EP3164373A1

EP3164373A1 - Part coated with a surface coating and associated methods

Info

Publication number: EP3164373A1
Application number: EP15732611.7A
Authority: EP
Inventors: Emilie Courcot; Eric Philippe; Eric Bouillon; Sébastien JIMENEZ
Original assignee: Safran Ceramics SA
Current assignee: Safran Ceramics SA
Priority date: 2014-07-03
Filing date: 2015-06-24
Publication date: 2017-05-10
Also published as: US20170159459A1; FR3023211A1; FR3023211B1; CN107001162A; WO2016001026A1

Abstract

The invention concerns a part made from composite material comprising a fibrous reinforcement densified by a ceramic matrix, the part having an outer surface and being characterised in that it is coated on at least one part of the outer surface of same with a surface coating in solid form comprising an alloy of silicon and nickel having a weight content of silicon of between 29% and 45% or an alloy of silicon and cobalt.

Description

Part coated with a surface coating and related processes

Background of the invention

The invention relates to ceramic matrix composite material (CMC) parts comprising a surface coating, their use in turbomachines and methods of manufacturing such parts.

Composite materials CMC are able to constitute parts intended to be exposed in service at high temperatures and have the advantage of maintaining good mechanical properties at high temperatures.

It is known to treat the surface of CMC materials according to the applications envisaged for the latter. For example, the following coatings can be produced on the surface of the CMC:

- smoothing coating for the turbine blade pale area to improve the aerodynamic character,

- environmental barrier to protect silicon carbide (SiC) from the phenomenon of wet corrosion at high temperature, or

- coating to limit the phenomena of wear and contact wear ("fretting") interfaces.

Currently, the functional coatings are made on the composite material in its final stage of elaboration.

There is therefore a total decoupling between the manufacture of the CMC and the formation of its coating. Oxide coatings used to improve corrosion resistance and smooth the surface can be developed by plasma spraying or flash sintering. Carbide type coatings can, for their part, be made by powder coating technologies (paint, dipping dip-coating, injection or overmoulding, for example) followed by consolidation by gas.

Current processes for producing coated CMC parts have two main disadvantages.

On the one hand, these methods can comprise a large number of steps and can therefore be relatively complex and expensive. On the other hand, the attachment to the composite material of the coating obtained may not be entirely satisfactory because of the decoupling existing between the manufacture of the CMC and the formation of its coating. In addition, another problem is to be considered for CMC parts which concerns the chemical interactions that these parts can undergo with the support on which they are mounted during their use. Such interactions can be problematic in that they can lead to damage to CMC parts and / or metal parts.

There is therefore a need to obtain new CMC parts with limited interactions with the support on which they are intended to be mounted during their use.

There is also a need to obtain new parts in

CMC with increased resistance to contact wear phenomena ("fretting").

There is still a need for simpler and less expensive methods of preparing CMC parts coated with a coating.

Obiet and summary of the invention

For this purpose, the invention proposes, in a first aspect, a composite material part comprising a fiber reinforcement densified by a ceramic matrix, the part having an external surface and being characterized in that it is coated on at least a part its outer surface by a surface coating in solid form comprising, in particular consisting of, a silicon and nickel alloy having a silicon content by mass of between 29% and 45% or an alloy of silicon and cobalt.

The use of such alloys within the coating advantageously makes it possible to limit the interactions, in particular the chemical reactions, between the part, on the one hand, and the constituent material of the support on which the part is intended to be mounted when it is assembled. use, on the other hand.

Thus, the inventors have found that the presence, within the surface coating, of an alloy as described above comprising silicon and a metal constituting mainly the support on which the part is intended to be mounted (nickel or cobalt) advantageously allowed to limit the interactions between the part and the support. Thus, the part according to the invention advantageously has interactions limited with the nickel-based superalloy and / or cobalt of the fixing support, and this thanks to the saturation of silicon by nickel or cobalt present in the coating.

"Surface coating" means a coating whose majority of the mass is present on the outer surface of the part. In other words, at least 50%, preferably at least 60%, preferably at least 70%, preferably at least 80%, preferably at least 90%, preferably at least 95%, preferably at least 100%. %, the mass of the surface coating is present on the outer surface of the part (thus outside the room).

It is possible that the surface coating penetrates slightly into the room, for example to ensure its attachment to the latter. However, the surface coating preferably does not penetrate the room.

