FR3141166A1 - Infiltration of a fibrous structure comprising an anti-wetting layer with liquid silicon - Google Patents

Abstract

INFILTRATION OF A FIBROUS STRUCTURE INCLUDING AN ANTI-WETTING LAYER WITH LIQUID SILICON The invention relates to a method of manufacturing a part made of ceramic matrix composite material, comprising: - the infiltration of a pre-densified fibrous structure (10) with a melt infiltration composition comprising silicon in order to form a ceramic matrix in a residual porosity of said pre-densified fibrous structure, said fibrous structure pre-densified comprising a pre-densification matrix comprising a first layer of silicon carbide (13), an anti-wetting layer (14) with fused silicon in boron nitride (BN), in silicon nitride (Si3N4), in SiNxOy or oxide, for example silica (SiO2), alumina (Al2O3), zirconia (ZrO2) or mullite (3Al2O3.2SiO2), or a mixture of these compounds, the anti-wetting layer covering the first layer , and a molten silicon wetting layer of silicon carbide or carbon (15) covering the anti-wetting layer Figure for abstract: Fig. 1

Description

Infiltration of a fibrous structure comprising an anti-wetting layer of liquid silicon

The invention relates to the manufacture of a part made of ceramic matrix composite material ("Ceramic Matrix Composite"; "CMC") during which the ceramic matrix is formed by infiltration in the molten state ("Melt-Infiltration"; "MI") of a silicon-based composition. The composite material part thus obtained can find an application as a hot part of a turbomachine, in particular an aeronautical turbomachine, such as a turbine part.

Ceramic matrix composite materials withstand temperatures ranging from 600°C to 1400°C. Due to their better resistance to high temperatures, CMCs require less cooling. Since this cooling traditionally comes from a tapping in the compressor which impacts the efficiency of the turbomachine, CMC materials therefore improve engine efficiency which reduces fuel consumption. In addition, their use helps to optimize the performance of turbomachines, in particular by reducing the overall mass of the turbomachine which further contributes to a reduction in fuel consumption and therefore to a significant reduction in pollutant emissions.

CMC parts can be densified by melt infiltration. In this technique, a molten silicon composition can be introduced into the porosity of a fibrous structure pre-densified by silicon carbide deposition and loaded with silicon carbide particles. This method makes it possible to obtain a fully dense Si-SiC matrix of high modulus and a composite with a high linearity limit. The composites obtained have good mechanical properties but the inventors have observed a certain variability in the elongation at break which reduces the damage tolerance zone of the material. It is desirable to propose a solution to address this drawback.

The invention aims precisely to meet this need.

To do this, it proposes a manufacturing process for a part in ceramic matrix composite material, comprising:

- infiltrating a pre-densified fibrous structure with a molten infiltration composition comprising silicon to form a ceramic matrix in a residual porosity of said pre-densified fibrous structure, said pre-densified fibrous structure comprising a pre-densification matrix comprising a first layer of silicon carbide, a molten silicon anti-wetting layer of boron nitride (BN), silicon nitride (Si ₃ N ₄ ), SiN _x O _y or oxide, in particular silica (SiO ₂ ), alumina (Al ₂ O ₃ ), zirconia (ZrO ₂ ) or mullite (3Al ₂ O ₃ .2SiO ₂ ), or a mixture of these compounds, the anti-wetting layer covering the first layer, and a molten silicon wetting layer of silicon carbide or carbon, covering the anti-wetting layer.

In the application, the expression “anti-wetting” must be understood in the usual sense of physical wetting between a surface and a liquid, the surface here being the surface of the anti-wetting layer and the liquid the infiltration composition. Wetting can be measured by the contact angle as it is usually defined, that is to say by the tangent to the liquid at the air/liquid/surface interface point. The wetting is all the better as the contact angle is small.

A layer will be said to be “anti-wetting” if the contact angle is greater than or equal to 50°, or even greater than or equal to 90°.

