anti-oxidation protection for C / C composite substrate

Abstract

This description relates to a process for manufacturing an anti-oxidation protection for a C / C composite substrate, as well as a mechanical part equipped with such protection. The process comprises the following steps: supplying a substrate to be protected (21), the substrate being made of C / C composite material; supplying a liquid suspension (15) comprising at least one active principle from the phosphate family; supplying a direct current electric generator (12); placing the substrate (21) in the suspension (15), as the first electrode (13), and connecting the substrate (21) to a first terminal of the electric generator (12); placing a second electrode (14) in the suspension (15), opposite the substrate (21), and connecting the substrate (21) to a second terminal of the electric generator (12); and applying a voltage (U) of at least 10 V between the two electrodes (13, 14) for at least 1 minute. Fig. 2.

Description

Title of the invention: Anti-oxidation protection for C / C composite substrates. Technical field

[0001] The present disclosure relates to a method for manufacturing an anti-oxidation coating for a carbon / carbon composite substrate, as well as a mechanical part equipped with such a coating. This method is applicable to any type of carbon / carbon composite part. However, it is particularly suitable for parts subjected to high temperatures, such as brakes, and exposed to particularly oxidizing environments, especially in the aerospace industry. Prior art

[0002] Thanks to their excellent tribological properties and their lightness, C / C composite materials have now established themselves as the reference material for aeronautical braking.

[0003] However, due to the very significant heating experienced by the C / C brakes, which can exceed 1400 °C and even sometimes reach 2000 °C, the carbon constituting these brakes is subject to oxidation phenomena by the ambient air, which considerably reduces the lifespan of these C / C brakes.

[0004] In order to combat these oxidation phenomena, anti-oxidation protective coatings are conventionally applied to the non-friction parts of the C / C brakes, i.e. to the parts exposed to oxygen in the air.

[0005] However, due to the wide variability of oxidizing conditions that such C / C brakes may encounter, depending on temperature levels, operating times, or the chemical elements of the environment, particularly the presence of water, it is generally necessary to combine two protective mechanisms. The first aims to trap carbon oxidation catalysts, such as potassium acetate, which originates in particular from de-icing products used on runways. The second aims to reduce the rate of oxygen diffusion to the carbon substrate.

[0006] However, to date, these two protective mechanisms are addressed by separate coatings. Indeed, anti-catalytic protection is generally obtained by applying a precursor to the surfaces to be protected, which must then undergo a transformation requiring a temperature below 1000 °C. Conversely, anti-diffusion protection is generally obtained by high-temperature deposition processes, above 1000 °C. Moreover, as shown in [Fig. 1], the conventional deposition process for anti-catalytic protection leads to the formation of islands. continuous active principle 91, here alumino-phosphate A1(PO3)3, leaving areas of the substrate 92 exposed, the precursor A1(H2PO4)3 in fact containing a part of water which evaporates during its transformation: the layer thus obtained, discontinuous, cannot therefore play the role of barrier against the diffusion of oxygen towards the substrate.

[0007] Therefore, it is necessary to multiply the deposition and stabilization steps to obtain a multi-layered anti-oxidation protection that offers the desired level of effectiveness. The cycle time for manufacturing such an anti-oxidation protection is thus substantial. Furthermore, the multiplication of layers generates additional design constraints, as it is necessary to match the coefficients of expansion of the different layers to avoid differential expansion that could damage the protection.

[0008] There is therefore a real need for a manufacturing process for an anti-oxidation protection for a C / C composite substrate, as well as for a mechanical part equipped with such protection, which are free, at least in part, from the disadvantages inherent in the aforementioned known method. Description of the invention

[0009] The present description relates to a process for manufacturing an anti-oxidation protection for a C / C composite substrate, comprising the following steps: - provision of a substrate to be protected, the substrate being made of C / C composite material - supply of a liquid suspension comprising at least one active ingredient from the phosphate family, - supply of a direct current electric generator, - placement of the substrate in the suspension, as the first electrode, and connection of the substrate to a first terminal of the electrical generator, - placement of a second electrode in the suspension, preferably opposite the substrate, and connection of the second electrode to a second terminal of the electrical generator, and - application of a voltage of at least 10 V between the two electrodes for at least 1 minute.

