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

Abstract

The present invention relates to a 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 solid metal silicide MxSiy is deposited on a surface of the substrate 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;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), whereby, at the end of step b), a composite material is obtained comprising an Ultra High Temperature ceramic matrix reinforced by carbon fibers.;

Description

Title of the invention: METHOD FOR PREPARING A COMPOSITE MATERIAL WITH AN ULTRA-HIGH TEMPERATURE CERAMIC MATRIX AND FIBER REINFORCEMENT OF CARBON Technical field

[0001] The present invention relates to a method for preparing a composite material comprising an ultra-high temperature ceramic matrix (“Ultra High Temperature Ceramic” or UHTC in English) 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.

[0002] 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.

[0003] Thus, the material prepared according to the process of the invention finds its application in particular in the 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. STATE OF THE PRIOR ART

[0004] The materials that make up heat shields are subjected to extreme conditions, particularly during re-entry into the atmosphere.

[0005] These materials are subject to very high temperatures, ablation phenomena, as well as oxidation reactions, in the presence of dissociated oxygen for example. Few materials are capable of withstanding these conditions.

[0006] For several decades, the preferred materials for withstanding these conditions have been ultra-high temperature ceramics (UHTC). By "UHTC ceramics" we mean ceramics whose melting temperature is higher than 2000°C, in particular higher than 2500°C, or even higher than 3000°C.

[0007] [Fig.l] shows the melting temperatures of the main UHTC ceramics.

[0008] UHTC ceramics have many advantages, such as high melting temperature, high modulus and good oxidation resistance.

[0009] However, these ceramics, manufactured in the form of monoliths, are very fragile.

[0010] It has been found that UHTC ceramic matrix composites (UHT-CMC) per- were trying to overcome this drawback.

[0011] In the following, the techniques used to manufacture a UHT-CMC composite material or to manufacture coatings on carbon / carbon composite materials are described.

[0012] With regard to the manufacture of UHTC and carbon fiber matrix composites, called Cf / UHTCm composites, the matrix of these composites can be manufactured by a reactive melt infiltration (RMI) technique or by combining the RMI technique with the Submicron Powder Aspiration (SPA) technique.

[0013] The manufacture of the UHTC matrix by RMI is notably described in document [1].

[0014] 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:

[0015] a) the surface is brought into contact with a solid metal disilicide (MSi2) in which M is chosen from Hafnium, Titanium, and Tantalum;

[0016] b) the substrate and the metal disilicide are heated to a temperature TP higher than the melting temperature of the metal disilicide;

[0017] c) a plateau is observed at temperature TP 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);

[0018] d) the part provided with the multi-layer coating is cooled.

[0019] The carbon layer of the substrate may be a layer of an all-carbon substrate.

[0020] The all-carbon substrate may be a carbon / carbon composite material such as a 2D or 3D composite material.

[0021] Optionally, at the end of step d), the following step e) is also carried out:

[0022] e) a layer of carbon is deposited on the surface of the multilayer coating.

[0023] Optionally, at the end of step d) or step e), the following step j) is also carried out:

[0024] j) siliciding 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.

[0025] The manufacture of the UHTC matrix by APS / RMI is notably described in the document [2]. In this document, a carbon / carbon composite material with a carbon matrix and carbon fibers called Cf / Cm material 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.

[0026] This technique, by chemical reaction of liquid silicon with the carbon of the matrix, forms SiC according to the following reaction equation, Eq 1:

[0027] [Math.l] Si(p + Qq SiC^ (Eq 1)

[0028] 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 C / C thus modified. In this document, the microstructures presented clearly show ZrB2 and SiC at the core of the composite, however no surface protection is visible.

[0029] As regards the manufacture of coatings on carbon / carbon composite materials such as carbon matrix and carbon fiber composite materials called Cf / Cm composite materials, 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).

[0030] The pack cementation (PC) technique makes it possible to produce SiC deposits on the surface of carbon-based materials. This technique consists of depositing a layer of silica and graphite powder C 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:

[0031] [Math.2] + Qq SiO^+CO^ (Eq2)

[0032] [Math.3] Si+ C(s) - SiC(s) + CO^ (Eq 3)

[0033] 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 makes it possible to obtain a more complex multi-layer system [3]. The disadvantage of the PC technique comes from the fact that the carbon is reacted in powder form. This results after reaction with the silicon in SiC also in powder form and therefore porous. The SiC formed is therefore not sufficiently dense to constitute a waterproof barrier to oxidizing agents [3-6].

