Part made of SiC / SiC material coated with a healing barrier

Abstract

Part made of SiC / SiC material coated with a healing barrier. The invention relates to a part (100) comprising a part made of SiC / SiC ceramic matrix composite material (11) of which at least a portion of the external surface has been machined, and of which at least the portion of the external surface that has been machined is directly covered with a healing layer, the healing layer (20) being made of a material selected from silicon nitride Si3N4, boron carbide B4C, a ternary Si-BC system, silicon carbide SiC or a mixture of two or more of these compounds. Figure for the abstract: Fig. 1.

Description

Title of the invention: Part made of SiC / SiC material coated with a healing barrier technical field

[0001] The present exposition relates to the field of aeronautical turbomachinery, and more specifically to the parts used in such turbomachinery. Previous technique

[0002] Ceramic matrix composite (CMC) materials can withstand temperatures up to 1400°C.

[0003] Due to their superior resistance to high temperatures, parts made of CMC materials require less cooling than similar structures made of metallic materials. Since this cooling is traditionally obtained from the compressor, which impacts the turbomachine's efficiency, CMC materials therefore improve engine efficiency, thereby reducing fuel consumption.

[0004] Furthermore, their use helps to optimize the performance of turbomachines, in particular by reducing the overall mass of the turbomachine, which further contributes to a decrease in fuel consumption and therefore to a significant reduction in pollutant emissions.

[0005] These advantages explain the industrial interest in developing such ceramic matrix composite materials.

[0006] For functional reasons, CMC parts may be subject to more or less extensive machining.

[0007] However, CMCs are materials with very high hardness, which makes their machining particularly complex. In particular, machining a CMC can generate micro-damage that can lead to the appearance of surface-breaking cracks in the CMC part.

[0008] The presence of such cracks can cause a reduction in the elastic range of the part (a phenomenon known as "Matrix Cracking Stress") and reduce the lifespan of the final part.

[0009] Furthermore, machining a CMC can lead to the exposure of the interphase present on the fibers of the fibrous structure of the CMC material and make it even more sensitive to oxidation and / or corrosion phenomena due to its exposure to the external environment, particularly in areas with a high rate of machining.

[0010] These consequences of machining on parts made of ceramic matrix composite material give rise to a need for solutions enabling machining of CMC parts while at least partially overcoming the aforementioned problems. Description of the invention

[0011] The present invention is specifically designed to meet this need.

[0012] For this purpose, it proposes according to a first of its aspects a part comprising a part in ceramic matrix composite material SiC / SiC of which at least a part of the external surface has been machined, and of which at least the part of the external surface having been machined is directly covered with a healing layer, the healing layer being made of a material chosen from silicon nitride Si3N4, boron carbide B4C, a silicon-doped boron carbide system Si-BC, silicon carbide SiC or a mixture of two or more of these compounds.

[0013] It is to the credit of the inventors that they have determined that the healing layer present on at least the external surface which has been machined of a part made of ceramic matrix composite material plays a perfect role as a mechanical and chemical healing agent.

[0014] On the one hand, the healing layer ensures excellent filling of cracks possibly created by machining the external surface of the ceramic matrix composite material.

[0015] This crack filling has two important effects. It prevents the propagation of cracks and therefore the total destruction of the part. Furthermore, it ensures that locally, the mechanical properties of the part, particularly its Young's modulus, are similar to those of the part's matrix made of composite material. This results in a part that is undoubtedly more robust than one containing microcracks.

[0016] Furthermore, the chemical compatibility between the healing layer and the CMC material is excellent. In particular, the adhesion of the healing layer to the ceramic matrix composite part is excellent. Also, the close coefficients of thermal expansion between the ceramic matrix composite material and the healing layer ensure excellent resistance to delamination.

[0017] Such an embodiment makes it possible to obtain a part with satisfactory mechanical properties that has nevertheless been machined. In other words, it makes it possible to produce parts with complex geometries in ceramic matrix composite material.