The surface coating is attached to the outer surface of the workpiece and can penetrate the pores of the outer surface of the workpiece.

The silicon and nickel alloy or the silicon and cobalt alloy may be in contact with the ceramic matrix.

On the other hand, the surface coating does not densify, preferably, the fibrous reinforcement. The surface coating can take the shape of the part it covers. Thus, the surface of the surface coating on the opposite side of the workpiece may have the same shape as the outer surface of the workpiece.

In an exemplary embodiment, the surface coating may comprise a NiSi phase ₂ and / or a NiSi phase. In particular, the surface coating may comprise:

a phase of NiSi ₂ and optionally a phase of Si, and / or

a NiSi phase and optionally an Si phase.

In an exemplary embodiment, the surface coating may comprise a CoSi ₂ phase and optionally an Si phase.

Preferably, the silicon and nickel alloy may have a silicon mass content of between 40% and 45%.

Preferably, the alloy of silicon and cobalt may have a silicon mass content of between 34% and 90%, for example between 40% and 90%, for example between 42% and 70%, for example between 45% and 60%.

The silicon-nickel alloy or the silicon-cobalt alloy may be present in a mass content greater than or equal to 5%, preferably greater than or equal to 50%, relative to the weight of the surface coating.

The thickness of the surface coating may, over all or part of the outer surface of the coated part, be between 20 μm and 1000 μm, preferably between 50 μm and 300 μm.

In particular, when the part constitutes an aeronautical engine blade, the thickness of the surface coating may, for example, be less than or equal to 300 μιη in the blade root area and / or be less than or equal to 100 μm. in the area of the blade.

The thickness of the surface coating may vary as one moves along the outer surface of the workpiece.

Such variation of the thickness advantageously allows to have a room whose coating has different functions depending on the area.

Alternatively, the thickness of the surface coating may be substantially constant as one moves along the outer surface of the workpiece.

The surface coating may further comprise fillers and / or ceramic material.

The charges present within the surface coating may be chosen from: SiC, S13N4 or BN, and mixtures thereof.

The ceramic material present within the surface coating may be chosen from ceramic materials derived from the pyrolysis of preceramic resins, the preceramic resins being for example chosen from: polycarbosilanes, polysilazanes, polyborosilanes, and mixtures thereof.

The surface coating may, in an exemplary embodiment, have substantially the same composition when moving along the outer surface of the workpiece.

Alternatively, the composition of the surface coating varies as one moves along the outer surface of the workpiece. Such a variation of the composition advantageously allows to have a room whose coating has different functions depending on the area.

The fibers of the fibrous reinforcement are advantageously coated with an interphase layer.

The use of an interphase is advantageous insofar as it makes it possible to increase the mechanical strength of the fibers constituting the fibrous reinforcement by allowing in particular a deflection of the possible cracks of the matrix so that these do not affect the integrity fibers.

The interphase layer may comprise, in particular, pyrocarbon (PyC), boron doped pyrocarbon or BN. The interphase layer may be multi-sequenced or not, for example comprising a repetition of [PyC / Carbide], [BC / Carbide] or [BN / Carbide] sequences.

The fibers of the fibrous reinforcement are advantageously coated with a barrier layer, which is, for example, in the form of a self-healing carbide matrix.

The use of such a barrier layer advantageously makes it possible to protect the fibers against oxidation and to generate a cracking network remote from the fibrous reinforcement.

The part may constitute an aeronautical engine blade having at least one blade root and a blade and may be such that the surface coating covers at least the blade root. Alternatively, the part may constitute a turbine ring sector comprising one or more attachment portions to a metal ring support structure and may be such that the surface coating covers at least one or more attachment portions. .

The present invention also relates to a turbomachine wheel comprising:

a wheel disk comprising a blade attachment part, said fixing part comprising an alloy comprising nickel and / or cobalt, and

- A blade as defined above fixed to the wheel disc, the blade root being mounted on the blade attachment portion. The present invention also relates to a method for manufacturing a part as defined above, comprising the following steps:

a) infiltration of a fibrous preform comprising a first set of charges, for example a first set of reactive charges, with a melt infiltration composition, the infiltration composition comprising silicon and having a first melting, in order to obtain, after contacting the infiltration composition with all or part of the charges of the first set of charges, a part made of a composite material comprising a fiber reinforcement densified by a ceramic matrix, and

b) application on at least a portion of the outer surface of the composite material part of an alloy of silicon and nickel or of a silicon and cobalt alloy in the molten state, the alloy of silicon and of nickel or silicon and cobalt having a second melting temperature lower than the first melting temperature, in order to obtain a surface coating in solid form on at least a portion of the outer surface of the composite material part.

