Manufacturing of composite material parts by modulated chemical infiltration followed by densification of a consolidated fibrous preform

Abstract

A process for manufacturing shaped parts in ceramic matrix composite (CMC) material for aeronautical applications in particular, comprising on the one hand a fibrous preform of geometry approaching or identical to the shaped part and on the other hand a matrix, the fibrous reinforcement and the matrix being separated by a thin layer serving as an interphase between fibers and matrix, a manufacturing process which includes: - an initial step of chemical infiltration from the gaseous phase of the fibrous preform, controlled in a specific double chamber where conditions prevail mainly of diffusion of the reactants towards the fibrous preform, diffusion conditions modulated in particular by the internal chamber according to the geometry of the preform;- then, after consolidation of the fibrous preform by the interphase and a matrix layer during this first step, at least a second step consisting of complete densification by the matrix outside this enclosure; - this second step being, or not being, preceded or followed by a third step of grinding or machining. Depending on the densification technique used and according to the geometry of the parts and / or their use, this process makes it possible to manufacture finished parts, parts to be ground or machined more deeply. In the latter case, a protective coating of the exposed fibers is then applied to the reworked parts.

Description

Title of the invention: Manufacture of composite material parts by modulated chemical infiltration then densification of a consolidated fiber preform

[0001] The present invention relates to a method for manufacturing parts made of ceramic matrix composite (CMC) material with optimal properties using a method which comprises an initial step of chemical infiltration from the gas phase of a fiber preform of geometry similar to the CMC part or identical to it in a specific double enclosure where mainly diffusion conditions of the reactants prevail, then after consolidation of the fiber preform during this first step, at least a second step which consists of a complete densification of the fiber preform by the matrix outside this enclosure. This densification leads to a finished part or a final rectification is carried out. Optionally, more significant machining precedes or follows the complete densification, the machining after complete densification being associated with a deposition of a protective coating of the fibers.

[0002] Ceramic matrix composites are in fact known lightweight materials used to manufacture parts exposed to conditions such as those encountered in aeronautical and space applications or in other fields, for example that of industrial turbines. They comprise a reinforcement by fibers, including carbon fibers and ceramic fibers, densified by a ceramic matrix. Between the fibers and the matrix, a continuous layer commonly called interphase makes it possible to adjust the bonding strength between these two constituent elements of the CMCs.

[0003] These materials, which are lighter than metal alloys, are used, or applications are envisaged, in more or less severe thermomechanical and environmental conditions. They can thus be stressed in more or less drastic mechanical conditions relative to their intrinsic mechanical properties, i.e. in their elastic deformation range, or in more severe stress conditions which lead to probabilities of almost permanently exceeding the elastic deformation threshold, the matrices of these composite materials with ceramic matrices then cracking, exposing the core of the material, possibly down to the fibres, to attacks from the surrounding atmosphere. The types of applications in corrosive atmospheres therefore depend on the degree of stress and the lifespan envisaged for these materials.

[0004] Applications are possible for medium-long lifetimes, from a few hundred to a few thousand hours with a simple protective coating. self-healing in an oxidizing atmosphere as shown in US 5194330. For more severe applications, self-healing matrices alternating layers of silicon carbide and layers containing the Si-BC elements have also offered solutions at moderately high temperatures, 600 to 1000°C, for durations compatible with military aeronautics for example, since 1990 (FR 2668477 and US 5246736).

[0005] Applications in the field of civil aeronautics require much longer service lives. We can then distinguish CMC parts which are used in static conditions, with moderate thermomechanical stresses, from parts which would be used in rotation under much more severe thermomechanical conditions. Solutions have already emerged for parts used in static conditions. This is not yet really the case for parts which would be used in rotation in the hottest areas of the engines.

[0006] In all the cases previously mentioned and for any application, it appears clearly that the intrinsic properties of the CMCs must be optimized: - to extend their elastic domain by the use of very strong fibers, interphase of well-controlled thickness and structure and perfectly densified matrices; - to protect the core of the material by new matrices, little oxidizable or self-healing by the formation of phases more resistant to oxidation; - which does not prevent in both cases having to protect them by self-healing external layers and / or offering thermal and / or anti-oxidation protection as in US 6759151 or US 20060073361.

[0007] These CMC materials are manufactured by different techniques where the fibers are joined in the form of threads. Among these, chemical deposition from the gas phase (CVD) directly on one or more threads allows them to be coated with interphases of well-controlled structure and thickness. Then, different steps including pre-impregnation and final infiltration in a molten medium currently allow the manufacture of high-performance parts for static applications ((Jim Steibell, American Ceramic Society Bulletin, Vol. 98, No. 3, pp. 30-33). Another technique consists of assembling the threads beforehand to form a fibrous texture which constitutes the fibrous preform reinforcing the material. This then undergoes chemical infiltration from the gas phase (CVI) to deposit the interphase in a first step. To obtain the best thermomechanical properties with fibers having the highest mechanical properties, it is also necessary to perfectly control the initial conditions of interaction of the gas phase with the fibers, to deposit an interphase of optimal structure and as constant a thickness as possible on all the fibers. M. Leparoux et al. have indeed demonstrated, as early as 1995, the important influence of the thickness of the interphases in boron nitride on the final mechanical properties of CMCs (M. Leparoux et al., Proc, of ICCM-10, Whistler, BC, Canada, August 1995, IV, pp. 633-640). The fiber preform must then be infiltrated with a first layer of matrix, perfectly controlling the infiltration speed at every point of the fiber preform coated with its interphase so as to avoid the formation of porosities in the very heart of the future composite material, inside the threads. To obtain optimal properties of CMCs, this initial stage of consolidation of the fiber preform, by a truly uniform interphase and first layer of matrix, is essential, as is the quality of the final densification of the matrix. This good control of the infiltration conditions of the initial layers in CVI followed by densification by the matrix of fibrous preforms of identical shape or close to the final shape of CMC parts is the subject of the present invention.