For example, the contact angle used to quantify wetting can be measured using a standing drop method, a hanging drop method using a goniometer, the Wilhelmy method or even capillary rise.

As opposed to anti-wetting, a layer will be said to be “wetting” if it is not anti-wetting, that is to say if its contact angle is less than 50°.

As described, the fused silicon wetting layer comprises silicon carbide, carbon, or a mixture of these two compounds.

In the method of the invention, the particular composition of the layers of the pre-densification matrix makes it possible to solve the technical problem.

In fact, the liquid silicon first reacts with the wetting layer of the molten silicon which it passes through to reach the anti-wetting layer.

Once the anti-wetting layer is reached, the latter physically blocks the progression of the liquid silicon which cannot wet it and even less pass through it.

The compounds of the anti-wetting layer are furthermore chosen to be inert with respect to molten silicon, i.e. they do not react chemically with it.

The liquid silicon is therefore chemically blocked by the anti-wetting layer with which it cannot react.

The liquid silicon is then unable to penetrate the first layer of silicon carbide and even less to reach the underlying fibrous reinforcements.

Stopping the progression of silicon ensures that the liquid silicon from the infiltration does not damage the pre-densified fiber reinforcements as it could do for prior art structures. The result is composite parts with less variable properties from one part to another.

The anti-wetting layer comprises a material selected from boron nitride (BN), silicon nitride (Si ₃ N ₄ ), SiN _x O _y or an oxide, in particular silica (SiO ₂ ), alumina (Al ₂ O ₃ ), zirconia (ZrO ₂ ) or mullite (3Al ₂ O ₃ .2SiO ₂ ), or a mixture of these compounds.

It is understood that a mixture of these compounds can be obtained either with a layer comprising several of these compounds, or with a subdivided anti-wetting layer comprising several sub-layers each comprising a different material from the list.

In the application, the expression "SiN _x O _y " is intended to characterize all the compounds comprising silicon, nitrogen and oxygen, which are present on the ternary diagram Si, N, O along the isopleth connecting silica (SiO ₂ ) and silicon nitride (Si ₃ N ₄ ).

In other words, the formula "SiN _x O _y " is intended to characterize compounds whose atomic content satisfies the relation SiN _x O _y with x between 0 and 4/3 (limits excluded), including between 0 and 2 (limits excluded) and further satisfying 1.5x+y=2. In particular, the species Si ₂ N ₂ O can be cited as a representative of the SiN _x O _y family. It should be noted that the exclusion of the limits for the definition intervals of x and y is not intended to exclude the compounds Si ₃ N ₄ and SiO ₂ as potential components of the silicon anti-wetting layer, but the latter will not be considered here as SiN _x O _y compounds to avoid redundancy in the description.

In one embodiment, the anti-wetting layer is comprised of boron nitride (BN).

This compound is preferred for the invention because it is easily deposited by a chemical vapor infiltration process. It therefore represents a good alternative for forming the molten silicon anti-wetting layer, especially when the remainder of the pre-densification of the fibrous structure is also carried out by chemical vapor infiltration.

In one embodiment, the molten silicon wetting layer has a thickness greater than or equal to 0.2 µm, for example between 0.2 µm and 10.0 µm or even between 1.0 µm and 10.0 µm.

In one embodiment, the fused silicon wetting layer has a columnar microstructure.

This embodiment can be obtained when the pre-densification of the fibrous structure is carried out by chemical vapor infiltration.

The columnar microstructure is then oriented with the grain boundaries along a direction transverse to a surface of the fibers. The columnar microstructure makes it possible to limit the liquid silicon reaching the anti-wetting layer due to the need for infiltration between the columns and therefore to allow good protection even with a thin layer of anti-wetting material.

In one embodiment, the thickness of the anti-wetting layer may be less than or equal to 1000 nm.

Having the smallest possible anti-wetting layer ensures that it does not affect the mechanical properties of the fiber structure.

In one embodiment, the thickness of the anti-wetting layer may be greater than or equal to 20 nm.

