Method for preparing an ultra-high temperature ceramic matrix composite material having carbon fibre reinforcements

Abstract

The present invention relates to a method for preparing a composite material comprising an ultra-high temperature ceramic matrix reinforced with carbon fibres, the method comprising the following successive steps: a) performing reactive melt infiltration (RMI) on an open-pore substrate made of a carbon / carbon (C / C) composite material having a carbon matrix reinforced with carbon fibres, during which reactive melt infiltration at least one solid metal silicide MxSiy is deposited on the surface of the substrate, where metal silicide M is a transition metal, x is an integer selected from the group consisting of 1, 2, 3, 4 and 5, and y is an integer selected from the group consisting of 1, 2, 3 and 4; b) depositing a mixture comprising an organic resin, preferably a furan or phenolic resin, and a metal silicon powder, on the surface of the substrate obtained at the end of step a), by means of which, at the end of step b), a composite material is obtained that comprises an ultra-high temperature ceramic matrix reinforced with carbon fibres.

Description

[0001] METHOD FOR PREPARING A COMPOSITE MATERIAL WITH AN ULTRA-HIGH TEMPERATURE CERAMIC MATRIX AND CARBON FIBER REINFORCEMENT

[0002] TECHNICAL FIELD

[0003] The present invention relates to a method for preparing a composite material comprising an ultra-high temperature ceramic (UHTC) matrix and carbon fibers. The carbon fibers act in particular as reinforcements for the matrix. The present invention also relates to the composite material thus prepared.

[0004] The applications of the material prepared according to the process of the invention are in particular those of thermal protection in an oxidizing atmosphere at high temperatures, for example above 2000°C, in particular above 2500°C, or even above 3000°C.

[0005] Thus, the material prepared according to the process of the invention finds its application in particular in heat shields which equip, for example, space vehicles, in the front tips of the leading edges of these vehicles and in high-temperature combustion chambers.

[0006] STATE OF THE PRIOR ART

[0007] The materials that make up heat shields are subjected to extreme conditions, particularly during re-entry into the atmosphere.

[0008] These materials are subject to very high temperatures, ablation phenomena, and oxidation reactions, for example in the presence of dissociated oxygen. Few materials are able to withstand these conditions.

[0009] For several decades, the preferred materials for withstanding these conditions have been ultra-high temperature ceramics (UHTC). By "UHTC ceramics" we mean ceramics with a melting temperature above 2000°C, particularly above 2500°C, or even above 3000°C.

[0010] Figure 1 shows the melting temperatures of the main UHTC ceramics. UHTC ceramics have many advantages, such as high melting temperature, high modulus and good oxidation resistance.

[0011] However, these ceramics, made in the form of monoliths, are very fragile.

[0012] It turned out that UHTC ceramic matrix composites (UHT-CMC) could overcome this drawback.

[0013] The following describes the techniques used to manufacture UHT-CMC composite material or to manufacture coatings on carbon / carbon composite materials.

[0014] Regarding the manufacture of UHTC and carbon fiber matrix composites, called Cf / UHTC composites m , the matrix of these composites can be manufactured by a reactive infiltration technique of molten metal ("Reactive Melt Infiltration" or RMI, in English) or by the association of the RMI technique with the Submicron Powder Aspiration (SPA) technique.

[0015] The manufacture of the UHTC matrix by RMI is notably described in document [1],

[0016] This document relates to a method for preparing a multilayer coating of metal carbides on at least one surface of a carbon layer of a substrate, and optionally under said surface inside said carbon layer, by a technique of reactive infiltration of a metal in the molten state, in which the following successive steps are carried out: a) the surface is brought into contact with a solid metal disilicide (MSI2) in which M is chosen from Hafnium, Titanium, and Tantalum; b) the substrate and the metal disilicide are heated to a temperature TP higher than the melting temperature of the metal disilicide;c) a plateau at temperature TP is observed for a sufficient time for the metal disilicide to react with the carbon and form a multilayer coating comprising a dense and continuous layer consisting of carbon silicide (SiC), completely covered by a dense and continuous layer consisting of metal carbide (MC); d) the part provided with the multilayer coating is cooled.;

[0017] The carbon layer of the substrate may be a layer of an all-carbon substrate.

[0018] The all-carbon substrate can be a carbon / carbon composite material such as a 2D or 3D composite material.

[0019] Optionally, at the end of step d), the following step e) is also carried out: e) a layer of carbon is deposited on the surface of the multi-layer coating.

[0020] Optionally, at the end of step d) or step e), the following step j) is also carried out: j) siliciding of the surface of the multilayer coating still containing carbon or of the carbon layer is carried out with liquid Si, whereby a layer of SiC is obtained on the multilayer coating.

[0021] The manufacture of the UHTC matrix by APS / RMI is notably described in document [2]. In this document, a carbon / carbon composite material with a carbon matrix and carbon fibers called Cf / C material m is first infiltrated by a suspension containing Zirconium boride (ZrB2) particles during a step called Submicron Powder Aspiration (SPA). Then the preform obtained, loaded with particles, is then infiltrated, during a second step by liquid silicon using a reactive molten metal infiltration (RMI) technique.

[0022] This technique, by chemical reaction of liquid silicon with the carbon of the matrix, forms SiC according to the reaction equation, Eq 1, below:

[0023] At the end of these two successive steps, a C / C composite material is obtained whose matrix contains ZrB2 and SiC. It is the reaction between ZrB2 and SiC which, during oxidation, protects the modified C / C. In this document, the microstructures presented clearly show ZrB2 and SiC at the core of the composite, however no surface protection is visible.

[0024] With regard to the manufacture of coatings on carbon / carbon composite materials such as carbon matrix and carbon fiber composite materials referred to as Cf / C composite materials m , it can be carried out in particular by the “Pack Cementation (PC)” technique or by the technique known as the loaded resin technique (“Slurry Sintering” in English).

[0025] The pack cementation (PC) technique allows SiC to be deposited on the surface of carbon-based materials. This technique consists of depositing a layer of silica and graphite C powder on the surface of the material to be coated. Then, a heat treatment makes it possible to obtain a layer of SiC on the surface of the material according to the following reaction equations, Eq 2 and Eq 3:

[0026] The PC step is often followed by a second step such as a chemical vapor deposition (CVD) or plasma spraying step. This succession of steps allows for a more complex multi-layer system to be obtained [3]. The disadvantage of the PC technique comes from the fact that the carbon is reacted in powder form. This results in SiC, which is also in powder form and therefore porous, after reaction with silicon. The SiC formed is therefore not sufficiently dense to constitute a waterproof barrier to oxidizing agents [3-6].

[0027] The technique known as the loaded resin technique (“Slurry Sintering” in English) is notably described in document [7] using a resin as is the case in the present invention.

