FR3120811A1 - Improved method of making a consolidated fibrous preform - Google Patents

Abstract

Improved method for producing a consolidated fibrous preform Method for producing a consolidated fibrous preform intended for the manufacture of a part made of composite material, comprising the steps of:- shaping a fibrous texture by impregnation with a material fleeting or fugitive, - placement of the pre-consolidated fibrous preform in a mold and injection of a polyurethane foam (50) into the mold to coat the fibrous preform (40) with polyurethane foam, - demoulding, after crosslinking of the polyurethane foam, of the fiber preform (40) coated with said foam,- impregnation of the polyurethane foam with a carbon precursor,- heat treatment of the fiber preform (40) so as to form a carbon foam from the carbon precursor around the fiber preform, and removing the polyurethane foam (50) and the fugitive or fugitive material present in the fiber preform,- consolidation by gas phase chemical infiltration d e the fibrous preform. Figure for abstract: Fig. 5.

Description

Improved method of making a consolidated fibrous preform

The invention relates to the consolidation of fiber preforms and the manufacture of parts made of composite material with a ceramic matrix or at least partially made of ceramic, hereinafter referred to as CMC material. A field of application of the invention is the production of parts intended to be exposed in service to high temperatures, in particular in the aeronautical and space fields, in particular parts of hot parts of aeronautical turbomachines, it being noted that the invention can be applied in other fields, for example the field of industrial gas turbines.

CMC composite materials have good thermostructural properties, that is to say high mechanical properties which make them suitable for forming structural parts and the ability to retain these properties at high temperatures.

The use of CMC materials instead of metallic materials for parts exposed in service to high temperatures has therefore been recommended, especially since CMC materials have a significantly lower density than the metallic materials for which they replace.

A known process for the manufacture of parts in CMC material comprises the following steps:
- weaving of a fibrous texture from fibrous strata of carbon fibers or silicon carbide (SiC),
- consolidation of a fibrous preform by depositing an interphase on the surface of the fibers of the texture produced by chemical infiltration in the gaseous phase (known as "CVI" for "Chemical vapor infiltration" in English), the fibrous texture being maintained in a conformation tools during CVI,
- injection of a slurry into the fibrous preform (known as "Slurry Cast" or "Slurry Transfer Molding" in English),
- infiltration of the preform with a composition based on molten silicon so as to form a ceramic matrix, densification process known as the MI process (from the English "Melt Infiltration"),
- machining,
- formation of a coating.

This process for manufacturing parts in CMC material requires the use of shaping tooling during the deposition of the interphase. This type of tool corresponds to a multi-perforated mold whose internal shape makes it possible to conform the fibrous texture, and the multi-perforations to freeze the texture in its geometry by allowing the gaseous phase used during the deposition of the interphase to penetrate into the texture and consolidate it. The shaping tool is made, for example, of graphite, because it is a material compatible with the reactive atmosphere used during the interphase deposition, while presenting harmlessness vis-à-vis carbon fibers or silicon carbide.

However, this type of shaping tool has drawbacks. In particular, graphite has a low mechanical strength (material with no tolerance to deformation), its cost is high (machining of a block of purified graphite). This type of tool is fragile and has limited closing forces (risk of breakage when tightening the graphite blocks, poor mechanical resistance to forces) and has a limited lifespan (clogging of the multi-perforations and clamping systems). It is necessary to replace the clamping members of the tooling frequently, and it presents a significant bulk due to the clamping members used to assemble and clamp the tooling. In addition, the supply of gases to the texture is only done via the channels machined in the mass. However, in certain geometrically complex areas of the mould, the number of channels must be reduced (to avoid the breakage of the blocks). The local gas supply can be affected, and the consolidation too, which induces undesired consolidation variations in the volume of the texture.

