Method for manufacturing a part made from cmc

Abstract

The invention relates to a method for manufacturing a part made of ceramic matrix composite material, the method comprising at least: - a step of heating a fibre preform (20, 30) to a temperature greater than or equal to 1450°C; then - a step of infiltrating the fibre preform with an infiltration composition, wherein the infiltration composition comprises at least liquid silicon; then - a step of cooling a portion of the surface of the fibre preform by exposing the surface to a cold gas flow; then - cooling the entire fibre preform.

Description

Description Title of the invention: Method for manufacturing a CMC part Technical Field

[0001] This disclosure relates to a method for manufacturing a part made of ceramic matrix composite material. Prior art

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

[0003] Due to their improved resistance to high temperatures, CMCs require less cooling. This cooling traditionally comes from a draw from the compressor, which impacts the efficiency of the turbomachine. CMC materials therefore improve engine efficiency, thereby reducing fuel consumption.

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

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

[0006] A known method for manufacturing such a part is infiltration with molten silicon, often called "MI" for the English acronym "Melt Infiltration".

[0007] In such a method, a fiber preform is impregnated with an infiltration composition generally comprising molten silicon to form the matrix of the CMC material in the porosity of the fiber preform. Generally, to carry out the infiltration, one end of the preform is dipped into a bath of infiltration composition, so that the latter fills the porosity of the preform by capillarity.

[0008] Such a method is satisfactory industrially, but improvements remain desirable.

[0009] In particular, silicon being denser in the solid state than in the liquid state, its cooling and solidification causes part of the liquid silicon to escape in the form of drops solidifying on the surface of the part, thus forming nodules of solid silicon. These nodules then cause significant difficulties since they modify the dimensions of the part beyond tolerances and degrade the adhesion of any surface coating subsequently deposited. In addition, the subsequent removal of these nodules by sandblasting or machining is slow, laborious, and therefore expensive; it can also affect the material health of the final part.

[0010] Consequently, in order to combat the appearance of such nodules, certain solutions have been considered. One of these aims to modify the composition of the densification material or ceramic slip, for example by adding diamond particles, sources of carbon that will consume the excess silicon to form SiC. However, it is not always possible or desirable to modify the composition of the slip in this way.

[0011] Another option is to provide a sacrificial layer of ceramic slip all around the intermediate part in order to protect the final part, and in particular its reinforcement, during sandblasting or machining of the nodules. However, naturally, such an option results in significant overconsumption of raw materials and requires complete machining of the final part, which is long and tedious.

[0012] Alternatively, it is possible to add thermal masses to the locations where nodules are desired to form. However, this alternative does not allow for complete control over where nodules appear, and is not applicable to all part geometries.

[0013] There is therefore a real need for a method of manufacturing a CMC part which allows better control of the densification stage of the part and which is free, at least in part, from the drawbacks inherent in the aforementioned known methods. Statement of the invention

[0014] This presentation aims precisely to meet this need.

[0015] According to a first of its aspects, it relates to a method for manufacturing a part made of ceramic matrix composite material, comprising at least the following steps: - a step of heating a fiber preform to a temperature higher than the melting temperature of the alloy; then - a step of infiltrating the fiber preform with a liquid infiltration composition, said infiltration composition comprising at least silicon; then - a step of cooling a portion of the surface of the fiber preform by exposing said surface to a flow of cold gas; then - cooling of the entire fiber preform.

[0016] In a method of the invention, the step of cooling a portion of the surface of the fiber preform by exposure to a flow of cold gas aims to prevent the appearance of nodules at this location.

[0017] Indeed, it is to the credit of the inventors to have understood that the nodules are formed mainly at the end of the cooling of the impregnation composition so that the exposure of a portion of the surface to a flow of cold gas guarantees that the latter is free of nodules after complete cooling.

[0018] In particular, an excellent surface condition can thus be ensured for the part and in particular for the surface of the part exposed to the flow of cold gas.

[0019] Of course, the process does not intend to completely prevent the appearance of nodules, the latter being inherent to the physics of molten silicon, but it does ensure that they do not form on preferentially cooled surfaces.