[0028] This document describes a process for manufacturing a refractory material and a protective coating that can be obtained by this process.

[0029] This process includes the following steps:

[0030] - depositing on the surface of a substrate a first dispersion containing a compound chosen from powders of borides, carbides or borocarbons of transition metals (for example: HfC, ZrC, ZrB2 or HfB2) and a resin, in particular of the phenolic or furanic type. Silicon is never mentioned among the compounds mixed with the resin; - heat-treating the substrate to dry it then crosslinking and carbonizing the resin, which has the consequence of bringing carbon into the system;

[0031] - cover the deposit with a second dispersion containing silicon in powder form and a binder;

[0032] - heat treat the deposit at a temperature at least equal to the melting temperature of silicon so that the latter reacts with the carbon of the binder to form SiC;

[0033] The resulting material consists of a substrate (e.g., a C / C substrate) coated with a dense mixture of transition metal carbides or borides or borocarbons and SiC.

[0034] The process of this document only allows coatings to be made on the surface of a substrate and the chemical nature of this substrate is not in any way profoundly modified. Therefore, the protection against oxidation conferred by this process is intrinsically limited.

[0035] All the processes described above do not make it possible to obtain a material providing sufficient thermal protection in an oxidizing atmosphere at high temperatures, for example, above 2000°C, in particular above 2500°C and even above 3000°C.

[0036] There is therefore, in view of the above, a need for a process which makes it possible to obtain a material having better resistance to oxidation and ablation at high temperatures. In particular, there is a need for a process leading to a material capable of protecting on-board systems and therefore having improved resistance to oxidation and resistance to ablation under the conditions prevailing during re-entry into the atmosphere.

[0037] The aim of the invention is to provide a method meeting, among other things, these needs.

[0038] STATEMENT OF THE INVENTION

[0039] This and other aims are achieved, in accordance with the invention, by a method for preparing a composite material comprising an Ultra High Temperature ceramic matrix reinforced with carbon fibers. By "Ultra High Temperature ceramic matrix reinforced with carbon fibers" is meant an UHTC ceramic matrix in which carbon fibers are distributed.

[0040] More particularly, the method according to the invention for preparing a composite material comprising an Ultra High Temperature ceramic matrix reinforced by (containing) carbon fibers comprises the following successive steps: a) reactive melt infiltration (RMI) is carried out on an open porosity substrate made of a carbon / carbon (C / C) composite material with a carbon matrix reinforced by carbon fibers, during which at least one metal silicide M is deposited on a surface of the substrate x If ysolid in which M is a transition metal, x is an integer selected from the group consisting of 1, 2, 3, 4 and 5 and y is an integer selected from the group consisting of 1, 2, 3 and 4; then the substrate and the metal silicide are heated to a temperature TP higher than the melting temperature of the metal silicide; then a plateau is observed at the temperature TP for a time sufficient for the metal silicide to react with the carbon of the matrix; and finally the substrate is cooled;b) a mixture comprising an organic resin, preferably a furanic or phenolic resin, and a metallic silicon powder is deposited on the surface of the substrate obtained at the end of step a), then the substrate and the mixture consisting of the organic resin and the silicon powder are heated, under an inert atmosphere, to a first temperature at which the organic resin is pyrolyzed and a plateau is observed at this first temperature for a time sufficient to pyrolyze the resin and to form carbon, then the substrate is further heated to a second temperature above the melting point of the silicon to form liquid silicon which reacts with the carbon to form a layer of silicon carbide (SiC) on the substrate obtained at the end of step a);finally the substrate is cooled, whereby, at the end of step b), a composite material is obtained comprising an Ultra High Temperature ceramic matrix reinforced by carbon fibers. As previously described, by "UHTC ceramic" is meant ceramics whose melting temperature is greater than 2000°C, in particular greater than 2500°C and even greater than 3000°C.;

[0041] Optionally, prior to step a), a Submicron Powder Aspiration (SPA) step aO) can be carried out during which a suspension of at least one powder of boride or carbide of a transition metal M' is infiltrated into the C / C composite material, i.e. into the open porosity of the C / C composite material, whereby, after drying, a C / C composite material loaded with powder of boride or carbide of a transition metal M' is obtained. The transition metal M' used during this optional step aO) can be identical to or different from the transition metal M present in the silicide of metal M x If y implemented during step a) of the method according to the invention.

[0042] The method according to the invention comprises a specific series of specific steps which has never been described in the prior art, as represented in particular by the documents cited above.

[0043] Indeed, the method according to the invention comprises the succession of a step a) which is a step of reactive infiltration in the molten state (RMI) of at least one metal silicide M x If y solid and a step b) which is a step of forming silicon carbide from an organic resin acting as a carbon precursor and a silicon powder.

[0044] Step a) may optionally be preceded by a Submicron Powder Aspiration (SPA) step of a transition metal boride or carbide powder, mentioned above, which is also a specific step.

[0045] According to an important characteristic of the process according to the invention, which is not disclosed in the prior art, during step a), the quantity of metal silicide M x If ysolid deposited on the surface of the substrate is just the quantity sufficient to infiltrate into the open porosity of the matrix of the C / C composite material in order to react with the carbon of the latter to form refractory carbides, without reacting with the carbon fibers distributed in the C / C composite material. The carbon fibers are therefore preserved in the material and are not affected by the RMI step. In other words, the quantity of solid metal disilicide MSÎ2 is used which, in theory, allows the entire volume of the pores of the open porosity of the matrix of the C / C composite material to be filled.

[0046] According to another important characteristic of the method according to the invention, during step b), the silicon carbide layer is formed by depositing on the substrate obtained at the end of step a) a mixture comprising an organic resin and a metallic silicon powder whereas, in document [1], a silicon carbide layer is formed following the melting and infiltration of the liquid Si, obtained from the metallic Si directly deposited on the substrate. In the present invention, the elements necessary for the formation of the SiC layer, i.e. carbon and silicon, are provided by the mixture used since the carbon comes from the pyrolysis of the organic resin and the silicon from the metallic silicon powder.

[0047] The method according to the invention makes it possible to obtain a composite material comprising a specific structure with, from the surface: a layer with a matrix consisting solely of SiC, free of matrix carbon and carbon fibers, and also free of MC (HfC for example); a layer with a matrix of MC (for example HfC) and SiC reinforced by carbon fibers, which have therefore not been affected by the RMI process, with a matrix carbon gradient increasing from the SiC layer; and a layer of C / C composite material with carbon matrix reinforced by carbon fibers which, again, have not been affected by the RMI process, as has the carbon matrix.

