WO2022069814A1

WO2022069814A1 - Method for manufacturing a hollow cmc part

Info

Publication number: WO2022069814A1
Application number: PCT/FR2021/051611
Authority: WO
Inventors: Amandine LORRIAUX; Matthieu Arnaud GIMAT; Emilie Chantal Gisèle MENDEZ; Wen Zhang
Original assignee: Safran; Safran Ceramics
Priority date: 2020-09-29
Filing date: 2021-09-21
Publication date: 2022-04-07
Also published as: FR3114532B1; FR3114532A1

Abstract

The invention relates to a method for manufacturing a hollow CMC part using a hybrid core (1) comprising an inner portion (10) and a coating (12) made of carbon, silicon or silicon alloy.

Description

Title of the invention: Process for manufacturing a hollow CMC part

Technical area

The invention relates to the general field of processes for manufacturing parts made of composite material with a matrix at least partially made of ceramic, called CMC parts, which comprise a hollow part.

Prior technique

To manufacture a hollow part, it is known from lost wax casting techniques to use an oxide ceramic or refractory metal core to form the hollow part, then to eliminate this core by chemical dissolution (also called shakeout step ). During this step, the parts can be placed in an autoclave, at high pressure and temperature, then different washing cycles using chemical baths (basic: NaOH and/or KOH or acids for example HF) can be applied.

Nevertheless, the direct application of these techniques to the manufacture of CMC parts can lead during chemical dissolution to damage to these parts by reaction with the chemical baths used, for example boron nitride interphase or carbon carbide. matrix silicon can be consumed during this step.

It is desirable to have a method for manufacturing a hollow CMC part that makes it possible to eliminate the core without affecting the part, while maintaining simple implementation.

Disclosure of Invention

The invention proposes a method for manufacturing a hollow part made of composite material with an at least partially ceramic matrix, comprising at least:

- the formation of an assembly comprising a fibrous preform having the shape of the part to be manufactured and defining an internal cavity in which is present a core, the core having a core covered with a fugitive coating of carbon, or a fugitive coating of silicon or a silicon alloy, the core being of a material different from the material of the fugitive coating,

- the formation of a ceramic matrix phase in the porosity of the fibrous preform around the core of the core,

- removal of the fugitive coating from the core by heat treatment, and

- evacuation of the core of the core outside the internal cavity after removal of the fugitive coating.

In the following, the expression “part made of composite material with an at least partially ceramic matrix” will be designated by the expression “part made of CMC” for reasons of brevity.

The core is hybrid and has a carbon coating, or else a silicon or silicon alloy coating. This coating is formed of a fugitive material which can be eliminated under the effect of a heat treatment, in order to allow the evacuation of the core from the internal cavity following this elimination. This evacuation is thus carried out mechanically in a simple manner without having to use a chemical bath liable to alter the CMC part obtained.

In an exemplary embodiment, the fugitive coating is made of carbon and is removed by oxidation heat treatment after formation of the ceramic matrix phase.

In particular, the oxidation heat treatment can be carried out at a temperature greater than or equal to 600° C. in air.

Alternatively, the fugitive coating is silicon or a silicon alloy, and the coating is melted away and the coating material molten infiltrates the pores of the fiber preform to form the ceramic matrix phase. According to this variant, there is removal of the coating from the core of the core by melting this coating. In this case, the coating serves as a source of silicon to form the ceramic matrix phase. The formation of the ceramic matrix phase takes place here concomitantly with the removal of the coating.

In an exemplary embodiment, the core is made of oxide material.

The implementation of a core having a core of oxide material makes it possible to manufacture a solid part of the core at low cost. In an exemplary embodiment, yarns of the fiber preform are coated with a boron nitride (BN) interphase.

In an exemplary embodiment, the fiber preform comprises ceramic yarns, for example silicon carbide (SiC) yarns.

The invention also relates to a turbomachine part manufactured by the method described above.

In an exemplary embodiment, the part is a turbomachine distributor or part of a turbomachine distributor.

Brief description of the drawings

[Fig. 1] FIG. 1 schematically and partially represents a step of a first example of a method according to the invention.

[Fig. 2] FIG. 2 schematically and partially represents a step of the first example of a method according to the invention.

[Fig. 3] FIG. 3 schematically and partially represents a step of the first example of a method according to the invention.

[Fig. 4] FIG. 4 schematically and partially represents a step of a second example of a method according to the invention.