[0010] The use of such an electrophoresis method makes it possible to form the anti-oxidation protection from a liquid suspension directly containing the active ingredient, and not a precursor as was the case in previous methods. It is then possible to form a continuous layer over the entire surface of the substrate immersed in the suspension, with a density sufficient to form an effective barrier against oxygen diffusion. In particular, in the absence of a partially evaporating precursor, the formation of discontinuous islands is avoided. The cycle time is also reduced since a separate precursor transformation step is no longer necessary.

[0011] Furthermore, since the active ingredient can be deposited directly and uniformly onto the substrate, it is possible to form a layer as thick as desired in a single electrophoresis step, without resorting to intermediate stabilization steps. This also makes it possible to reduce the cycle time.

[0012] Thus, in a single layer, deposited in a single electrophoresis step, an anti-oxidation coating sufficiently dense and thick to form a barrier against oxygen diffusion can be obtained, incorporating an active principle from the phosphate family that traps carbon oxidation catalysts. This results in a dual anti-oxidation coating, possessing both an anti-catalytic function and a diffusion barrier function, exhibiting an effectiveness at least as good as prior art anti-oxidation coatings but at a significantly lower manufacturing cost.

[0013] This electrophoresis technique, resulting in a single uniform layer, also allows, where appropriate, the inclusion in the suspension of several different active ingredients in order to provide the anti-oxidation protection with additional functions without multiplying the layers and therefore without multiplying the manufacturing costs and without being limited by differential expansion problems.

[0014] In some embodiments, the liquid phase of the suspension comprises 1-propanol and / or 2-propanol. These two species together may constitute at least 90%, or even 100%, of the liquid phase. In particular, 1-propanol and 2-propanol may be present in equal proportions in the liquid phase.

[0015] In some embodiments, the liquid phase of the suspension consists of a 50 / 50 mixture of 1-propanol and / or 2-propanol.

[0016] In some embodiments, the active ingredient is from the alumino-phosphate family. Alumino-phosphates have a strong scavenging capacity, particularly against carbon oxidation catalysts.

[0017] In some embodiments, the active ingredient comprises Al(PO3)3. Preferably, the active ingredient is exclusively Al(PO3)3.

[0018] In some embodiments, the concentration of active ingredient in the suspension is between 1 and 10% by mass, preferably between 2 and 8% by mass, preferably still between 4 and 6% by mass.

[0019] In some embodiments, the active principle takes the form, in the suspension, of particles whose D50 is between 0.5 and 5 pm, preferably between 1 and 3 pm.

[0020] In some embodiments, the suspension includes a stabilizer. This stabilizer reduces the sedimentation rate of the particles placed in suspension, by steric or electrostatic repulsion between particles.

[0021] In some embodiments, the stabilizer comprises phosphoric acid. Preferably, the stabilizer is exclusively phosphoric acid.

[0022] In some embodiments, the concentration of stabilizer in the suspension is between 1 and 10 g / L, preferably between 2 and 8 g / L, preferably still between 3 and 5 g / L.

[0023] In certain embodiments, the suspension comprises a glassy material, preferably borosilicate. Such a glassy material allows for the addition of a healing glass function to the anti-oxidation protection, all in a single layer and a single application step. Indeed, thanks to its glassy nature, the anti-oxidation protection can soften at high temperatures in order to closely conform to the surface to be protected and to repair any damage that may have occurred in the anti-oxidation protection.

[0024] In some embodiments, the concentration of vitreous species in the suspension is between 1 and 5% by mass, preferably between 2 and 3% by mass.

[0025] In some embodiments, the borosilicate takes the form, in the suspension, of particles whose D50 is between 1 and 5 pm, preferably between 2 and 4 pm.

[0026] In some embodiments, the suspension includes boron. The presence of boron significantly improves the wettability of the carbon substrate with respect to the glassy species present. In this way, the healing glasses adhere better to the substrate surface, thereby increasing the performance of the oxygen diffusion barrier.