[0034] The technique known as the loaded resin technique (“Slurry Sintering” in English) is in particular described in document [7] using a resin as is the case in the present invention.

[0035] This document describes a method for manufacturing a refractory material and a protective coating that can be obtained by this method.

[0036] This method comprises the following steps:

[0037] - 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;

[0038] - heat treat the substrate to dry it then crosslink and carbonize the resin which results in bringing carbon into the system;

[0039] - cover the deposit with a second dispersion containing silicon in the form powder and a binder;

[0040] - heat treat the deposit at a temperature at least equal to the temperature of melting the silicon so that it reacts with the carbon in the binder to form SiC;

[0041] The material obtained consists of a substrate (for example a C / C substrate) coated with a dense mixture of carbides or borides or borocarbons of transition metals and SiC.

[0042] The method of this document only allows coatings to be produced on the surface of a substrate and the chemical nature of this substrate is not in any way modified in depth. As a result, the protection against oxidation conferred by this method is intrinsically limited.

[0043] 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.

[0044] There is therefore, in view of the above, a need for a method 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 method 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.

[0045] The aim of the invention is to provide a method meeting, among other things, these needs. Statement of the invention

[0046] This aim, and others still, are achieved, in accordance with the invention, by a method of 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.

[0047] More particularly, the method according to the invention for preparing a composite material comprising an Ultra High Temperature ceramic matrix reinforced by 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 solid metal silicide MxSiy is deposited on a surface of the substrate, 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 at the temperature TP is observed 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.;

[0048] 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.

[0049] Optionally, prior to step a), a step aO) of Submicron Powder Aspiration (SPA) can be carried out during which a suspension of at least one boride or carbide powder of a transition metal is infiltrated. M', inside the C / C composite material, i.e. in the open porosity of the C / C composite material, whereby, after drying, a C / C composite material loaded with boride or carbide powder of a transition metal M' is obtained. The transition metal M' used during this optional step aO) may be identical to or different from the transition metal M present in the metal silicide MxSiy used during step a) of the process according to the invention.

[0050] 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.

[0051] 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 solid metal silicide MxSiy and a step b) which is a step of formation of silicon carbide from an organic resin acting as a carbon precursor and a silicon powder.

[0052] 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.

[0053] According to an important characteristic of the method according to the invention, which is not disclosed in the prior art, during step a), the quantity of solid metal silicide MxSiy deposited on the surface of the substrate is the quantity just 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 MSi2 is used which, in theory, makes it possible to fill, in its entirety, the volume of the pores of the open porosity of the matrix of the C / C composite material.

[0054] 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.

[0055] 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 (e.g. HfC); a layer with a matrix of MC (e.g. HfC) and SiC reinforced by carbon fibers, which were therefore not affected by the RMI process, with an increasing gradient in matrix carbon from the SiC layer; and a layer of C / C composite material with a carbon matrix reinforced by carbon fibers which, again, were not affected by the RMI process, as was the carbon matrix.

[0056] 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 MSi2 during the RMI step, beyond which the layer of C / C composite material with carbon matrix reinforced by carbon fibers begins.

[0057] 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.

[0058] The layer with a matrix of MC (e.g. HfC) and SiC containing carbon fibers may be a layer with a concentration gradient 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.

[0059] 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), a step aO) of APS has been carried out.

[0060] 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”.

[0061] The material prepared by the method according to the invention, due to its specific structure, and in particular due to the association 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 method according to the invention has improved resistance to oxidation and ablation under the conditions prevailing during re-entry into the atmosphere.

[0062] In other words, the composite prepared by the process according to the invention is composed at the 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.

[0063] 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 which 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 the material with better resistance to oxidation.

[0064] 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.

[0065] 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 properties that are much superior (2 to 3 times better) to those of materials lacking this matrix continuum, as demonstrated in the examples provided below (see in particular example 3).

[0066] There is no limitation 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.

[0067] Thus, the carbon fiber reinforced carbon matrix C / C composite material may be a 2D, 2.5D or 3D composite material.

[0068] The C / C composite material may have an average open porosity of 15% to 50% by volume, preferably 20% to 30% by volume.

[0069] In particular, the carbon fiber reinforced carbon matrix composite material can even be implemented with a 3D composite material with a dense matrix, in particular with a density greater than 1.8.