[Fig. 5] FIG. 5 schematically and partially represents a step of the second example of a method according to the invention.

[Fig. 6] FIG. 6 schematically and partially represents a step of the second example of a method according to the invention.

Description of embodiments

A description will be given, in connection with FIGS. 1 to 3, of the progress of a first example of a method according to the invention in which a core 1 with a coating 12 of carbon is used.

A fibrous preform 3 of the part to be obtained is first formed in a manner known per se, for example by weaving yarns. The weave may be a three-dimensional weave, for example with an interlock weave. The wires can be ceramic, for example silicon carbide, or carbon. The fibrous preform 3 is intended to form the fibrous reinforcement of the part to be obtained. The fibrous preform 3 can define an internal cavity 5 in which a core 1 can be inserted. Before insertion of core 1, the wires of the preform may have been coated with an interphase. The interphase has a function of weakening the composite material which promotes the deflection of any cracks reaching the interphase after having propagated in the matrix, preventing or delaying the breaking of wires by such cracks. As a variant, the formation of the interphase can be done after inserting the core 1 into the preform 3. The interphase can be made of boron nitride. The techniques for forming an interphase are known per se and do not need to be further detailed here.

After insertion of the core 1, an assembly 9 is obtained comprising the fibrous preform 3 around the core 1. The core 1 is present inside the internal cavity 5. The core 1 can have the same shape and the same dimensions as the hollow part of the part to be obtained. The core 1 can completely fill the internal cavity 5. Once inserted the core 1 can go from one end 3a to the other 3b of the preform, that is to say pass through it entirely. The core 1 is in contact with the preform 3. The assembly 9 can be present in a shaper making it possible to bring the preform 3 surrounding the core 1 to the desired shape.

The core 1 is made of different materials and comprises, in the example shown, a core 10 of a material other than carbon coated with a coating 12 of carbon. Coating 12 may be made of pyrolytic carbon. As illustrated, the coating 12 can be in contact with the core 10. The coating 12 can be monolayer. Coating 12 may be in contact with fiber preform 3 located around core 1.

The core 10 is made of refractory material, which is stable under the conditions of use. The core 10 can be made of ceramic material, for example silicon carbide or oxide, or alternatively be metallic, for example superalloy. In the case where the core 10 is made of oxide, it can comprise silica (SiO ₂ ), alumina (Al ₂ O ₃ ) and/or zirconia (ZrO ₂ ). The core 10 can be obtained by an injection molding process or by additive manufacturing. A core of substantially cylindrical shape has been shown, but this does not depart from the scope of the invention when the latter has another shape, such as a parallelepipedic shape for example. Once the core 10 has been obtained, the coating 12 can be formed thereon, for example so as to entirely cover its surface S intended to be surrounded by the preform 3. The coating 12 can cover the entire surface S core 10 as shown. Alternatively, the coating 12 can partially cover the surface S, only on the areas of this surface S facing the preform 3. The coating 12 can be formed on the core 10 by vapor phase deposition, for example by deposition chemical vapor phase (“Chemical Vapor Deposition”; “CVD”) or physical vapor phase deposition (“Physical Vapor Deposition”; “PVD”), by technique of calefaction or polymer pyrolysis. In some cases, the deposition of the coating 12 can be followed by a heat treatment in order to consolidate the coating 12, and the core 10 possibly. The thickness el of the coating 12 can range from a few nanometers to a few millimeters. This thickness el can be between 1 nm and 10 mm.

The process continues with the densification of the preform 3 surrounding the core 1, that is to say by the formation of a matrix in the porosity of this preform 3. The matrix can comprise at least one ceramic matrix phase, for example silicon carbide. The ceramic matrix phase can be obtained by chemical vapor infiltration or infiltration of silicon or a silicon alloy in the molten state. It is possible in particular to carry out a first step of forming a first phase of ceramic matrix by chemical vapor infiltration followed by a second step of forming a second phase of ceramic matrix by infiltration of silicon or an alloy of molten silicon. The CMC part 15 is thus obtained comprising the fibrous preform 3 densified by at least one ceramic matrix phase 17.