Having a sufficiently thick anti-wetting layer ensures that the liquid silicon does not pass through it during impregnation.

In one embodiment, the thickness of the anti-wetting layer is between 20 nm and 1000 nm, or even between 200 nm and 500 nm.

Such a thickness of the anti-wetting layer represents an optimum between the two effects described above.

In one embodiment, the ratio of the thickness of the molten silicon wetting layer to the thickness of the first silicon carbide layer is between 10/90 and 90/10.

This report fixes the positioning of the anti-wetting layer within the pre-densification matrix.

A ratio between the values proposed above ensures sufficient thickness of the first silicon carbide layer so that the pre-densified fibrous structure has the expected properties. The ratio also ensures that the anti-wetting layer is far enough from the external surface of the pre-densification matrix (surface furthest from the fibers) so that the molten silicon wetting layer prevents the liquid silicon from coming into contact with the anti-wetting layer too easily, which is not desirable.

The invention has just been described with a single anti-wetting layer.

In other embodiments, the pre-densification matrix may comprise above the fused silicon wetting layer between one and eight additional protective structures, each additional protective structure comprising a fused silicon anti-wetting layer of boron nitride (BN), silicon nitride (Si ₃ N ₄ ), SiN _x O _y or oxide, in particular silica (SiO ₂ ), alumina (Al ₂ O ₃ ), zirconia (ZrO ₂ ) or mullite (3Al ₂ O ₃ .2SiO ₂ ), or a mixture of these compounds, and an additional fused silicon wetting layer of silicon carbide or carbon covering the additional fused silicon anti-wetting layer.

In the event that several additional protection structures are present, they can be placed in succession and in contact with each other.

This results in an alternation of anti-wetting layers and wetting layers with molten silicon, which ensures that even if the silicon passes through an anti-wetting layer, it will be stopped at the next anti-wetting layer.

In one embodiment, the pre-densified fibrous structure further comprises a boron nitride interphase between a fibrous reinforcement and the pre-densification matrix.

The presence of a boron nitride interphase advantageously makes it possible to deflect cracks which may appear in the matrix of the composite part during operation so as to preserve the fibrous reinforcement.

In one embodiment, the pre-densified fibrous structure comprises a fibrous reinforcement formed by three-dimensional weaving or from a plurality of two-dimensional fibrous layers.

The particular choice of the weaving structure makes it possible to give the pre-densified fibrous structure and consequently the resulting part particular mechanical properties.

In particular, such structures are particularly suitable for parts used in the aeronautical field.

In one embodiment, the part may be a turbomachine part.

There schematically represents a pre-densified structure useful for the invention.

There schematically represents the behavior of molten silicon on a pre-densified structure during the implementation of the method of the invention.

The invention is now described by means of figures, present for descriptive purposes to illustrate certain embodiments of the invention and which should not be interpreted as limiting the latter.

Furthermore, the figures are represented with non-realistic scales that allow easy understanding, and which should not be interpreted as the real scales between the different elements.

There represents a pre-densified fibrous structure useful for carrying out a method of the invention.

Such a pre-densified structure 10 may comprise a fibrous reinforcement 11, a boron nitride interphase 12, a first silicon carbide layer 13, an anti-wetting layer 14 of fused silicon made of boron nitride (BN), silicon nitride (Si ₃ N ₄ ), SiN _x O _y or oxide, in particular silica (SiO ₂ ), alumina (Al ₂ O ₃ ), zirconia (ZrO ₂ ) or mullite (3Al ₂ O ₃ .2SiO ₂ ), or a mixture of these compounds, and a wetting layer of fused silicon made of silicon carbide or carbon15.

There is a projection in a plane perpendicular to the direction in which the greatest direction of a fibrous reinforcement 11 of the structure 10 extends.

There further represents the thickness e1 of the molten silicon wetting layer 15, the thickness e2 of the anti-wetting layer 14 and the thickness e3 of the first silicon carbide layer 13.

