FR3055625A1 - FIBROUS PREFORM FOR MANUFACTURING A COMPOSITE MATERIAL PART AND ASSOCIATED METHOD - Google Patents

Abstract

The invention relates to a fibrous preform (100) woven from a plurality of yarns or strands (110, 120), the preform being intended to form the fibrous reinforcement of a piece of composite material, the preform further comprising a integrated armature (120) made of a shape memory alloy capable of conforming to a predefined shape when exposed to a transition temperature. The invention also relates to a method of manufacturing a composite material part.

Description

Holder (s): SAFRAN CERAMICS Public limited company, SAFRAN AIRCRAFT ENGINES Simplified joint-stock company.

Extension request (s)

Agent (s): CABINET BEAU DE LOMENIE.

FIBROUS PREFORM FOR MANUFACTURING A PART OF COMPOSITE MATERIAL AND ASSOCIATED METHOD.

FR 3 055 625 - A1 (6 /) The invention relates to a fiber preform (100) woven from a plurality of threads or strands (110, 120), the preform being intended to form the fiber reinforcement of a part. made of composite material, the preform further comprising an integrated armature (120) made of a shape memory alloy capable of conforming to a predefined shape when it is exposed to a transition temperature. The invention also relates to a method of manufacturing a part made of composite material.

Invention background

The present invention relates to the general field of manufacturing parts made of composite material and relates in particular to a woven fibrous preform intended to form the fibrous reinforcement of such a part.

When manufacturing parts made of ceramic matrix composite material (CMC), it is common to deposit an interphase coating, comprising for example boron nitride BN or silicon carbide SiC, on the ceramic fibers of the fibrous preform . The preform can then be densified by a matrix. The deposition of the interphase and the densification of the preform can be carried out by a process of the chemical gas infiltration type (CVI).

To carry out the deposition of the interphase coating and the densification of a preform of complex shape, it is necessary to use a conformator making it possible to shape the preform and to keep it in shape in the oven used for the CVI. The conformers must therefore be able to withstand the temperature and pressure conditions imposed during the CVI process and be sized precisely. For this, graphite conformers are generally used, which are machined to the dimensions of the part and pierced with vents to let the gas penetrate the preform. Such graphite conformers are difficult to machine and costly to implement. In addition, they have a limited lifespan because of their fragility, and successive deposits on their surfaces which modify their dimensions from around ten cycles of use in a CVI oven.

There is therefore a need for a fiber preform and for a method of manufacturing a part made of composite material which makes it possible to dispense with the use of a shaping device, in particular for depositing an interphase coating or during densification of the preform.

Subject and summary of the invention

The main object of the present invention is therefore to overcome such drawbacks by proposing a fibrous preform woven from a plurality of threads or strands, the preform being intended to form the fibrous reinforcement of a piece of composite material, the preform comprising in addition an integrated armature made of a shape memory alloy capable of conforming to a predefined shape when it is exposed to a transition temperature.

The fibrous preform according to the invention is remarkable in that it comprises an integrated reinforcement made of a shape memory alloy. The role of the reinforcement is to maintain the preform in its shape without the need to use a specific holding tool. The shape memory alloy of the armature makes it possible to shape the preform automatically after exposure of the preform to a temperature greater than or equal to the transition temperature of the shape memory alloy. To do this, it suffices to give the reinforcement, during its design (for example by foundry), the final desired shape for the preform formed, in a manner known per se. In addition, the material of the reinforcement can withstand temperature and pressure conditions which may be imposed for example during a densification step in an oven. Thus, it is possible to shape the fibrous preform before its densification without tools, and to proceed with its densification by the gaseous route by dispensing with the use of a holding tool such as a graphite conformator.

In an exemplary embodiment, the shape memory alloy can be chosen from the following: NiTi, CuAINi, CuAIBe.

In an exemplary embodiment, the shape memory alloy has a transition temperature between 100 ° C and 250 ° C. This temperature can be adjusted, in a manner known per se, by modifying the proportion of the elements present in the selected shape memory alloy.

In an exemplary embodiment, the preform comprises wires or strands of silicon carbide. Examples of silicon carbide wires which can be used can be “Nicalon”, “Hi-Nicalon” or “Hi-Nicalon-S” wires sold by the Japanese company NGS. The silicon carbide wires can have an oxygen content of less than or equal to 1% in atomic percentage. “Hi-Nicalon-S” wires have such a characteristic.

According to a first embodiment of the invention, the preform may comprise a first set of wires or strands woven with a second set of wires of shape memory alloy, the wires or strands of the first set being made of a different material. wires or strands of the second set.

According to a second embodiment of the invention, the armature may comprise sheets or strips of shape memory alloy. The use of sheets or strips is easier to implement, in particular since their orientation is easily determinable in the preform.