[0008] The subject of the invention is therefore a method for manufacturing a shaped part in ceramic matrix composite material comprising on the one hand a fibrous reinforcement made up of fibers forming a fibrous preform of geometry close to or identical to the shaped part and on the other hand a matrix, the fibrous reinforcement and the matrix being separated by a thin layer serving as an interphase between fibers and matrix, a manufacturing method which comprises: - a first step of consolidation of said fibrous preform by two layers, an interphase and a matrix layer successively produced by chemical infiltration from the gas phase in a specific double enclosure where diffusion conditions prevail mainly characterized by a random and undirected movement of said gas phase towards the fibrous preform, said specific double enclosure comprising two walls, external and internal, separated by a space free of any material where: i) the first external wall which is placed in the reactive gas flow is characterized by the fact that any part of its wall which is directly exposed to a reactive gas flow whose direction makes an angle greater than 30 degrees with respect to its external surface is kept solid and prevents any direct entry of the convective gas flow inside the enclosure,and any part of its wall which is not exposed to a direct flow or makes an angle of less than 30 degrees with respect to the direction of this flow may be pierced with cylindrical and / or oblong openings, these having respectively a diameter or a width perpendicular to the projection on the surface of the direction of the gas flow, less than approximately one time the thickness of this first external wall in its pierced zone; ii) the second internal wall, arranged inside the first wall, consists of two elements of a mold applied against each other on their periphery, these elements of the mold having on the one hand an internal surface adapted to the fiber preform and on the other hand an external surface against which is applied a layer of porous material of the felt type, or fabric leaving the two external and internal walls of the double enclosure separated by said space free of any material with a thickness greater than approximately 3 mm, said mold elements being pierced on all or part of their wall with cylindrical and / or oblong openings whose diameter or width is less than approximately 5 mm and the maximum spacing is less than approximately 3 mm; iii) the openings in the external wall are characterized by a spacing and a section which are possibly variable depending on their position on the wall and the openings made in the internal wall have a spacing, a section and especially a depth which are possibly modulated depending on the geometry of the fiber preform to be infiltrated; - at least a second stage of complete densification by the matrix of the consolidated preform, outside of said specific double enclosure; - the second step being, or not being, preceded or followed by a third step of grinding or machining, the machining after complete densification being associated with a deposit of a protective coating of the fibers.

[0009] A certain number of advantages explained below already emerge from these general conditions of chemical infiltration of the interphase and the matrix layer. Limiting the size of the openings made in the first external wall, choosing the direction of the gas flow relative to the surface allowing the gas to enter and closing the surfaces located on the gas arrival side minimize the arrival of a convective gas flow towards the zone located inside this first external wall. The limited dimensioning of the openings made in the mold elements and the small maximum spacing between these openings make it possible to obtain a possibility of entry of the gas phase towards the fiber preform without a significant blocking zone by the solid wall of the mold elements themselves. Pressing the mold elements against each other on all sides allows the enclosure and processing conditions of the fiber preform to be perfectly defined. In the case where the fiber preform does not have a texture that allows it to maintain its geometry without support by walls, pressing their inner faces against this fiber preform ensures that its shape is preserved and that the fiber density in the fiber preform is maintained at the desired value. The provision of a free space between the inside of the first external wall and the outside of the mold elements is added to the choice of the direction of flow of the gas phase outside the external wall relative to the pierced areas of this first wall. These characteristics make it possible to homogenize the gas phase mainly by diffusion and the localized homogenization in this free space is favored by the interposition of a layer of textured or woven porous material at the outer surface of the mold elements. This layer of material also prevents the supply of fresh reagents to the areas of the fiber preform located at the openings made in the mold elements. Modulating the spacing, section and depth of the openings made especially in the mold elements allows to modify, if necessary, the local infiltration conditions according to the geometry of the fiber preform, more precisely according to the depth of the underlying fiber structure to be infiltrated which varies locally for shaped parts. It is this characteristic which makes it possible to define modulated chemical infiltration.

[0010] The chemical infiltration method as described above is implemented in such a way that the reactive gas flow is as parallel as possible to the pierced surfaces of the first external wall, that is to say that it does not make an angle greater than approximately 30° with respect to these surfaces. Very generally, but without this excluding any other possibility, the first external wall has a parallelepiped shape with larger flat surfaces and smaller sides. In this case, the chemical infiltration method is implemented in a chemical infiltration installation where the large flat surfaces are arranged vertically in an installation where the gas flows flowing between the different double enclosures are identical and have an upward or downward vertical direction.

[0011] In all cases, the chemical infiltration installation is designed to allow an identical flow along each large face of all the double enclosures arranged vertically in the installation. In the case of a horizontally elongated chemical infiltration installation, multiple vertically directed inlets allow equal upward or downward flows of the reactive gas phase to be introduced.But it is also possible to use a horizontal installation with inlets-outlets themselves in a horizontal direction; the change towards the vertical upward or downward direction of the flow is then produced when crossing a wall or a good distribution of the gas flow along each large face of the double enclosures is produced by a singular pressure drop caused by small openings made in the said wall, all of the openings made in the wall leading to a narrowing for the flow of the gas phase relative to the gas arrival section in front of this wall.

[0012] The chemical infiltration process is also implemented in a chemical deposition installation where the double enclosures are arranged vertically in a chemical infiltration installation where the gas flows flowing between the different double enclosures are identical and have a horizontal direction. In the latter case, the process of chemical infiltration from a gas phase of an interphase and a matrix layer can be carried out for example in a cylindrical chemical infiltration installation which comprises: - a gas inlet then a gas preheating zone; - a gas outlet, these inlets and outlets being located at each end of the vertical cylinder; - a cylindrical deposition zone forming a crown where groups of double enclosures positioned along radii of the cylinder are arranged, an identical horizontal gas flow being introduced along each double enclosure using, through a cylindrical wall inside or outside the deposition zone, a singular pressure drop between the vertical gas flow leaving the preheating zone and the gas flow of radial main component which crosses the cylindrical deposition zone in a main direction which is respectively centrifugal or centripetal.

[0013] Generally speaking, the method of manufacturing a shaped part made of composite material of the invention comprises: - the placement of a fiber preform in a double treatment enclosure; - consolidation of the fiber preform by chemical infiltration of an interphase and a matrix layer in this enclosure; - then the densification of the consolidated preform outside this enclosure using known techniques.

[0014] This second densification step to form the entire matrix is ​​carried out: - either at least in part by chemical infiltration from the isothermal gas phase (ICVI), or by chemical infiltration from the gas phase in a temperature and / or pressure gradient; - either at least in part by impregnation with at least one ceramic precursor polymer followed by pyrolysis; - either at least in part by introducing carbon and a ceramic powder into the fibers and by infiltrating a silicon-based metal in the molten state.

