Method for protecting a part made of carbon-carbon composite material against oxidation

Abstract

The invention relates to a method for producing a coating for protecting against oxidation on at least one outer surface of a substrate made of a carbon-carbon composite material, the method comprising at least the following steps: - a step (20) of applying an impregnation composition to at least part of an outer surface of a substrate made of carbon-carbon composite material, said impregnation composition comprising at least one metal phosphate; and - a heat treatment step (30) carried out at a temperature of between 700°C and 900°C; subsequently - one or more steps (40) involving the dry deposition of a solid composition on at least part of the outer surface of the substrate made of carbon-carbon composite material, said solid composition being capable of forming a glass coating for protecting against oxidation, the method being characterised in that the solid composition comprises glass powder, a refractory ceramic compound and a rare earth oxide.

Description

Description Title of the invention: Method for protecting a carbon / carbon composite material part against oxidation Technical Field

[0001] The invention relates to the field of carbon / carbon composite material parts and more specifically to methods of protecting such parts against oxidation. Previous technique

[0002] The invention relates to the protection against oxidation of parts made of carbon / carbon composite material, that is to say in a material comprising a fibrous reinforcement densified by a matrix in which the fibrous reinforcement and the matrix comprise carbon.

[0003] A particular area of ​​application of the invention is the protection against oxidation of C / C composite brake discs, and in particular of aircraft brake discs, for example airplanes, or brake discs of land vehicles.

[0004] In an oxidizing environment, the ability of such parts to maintain good mechanical properties at high temperatures depends on the presence of effective protection against carbon oxidation. Indeed, after its fabrication, the composite material usually exhibits residual internal porosity, allowing the surrounding environment access to the core of the material.

[0005] Furthermore, in certain applications, oxidation protection must remain effective in the presence of moisture and / or carbon oxidation catalysts. This is particularly true for C / C composite aircraft brake discs, which may be exposed to moisture present on runways and come into contact with carbon oxidation catalysts such as potassium acetates or formates found in de-icing products commonly used on runways.

[0006] Oxidation protection for such parts is generally provided by coatings applied to the carbon / carbon composite material. However, such external coatings are susceptible to mechanical degradation caused by the friction, shocks, and vibrations that are inevitable for such parts.

[0007] It is also considered to introduce a protective layer against oxidation within the internal porosity of composite parts to overcome such drawbacks. For example, documents FR 2 726 554 and EP 3 072 866 describe methods for protecting a carbon / carbon composite part against oxidation using aqueous compositions that, after heat treatment, form an oxidation barrier within the part's internal porosity.

[0008] However, it is desirable to improve the oxidation resistance of such parts in order to increase their lifespan. Description of the invention

[0009] The inventors found that it is possible to improve the homogeneity of the protective layer formed in the porosity of the part, while increasing deposition yields and further improving the oxidation resistance properties and temperature resistance of carbon / carbon composite material parts.

[0010] To this end, the inventors propose a method for manufacturing a protective coating against oxidation on at least one external surface of a carbon / carbon composite substrate, the method comprising at least the following steps: - a preparation step of at least the external surface of the substrate intended to be coated; - an application step on at least part of an external surface of a carbon / carbon composite substrate of an impregnation composition comprising at least one metallic phosphate; and - a heat treatment step of the impregnation composition carried out at a temperature between 700°C and 900°C; then - one or more dry deposition steps on at least part of the external surface of the substrate, using a carbon / carbon composite material of a solid composition suitable for forming an amorphous protective coating against oxidation, the process being characterized in that the solid composition comprises glass powder, a refractory ceramic compound and / or a rare earth oxide.

[0011] The inventors observed that such a protection process allows the formation of an oxidation barrier within the substrate's internal porosity. It is advantageous for the protection to be present within the internal porosity because it is thus protected from the shocks or friction that the part may experience.

[0012] Furthermore, unlike the protection processes considered in the prior art, the solid composition of an amorphous protective coating is deposited by dry process.

[0013] In one embodiment, the solid composition comprises a rare earth oxide. It is to the inventors' credit that they introduced this rare earth oxide into the process of the invention.