[0048] The layer with a matrix of MC (for example HfC) and SiC containing carbon fibers, with an increasing matrix carbon gradient therefore extends, in the composite material prepared according to the method of the invention, from the SiC layer, to the infiltration front of the liquid metal disilicide MSÎ2 during the RMI step, beyond which the layer of C / C composite material with carbon matrix reinforced by carbon fibers begins.

[0049] The matrix carbon concentration is close to zero in the vicinity of the SiC layer and increases up to the C / C composite material layer. The layer with a matrix of MC (e.g. HfC) and SiC containing carbon fibers may be a layer with a gradient of concentration of MC carbide, such as HfC, decreasing from the SiC layer or may be a layer comprising MC and SiC grains distributed in the layer.

[0050] The matrix of MC (for example HfC) and SiC may further contain a boride or a carbide of transition metal M' if, prior to step a), an APS step aO) has been carried out.

[0051] According to a fundamental characteristic of the material prepared by the process according to the invention, the matrix consisting solely of SiC and the matrix of MC and SiC form a single continuous matrix, in other words a “matrix continuum”.

[0052] The material prepared by the process according to the invention, due to its specific structure, and in particular due to the combination in this material of carbon fibers and a matrix continuum, has better resistance to oxidation and ablation at high temperatures. In particular, the material prepared by the process according to the invention has improved resistance to oxidation and ablation under the conditions prevailing during re-entry into the atmosphere.

[0053] In other words, the composite prepared by the process according to the invention is composed at its core of carbon fibers and a gradient matrix consisting of carbon, ultra-high temperature ceramics (UHTC) and silicon carbide (SiC). The surface of the composite is free of fibers and composed solely of the matrix continuum. It is this assembly of fibers plus matrix continuum which gives the material prepared by the process according to the invention advantageous improved properties.

[0054] During thermal stresses in an oxidizing atmosphere (oxygen and water vapor) at temperatures above 2000°C (and possibly exceeding 2500°C), the extreme surface matrix continuum - namely the layer with a matrix consisting solely of SiC - oxidizes and forms a layer that protects the underlying material while preheating it. There is a real synergy between the SiC surface layer and the underlying structure obtained by RMI which provides better oxidation resistance to the material. The structure of the material obtained by the process according to the invention therefore makes it possible to structure the oxide layer created by oxidation of the SiC layer, which thus improves the resistance properties of the material as a whole.

[0055] The material prepared by the process according to the invention, composed of carbon fibers, a matrix composed of carbide and / or boride with a "matrix continuum" of SiC at the extreme surface of the material allows a clear improvement in the behavior of UHT-CMCs upon atmospheric reentry. Indeed, when composite materials are subjected to a thermal flux simulating atmospheric reentry, the materials prepared by the process according to the invention having the specific structure described above with in particular a "matrix continuum" of SiC have much superior properties (2 to 3 times better) than those of materials lacking this matrix continuum, as demonstrated in the examples provided below (see in particular example 3).

[0056] There are no limitations on the carbon / carbon (C / C) composite material with a carbon matrix reinforced by carbon fibers. The method according to the invention can be implemented with any type of carbon / carbon (C / C) composite material.

[0057] Thus, the carbon fiber reinforced carbon matrix C / C composite material can be a 2D, 2.5D or 3D composite material.

[0058] The C / C composite material may have an average open porosity of 15% to 50% by volume, preferably 20% to 30% by volume.

[0059] In particular, the carbon fiber reinforced carbon matrix composite material can even be implemented with a 3D composite material with a dense matrix, especially with a density greater than 1.8.

[0060] In step a), at least one solid metal disilicide MSi2 is deposited on a surface of the substrate, in which M is a transition metal.

[0061] The substrate can have any shape. It can be a rectangular or square plate with a specific thickness, in particular from 2 mm to 50 mm, for example 4 mm. The surface on which the metal silicide M is deposited x If y is usually a horizontal top surface of the substrate, for example the top surface of a horizontally arranged rectangular or square plate.

[0062] Preferably, the transition metal M present in the silicide and the transition metal M' present in the boride or carbide, identical or different, are chosen from Hafnium, Titanium, Zirconium and Tantalum. Advantageously, the transition metals M and M' are identical. Preferably, the transition metals M and M' are Hafnium.

[0063] Advantageously, the couple (x,y) in the metal silicide M x If yis chosen from the group consisting of the pairs (1,1), (1,2), (2,1), (3,2), (5,3) and (5,4). More particularly, x represents 1 and y represents 2 whereby the metal silicide M x If y is a disilicide of a transition metal M as previously defined (MSÏ2) and in particular a disilicide of Hafnium (HfSi2).

[0064] Indeed, it has been determined that Hafnium disilicide (HfSi2) is, among many other compounds, the most suitable intermetallic compound for carrying out reactive melt infiltration "RMI", in particular from mixtures of compacted metal powders, in particular at a temperature below 1800°C.

[0065] The use of Hafnium disilicide not only allows for an equal distribution of Hafnium across the entire width of the infiltration, but also for a compound with a single melting temperature (because it is a defined compound), which avoids premature infiltration of silicon into the part.

[0066] Furthermore, molten HfSi2 is very fluid and permeates even very low porosities. Therefore, the process according to the invention can be successfully implemented both with porous C / C composite materials and with dense or even very dense C / C carbon materials.

[0067] The advantageous properties of HfSi2, in the context of the process according to the invention, are also presented by titanium disilicide (TiSi2), and tantalum disilicide (TaSi2).

[0068] Indeed, the formation enthalpies of TaC (-178 kJ / mol at 25°C), TiC (-184 kJ / mol at 25°C) and HfC (-210 kJ / mol at 25°C) are proof that Ta-Si and Ti-Si systems behave in the same way as Hf-Si. Advantageously, the deposition of the metal silicide M x If y solid on the surface is made by depositing the metal silicide M x If y on the surface or by depositing the substrate and M x If y in a crucible.

[0069] Metal silicide M x If y can be deposited on the surface in the form of a compacted or uncompacted powder, or in the form of a slip consisting of a powder of the metal silicide M x If y and a liquid.

[0070] As previously indicated, the surface is brought into contact with a volume of the metal silicide M x If ysolid, sufficient to infiltrate the average open porosity volume of the carbon substrate.

[0071] When step aO) is carried out before step a), then the volume of metal silicide M x If y implemented is lower because part of the open porosity has already been infiltrated, sealed by the boride or the transition metal carbide M' as previously defined.

[0072] Advantageously, the temperature TP can be from 900°C to 2500°C, for example 1800°C.

[0073] Advantageously, during step a), a rapid temperature increase can be carried out, preferably at a rate of 1000°C to 3000°C / minute, for example at a rate of 2800°C / minute up to temperature Tp.

[0074] Advantageously, the plateau at TP temperature can be observed for a period of 5 minutes to 1 hour.