[0015] A second densification step by chemical infiltration from the gas phase in a temperature and / or pressure gradient often requires the use of simpler shapes than those of the final shaped part. It is then necessary to use a fiber preform whose geometry is simplified and constitutes a rough cut of the shaped part. For other matrix densification techniques, this choice can also be made by using a rough cut of the shaped part. In these cases, machining is carried out after densification to finish manufacturing the CMC part.

[0016] It is also possible to manufacture a self-healing matrix, in particular by chemical infiltration, consisting of phases of different natures which include a carbide of a metallic or metalloid element and at least one carbide taken among the binary boron-carbon, the ternary silicon-boron-carbon, or a metal boride. The boron element is preferentially provided in this case by a gaseous phase comprising a boron trichloride of purity less than approximately 99%.

[0017] More generally, the entire matrix is ​​made up of at least one material taken from the groups of oxides, carbides, nitrides or silicides or by a combination of materials taken from at least one of these groups.

[0018] A more detailed and more understandable description of this invention will be provided with the support of examples of descriptive figures and examples of implementation. This description will initially be based on conditions where the double enclosure is made up of two mechanically integral walls and used to manufacture parts of a shape that is not too thick or does not have significant transverse protrusions, in the shape of a T for example. The first external wall is in this case made up of plates and spacers. We will then see that in a more general context of the invention, to infiltrate parts of any shape including parts of more complex geometry, an internal enclosure formed by the mold elements is used which is simply arranged on supports inside the first external wall.

[0019] [Fig. 1] is an example of a view of the outer face of a flat plate of the first outer wall; [Fig.2] shows the inner face of the same flat plate; [Fig.3] is another example of a view of the outer face of a flat plate of the first outer wall; [Fig.4] shows another example of a view of the outer face of a flat plate of the first outer wall with different oblong openings; [Fig.5] shows an example view of the flat outer face of a mold element constituting part of the second inner wall; [Fig.6] shows another example of a view of the flat outer face of a mold element; [Fig.7] shows an example of a longitudinal section of a double enclosure for chemical infiltration of an interphase and a matrix layer in a fiber preform, an example where the two enclosures are mechanically connected; [Fig.8] shows an example of a chemical infiltration installation where the double treatment chambers are arranged vertically in a chemical infiltration installation where the gas flows flowing between the different double chambers are identical and have an upward vertical direction; [Fig.9] shows an example of a cylindrical chemical infiltration installation where the double treatment chambers are arranged vertically in a chemical infiltration chamber where the gas flows between the different doubles enclosures are identical and have a horizontal and radial centripetal direction; [Fig. 10] is an example of a longitudinal section of a double enclosure for chemical infiltration of a fibrous preform shown schematically with a shape close to or identical to a final part; [Fig.l 1] shows another example of a view of the flat outer face of a mold element; [Fig. 12] is another example of a longitudinal section of a double chemical infiltration enclosure of a fibrous preform shown schematically with a shape close to or identical to a final part, an example where the mold elements have a non-planar external surface; [Fig. 13] shows an example where the second internal wall containing the fiber preform is simply arranged in the external enclosure without a mechanical link between the two enclosures. [Fig. 14] shows an example where the fiber preform is self-supporting and retains its general shape without requiring total support by the walls of the mold elements, this fiber preform being contained in the second internal wall which is simply arranged in the external enclosure as in the previous case.

[0020] The present invention relates, as already indicated, to a manufacture of CMC parts which comprises an initial step of chemical infiltration from the gas phase of a fiber preform of geometry identical or close to that of the CMC part under conditions of diffusion of the reagents towards the surface of this preform in a specific double enclosure, then a step of complete densification by the matrix outside this enclosure. The step of chemical infiltration of a fiber preform is initially carried out here in a double enclosure which comprises, according to the example of Figures 1 to 7, flat surfaces constituted by plates.

[0021] [Fig.l] shows an example of a plate 100 constituting the first external wall, seen from the side of its flat external face 105. In the method of the invention, this flat surface of the first wall is exposed to a flow of reactive gases flowing parallel to or not at an angle of more than 30° relative to it. This flat plate is pierced with openings 190 which are here cylindrical. These have a diameter smaller than the thickness of the plate in the area crossed. Holes 110 make it possible to fix two flat plates at a determined distance from each other by means of spacers and the use of bolts and nuts.

[0022] [Fig. 2] shows the inner face of the flat plate 100 and more particularly the recessed area 170 which constitutes a shoulder on which a mold element 200 rests, holding the porous layer 400 there as can be seen in [Fig. 7]. The recessed area 180 is pierced by the openings 190. This recessed area 180 also allows space 300 to be left free of any material according to [Fig.7], where the gas phase is homogenized mainly by diffusion.

[0023] Another example of a flat plate 100 with its outer face 105 is provided by [Fig. 3]. The openings 195 are this time oblong with a dimension along the direction of the main component of the convective gas flow, here vertical, less than approximately one time the thickness of the plate in its recessed zone. The length of these oblong openings can be variable as shown in [Fig. 4]; their spacing can also be varied. The geometry, the dimension and the spacing between these openings in the flat plates make it possible to vary the open section in the first external wall and thus to promote more or less the exchange between the gaseous phase flowing outside this first wall and the gaseous phase located inside, in the space left free of any material located between the plates 100 and the mold elements 200 presented below.

[0024] [Fig. 5] shows an example of a mold element 200 seen according to its external face 220. It is pierced with cylindrical openings 290 whose diameter is less than approximately 5 mm and the maximum spacing is less than approximately 3 mm. [Fig.6] shows another example of a mold element 200 which is pierced with oblong openings 295 whose width is less than about 5 mm and the maximum spacing is less than about 3 mm. In both cases, these mold elements are machined to allow, on the one hand, good mechanical strength of a fiber preform pressed against their inner face, and on the other hand a distributed entry of the reactive gas phase while avoiding pressing a large surface area, with a dimension greater than approximately 3 mm, which would mask the surface of the fiber preform to be infiltrated. The direction of the largest dimension of the oblong openings can be chosen so as to ensure good support of the outermost fibers of the fiber preform.

