FR3063500A1 - PROCESS FOR MANUFACTURING COATED PART - Google Patents

Abstract

The invention relates to a method for manufacturing a coated part, comprising at least the following steps: depositing a solid composition of silicon or a silicon alloy on a surface of a composite material substrate comprising a reinforcement carbon fiber and a carbon matrix, and - heat treatment of the substrate and of the solid composition deposited at a temperature greater than or equal to 1610 ° C. during which this composition is melted and reacts with the carbon of the matrix to form a silicon carbide coating on the substrate.

Description

(57) The invention relates to a method for manufacturing a coated part, comprising at least the following steps:

deposition of a solid composition of silicon or of a silicon alloy on a surface of a substrate of composite material comprising a carbon fiber reinforcement and a carbon matrix, and

heat treatment of the substrate and of the solid composition deposited at a temperature greater than or equal to 1610 ° C. during which this composition is melted and reacts with the carbon of the matrix in order to form a coating of silicon carbide on the substrate.

Invention background

The invention relates to the coating of a carbon-carbon composite material substrate with silicon carbide in order to improve the oxidation resistance of this substrate.

It is known to produce a protective coating against oxidation on the surface of carbonaceous materials in order to prolong their service life at high temperatures in an oxidizing atmosphere. Particularly known is the production of a coating of silicon carbide on parts made of carbon-carbon composite material. Such a coating constitutes a barrier against oxygen and oxidizing species. This coating also produces, in operation, silica which makes it possible to heal the cracks formed due to the differences in thermal expansion between the silicon carbide and the underlying carbonaceous part. In the prior art, the coating of silicon carbide can be formed by chemical vapor deposition ("Chemical Vapor Deposition"; "CVD") on the surface of the part to be protected after manufacture of the latter. In known techniques, the formation of the protective coating therefore constitutes an additional step, subsequent to the steps for obtaining the underlying part, which therefore lengthens the manufacture of the coated part.

There is a need to have methods, comprising a reduced number of steps, making it possible to coat silicon carbide on substrates made of carbon-carbon composite material.

Subject and summary of the invention

To this end, the invention proposes, according to a first aspect, a method of manufacturing a coated part, comprising at least the following steps:

deposition of a solid composition of silicon or of a silicon alloy on a surface of a substrate of composite material comprising a carbon fiber reinforcement and a carbon matrix, and

heat treatment of the substrate and of the solid composition deposited at a temperature greater than or equal to 1610 ° C. during which this composition is melted and reacts with the carbon of the matrix in order to form a coating of silicon carbide on the substrate.

In the following, the coating of silicon carbide thus formed will be designated by the expression “coating SiC”.

The substrate is, in the invention, treated by a final heat treatment at high temperature making it possible to reorganize the carbon planes in order to reduce the sensitivity to oxidation of the substrate. The invention advantageously makes it possible to simplify the formation of the SiC coating by taking advantage of the final reorganization heat treatment to form this coating, thus leading to a reduction in the number of manufacturing steps compared with the techniques of the prior art. The infiltration of the silicon element in the molten state through the surface pores of the substrate makes it possible to form the coating SiC by reaction with the carbon of the matrix.

In an exemplary embodiment, the solid composition is deposited on the surface of the substrate in a surface content less than or equal to 15 mg / cm ² .

The deposition of a limited quantity of solid composition advantageously makes it possible to form an SiC coating having a reduced thickness. As a result, the SiC coating formed has reduced cracking compared to the SiC coatings formed by the techniques of the prior art which can be thicker. This reduced cracking further improves the protection provided by the SiC coating.

In an exemplary embodiment, the method further comprises a step of forming a layer comprising a metal phosphate devoid of boron on the coating of silicon carbide obtained.

The layer formed, in this case, on the SiC coating is devoid of a boron-based compound which constitutes a wetting agent for carbon and which can limit the optimum temperature for use to 1400 ° C. The SiC coating formed as described above advantageously makes it possible to obtain a good coating of the substrate with such a layer, even if the latter is devoid of carbon-wetting agent.