[0075] In step a), a chemical modification of the matrix of the C / C composite material occurs with the formation of silicon carbide and the carbide of the transition metal M used, for example, HfC.

[0076] At the end of step a), a material is therefore obtained comprising, from the surface: a layer with a matrix of MC (for example HfC) and SiC containing carbon fibers which have not been affected by the RMI process, with a matrix carbon gradient increasing from the surface, and a layer of C / C composite material with a carbon matrix reinforced by carbon fibers which have not been affected by the RMI process. The matrix carbon concentration is close to zero in the vicinity of the SiC layer.

[0077] The layer with a matrix of MC (for example HfC) and SiC containing carbon fibers obtained at the end of step a) may be a layer with a concentration gradient of MC carbide, such as HfC, decreasing from the surface or may be a layer comprising grains of MC and SiC distributed in the layer.

[0078] In step b), a mixture comprising an organic resin, preferably a furanic or phenolic resin, and a metallic silicon powder is deposited on the surface of the substrate obtained at the end of step a).

[0079] The surface on which the mixture is deposited is the same as that on which the metal silicide M was deposited x If y during step a).

[0080] The organic resin can be chosen from any resin that forms carbon when pyrolyzed. Furanic or phenolic resins are preferred because they are commercially available and their carbon yield is controlled.

[0081] Advantageously, the mixture deposited during step b) further comprises at least one addition element chosen from powders of carbides, oxides, borides and borocarbons of metals such as powders of carbides, oxides, borides and / or borocarbons of transition metals.

[0082] Carbides, oxides, borides and / or borocarbons include mixed carbides, oxides, borides and / or borocarbons of several transition metals.

[0083] In particular, the addition element may be chosen from Ta^fCs, HfCh, and mixtures thereof.

[0084] A solvent such as ethanol can be added to the mixture to reduce its viscosity and facilitate its deposition and application to the surface.

[0085] The operation of depositing the mixture can be repeated several times, in particular from 1 to 10 times, for example 2 times, to obtain a deposit having the required thickness, for example, a thickness of 10 μm to 200 μm.

[0086] The deposition can be carried out by any deposition technique, for example the deposition can be carried out by applying the mixture to the surface using a brush or a paintbrush. The mixture deposited on the surface is then dried, for example, in an oven at 100°C for 1 hour.

[0087] The first temperature may be a temperature of 900°C to 1200°C, for example, 1000°C and the hold at this temperature may be of a duration of 5 minutes to 30 minutes, for example, of a duration of 15 minutes.

[0088] The second temperature is a temperature higher than the melting temperature of silicon, namely 1410°C, which allows liquid silicon to be obtained.

[0089] The second temperature can be a temperature of 1410°C to 1600°C, for example, 1500°C.

[0090] The heat treatment comprising the two successive heating steps up to the first temperature and then up to the second temperature can be carried out according to the temperature profile shown in Figure 4.

[0091] A primary vacuum is usually required during heat treatment.

[0092] This liquid silicon will then react with the carbon obtained following the pyrolysis of the resin, to form silicon carbide (SiC).

[0093] The substrate is then cooled, usually to room temperature.

[0094] The optional step aO) is a Submicron Powder Aspiration (SPA) step during which a suspension or slip of at least one submicron powder of boride or transition metal carbide M' is infiltrated into the C / C composite material, whereby, after drying, a C / C composite material loaded with powder of boride or transition metal carbide M' is obtained.

[0095] By “submicron powder” we generally mean that the particles of this powder have a size (defined by their largest dimension such as the diameter) less than or equal to 1 pm and in particular between 100 nm and 1 pm.

[0096] The transition metal boride M' can notably be hafnium boride HfB2.

[0097] The transition metal carbide M' may in particular be hafnium(ll) carbide Hf2C or hafnium(IV) carbide HfC.

[0098] The suspension or slip comprises a solvent generally chosen from organic solvents, water and their mixtures. For example, this solvent can be a mixture of water and an aliphatic alcohol such as ethanol.

[0099] In this step aO), we can generally proceed as follows:

[0100] - the substrate made of a carbon / carbon (C / C) composite material with a carbon matrix reinforced by carbon fibers, is placed in a closed enclosure which can be put under vacuum or pressure.

[0101] - the suspension or slip is placed on a surface of the substrate, the surface on which the slip is deposited being the same as that on which the metal silicide M is then deposited x If y during step a).

[0102] - a primary vacuum is then applied to the enclosure for a period of 30 minutes to 90 minutes, for example for one hour.

[0103] - a gas, such as an inert gas like argon, is injected into the enclosure in order to create pressure above the suspension and force its infiltration into the heart of the substrate.

[0104] This pressure can be a pressure of 2 bars to 5 bars, for example 3 bars. This pressurization can have a duration of 30 minutes to 2 hours, for example, a duration of one hour.

[0105] - the substrate is dried in order to evaporate the solvent, for example, at a temperature of 100°C.

[0106] At the end of this step, a carbon / carbon (C / C) composite material is obtained with a carbon matrix reinforced by carbon fibers whose porosity, more precisely the open porosity, has been infiltrated by the powder of boride or transition metal carbide M'.

[0107] The invention will be better understood upon reading the following description, given for illustrative and non-limiting purposes, of embodiments of the invention given in the form of examples.

[0108] This description is made in relation to the attached drawings.

[0109] BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows the melting temperature (in °C) of the main Ultra High Temperature Ceramics (UHTC).

[0110] Figure 2A is a photograph of the 2D architecture Cf / Cm carbon fiber (Cf) and pyrocarbon matrix (Cm) composite material preform (CF 227 / 2 available from Schunk®) used in the examples. The scale in this figure represents 20 mm.

[0111] Figure 2B is another photograph of the 2D architecture Cf / Cm carbon fiber (Cf) and pyrocarbon matrix (Cm) composite preform (CF 227 / 2 available from Schunk®) used in the examples. The scale in this figure represents 20 mm.

[0112] Figure 3 is a Scanning Electron Microscope (SEM) photograph of the microstructure of a Cf / Cm composite preform obtained after infiltration of an HfSÏ2 alloy using a reactive melt infiltration (RMI) technique, during the first step of Example 1. The scale shown in this Figure represents 300 pm.

[0113] Figure 4 is a graph showing the temperature profile during the heat treatment of the silicon-filled resin during the second step of Example 1. The abscissa plots the time (in minutes), and the ordinate plots the temperature (in °C).

[0114] Figure 5 is a SEM photograph of the microstructure of a Cf / Cm composite preform obtained after infiltration of an HfSÏ2 alloy using a reactive melt infiltration (RMI) technique followed by treatment with a Furolite® resin loaded with silicon powder and subjected to heat treatment (Example 1, second step). The scale shown in this figure represents 300 pm.