[0025] [Fig.7] will allow a better understanding of the general arrangement of the preceding elements, the specificities of the entire double chemical infiltration enclosure relative to the fiber preform and its arrangement in the reactive gas flow. It shows a vertical section of the double enclosure 50 with the two plates 100 with a flat outer surface 105, recessed on the inner side in the support zone 170 and the most recessed zone 180. These plates 100 are here pierced with cylindrical openings 190. The mold elements 200, with an inner surface 210 and outer surface 220 are pierced by the cylindrical openings 290. The inner surface 210 is here flat to infiltrate fiber preforms which are used for mechanical tests. The outer surface 220 and the recess 170, forming a shoulder, make it possible to maintain the porous layer 400 against the mold elements while leaving free of any material space 300. It is the free space which allows the gas phase to be homogenized and this localized homogenization is favored by the interposition of the layer of textured or woven porous material on the outer surface of the molds. The entire double enclosure is held by means of the two plates 100 and the bolts 101 and nuts 102. The spacers 160 and 165 make it possible to hold the two plates 100 taking into account the application of the mold elements 200 against each other at their periphery and here against the fiber preform. The spacer 165, located on the gas inlet side, necessarily completely closes the space between the two plates. The lateral spacers, not visible in this figure, also preferably make it possible to prevent the entry of gas flow between the two supports in the case of this configuration where a relatively thin preform is infiltrated which must be held by the mold elements. According to [Fig.7], the double enclosure 50 is placed in a reactive gas flow 20 which is here vertical and descending, especially essentially parallel to the outer faces of the plates 100. The convective flow towards the free space zone 300, through the openings 190 or 195 of reduced size compared to their depth, is thus minimized and the complementary interposition of the porous material 400 makes it possible to then put, behind this layer of porous material and through the cylindrical or oblong openings of the mold elements, the reactive gas phase in contact with the fiber preform mainly under diffusion conditions. In this free space 300 we find the gaseous reactants entering the external enclosure but also any intermediates generated in the gas phase, possibly precursors of the deposit, and the products of homogeneous and heterogeneous chemical reactions coming from the surfaces and mainly from the fiber preform.

[0026] The chemical infiltration step of the method according to the invention is implemented in installations where the double enclosures are arranged so that the plates of the external wall are vertical. In these installations, the gas flows flowing between the double enclosures are identical and have either an upward or downward vertical direction, or a horizontal direction.

[0027] [Fig. 8] schematically shows an example of a chemical infiltration installation 500 where the double enclosures 50 are arranged vertically in a chemical infiltration installation where the gas flows 520 flowing between the different plates 100 of the double enclosures are identical and have an upward vertical direction. In this example, the installation has a horizontal gas inlet and outlet, which makes it possible to arrange the heating of the installation throughout the device. The wall 550 of the installation is pierced with small openings 555 which are shown on the external surface 560 of the wall 550. They allow the entry of gases along the double enclosures. The dimensions of these openings are chosen so that the sum of their sections is less than the gas arrival section in front of the wall 550 so as to ensure a singular pressure drop and thus a good distribution of the ascending gas flow along each large external surface of the double enclosures. This is obviously a schematic representation with a single double enclosure 50 in each ascending gas flow zone. It is clear that several chemical infiltration enclosures 50 can be arranged in vertical series by superimposing them directly or by means of spacers leaving a free space for the gas phase between two double enclosures. Note that these enclosures 50 are easily held on or above the wall 550 by slides for example.

[0028] [Fig. 9] shows an example of a schematic representation of a cylindrical chemical infiltration installation 600 where the double enclosures 50 are arranged vertically in a chemical infiltration installation where the gas flows 620 flowing between the different enclosures are identical and have an essentially horizontal and radial centripetal direction between two concentric cylindrical walls 650 and 670. In this example a reactive mixture is introduced at the inlet 610 of the installation. It then passes into a gas preheating zone 640 of geometry not specified here, for the sake of clarity of the drawing. The trajectory of the gases is then ascending along 615. [Fig. 9] shows the cylinder 650, which allows the introduction of the gases into the chemical infiltration zone, shown in vertical view but also according to a section at the bottom of the figure.At the top of the figure, the openings 655 which are made in the cylinder 650 have been shown, on a level and for introduction along a plate constituting the first external wall of the double enclosure, these openings are also visible at the bottom of the figure in the section where a double enclosure 50 is shown in a vertical position or a set of enclosures 51, 52 and 53, depending on the relative dimensions of the enclosures and the chemical infiltration installation. The gases are evacuated by the central pipe 670 towards the outlet of the installation 680 where they are treated and pumped. As in the horizontal installation, a good distribution of the gases in front of all the double enclosures is ensured by the dimension of the openings 655 relative to the crown section of gas passage delimited by the external wall of the installation 600 and the cylinder 650 which are concentric.This good distribution is ensured at all levels of the installation and along all its radii by making openings 655 and relative diameters of the cylinders such that a singular pressure drop is produced at the gas inlet through the openings 655 in the area where the double chemical infiltration enclosures are arranged. The section of [Fig.9] also shows that shims 660 make it possible to keep the reactive gases as close as possible to their external walls. These shims can make it possible to maintain the speed of the gases along these walls but also, . advantageously, to accelerate these with the distance traveled along the enclosures.

[0029] In the chemical infiltration installations of figures 8 and 9, the double enclosures 50 can be arranged vertically resting on the small or large side of the enclosure by necessarily using a spacer or a wall closing the enclosure on the gas arrival side.

[0030] The subject of the method of the invention is the manufacture of shaped parts made of ceramic matrix composite material, a material which begins with the consolidation of a fiber preform of geometry similar to or identical to each shaped part. [Fig. 10] schematically shows a fiber preform 10 of geometry which is not parallelepipedal. The same elements as in [Fig. 7] are found in vertical section, i.e. the double enclosure 50 with the two plates 100 of flat outer surface, recessed on the inner side and pierced with cylindrical openings. The mold elements 200, of inner 210 and outer 220 surface are pierced by the cylindrical openings 290. It is important to note that the inner surface is no longer flat but is adapted to the desired geometry for the fiber preform.The outer surface 220 is here kept flat and allows, with the shoulder 170, to hold the porous layer 400 against the mold elements while leaving the space 300 free of any material. The spacers 160 and 165 allow the two plates 100 to be held while taking into account the application of the mold elements 200 against each other. The spacer 165, located on the gas inlet side, necessarily completely closes the space between the two plates 100.