[0018] In one embodiment, the healing layer may be made of silicon nitride Si3N4. Such an embodiment is particularly advantageous because the healing layer then has a coefficient of expansion lower than that of the underlying ceramic matrix composite material, which ensures that in operation the coating is in a state of compression, which further increases the resistance of the healing layer to cracking.

[0019] In one embodiment, the healing layer may be made of boron carbide B4C or a ternary Si-BC mixture. This embodiment is particularly advantageous because the healing layer exhibits behavior that ensures healing at even lower temperatures than other proposed alternatives.

[0020] In addition, a layer of Si-BC is particularly interesting for reducing the sensitivity of the healing layer to moisture.

[0021] In one embodiment, the healing layer may be made of silicon carbide (SiC). This embodiment is particularly advantageous because it offers excellent chemical compatibility with the underlying SiC / SiC ceramic matrix composite material.

[0022] In one embodiment, the healing layer may comprise a thickness of between 10 pm and 50 pm.

[0023] In one embodiment, the healing layer may comprise "a mixture" of compounds selected from silicon nitride Si3N4, boron carbide B4C, a silicon-doped boron carbide system Si-BC, silicon carbide SiC.

[0024] It is understood by this expression that the healing layer may be a single layer made up of a mixture of two or more of the compounds in the list.

[0025] This expression also implies that the healing layer can be a stack of layers, each made up of one or more of the compounds described. In this way, a healing layer can be obtained that offers excellent protection over a very wide temperature range.

[0026] In one embodiment, the healing layer may be a stack comprising, or even be made up of: - a layer made of boron carbide B4C; - a layer consisting of a silicon-doped boron carbide system Si-BC disposed on the boron carbide layer; - a layer made of silicon carbide SiC disposed on the silicon-doped boron carbide layer Si-BC. In this application, it is understood that the "machined external surface" of a SiC / SiC ceramic matrix composite material is a surface in which the fibrous reinforcement of the SiC / SiC ceramic matrix composite material is exposed by machining.

[0027] Such a surface exposed by machining is particularly reactive and reduces the resistance of the part made of SiC / SiC ceramic matrix composite material to oxidation and corrosion.

[0028] The healing layer deposited directly in contact with this machined surface not only protects the machined surface from oxidation but also seals any cracks that may be caused by machining.

[0029] In one embodiment, the healing layer can be deposited on the entire external surface of the part made of SiC / SiC ceramic matrix composite material.

[0030] This embodiment ensures simplicity in manufacturing the part covered by the healing layer. Indeed, the healing layer can then be deposited on the machined part without taking any precautions, for example by a chemical vapor infiltration process.

[0031] Indeed, the presence of the healing layer on a portion of the part made of SiC / SiC composite material whose surface is not machined does not in any way risk harming it and even presents an excellent chemical compatibility with it.

[0032] In one embodiment, the part may be a turbomachine part, in particular a blade, fixed or moving, a ring sector, a distributor, a portion of a distributor, a portion of a combustion chamber or a combustion chamber.

[0033] Indeed, on the one hand, for such parts the alternative of a SiC / SiC ceramic matrix composite material is desirable compared to the metal blades currently used, and on the other hand the machining of such parts is very important, for example for the manufacture of their trailing edges, to meet aerodynamic requirements.

[0034] The proposed solution therefore has a particular advantage when used in the context of turbomachine parts, and in particular the aforementioned parts.

[0035] In addition, the healing layer does not in any way interfere with the usual applications of ceramic matrix composite materials.

[0036] In particular, it may be necessary to deposit on such a part a layer of environmental barrier and / or thermal barrier, for the needs of the final application of the part.

[0037] In a conventional manner in the field of ceramic matrix composite materials, such an environmental barrier layer and / or a thermal barrier can be disposed on a bonding layer, which generally includes silicon.

[0038] The part described above, at least a portion of whose external surface is machined and covered by a healing layer, is compatible with the deposition of such an environmental barrier layer and / or a thermal barrier.