[0115] Figure 6 is a photograph taken by SEM of the microstructure of a preform made of Cf / Cm composite material obtained after infiltration of HfB2 by an APS technique, during the first step of Example 2. The scale shown in this figure represents 100 pm.

[0116] Figure 7 is a photograph, taken by SEM, of the microstructure of a Cf / Cm composite preform obtained after infiltration of HfB2 by an APS technique, followed by infiltration of an HfSi2 alloy by a reactive melt infiltration (RMI) technique (Example 2, second step). The scale shown in this figure represents 50 pm.

[0117] Figure 8 is a SEM photograph of the microstructure of a Cf / Cm composite preform obtained after infiltration of HfB2 using an APS technique, followed by infiltration of an HfSi2 alloy using a reactive melt infiltration (RMI) technique, and then treatment with a Furolite® resin loaded with silicon powder and subjected to heat treatment (Example 2, third step). The scale shown in this figure represents 50 pm.

[0118] Figure 9A is a graph showing the surface temperature (in °C) on the front face (curve A) and back face (curve B) of sample 2 as a function of the duration of exposure to the flame (in seconds).

[0119] Figure 9B is a graph showing the surface temperature (in °C) on the front face (curve A) and back face (curve B) of sample B as a function of the duration of exposure to the flame (in seconds).

[0120] Figure 10A is a graph which gives the mass ablation coefficient at the oxyacetylene torch (in mg / s) for exposure times of 120 seconds and 180 seconds for sample 1 according to the invention (right bars for each time) and for sample A (left bars for each time).

[0121] Figure 10B is a graph that gives the linear ablation coefficient at the oxyacetylene torch (in pm / s) for exposure times of 120 seconds and 180 seconds for sample 1 according to the invention (right bars for each time) and for sample A (left bars for each time).

[0122] Figure 11A is an SEM photograph of the microstructure of the oxide layer formed on sample A, following the oxyacetylene torch (OAT) test. The scale bar on this figure represents 200 pm.

[0123] Figure 11B is a SEM photograph of the microstructure of the oxide layer formed on sample 1, following the oxyacetylene torch (OAT) test. The scale shown in this figure represents 250 pm. Figure 12A is a graph showing the mass ablation coefficient at the oxyacetylene torch (in mg / s) for exposure times of 120 seconds and 180 seconds for sample 2 according to the invention (right bars for each time) and for sample B (left bars for each time).

[0124] Figure 12B is a graph that gives the linear ablation coefficient at the oxyacetylene torch (in pm / s) for exposure times of 120 seconds and 180 seconds for sample 2 according to the invention (right bars for each time) and for sample B (left bars for each time).

[0125] Figure 13A is an SEM photograph of the microstructure of the oxide layer formed on sample B, following the oxyacetylene torch (OAT) test. The scale bar on this figure represents 200 pm.

[0126] Figure 13B is a SEM photograph of the microstructure of the oxide layer formed on Sample 2, following the oxyacetylene torch (OAT) test. The scale bar on this figure represents 200 pm.

[0127] DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0128] The invention will now be described with reference to the following examples, given for illustrative and non-limiting purposes.

[0129] EXAMPLES

[0130] Two examples which illustrate the preparation of two composite materials according to the invention are presented in the following.

[0131] In the first example (Example 1), a boride-free UHTC-CMC material according to the invention is prepared in two steps. These steps have already been described above in general.

[0132] In the second example (Example 2), a UHTC-CMC material with boride according to the invention is prepared in three steps. These steps have already been described above in general.

[0133] The initial carbon substrate, or initial carbon preform, is identical for both examples; it is a substrate or preform made of C / C composite material, namely a Cf / Cm composite material with carbon fibers (Cf) and pyrocarbon matrix (Cm) of 2D architecture. The Cf / Cm composite material used in the examples is CF 227 / 2 available from Schunk®.

[0134] Figures 2A and 2B show photographs of the CF 1227 / 2 carbon C / C preform used in both examples.

[0135] The characteristics of this C / C preform are as follows:

[0136] Dimensions: 20 x 20 x 4 mm 3

[0137] Density: 1.33 g. cm -3

[0138] Weaving Architecture: 2D

[0139] Porosity: 25% VOi

[0140] Pore ​​volume: 0.45 cm 3

[0141] Example 1

[0142] In this example, a UHT-CMC composite material according to the invention is prepared, the matrix of which is made up of C fibers and a SiC / HfC matrix at the core, and of SiC at the periphery according to a “continuum” already described above.

[0143] In a first step, reactive melt infiltration (RMI) of HfSi2 is carried out in the C / C composite material preform.

[0144] The objective of this step is to obtain a matrix comprising or even composed of hafnium carbide and silicon.

[0145] This RMI step will allow the material to be densified by adding two new phases to the matrix, namely HfC and SiC.

[0146] For this, an alloy composed of Hf x If y with x and y as previously defined is used. The values ​​of x and y as previously defined allow to modify the quantity of HfC and SiC ultimately in the matrix.

[0147] In this example, an HfSÏ2 alloy is used.

[0148] The general principle of RMI consists of a complete or partial fusion of an alloy on the surface of a porous material. The alloy, then present in liquid form, infiltrates the material by gravity.

[0149] In this example, liquid silicon and hafnium will infiltrate the carbon preform. These two metals then react with the pyrocarbon present on the surface of the carbon fibers to form the two carbides SiC and HfC according to equations 4 and 5 below:

[0150] 4.3 g of HfSi2 alloy are placed on top of the C / C composite preform. This alloy mass corresponds to the pore volume. The HfSi2 alloy then undergoes heat treatment at 1950°C under argon.

[0151] Figure 3 shows the microstructure of the C / C preform infiltrated by the molten HfSi2 alloy under the conditions mentioned above. The white areas represent HfC while the light gray areas represent SiC. The carbon is in dark gray here and the pores of the preform are in black.

[0152] Table 1 below summarizes the characteristics of this composite preform before carbon / carbon and after infiltration of HfSi2- The liquid phase during heat treatment consists of 0.18 cm 3 of hafnium and 0.36 cm 3 of silicon. Only 2.00 g infiltrated the preform, which corresponds to a volume of 0.247 cm 3 This corresponds to 33% VOi of hafnium and 66% VOi of silicon.

[0153] Dimensions Volume of Mass Mass after Volume % volume of preform C / C pores before RMI RMI infiltrated pores infiltrated

[0154] 20 x 20 x 4 mm 3 0.45 cm 3 2.27 g 4.26 g 0.247 cm 3 55%

[0155] Table 1:

[0156] Characteristics of the preform before and after infiltration of HfSi2 in relation to Figure 3.