[0031] According to this [Fig. 10], the double enclosure 50 is placed in a reactive gas flow 20 which is here vertical and descending, especially essentially parallel to the outer faces of the plates 100. The convective flow towards the free space zone 300, through the openings made in the plates 100, is thus minimized and the complementary interposition of the porous material 400 makes it possible to then put, behind this layer of porous material and through the openings 290 of the mold elements, the reactive gas phase in contact with the fiber preform mainly under diffusion conditions. In the case presented, it clearly appears that the diffusion distance through the openings 290 varies according to the geometry of the fiber preform. It can however be noted that the diffusion distance is all the greater as the thickness of the fiber preform in one place is smaller.The consumption of the precursors for deposition on the fibers is therefore lower, which makes it possible to minimize the differences in deposition speed at each point of the fiber preform.

[0032] For certain more complex geometries of the fiber preform, it is necessary to refine the previous arrangements and to modify the supply of precursors at different entry points of these through the surface of the fiber preform. [Fig.l 1] shows the flat outer surface 220 of a mold 200 which uses or cylindrical openings 290 and at the same time oblong openings 295 of variable dimensions depending on their length from one point to another of the mold. An adjustment by the diameter of the cylindrical openings and also by the width as well as the length of the oblong openings is also possible provided that at least one dimension of all the openings is limited to a value less than approximately 5 mm while maintaining a spacing between the openings less than approximately 3 mm. This configuration makes it possible to reduce and increase, depending on the position, the section through which the gas phase diffuses so as to adjust the deposition speeds at each point for a preform of given geometry. The depth of these openings is the other very important parameter for adjusting this local speed of supply of the gas phase. It should also be noted that the supply of reagents through the first external wall to the area left free of any material 300 can also be modified by varying the shape of the openings, cylindrical 190 or oblong 195, and the distance between these openings made in the external wall. Such variations can also be made on the same external surface of the double enclosure.

[0033] Thus, according to one embodiment, the method according to the invention may comprise a first consolidation step in a double enclosure consisting of two walls where the external wall (100) and the mold elements (200) are pierced with cylindrical and / or oblong openings whose sections are, in each of the walls, identical from one point to another of their surface. According to another embodiment, the method of the invention may comprise a first consolidation step in a double enclosure consisting of two walls where the external wall (100) and the mold elements (200) are pierced with cylindrical and / or oblong openings whose sections are, in at least one of the walls, different from one point to another of the surface.

[0034] [Fig. 12] schematically shows a variant of the double enclosure 50 where the outer surface 220 of the mold elements is no longer flat but modified taking into account the geometry of the fiber preform, which leads to modifying the depth of the cylindrical 290 or oblong 295 openings. These depths can be chosen to be identical for fiber preforms and therefore for final parts that are not flat but have a thickness that varies little. These depths can be chosen to be variable and a function of the geometry of the fiber preform to be infiltrated.

[0035] The preceding figures present a detailed example of implementation where the external and internal walls are mechanically connected. More generally, the two walls of the double enclosure 50 are not in direct contact with each other. This arrangement of the two walls which constitutes the double enclosure is used by the method according to the invention with a first external wall around which the reactive gas phase and a second internal wall consisting of mold elements which are applied completely or not to the fiber preform, the two external and internal walls being separated by the free space 300.

[0036] [Fig. 13] schematically shows a double enclosure where the mold elements are simply arranged inside the first external enclosure on supports 260 without any direct contact between the two walls of the double enclosure. In [Fig.13], an ascending vertical flow 20 flows around the double enclosure as in the chemical infiltration installation shown in [Fig.8]. This double enclosure is obviously shown here as is the shape of the fiber preform 10 which here has a central body and protrusions at its two ends to show the adaptability of the process. However, we find there all the essential elements for good operation of the double enclosure with the vertical walls 100 pierced but also the high horizontal wall 100, pierced because located opposite the gas arrival.This also allows an inlet / outlet of the gas phase towards the upper part of the mold elements 200 which themselves have openings in their vertical walls but also in the upper and lower horizontal walls. This arrangement allows, with the use of distances and sections for variable diffusion through the mold elements 200, to process a fiber preform 10 of geometry having a protrusion at both ends, for example a turbine blade blank with root and heel which will have to be ground during or after complete densification. The mold elements 200 are arranged on the supports 260 supporting them on a part of their periphery, also leaving free the space between the first external wall and the openings of the lower horizontal face of the mold elements 200. Let us thus note: . - that the entire surface of the mold elements 200 can be pierced; - that we find, in place of the spacer 165 closing the external wall, the solid wall 165 of the external enclosure facing the arrival of the reactive gases, thus avoiding direct entry into the free space 300 located between the two external and internal enclosures; - that the felt or fabric 400 is everywhere attached to the mold elements constituting the internal enclosure; - that the fiber preform can be infiltrated from all sides of the mold elements 200 which are here pressed against the fiber preform; - that the supply of reagents at different points on the surface of the fiber preform can be modulated above all by the geometry of the openings made in the walls of the mold elements 200 but also by the geometry and / or the spacing of the openings made in the first external wall.

[0037] [Fig. 14] is close to the previous one with mold elements 200 which are simply arranged inside the first external enclosure 100 on supports 260 without any direct contact between the two walls of the double enclosure. The difference comes from the fact that the fiber preform is in this case self-supporting. It does not require support by the internal walls of the mold elements over its entire surface. It is also a fiber preform 10 of geometry presenting an outgrowth at both ends, for example a turbine blade blank with root and heel which will have to be rectified during or after complete densification. Note that this configuration allows for free spaces to be provided in front of parts of the preform surface that have been chosen.

[0038] Several molds comprising two adjoining mold elements 200 can also be arranged inside the same external wall of larger dimension.

[0039] Despite all these provisions, some parts with too complex geometry cannot be manufactured directly. The method of the invention is then carried out on a rough geometry as close as possible to the final part. Depending on the densification technique used, the following are carried out: - either complete densification of the consolidated preform and final machining; - or further consolidation of the fiber preform by the matrix layer followed by machining according to the geometry of the final part, then complete densification by the matrix.

[0040] The materials of the walls of the double enclosure must have little or no chemical interference with the chemical infiltration process. They are made of carbon or a carbon-carbon composite material coated or not with a ceramic layer, or a ceramic material, or a ceramic matrix composite material. According to a variant of the method of the invention, the external wall and the mold elements are made of carbon or a carbon-carbon composite material coated or not with a ceramic layer, or a ceramic material, or a ceramic matrix composite.