Document WO2018162827 A1 proposes a solution in which a ceramic former is produced by a “lost wax” type operation on a pre-consolidated part. Nevertheless, according to this process, the gases have difficulty reaching the texture because the ceramic “mould” absorbs all or a large part of the reactive gas phase, to the detriment of the texture, making consolidation difficult. Conversely, the production of a shell with low porosity requires the use of oxides which are incompatible or not very compatible with the reactive gases used for gaseous consolidation.

The object of the invention is in particular to provide a solution for the consolidation of a fiber preform intended for the manufacture of a part made of composite material, making it possible to overcome at least in part the aforementioned drawbacks.

This object is achieved by means of a process for producing a consolidated fibrous preform intended for the manufacture of a part made of composite material, comprising the steps of:
- shaping of a fibrous texture by impregnation with a fugitive or fugitive material so as to pre-consolidate the fibrous preform,
- placement of the pre-consolidated fiber preform in a mold and injection of a polyurethane foam into the mold so as to coat the fiber preform with polyurethane foam,
- demoulding, after crosslinking of the polyurethane foam, of the fibrous preform coated with said polyurethane foam,
- impregnation of the polyurethane foam with a carbon precursor,
- heat treatment of the coated fiber preform so as to form a carbon foam from the carbon precursor around the fiber preform, and to eliminate the polyurethane foam and the fugitive or fugitive material present in the fiber preform,
- consolidation by gas phase chemical infiltration of the fibrous preform.

The method according to the invention makes it possible to dispense with the use of graphite shaping tooling, and therefore the aforementioned drawbacks associated with this material. In particular, the use of a polyurethane foam (hereinafter referred to as "PU foam"), and a carbon precursor for the production of a carbon foam former, has a lower cost than a graphite former . The carbon foam former is also compatible with the reactive gases used for gaseous consolidation, and does not absorb them to the detriment of the texture, thus improving the consolidation of the fiber preform.

The carbon foam former, thus serving as a mould, is particularly advantageous in that it is significantly more favorable to the conduct of the reactive gases towards the fiber preform, compared to the use of a slip for example which, by its intrinsic porosity, consumes a large volume of reactive gases, to the detriment of the preform. In addition, a carbon foam former is suitable for complex part shapes. Indeed, the implementation of the PU foam can be made by injection into a counter mold, for example a metal mold, produced by machining or 3D printing, it is possible to achieve all the desired shapes.

In certain embodiments, the step of shaping the fibrous texture comprises:
- placing the fibrous texture in a heated metal mould, the texture being impregnated beforehand with the fleeting or fugitive material, or shaping a fibrous texture in a metal mold and injecting a fugitive material or fugitive in the fibrous texture held in shape in the metal mold,
- mold cooling,
- demoulding of the pre-consolidated fibrous preform.

It is thus possible to significantly reduce production costs, in particular thanks to the use of a metal mold which has a strength and a much longer life than a confirmation tool in graphite, which makes it possible to save the recurring cost of replacing graphite formers. The dimensional control of the preform is also optimized with shaping in a metal mold compared to a graphite mold.

In certain embodiments, the step of impregnating the polyurethane foam is carried out by injecting the carbon precursor into the polyurethane foam.

Alternatively, the impregnation step of the polyurethane foam is carried out by immersing the polyurethane foam in the carbon precursor.

In some embodiments, the carbon precursor is a phenolic resin or polyacrylonitrile.

In certain embodiments, the fugitive or fugitive material corresponds to an injection wax or a fugitive resin.

In certain embodiments, the fibrous preform is formed by a fibrous texture produced in a single piece by three-dimensional or multilayer weaving or from a plurality of two-dimensional fibrous strata.

In certain embodiments, the fibrous texture is made from fibers of silicon carbide (SiC), silicon nitride (S13N4) or carbon (C).

In some embodiments, the step of consolidating the fibrous preform by gas-phase chemical infiltration comprises the deposition of an interphase in the preform, the interphase consisting of one of the following materials: pyrolytic carbon (PyC), boron nitride (BN), boron doped carbon (BC) and silicon carbide (SiC).