[0157] In a second step, the preform obtained at the end of the first step is treated with a resin loaded with Si powder subjected to heat treatment. This step allows for infiltration and deposition of silicon carbide on the preform (infiltrated preform) obtained at the end of the previous step. To do this, a Furolite® resin loaded with silicon particles is used.

[0158] More specifically, Furolite® resin is Furolite 050915 A resin, available from TransFurans Chemicals of Geel, Belgium. This resin is a thermosetting resin based on poly(furfuryl alcohol) (PFA or Poly-FA) that acts as a carbon supply source for obtaining silicon carbide.

[0159] Silicon is supplied in powder form (“grade AX 20”, d = 2.3 pm, from HC Starck).

[0160] The successive stages of preparation of the resin loaded with silicon powder are as follows:

[0161] 10 g of Furolite® resin are weighed into a beaker,

[0162] 13 g of silicon powder is added,

[0163] 25 mL of ethanol is added to decrease the viscosity of the resin and powder mixture, also facilitating the mixing and homogeneity of the loaded resin, the loaded resin is mixed with a glass rod to obtain a homogeneous mixture.

[0164] The silicon-filled resin is applied with a brush to the preform.

[0165] A layer is deposited before being dried in an oven at 100°C for 1 hour.

[0166] This deposition process is repeated twice, increasing the thickness of the coating. When the deposit is dry, it is placed in a heat treatment oven.

[0167] The heat treatment is carried out according to the temperature profile shown in Figure 4. A primary vacuum is required during the heat treatment.

[0168] As described in Figure 4, heat treatment includes the following successive steps:

[0169] First rise from 25°C to 1000°C at a speed of 20°C / min,

[0170] 15 min stage at 1000°C maintained to pyrolyze the Furolite® resin into carbon, Second rise up to 1500°C at a speed of 10°C / min. This temperature of 1500°C, above the melting temperature of silicon, makes it possible to obtain liquid silicon. This silicon will then react with the carbon obtained after the pyrolysis of the resin, to form silicon carbide SiC according to the following reaction equation no. 6:

[0171] Temperature reduction to 25°C, at a speed of 20°C / min.

[0172] Figure 5 shows the microstructure of the C / HfC - SiC / SiC composite material obtained after the second step. The matrix is ​​composed of a gradient of silicon carbide composition. At the core of the composite, the matrix is ​​made of HfC - SiC from the RMI of HfSi2- On the surface, the matrix is ​​made only of SiC from the pyrolysis of the resin loaded with silicon powder.

[0173] It is particularly interesting to note that the core and surface matrix are continuous within the material. This synergy provided by the excess silicon within the resin allows for a strong chemical intimacy between the core and the surface of the material.

[0174] Example 2

[0175] In this example, a UHT-CMC composite material according to the invention is prepared, the matrix of which is made up of carbon fibers at the core and an HfB2 / SiC / HfC matrix, and SiC at the periphery with the “matrix continuum” already described above.

[0176] In a first step, a HfB2 boride powder is inserted into the C / C composite material preform.

[0177] This step is carried out by a Submicron Powder Aspiration process known as the APS process, which is therefore a process of infiltrating submicron powders into the heart of a porous preform.

[0178] This process allows to fill part of the porosity with boride powders whose particle size is close to 1 μm. To do this, the powder is suspended in a solvent which allows to obtain a slip. 7 mL of slip are necessary to infiltrate 25% of the pore volume of the C / C composite material preform whose dimensions have already been given above. The successive steps of slip preparation are as follows:

[0179] 1) Mixture of 1.7 mL of water with 4.0 mL of ethanol,

[0180] 2) Stirring with a magnetic bar,

[0181] 3) Addition of 0.13 g of branched polyethyleneimine (PEI) (32,000 molar mass),

[0182] 4) Stirring for 15 minutes,

[0183] 5) Addition of 13 g of HfB2 (Hafnium boride, 99.5%, dso = 0.8 pm, available from Neyco®),

[0184] 6) Stirring for 30 minutes,

[0185] 7) Subjecting the mixture to the action of a sonotrode for 2 minutes,

[0186] 8) Repeat steps 7) and 8).

[0187] Simultaneously with the preparation of the slip, the C / C composite preform is placed in the APS system. This APS system includes a steel jacket that will allow vacuum and then pressure to be applied. A Teflon® mold is placed inside this steel jacket. The C / C composite is placed inside the mold with a filter to retain the slip. The slip is then placed above the preform, then a primary vacuum is established for 1 hour. Next, 3 bars of argon are injected above the slip to force the infiltration of the slip into the heart of the preform. This step also lasts 1 hour. After this, the composite is removed and placed in an oven at 100°C to evaporate the solvent consisting of water and ethanol.

[0188] At the end of the infiltration, the preform is dried, then cleaned and the mass gain inside the porosity is measured. This mass gain therefore gives the volume of pores infiltrated by HfB2 using the APS process.

[0189] Figure 6 shows the microstructure of the C / C composite material infiltrated by HfB2 using the APS process.

[0190] It is observed that the HfB2 powder is distributed within the pores of the preform, also called "infiltration channels". The spaces defined by these pores or channels allow for homogeneous infiltration throughout the entire thickness of the preform. However, closed porosities are not accessible and therefore are not infiltrated. Table 2 summarizes the quantities of powder infiltrated into the C / C composite.

[0191] Only 26% of the pores are infiltrated by hafnium boride.

[0192] Dimensions Volume of Mass before Mass after Volume % volume of preform C / C pores infiltration infiltration infiltrated pores infiltrated

[0193] 20 x 20 x 4 mm 3 0.45 cm 3 2.27 g 3.59 g 0.125 cm 3 26%

[0194] Table 2: Characteristics of the composite infiltrated by HfB2 using the APS process.

[0195] In a second step, reactive melt infiltration (RMI) of HfSi2 is carried out into the HfB2-infiltrated C / C composite material preform that was prepared in the first step of this Example 2, using the APS process.

[0196] This step is identical to the first step of the process carried out in Example 1 described above. However, it is not necessary to use the same quantity of powder. Indeed, since part of the porosity is already filled by the HfB2 infiltrated by APS, only 3 g of HfSi2 alloys are required.

[0197] Figure 7Error! Reference source not found, shows the microstructure of a carbon / carbon composite preform infiltrated with HfB2 using an APS process, then infiltrated with a molten HfSi2 alloy using an RMI process under the conditions described above. The white areas represent HfC, the light gray areas HfB2, while the dark gray areas SiC. The carbon is shown in very dark gray and the pores of the preform are in black.

[0198] In a third step, the infiltrated preform obtained at the end of the second step is treated with a resin loaded with Si powder.

[0199] This step is identical to the second step of the process carried out in Example 1 described above.