[0041] The method is implemented with various reinforcing fibers. In a non-limiting manner, the reinforcing fibers are carbon, alumina, mullite or silicon carbide fibers. These are in particular carbon, alumina, mullite or silicon carbide fibers which form elongated threads incorporated in the fiber preform so as to constitute a reinforcement by threads following a main reinforcement direction (1D composite), by threads which constitute textiles with two main reinforcement directions (2D composite) or which additionally comprise a partial reinforcement following a third direction (2.5D composite), or which constitute a reinforcement following N directions where N> 3.Generally, the fiber preform can constitute a reinforcement by fibers which form elongated threads following a main reinforcement direction (1D composite), by threads which constitute textiles with two main reinforcement directions (2D composite) or which additionally comprise a partial reinforcement following a third direction (2.5D composite), or which constitute a reinforcement following N di. ctions where N> 3. Some parts with complex geometry require main reinforcement directions that can vary within the same part. The method of the invention uses fiber preforms manufactured ex-situ to meet the mechanical characteristics expected for the final part. It thus makes it possible to directly manufacture this type of part by chemical infiltration in the double enclosure then densification, rectification or machining being carried out after sufficient consolidation of the fiber preform or after the complete densification step by the matrix.

[0042] The interphase which is deposited by chemical infiltration comprises at least one layer consisting of pyrocarbon, boron nitride and / or the ternary Si-BN. Isothermal chemical infiltration from the gas phase in continuous mode (ICVI) requires a deposition temperature which is relatively low compared to chemical deposition processes from the gas phase (CVD) directly on a wire or a group of wires. This chemical infiltration of the fiber preform by the interphase is followed, without re-exposure to air, by a stabilization heat treatment at a temperature higher than that used for the infiltration. In the method of the invention, the heat treatment is carried out at a temperature and for a duration which, under an inert atmosphere, do not alter by more than 5% the nominal intrinsic modulus of elasticity of the fibers indicated by the fiber manufacturer.

[0043] The matrix layer is also manufactured by continuous isothermal chemical infiltration from the gas phase (ICVI) and is made of at least one material taken from the groups of oxides, carbides, nitrides or silicides or by a combination of materials taken from at least one of these groups. Among these materials, silicon carbide is very often incorporated as a matrix material. Alternatively, it is however possible to incorporate, on the interphase, a first layer which resists even better to a following densification step such as the final infiltration in a high-temperature molten medium. The matrix layer produced by isothermal chemical infiltration from the gas phase (ICVI) is then made up of either a single layer of one of the materials taken from at least one of the groups mentioned above, or at least two sub-layers each made up of one of these materials. It should also be noted that the layers of these refractory materials can only be deposited on fiber preforms already having the final texture.

[0044] Four examples of tests carried out with the manufacturing method according to the invention are reported here. The first example reports a test carried out with a fiber preform made of Nicalon™ fibers that are woven to form two-dimensional plates. These fabric plates are superimposed and reinforcement is carried out according to the third direction to avoid thermomechanical delaminations. This parallelepiped fiber preform was intended to carry out mechanical tests. It was placed in a double enclosure of the type shown [Fig.7]. The plates of the external wall had a thickness in the recessed area of ​​8 mm and were pierced with 5 mm cylindrical holes. The mold elements had a thickness of 5 mm and were pierced with 2.5 mm holes spaced 2 mm apart. The porous layer pressed against the mold elements consisted of a two-dimensional plate of fabric identical to those constituting the fiber preform. Note here that the porous layer 400 consists for example of a two-dimensional fabric or a felt which incorporates fibers whose nature is similar or not to that of the fibers of the fiber preform. The space free of any material between the excavated area of ​​the plates and this layer of fabric was 6 mm. The assembly thus constituted was placed in a chemical infiltration installation where the reactive gas flow was descending parallel to the plates of the double enclosure, according to the arrangement of [Fig.7]. A boron nitride interphase from a BC13 - NH3 - H2 mixture and a silicon carbide matrix layer from a methyltrichlorosilane (MTS) -H2 mixture were deposited on the fibers by ICVI under composition, temperature and pressure conditions well known to those skilled in the art, reported for example in FR 2756277 and FR 2401888 respectively. After heat treatment of the interphase then chemical infiltration of the silicon carbide matrix layer, the fiber preform was removed from the double enclosure and infiltrated with a resin so as to be able to make transverse sections which, after polishing, made it possible to measure the thicknesses of the two deposited layers. These sections were made 1.5 cm from each end of the fiber preform and in the middle of it. Thickness measurements of the two layers were carried out on these sections, as close as possible to the two surfaces of the fiber preform and in the center of the latter.The desired thickness for the interphase was 0.2 pm. Measurements showed thicknesses between 0.17 and 0.23 pm. For the silicon carbide layer, measurements showed thickness variations between 0.45 pm and 0.58 pm. In both cases, thickness variations relative to the average thickness were less than 20%. An identical chemical infiltration was carried out until the fiber preform consolidated. This was removed from the double enclosure and completely infiltrated. Cross sections of the composite thus produced revealed a near absence of porosity between fibers within the threads, an essential initial condition for the final composite to achieve the best mechanical properties.

[0045] The second example reports a test carried out with a fiber preform constituting the reinforcement of a part of thin but not parallelepipedal shape. It was a secondary flap of an aeronautical nozzle. In this example, the conditions were identical to those of the previous example except for the use of mold elements where the inner surfaces of the two mold elements corresponded to the surfaces of the composite material part to be produced. Taking into account the geometry of the part and its thickness, equal thicknesses of the mold elements were used opposite areas of the part with the same thickness while slightly smaller and larger thicknesses were used opposite areas of the part with respectively larger and smaller thicknesses to be infiltrated. Results as good as in the first example were obtained with this new arrangement.