The implementation of such a method advantageously simplifies the preparation of a CMC part covered with a surface coating.

The fact of using an alloy of silicon and nickel or silicon and cobalt with a melting temperature below the melting temperature of the infiltration composition advantageously makes it possible, during the formation of the surface coating, not to make to melt, again, the infiltration composition which would not have reacted.

The method may further comprise, after step a) and before step b), a step c) of depositing on the external surface of the composite material part of a second set of charges and / or a preceramic resin and the process may be such that the alloy of silicon and nickel or the alloy of silicon and cobalt in the molten state infiltrates during step b) within the second set of charges and / or preceramic resin to form the surface coating.

The charges of the second set of charges may or may not be reactive. The non-reactive charges of the second set of charges may, for example, be chosen from: SiC, S13IM4 or BN, and their mixtures. The reactive charges of the second set of charges may, for example, be chosen from: C, B ₄ C, SiB ₆ , and mixtures thereof.

The silicon and nickel alloy or the molten silicon and cobalt alloy may react chemically with the reactive charges deposited in step c) when it is brought into contact with the latter. Alternatively, the alloy of silicon and nickel or the alloy of silicon and cobalt can, once solidified, participate in ensuring the bond charges deposited in step c).

The method according to the invention can therefore implement two steps of infiltration in the molten state ("melt-infiltration"), the first to form the ceramic matrix and the second to form the surface coating.

Using the same type of process twice advantageously contributes to simplifying the preparation of the coated part.

The deposit made during step c) may advantageously be of variable thickness and / or of variable composition when moving along the outer surface of the part, for example according to the different functional areas of the part.

Such a deposit advantageously makes it possible to obtain a coating having different functions depending on the position on the outer surface of the part.

The present invention also relates to a method of manufacturing a part as defined above, comprising a step:

- Of formation on the outer surface of a composite material part comprising a fiber reinforcement densified by a ceramic matrix of a surface coating in solid form comprising an alloy of silicon and nickel or an alloy of silicon and cobalt.

The formation of the surface coating may comprise a step of contacting an alloy of silicon and nickel or a silicon and cobalt alloy in the molten state with fillers, for example reactive fillers or alternatively non-reactive fillers, and / or with a preceramic resin.

Non-reactive fillers may, for example, be selected from: SiC, Si ₃ N ₄ or BN, and mixtures thereof. Reactive loads can, for example, be chosen from: C, B ₄ C, SiB ₆ , and mixtures thereof.

The alloy of silicon and nickel or the alloy of silicon and cobalt in the molten state can react chemically with the reactive charges when it comes into contact with the latter. Alternatively, the silicon-nickel alloy or the silicon-cobalt alloy can, once solidified, participate in bonding the charges.

The part can be covered, before melting of the alloy of silicon and nickel or of the alloy of silicon and cobalt, on its external surface by a precursor coating layer comprising, on the one hand, the silicon alloy and nickel or the alloy of silicon and cobalt and, on the other hand, fillers, for example reactive fillers or alternatively non-reactive fillers, and / or preceramic resin. Brief description of the drawings

Other characteristics and advantages of the invention will emerge from the following description of particular embodiments of the invention, given by way of non-limiting examples, with reference to the appended drawings, in which:

FIG. 1 represents a schematic and partial section of a part according to the invention,

FIG. 2 is a flow diagram of an exemplary method for preparing a part according to the invention,

FIG. 3 is a more detailed flow chart of an exemplary method for preparing a part according to the invention,

FIG. 4 is a flow diagram of an alternative method for preparing a part according to the invention,

FIG. 5 is a perspective view of a part according to the invention constituting a turbomachine blade, and

FIG. 6 is a perspective view of a turbomachine wheel according to the invention.

Detailed description of embodiments

FIG. 1 shows a section of a part 1 made of composite material comprising a fibrous reinforcement (not shown) densified by a ceramic matrix 2. The part 1 has on its surface external 3 a surface coating in solid form 4 comprising a, in particular formed of a silicon alloy and nickel or an alloy of silicon and cobalt.