The interphase can also include all types of refractory or ultra-refractory ceramics such as hafium or zirconium carbides. The precursors and mixtures of precursors can depend on the infiltrated ceramic.

In certain embodiments, the method also comprises, before the step of consolidation by chemical infiltration in the gas phase, an unloading step making it possible to evacuate the residues of polyurethane foam and of fugitive or fugitive material remaining after the step of thermal treatment.

In certain embodiments, the method further comprises, after the step of consolidation by chemical infiltration in the gas phase, a step of shake-out of the carbon foam coating the fiber preform.

This presentation also relates to a process for manufacturing a composite material part comprising the production of a consolidated fibrous preform via a process according to any one of the preceding embodiments, a step of injecting a slip in the fibrous preform and a step of infiltrating the preform with a composition based on molten silicon so as to form a ceramic matrix in said preform.

The invention and its advantages will be better understood on reading the detailed description given below of various embodiments of the invention given by way of non-limiting examples. This description refers to the pages of appended figures, on which:

The is a schematic view showing a fibrous texture before shaping,

The is a schematic view showing the fibrous texture of the , in a configuration corresponding to the shape of the final part,

The represents the impregnation of the fibrous texture of the by a fugitive or fugitive material,

The is a schematic view showing a pre-consolidated fibrous preform,

The is a schematic view representing the step of injecting polyurethane foam around the fiber preform of the ,

The is a schematic view showing the fibrous preform of the , coated with polyurethane foam,

The is a schematic view representing the impregnation of the polyurethane foam coating the fiber preform with a carbon precursor,

The is a schematic view showing the heat treatment of the fiber preform of the ,

The is a schematic view representing the fiber preform coated with carbon foam, after the heat treatment,

The is a schematic sectional view of a gas-phase chemical infiltration installation used for the densification of a fibrous preform,

The is a schematic sectional view of a fiber preform consolidated in accordance with one embodiment of the invention,

The is a flowchart of the steps of a method for consolidating a fiber preform according to one embodiment of the invention.

The invention firstly proposes a process for producing a consolidated fibrous preform intended for the manufacture of parts made of ceramic matrix composite material (CMC), that is to say a material formed from a fiber reinforcement. carbon or ceramic densified by an at least partially ceramic matrix.

The process of the invention is remarkable in that it does not use graphite shaping tools for the consolidation by chemical infiltration in the gas phase of the fiber preform. As explained below in detail and in accordance with the invention, the graphite shaping tool is replaced by a carbon shaper formed around the shaped fibrous texture, and making it possible to maintain the fibrous texture in shape during its consolidation. by gas phase chemical infiltration.

An embodiment in accordance with the method of the invention will be described with reference to FIGS. 1 to 12.

A first step S1 ( ) consists in producing a fiber texture 10 from which a fiber preform having a shape similar to that of a part to be manufactured will be produced ( ). Such a fibrous texture can be obtained by multilayer or three-dimensional weaving from yarns or cables. It is also possible to start from two-dimensional fibrous textures such as fabrics or sheets of threads or cables to form strata which will then be draped over a form and possibly linked together, for example by stitching or implantation of threads. In the example described here, the fibrous texture 10 is intended to form a sector of a turbine ring made of CMC material having the shape of an inverted Pi or π with an annular base from which extend two hooking lugs. To this end, the fibrous texture 10 is produced by three-dimensional weaving of silicon carbide or carbon yarns with the arrangement of unbinding zones 11 and 12 making it possible to separate texture parts 13 and 14 corresponding to the fastening flanges of the sector of ring ( ).

The weaving may be of the interlock type, as shown. Other three-dimensional or multi-layer weaving weaves can be used, such as multi-linen or multi-satin weaves, for example. Reference may in particular be made to document WO 2006/136755.