[0046] The third example uses a double enclosure arrangement similar to that shown in [Fig. 13]. This example reports the tests carried out on a fiber preform which included 3D reinforcement. This preform represented a blank blade with a blade in the longitudinal direction, a fir tree root and plate at one end and a heel at the other end forming transverse protrusions. This preform was placed in a vertical position as in [Fig. 13]. Successive tests of chemical infiltration by a boron nitride interphase with heat treatment of the interphase, then chemical infiltration of the silicon carbide matrix layer, were carried out. Each time, the fiber preform was removed from the double enclosure and infiltrated with a resin so as to be able to measure the thicknesses of the two deposited layers.Chemical infiltration results as good as before were obtained after modifications were made: . - at the entry of the gases into the space 300 with oblong openings, replacing cylindrical openings in the lower part of the first external wall 100, close to the arrival of the reactive gases; - at the height of the supports 260 so as to increase the volume of the space 300 in its lower zone; - the shape of the mold elements and their drilling by oblong openings in the concave zones located between the blade blank and the transverse ends, these oblong openings having their length in the longitudinal direction of the part. - the geometry and depth of the openings made in the horizontal ends of the mold elements close to the longitudinal axis of the fiber preform. After optimizing the infiltration conditions, an identical chemical infiltration was carried out until the fiber preform consolidated. This was removed from the double enclosure and completely infiltrated. Cross sections of the composite thus produced revealed a virtual absence of intra-strand porosity, an initial condition necessary for the final composite to achieve the best mechanical properties.

[0047] The fourth example uses a double enclosure arrangement similar to that shown schematically in [Fig. 14]. The important difference with the previous example lies in the fact that the inner surface of the mold elements 200 is not, at all points, in direct contact with the fiber preform. More precisely, the mold elements 200 are set back from the central part of the blank shown schematically in [Fig. 14], that is to say that which corresponds to the blade. This central part has a constant thickness which does not require modulating the diffusion conditions through the mold elements 200 towards this part of the blank. There is therefore a free space 350 between these parts of the mold elements and the fiber preform. This arrangement is used here with a 3D fiber preform whose texture is such that it is self-supporting and retains its general shape without requiring total support by walls.The other arrangements were kept similar to those of Example 3 with two exceptions. There was no longer, in the mold elements, a concave zone located between the blade blank and the transverse ends. A modulation of the geometry and depth of the openings made in the horizontal ends of the mold elements was retained and the section of the openings towards the central part of the blank was modified to take into account their change in depth and the new free space 350. Chemical infiltration results as good as the previous ones were obtained with this arrangement. After complete densification outside the double enclosure, cross-sections of the composite thus produced revealed a near absence of intra-wire porosity, a necessary condition for the final composite to achieve the best mechanical properties.

[0048] These examples show that the layers deposited during the step of consolidating the fiber preform by chemical infiltration are, in the method of the invention, characterized by a variation in thickness within the fiber preform such that the extreme thickness values ​​do not vary by more than 20% relative to the average thickness of these layers. Thus, in a non-limiting manner, the variation in thickness of the interphase and the matrix layer is such that the extreme thickness values ​​within the consolidated fiber preform do not vary by more than 20% relative to the average thickness of these layers.

[0049] The examples provided here are obviously not limiting and parts of different geometry are also manufactured using the method of this invention with a controlled chemical infiltration step to manufacture the interphase then consolidate the fiber preform before carrying out densification by the matrix in a second step.

[0050] Some parts may be made from fibrous preforms that have a texture that allows them to maintain the desired geometry as shown with example 4. These self-supporting fiber preforms can be infiltrated into the specific double enclosure without there being close contact at any point of the fiber preform with the mold elements. It can therefore be emphasized that the mold elements are adapted to the fiber preform, whether to its geometry in the case of complete support by their internal surfaces but also to its texture in the case where this total support is not obligatory, finally by the possible modulation of the diffusion conditions through the mold elements according to the underlying depth of the fiber preform to be infiltrated, modulation obtained by locally modifying the section and the depth of the openings made in the mold elements.Generally speaking, this adaptation between mold element and fiber preform which allows the modulation of infiltration conditions according to the geometry of the preform is obviously an integral part of the invention.

[0051] Furthermore, it is clear that densification techniques which allow the most complete densification by the matrix are preferred for many parts in order to obtain the best final mechanical properties. These techniques, for example those which use at least in part an introduction of carbon and a ceramic powder within the fibers followed by infiltration of a silicon-based metal in the molten state, or else chemical infiltration in a temperature and / or pressure gradient, can only be easily used on blanks of the fiber preforms. In this case, machining of the fully densified blank is finally carried out according to the geometry of the shaped part. In other cases, such as the production of secondary flaps for aeronautical nozzles, densification is carried out on a fiber preform of geometry identical to the final part and this is finished with densification. Finally, in intermediate cases, grinding machining is carried out after densification. The majority of these parts require perfect dimensions, mass and adjustment.

[0052] Thus, the method of the invention, depending on the final densification technique used and depending on the geometry of the parts and / or their use, makes it possible to manufacture finished parts, parts to be ground or machined more deeply. A protective coating of the exposed fibers can then be applied to the retouched parts. As previously described, this protective coating is not necessary when the part has been machined before the final stage of densification. In many cases, a thermal and / or environmental barrier is finally deposited on the shaped part.

[0053] More generally, the entire preceding description is obviously not of a limiting nature. Variations or modifications may be made thereto by those skilled in the art without these departing from the scope of the invention which is conventionally determined by the following claims.

Claims

1. Claims Method for manufacturing a shaped part made of ceramic matrix composite material comprising on the one hand a fibrous reinforcement made up of fibers forming a fibrous preform of geometry similar to or identical to the shaped part and on the other hand a matrix, the fibrous reinforcement and the matrix being separated by a thin layer serving as an interphase between the fibers and the matrix, manufacturing method which comprises: a. a first step of consolidating said fibrous preform (10) by two layers, an interphase and a matrix layer successively produced by chemical infiltration from the gas phase in a specific double enclosure (50) where diffusion conditions characterized by a random and undirected movement of said gas phase towards the fibrous preform mainly prevail, said specific double enclosure comprising two walls, external and internal, separated by a space free of any material (300), where: i) the first external wall which is placed in the reactive gas flow is characterized by the fact that any part of its wall (165) which is directly exposed to a reactive gas flow (20) whose direction makes an angle greater than 30 degrees with respect to its external surface is kept full and prevents any direct entry of the convective gas flow inside the enclosure,and any part of its wall (100) which is not exposed to a direct flow or makes an angle of less than 30 degrees with respect to the direction of this flow can be pierced with cylindrical (190) and / or oblong (195) openings, these having respectively a diameter or a width perpendicular to the projection on the surface of the direction of the gas flow, less than approximately one time the thickness of this first external wall in its pierced zone; ii) the second internal wall, arranged inside the first wall, consists of two elements of a mold (200) applied against each other on their periphery, these elements of the mold having on the one hand an internal surface (210) adapted to the fiber preform and on the other hand an external surface (220) against which a layer of material is applied, porous (400) of felt or fabric type leaving the two external and internal walls of the double enclosure separated by said space free of any material (300) of thickness greater than approximately 3 mm, said mold elements being pierced on all or part of their wall with cylindrical (290) and / or oblong (295) openings of which, respectively, the diameter or width is less than approximately 5 mm and the maximum spacing is less than approximately 3 mm; iii) if necessary in the event of significant variations in the thickness of the fiber preform to be infiltrated, local variations in the geometry of the openings made in the walls, especially in the internal wall, modulate the chemical infiltration conditions; b. at least a second step of complete densification by the matrix of the consolidated preform, outside said specific double enclosure.