[0020] The invention therefore proposes an alternative solution to the use of thermal masses to allow slower cooling of the areas where the presence of nodules is accepted. The proposed method aims to ensure rapid cooling of the surfaces of the preform on which the appearance of silicon nodules must be avoided.

[0021] Furthermore, the method of the invention makes it possible to protect areas from the appearance of nodules more effectively than the application of thermal masses, and / or for complex geometries where thermal masses cannot be put in place.

[0022] In one embodiment, the fibrous preform comprises a cavity, and the portion of the surface of the fibrous preform exposed to a flow of cold gas is the inner surface of said cavity.

[0023] Indeed, for such a cavity, it is very difficult in the prior art processes to guarantee rapid cooling which guarantees the absence of nodules.

[0024] Also, on the internal surface of a cavity it is very complicated to consider subsequent machining steps to eliminate the nodules once they have formed.

[0025] This is why it is even more advantageous for such a part to consider the embodiments described above.

[0026] In one embodiment, the portion of the surface of the fibrous preform exposed to a flow of cold gas is a surface of the preform forming an angle less than or equal to 20°.

[0027] In fact, when a preform forms such an angle, the presence of nodules is generally observed.

[0028] Without wanting to be bound by theory, the inventors believe that it is the geometry of such parts that explains the presence of nodules. Indeed, these areas cool more slowly than the rest of the preform because their external surfaces are close to other hot surfaces.

[0029] However, as with cavities, it is complex, if not impossible, to machine such surfaces if nodules were to form there.

[0030] The process described ensures that nodules do not form on surfaces cooled by the flow of cold gas, and thus ensures that the parts have optimal properties once densified.

[0031] In one embodiment, the temperature above the melting temperature of the alloy is greater than or equal to 1450°C. Such a temperature is in particular greater than the melting temperature of the infiltration compositions comprising a silicon alloy.

[0032] In one embodiment, the preform may comprise silicon carbide fibers, carbon fibers, or a mixture of silicon carbide fibers and carbon fibers.

[0033] Indeed, it is for such preforms that it is particularly advantageous to use infiltration processes using molten silicon.

[0034] According to a particular characteristic of the invention, the flow of cold gas may comprise gases chosen from helium or argon or a mixture of these compounds.

[0035] The particular choice of such gases ensures that there is no reaction between the gas and the CMC material part.

[0036] Such an embodiment makes it possible to ensure that the cold gas supplied for the particular step of exposing a surface of the preform to a flow of cold gas does not react with the preform, or with the liquid infiltration composition.

[0037] In addition, the temperature of the cold gas flow also ensures sufficient cooling of the preform to ensure the absence of nodules on the surface of the preform.

[0038] In one embodiment, the step of cooling a portion of the surface of the preform is performed after the entire surface of the preform has dropped below a target temperature.

[0039] In one embodiment, the target temperature may be 1420°C which is particularly suitable for the case where the infiltration composition comprises a silicon alloy.

[0040] For example, the target temperature may be 5°C higher than the solidification temperature of the alloy chosen for the infiltration composition.

[0041] A temperature slightly above the solidification temperature of the infiltration composition ensures that solidification is close throughout the preform before initiating solidification where the part is exposed to the cold gas flow.

[0042] In one embodiment, the part is selected from a distributor or a turbomachine blade.

[0043] In one embodiment, the part may include more than one cavity, the inner surface of each of which is exposed to a flow of cold gas.

[0044] It is in fact for such parts that the advantages described above are the most interesting, in particular since it is difficult by the methods of the prior art to guarantee the absence of nodules on the surfaces of interest of such parts.

[0045] In one embodiment, the part is a SiC / SiC composite material part. Brief description of the drawings

[0046] [Fig. 1] Figure 1 is a schematic representation of a cold gas injection rod useful for carrying out a method of the invention.

[0047] [Fig. 2] Figure 2 schematically represents an embodiment of a step of cooling a portion of the surface of a fiber preform by means of an injection rod of Figure 1.