The fibers constituting the fibrous texture are preferably ceramic fibers, for example fibers formed essentially of silicon carbide SiC (hereinafter referred to as SiC fibers) or of silicon nitride Si ₃ N ₄ . Use may in particular be made of SiC fibers marketed under the names “Tyranno ZMI”, “Tyranno Lox-M” and “Tyranno SA3” by the Japanese company Ube Industries, Ltd or “Nicalon”, “Hi-Nicalon” and “Hi-Nicalon (S)” by the Japanese company Nippon Carbon. As a variant, it is possible to use carbon fibers. In known manner, in the case of ceramic fibers, in particular SiC fibers, a surface treatment thereof prior to the formation of an interphase deposit is preferably carried out to eliminate the size and a surface layer of oxide such as silica Si0 ₂ present on the fibers.

The following steps consist in keeping the fibrous texture in shape in a metal mold 20 and freezing it to obtain a preform having a shape similar to that of the part to be manufactured ( ). For this purpose, the fibrous texture 10 is placed in the metal mold 20 whose molding cavity 21 corresponds to the shape of the part to be manufactured (step S2), a fleeting or fugitive material 30 being injected into the texture thus maintained in shape. (step S3) (FIG. 3). According to an implementation variant, the fibrous texture 10 can be impregnated with a fugitive or fugitive material (step S4) before it is shaped in the metal mold (step S5). The fugitive or fugitive material preferably has a melting and evaporation temperature significantly above ambient temperature (20°C ± 5°C), for example at least 50°C above ambient temperature (20 °C ± 5°C). The fugitive or fugitive material may consist in particular of an injection wax or a fugitive resin, for example an acrylic resin PPMA or polyvinyl alcohol (PVA).

After the metal mold has cooled, a fibrous preform 40 is unmolded, the preform being fixed and self-supporting thanks to the presence of the fugitive or fugitive material in the solid state therein (step S6, ). Steps S2 to S6 thus constitute the shaping of the fibrous texture 10, making it possible to obtain a pre-consolidated fibrous preform 40.

The pre-consolidated fiber preform 40 is then placed in a polyurethane (PU) injection mold 22 (step S7) ( ). Mold 22 can be metal or composite (such as a thermosetting resin), or even plastic. The mold 22 is suitable for repeated use because it can be easily cleaned, unlike graphite molds or formers.

A space is provided between the walls of the mold 22 and the fiber preform 40 so as to allow the PU foam, injected in the next step, to swell around the preform 40. To do this, the fiber preform 40 can be placed on one of its slices inside the mould, or on occasional supports (not visible on the ). The space between the preform 40 and the mold 22 can be between 5 mm and 30 mm, preferably between 10 and 20 mm, to achieve an equivalent foam thickness.

A polyurethane foam 50 is then injected into this space, so as to coat the fibrous preform 40 (step S8)( ). All types of PU foams formed from a polyol and an isocyanate, and comprising a blowing agent (for example CO2) can be used. Preferably, the molar masses of the isocyanate prepolymers (produced by a mixture of diisocyanates and a polyol) and of the functional polyol are close. The injection duration can also be adjusted, to control the injection time and the foam formation kinetics, based on the generation of the blowing agent, via catalysis.

After crosslinking, the fibrous preform 40 coated with PU foam 50 is unmolded, thus making it possible to obtain a polyurethane former (PU former), integrating the pre-consolidated fibrous preform 40 (step S9)( ).

A step of impregnating the PU foam 50 with a carbon precursor, for example phenolic resin 62, is then carried out (step S10)( ). This step can be carried out by immersing the PU former incorporating the fiber preform 40, in the phenolic resin 62, but is preferably carried out by injecting the phenolic resin 62 into the PU foam. The injection is preferably carried out under the conditions of implementation of the phenolic resin 62, so that the viscosity of the resin to be injected is compatible with the injection process. For example, the injection of the phenolic resin 62 can be carried out via a nozzle 64, placed in the PU foam 50. The injection can involve a pressure of between 2 and 15 bars. The viscosity of the phenolic resin 62 is preferably between 10 and 400 mPa.s-1. Although a single nozzle 64 is shown in the , several nozzles 64 can be arranged on either side of the part depending on the geometry of the latter, in order to provide several injection points and to ensure homogeneous impregnation of the PU foam.