The surface coating 4 may further comprise fillers and / or ceramic material.

As illustrated, the surface coating 4 does not penetrate within the matrix 2. The surface coating 4 remains, in fact, in the example shown entirely on the outer surface 3 of the piece 1. We do not leave the frame of the invention if the surface coating penetrates within the matrix as the majority of the mass of the latter remains on the outer surface of the part (and therefore outside thereof).

The thickness e of the surface coating 4 may, as illustrated, be substantially constant as one moves along the outer surface 3 of the part. In a variant not shown, the thickness e of the surface coating varies as one moves along the outer surface of the part.

The surface coating 4 can, as illustrated, take the shape of the piece 1. In the example illustrated, the surface S of the surface coating located on the side opposite the piece 1 has the same shape as the external surface 3 of the piece 1 .

We will now describe in more detail some elements relating to the manufacture of composite materials comprising a fiber reinforcement densified by a ceramic matrix used in the context of the present invention.

The fibrous preform intended to form the fibrous reinforcement of the part according to the invention can be obtained by multilayer weaving between a plurality of warp layers and a plurality of weft layers. The multilayer weave produced can be in particular an "interlock" weave, that is to say a weave weave in which each layer of weft son binds several layers of warp son with all the son of the same column weft with the same movement in the plane of the armor.

Other types of multilayer weaving may of course be used.

When the fiber preform is made by weaving, the weaving can be carried out with warp yarns extending in the direction longitudinal of the preform, being noted that weaving with weft yarns in this direction is also possible.

In an exemplary embodiment, the son used may be silicon carbide (SiC) son provided under the name "Nicalon", "Hi-Nicalon" or "Hi-Nicalon-S" by the Japanese company Nippon Carbon or "Tyranno SA3 "by the company UBE and having a titre (number of filaments) of 0.5K (500 filaments).

Various multilayer weaving modes are described in particular in document WO 2006/136755.

The fibrous reinforcement of the piece according to the invention can also be formed from a fibrous preform obtained by assembling two fibrous textures. In this case, the two fibrous textures can be bonded together, for example by sewing or needling. The two fibrous textures can in particular be each obtained from a layer or a stack of several layers of:

- one-dimensional fabric (UD),

- two-dimensional fabric (2D),

- braid,

- knit,

- felt,

- Unidirectional web (UD) of son or cables or multidirectional webs (nD) obtained by superposition of several UD webs in different directions and UD web connection between them for example by sewing, by chemical bonding agent or by needling.

In the case of a stack of several layers, they are interconnected for example by sewing, by implantation of son or rigid elements or by needling.

As described above, a fibrous preform intended to form the fibrous reinforcement of a part according to the invention can be obtained by multilayer weaving, or by stacking fibrous structures. For turbomachine blades intended for use at high temperature and in particular in a corrosive environment (especially humidity), it is advantageously used for weaving son formed of ceramic fibers, in particular silicon carbide (SiC) fibers. For parts with shorter durations of use, carbon fibers can also be used. The densification of the fiber preform intended to form the fibrous reinforcement of the part according to the invention consists in filling the porosity of the preform, in all or part of the volume thereof, with the material constituting the matrix. This densification can for example be carried out in a manner known per se according to the liquid process (CVL) or the gaseous process (CVI), or alternatively in a sequence of these two processes.

The liquid process consists of impregnating the preform with a liquid composition containing a precursor of the matrix material. The precursor is usually in the form of a polymer, such as a resin, optionally diluted in a solvent. The preform is placed in a mold which can be sealed with a housing having the shape of the molded end piece. Then, the mold is closed and the liquid matrix precursor (for example a resin) is injected throughout the housing to impregnate the entire fibrous portion of the preform.

The conversion of the precursor into a matrix is carried out by heat treatment, generally by heating the mold, after removal of the optional solvent and crosslinking of the polymer, the preform being always maintained in the mold having a shape corresponding to that of the part to be produced.

In the case of the formation of a ceramic matrix, the heat treatment comprises a step of pyrolysis of the precursor to form the ceramic matrix. By way of example, liquid precursors of ceramics, in particular of SiC, may be polycarbosilane (PCS) or polytitanocarbosilane (PTCS) or polysilazane (PSZ) type resins. Several consecutive cycles, from impregnation to heat treatment, can be performed to achieve the desired degree of densification.