Preferably, the volume ratio of shape memory alloy in the preform is between 5% and 30%, the volume ratio of shape memory alloy in the preform being equal to the ratio between the volume of shape memory alloy and the volume occupied by the wires or strands in the preform. In general, the volume ratio of shape memory alloy in the preform can be chosen on the one hand so that the preform can be maintained in its shape without requiring holding tools, and on the other hand to prevent the the presence of the reinforcement does not alter the mechanical properties of the part made of composite material.

The invention also relates to a part made of composite material comprising a fibrous reinforcement densified by a matrix, the fibrous reinforcement comprising a fibrous preform such as that described above forming.

Finally, the invention relates to a method of manufacturing a part made of composite material comprising at least the following steps:

the production of a fibrous preform such as that presented above,

- exposing the fiber preform to a temperature greater than or equal to the transition temperature of the shape memory alloy of the armature in order to shape the fiber preform and obtain the fiber reinforcement of the part, and

- The formation of a matrix in the porosity of the fibrous reinforcement by gas.

The exposure of the preform to a temperature greater than or equal to the transition temperature of the shape memory alloy and the step of forming the matrix can be carried out in the same oven. The matrix can be a ceramic matrix or a carbon matrix.

In an exemplary embodiment, the part produced can be a turbine ring sector.

Brief description of the drawings

Other characteristics and advantages of the present invention will emerge from the description given below, with reference to the appended drawings which illustrate exemplary embodiments thereof without any limiting character. In the figures:

FIG. 1 shows a fibrous preform intended to form the fibrous reinforcement of a ring sector of composite material with ceramic matrix,

FIGS. 2 and 3 respectively show views of fibrous preforms according to two embodiments of the invention,

FIG. 4 is a flowchart illustrating the different stages of a process for manufacturing a part made of a composite material with a ceramic matrix according to the invention, and

- Figures 5A to 5C also illustrate steps of such a manufacturing process.

Detailed description of the invention

The invention will now be described in its application to the manufacture of a turbine ring sector made of CMC material.

A fibrous preform 1 is shown diagrammatically in FIG. 1 after its weaving, that is to say before any densification. The preform 1 shown can be obtained from woven wires or strands comprising, for example carbon fibers, or ceramic fibers. The preform 1 can be obtained by two-dimensional, three-dimensional or multi-layer weaving.

The ceramic wires or strands can for example be made of silicon carbide. Examples of silicon carbide wires which can be used can be “Nicalon”, “Hi-Nicalon” or “Hi-Nicalon-S” wires sold by the Japanese company NGS. The silicon carbide wires can have an oxygen content less than or equal to

1% in atomic percentage. “Hi-Nicalon-S” wires have such a characteristic.

The preform 1 comprises a lower part 2 intended to form the base of the ring sector, and an upper part 4 connected to the lower part 2 by a central portion 6. The upper part 4 is not linked with the lower part 2 at two opposite lateral ends and over a predetermined distance from the central portion 6. In other words, the preform 1 comprises two unbinding zones 8 at two opposite edges in a transverse direction of the preform 1, so as to leave two free side portions 10. The two lateral portions 10 can then be folded back towards the central portion 6 so as to form, after densification, attachment flanges of the ring sector on a ring support structure in a turbine. The ring sector to be manufactured can thus have a section in π or in K.

According to the invention, an armature which can take different forms which will be described below is integrated into the preform 1. The armature consists of a shape memory alloy which can deform at room temperature, and which can recover a predefined shape when exposed to a transition temperature T _t depending in particular on its composition. The shape memory alloy of the armature must be strong enough to withstand the high temperatures that can be encountered in a CVI type process, and be chemically inert with respect to the ceramic material or the carbon of the preform 1 under these conditions. Such shape memory alloys can be chosen, for example, from the following: NiTi, CuAINi, CuAIBe. As will be seen later, this frame makes it possible to shape the preform 1 thanks to its shape memory properties. In addition, the frame allows the preform 1 to then retain its shape without requiring holding tools such as a shaper. For this, the volume ratio of shape memory alloy in the preform, corresponding to the ratio between the volume of shape memory alloy and the volume occupied by the wires or strands in the preform, can be between 5% and 30 %. It is therefore advantageous to choose a volume ratio of a shape memory alloy sufficient to maintain the preform 1 when it is shaped, while avoiding altering the mechanical properties of the final part because of the presence of the frame.

FIG. 2 shows an enlarged view of a preform 100 according to a first embodiment of the invention. The preform 100 is obtained by weaving a first set of wires 110, for example ceramic or carbon, with a second set of wires 120 of shape memory alloy. For reasons of simplification, the threads are not shown woven in the figures, but it is obvious that the preform is obtained by weaving the threads 110, 120 as described above. The distribution of the wires 110 and 120 can for example be random or alternated regularly in the preform. In general, it can be ensured that the wires 120 of shape memory alloy are present in the portions of the preform 100 which must be shaped and kept in their shape. The son 120 of shape memory alloy will be oriented precisely during their weaving according to the predefined shape which they will take when they are exposed to the transition temperature Tt of the shape memory alloy. Thus, the armature is here constituted by the wires 120 of the second assembly made of shape memory alloy.