The fibrous preform 40 thus coated with a PU foam 50 impregnated with a carbon precursor 62, is then subjected to a heat treatment in an oven 70 (step S11)( ). The heat treatment is carried out under neutral gas. During this treatment, the PU 50 foam is replaced by a carbon 60 foam. More specifically, the rise in temperature causes the degradation of the PU 50 foam and, simultaneously, the carbonization of the phenolic resin skeleton 62 present in the PU foam. The temperature rise ramp can be between 1°C/min and 120°C/min. A plateau of between 2 and 10 hours is planned, at a temperature of between 700°C and 1400°C, depending on the implementation of the gaseous consolidation carried out subsequently. The removal of the fugitive or fugitive material from the preform 40 is also carried out during this step, the heat treatment being carried out at a temperature above the melting and/or evaporation temperature of the fugitive or fugitive material.

A preform 80 corresponding to the preform 40 is thus obtained in which the network of pores present between the fibers has been reopened by the removal of the fugitive or fugitive material 40, the geometry of the preform 80 being maintained thanks to the presence of the carbon 60 former ( ). The latter is in the form of carbon foam, and is therefore compatible for chemical infiltration in the gas phase of the preform 80.

An unloading step, making it possible to evacuate the residues of PU foam 50 and of fugitive or fugitive material 30 remaining after the heat treatment step, can take place before the step of consolidation by chemical infiltration in the gas phase.

One then proceeds to the consolidation by chemical infiltration in the gaseous phase of the fibrous preform (step S12). For this purpose, as illustrated in the , the preform 80, held inside the carbon former 60, is placed in a gas phase chemical infiltration installation or furnace 200. In a manner known per se, the gas phase chemical infiltration installation 200 comprises a cylindrical enclosure 201 delimiting a reaction chamber 210 closed in its upper part by a removable cover 220 fitted with a gas inlet pipe 221 which opens into a preheating zone 222 allowing the gas to be heated before it is diffused into the reaction 210 containing the preform(s) to be densified. The residual gases are extracted at the bottom 230 of the installation by an evacuation pipe 231 which is connected to suction means (not shown). The bottom 230 comprises a support 232 on which the preform 80 coated with the carbon foam 60 is intended to be deposited.

The heating in the preheating zone as well as inside the reaction chamber 210 is produced by a graphite susceptor 211 forming an armature electromagnetically coupled with an inductor (not shown).

The preform 80 is consolidated by gas phase chemical infiltration. In order to ensure the consolidation of the preform, a reactive gas containing at least one or more precursors of the material of a consolidation interphase is introduced into the reaction chamber 210. The treatment temperature can be between 700° C. and 1100° C. °C, and the pressure between 80 and 130 mbar. The duration of infiltration is between 5h and 50h, preferably between 10h and 30h.

The interphase deposited in the preform can be in particular in pyrolytic carbon or PyC, or in boron nitride (BN), in carbon doped with boron or BC (with 5% at to 20% at boron, the remainder being carbon) , or silicon carbide. The thickness of the deposited interphase is preferably between 100 nm and 1500 nm. The total thickness of the interphase and the first matrix phase is chosen to be sufficient to consolidate the fibrous preform, that is to say to bind together the fibers of the preform sufficiently so that the preform can be manipulated in retaining its shape without the assistance of holding tools. This thickness may be at least equal to 500 nm. After consolidation, the preform remains porous, the initial porosity being for example filled only for a minority part by the interphase and the first matrix phase.

The production of deposits of PyC, BC, B4C, Si-BC, Si ₃ N ₄ , BN and SiC by CVI is known. Reference may in particular be made to documents US 5,246,736, US 5,738,951, US 5,965,266, US 6,068,930 and US 6,284,358.