[0070] During step a), at least one solid metal disilicide MSi2 is deposited on a surface of the substrate, in which M is a transition metal.

[0071] The substrate may have any shape. It may in particular be a rectangular or square plate having a determined thickness, in particular from 2 mm to 50 mm, for example 4 mm.

[0072] The surface on which the metal silicide MxSiy is deposited is generally a horizontal upper surface of the substrate, for example the upper surface of a rectangular or square plate arranged horizontally.

[0073] Preferably, the transition metal M present in the silicide and the transition metal M' present in the boride or the 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.

[0074] Advantageously, the pair (x,y) in the metal silicide MxSiy is 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 MxSiy is a disilicide of a transition metal M as previously defined (MSi2) and in particular a Hafnium disilicide (HfSi2).

[0075] Indeed, it has been determined that Hafnium disilicide (HfSi2) was, among many other compounds, the intermetallic compound most suitable for carrying out reactive molten infiltration "RMI", in particular from mixtures of compacted metal powders, in particular at a temperature below 1800°C.

[0076] The use of Hafnium disilicide not only makes it possible to obtain an equi-distribution of Hafnium over the entire width of the infiltration, but also to have a compound with a single melting temperature (because it is a defined compound), which avoids premature infiltration of silicon into the part.

[0077] Furthermore, molten HfSi2 is very fluid and it permeates even very low porosities. Therefore, the method according to the invention can be successfully implemented both with porous C / C composite materials and with dense, even very dense, C / C carbon materials.

[0078] 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).

[0079] Indeed, the enthalpies of formation 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 the Ta-Si and Ti-Si systems behave in the same way as Hf-Si.

[0080] Advantageously, the deposition of the solid metal silicide MxSiy on the surface is carried out by depositing the metal silicide MxSiy on the surface or by depositing the substrate and MxSiy in a crucible.

[0081] The metal silicide MxSiy 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 MxSiy and a liquid.

[0082] As previously indicated, the surface is brought into contact with a volume of the solid metal silicide MxSiy, sufficient to infiltrate the volume of the average open porosity of the carbon substrate.

[0083] When a step aO) is carried out before step a), then the volume of metal silicide MxSiy used is lower because part of the open porosity has already been infiltrated, clogged by the boride or the transition metal carbide M' as previously defined.

[0084] Advantageously, the temperature TP can be from 900°C to 2500°C, for example 1800°C.

[0085] Advantageously, during step a), a rapid temperature rise 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 the temperature TP.

[0086] Advantageously, the plateau at temperature TP can be observed for a period of 5 minutes to 1 hour.

[0087] During 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.

[0088] 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.

[0089] The matrix carbon concentration is close to zero in the vicinity of the SiC layer.

[0090] 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.

[0091] During 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).

[0092] The surface on which the mixture is deposited is the same as that on which the metal silicide MxSiy was deposited during step a).

[0093] The organic resin can be chosen from all the resins which, during their pyrolysis, form carbon. Furanic or phenolic resins are preferred because they are commercially accessible and their carbon yield is controlled.

[0094] Advantageously, the mixture deposited during step b) further comprises at least one addition element chosen from powders of carbides, oxides, borides and boro-carbides of metals such as powders of carbides, oxides, borides and / or boro-carbides of transition metals.

[0095] Carbides, oxides, borides and / or borocarbons include mixed carbides, oxides, borides and / or borocarbons of several transition metals.

[0096] In particular, the addition element may be chosen from Ta4HfC5, HfO2 and their mixtures.

[0097] A solvent such as ethanol may be added to the mixture in order to reduce its viscosity and facilitate its deposition and application to the surface.

[0098] 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.

[0099] 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.

[0100] The mixture deposited on the surface is then dried, for example, in an oven at 100°C for 1 hour.

[0101] 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.

[0102] The second temperature is a temperature higher than the melting temperature of silicon, namely 1410°C, which makes it possible to obtain liquid silicon.

[0103] The second temperature may be a temperature of 1410°C to 1600°C, for example, 1500°C.

[0104] 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 [Fig.4].

[0105] A primary vacuum is generally required during heat treatment.

[0106] This liquid silicon will then react with the carbon obtained following the pyrolysis of the resin, to form silicon carbide (SiC).

[0107] The substrate is then cooled, generally to room temperature.