Once the CMC part 15 has been obtained, the coating 12 is removed by treatment with a hot oxidizing atmosphere. This treatment can be carried out at a temperature greater than or equal to 600° C., for example in air. The elimination of the coating 12 leads, as illustrated, to the appearance of a clearance J between the core 10 and the part 15 which makes it possible to evacuate the core 10 (retraction arrow R) without difficulty outside the internal cavity 5. The evacuation here is mechanical and does not require, in particular, the use of a chemical bath. By leaving the core 10 of the cavity 5, the hollow part 18 of the part 15 is thus released. An exemplary embodiment has just been described where the coating 12 of the core 1 is made of carbon and where the coating 12 of the core is removed after formation of the ceramic matrix phase. The invention is however not limited to this case, the second example which will now be described in connection with FIGS. 4 to 6 relates to a coating 22 comprising silicon covering the core of the core and in which the phase of ceramic matrix is formed during the removal of the coating from the core.

The elements identical to those of FIGS. 1 to 3 bear the same reference symbols and the description given above applies to the present case and is not repeated for reasons of brevity.

As described above, an assembly 19 is obtained comprising the core 11 inside the fiber preform 3. The core 11 differs from that described above in that it comprises a coating 22 of silicon or of a silicon alloy. silicon covering the core 10 which is made of a material distinct from the coating 22. As above, the coating 22 can be in contact with the core 10. The coating 22 can be monolayer. Coating 22 may be in contact with fiber preform 3 located around core 11.

The coating 22 can be formed on the core 10 by vapor phase deposition, for example by chemical vapor phase deposition (“Chemical Vapor Deposition”; “CVD”) or physical vapor phase deposition (“Physical Vapor Deposition”; “ PVD”), or by lost wax casting technique.

The method comprises the densification of the preform 3 surrounding the core 11. A first phase of ceramic matrix can be produced by chemical vapor infiltration, then proceed to infiltration in the melt state. In this example, the removal of the coating 22 is done by melting this coating 22 under heat treatment. The temperature imposed to achieve this fusion can be greater than or equal to 1400°C. The coating 22 thus molten can infiltrate by capillarity (arrows I) the porosity of the fibrous preform 3. The coating 22 serves as a source of silicon for the infiltration in the molten state. The thickness e2 of the coating 22 is determined according to the quantity of silicon to be added to form the ceramic matrix phase and so as to limit the quantity of excess silicon leading to free silicon at the end of infiltration. Infiltration in the molten state can be non-reactive or reactive, in the latter case the fibrous preform 3 can comprise carbon particles in its porosity reacting with the molten silicon. When the melt infiltration is complete, it is possible to recover the core (arrow R), which, as in the previous example, is no longer attached to the CMC part.

Regardless of the embodiment considered, the part obtained 15 may have a matrix which is predominantly ceramic by volume, for example entirely ceramic. Whatever the embodiment considered, the hollow part 18 of the part can constitute a cooling cavity, through which cooling air is intended to circulate in operation.

Whatever the embodiment considered, the manufactured part can be a part of a turbomachine, for example of an aeronautical turbomachine. The part may be a distributor or part of a turbomachine distributor. As a variant, the part can be a vane, fixed or mobile, of a turbomachine turbine.

The expression "between ... and ..." must be understood as including the limits.

Claims

8 Claims

[Claim 1] A method of manufacturing a hollow part (15) made of composite material with an at least partially ceramic matrix, comprising at least:

- the formation of an assembly (9; 19) comprising a fibrous preform (3) having the shape of the part to be manufactured and defining an internal cavity (5) in which is present a core (1; 11), the core having a core (10) covered with a fugitive coating (12) of carbon, the core being of a material different from the material of the fugitive coating,

- removal of the fugitive coating from the core by heat treatment, and

- the evacuation (R) of the core of the core outside the internal cavity after elimination of the fugitive coating.

[Claim 2] A method according to claim 1, wherein the fugitive coating (12) is carbon and is removed by oxidative heat treatment after formation of the ceramic matrix phase.

[Claim 3] Process according to claim 2, in which the oxidation heat treatment is carried out at a temperature greater than or equal to 600°C in air.

[Claim 4] A method according to any of claims 1 to 3, wherein the core is of oxide material.

[Claim 5] A method according to any one of claims 1 to 4, wherein yarns of the fiber preform (3) are coated with an interphase of boron nitride.

[Claim 6] A method according to any of claims 1 to 5, wherein the fibrous preform (3) comprises ceramic yarns.

[Claim 7] A method according to any one of claims 1 to 6, wherein the manufactured part is a turbomachine part.

[Claim 8] A method according to claim 7, wherein the part is a turbomachine nozzle or part of a turbomachine nozzle.