[0039] According to one embodiment, the part further comprises: - an adhesion layer comprising silicon, the adhesion layer being disposed directly on at least part of the external surface of the healing layer; and - an environmental barrier layer comprising at least mullite and / or a rare earth silicate, the environmental barrier layer being disposed directly on at least part of the external surface of the bonding layer.

[0040] In one embodiment, the rare earth silicate may be selected from ytterbium silicate, yttrium silicate, ytterbium disilicate, yttrium disilicate or mixtures of two or more of these compounds.

[0041] In one embodiment, the environmental barrier layer may comprise a mixture comprising only components selected from mullite and rare earth silicates, for example selected from ytterbium silicate, yttrium silicate, ytterbium disilicate, yttrium disilicate.

[0042] This embodiment is particularly advantageous in the case where the part is located in the thermal and chemical environment of a turbojet engine.

[0043] In one embodiment, the invention relates in another of its aspects to an assembly comprising a first part comprising a SiC / SiC ceramic matrix composite material, at least a portion of whose external surface is covered with a healing layer, the healing layer being made of a material selected from silicon nitride Si3N4, boron carbide B4C, a ternary Si-BC system, silicon carbide SiC or a mixture of these compounds, and a second part, at least the external surface of which is metallic, a portion of the first part coated with the healing layer being intended to be in contact by rubbing with the external surface of the second part.

[0044] Indeed, the inventors observed that the wear caused by the rubbing contact between the first and second part caused wear on the surface of the first part which caused the fibers of the SiC / SiC composite material part of the first part to be exposed, thus reducing the resistance to oxidation and corrosion of the first part, and therefore of the assembly.

[0045] More specifically, the inventors believe that machined surfaces exhibit different hardnesses depending on whether they are in a matrix or fibrous area. This results in uneven wear in contact with a metal part, forming pits and bumps, and increasing the risk of leakage. Applying a self-healing coating homogenizes the surface hardness and therefore the wear.

[0046] The inventors further determined that the healing layer provided excellent protection to the first part against wear by friction, contributing to improving the service life of the entire first and second part.

[0047] In one embodiment, the first part may be a part as described above, at least part of whose external surface has been machined, and at least the part of whose external surface that has been machined is directly covered with a healing layer, the healing layer (20) being made of a material selected from silicon nitride Si3N4, boron carbide B4C, a ternary system Si-BC, silicon carbide SiC or a mixture of these compounds.

[0048] In one embodiment, the first part of the assembly may be a bulb foot of a blade made of SiC / SiC composite material and the second part may be a metal disc, or the first part may be a sail made of SiC / SiC composite material and the second part may be a metal mast passing through the first part.

[0049] According to another aspect, the invention relates to a method for manufacturing a part as described above.

[0050] In one embodiment, the invention relates to a method for manufacturing a part comprising a part made of a SiC / SiC ceramic matrix composite material, at least a portion of whose external surface has been machined, and at least the portion of whose external surface that has been machined is directly covered with a healing layer, the healing layer being made of a material selected from silicon nitride Si3N4, boron carbide B4C, a ternary Si-BC system, silicon carbide SiC or a mixture of these compounds, the method comprising: - a manufacturing step of a part made of SiC / SiC ceramic matrix composite material; - a machining step of the resulting composite material part; then - a step of depositing a healing layer over the entire machined external surface of the part made of SiC / SiC composite material, the healing layer being made of a material chosen from silicon nitride Si3N4, boron carbide B4C, a ternary system Si-BC, silicon carbide SiC or a mixture of these compounds.

[0051] Such a manufacturing process makes it possible to obtain machined parts made of ceramic matrix composite material which nevertheless exhibit excellent mechanical properties.

[0052] In one embodiment, the deposition of the healing layer on at least the machined external surface of the composite material part can be done by chemical vapor deposition.

[0053] In one embodiment, the manufacture of a part in SiC / SiC composite material may include a step of infiltrating a fibrous texture with a molten infiltration composition comprising liquid silicon.

