Method for injecting ceramic powders with an in-situ filter into the fiber preform

Description

Technical Field

[0001] The present invention relates to a method for injecting ceramic particles into a fibrous texture for the manufacture of a part made of composite material of the Oxide / Oxide or ceramic matrix (CMC) type, i.e. comprising a fibrous reinforcement formed from fibers of refractory ceramic material densified by a matrix also made of refractory ceramic material. Prior art

[0002] The manufacture of parts made of ceramic matrix composite material of the Oxide / Oxide or SiC / SiC type by injection generally comprises a step of impregnation of a fibrous texture with a loaded suspension, for example alumina particles in the case of an Oxide / Oxide type CMC or silicon carbide (SiC) particles in the case of a SiC / SiC type CMC. The impregnation step is carried out by pressure injection of a loaded suspension within the fibrous texture (STM process for "Slurry Transfer Molding"). In such a case, it is necessary to drain or filter the liquid phase of the suspension in order to obtain optimal filling of the residual porosities present in the fibrous texture with the solid fillers. Such a process is described in particular in document WO 2016 / 102839. The use of a filter element interposed between the fibrous texture and the part of the mold on which the solvent of the suspension is evacuated is, therefore, necessary.The filtration element may consist of a rigid piece of porous material which must be detached from the fibrous texture when demolding it after injection of the loaded suspension and filtration of the solvent.

[0003] The use of such a filter element can pose difficulties. Indeed, its removal from the fibrous texture can be tricky and lead to degradation of the injected fibrous texture. In addition, such a filter element being rigid, it is difficult to adapt to complex part geometries. To resolve these problems, it may be necessary to replace the rigid part made of porous material with a filtration layer, comprising a partially densified fibrous structure, which will be an integral part of the final composite material part. Such a filtration layer is notably described in document WO 2019 / 129983 which discloses a method for injecting ceramic particles into a fibrous texture comprising the following steps: placing a fibrous texture in a mold, the fibrous texture being interposed between one or more first ports and one or more second ports, injecting through the second port(s) a slip into the fibrous texture, the slip comprising a powder of refractory ceramic particles with a particle size smaller than the size of the interstices of the pore network of the fibrous texture, draining through the filtration layer the liquid phase of the slip having passed through the fibrous texture and retaining the powder of refractory ceramic particles inside said fibrous texture by the filtration layer so as to obtain a fibrous preform comprising at least the fibrous texture loaded with refractory ceramic particles and the filtration layer, the liquid phase of the slip being evacuated through the first port(s).

[0004] However, there are still disadvantages to using a filtration layer. The filtration layer comprises a fibrous structure, which must be partially densified to form a network of pores of a specific size within the layer, allowing the solvent in the suspension to pass through while retaining the refractory ceramic particles. Therefore, the filtration layer must be manufactured and treated before it can be placed in the mold, adding additional steps to the injection process. Statement of the invention

[0005] The present invention aims to overcome the aforementioned drawbacks and to propose a solution which makes it easier to produce parts by injection from ceramic matrix composite material (CMC), oxide, carbide or carbon base by injecting a suspension loaded into a fibrous texture.

[0006] To this end, the invention proposes a method for injecting ceramic particles into a fibrous texture comprising the following steps: placing a fibrous texture in a mold, the fibrous texture being interposed between one or more first ports and one or more second ports, injecting through the first port(s) a first suspension comprising a powder of filtration particles having a particle size greater than the size of the interstices of the pore network of the fibrous texture, draining the liquid phase of the first suspension through the fibrous texture, evacuating said liquid phase through the second port(s) and retaining the filtration particles by the fibrous texture so as to form a filtration layer between said fibrous texture and the first port(s), injecting through the second port(s) a second suspension into the fibrous texture, the second suspension comprising a powder of refractory ceramic particles having a particle size smaller than the size of the interstices of the pore network of the fibrous texture,drainage through the filtration layer of the liquid phase of the second suspension having passed through the fibrous texture and retention of the powder of refractory ceramic particles inside said fibrous texture by the filtration layer so as to obtain a fibrous preform comprising at least the fibrous texture loaded with refractory ceramic particles and the filtration layer, the liquid phase of the second suspension being evacuated through the first port(s).