The densification of the fiber preform can also be carried out, in a known manner, by gaseous method by chemical vapor infiltration of the matrix (CVI). The fiber preform corresponding to the structure to be produced is placed in an oven in which a gaseous reaction phase is admitted. The pressure and the temperature prevailing in the furnace and the composition of the gas phase are chosen so as to allow the diffusion of the gas phase within the porosity of the preform to form the matrix by depositing, at the core of the material in contact with the fibers, a solid material resulting from a decomposition of a component of the gas phase or a reaction between several components.

The formation of an SiC matrix can be obtained with methyltrichlorosilane (MTS) giving SiC by decomposition of the MTS.

A densification combining liquid route and gaseous route can also be used to facilitate implementation, limit costs and production cycles while obtaining satisfactory characteristics for the intended use.

The part may comprise a reinforcement of carbon fibers and / or ceramic densified by a ceramic matrix, for example chosen from SiC / Si, Si3N ₄ / SiC / Si, SiB or SiMo matrices.

As will be detailed below, it is possible to manufacture the part according to the invention by implementing other methods for densifying the fibrous reinforcement with a ceramic matrix such as in particular melt infiltration processes ("melt -infiltration ").

FIGS. 2 to 4 will now describe processes for preparing parts according to the invention which implement a step of infiltrating a fibrous preform in order to form the ceramic matrix.

FIG. 2 is a flow chart showing the steps of a first exemplary embodiment of a method according to the invention.

A fibrous preform having reactive fillers, for example selected from SiC, SiO ₄ , C, B and mixtures thereof, is first infiltrated by a melt infiltration composition comprising silicon (step 10). After reaction between the infiltration composition and the reactive charges, a piece of composite material comprising a ceramic matrix is obtained. During the reaction between the infiltration composition and the reactive charges, substantially all of the reactive charges can be consumed. Alternatively, only a portion of the reactive charges are consumed during this reaction.

The infiltration composition may consist of molten silicon or alternatively may be in the form of a molten silicon alloy and one or more other components. The constituent (s) present at Within the silicon alloy may be selected from B, Al, Mo, Ti, and mixtures thereof.

The fibers of the fibrous reinforcement may, before infiltration of the infiltration composition, have been coated with an interphase layer, for example silicon-doped BN or BN, as well as with a carbide layer, for example made of SiC and / or S13N4, for example made by gas.

The matrix may be obtained by reaction between solid charges, for example of C, SiC or Si ₃ N ₄ introduced by slip or prepreg, and a molten alloy based on silicon. The reaction can occur at a temperature greater than or equal to 1420 ° C.

Given the high temperatures used, it may be advantageous for the fibrous reinforcement to consist of thermostable fibers, for example of the Hi-Nicalon or even Hi-Nicalon S type.

Once the ceramic matrix obtained, it is then possible to proceed to an optional step of depositing charges and / or a preceramic resin on the outer surface of the part (step 20).

The step 30 carried out thereafter consists in applying on the outer surface of the CMC part an alloy of silicon and nickel or silicon and cobalt in the molten state, this alloy having a melting temperature below the temperature melting of the infiltration composition which made it possible to form the ceramic matrix for densifying the fibrous reinforcement.

When fillers and / or preceramic resin have been deposited on the outer surface of the workpiece (ie when a step 20 has been performed), the alloy of silicon and nickel or silicon and cobalt in the molten state can infiltrate these charges and / or this resin during step 30.

Thus, in such a case, two successive steps of infiltration in the melt ("melt-infiltration") are performed, the first to make the ceramic matrix (step 10) then the second to achieve the surface coating (step 30).