[0027] In some embodiments, the concentration of boron in the suspension is between 0.5 and 3% by mass, preferably between 1 and 2% by mass.

[0028] In some embodiments, the boron takes the form, in the suspension, of particles whose D50 is between 0.5 and 3 pm, preferably between 1 and 2 pm.

[0029] In some embodiments, the distance separating the electrodes is between 1 and 33 cm.

[0030] In some embodiments, the voltage applied between the electrodes is between 10 and 100 V, preferably between 30 and 80 V, and even more preferably between 40 and 60 V.

[0031] In some embodiments, the voltage is applied between the electrodes for a period of between 1 and 30 minutes, preferably between 5 and 20 minutes, preferably between 8 and 12 minutes.

[0032] In certain embodiments, the process further comprises, after the voltage application step, a stabilization step of the coating obtained at a stabilization temperature above 500 °C. This stabilization step, by heating them, improves the cohesion between the particles and thus strengthens the durability of Anti-oxidation protection. Indeed, at this temperature, the softening point of the oxide with the lowest softening point among all the oxides present in the system is reached or exceeded.

[0033] In some embodiments, the stabilization temperature is between 500 and 900°C, preferably between 600 and 750°C, preferably between 650 and 700°C.

[0034] In certain embodiments, the resulting coating has a thickness of between 100 and 300 µm, preferably between 150 and 250 µm. Such thickness ranges effectively restrict oxygen diffusion within the anti-oxidation protection.

[0035] In certain embodiments, the resulting coating has a surface mass between 10 and 50 mg / cm2, preferably between 20 and 50 mg / cm2, and even more preferably between 30 and 40 mg / cm2. Such density ranges effectively restrict oxygen diffusion within the anti-oxidation protection.

[0036] The present exposition also relates to a mechanical part, comprising a substrate in C / C composite material, having a surface to be protected, and an anti-oxidation protection, covering at least the surface to be protected and including a continuous and waterproof single-layer coating, comprising an active principle from the phosphate family.

[0037] This mechanical part therefore benefits from dual anti-oxidation protection, possessing both an anti-catalytic function and a diffusion barrier function, in a single layer. This anti-oxidation protection can notably be obtained using a manufacturing process according to any of the preceding embodiments. Consequently, all the advantages mentioned above concerning the process follow. In particular, all the optional characteristics of the process, and all the advantages associated with them, can be directly applied to the mechanical part.

[0038] The present description also relates to an aircraft brake, comprising a mechanical part according to any one of the preceding embodiments.

[0039] The aforementioned features and advantages, as well as others, will become apparent from the following detailed description, examples of the process, and the proposed mechanical part. This detailed description refers to the accompanying drawings. Brief description of the drawings

[0040] The attached drawings are schematic and are intended primarily to illustrate the principles of the exposition.

[0041] In these drawings, from one figure to another, identical elements (or parts of elements) are identified by the same reference numerals. Furthermore, elements (or parts of elements) belonging to different embodiments but having a function analogous ones are identified on the figures by numerical references incremented by 100, 200, etc.

[0042] [Fig. 1] The [Fig.1] is a macrograph of an alumino-phosphate A1(PO3)3 layer of the prior art.

[0043] [Fig.2] The [Fig.2] is a schematic diagram of the electrophoresis step.

[0044] [Fig.3] Fig.3 is a photograph of a first example of anti-protection oxidation.

[0045] [Fig.4] The [Fig.4] is a cross-sectional micrograph of the first example of anti-oxidation protection.

[0046] [Fig.5] The [Fig.5] is a cross-sectional micrograph of a second example of anti-oxidation protection.

[0047] [Fig.6] The [Fig.6] is another cross-sectional micrograph of the second example of anti-oxidation protection. Description of the implementation methods

[0048] To make the explanation more concrete, examples of a manufacturing process for an anti-oxidation coating are described in detail below, with reference to the accompanying drawings. It should be noted that the invention is not limited to these examples.

