Characterization and repair of micrometric defect networks in ceramic or metallic matrix composites

Abstract

Characterization and repair of micrometric defect networks in ceramic or metallic matrix composites. One aspect of the invention relates to a method for treating micrometric defect networks of the crack or porosity type located on the surface of a ceramic or metallic matrix composite, said method being characterized in that it comprises the following successive steps: immersion of the surface of the composite exhibiting the defect networks in a solution of salts of a treatment material in suspension comprising predominantly a silicon-based compound or at least one chemical element having an atomic number greater than or equal to 21; placement of said surface of the composite and of the salt solution under vacuum at a pressure P1 and a temperature T1 for a duration D1 and infiltration of the treatment material into the defects; extraction of the ceramic or metallic matrix composite from the solution;and drying of the ceramic or metallic matrix composite and precipitation of the salts of the treatment material within the defects. Another aspect of the invention relates to a method for characterizing said defect networks comprising an additional step of detecting and visualizing the treatment material infiltrated within the defects by a phase contrast or density gap imaging technique, preferably by tomography. A further aspect of the invention relates to a method for repairing said defect networks comprising an additional step of nitriding or carburizing the treatment material infiltrated within the defects carried out by placing said composite surface under a nitrogen or carbon atmosphere. Figure to be published with the abbreviation: None;

Description

Title of the invention: Characterization and repair of micrometric defect networks in ceramic or metallic matrix composites TECHNICAL FIELD OF THE INVENTION

[0001] The technical field of the invention is that of composite material parts.

[0002] The present invention relates to a method for detecting and repairing micrometric defects on the surface and at the core of parts made of composite material, and in particular parts made of ceramic matrix composite material, oxide / oxide ceramic matrix composite material or metal matrix composite material. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] When manufacturing high-pressure and low-pressure turbine parts, ceramic matrix composites (CMC) based on silicon carbide, generally called SiC / SiC CMC, are used, which have high temperature resistance, which makes it possible to reduce or even eliminate the cooling conventionally used for these parts. These CMCs therefore allow an increase in the operating temperatures of the turbines while reducing the specific fuel consumption which results from the reduction in the intake of cooling air.

[0004] The manufacture of parts in the latest generation CMC, for example CMC SiC / SiC, involves many steps. These steps begin in particular with weaving of latest generation SiC fibers, for example SiC fibers marketed under the name Hi-Nicalon S, into the shape of the part. Then comes the consolidation of this preform by successive deposition of boron nitride (BN) as interphase and silicon carbide (SiC) as matrix by chemical vapor infiltration (CVI), then a first pre-densification of SiC by CVI. The densification of the preform is then ensured by a first incorporation of SiC phase then by a capillary rise according to a process of impregnation by liquid Si (MI, from the English Melt Infiltration) within the remaining pore network.At the end of these steps, there may be a network of filling defects due to the lack of control of the MI impregnation, resulting in particular in porosity of the surface and core of the CMC. In addition, machining of the part is usually carried out to bring it to the correct size. This machining, coupled with the high stresses created during manufacturing, can cause a network of cracks in the CMC.

[0005] These defect networks, by their nature, are extremely fine. Indeed, their di- dimensions were estimated to be less than 5 pm, these 5 pm being able to correspond to a width or a length. At present, due to their very small dimensions, these defects are undetectable by existing control means.

[0006] These defect networks can cause a reduction in the mechanical properties of the CMCs. Indeed, in turbines, composite material parts are subjected to harsh environments. In the case of defect networks, water vapor is likely to migrate into the cracks and deteriorate the boron nitride interphase. However, this interphase plays a key role in the mechanical properties of the material and is very sensitive to oxidation / corrosion phenomena. If the latter is subjected to a corrosive flow, the material then loses its mechanical properties and the composite material parts no longer meet the specifications expected of them, which can cause a loss of performance for the entire turbine. During the studies carried out by the applicant, it was notably noted that the boron nitride at the interphase, subjected to a corrosive flow, had been transformed into boron trioxide (B2O3).

[0007] An object of the invention is to at least partially fill the networks of micrometric crack or porosity defects in a ceramic or metal matrix composite material in order to at least partially block access to oxidizing and corrosive gases. Another object of the invention is also to prepare such a composite material in order to allow the detection and visualization of the networks of defects and / or to allow the elimination of said defects to repair the composite material.

[0008] A first additional object of the invention is to make it possible to detect and visualize networks of micrometric crack or porosity defects in ceramic or metal matrix composite materials, while a second additional object of the invention is to eliminate them.