[0014] This significantly increases the temperature resistance properties of the coating of the invention, as it has been determined that rare earths increase the emissivity properties of coatings, enabling them to dissipate heat by radiation and thus increasing their temperature resistance.

[0015] In general, the coating composition can be adapted to modify its emissivity. This allows the thermal properties to be adapted to environmental constraints or those intrinsic to the substrate.

[0016] "Dry deposition" means that the process of the invention does not require the use of a third carrier liquid when depositing the solid composition and infiltrating the internal porosity, unlike prior art processes which use slips.

[0017] In a dry deposition process the solid composition can be sprayed in a liquid, solid or paste form, without third carrier liquid, and it forms a solid deposit once its deposition is complete.

[0018] For example, dry deposition of the solid composition can be achieved by plasma spraying, electrostatic spraying, or high-speed thermal powder spraying.

[0019] Preferably, the dry deposition of the solid composition is carried out by plasma spraying. Indeed, this particular deposition method offers the best properties for the resulting parts.

[0020] For the purposes of this invention, it is understood that the impregnation of the internal porosity of the part should be understood as a deep impregnation of the internal porosity, that is to say that the amorphous coating for protection against oxidation is not only formed on the surface of the part, but that it extends from the surface deep into the part in its near-surface internal porosity.

[0021] For example, heat impregnation treatment allows the formation of an amorphous coating for protection against oxidation up to a depth greater than or equal to 0.5 mm, measured from the external surface of the part.

[0022] The choice of the dry method for depositing the solid composition makes it possible to obtain, after a heat treatment of impregnation, an amorphous coating for protection against oxidation directly in the internal porosity of the part with an increased deposition yield compared to prior art deposition methods.

[0023] Also, the amorphous coating obtained is more homogeneous than with processes requiring carrier liquids for the solid composition.

[0024] Furthermore, unlike prior art processes, it is to the inventors' credit that they understood that no heat treatment subsequent to dry deposition is necessary.

[0025] In one embodiment, the process includes no heat treatment steps other than the impregnation compounding step. In particular, the carbon / carbon composite part includes a protective coating that is directly usable as such after the dry deposition step. This reduces the process time and cost.

[0026] The substrate preparation step allows for obtaining a surface tension compatible with the application of the impregnation solution.

[0027] In one embodiment, the substrate preparation step may be a step of immersing the substrate in a surfactant solution under ultrasound, possibly followed by drying.

[0028] Such a substrate preparation step allows for an improvement in the surface condition for the impregnation step, and thus of the final part.

[0029] In one embodiment, the amorphous oxidation protection coating can be formed in the internal porosity of the part and throughout the entire thickness of said porosity.

[0030] In one embodiment, the impregnation composition may include a metallic phosphate salt, for example dihydrogen phosphate A I-bPO s.

[0031] The impregnation composition improves the impregnation of the porosity by the solid composition during the dry deposition stage.

[0032] In one embodiment, the heat treatment of the impregnation composition can be carried out for a period of between 7 and 15 hours.

[0033] Heat treatment allows the impregnation composition to penetrate the internal porosity of the part more deeply, forming a layer that traps carbon oxidation catalysts and thus improves the part's oxidation resistance. Furthermore, the presence of the impregnation composition ensures better penetration of the preform's internal porosity by the solid composition.

[0034] In one embodiment, the solid composition may consist of a plurality of particles, the average size of which is less than or equal to 10 pm. Unless otherwise specified, "size" refers to the dimension given by the statistical particle size distribution at half the number of the population, known as D50.

[0035] In one embodiment, the solid composition suitable for forming an amorphous coating for protection against oxidation can comprise between 40% and 100% by mass of glass powder, or even between 70% and 100% by mass of glass powder.

[0036] In one embodiment, the amorphous protective coating can be a glass-based coating.

[0037] In one embodiment, the glass powder of the solid composition can be chosen from a silicate glass powder, or even a borosilicate glass powder.