FIG. 3 shows a more detailed flow chart of a method for manufacturing a part according to the invention according to the variant represented in FIG. 2. This method may comprise the following steps: - Preparation of a fiber preform, for example based on Hi-Nicalon S fibers (step 5), for example by weaving and preforming liquid and / or gaseous, the fibers of the fiber preform being coated with a layer of interphase (step 6), for example PyC or BN, and a coating for (i) avoiding a reaction between the infiltration composition on the one hand and the fibers and the interphase on the other part and (ii) consolidate the fiber preform (step 7), the coating being for example carbide, for example SiC, B ₄ C and / or SiBC, and may include a self-healing matrix, the coating can be deposited by CVI,

machining of the fiber preform (step 8, this step is optional in the embodiment considered),

introducing, into the fibrous preform, a first set of fillers, for example reactive fillers, by slip ("slurry cast") (step 9), the fillers being chosen, for example, from SiC, SiO ₄ , C, B, and mixtures thereof, and the excess of surface charges being optionally eliminated wholly or partially at the end of "slurry cast",

infiltration of the fibrous preform with the melt infiltration composition (step 10, melt infiltration process) to form the ceramic matrix, this infiltration optionally being preceded by a step of deoxidation of the fiber preform and infiltration composition, the infiltration allowing for example to form predominantly silicon carbide with a minimum of residual silicon,

cleaning the composite for example by simple operation of sanding or peeling (this step is optional in the embodiment considered),

depositing on the outer surface of the composite material part a second set of charges (step 20), for example chosen from: SiC, SiO ₄ , C, MO ₂ C, B ₄ C and mixtures thereof, and / or a preceramic resin, for example PCS, PSZ or a phenolic resin, the deposition being for example carried out by soaking ("dip-coating"), overmoulding or RTM, the deposition carried out being of variable thickness and / or variable composition when moving along the outer surface of the part, for example according to different functional areas of the part, in the example illustrated in FIG. 3, a deposition of SiC charges has been realized,

infiltration of the outer surface of the part with an alloy of silicon and nickel or silicon and cobalt in the molten state, the alloy having a melting point lower than that of the infiltration composition (step 30) this infiltration possibly being preceded by a stage of deoxidation of the part and the alloy of silicon and nickel or silicon and cobalt,

- finishing machining (step 31, this step is optional in the exemplary embodiment considered).

A flow chart showing the steps of a variant of a method for preparing a part according to the invention will now be described with reference to FIG.

Unlike the processes previously described in the detailed description, the process of FIG. 4 applies whatever the method of preparation of the composite material part (ie not only for parts made of composite material whose ceramic matrix has been obtained by infiltration in the molten state).

The composite material part may, firstly, be covered on its outer surface by a precursor coating layer comprising both the alloy of silicon and nickel or silicon and cobalt and fillers and / or a resin pre-ceramic (optional step 70).

Then, during step 80, the alloy of silicon and nickel or silicon and cobalt in the molten state is present on the outer surface of the composite material part to form the surface coating. If the optional step 70 has been performed, the alloy of silicon and nickel or silicon and cobalt in the molten state is contacted with the charges and / or the resin (optional step 90).

The following is a more detailed example of a method for preparing a part according to the invention according to the variant shown in FIG. 4. The method may comprise the following steps:

- forming on the outer surface of a part made of composite material, a precursor coating layer comprising reactive fillers, for example selected from SiC, C, S13N4, Mo ₂ C, B ₄ C and mixtures thereof, and / or a preceramic resin, for example PCS, PSZ or a phenolic resin, and / or an alloy of silicon and nickel or silicon and cobalt, the coating precursor layer being formed for example after soaking ("dip-coating"), overmoulding or RTM, the precursor coating layer being be of variable thickness and / or variable composition when moving along the outer surface of the part, for example according to the different functional areas of the part, the precursor coating layer may, in addition, possibly smooth all or part of the area of the outer surface of the part on which it is formed, and

infiltration of the alloy of silicon and nickel or of silicon and cobalt in the molten state onto the external surface of the composite material part in order to form the surface coating, this infiltration possibly being preceded by a step of deoxidation of the workpiece and the alloy of silicon and nickel or silicon and cobalt.

The invention is applicable to various types of turbomachine blades, in particular compressor and turbine blades of different gas turbine bodies, for example a low-pressure turbine wheel vane, such as that illustrated in FIG. 5. .

The blade 100 of FIG. 5 comprises, in a well-known manner, a blade 101, a foot 102 formed by a part of greater thickness, for example with a bulbous section, extended by a stilt 103, an inner platform 110 located between the stilt 103 and the blade 101 and an outer platform or heel 120 in the vicinity of the free end of the blade. The blade root 102 is, in the example illustrated, covered by a surface coating comprising an alloy of silicon and nickel or an alloy of silicon and cobalt (not shown). Of course, it is not beyond the scope of the present invention if the blade root is coated with a first surface coating comprising an alloy of silicon and nickel or silicon and cobalt and the blade is coated with a second coating surface, identical or different from the first surface coating, for example to smooth the surface of said blade.