[0048] [Fig. 3] Figure 3 schematically represents an embodiment of a step of cooling a portion of the surface of another fiber preform by means of an injection rod of Figure 1. Description of the embodiments

[0049] The invention is now described by means of figures, present for descriptive purposes to illustrate certain embodiments of the invention and which should not be interpreted as limiting the latter.

[0050] Figure 1 represents a gas injection rod 10 for carrying out a method as described above.

[0051] In one embodiment, the gas injection rod 10 may be supplied via an orifice 12 located at one of its ends. Preferably, the rod further comprises one or more outlet orifices 11, which ensure evacuation of the gas introduced into the rod 10 via the orifice 12.

[0052] In one embodiment, the step of cooling a portion of the surface of the fiber preform may be performed by performing the following substeps: - supplying a gas injection rod 10 with a gas; then - the arrangement of the gas injection rod 10 on the surface of the preform to be cooled.

[0053] These sub-steps allow excellent precision of the surface exposed to a cold gas flow.

[0054] Generally speaking, in the application, a gas flow will be said to be “cold” if it allows a reduction in the temperature of the surface exposed to said gas flow compared to the rest of the surface of the preform.

[0055] Preferably, the step of cooling a portion of the surface of the fibrous preform is carried out as soon as the infiltration of the preform by the infiltration composition is complete.

[0056] In one embodiment, the cold gas stream is introduced into the circuit for exposing the surface to a cold gas stream at room temperature.

[0057] It is understood that the cold gas flow can nevertheless heat up at least due to its passage near the hot preform, or even in the still hot oven used for infiltration.

[0058] However, this heating of the cold gas flow as it travels towards the surface of the preform does not prevent the gas flow from cooling the surface of the preform that it encounters.

[0059] In one embodiment, it is possible to envisage the step of cooling a portion of the surface of the preform only after the entire surface of the preform has fallen below a target temperature.

[0060] In one embodiment, the target temperature may be 1420°C. This temperature is particularly advantageous in the case where the infiltration composition comprises a silicon alloy. Indeed, with a temperature slightly higher than the solidification temperature of the infiltration composition, it is ensured that the solidification of the infiltration composition is close before initiating solidification where the part is exposed to the flow of cold gas and excessively large temperature gradients are avoided.

[0061] Alternatively, the target temperature may be 5°C higher than the solidification temperature of the infiltration composition.

[0062] For example, the preform may be removed from the enclosure in which the infiltration with the infiltration composition was carried out, before exposing a portion of its surface to a flow of cold gas.

[0063] In one embodiment, it is understood that the portion of the surface of the preform exposed to a flow of cold gas is less than or equal to 50% of the total surface of the preform.

[0064] Indeed, such an embodiment ensures that there remain, after the exposure of a portion of the surface of the preform to a flow of cold gas, parts of the surface of the preform where the temperature is sufficiently high so that the infiltration composition is not yet solidified there.

[0065] According to a particular characteristic of the invention, the gas injection rod 10 may comprise a device for controlling the flow rate of the gas flow.

[0066] In the embodiment of Figure 1, the gas injection rod 10 is cylindrical, like the cavity of the preform.

[0067] The shape of the cane is in no way limiting.

[0068] However, in one embodiment, the gas injection rod 10 may have the same shape as a cavity of the part. This ensures that cold gas is projected over the entire internal surface of the cavity.

[0069] Figure 2 represents an example of carrying out a cooling step of a method described above.

[0070] In Figure 2, the gas injection rod 10 is arranged in the internal cavity 22 of a fiber preform 20.

[0071] The orifice 12 of the gas injection rod 10 is supplied by a flow of cold neutral gas, represented in Figure 2 by an arrow.

[0072] This is not shown in Figure 2, but in one embodiment, the gas injection rod 10 is connected to one or more gas sources, which ensures that the cold gas has the desired composition.

[0073] Similarly, in one embodiment, the gas injection rod 10 is connected to a thermostat, which ensures that the cold gas is at the desired temperature.