[0200] Figure 8 represents the microstructure of the preform obtained at the end of the third step, namely a carbon / carbon preform infiltrated by an APS of HfB2 as well as by an RMI of molten HfSi2 alloy, this preform further comprising a continuous matrix of SiC on the surface prepared from the Furolite® resin loaded with silicon powder.

[0201] The white areas represent HfC and HfB2 (not dissociable at this magnification), while the dark gray areas represent SiC. In Figure 8, the carbon is in very dark gray and the pores of the preform are in black. The microstructure shows a Cf / HfB2 - HfC - SiC / SiC composite. The matrix of the material has a composition gradient. At the core of the composite, the matrix is ​​made of HfB2 - HfC - SiC resulting from the APS of HfB2 then from the RMI of HfSÏ2- On the surface, the matrix is ​​only made of SiC resulting from the pyrolysis of the resin loaded with silicon powder.

[0202] Example 3

[0203] In this example, the behavior of the composite materials according to the invention prepared previously in Examples 1 and 2, as well as of comparative composite materials, is studied.

[0204] In this example, ablation and oxidation resistance tests are carried out in order to show the advantageous properties of the UHT-CMC composite materials according to the present invention, prepared in Examples 1 and 2 above (referred to as Sample 1 and Sample 2 in the rest of the text) compared to comparative UHT-CMC composite materials according to the prior art.

[0205] These comparative composite materials according to the prior art are:

[0206] - a HfC-SiC composite material prepared only by RMI of HfSi2 according to document [1], This comparative composite material is called sample A.

[0207] - a HfB2-HfC-SiC composite material prepared by APS of HfB2 powder then RMI of HfSi2, according to document [2], This comparative composite material is called sample B.

[0208] The behaviors of samples 1 and A are compared, as well as the behaviors of samples 2 and B.

[0209] More specifically, in this example, we study the behavior of the samples described above during an atmospheric reentry simulation test. Description of the atmospheric reentry simulation test carried out in this example.

[0210] Atmospheric reentry presents extreme conditions for materials used as heat shields. Numerous physicochemical phenomena appear due to the very high temperatures (above 2000°C), oxidizing species (dissociated oxygen) as well as ablation phenomena.

[0211] In order to simulate some of these conditions, many tests are possible. The most common is the oxyacetylene torch test (OAT) which is therefore implemented in this example.

[0212] The flame produced by this type of torch reaches 3000°C and can heat materials to nearly 2500°C. The presence of oxidizing species such as water vapor or oxygen in the flame also makes it possible to characterize the material's resistance to oxidation. The test bench used includes a sample holder holding the sample and an OAT torch producing a flame. The torch is mounted on a robotic arm.

[0213] The bench is equipped with numerous measuring devices to monitor several parameters during the test. The surface temperatures on the front and back of the sample are monitored and recorded by two bichromatic pyrometers. A thermal camera also records the surface of the sample. This measurement allows, thanks to the pyrometer placed on the front face, to have an estimate of the surface emissivity. In addition, a visible camera records the surface of the sample to monitor the appearance of various phenomena during the test.

[0214] In this test, in addition to the surface temperatures of the sample, the linear ablation coefficient (CAL) and the mass ablation coefficient (CAM) are also measured.

[0215] The linear and mass ablation coefficients are indicators of resistance to atmospheric reentry tests commonly used in the literature. The lower these two coefficients are, the better the material behaves. The two coefficients are calculated using the two equations (Eq 7 and Eq 8) given below: Or :

[0216] - CAM is the Mass Ablation Coefficient, in mg / s.

[0217] - CAL is the Linear Ablation Coefficient, in pm / s.

[0218] - 1 is the flame exposure time, in seconds.

[0219] - mo and mi are respectively the masses of the sample at the initial instant (start of exposure to the flame) and after t seconds of exposure to the flame, in mg.

[0220] - eo and ei are respectively thicknesses at the initial instant and after t seconds, in pm.

[0221] Test results.

[0222] Behavior at the macroscopic scale. Surface temperature.

[0223] One of the notable effects obtained with the new architecture of the material according to the invention is the lowering of the surface temperature. As shown in Figures 9A and 9B, the material according to the invention which has an extreme surface matrix gradient (sample 2) has a lower surface temperature, namely approximately 2100°C, compared to approximately 2500°C for the comparative UHT-CMC material not having this matrix gradient (sample B). The presence of SiC on the surface in the material according to the invention made it possible to delay, by almost 300 seconds, the time required to reach 2500°C.

[0224] Results of the oxidation tests carried out on comparative sample A and on sample 1 according to the invention.

[0225] The two oxyacetylene torch ablation coefficients obtained for the two materials are presented in Figures 10A and 10B. These coefficients show a clear improvement in the performance for sample 1 (prepared in example 1 above). Indeed, for an exposure time of 120 seconds, comparative sample A has a linear ablation coefficient of 7.7 pm / s, while sample 1 has a linear ablation coefficient of 3.6 pm / s. When the material is subjected to an exposure time of 180 sec, this linear ablation coefficient goes from 3.8 pm / s for sample A to 1.2 pm / s for sample 1. This trend is also found with the mass ablation coefficient. The microstructures (Figures 11A and 11B) of the oxide layer, following the torch test, provide information on the behavior of the samples during the OAT torch test.

[0226] Figure 11A shows the microstructure of the oxide layer formed on sample A. Figure 11B shows the microstructure of the oxide layer formed on sample 1.

[0227] The microstructure shown in Figure 11A comprises a two-phase oxide layer, namely a liquid phase of frozen silicon oxide SiCh and a solid phase of hafnium oxide HfCh. This solid phase of HfCh is in dendritic form. This architecture is identical throughout the oxidized layer.

[0228] The microstructure of Sample 1 after the OAT torch test is very different (Figure 11B). The surface of the oxide layer consists mainly of a SiO2 layer located above a dense hafnium oxide phase. The healthy material is located below this HfO2 layer.

[0229] Results of the oxidation tests carried out on comparative sample B and on sample 2 according to the invention.

[0230] The two oxyacetylene torch ablation coefficients obtained for the two materials are shown in Figures 12A and 12B.

[0231] These coefficients also show a clear improvement in ablation resistance for sample 2. In a similar manner to the previous system (sample 1), sample 2 according to the invention exhibits better behavior in the OAT test than sample B due to the presence of silicon carbide on the surface.

[0232] From a microstructural point of view, the structure of the oxide layer of the material without matrix continuum (sample B, Figure 13A) shows similarities with the HfC - SiC structure (sample A, Figure 11A). The oxide layer is biphasic with a liquid ex-phase of SiO2 as well as a solid phase of dendritic HfO2.