[0009] It will be noted that if the invention was developed for ceramic matrix composites based on silicon carbide, it can also be used for other materials, for example metal matrix composites (MMC) or oxide / oxide ceramic matrix composites (Ox / Ox CMC), which can have the same defect networks. Summary of the invention

[0010] The preliminary treatment of a composite material having networks of micrometric defects of the crack or porosity type consists of incorporating a treatment material within the defects. To detect the networks of micrometric defects, the invention consists of incorporating heavy elements within the defects, which can then be detected, for example by a phase contrast or density difference imaging technique, such as tomography. To repair the networks of micrometric defects, the invention consists of incorporating silicon within the defects, then reacting it with a reactive gas and an appropriate heat treatment to give it properties similar to those of CMC, which makes it possible to fill these defects and repair a potentially damaged CMC.

[0011] One aspect of the invention relates to a method for treating micrometric defect networks of the crack or porosity type located on the surface of a ceramic or metal matrix composite, said method comprising the following successive steps: • immersion of the surface of the composite having the defect networks in a solution of salts of a treatment material in suspension comprising mainly a compound based on silicon or based on at least one chemical element having an atomic number greater than or equal to 21; • placement of said surface of the composite and the salt solution under vacuum at a pressure PI and at a temperature Tl for a duration DI and infiltration of the treatment material within the defects; • extraction of the ceramic or metal matrix composite from the solution; and • drying of the ceramic or metal matrix composite and precipitation of the salts of the treatment material within the defects.

[0012] This treatment method advantageously makes it possible to incorporate treatment material into the defects. The vacuum step advantageously makes it possible to expel the air located in the defects and to insert the solution therein so that the treatment material is well housed in the defects. The infiltration of the treatment material into the defects and the precipitation thereof during drying advantageously make it possible to form clusters of precipitates within the defects and to at least partially block access to the gas of the oxidizing and corrosive species.

[0013] Furthermore, when the treatment material is heavy, with an atomic number greater than or equal to 21, and forms clusters of precipitates within the defects after drying, it can serve as tracers to detect and visualize the defects of the composite by means of a suitable imaging technique.

[0014] Finally, because it is housed in the defects, the treatment material also makes it possible to at least partially fill said defects and therefore to partially repair the composite, this at least partial repair being able to be improved and completed by means of a suitable subsequent additional treatment.

[0015] Thus, this treatment method, in addition to at least partially correcting the networks of micrometric defects of the crack or porosity type located on the surface of a composite, advantageously makes it possible to subsequently subject said composite to a method of characterizing the networks of micrometric defects and / or to a method of repairing said networks of defects.

[0016] In addition to the characteristics which have just been mentioned in the preceding paragraph, the treatment method according to one aspect of the invention may have one or more complementary characteristics among the following, considered individually or according to all technically possible combinations: • the processing material is a material whose melting point is higher than 1300°C and which does not react chemically with the ceramic or metal matrix composite at a temperature lower than or equal to 1300°C; • the treatment material mainly comprises at least one metal and / or at least one rare earth; • the treatment material mainly comprises ytterbium or yttrium; • the PI pressure is between 0.1 and 50 kPa, preferably between 0.5 and 20 kPa and more preferably between 1 and 10 kPa; • the DI duration is greater than 1 minute, preferably greater than 10 minutes and more preferably greater than 15 minutes; • the temperature Tl is between 10 and 40°C, preferably between 15 and 30°C and more preferably between 20 and 25°C.

[0017] Another aspect of the invention relates to a method for characterizing networks of micrometric defects of the crack or porosity type located on the surface of a ceramic or metal matrix composite, said method comprising the successive steps of the treatment method previously described in which the treatment material in suspension mainly comprises a compound based on a chemical element having an atomic number greater than or equal to 21, and comprising the following additional step after the drying step: • detection and visualization of treatment material infiltrated within defects by phase contrast or density difference imaging technique.

[0018] This treatment method is particularly advantageous in that it makes it possible to detect and visualize micrometric defects in the composite, the dimensions of which are, for example, less than 5 μm. Being able to detect and visualize the networks of defects advantageously makes it possible to optimize the various manufacturing parameters of the composite material parts, so as to minimize these defects. This also makes it possible to identify the areas of the composite material parts which must be repaired or replaced. The phase contrast or density difference imaging technique is particularly advantageous in that it is non-destructive.