[0054] Such a step, also called MI for the English acronym "Melt Infiltration", makes it possible to obtain a part made of composite material whose matrix includes silicon carbide and silicon.

[0055] In one embodiment, the manufacturing process may further comprise the following steps: - the deposition of an adhesion layer containing silicon on at least a portion of the healing layer; then - the application of an environmental barrier on the tack coat.

[0056] This embodiment makes it possible to obtain a part made of composite material which can be machined, and which nevertheless presents an environmental barrier layer.

[0057] In one embodiment, the first part of an assembly as described above may comprise: - a manufacturing step of a part made of SiC / SiC ceramic matrix composite material; - a step of depositing a healing layer over the entire machined external surface of the SiC / SiC composite part, the healing layer being made of a material selected from silicon nitride Si3N4, boron carbide B4C, a Si-BC ternary system, silicon carbide SiC, or a mixture of these compounds.

[0058] The characteristics described above for the healing layer deposition process can be used in such a process to obtain the same effects.

[0059] In one embodiment and to form an assembly as described above, it is possible to place a first part obtained by a process which has just been described in rubbing contact with a metallic part.

[0060] For example, such an assembly can be formed by shrink fitting or by partial encapsulation of one of the first and second parts in the other. Brief description of the drawings

[0061] [Fig.1] Fig.1 schematically represents a manufacturing process for a part in one embodiment of the invention. Description of the implementation methods

[0062] The invention is now described by means of a figure, presented for descriptive purposes to illustrate certain embodiments of the invention and which should not be interpreted as limiting the latter.

[0063] Fig. 1 schematically shows a manufacturing process for a part 100 in one embodiment of the invention.

[0064] The following description clarifies characteristics of both part 100 and the manufacturing process of the latter.

[0065] The part includes firstly a part made of SiC / SiC 10 ceramic matrix composite material.

[0066] A composite material comprises a fibrous reinforcement whose internal porosity is densified by a matrix.

[0067] In one embodiment, the fibrous texture can be obtained by three-dimensional weaving. By "three-dimensional weaving" or "3D weaving", we mean here a weaving method in which at least some of the warp yarns bind weft yarns over several weft layers.

[0068] The fibrous texture can be obtained by multilayer weaving between a plurality of warp yarn layers and a plurality of weft yarn layers. The resulting multilayer weave can, in particular, be an interlock weave, that is to say, a weave in which each weft yarn layer connects several warp yarn layers with all the yarns in the same weft column having the same movement in the plane of the weave. Other types of multilayer weaves can, of course, be used.

[0069] The fibrous texture can be achieved by weaving, for example with warp yarns extending in the longitudinal direction of the fibrous texture, it being noted that weaving with weft yarns in this direction is also possible.

[0070] Various usable multilayer weaving methods are described in document WO 2006 / 136755.

[0071] The fibrous texture can also be obtained by assembling at least two fibrous structures. In this case, the two fibrous structures can be linked together, for example by stitching or needle punching. The fibrous structures can, in particular, each be obtained from a layer or a stack of several layers of: - one-dimensional fabric (UD), - two-dimensional (2D) fabric - braid, - knitting, - felt, - unidirectional (UD) web of wires or cables or multidirectional (nD) web obtained by superimposing several UD webs in different directions and joining the UD webs together for example by sewing, by chemical bonding agent or by needle punching.

[0072] In the case of a stack of several layers, these can be linked together for example by sewing, by implantation of threads or rigid elements or by needle punching.

[0073] In one embodiment, the fibers of the fibrous texture can be coated with an interphase, for example boron nitride, to improve the resistance of the fibers to oxidation.

[0074] In the case of the invention, the composite material is a SiC / SiC material. This term takes on the classical meaning of the field and is intended to signify that the fibers of the texture fibrous components consist mainly of, or are made up of, silicon carbide SiC fibers and likewise, the matrix is ​​composed mainly of, or is made up of, silicon carbide SiC.