FIG. 6 shows an example of a turbomachine wheel 200 according to the invention.

The parts according to the invention can be fixed on different types of turbine rotors, in particular compressor and compressor rotors. turbine of different gas turbine bodies, for example a low pressure turbine (LP) impeller, such as that illustrated in FIG.

FIG. 6 shows a turbomachine wheel 200 comprising a hub 130 on which are mounted a plurality of blades 100 according to the invention, each blade 100 comprising a base 102 formed by a part of greater thickness, for example with shaped section. bulb, which is engaged in a corresponding housing 131 formed at the periphery of the hub 130 and a blade 101. The housing wall 131 comprises nickel and / or cobalt.

The wheel 200 further comprises a plurality of blade heel elements 120 mounted on each of the blades 100.

Parts according to the invention can be attached to turbines of low or high pressure turbojets.

The parts according to the invention can equip turbojets, for example CFM 56 type, LEAP X or M88. The parts according to the invention can also equip gas turbines.

Example

A Guipex® texture was used to form the fibrous reinforcement of a part according to the invention. This texture was formed of Hi-Nicalon® Type S fibers marketed by the company Nippon Carbon, had a weave weave type "Interlock" and verified the following characteristics: ratio warp / weft son = 55/45, 10 threads of chain / cm and 7.5 weft / cm.

This texture was placed in a graphite shaper to obtain a fiber content of 40% by volume. The texture maintained in the shaper was then consolidated by a chemical vapor infiltration process in order to deposit on the fibers a layer of boron nitride (BN) and a layer of silicon carbide. The consolidated texture was extracted from the shaper and a new step of chemical vapor infiltration was performed to complete the densification of the texture and deposit in its porosity silicon carbide. The consolidated and partially densified texture thus obtained had a density of 2.0 and a residual porosity of 30% by volume. A slurry comprising an aqueous liquid medium loaded to 20% by volume of a silicon carbide powder was injected into the partially densified consolidated texture by a submicron powder suction process. The silicon carbide powder used had a particle size d50 of 0.6 μιτι. The texture impregnated with the slurry was then placed in an oven and dried for three hours at 60 ° C. At the end of this step, the resulting texture had a density of 2.3 and a porosity of 23% by volume.

The densification of the texture thus obtained was then finalized by infiltration of silicon in the molten state. Prior to infiltrating the texture with molten silicon, a boron nitride anti-wetting composition was applied to the faces of the texture to prevent molten silicon from spilling out of the workpiece. The texture was then infiltrated with silicon in the molten state. The infiltration by the molten silicon was carried out under 5 mbar of argon with two consecutive temperature stages:

a first temperature of 1395 ° C. was imposed for one hour, this temperature was reached with a ramp of 600 ° C./hour,

- A second temperature of 1450 ° C was imposed for 30 minutes, this temperature was reached with a ramp of 120 ° C / hour.

During the infiltration, the piece was placed on a C / C drain which allowed it to be fed with silicon.

After the infiltration, the anti-wetting composition was removed by cleaning with distilled water and ultrasound. At this stage, the part had a density of 2.8 and a porosity of the order of 2% by volume.

The outer surface of the part obtained was then coated with a coating composition comprising particles of silicon carbide particle size 9 μιη, polycarbosilane and a solvent (xylene). The polycarbosilane was then crosslinked under argon by carrying out the following heat treatment:

- rise to 90 ° C in 1 hour,

- Bearing at 90 ° C for 1 hour,

- rise to 220 ° C in 100 minutes, - Bearing at 220 ° C for 1 hour,

- rise to 350 ° C in 1 hour,

- Bearing at 350 ° C for 1 hour,

- natural cooling.

The polycarbosilane was then pyrolyzed under nitrogen at 900 ° C for 1 hour (mounted at 100 ° C / hour).