[0038] For example, glass powder can be obtained from silica SiCh and one or more of the compounds chosen from phosphorus pentoxide P2O5, potassium oxide K2O, sodium oxide Na2O, aluminium oxide Al2O3, boron sesquioxide B2O3, zinc oxide ZnO, barium oxide BaO, titanium dioxide TiCh, lithium oxide Li2O, iron(III) oxide Fe2O3, calcium oxide CaO.

[0039] In one embodiment, the solid composition suitable for forming an amorphous coating for protection against oxidation may comprise between 0% and 30% by mass of a refractory ceramic compound.

[0040] In one embodiment, the refractory ceramic compound of the solid composition may be selected from metallic borides, for example titanium boride TiB2, zirconium boride ZrB2, carbides, for example boron carbide B4C, silicon carbide SiC, zirconium carbide ZrC, tantalum carbide TaC, tungsten carbide WC, nitrides, for example boron nitride BN, aluminium nitride AIN, titanium nitride TiN, silicon nitride Si3N4 or a mixture of two or more of the compounds in this list.

[0041] In one embodiment, the solid composition suitable for forming an amorphous coating for protection against oxidation may comprise between 0% and 30% by mass of a rare earth oxide.

[0042] In one embodiment, the rare earth oxide of the solid composition can be chosen from samarium oxide SrmCh, neodymium oxide Nd?O3, gadolinium oxide Gd2O3, holmium oxide HO2O3, praseodymium oxide Pr2O3, europium oxide EU2O3, dysprosium oxide Dy2O3, ytterbium oxide Yb2O3.

[0043] Rare earths are understood here and in the present application in the usual sense of the field, namely as the set of elements comprising scandium, yttrium and all the lanthanides, i.e. the elements with atomic numbers 21, 39 and 57 to 71, as well as actinium and all the actinides, i.e. the elements with atomic numbers 89 to 102.

[0044] In one embodiment, the process comprises a plurality of dry deposition steps.

[0045] Indeed, it is to the credit of the inventors that they determined that, surprisingly, for a given quantity of solid composition, it is more advantageous to carry out multiple deposition steps, each with a fraction of the quantity of solid composition, rather than a single step.

[0046] For example, the process includes between 2 and 5 steps of depositing a solid composition.

[0047] In one embodiment, the solid composition has the same composition for each of the deposition steps.

[0048] Alternatively, the solid composition may have a composition that varies between each of the deposition stages.

[0049] In one embodiment, the carbon / carbon composite material substrate is a friction part, for example, an aircraft brake disc.

[0050] Indeed, it is for such parts that the advantages of the invention offer optimal performance. Brief description of the drawings

[0051] [Fig. 1] Figure 1 schematically represents a process in one embodiment. Description of the implementation methods

[0052] The invention is now described by means of figures illustrating particular embodiments of the invention which are present only for illustrative purposes in order to better understand the invention, and which should not be interpreted as limiting the invention.

[0053] Figure 1 represents a diagram of a method for implementing the invention.

[0054] Such a process includes a first step 10 of preparing a substrate in carbon / carbon composite material.

[0055] As described, preparing the carbon / carbon substrate or the substrate surface to be covered by the protective coating allows for better impregnation of the impregnation composition.

[0056] As shown, step 10 is followed, and preferably directly followed by a step 20 of application of the impregnation composition.

[0057] Step 20 is an application step to at least part of a carbon / carbon composite material substrate of an impregnation composition comprising at least one metallic phosphate.

[0058] This step allows the internal porosity of the substrate to be impregnated by the impregnation composition to obtain the effects described above.

[0059] In particular, the impregnation composition improves the oxidation resistance of the substrate, compared to a process in which this step 20 would be omitted.

[0060] In one embodiment, the metallic phosphate in the impregnation composition is aluminum phosphate. Alternatively, manganese, zinc, calcium, or magnesium phosphate could be used, with or without the addition of phosphoric acid. In another embodiment, the metallic phosphate is mono-aluminum phosphate, Al(H₂PO₄)₃.

[0061] In other embodiments, complex phosphates can also be used, for example, complex aluminum and calcium phosphates.