[0019] According to one aspect of the invention, the imaging technique used is tomography.

[0020] A further aspect of the invention relates to a method for repairing networks of micrometric defects of the crack or porosity type located on the surface of a ceramic or metal matrix composite, said method comprising the following steps: steps of the treatment method previously described in which the suspended treatment material mainly comprises a silicon-based compound, and comprising the following additional step after the drying step: • placing said surface of the composite under a nitrogen atmosphere or under a carbon atmosphere at a pressure P2 and at a temperature T2 for a duration D2, and nitriding or carburizing the treatment material infiltrated within the defects

[0021] Nitriding or carburizing the treatment material advantageously makes it possible to fill micrometric defects such as cracks or porosity by the formation of silicon nitride (Si3N4) or silicon carbide (SiC), slightly increasing the volume of the treatment material infiltrated into the defects. It makes it possible, for example, to repair a potentially damaged composite. Silicon nitride and silicon carbide are advantageous in that they have chemical and mechanical properties very similar to those of the composite material. Thus, nitriding or carburizing the treatment material also makes it possible to improve its surface hardness, wear resistance, service life, corrosion resistance and dimensional stability.

[0022] Nitriding the treatment material is advantageous in that it is simple to implement and inexpensive. In addition, nitriding silicon to Si3N4 causes a significant increase in the volume of the precipitate clusters lodged within the defects, which allows them to be better filled.

[0023] Carburizing the treatment material is advantageous in that it causes an increase in the volume of the precipitate clusters lodged within the defects, although this increase in volume is less than that obtained by nitriding. However, silicon carbide has generally more satisfactory mechanical and chemical properties than silicon nitride, in particular due to its much higher hardness and melting point.

[0024] In addition to the characteristics which have just been mentioned in the preceding paragraph, the treatment method according to one aspect of the invention may have one or more complementary characteristics among the following, considered individually or according to all technically possible combinations: • the surface of the composite is placed under a nitrogen atmosphere composed of more than 90% nitrogen, ammonia, a nitriding gas or a mixture of these gases. • the surface of the composite is placed under a carbon atmosphere composed of more than 90% carbon monoxide, carbon dioxide, gaseous hydrocarbon or a mixture of these gases. • the pressure P2 is between 500 and 1500 kPa, preferably between 800 and 1300 kPa and more preferably between 1000 and 1100 kPa. • the temperature T2 is between 800 and 1300°C, preferably between 900 and 1100°C and more preferably between 950 and 1050°C. • duration D2 is greater than 15 minutes, preferably greater than 30 minutes and more preferably greater than 60 minutes.

[0025] The invention and its various applications will be better understood upon reading the following description and examining the accompanying figures. BRIEF DESCRIPTION OF THE FIGURES

[0026] The figures are presented for information purposes only and in no way limit the invention.

[0027] [Fig. 1] is a flowchart illustrating the steps of the treatment method according to the invention.

[0028] [Fig.2] is a flowchart illustrating the steps of the characterization process according to the invention.

[0029] [Fig.3] is a flowchart illustrating the steps of the repair process according to the invention.

[0030] [Fig.4] is an image obtained by tomography of a composite subjected to the process of repair according to the invention and on which a precipitate of ytterbium infiltrated into a crack is marked by an arrow.

[0031] [Fig.5] is an image similar to [Fig.4] but for another area of ​​the composite subjected to the treatment method according to the invention. DETAILED DESCRIPTION

[0032] The invention relates to a method for treating networks of micrometric defects of the crack or porosity type located on the surface of a ceramic or metal matrix composite.

[0033] By micrometric defects is meant filling defects or cracks present on the surface of the composite material and whose width and / or length is of the order of a micrometer, for example less than 5 μm.

[0034] The composites concerned by the invention are, for example, ceramic matrix composites based on silicon carbide, metal matrix composites and oxide / oxide ceramic matrix composites.

[0035] As illustrated in [Fig.l], the treatment method according to the invention comprises several successive steps.

[0036] A first step consists of immersing the surface of the composite having the defect networks in a solution, preferably aqueous, comprising salts of a treatment material. When the dimensions of the composite material part allow it, it is of course possible to immerse the entirety of said composite in the solution comprising salts of a treatment material.

[0037] For example, in the case where the treatment material comprises ytterbium, ytterbium in solution is in the form of Yb 3+ ions.