Figure 3 shows an enlarged view of a preform 200 according to a second embodiment of the invention. The preform 200 comprises a set of woven wires 210, for example carbon or ceramic wires, and a frame constituted by a set of strips or sheets 220 of shape memory alloy inserted into the preform 200 during its weaving, or after its weaving. The strips or sheets 220 must be positioned and oriented precisely as a function of the predefined shape which they will take when they are exposed to the transition temperature T _t of the shape memory alloy which constitutes them. Thus, the frame is here constituted by strips or sheets 220 of shape memory alloy.

A method of manufacturing a ring sector from CMC material will now be described in connection with the flow diagram of FIG. 4 and FIGS. 5A to 5C.

In a first step E1, the fibrous preform 1 is first produced which will form the fibrous reinforcement of the ring sector. According to the embodiment of the invention chosen, by weaving wires 110, for example made of silicon carbide, with wires 120 of shape memory alloy (preform 100), or even by inserting strips or sheets 220 of alloy shape memory in the preform 200 during its weaving or after its weaving.

Then, in a second step E2, the fiber preform 1 is exposed to a temperature T at least equal to the transition temperature T _t of the shape memory alloy. This step can be carried out in the oven 20 which will be used to then densify the fibrous preform 1. During this step E2, the alloy with shape memory of the reinforcement regains its predefined shape, which has the effect of shaping the preform 1 (FIG. 5A). In the example illustrated, the shaping of the preform corresponds to the folding of the lateral portions 10 of the fibrous preform 1 towards the central portion 6. At the end of this step E2, the fibrous preform 1 is thus obtained (Figure 5B).

We can then proceed to the densification of the shaped fiber preform 1 (step E3). The densification of the preform 1 can consist of the formation of a ceramic or carbon matrix within its free porosity. One can in particular densify the preform 1 by gas, by penetrating a precursor gas of the ceramic or carbon matrix into the preform 1 under predetermined conditions of temperature and pressure. Such a densification process can be a chemical gas infiltration (CVI), known per se. The method according to the invention makes it possible to dispense with the use of a shaping device during the densification step of the preform 1, the preform 1 being maintained in its shape thanks to the shape memory alloy of its frame. . It is also possible to perform a partial densification step of the preform 1 to consolidate it before densifying it completely. At the end of this step, the part made of composite material is obtained (FIG. 5C).

It should be noted that the invention can also be applied to any process making it possible to form an interphase coating on the threads of a fiber preform by the gaseous route. In this case, instead of densifying the preform 1, an interphase coating is formed on the wires or strands of the shaped preform 1.

Claims (10)

1. Fibrous preform (100; 200) woven from a plurality of threads or strands (110, 120; 210), the preform being intended to form the fibrous reinforcement of a part (13 made of composite material, the preform comprising in addition an integrated armature (120; 220) made of a shape memory alloy capable of conforming to a predefined shape when it is exposed to a transition temperature (T _t ). 2. A fiber preform according to claim 1, in which the shape memory alloy is chosen from the following: NiTi, CuAINi, CuAIBe. 3. A fiber preform according to claim 1, in which the shape memory alloy has a transition temperature (T _t ) of between 100 ° C and 250 ° C. 4. A fiber preform according to any one of claims 1 to 3, comprising wires or strands of silicon carbide. 5. A fiber preform (100) according to any one of claims 1 to 4, comprising a first set of wires or strands (110) woven with a second set of wires (120) of shape memory alloy, the wires or strands. of the first set being made of a material different from the wires or strands of the second set. 6. A fiber preform (200) according to any one of claims 1 to 4, in which the reinforcement comprises sheets or strips (220) of shape memory alloy. 7. A fiber preform according to any one of claims 1 to 6, in which the volume ratio of shape memory alloy in the preform is between 5% and 30%, the volume ratio of shape memory alloy in the preform being equal to the ratio between the volume of shape memory alloy and the volume occupied by the wires or strands in the preform. 8. Piece of composite material (1 *) comprising a fibrous reinforcement densified by a matrix, the fibrous reinforcement comprising a fibrous preform (100; 200) according to any one of claims 1 5 to 7 shaping. 9. Method for manufacturing a part made of composite material (1 ′) comprising at least the following steps: - the production of a fibrous preform (100; 200) according to any one of claims 1 to 7, - exposing the fiber preform to a temperature greater than or equal to the transition temperature (T _t ) of the shape memory alloy of the armature (120; 220) in order to shape the fiber preform and d '' obtain the fibrous reinforcement of the part, and 15 - the formation of a matrix in the porosity of the fibrous reinforcement by the gaseous route. 10. The method of claim 9, wherein the manufactured part (1 ') is a turbine ring sector. 1/4