In one embodiment, the pre-densified fibrous structure does not comprise any elements other than the fibrous reinforcement 11 and the layers 12, 13, 14 and 15 which have just been described.

In one embodiment, the interphase layer 12 is in contact with the fibrous reinforcement 11, and in contact with the first layer of silicon carbide 13.

In one embodiment, the first silicon carbide layer 13 is in contact with the boron nitride interphase layer 12, and in contact with the anti-wetting layer 14.

In one embodiment, the anti-wetting layer 14 is in contact with the first silicon carbide layer 13, and in contact with the molten silicon wetting layer 15.

In one embodiment, the molten silicon wetting layer 15 is in contact with the anti-wetting layer 14.

The fibrous structure may be formed by implementing one or more textile operations such as three-dimensional weaving. The fibrous structure may be formed of ceramic yarns, for example silicon carbide yarns.

In one embodiment, the fibrous reinforcements 11 of the pre-densified fibrous structure 10 may be formed of ceramic wires, for example silicon carbide wires. The fibrous structure may constitute the fibrous reinforcement of the composite material part to be obtained. Examples of usable silicon carbide wires may be wires marketed under the reference “Nicalon”, “Hi-Nicalon” or “Hi-Nicalon-S”. The ceramic wires of the fibrous structure may have an oxygen content of less than or equal to 1% in atomic percentage. The “Hi-Nicalon-S” wires, for example, have such a characteristic.

By "three-dimensional weaving" or "3D weaving" is meant a weaving method by which at least some of the warp threads bind weft threads on several weft layers. A reversal of roles between warp and weft is possible in the present text and must be considered as also covered by the claims. The fibrous structure may for example have an interlock weave. By "interlock weave or fabric" is meant a 3D weave weave in which each layer of warp threads binds several layers of weft threads with all the threads of the same warp column having the same movement in the plane of the weave. It is also possible to start from fibrous textures such as two-dimensional fabrics or unidirectional sheets, and to obtain the fibrous structure by draping such fibrous textures on a form. These textures can optionally be linked together for example by sewing or implantation of threads to form the fibrous structure.

In one embodiment, the interphase layer 12 may be formed by chemical vapor infiltration on the fibrous reinforcements 11 of the fibrous structure. The fibrous structure may be positioned in a shaping tool allowing it to be shaped to the part to be obtained during the deposition of the interphase. The thickness of the interphase may for example be between 10 nm and 1000 nm, and for example between 100 nm and 600 nm. After formation of the interphase, the fibrous structure remains porous, the initial accessible porosity being filled only for a minor part by the interphase. The interphase may be single-layer or multi-layer. The interphase may comprise at least one layer of pyrolytic carbon (PyC), boron nitride (BN), silicon-doped boron nitride (BN(Si), with silicon in a mass proportion of between 5% and 40%, the remainder being boron nitride) or boron-doped carbon (BC, with boron in an atomic proportion of between 5% and 20%, the remainder being carbon). The interphase here has a function of weakening the composite material which promotes the deflection of any cracks reaching the interphase after having propagated in the matrix, preventing or delaying the breakage of fibers by such cracks. Alternatively, it will be noted that it is possible to form the interphase on the threads before the formation of the fibrous structure.

In one embodiment, the pre-densification of the fibrous structure may be achieved by a chemical vapor infiltration process.

For example, the first silicon carbide layer 13 may be formed from a gas phase comprising methyltrichlorosilane (MTS) and hydrogen (H ₂ ).

In one embodiment, the thickness e3 of the silicon carbide layer 13 may be between 0.2 µm and 10 µm.

For example, the first layer of silicon carbide 13 can be obtained in two successive phases of chemical vapor infiltration.