[0075] In one embodiment, the matrix can be formed in the internal porosity of the fibrous texture by methods known as such.

[0076] In particular, it can be deposited by a chemical vapor infiltration process (in English “Chemical Vapor Infiltration” or CVI).

[0077] In another embodiment, the matrix can be formed by infiltration with molten silicon, often called "MI" for the English acronym "Melt Infiltration".

[0078] In such a method, a fibrous preform is impregnated with an infiltration composition generally comprising molten silicon to form the matrix of the ceramic matrix composite material in the porosity of the fibrous preform.

[0079] Generally, for the infiltration process, one end of the preform is dipped into an infiltration composition bath, so that the latter fills the porosity of the preform by capillarity.

[0080] In one embodiment, the porosity of the fibrous preform can be impregnated by particles before the step of infiltrating the fibrous preform with the infiltration composition comprising liquid silicon.

[0081] For example, such particles make it possible to introduce into the porosity of the fibrous preform particles which react with liquid silicon to ensure the formation of a ceramic matrix, for example in silicon carbide.

[0082] In one embodiment, the particles impregnating the preform before the infiltration step can be ceramic and / or carbon particles.

[0083] Once the ceramic matrix composite material part 10 has been formed, it can be machined to form a machined part 11 of the desired dimensions.

[0084] Nevertheless, the ceramic matrix composite material part 10 is hard in the sense that its Vickers hardness is high, which makes its machining complex.

[0085] For example, machining can be carried out by grinding, milling, electrical discharge machining (EDM), waterjet cutting or any other known machining technique.

[0086] Mechanical machining methods can cause the appearance of cracks 101 starting from the surface of the part and extending into it.

[0087] It has been observed that such cracks can serve as initiators when the part is subjected to mechanical stress, and thus they are by no means desirable in the final part.

[0088] In order to present, despite possible cracks 101, mechanical characteristics allowing the desired use, the machined external surface of the part in SiC / SiC composite material is covered with a healing layer 20.

[0089] Such a layer is preferably deposited by a chemical vapor deposition (CVD) process.

[0090] Indeed, this deposition method makes it possible to ensure a uniform and complete coverage of the external surface of the part 11 made of ceramic matrix composite material.

[0091] Furthermore, this method is suitable regardless of the shape of the part to be covered.

[0092] It is thus possible to ensure the production of a part with a complex geometry.

[0093] The healing layer 20 is made of a material selected from nitride of silicon Si3N4, boron carbide B4C, a silicon-doped boron carbide system Si-BC, silicon carbide SiC or a mixture of these compounds.

[0094] Only one thickness of the healing layer is described in the figure. However, as described above, it is not excluded that the healing layer 20 is a stack of several layers, it being understood that each of these layers is then made up of a material chosen from silicon nitride Si3N4, boron carbide B4 C, a silicon-doped boron carbide system Si-BC, silicon carbide SiC or a mixture of these compounds.

[0095] In one embodiment, the thickness ei of the healing layer 20 can be between 10 pm and 50 pm.

[0096] Such a thickness is an excellent compromise between the additional mass added to the part and the improvement in mechanical properties that the healing layer 20 gives to the part.

[0097] The thickness ei is intended to characterize the average thickness of the healing layer 20. The possible filling of a crack 101 should not be understood as counting towards the thickness of the healing layer 20.

[0098] The thickness ei also ensures that the layer 20 is sufficient to fulfill its role of healing the machined composite material part 11, and in particular to give the whole much better mechanical properties than those obtained after machining, and in particular after the possible appearance of cracks.

[0099] This embodiment is particularly desirable in the case of a turbomachine component. Optionally, the component 100 can, according to an optional embodiment shown in dashed lines in [Fig. 1], be covered with an environmental barrier layer 40.

[0100] In a conventional manner in the field, an environmental barrier layer 40 is not placed directly in contact with the coated part 100 but is separated from the latter by a tack layer 30.

[0101] Such an adhesion layer 30 may for example include silicon, or even be made of silicon.