[0007] Thus, by making a filtration layer an integral part of the final composite material part, the problem of removing a filtration element is eliminated and the surface finish of the filter side of the part is greatly improved. In addition, the manufacture of the filter is simplified compared to the filtration layers used in the prior art, the filter interface being formed inside the mold itself. This avoids the preliminary steps necessary for manufacturing a partially densified fiber texture and the difficulties inherent in producing a porosity network of a precise size. The operations of installing the filtration layer are also eliminated.

[0008] According to a particular characteristic of the process of the invention, the powder of the first suspension is a precursor of ceramic or glass.

[0009] According to another particular characteristic of the method of the invention, the filtration layer has an average thickness of between 100 µm and 200 µm.

[0010] According to another particular characteristic of the process of the invention, the size of the particles of the second suspension is on average 5 to 15 times smaller than the average size of the interstices of the pore network of the fibrous texture.

[0011] According to another particular characteristic of the method of the invention, the particles of the second suspension are made of a material chosen from: alumina, mullite, silica, an aluminosilicate, an aluminophosphate, zirconia, a carbide, a boride, a silicide and a nitride or a mixture of several of these materials.

[0012] According to another particular characteristic of the method of the invention, in which the fibrous texture comprises a fibrous structure obtained by two-dimensional weaving, or three-dimensional or multi-layer weaving, or automatic placement of unidirectional fibers.

[0013] According to another particular characteristic of the process of the invention, the threads of the fibrous texture are formed from fibers made of one or more of the following materials: alumina, mullite, silica, an aluminosilicate, a borosilicate, silicon carbide and carbon.

[0014] According to another particular characteristic of the method of the invention, the mold has an annular or truncated cone-shaped geometry, the fibrous texture being shaped according to an annular or truncated cone-shaped geometry when it is placed in the mold. Brief description of the drawings

[0015] [ Fig. 1 ] There figure 1is a schematic exploded perspective view of a tool in accordance with one embodiment of the invention, [ Fig. 2 ] There figure 2 is a schematic sectional view showing the tooling of the figure 1 closed with a fibrous texture positioned therein, and showing the formation of a filtration layer by injection of a first suspension loaded with filtration particles having a particle size greater than the size of the interstices of the pore network of the fibrous texture, [ Fig. 3 ] There figure 3 is a schematic sectional view showing the tooling of the figure 1 closed with a fibrous texture and a filtration layer positioned therein, and showing the impregnation of the fibrous texture with a second suspension loaded with particles having a particle size smaller than the size of the interstices of the pore network of the fibrous texture. Description of the embodiments

[0016] The fibrous texture was achieved in a known way by two-dimensional weaving or three-dimensional weaving.

[0017] By "two-dimensional weaving" is meant here a conventional weaving method by which each weft thread passes from one side to the other of threads of a single warp layer or vice versa. The method of the invention is particularly suitable for allowing the introduction of a loaded suspension into 2D fibrous textures, namely textures obtained by stacking 2D plies or layers, of significant thickness, that is to say 2D fibrous structures having a thickness of at least 0.5 mm, preferably at least 1 mm.

[0018] By "three-dimensional weaving" or "3D weaving" or even "multi-layer weaving" is meant here a weaving method by which at least some of the weft threads bind warp threads over several layers of warp threads or vice versa following a weave corresponding to a weaving pattern which can be chosen in particular from one of the following weaves: interlock, multi-plain, multi-satin and multi-twill.

[0019] By "interlock weave or fabric" is meant here a 3D weave in which each layer of warp yarns binds together several layers of weft yarns with all yarns in the same warp column having the same movement in the plane of the weave.

[0020] By "multi-plain weave or fabric" is meant here a 3D weave with several layers of weft threads whose basic weave of each layer is equivalent to a classic plain weave but with certain points of the weave which bind the layers of weft threads together.

[0021] By "multi-satin weave or fabric" is meant here a 3D weave with several layers of weft threads whose basic weave of each layer is equivalent to a classic satin weave but with certain points of the weave which bind the layers of weft threads together.

[0022] By "multi-twill weave or fabric" is meant here a 3D weave with several layers of weft yarns where the basic weave of each layer is equivalent to a classic twill weave type but with certain points of the weave which bind the layers of weft yarns together.

[0023] 3D textures have a complex geometry in which it is difficult to introduce and distribute suspended solid particles homogeneously. The method of the invention is also very well suited for the introduction of a loaded suspension into 3D woven fibrous textures.

[0024] The fibrous texture may also have been made from unidirectional (UD) layers or webs.