For example, during a first phase, the fibrous structure is still positioned in the shaping tool and a first part of the first silicon carbide layer 13, called the consolidation layer, is deposited on the interphase 12 and the fibrous reinforcement 10. This consolidation layer can be deposited in contact with the interphase 12. This layer has a sufficient thickness to sufficiently bind the fibers so that the structure retains its shape without assistance from the holding tool. This layer provides protection to the interphase against oxidation and can be formed by chemical vapor infiltration in a manner known per se, for example from a gas phase comprising methyltrichlorosilane (MTS) and hydrogen (H ₂ ). For example, the thickness of the consolidation layer can be greater than or equal to 0.1 µm, for example between 0.1 µm and 5.0 µm.

In the second phase, the consolidated and shaped fibrous structure of the part to be obtained can be removed from the tool and the formation of the pre-densification matrix can resume by depositing a second part of the first layer of silicon carbide 13 on the consolidation layer.

This first layer of silicon carbide 13 makes a large contribution to the mechanical performance of the composite material and provides protection against the molten silicon used during subsequent infiltration.

In one embodiment, and according to the variant illustrated in , the consolidation layer may not be subject to any particular deposition, and the first layer of silicon carbide 13 of pre-densification matrix could be directly formed on the interphase 12.

The formation of the first layer of silicon carbide 13 can be followed by deposition of an anti-wetting layer 14.

The anti-wetting layer 14 can be deposited by chemical vapor infiltration.

Chemical vapor infiltration can be carried out in the same reactor as the chemical vapor infiltration allowing the first layer of silicon carbide to be obtained 13.

This makes it possible in particular to reduce the number of operations involving moving the fibrous reinforcement to be impregnated.

For example, the first silicon carbide layer 13 may be deposited by a chemical vapor infiltration process. For example, a reactor is fed with silicon carbide precursors, the reactor being maintained at a temperature of between 950°C and 1080°C and at a pressure of between 10 and 40 mbar.

To switch from a silicon carbide deposit 13 to an anti-wetting layer deposit 14, the supply of silicon carbide precursors is cut off, and precursors of the anti-wetting layer are then introduced, possibly after purging the reactor.

The reactor pressure and temperature may or may not be changed.

For example, the fused silicon anti-wetting layer 14 comprises boron nitride (BN), silicon nitride (Si ₃ N ₄ ), SiN _x O _y , or an oxide, including silica (SiO ₂ ), alumina (Al ₂ O ₃ ), zirconia (ZrO ₂ ), mullite (3Al ₂ O ₃ .2SiO ₂ ), or a mixture of these compounds.

The anti-wetting layer can be obtained from gaseous precursors, for example chosen according to the desired composition for the anti-wetting layer.

For example, for a BN anti-wetting layer, the precursors can be chosen from the pairs BCl ₃ and NH ₃ or BF ₃ and NH ₃ .

For an anti-wetting layer in Si ₃ N ₄ , the precursors can be chosen from the group SiH ₄ , SiH ₂ Cl ₂ , SiCl ₄ possibly in association with NH ₃ .

For a SiN _x O _y anti-wetting layer, the precursors may include SiHCl ₃ in combination with NH ₃ and N ₂ O.

For a _SiO2 anti-wetting layer, precursors may include _SiHCl3 in combination with _N2O .

For a _ZrO2 anti-wetting layer, precursors may include _ZrCl4 in combination with _H2 and _N2O .

The anti-wetting layer 14 deposited by a chemical vapor infiltration process makes it possible to obtain a uniform layer on the fibrous reinforcements 11.

The thickness e2 of the anti-wetting layer can be between 20 and 1000 µm.

As shown in the , the anti-wetting layer 14 may be covered with a molten silicon wetting layer 15.

For example, the molten silicon wetting layer 15 may be deposited by chemical vapor infiltration, for example under the same conditions as the first silicon carbide layer 13.

In one embodiment, to switch from deposition of an anti-wetting layer 14 to deposition of the molten silicon wetting layer 15, the supply of anti-wetting layer precursors is cut off, then silicon carbide precursors are introduced into the reactor, optionally after purging the reactor.

The reactor pressure and temperature may or may not be changed.