A silicon carbide phase resulting from the pyrolysis of the PCS and a particulate phase of silicon carbide were present on the outer surface of the composite material part. A silicon-nickel alloy in the molten state having a nickel atomic content of 44% and a silicon atomic content of 56% (corresponding to a silicon content in the alloy of about 38%). applied to infiltrate the silicon carbide phases present on the surface. The infiltration by the alloy of silicon and nickel was carried out under secondary vacuum with two consecutive temperature stages:

a first temperature of 950 ° C. was imposed for two hours, this temperature was reached with a ramp of 600 ° C./hour,

a second temperature of 1020 ° C. was imposed for 30 minutes, this temperature was reached with a ramp of

120 ° C / hour.

The zone to be densified by the alloy is in contact with a carbon mat which is used to feed the alloy part. A solid coating 100 m thick was obtained.

The expression "containing / containing a" must be understood as "containing / containing at least one".

The expression "understood between ... and ..." or "from ... to ..." must be understood as including the boundaries.

Claims

1. Part (1; 100) of composite material comprising a fibrous reinforcement densified by a ceramic matrix (2), the part (1; 100) having an outer surface (3) and being characterized in that it is coated on with least part of its external surface (3) by a surface coating (4) in solid form comprising a silicon and nickel alloy having a silicon content by mass of between 29% and 45% or an alloy of silicon and cobalt .

2. Part (1; 100) according to claim 1, characterized in that the surface coating (4) comprises a NiSi phase ₂ and / or a NiSi phase.

3. Part (1; 100) according to claim 1, characterized in that the surface coating (4) comprises a phase of CoSi ₂ .

4. Part (1; 100) according to any one of claims 1 to 3, characterized in that the alloy of silicon and nickel or the alloy of silicon and cobalt is present in a mass content greater than or equal to 5% with respect to the mass of the surface coating (4).

5. Part (1; 100) according to any one of claims 1 to 4, characterized in that the surface coating (4) further comprises charges and / or a ceramic material.

6. Part (1; 100) according to any one of claims 1 to 5, characterized in that the alloy of silicon and cobalt has a silicon mass content of between 34% and 90%.

7. Part (100) according to any one of claims 1 to 6, characterized in that it constitutes an aircraft engine blade having at least one blade root (102) and a blade (101) and in that the surface coating (4) covers at least the blade root (102).

Turbomachine wheel (200) comprising: a wheel disk (130) having a blade attachment portion (131), said attachment portion (131) comprising an alloy comprising nickel and / or cobalt, and

a workpiece (100) according to claim 7 attached to the wheel disc (130), the blade root (102) of the workpiece being mounted on the blade attachment portion (131).

9. Process for the manufacture of a part (1; 100) according to any one of claims 1 to 7, comprising the following steps: a) infiltration of a fibrous preform comprising a first set of fillers with a composition of infiltration in the molten state, the infiltration composition comprising silicon and having a first melting temperature, in order to obtain, after contacting the infiltration composition with all or part of the charges of the first set of charges, a part made of a composite material comprising a fibrous reinforcement densified by a ceramic matrix (2), and

b) applying to at least a portion of the outer surface (3) of the composite material part of an alloy of silicon and nickel or a silicon and cobalt alloy in the molten state, the alloy of silicon and nickel or silicon and cobalt having a second melting temperature lower than the first melting temperature, to obtain a surface coating (4) in solid form on at least a portion of the outer surface (3) of the composite material part.

10. The method of claim 9, characterized in that it further comprises, after step a) and before step b), a step c) deposition on the outer surface (3) of the piece of material composite of a second set of charges and / or a preceramic resin and in that the alloy of silicon and nickel or the alloy of silicon and cobalt in the molten state infiltrates during the step b) within the second set of charges and / or preceramic resin to form the surface coating (4).

11. A method of manufacturing a part (1; 100) according to any one of claims 1 to 7, comprising a step: forming on the outer surface (3) of a composite material part comprising a fiber reinforcement densified by a ceramic matrix (2) of a surface coating (4) in solid form comprising a silicon and nickel alloy or a silicon and cobalt alloy.

12. The method of claim 11, characterized in that the formation of the surface coating (4) comprises a step of contacting an alloy of silicon and nickel or an alloy of silicon and cobalt to the molten state with fillers and / or with a pre-ceramic resin.

13. The method of claim 12, characterized in that the part is covered, before melting of the alloy of silicon and nickel or the alloy of silicon and cobalt, on its outer surface (3) by a precursor layer. coating material comprising, on the one hand, the alloy of silicon and nickel or the alloy of silicon and cobalt and, on the other hand, the fillers and / or the preceramic resin.