[0038] Preferably, this treatment material is chemically compatible with the composite material, and once precipitated it remains in the solid state during the various stages of treatment of the composite and during any subsequent characterization and / or repair stages. Thus, the treatment material is preferably a material whose melting point is greater than 1300°C and which does not react chemically with the ceramic or metal matrix composite at a temperature less than or equal to 1300°C.

[0039] The treatment material is preferably a compound comprising mainly silicon or a compound comprising mainly at least one so-called heavy chemical element, that is to say a chemical element having an atomic number greater than or equal to 21, for example at least one metal and / or at least one rare earth. Ytterbium and yttrium are preferred metals from the rare earth group.

[0040] According to a preferred embodiment of the invention, this immersion step is carried out at ambient temperature and pressure.

[0041] It will be noted that this treatment process is preferably carried out at the end of the manufacture of the composite material parts, in particular after their possible machining because the machining step is likely to create cracks.

[0042] A second step consists of placing the surface of the composite under vacuum, as well as the solution in which it is immersed. This vacuum step is carried out at a pressure PI and at a temperature Tl for a duration DI so that the treatment material infiltrates into the defects. These parameters are notably chosen so that the solution does not boil.

[0043] According to a preferred embodiment of the invention, the pressure PI is between 0.1 and 50 kPa, preferably between 0.5 and 20 kPa and more preferably between 1 and 10 kPa.

[0044] According to this preferred embodiment of the invention, the duration DI is greater than 1 minute, preferably greater than 10 minutes and more preferably greater than 15 minutes.

[0045] According to this preferred embodiment of the invention, the temperature T1 is between 10 and 40°C, preferably between 15 and 30°C and more preferably between 20 and 25°C.

[0046] A third step is to dry the surface of the composite, the surface of the composite that was previously immersed and placed under vacuum. The purpose of this drying is to remove liquid from the solution, for example water, so that the ions of the treatment material precipitate in the cracks and pores of the micrometric defects. They are also said to segregate.

[0047] According to a preferred embodiment of the invention, this drying step is carried out at ambient pressure and at a temperature of approximately 100°C for one hour.

[0048] The invention also relates to a method for characterizing networks of micrometric defects of the crack or porosity type located on the surface of a ceramic or metal matrix composite. By characterization method is meant a method for detecting and visualizing these defects, in particular in order to reveal them and / or locate them on the surface of the composite.

[0049] As illustrated in [Fig.2], the characterization method comprises the treatment steps previously described and comprises an additional step carried out after the drying step, consisting of detecting and visualizing the treatment material infiltrated within the defects by a phase contrast or density difference imaging technique.

[0050] For this characterization method, the treatment material in suspension mainly comprises a heavy compound based on a chemical element having an atomic number greater than or equal to 21.

[0051] According to a preferred embodiment of the invention, the imaging technique used is tomography.

[0052] If the imaging technique used provides two-dimensional images of the treated surface of the composite, it is for example possible to compile these two-dimensional images to obtain a three-dimensional image of the treated surface of the composite, which advantageously makes it possible to better visualize the clusters of precipitates of the treatment material, and therefore to better detect and visualize the networks of micrometric defects present on the surface of the composite.

[0053] The resolution of the imaging technique used determines the range of micrometric dimensions of the defects that can be characterized. Tests carried out with the tomography technique have made it possible to detect and visualize defects whose dimensions have been estimated to be less than 5 μm.

[0054] The invention also relates to a method for repairing networks of micrometric defects of the crack or porosity type located on the surface of a ceramic or metal matrix composite. By repair method is meant a method for improving the less partial filling of the defects of the crack or porosity type already obtained during the treatment method, in particular in order to protect the internal layers of the composite from an oxidizing and / or corrosive environment, for example in order to prevent the boron nitride at the interphase from transforming into boron trioxide when the composite is subjected to a corrosive flow.

[0055] For this repair process, the treatment material in suspension mainly comprises a silicon-based compound.

[0056] As illustrated in [Fig.3], the repair method comprises the previously described processing steps and comprises an additional step carried out after the step of drying, consisting of placing said surface of the composite under a nitrogen or carbon atmosphere at a pressure P2 and at a temperature T2 for a duration D2.

[0057] By nitrogen atmosphere is meant an atmosphere composed respectively of more than 90% nitrogen, ammonia, a nitriding gas or a mixture of these gases.

[0058] By carbonaceous atmosphere is meant an atmosphere composed respectively of more than 90% of carbon monoxide, carbon dioxide, gaseous hydrocarbon or a mixture of these gases.