[0025] The threads used to weave the fibrous texture intended to form the fibrous reinforcement of the composite material part may in particular be formed from refractory ceramic fibers made of one of the following materials: alumina, mullite, silica, an aluminosilicate, a borosilicate, silicon carbide, carbon or a mixture of several of these materials.

[0026] According to a first example illustrated on the figures 1-3, a fibrous texture 10 is placed in a tool 100. In the example described here, the fibrous texture 10 is produced according to one of the techniques defined above (UD or 2D layer stacking or 3D weaving) with Nextel 610TM alumina threads. The fibrous texture 10 is here intended to form the fibrous reinforcement of a part made of composite material of the Oxide / Oxide type.

[0027] The tool 100 comprises a mold 110 and a counter-mold 120. The mold 110 comprises a bottom 111 provided with a plurality of ports 112. The mold 110 also comprises a side wall 113 which forms with the bottom 111 a molding cavity 114. In the example illustrated, the tool 100 in which the fibrous texture 10 is present is closed in its lower part by the mold 110 and is closed in its upper part by the counter-mold 120 forming a cover closing the tool 100. The mold 110 and the counter-mold 120 are used to size the preform and therefore the part to be obtained as well as to adjust the fiber content in the part to be obtained.

[0028] The mold 110 comprises a plurality of ports 112 opening into different zones of the molding cavity 114, through which a first suspension loaded with filtration particles having a particle size greater than the size of the interstices of the fibrous texture 10 is in particular intended to be injected in order to form a filtration layer 130 between the bottom of the mold 111 and the second face 10b of the fibrous texture. However, it does not depart from the scope of the invention when the mold comprises a single port. In the case of several ports, the first suspension can be injected through only a portion of the ports of the mold, to reserve the other portion of the ports for the evacuation of a second suspension as detailed in the remainder of the description.

[0029] The counter-mold 120 comprises, for its part, a plurality of ports 121 through which the solvent of the first suspension will be evacuated after having passed through the fibrous texture 10. In addition, a second suspension loaded with refractory ceramic particles is intended to be injected through the plurality of ports 121 of the counter-mold 120 in order to penetrate into the porosities of the fibrous texture 10 through the first face 10a of the fibrous texture 10. In the example illustrated in the figures 1-3, the solvent of the first suspension is discharged through all the ports 121 of the counter-mold 120 and the second suspension is injected through all the ports 121 of the counter-mold 120. It is not outside the scope of the invention when the counter-mold comprises a single port. In the case of several ports, the solvent of the first suspension can be discharged through only a portion of the ports of the counter-mold, to reserve the other portion of the ports of the counter-mold for the injection of the second suspension.

[0030] The solvent of the second suspension is intended to be evacuated through the plurality of ports 112 of the mold 110. In the example illustrated in the figures 1-3, all of the ports 112 of the mold 110 have also previously been used for injecting the first suspension. In the case where the mold comprises several ports, the solvent of the second suspension can be discharged through only a portion of the mold ports, the other portion of the mold ports having been reserved for injecting the first suspension.

[0031] According to the invention, a filtration layer 130 is interposed between the fibrous texture 10 and the bottom of the mold 111. The filtration layer 130 is formed following the injection of the first suspension loaded with filtration particles having a particle size greater than the size of the interstices of the fibrous texture 10, the liquid phase of said suspension being drained by the fibrous texture 10 then evacuated through the ports 121 of the counter-mold 120, the filtration particles thus remaining interposed between the fibrous texture 10 and the bottom of the mold 111. In the example described here, the filtration particles are ceramic or glass precursors. The liquid phase of the suspension may for example be water.

[0032] The arrows 1000 represent the movement of the first suspension injected into the mold 110. The arrows 2000 represent the movement of the medium or liquid phase of the suspension drained by the fibrous texture 10 as illustrated in the figure 2 .

[0033] The preform can be held in compression in the mold and can completely fit the mold walls. In addition, the preform forms a network permeable to the liquid phases of the first and second injections. Thus, there is no risk of deformation of the fiber structure under the effect of the pressure of the first or second injection.

[0034] Pumping P1 may, in addition, be carried out at the ports 121 of the counter-mold 120 during drainage, for example by means of a primary vacuum pump. Carrying out such pumping makes it possible to improve drainage and to dry the filter layer 130 more quickly.

[0035] For example, the filtration layer 130 has an average thickness of between 100 µm and 200 µm.

