the fibrous preform with the aforementioned slip composition highlights a homogeneous filling of the fibrous preform with a low defect area of ​​0.1%.

[0065] Figure 3c showing the CMC object after Ml densification highlights good filling of the granular matrix by liquid silicon with a low defect area of ​​0.18%.

[0066] Figures 3d and 3e are cross-sectional views of a CMC part obtained by a process according to the invention, respectively on the side opposite the liquid silicon feed and on the side receiving the liquid silicon during the densification step M1. These figures show the fibers 1 of the fibrous preform covered by a layer of SiC / CVi 2, as well as the granular silicon carbide matrix 3 obtained during the slurry cast process. The white areas 5 correspond to silicon from the densification step.

[0067] Figures 3d and 3e highlight that the aforementioned slurry composition prevents the SiC / CVI layer from being attacked by liquid silicon during the M1 densification step. The integrity of the SiC / CVI layer is preserved even on the side opposite the liquid silicon feed where The accumulation of metallic impurities (such as aluminum or iron) along the fibrous preform increases the level of reactivity of the liquid silicon.

[0068] Following a second embodiment example, the slip composition having a filler content of 20% comprises a carrier liquid consisting of water, silicon carbide powder at a level of 72.5% by volume of powder, carbon powder at a level of 22.5% by volume of powder, and boron powder at a level of 5% by volume of powder.

[0069] The particle size range of silicon carbide powder, carbon powder and boron species powder is as follows: d10 = 0.40 pm, d50 = 0.82 pm, and d90 = 1.47 pm.

[0070] The binder is PEG10000, the weight of which is equal to 1% of the total weight of all the powders.

[0071] The plasticizer is PEG200, the weight of which is equal to 5% of the total weight of all the powders.

[0072] The dispersant is PEI, the weight of which is equal to 1.4% of the total weight of all the powders.

[0073] The wetting agent is DisperBYK 181, the weight of which is equal to 0.6% of the total weight of all the powders.

[0074] The jar-turning time (TJ) is 72 hours. TJ corresponds to the duration of the deagglomeration phase, which disperses the particles within the suspension. Specifically, a jar is used in which 33% slip, 33% silicon carbide (SiC) beads (for example, 10 mm in diameter), and 33% empty space are mixed by volume. The system is positioned on a rotating device (the jar turner) to ensure mixing at a speed between 20 and 100 rpm. This mixing process lasts 72 hours and allows the suspension to achieve the correct particle size distribution and viscosity.

[0075] Figure 4a shows graphical representations, as a function of a shear rate Te, of a viscosity V of the slurry having the aforementioned composition. The average viscosity curve CT of the slurry composition according to the invention lies between the upper limit (curve C2') and the lower limit (curve C3') of viscosity acceptable for the implementation of the "Slurry Cast" process.

[0076] The slip composition has a Shear Thinning Index of 0.74.

[0077] The rheological and granulometric characteristics are repeatable and compatible with good filling of the fibrous preform when implementing the "Slurry cast" process.

[0078] Thus, Figure 4b showing the CMC object after the step of impregnating the fibrous preform with the aforementioned slip composition highlights a homogeneous filling of the fibrous preform with a low defect area of ​​0.38%.

[0079] Figure 4c showing the CMC object after Ml densification highlights good filling of the granular matrix by liquid silicon with a low defect area of ​​0.04%.

[0080] Figures 4d and 4e show cross-sectional views of a CMC part obtained by a process according to the invention, respectively on the side opposite the feed and on the side fed with liquid silicon during the densification step M1. These figures show the fibers 1 of the fibrous preform covered by a layer of SiC / CVi 2, as well as the granular silicon carbide matrix 3 obtained during the slurry cast process. The areas 5 correspond to silicon from the densification step.

[0081] Figures 4d and 4e highlight that the aforementioned slurry composition prevents the SiC / CVI layer from being attacked by liquid silicon during the M1 densification step. The integrity of the SiC / CVI layer is preserved even on the side opposite the liquid silicon feed where The accumulation of metallic impurities such as aluminum or iron along the fibrous preform increases the level of reactivity of the liquid silicon.

[0082] Of course, the different features, variants and / or embodiments of the present invention can be combined with each other in various ways as long as they are not incompatible or mutually exclusive.

[0083] Furthermore, the invention is not limited to the embodiments described above and provided solely by way of example. It encompasses various modifications, alternative forms, and other variations that a person skilled in the art might envision within the scope of the present invention, and in particular all combinations of the different modes of operation described above, which may be considered separately or in combination.

Claims

DEMANDS 1. A method for manufacturing a ceramic matrix composite part characterized in that it comprises: - a step (100) of producing a fibrous preform from carbon fibers or silicon carbide (SiC), - a step (101) of consolidation of a fibrous preform carried out by chemical gas infiltration (CVI) of silicon carbide, - a step (102) of impregnating the fibrous preform with a slip comprising: - a carrier liquid, - a silicon carbide powder suspended in the carrier liquid, comprising between 50% and 77.5% by volume of powder, preferably between 72.5% and 77.5% by volume of powder, - a carbon powder suspended in the carrier liquid comprising between 7.5% and 40% by volume of powder, preferably between 7.5% and 22.5% by volume of powder, the carbon being amorphous carbon, graphite, or diamond alone or in mixtures, and - a boron species powder suspended in the carrier liquid, comprising between 5% and 20% by volume of powder, preferably between 5% and 15% by volume of powder, the boron species being boron, boron carbide B4C, or silicon boride SiB3 or SiB6 alone or in mixture, - the total volume percentages of silicon carbide powder, carbon powder and borate species powder being equal to 100%, - a step (103) of infiltrating the fibrous preform with a molten silicon-based composition so as to form a ceramic matrix.

2. A process according to claim 1, characterized in that the silicon carbide powder, the carbon powder and the boron species powder each exhibit a unimodal distribution.

3. A method according to claim 1 or 2, characterized in that a ratio between a median particle size of carbon and boron (d50C / B) divided by a median size of silicon carbide particles (d50SiC) is less than 1.

5.

4. A method according to any one of claims 1 to 3, characterized in that a particle size range of silicon carbide powder, carbon powder and boron species powder is as follows: 0.1 < d10 < 0.5 pm, 0.5 < d50 < 1.5 pm, preferably 0.5 < d50 < 1 pm, and d90 < 2 pm preferably d90 < 1.5 pm.

5. A method according to any one of claims 1 to 4, characterized in that the carrier liquid is water.

6. A process according to any one of claims 1 to 5, characterized in that the slip composition comprises a polyelectrolyte type dispersant having a mass average molar mass Mw greater than or equal to 20000 g / mol.

7. A process according to any one of claims 1 to 6, characterized in that the slip composition comprises an organic binder selected for example from the following products: polyvinyl alcohol (PVA), polyethylene glycol (PEG), glycerol, polyvinylpyrrolidone (PvP).

8. A process according to any one of claims 1 to 7, characterized in that the slip composition comprises a plasticizer having a mass average molar mass (Mw) less than or equal to 1000 g / mol.

9. A process according to any one of claims 1 to 8, characterized in that the slip composition comprises a wetting agent based on an alkylol ammonium salt solution of a polyfunctional polymer.

10. A process according to any one of claims 1 to 9, characterized in that a filler content of the slip composition is between 15% and 25% by volume of slip.

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