Once the consolidation is complete, the carbon former 60 is shaken out (step S13), in which the carbon former 60 is mechanically destroyed in order to release, as illustrated in the a preform 100 corresponding to the consolidated preform 80. The preform 100 is self-supporting and does not require any shape-holding tools for subsequent operations. The preform 100 can in particular be subjected to the subsequent stages of manufacturing a part in CMC material, namely:
- injection of a slurry into the fibrous preform,
- infiltration of the preform with a composition based on molten silicon so as to form a ceramic matrix, densification process (“MI” process),
- machining,
- formation of a coating.

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

It is also obvious that all the characteristics described with reference to a method can be transposed, alone or in combination, to a device, and conversely, all the characteristics described with reference to a device can be transposed, alone or in combination, to a method.

Claims (11)

Method for producing a consolidated fibrous preform (100) intended for the manufacture of a part made of composite material, comprising the steps of:
- shaping of a fibrous texture (10) by impregnation with a fugitive or fugitive material (30) so as to pre-consolidate the fibrous preform (40),
- placement of the pre-consolidated fiber preform in a mold (22) and injection of a polyurethane foam (50) into the mold (22) so as to coat the fiber preform (40) with polyurethane foam,
- demoulding, after crosslinking of the polyurethane foam (50), of the fiber preform (40) coated with said polyurethane foam,
- impregnation of the polyurethane foam (50) with a carbon precursor (62),
- heat treatment of the fiber preform (40) coated so as to form a carbon foam (60) from the carbon precursor around the fiber preform, and to eliminate the polyurethane foam (50) and the fugitive or fugitive material (30 ) present in the fibrous preform (80),
- consolidation by gas phase chemical infiltration of the fibrous preform (80). A method according to claim 1, wherein the step of shaping the fibrous texture (10) comprises:
- the placement of the fibrous texture (10) in a heated metal mold (20), the texture being previously impregnated with the fleeting or fugitive material (30), or the shaping of the fibrous texture in a metal mold and the injection of a fugitive or fugitive material into the fibrous texture held in shape in the metal mould,
- mold cooling,
- demoulding of the pre-consolidated fibrous preform (40). Method according to claim 1 or 2, in which the step of impregnating the polyurethane foam (50) is carried out by injecting the carbon precursor (62) into the polyurethane foam (50). A method according to any of claims 1 to 3, wherein the carbon precursor (62) is a phenolic resin or polyacrylonitrile. A method according to any of claims 1 to 4, wherein the fugitive or fugitive material (30) is an injection wax or a fugitive resin. Method according to any one of Claims 1 to 5, in which the fibrous preform (40) is formed by a fibrous texture (10) produced in a single piece by three-dimensional or multilayer weaving or from a plurality of two-dimensional fibrous strata . Process according to Claim 6, in which the fibrous texture (10) is made from fibers of silicon carbide (SiC), silicon nitride (S13N4) or carbon (C). A method as claimed in any one of claims 1 to 7, wherein the step of consolidating the fibrous preform (80) by gas phase chemical infiltration comprises depositing an interphase into the preform, the interphase consisting of one of the following materials: pyrolytic carbon (PyC), boron nitride (BN), boron-doped carbon (BC), and silicon carbide (SiC). Method according to any one of Claims 1 to 8, further comprising, before the step of consolidation by chemical infiltration in the gas phase, an unloading step making it possible to evacuate the residues of polyurethane foam (50) and of fugitive material or fugitive (30) remaining after the heat treatment step. Method according to any one of claims 1 to 9, further comprising, after the step of consolidation by chemical infiltration in the gas phase, a step of shake-out of the carbon foam (60) coating the fiber preform (80). Method for manufacturing a composite material part comprising the production of a consolidated fiber preform by means of a method according to any one of the preceding claims, a step of injecting a slip into the fiber preform and a step of infiltrating the preform with a composition based on molten silicon so as to form a ceramic matrix in said preform.