[0233] The oxide layer of the material with the extreme surface gradient (sample 2 according to the present invention) has a completely different architecture (Figure 13B). As in the case of the microstructure of the oxide layer of the HfC - SiC / SiC material (Figure 11B), the structure is organized in three parts with an ex-liquid phase mainly composed of frozen liquid SiCh, a layer of dense HfCh and finally the healthy material.

[0234] Conclusion of the tests.

[0235] Microstructural observations as well as the overall behavior of the material at the macroscopic scale show that the presence of a "matrix continuum" is very beneficial for the material. Indeed, the oxide layer formed is much more protective when the matrix continuum is present on the surface of the material. This results in significantly lower mass and linear ablation coefficients.

[0236] The explanation for this better behavior comes from the better organization of the oxide layer. Indeed, in the case of a composite made without matrix continuum (samples A and B), an oxide layer composed of silica in the liquid state as well as HfO2 in dendritic solid form is formed. This organization is fragile, it is subject to the blast encountered during atmospheric reentry. On the contrary, when an extreme surface gradient of SiC is present, which is the case in the samples prepared by the process according to the invention, two very distinct oxide layers are formed. The first layer is composed almost exclusively of liquid silica although some traces of solid HfCh are visible. This silica layer will allow the Hafnium to oxidize more slowly and to organize itself into a much denser layer.This will then result in, once the silica layer is completely consumed, the sample having a much better organized HfCh layer at the extreme surface. This architecture of oxide layers created in the composite material prepared according to the invention is, consequently, much more resistant to ablation caused by atmospheric re-entry.

[0237] REFERENCES

[0238] [1] FR-A-3 002 952.

[0239] [2] C. Liégaut, P. Bertrand, L. Maillé, F. Rebillat, “UHTC-based matrix as protection for Cf / C composites: Original manufacturing, microstructural characterization and oxidation behavior at temperature above 2000 °C”, J. Eur. Ceram. Soc. 42 (2022) 3168-3182. https: / / doi.Org / 10.1016 / j.jeurceramsoc.2022.02.029. [3] JP Zhang, QG Fu, L. Wang, Preparation, "Ablation behavior and thermal retardant ability of C / C-HfB2-SiC composites", Mater. Of the. 132 (2017) 552-558. https: / / doi.Org / 10.1016 / j.matdes.2017.07.041.

[0240] [4] P. Wang, S. Zhou, P. Hu, G. Chen, X. Zhang, W. Han, "Ablation resistance ofZrB2- SiC / SiC coating prepared by pack cementation for graphite", J. Alloys Compd. 682 (2016) 203-207. https: / / doi.Org / 10.1016 / j.jallcom.2016.04.010.

[0241] [5] X. Ren, H. Li, Q. Fu, K. Li, "Oxidation protective TaB2-SiC gradient coating to protect SiC-Si coated carbon / carbon composites against oxidation", Compos. Part B Eng. 66 (2014) 174-179. https: / / doi.Org / 10.1016 / j.compositesb.2014.05.021.

[0242] [6] P. Wang, C. Zhou, X. Zhang, G. Zhao, B. Xu, Y. Cheng, P. Zhou, W. Han, "Oxidation protective ZrB2-SiC coatings with ferrocene addition on SiC coated graphite", Ceram. Int. 42 (2016) 2654-2661. https: / / doi.Org / 10.1016 / j.ceramint.2015.10.072.

[0243] [7] FR-A1-2 843 109.

Claims

CLAIMS 1. Method for preparing a composite material comprising an Ultra High Temperature ceramic matrix reinforced with carbon fibers, comprising the following successive steps: a) reactive melt infiltration (RMI) is carried out on an open porosity substrate made of a carbon / carbon (C / C) composite material with a carbon matrix reinforced with carbon fibers, during which at least one metal silicide M is deposited on a surface of the substrate x If ysolid in which M is a transition metal, x is an integer selected from the group consisting of 1, 2, 3, 4 and 5 and y is an integer selected from the group consisting of 1, 2, 3 and 4; then the substrate and the metal silicide are heated to a temperature TP higher than the melting temperature of the metal silicide; then a plateau is observed at the temperature TP for a time sufficient for the metal silicide to react with the carbon of the matrix; and finally the substrate is cooled;b) a mixture comprising an organic resin, preferably a furanic or phenolic resin, and a metallic silicon powder is deposited on the surface of the substrate obtained at the end of step a), then the substrate and the mixture consisting of the organic resin and the silicon powder are heated, under an inert atmosphere, to a first temperature at which the organic resin is pyrolyzed and a plateau is observed at this first temperature for a time sufficient to pyrolyze the resin and to form carbon, then the substrate is further heated to a second temperature above the melting point of the silicon to form liquid silicon which reacts with the carbon to form a layer of silicon carbide (SiC) on the substrate obtained at the end of step a);finally, the substrate is cooled, whereby, at the end of step b), a composite material is obtained comprising an Ultra High Temperature ceramic matrix reinforced by carbon fibers.; 2. Method according to claim 1, in which, prior to said step a), a Submicron Powder Aspiration (SPA) step is carried out during which infiltrates a suspension or slip of at least one submicron powder of boride or transition metal carbide M', inside the C / C composite material, whereby, after drying, a C / C composite material loaded with powder of boride or transition metal carbide M' is obtained.

3. Method according to claim 2, in which said transition metal M and said transition metal M', identical or different, are chosen from Hafnium, Titanium, Zirconium and Tantalum, and, preferably, are Hafnium.

4. A method according to any preceding claim, wherein the metal silicide M x If y is a disilicide of a transition metal M (MSÎ2).

5. A method according to any preceding claim, wherein the carbon fiber reinforced carbon matrix composite material is a 2D, 2.5D or 3D composite material.

6. A method according to any preceding claim, wherein said carbon fiber reinforced carbon matrix composite material is a 3D composite material with a density matrix greater than 1.

8.

7. A method according to any one of the preceding claims, wherein the deposition of the metal silicide M x If y solid on the surface is made by depositing the metal silicide M x If y on the surface or by depositing the substrate and M x If y in a crucible.

8. The method of claim 7, wherein the metal silicide M x If y is deposited on the surface in the form of a compacted or uncompacted powder, or in the form of a slip consisting of a powder of the metal silicide M x If y and a liquid.

9. A method according to any preceding claim, wherein said temperature TP is from 900°C to 2500°C, for example, 1800°C.

10. Method according to any one of the preceding claims, in which the mixture deposited during step b) further comprises at least one addition element chosen from powders of carbides, oxides, borides and borocarbons of metals such as powders of carbides, oxides, borides and / or borocarbons of transition metals.

11. The method of claim 10, wherein said addition element is selected from Ta^fCs, HfCh, and mixtures thereof.

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