In an exemplary embodiment, the matrix has an external pyrocarbon phase obtained from at least one precursor in the gaseous state. By "external matrix phase" is meant the matrix phase formed last, furthest from the fibers of the reinforcement.

In an exemplary embodiment, the temperature imposed during the heat treatment is greater than or equal to 1650 ° C.

In an exemplary embodiment, the substrate is a friction element and the surface is a friction surface of this element.

In an exemplary embodiment, the substrate is a brake disc.

Brief description of the drawings

Other characteristics and advantages of the invention will emerge from the following description given without limitation, with reference to the appended drawings, in which:

FIG. 1 is a flowchart showing a succession of steps of an example of a method according to the invention,

FIGS. 2 to 6 illustrate, schematically and partially, the formation of an SiC coating in the context of an example of a method according to the invention,

FIG. 7 is a photograph of a coated part obtained by implementing an example of a method according to the invention, and

- Figure 8 is a test result comparing the performance in terms of resistance to oxidation of a part coated by a method according to the invention and a part coated by a method outside the invention.

Detailed description of embodiments

In the description which follows, consideration is more particularly given to coating a substrate forming a brake disc of carbon-carbon composite material, it being understood that other types of carbon-carbon composite materials can be coated in the same way, such as brake pads for example.

The production of a brake disc includes the development of an annular fibrous preform made of carbon fibers and the densification of the preform by a carbon matrix. The fibrous preform is intended to form the fibrous reinforcement of the substrate made of carbon-carbon composite material to be obtained.

In a first step E1, the fibrous preform is firstly manufactured from a plurality of carbon fibers. The preform is produced by superimposing fibrous layers and bonding the layers together by needling. The fibrous layers can be formed by a felt, a fabric, a knitted fabric, a unidirectional sheet of threads, cables or strands, or a complex formed by several unidirectional sheets superimposed with different directions and linked together by light needling. The different layers are stacked and needled one by one in a manner known per se. The layers are stacked and needled until the desired preform thickness is obtained.

The fibrous layers are made of carbon fibers or carbon precursor fibers, for example preoxidized polyacrylonitrile fibers. In the latter case, the transformation of the precursor into carbon is carried out by heat treatment carried out on the fibrous layer before or after preparation of the preform.

An annular preform can be obtained by stacking and needling layers of planar shape and cutting the preform by punching at the end of the needling process. It is also possible to use precut annular fibrous layers. These methods are well known, so there is no need to describe them here in detail.

In a second step E2, the carbon fiber preform obtained is densified by a carbon matrix. The preform can be densified by a pyrocarbon matrix formed by chemical vapor infiltration from one or more precursors in the gaseous state. One can for example use a gaseous phase formed of a mixture of methane and propane and the densification can be carried out at a temperature between approximately 850 ° C and 1050 ° C under a reduced pressure ranging between approximately 0.5 kPa and 3 , 3 kPa. The matrix may be formed, in whole or in part, of pyrocarbon obtained from one or more precursors in the gaseous state. The matrix can be entirely formed of pyrocarbon obtained from at least one precursor in the gaseous state. Alternatively, the matrix may at least partly be formed from carbon formed from a precursor in the liquid state. In the latter case, the carbon is formed by pyrolysis of at least one precursor in the liquid state, such as a phenolic or furanic resin. In an exemplary embodiment, the matrix may comprise a first phase in pyrocarbon obtained from at least one precursor in the gaseous state and a second phase in carbon obtained from a precursor in the liquid state. In an exemplary embodiment, the external matrix phase is made of pyrocarbon obtained from at least one precursor in the gaseous state, for example by chemical vapor infiltration.

The matrix densifies the fibrous reinforcement by being present in the porosity of the latter. The matrix constitutes a continuous material phase. The matrix coats the fibers of the fibrous reinforcement. The fibers are present in the matrix. The matrix can occupy the majority (i.e. more than 50%) of the volume of the accessible porosity of the fibrous reinforcement. In particular, the matrix can occupy more than 75%, or even substantially all, of the volume of this accessible porosity.