[0059] During this additional step, the treatment material infiltrated within the defects is nitrided or carburized, which slightly increases its dimensions and makes it possible to at least partially seal the micrometric defects.

[0060] For example, if the infiltrated treatment material is silicon, and it is exposed to a nitriding atmosphere, it transforms into silicon nitride (Si3N4), whereas if it is exposed to a fueling atmosphere, i.e. causing carburization of the silicon, it transforms into silicon carbide (SiC). Carburization means the enrichment of a material with carbon.

[0061] A characterization method may be used after the repair process, for example in order to control the quality and effectiveness of said repair.

[0062] According to a preferred embodiment of the invention, the pressure P2 is between 500 and 1500 kPa, preferably between 800 and 1300 kPa and more preferably between 1000 and 1100 kPa.

[0063] According to this preferred embodiment of the invention, the duration D2 is greater than 15 minutes, preferably greater than 30 minutes and more preferably greater than 60 minutes.

[0064] According to this preferred embodiment of the invention, the temperature T2 is between 800 and 1300°C, preferably between 900 and 1100°C and more preferably between 950 and 1050°C.

[0065] In conclusion of the studies carried out by the applicant, it is considered that the repair method of the invention makes it possible to repair extremely fine crack networks, for example whose dimensions have been estimated to be less than 5 μm.

[0066] By way of example, [Fig.4] and [Fig.5] illustrate a composite subjected to the repair method according to the invention and in which a precipitate of ytterbium infiltrated into a crack has sealed it.

[0067] Although described through a number of examples, variations and embodiments, the treatment, characterization and repair methods according to the invention include various variations, modifications and improvements which will be obvious to those skilled in the art, it being understood that these variations, modifications and improvements are part of the scope of the invention.

Claims

Demands

1. A method for treating micrometric defect networks of the crack or porosity type located on the surface of a ceramic or metallic matrix composite, said method being characterized in that it comprises the following successive steps: - immersion of the surface of the composite having the defect networks in a solution of salts of a treatment material in suspension comprising predominantly a silicon-based compound or a compound based on at least one chemical element having an atomic number greater than or equal to 21; - placement of said surface of the composite and of the salt solution under vacuum at a pressure PI and at a temperature Tl for a duration DI and infiltration of the treatment material into the defects; - extraction of the ceramic or metallic matrix composite from the solution; and - drying of the ceramic or metallic matrix composite and precipitation of the salts of the treatment material into the defects.

2. A treatment process according to claim 1, characterized in that the treatment material comprises predominantly at least one metal and / or at least one rare earth.

3. Processing method according to claim 1 or 2, characterized in that the processing material comprises predominantly ytterbium or yttrium.

4. A treatment method according to any one of the preceding claims, characterized in that the pressure PI is between 0.1 and 50 kPa, preferably between 0.5 and 20 kPa and more preferably between 1 and 10 kPa.

5. A method for characterizing micrometric defect networks of the crack or porosity type located on the surface of a ceramic or metallic matrix composite, said method being characterized in that it comprises the successive steps of the treatment process according to any one of the preceding claims, in that the treatment material in suspension comprises predominantly a compound based on of a chemical element having an atomic number greater than or equal to 21, and in that it includes the following additional step after the drying step: - detection and visualization of the treatment material infiltrated within the defects by a phase contrast or density gap imaging technique.

6. A characterization method according to the preceding claim, characterized in that the imaging technique used is tomography.

7. A method for repairing networks of micrometric defects such as cracks or porosity located on the surface of a ceramic or metallic matrix composite, said method being characterized in that it comprises the successive steps of the treatment process according to any one of claims 1 to 4, in that the treatment material in suspension comprises predominantly a silicon-based compound, and in that it comprises the following additional step after the drying step: - placing said composite surface under a nitrogen or carbon atmosphere at a pressure P2 and a temperature T2 for a duration D2, and nitriding or carburizing the treatment material infiltrated within the defects

8. Repair method according to the preceding claim, characterized in that the surface of the composite is placed under a nitrogen atmosphere composed of more than 90% nitrogen, ammonia, a nitriding gas or a mixture of these gases.

9. Repair method according to claim 7, characterized in that the surface of the composite is placed under a carbonaceous atmosphere composed of more than 90% carbon monoxide, carbon dioxide, gaseous hydrocarbon or a mixture of these gases.

10. Repair method according to any one of claims 7 to 9, characterized in that the temperature T2 is between 800 and 1300 °C, preferably between 900 and 1100 °C and more preferably between 950 and 1050 °C.

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