[0062] The impregnation composition, after impregnation into the internal porosity, allows the formation of a layer that traps the catalysts of carbon oxidation, thus improving resistance to oxidation.

[0063] Indeed, it is known that phosphates help to counteract the effect of catalytic agents of carbon oxidation, and in particular alkali or alkaline earth elements.

[0064] The impregnation composition can be applied by brush, spraying or by projection onto an external surface of the part.

[0065] In one embodiment, the amount of impregnation composition deposited during step 20 may be greater than or equal to 15 mg / cm² 2 , or even greater than or equal to 25 mg / cm² 2 The measurement refers to the impregnated composition before heat treatment.

[0066] The amount of impregnation compound deposited is expressed as a function of the surface area of ​​the coated part in order to compare the oxidation resistance properties observed for parts with different surface areas. The same will be done for the quantities of solid compounds described below.

[0067] As shown in Figure 1, step 20 of applying the impregnation composition is followed, and is preferably directly followed, by a heat treatment step 30.

[0068] For example, such a heat treatment step 30 can be carried out between 700°C and 900°C under an inert atmosphere.

[0069] Such a heat treatment step 30 allows the impregnation composition to permeate the internal porosity of the part and form a layer trapping the carbon oxidation catalysts, thus improving the oxidation resistance of the part.

[0070] The heat treatment step is followed, and preferably directly followed, by a step 40 of dry application of the solid composition.

[0071] Step 40 provides excellent protection against oxidation of the carbon / carbon composite substrate, or at least of the surface coated by the coating process.

[0072] Unlike prior art processes, once the solid composition has been deposited by dry means, the process requires no further steps to impart its improved properties to the substrate.

[0073] In particular, the process does not require a final heat treatment step for the part to be functional and to have its properties improved.

[0074] Thus, we have a process that is greatly improved compared to prior art processes, particularly those using liquid-based amorphous protective coating deposition processes, or those requiring dry-based softening of the deposited composition.

[0075] As described above, it is possible that step 40 may be repeated more than once, and Figure 1 should not be interpreted restrictively, particularly on this point.

Claims

Demands

1. A method for manufacturing a protective coating against oxidation on at least one external surface of a carbon / carbon composite substrate, the method comprising at least the following steps: - a step (10) of preparing at least the external surface of the substrate intended to be coated; - a step (20) of applying to at least part of an external surface of a carbon / carbon composite substrate an impregnation composition comprising at least one metallic phosphate; and - a heat treatment step (30) of the impregnation composition carried out at a temperature between 700°C and 900°C; then - one or more steps (40) of dry deposition on at least a part of the external surface of the substrate of carbon / carbon composite material of a solid composition suitable for forming an amorphous coating for protection against oxidation, the solid composition comprising glass powder, a refractory ceramic compound and / or a rare earth oxide the process being characterized in that no heat treatment is carried out after the dry deposition of the solid composition.

2. A method according to claim 1, wherein step (10) is carried out by immersing the substrate in a surfactant solution and under ultrasound.

3. A method according to claim 1 or 2, wherein the impregnation composition comprises a metallic phosphate salt.

4. A method according to any one of claims 1 to 3, wherein the dry deposition of the solid composition is carried out by plasma spraying, by electrostatic spraying, or by high-speed thermal powder spraying.

5. A method according to any one of claims 1 to 4, wherein the solid composition suitable for forming an amorphous oxidation protection coating comprises between 70% and 100% by mass of glass powder.

6. A method according to any one of claims 1 to 5, wherein the solid composition suitable for forming an amorphous oxidation protection coating comprises between 0% and 30% by mass of a refractory ceramic compound.

7. A method according to any one of claims 1 to 6, wherein the solid composition suitable for forming an amorphous oxidation protection coating comprises between 0 and 30 wt% of a rare earth oxide.

8. A method according to any one of claims 1 to 7, wherein the method comprises between 2 and 5 steps (40) of depositing a solid composition.

9. A method according to any one of claims 1 to 8, wherein the substrate is an aircraft brake disc.

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