In a third step E3, the solid composition of silicon or of a silicon alloy is deposited on the external surface of the substrate made of carbon-carbon composite material thus produced. The solid composition is deposited on the substrate after densification of the latter by the carbon matrix. The residual porosity of the substrate, before deposition of the solid composition, may be less than or equal to 20% by volume percentage. The solid composition is deposited in contact with the surface of the substrate made of composite material. The solid composition is deposited in contact with the carbon matrix of the substrate.

The solid composition can be formed from pure silicon. Alternatively, the solid composition can be formed from a silicon alloy, such as an alloy of silicon and nickel, an alloy of silicon and germanium or an alloy of silicon and aluminum. The solid composition may be in the form of a powder. The average size (D50) of the grains of this powder can be between 0.1 μm and 25 μm.

The solid composition can be deposited by the liquid route. In this case, the deposition of the solid composition can comprise a first step during which a suspension comprising the solid composition in a liquid medium is deposited on the surface of the substrate, and a second step of drying this deposited suspension in order to remove the liquid medium. Heating can be carried out in order to carry out the drying. In the latter case, the liquid medium can be removed by evaporation. The liquid medium can be aqueous or organic. After drying, the solid composition initially present in suspension in the liquid medium remains on the surface of the substrate. The suspension comprising the solid composition can be applied using an applicator, such as a brush, or by spraying. As a variant, the solid composition could be directly deposited on the surface of the substrate (without a liquid medium). In the latter case, the solid composition may be in the form of a powder or a veil of material.

The solid composition is advantageously deposited on the surface of the substrate in a surface content less than or equal to 15 mg / cm ² , for example less than or equal to 10 mg / cm ² . This surface content may for example be between 4 mg / cm ² and 15 mg / cm ² , or even between 1 mg / cm ² and 15 mg / cm ² . When the solid composition is deposited by the liquid route (suspension), the surface content is evaluated after elimination of the liquid medium from the suspension.

In a fourth step E4, a high temperature heat treatment is carried out which makes it possible, on the one hand, to reorganize the carbon of the substrate and on the other hand to form the coating SiC by reaction of the silicon deposited with the carbon of the matrix. The temperature imposed during this heat treatment is higher than the melting temperature of the solid composition and therefore makes it possible to melt the latter. The molten silicon element reacts with the carbon in the matrix to form the SiC coating. The adhesion of this SiC coating is ensured by chemical bond between the deposited silicon element and the carbon of the substrate. The temperature imposed during the heat treatment can be greater than or equal to 1610 ° C, for example between 1650 ° C and 1850 ° C. The duration of the heat treatment may be greater than or equal to 10 seconds, for example greater than or equal to 15 minutes, for example between 15 minutes and 20 hours. The heat treatment can be carried out under a neutral atmosphere, for example under nitrogen or argon.

A fifth step E5 can optionally be carried out during which an additional protective layer is deposited in contact with the SiC coating formed on the surface of the part. This protective layer is a protective layer against oxidation. This protective layer comprises a metal phosphate, such as an aluminum phosphate, and is advantageously devoid of boron. The metal phosphate can for example be mono-aluminum phosphate AI (H ₂ PO4) 3 (“MALP”: “Mono-Aluminum-Phosphate”). The protective layer can be formed by applying a liquid composition devoid of boron comprising the metal phosphate followed by a heat treatment of this deposited liquid composition.

The formation of the SiC coating which has just been described is illustrated diagrammatically in connection with FIGS. 2 to 6.