2. Method according to claim 1 where the chemical infiltration from the gas phase of a thick layer of matrix is ​​followed by an intermediate step of machining according to the geometry of the final part, before the step of complete densification by the matrix outside the specific double enclosure.

3. Method according to claim 1 comprising a first step of consolidation of the fiber preform by the interphase and a matrix layer, a second step of complete densification of the consolidated preform outside the specific double enclosure, then a third step of rectification or machining followed by a step of depositing a fiber protection layer.

4. Method according to any one of claims 1 to 3 where the external wall (100) and the mold elements (200) are pierced with cylindrical and / or oblong openings whose sections are, in each of the walls, identical from one point to another on their surface.

5. Method according to any one of claims 1 to 3 wherein the external wall (100) and the mold elements (200) are pierced with cylindrical and / or oblong openings whose sections are, in at least one of the walls, different from one point to another on the surface.

6. A method according to any one of claims 1 to 5 wherein the mold elements (200) are pierced with cylindrical and / or oblong openings whose depth varies according to the position of these openings on the surface of the mold elements.

7. A method according to any one of claims 1 to 6 wherein the variation in thickness of the interphase and the matrix layer is such that the extreme values ​​of thickness within the consolidated fibrous preform do not vary by more than 20% relative to the average thickness of these layers.

8. A method according to any one of claims 1 to 6 wherein the outer wall and the mold elements are made of carbon or a carbon-carbon composite material coated or not with a ceramic layer, or a ceramic material, or a ceramic matrix composite.

9. A method according to any one of claims 1 to 6 wherein the fibers are carbon, alumina, mullite or silicon carbide fibers.

10. Method according to any one of claims 1 to 9 where the fibrous preform constitutes a reinforcement by fibers which form elongated threads in a main reinforcement direction (1D composite), by threads which constitute textiles with two main reinforcement directions (2D composite) or which additionally comprise a partial reinforcement in a third direction (2.5D composite), or which constitute a reinforcement in N directions where N> 3.

11. Method according to any one of claims 1 to 10 wherein the interphase is constituted by at least one layer constituted by pyrocarbon, boron nitride and / or by the ternary Si-BN.

12. A method according to claim 11 wherein the manufacture of the interphase is carried out by isothermal chemical infiltration from the gas phase and is followed, without re-exposure to air, by a heat treatment at a temperature higher than that used for the infiltration.

13. A method according to claim 12 wherein the heat treatment is carried out at a temperature and for a duration which, under an inert atmosphere, do not alter by more than 5% the nominal intrinsic modulus of elasticity of the fibers indicated by the manufacturer of the fibers.

14. A method according to any one of claims 1 to 7 wherein the fabrication of the matrix layer carried out by isothermal chemical infiltration from the gas phase (ICVI) consists of: - either a single layer of a material taken from the groups of oxides, carbides, nitrides or silicides or by a combination of materials taken from at least one of these groups; - or at least two sub-layers each made up of one of these materials.

15. A method according to any one of claims 1 to 14 wherein the entire matrix is ​​made of at least one material taken from the groups of oxides, carbides, nitrides or silicides or by a combination of materials taken from at least one of these groups.

16. A method according to claim 15 wherein the matrix consists primarily of silicon carbide.

17. A method according to any one of claims 1 to 16 wherein the second step of densifying the matrix is ​​carried out at least in part by chemical infiltration from the isothermal gas phase (ICVI), or by chemical infiltration from the gas phase in a temperature and / or pressure gradient.

18. Method according to claim 17 where the matrix is ​​made up of phases of different natures which comprise a carbide of a metallic or metalloid element and at least one carbide taken from the binary boron-carbon, the ternary silicon-boron-carbon, or a metallic boride, the element boron being preferentially brought into all these layers by a gaseous phase comprising a boron trichloride of purity less than approximately 99%.

19. Method according to any one of claims 1 to 16 wherein the second step of densification of the matrix is ​​carried out at least in part by impregnation with at least one ceramic precursor polymer followed by pyrolysis.

20. A method according to any one of claims 1 to 16 wherein the second step of densifying the matrix is ​​carried out at least in part by introducing carbon and a ceramic powder and by infiltrating a silicon-based metal in the molten state.

21. A method of chemical infiltration from a gaseous phase of an interphase and a matrix layer according to any one of claims 1 to 14 which is implemented in a chemical infiltration installation (500) where the walls (100) of the double enclosure (50) are arranged vertically and where the gas flows flowing along the different double enclosures are identical and have an ascending or descending vertical direction.

22. A method of chemical infiltration from a gas phase of an interphase and a matrix layer according to any one of claims 1 to 14 which is implemented in a chemical infiltration installation where the walls (100) of the double enclosure (50) are arranged vertically and where the gas flows flowing along the different double enclosures are identical and have a horizontal direction.

23. A method of chemical infiltration from a gas phase of an interphase and a matrix layer according to claim 22 which is carried out in a cylindrical chemical infiltration device (600) which comprises: - a gas inlet (610) to a gas preheating zone (640), - a gas outlet (680), these inlets-outlets being located at each of the ends of the vertical cylinder, - a cylindrical deposition zone where, between two concentric cylindrical walls (650) and (670), groups of double chemical infiltration enclosures (50) having vertical walls are arranged along radii of the cylinder, an identical horizontal gas flow (620) being introduced between each group of double enclosures using, through the outer or inner cylindrical wall of the deposition zone,a singular pressure drop through openings (655) between the vertical gas flow (615) exiting the preheating zone and the horizontal gas flow of radial main component (620) which crosses the cylindrical deposition zone in a centripetal or centrifugal main direction.,

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