This makes it possible to simply switch from a deposition of the anti-wetting layer 14 to a deposition of the molten silicon wetting layer 15.

The thickness e1 of the molten silicon wetting layer 15 can be between 0.2 µm and 10 µm.

There illustrates the interest of the anti-wetting layer during the infiltration of a fibrous structure.

Identical reference numbers indicate identical items between the and 2.

There shows the infiltration of liquid silicon 21 into the molten silicon wetting layer 15.

Infiltration 21 is shown on the in a very schematic manner. However, it should be seen that the silicon has a progression in the second layer of silicon carbide aligned with the direction transverse to the fibers. In addition, the attack of the liquid silicon can take place in several places on the external surface of the fiber 10 as shown in the .

The molten silicon wetting layer 15, due to its columnar structure, nevertheless limits the access of the liquid silicon 21 to the anti-wetting layer 14.

The liquid silicon 21 which has nevertheless passed through the molten silicon wetting layer 15 and which reaches the anti-wetting layer 14 then remains blocked, unable to react with the anti-wetting layer.

The anti-wetting layer 14 hinders the progression of the liquid silicon towards the fibrous reinforcement 11 and ensures that the first layer of silicon carbide 13, and especially the interphase 12 and the fibrous reinforcement 11 are protected from the liquid silicon 21.

Claims (10)

Method for manufacturing a part made of ceramic matrix composite material, comprising:
- infiltrating a pre-densified fibrous structure (10) with a molten infiltration composition comprising silicon in order to form a ceramic matrix in a residual porosity of said pre-densified fibrous structure, said pre-densified fibrous structure comprising a pre-densification matrix comprising a first layer of silicon carbide (13), an anti-wetting layer (14) of molten silicon in boron nitride (BN), in silicon nitride (Si₃N₄), in SiN_xO_y or oxide, for example silica (SiO₂), in alumina (Al₂O₃), in zirconia (ZrO₂), in mullite (3Al₂O₃.2SiO₂), or a mixture of these compounds, the anti-wetting layer covering the first layer, and a fused silicon wetting layer of silicon carbide or carbon (15) covering the anti-wetting layer. The method of claim 1, wherein the anti-wetting layer is comprised of boron nitride (BN). A method according to claim 1 or 2, wherein the molten silicon wetting layer (15) has a thickness of between 0.2 µm and 10.0 µm. The method of claim 1 to 3, wherein the molten silicon wetting layer (15) has a columnar microstructure. Method according to any one of claims 1 to 4, in which the thickness (e2) of the anti-wetting layer (14) is less than or equal to 1000 nm. Method according to any one of claims 1 to 5, in which the ratio between the thickness (e1) of the molten silicon wetting layer (15) and the thickness (e3) of the first silicon carbide layer (13) is between 90/10 and 10/90. A method according to any one of claims 1 to 6, wherein the pre-densification matrix may comprise, above the second silicon carbide layer (15), between one and eight additional protective structures, each additional protective structure comprising a fused silicon anti-wetting layer of boron nitride (BN), silicon nitride (Si ₃ N ₄ ), SiN _x O _y or oxide, in particular silica (SiO ₂ ), alumina (Al ₂ O ₃ ), zirconia (ZrO ₂ ) or mullite (3Al ₂ O ₃ .2SiO ₂ ), or a mixture of these compounds, and an additional fused silicon wetting layer of silicon carbide or carbon covering the additional fused silicon anti-wetting layer. A method according to any one of claims 1 to 7, wherein the pre-densified fibrous structure further comprises a boron nitride interphase (12) between a fibrous reinforcement (11) and the pre-densification matrix (13, 14, 15). A method according to any one of claims 1 to 8, wherein the pre-densified fibrous structure (10) comprises a fibrous reinforcement (11) formed by three-dimensional weaving or from a plurality of two-dimensional fibrous layers. A method according to any one of claims 1 to 9, wherein the part is a turbomachine part.