[0102] This bonding layer 30 improves the compatibility between the coated ceramic matrix composite material part 100 and the environmental barrier layer 40.

[0103] In particular, such an adhesion layer 30 has a coefficient of thermal expansion close to that of the ceramic matrix composite material part and that of the environmental barrier layer 40.

[0104] For example, the tack coat 30 can have a thickness e2 between 10 pm and 50 pm.

[0105] For example, the tack coat 30 can be deposited by plasma spraying under air.

[0106] Similarly, the environmental barrier layer 40 can be deposited by a liquid-based process.

[0107] In one embodiment, the environmental barrier layer may have a thickness e3 between 20 pm and 300 pm.

[0108] In one embodiment, parts 100, 200 can be turbomachine parts, in particular fixed or moving blades, portions of distributors, a ring sector, a portion of combustion chamber, or a combustion chamber.

[0109] Indeed, it is for such parts that the described embodiments are the most advantageous.

Claims

Demands

1. Part (100) comprising a part of a SiC / SiC ceramic matrix composite material (11) of which at least a portion of the external surface has been machined, and of which at least the portion of the external surface which has been machined is directly covered with a healing layer, the healing layer (20) being made of a material selected from silicon nitride Si3N4, boron carbide B4C, a ternary system Si-BC, silicon carbide SiC or a mixture of two or more of these compounds.

2. Part (100) according to claim 1, wherein the healing layer (20) comprises a thickness (ej) between 10 pm and 50 pm.

3. Part (100) according to claim 1 or 2, wherein the healing layer (20) is deposited over the entire external surface of the part made of SiC / SiC composite material.

4. Part (100) according to any one of claims 1 to 3, wherein the healing layer (20) is a stack comprising: - a layer made of boron carbide B4C; - a layer made of a silicon-doped boron carbide system Si-BC disposed on the boron carbide layer; - a layer made of silicon carbide SiC disposed on the silicon-doped boron carbide layer Si-BC.

5. Part (100) according to any one of claims 1 to 4, further comprising: - an adhesion layer (30) comprising silicon, the adhesion layer being disposed directly on at least a portion of the healing layer (20); and - an environmental barrier layer (40) comprising at least mullite and / or a rare earth silicate, the environmental barrier layer (40) being disposed directly on at least a portion of the external surface of the adhesion layer (30).

6. Part (100) according to any one of claims 1 to 5, which is a turbomachine part, in particular a blade, fixed or movable, a ring sector, a distributor, a portion of a distributor, a portion of a combustion chamber or a combustion chamber.

7. Assembly comprising a first part comprising a SiC / SiC ceramic matrix composite material of which at least a portion of the external surface is covered with a healing layer, the healing layer being made of a material selected from silicon nitride Si3N4, boron carbide B4C, a ternary system Si-BC, silicon carbide SiC or a mixture of these compounds, and a second piece of which at least the external surface is metallic, a portion of the first piece coated with the healing layer being intended to be in rubbing contact with the external surface of the second piece.

8. Assembly according to claim 7, wherein the first part (100) is according to any one of claims 1 to 6.

9. A method for manufacturing a part (100) according to any one of claims 1 to 6, the method comprising: - a step of manufacturing a part (10) from SiC / SiC ceramic matrix composite material; - a step of machining the part from the composite material thus obtained; then - a step of depositing a healing layer (20) over the entire machined external surface of the part from the SiC / SiC composite material, the healing layer being made of a material selected from silicon nitride Si3N4, boron carbide B4C, a ternary Si-BC system, silicon carbide SiC or a mixture of these compounds.

10. A manufacturing method according to claim 9, wherein the manufacturing step of a part (10) made of SiC / SiC ceramic matrix composite material includes a molten silicon infiltration step.

11. A manufacturing method according to any one of claims 9 or 10, wherein the step of depositing a silicon carbide coating (20) over the entire machined external surface of the composite material part (11) is carried out by chemical vapor deposition.