[0036] The filtration layer 130 allows the drainage outside the fibrous texture 10 of the liquid phase of the second suspension, comprising a powder of refractory ceramic particles having a particle size smaller than the size of the interstices of the fibrous texture 10, and the evacuation of said liquid phase through the ports 112 of the mold 110 due to the application of a pressure gradient between the ports of the mold 112 and the ports of the counter-mold 121.

[0037] Before injecting the second suspension loaded with particles having the smallest particle size into the fibrous texture 10, a compaction pressure making it possible to compact the fibrous texture 10 between the mold 110 and the counter-mold 120 can be applied by clamping the mold 110 or by means of a press, this compaction pressure being able to be maintained during the injection. The compaction pressure can also be exerted by a compaction liquid via a membrane as in the Polyflex process.

[0038] Alternatively, the compaction pressure may be applied after the start of injection of the second suspension and may then be maintained. The application of compaction pressure may compact the texture to assist in the drainage of liquid through the filtration layer and achieve a target thickness for the fiber preform without damaging it.

[0039] In the example described here, the second loaded suspension corresponds to a liquid phase loaded with refractory ceramic particles. figure 3 illustrates the configuration obtained during the injection of a second loaded suspension and the drainage of the liquid medium thereof. The suspension was injected under pressure through the ports 121 of the counter-mold 120 so as to penetrate into the fibrous texture 10 through its first face 10a. The refractory ceramic particles present in the suspension are intended to allow the formation of a refractory ceramic matrix in the porosity of the fibrous texture 10. This refractory ceramic matrix may, in an exemplary embodiment, be a refractory oxide matrix.

[0040] The second suspension may, for example, be a suspension of an alumina powder in water. The average particle size (D50) of the alumina powder may be between 0.1 µm and 2 µm. The alumina powder used may be an alpha alumina powder.

[0041] More generally, the second suspension may be a suspension comprising refractory ceramic particles having a particle size on average 5 to 15 times smaller than the average size of the interstices of the pore network of the fibrous texture.

[0042] The volume content of particles in the suspension may, before injection, be between 5% and 50%. The refractory ceramic particles may comprise a material chosen from: alumina, mullite, silica, an aluminosilicate, an aluminophosphate, zirconia, a carbide, a boride, a silicide and a nitride or a precursor of one or more of these materials. Depending on their basic composition, the refractory ceramic particles may, in addition, be mixed with particles of alumina, zirconia, aluminosilicate, a rare earth oxide, rare earth silicate (which may for example be used in environmental or thermal barriers) or any other filler allowing functionalization of the composite material part to be obtained such as carbon black, graphite or silicon carbide.

[0043] The liquid phase of the second suspension may, for example, comprise an aqueous phase having an acidic pH (i.e. a pH lower than 7) and / or an alcoholic phase comprising, for example, ethanol. The suspension may comprise an acidifier such as nitric acid and the pH of the liquid medium may, for example, be between 1 and 5. The suspension may, in addition, comprise an organic binder such as polyvinyl alcohol (PVA) which is in particular soluble in water.

[0044] As illustrated in the figure 3 , the refractory ceramic particles are present after injection of the second suspension into the porosity of the fibrous texture 10. The arrows 3000 represent the movement of the suspension injected into the fibrous texture 10. The arrows 4000 represent the movement of the medium or liquid phase of the suspension drained by the filtration layer 130 as illustrated in the figure 3 .

[0045] The counter-mold 120 exerts pressure on the fibrous texture 10 during and after the injection step of the second suspension.

[0046] Pumping P2 may, in addition, be carried out at the ports 112 of the mold 110 during drainage, for example by means of a primary vacuum pump. Carrying out such pumping makes it possible to improve drainage and to dry the fibrous texture 10 more quickly.

[0047] In this configuration, the filtration layer 130 makes it possible to retain in the fibrous texture 10 the particles initially present in the second suspension and for all or part of these particles to be deposited by filtration in the fibrous texture 10.

[0048] In the example presented here, the mold does not include a membrane. It is of course not outside the scope of the invention if the injections of the first and / or second suspensions are carried out under a membrane in a well-known manner, to improve the impregnation of the fibrous texture.

[0049] Once the injection and drainage steps have been carried out, a fibrous preform is obtained comprising the fibrous texture 10 loaded with refractory ceramic particles and the filtration layer 130 which is bonded to the fibrous texture 10. The adhesion between the filtration layer 130 and the fibrous texture 10 is achieved during the injection of refractory ceramic particles. Material is deposited between the filtration layer 130 and the fibrous texture 10 and, thanks to the compaction, the assembly is secured. The sintering heat treatment then creates bridges between the particles which completes the adhesion.