In the example illustrated, a suspension comprising a powder 5 of silicon or of a silicon alloy in a liquid medium 7 is firstly deposited on the surface S of the substrate 1 (FIG. 2). The liquid medium 7 is then removed by evaporation in order to leave only the silicon powder or the silicon alloy 5 on the surface S of the substrate (FIG. 3). The heat treatment is then carried out at high temperature in order to melt the powder 5 comprising silicon present on the surface of the substrate (FIG. 4). A molten composition 15 of silicon or of a silicon alloy is thus obtained. After reaction between the silicon of the molten composition 15 and the carbon of the substrate 1, a part 10 is obtained comprising the SiC coating 17 covering the underlying substrate 1 (FIG. 5). If a limited amount of solid composition has been deposited, the thickness e of the SiC coating formed may be less than or equal to 5 μm, for example 4 μm. This thickness e can for example be between 1 pm and 5 pm, or even between 2 pm and 5 pm. It is then possible to form a layer of protection against oxidation 18 on the SiC coating 17 thus formed (FIG. 6).

The coated part obtained after the high temperature heat treatment can then optionally be machined to the desired dimensions before being used. The SiC coating formed gives the part effective and lasting anti-oxidation protection over time.

Example

A suspension having the formulation below was first prepared:

- 50% by mass of a silicon powder whose average particle size (D50) is close to 7.5 μm,

- 47.5% by mass of demineralized water, and

- 2.5% by mass of polyvinyl alcohol (PVA).

This suspension was applied by brush on a C / C substrate before final heat treatment. The suspension thus applied was then dried by heating to 90 ° C in air. The amount of silicon powder deposited on the substrate after drying was less than or equal to 15 mg / cm ² .

A heat treatment at 1650 ° C under nitrogen was carried out in order to reorganize the carbon of the substrate and form the SiC coating. A non-cracked SiC 17 coating, chemically bonded to the underlying C / C 1 substrate, was obtained on the surface of this substrate.

A layer of aluminum phosphate 18 was then deposited on the SiC coating 17 obtained.

Figure 7 is a photograph of the part obtained by the method described above. The performances in terms of oxidation resistance of the part thus obtained were compared with those presented by a part treated by a process outside the invention in which an aluminum phosphate layer is deposited (without formation of the SiC coating by the process according to the invention).

The protected parts were subjected to the oxidation protocol comprising the following sequence of steps:

- thermal cycle comprising the following sequence of steps: exposure to 650 ° C in air for 5 hours, return to ambient temperature, exposure to 850 ° C in air for 1 hour, return to ambient temperature, exposure to 650 ° C in air for 5 hours,

- repetition of the thermal cycle defined above,

- pollution of the room with potassium acetate at room temperature,

- carrying out the thermal cycle defined above repeated once.

FIG. 8 represents the results obtained. The curve denoted C corresponds to the part treated by the process outside the invention. The curve denoted I corresponds to the part coated by the method according to the invention. It can be seen that the invention gives the part an increased resistance to oxidation compared with the process outside the invention.

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

Claims (7)

1. Method for manufacturing a coated part (10), comprising at least the following steps: depositing a solid composition (5) of silicon or of a silicon alloy on a surface (S) of a substrate (1) of composite material comprising a carbon fiber reinforcement and a carbon matrix, and heat treatment of the substrate (1) and of the solid composition (5) deposited at a temperature greater than or equal to 1610 ° C. during which this composition is melted and reacts with the carbon of the matrix in order to form a coating (17) of silicon carbide on the substrate d). 2. Method according to claim 1, wherein the solid composition (5) is deposited on the surface (S) of the substrate (1) in a surface content less than or equal to 15 mg / cm ² . 3. The method of claim 1 or 2, wherein the method further comprises a step of forming a layer (18) comprising a metal phosphate devoid of boron on the coating (17) of silicon carbide obtained. 4. Method according to any one of claims 1 to 3, wherein the matrix has an external phase of pyrocarbon obtained from at least one precursor in the gaseous state. 5. Method according to any one of claims 1 to 4, wherein the temperature imposed during the heat treatment is greater than or equal to 1650 ° C. 6. Method according to any one of claims 1 to 5, wherein the substrate (1) is a friction element and wherein the surface (S) is a friction surface of this element. 7. The method of claim 6, wherein the substrate (1) is a brake disc. 1/2