[0074] In one embodiment, the gas injection rod 10 is connected to a member for adjusting the pressure and the flow rate of the cold gas.

[0075] The gas supplied into the gas injection pipe 10 exits the latter through the orifices 11 and thus comes into contact with the surface of the cavity 22 of the preform 20.

[0076] The gas thus supplied then cools the surface of the cavity 22 of the preform 20, and the infiltration composition which impregnates the preform solidifies there first.

[0077] This controls the thermal expansion of the silicon and the flow of cold gas prevents the appearance of silicon nodules on the surface of the cavity 22 of the preform 20.

[0078] This results in an excellent surface condition for the surface of the cavity 22 of the preform 20, and it is thus observed that no silicon nodules are present there once the silicon has completely cooled.

[0079] Figure 3 describes another exemplary embodiment in which the preform 30 comprises an angle, preferably less than or equal to 20°.

[0080] The angle referred to herein is intended to characterize the relative extent of the two portions of the preform 30 with respect to each other and is understood independently of the exact shape of the junction, whether rounded or angular as shown here.

[0081] The internal surface 32 forming the angle of such a preform 30 benefits greatly from a method according to the invention.

[0082] Indeed, such an internal surface 32 is difficult to access and machining aimed at removing a possible nodule is difficult to envisage.

[0083] Thus, it is particularly beneficial to be able to implement a method as described for such parts, which ensures that silicon nodules do not form on such an internal surface 32.

[0084] In one embodiment, the particular method of infiltrating the preform 20, 30 with molten silicon can be carried out in an installation known as such.

[0085] To carry out a method according to the invention, it is appropriate to add a gas infiltration rod 10 to such an installation, and to connect such a rod 10 to a source of cold gas.

[0086] Alternatively, the step of cooling a portion of the surface of the fiber preform 20, 30 by exposing said surface to a flow of cold gas can be carried out outside the enclosure in which the infiltration step was carried out.

[0087] In one embodiment, the porosity of the fibrous preform 20, 30 may be impregnated with particles before the step of infiltrating the fibrous preform 20, 30 with the infiltration composition comprising liquid silicon.

[0088] For example, such particles make it possible to introduce into the porosity of the fiber preform 20, 30 particles which react with the liquid silicon to ensure the formation of a ceramic matrix, for example made of silicon carbide.

[0089] In one embodiment, the particles impregnating the preform 20, 30 before the infiltration step may be ceramic and / or carbon particles.

[0090] In a process as described, the step of complete cooling of the preform must allow a return to ambient temperature of the preform into which the silicon has been infiltrated.

[0091] Such a cooling step can be controlled or, on the contrary, carried out by venting the part once the cooling step of a portion of the surface has been carried out.

Claims

Claims

1. Method for manufacturing a part made of ceramic matrix composite material, comprising at least the following steps: - a step of heating a fibrous preform (20, 30) to a temperature higher than the melting temperature of the alloy; then - a step of infiltrating the fiber preform with a liquid infiltration composition, said infiltration composition comprising at least silicon; then - a step of cooling a portion of the surface of the fiber preform by exposing said surface to a flow of cold gas; then - a step of cooling the entire fiber preform, the method being characterized in that the fiber preform (20) comprises a cavity (22), and in which the portion of the surface of the fiber preform exposed to a flow of cold gas is the internal surface of said cavity and / or in that the portion of the surface of the fiber preform exposed to a flow of cold gas is a surface (32) of the preform (30) forming an angle less than or equal to 20°.

2. The manufacturing method of claim 1, wherein the fibrous preform (20, 30) comprises silicon carbide fibers, carbon fibers, or a mixture of silicon carbide fibers and carbon fibers.

3. Manufacturing method according to one of claims 1 or 2, in which the cold gas flow may comprise gases chosen from helium or argon or a mixture of these compounds.

4. Manufacturing method according to one of claims 1 to 3, in which the part is chosen from a distributor or a turbomachine blade.

5. A manufacturing method according to one of claims 1 to 4, wherein the step of cooling a portion of the surface of the preform is carried out after the entire surface of the preform has fallen below a target temperature.

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