[0050] The preform obtained is then dried and then demolded, the preform being able to retain after demolding the shape adopted after compaction between the mold 110 and the counter-mold 120 thanks to the presence of a binder in the suspension of refractory ceramic particles such as PVA.

[0051] The preform is then subjected to a heat treatment, here sintering, for example in air at a temperature between 1000°C and 1200°C in order to pre-sinter the refractory ceramic particles and thus form a refractory ceramic matrix in the porosity of the fibrous texture 10. A part made of Oxide / Oxide composite material is then obtained, provided on the one hand with a fibrous reinforcement having a high matrix volume ratio with a homogeneous distribution of the refractory ceramic matrix throughout the fibrous reinforcement, and provided on the other hand with a surface covered with a smooth layer of ceramic or glass with an excellent surface condition, originating from the filtration layer 130.

[0052] A part made of CMC composite material other than Oxide / Oxide can be obtained in the same way by making the fibrous texture and the filtration layer with silicon carbide and / or carbon fibers and using a second suspension loaded with carbide particles (e.g. SiC), boride (e.g. TiB2), silicide (e.g. MoSi2) or nitride (e.g. Si3N4).

[0053] The second loaded suspension injected into the fibrous texture may, as a variant, comprise particles of a refractory ceramic precursor, for example of the sol-gel or polymer type. In this case, the heat treatment comprises at least one step of transforming the refractory ceramic precursor into a ceramic material (so-called ceramization step) followed possibly by an additional sintering step in order to further densify the composite material part.

Claims

1. A method for injecting ceramic particles into a fibrous texture (10) comprising the following steps: - placing a fibrous texture (10) in a mould (110), the fibrous texture (10) being interposed between one or more first ports (112) and one or more second ports (121), - injecting through the first port(s) (112) a first suspension comprising a powder of filtration particles having a particle size greater than the size of the interstices of the pore network of the fibrous texture (10); - draining the liquid phase of the first suspension by the fibrous texture (10), evacuating said liquid phase through the second port(s) (121) and retaining the filtration particles by the fibrous texture (10) so as to form a filtration layer 130 between said fibrous texture and the first port(s) (112), - injecting a second suspension into the fibrous texture through the second port(s) (121), the second suspension comprising a powder of refractory ceramic particles with a particle size smaller than the size of the interstices of the pore network of the fibrous texture (10), - draining through the filtration layer (130) the liquid phase of the second suspension having passed through the fibrous texture (10) and retaining refractory ceramic particle powder inside said fibrous texture (10) by the filtration layer (130) so as to obtain a fibrous preform comprising at least the fibrous texture (10) filled with refractory ceramic particles and the filtration layer (130), the liquid phase of the second suspension being evacuated through the first port(s) (112).

2. A method according claim 1, in which the powder of the first suspension is a ceramic or glass precursor.

3. A method according to claim 1 or 2 in which the filtration layer (130) has an average thickness comprised between 100 µm and 200 µm.

4. A method according to any one of claims 1 to 3, in which the size of the particles of the second suspension is, on average, 5 to 15 times smaller than the average size of the interstices of the pore network of the fibrous texture(10).

5. A method according to any one of claims 1 to 4, characterized in that the particles of the second suspension are made of a material chosen from: alumina, mullite, silica, an aluminosilicate, an aluminophosphate, zirconia, a carbide, a boride, a silicide and a nitride or a mixture of several of these materials.

6. A method according to any one of claims 1 to 5, in which the fibrous texture (10) comprises a fibrous structure obtained by two-dimensional weaving, or three-dimensional or multilayer weaving, or automatic placement of unidirectional fibres.

7. A method according to any one of claims 1 to 6, characterized in that the threads of the fibrous texture (10) are formed of fibres consisting of one or more of the following materials: alumina, mullite, silica, an aluminosilicate, a borosilicate, carbide silicon and carbon.

8. A method according to any one of claims 1 to 7, in which the mould (110) has an annular or frustoconical geometry of revolution, the fibrous texture (10) being shaped according to an annular or frustoconical geometry of revolution when placed in the mould (110).

9. A method of manufacturing a composite material comprising an injection method according to any one of claims 1 to 8, further comprising a heat treatment of the refractory ceramic particles present in the fibrous texture (10) of the preform in order to form a composite material part comprising at least said fibrous texture (10) densified by a refractory ceramic matrix and the filtration layer (130).