[0049] Figure 2 schematically represents an electrophoresis device 10 used in the processes described below. It comprises a cell 11, a direct current power supply 12, a first electrode 13 connected to the negative terminal of the power supply 12, and a second electrode 14 connected to the positive terminal of the power supply 12. The cell 11 is filled with a suspension 15 comprising particles 16 suspended in a liquid phase. The two electrodes 13 and 14 are immersed in the suspension 15. They are preferably positioned facing each other, parallel to one another. A distance D separates the two electrodes 13 and 14.

[0050] In the methods described, one of the electrodes, more particularly electrode 13 connected to the negative terminal of the electric generator 12, is constituted by the substrate 21, which must be protected. This substrate 21 being made of a C / C (carbon / carbon) composite material, it is conductive and can therefore constitute such an electrode.

[0051] When the electric generator 12 applies a voltage U between the two electrodes 13, 14, an electric field E passes through the suspension 15 and causes the particles 16 to migrate towards one or the other of the electrodes 13, 14 depending on their electric charge. Thus, the particles 16 carrying an electric charge migrate towards the substrate 21 forming the negative electrode 13 and are deposited there, thereby covering the substrate 21 in a continuous and regular manner.

[0052] In a first example of the process, the suspension 15 consists of: - a 50 / 50 mixture of 1-propanol and 2-propanol, constituting the liquid phase of the suspension, - 5% by mass of Al(PO3)3, in the form of a powder having a D50 between 1 and 3 pm, preferably between 1.2 and 2.5 pm, suspended in the liquid phase, and - 4 g / L of phosphoric acid, acting as a stabilizer, in solution in the liquid phase.

[0053] The electrodes 13, 14 are separated by a distance D between 1 and 33 cm, this distance being variable due to the geometry of the part to be coated, and the electric generator 12 applies a voltage U of 50 V between them.

[0054] This voltage U is maintained for 10 minutes. During this electrophoresis step, the Al(PO3)3 particles, carrying a positive charge, in the suspension, migrate and are deposited on the substrate 21 forming the negative electrode 13, i.e. the cathode, of the system.

[0055] After this electrophoresis step, the substrate 21, now bearing a layer of Al(PO3)3 particles, is removed from the tank 11 and undergoes a stabilization step carried out at 700°C for 1 to 5 hours in a nitrogen atmosphere. This consolidates the protective layer 22 thus obtained.

[0056] This protective layer 22 is shown in Figures 3 and 4. It can be seen that this protective layer 22 is continuous, uniform, and level. It is also free of porosity, which ensures sufficient density to effectively restrict oxygen diffusion. The active ingredient A1(PO3)3, for its part, traps the carbon oxidation catalysts.

[0057] In this first example, the protective layer 22 has a thickness of 160 pm and a surface mass of the order of 40 mg / cm2.

[0058] In a second example of the process, the suspension 15 is made up of: - a 50 / 50 mixture of 1-propanol and 2-propanol, constituting the liquid phase of the suspension, - 5% by mass of Al(PO3)3, in the form of a powder having a D50 between 1 and 3 pm, preferably between 1.2 and 2.5 pm, suspended in the liquid phase, - 4 g / L of phosphoric acid, acting as a stabilizer, in solution in the liquid phase, - 2.2% by mass of borosilicate, having a glass transition temperature Tg of 570 °C, in the form of a powder with a D50 of approximately 3 pm, suspended in the liquid phase, and - 1.1% by mass of boron, in the form of a powder having a D50 of the order of 1 pm, suspended in the liquid phase.

[0059] The parameters of the electrophoresis step are identical to those of the first example: the electric field E passing through the suspension 15 is maintained for 10 minutes.

[0060] After the electrophoresis step, the substrate 121 undergoes a stabilization step carried out at 650°C for 5 minutes in air. This consolidates the protective layer 122 thus obtained.

[0061] This protective layer 122 is shown in Figures 5 and 6. It is again noted that the protective layer 122 is continuous, uniform, and level. It is also free of porosity, which ensures sufficient density to effectively restrict oxygen diffusion. The active ingredient A1(PO3)3 traps carbon oxidation catalysts. Furthermore, the presence of the borosilicate adds a healing glass function to this protective layer 122.

[0062] It can also be noted on [Fig.6] that the proposed process allows coating of both flat and curved surfaces.

[0063] In this second example, the protective layer 122 has a thickness of 230 pm and a surface mass of the order of 30 mg / cm2.

[0064] In a third example, completely identical to the second example except that the duration of the electrophoresis is reduced to 1 minute, a coating of lesser thickness is obtained, on the order of 25 pm.

[0065] Although the present invention has been described with reference to specific embodiments, it is evident that modifications and changes can be made to these examples without departing from the general scope of the invention as defined by the claims. In particular, individual features of the various embodiments illustrated / mentioned can be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than a restrictive sense.

[0066] It is also evident that all the characteristics described with reference to a process are transposable, alone or in combination, to a device, and conversely, all the characteristics described with reference to a device are transposable, alone or in combination, to a process.

Claims

Demands

1. A method for manufacturing a single-layer anti-oxidation protection for a C / C composite substrate, comprising the following steps: - supplying a substrate to be protected (21), the substrate being made of C / C composite material, - supplying a liquid suspension (15) comprising at least one active principle from the phosphate family, - supplying a DC electric generator (12), - placing the substrate (21) in the suspension (15), as the first electrode (13), and connecting the substrate (21) to a first terminal of the electric generator (12), - placing a second electrode (14) in the suspension (15) and connecting the second electrode (14) to a second terminal of the electric generator (12), and - applying a voltage (U) of at least 10 V between the two electrodes (13, 14) for at least 1 minute.

2. A method according to claim 1, wherein the liquid phase of the suspension (15) comprises 1-propanol and / or 2-propanol.

3. A method according to claim 1 or 2, wherein the active ingredient comprises Al(PO3)3.

4. A method according to any one of claims 1 to 3, wherein the concentration of the active ingredient in the suspension (15) is between 1 and 10% by mass, preferably between 2 and 8% by mass, preferably again between 4 and 6% by mass.

5. A method according to any one of claims 1 to 4, wherein the suspension (15) comprises a stabilizer, preferably phosphoric acid, and wherein the concentration of stabilizer in the suspension (15) is between 1 and 10 g / L, preferably between 2 and 8 g / L, preferably again between 3 and 5 g / L.

6. A method according to any one of claims 1 to 5, wherein the suspension (15) comprises a glassy species, preferably borosilicate, wherein the concentration of the glassy species in the suspension (15) is between 1 and 5% by mass, preferably between 2 and 3% by mass, wherein the suspension (15) comprises boron, and in which the concentration of boron in the suspension (15) is between 0.5 and 3% by mass, preferably between 1 and 2% by mass.

7. A method according to any one of claims 1 to 6, wherein the voltage (U) applied between the electrodes (13, 14) is between 10 and 100 V, preferably between 30 and 80 V, preferably further between 40 and 60 V, and wherein the voltage (U) is applied between the electrodes (13, 14) for a period of between 1 and 30 minutes, preferably between 5 and 20 minutes, preferably between 8 and 12 minutes.

8. A method according to any one of claims 1 to 7, further comprising, after the tension application step (U), a stabilization step of the resulting coating (22) at a stabilization temperature above 500 °C, and wherein the stabilization temperature is between 500 and 900 °C, preferably between 600 and 750 °C, preferably between 650 and 700 °C.

9. A method according to any one of claims 1 to 8, wherein the resulting coating (22) has a thickness of between 10 and 300 pm, preferably between 150 and 250 pm.

10. A method according to any one of claims 1 to 9, wherein the resulting coating (22) has a surface mass between 10 and 50 mg / cm2, preferably between 30 and 40 mg / cm2.

11. Mechanical part, comprising a substrate (21) of C / C composite material, having a surface to be protected, and a single-layer, continuous and watertight anti-oxidation protection, covering at least the surface to be protected and comprising an active principle of the phosphate family.

12. Aircraft brake, comprising a mechanical part according to claim 11.

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