[0108] 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 carbide of transition metal M' is infiltrated into the C / C composite material, whereby, after drying, a C / C composite material loaded with powder of boride or carbide of transition metal M' is obtained.

[0109] By “submicron powder” is generally meant 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.

[0110] The transition metal boride M' may in particular be hafnium boride HfB2.

[0111] The transition metal carbide M' may in particular be hafnium(II) carbide Hf2C or hafnium(IV) carbide HfC.

[0112] The suspension or slip comprises a solvent generally chosen from organic solvents, water and their mixtures.

[0113] For example, this solvent may be a mixture of water and an aliphatic alcohol such as ethanol.

[0114] During this step aO), the procedure can generally be as follows: - 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 placed under vacuum or under pressure. - 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 MxSiy is then deposited during step a). - a primary vacuum is then applied to the enclosure for a period of 30 minutes to 90 minutes, for example for one hour. - 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.

[0115] 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. - the substrate is dried in order to evaporate the solvent, for example, at a temperature of 100°C.

[0116] 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'.

[0117] The invention will be better understood upon reading the following description, given by way of illustration and not limitation, of embodiments of the invention given in the form of examples.

[0118] This description is made in relation to the attached drawings. Brief description of the drawings

[0119] [Fig. 1] shows the melting temperature (in °C) of the main Ultra High Temperature Ceramics (UHTC).

[0120] [Fig.2A] is a photograph of the preform made of Cf / Cm composite material with carbon fibers (Cf) and pyrocarbon matrix (Cm) of 2D architecture (CF 227 / 2 available from Schunk®) used in the examples. The scale shown in this figure represents 20 mm.

[0121] [Fig.2B] is another photograph of the Cf / Cm composite material preform at carbon fibers (Cf) and pyrocarbon matrix (Cm) of 2D architecture (CF 227 / 2 available from Schunk®) used in the examples. The scale shown in this figure represents 20 mm.

[0122] [Fig.3] is a photograph taken with a Scanning Electron Microscope (SEM) of the microstructure of a Cf / Cm composite material preform obtained after infiltration of an HfSi2 alloy by a reactive melt infiltration (RMI) technique, during the first step of Example 1. The scale shown in this Figure represents 300 pm.

[0123] [Fig.4] is a graph showing the temperature profile during the heat treatment of the silicon-filled resin during the second stage of Example 1. The time (in minutes) is plotted on the abscissa, and the temperature (in °C) is plotted on the ordinate.

[0124] [Fig.5] is a photograph taken by SEM of the microstructure of a preform made of Cf / Cm composite material obtained after infiltration of an HfSi2 alloy by a reactive melt infiltration (RMI) technique followed by treatment with a Furolite® resin loaded with silicon powder and subjected to a heat treatment (Example 1, second step). The scale shown in this figure represents 300 pm.

[0125] [Fig.6] is a photograph taken by SEM of the microstructure of a preform in 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.

[0126] [Fig.7] is a photograph, taken with a SEM, of the microstructure of a preform made of Cf / Cm composite material 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.

[0127] [Fig.8] 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, followed by infiltration of an HfSi2 alloy by a reactive melt infiltration (RMI) technique, and followed by treatment with a Furolite® resin loaded with silicon powder and subjected to a heat treatment (Example 2, third step). The scale shown in this figure represents 50 pm.

[0128] [Fig.9A] is a graph which gives the surface temperature (in °C) on the front face (curve A) and on the back face (curve B) of sample 2 as a function of the duration of exposure to the flame (in seconds).

[0129] [Fig.9B] is a graph which gives the surface temperature (in °C) on the front face (curve A) and on the back face (curve B) of sample B as a function of the duration of exposure to the flame (in seconds).

[0130] [Fig. 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).

[0131] [Fig.10B] is a graph which 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).

[0132] [Fig. 11 A] is a photograph taken with an SEM of the microstructure of the oxide layer formed on sample A, following the oxyacetylene torch (OAT) test. The scale shown in this figure represents 200 pm.

[0133] [Fig. 1 IB] is a photograph taken with an SEM 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.

[0134] [Fig. 12A] 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 2 according to the invention (right bars for each time) and for sample B (left bars for each time).

[0135] [Fig. 12B] is a graph which 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).

[0136] [Fig. 13 A] is a photograph taken with an SEM of the microstructure of the oxide layer formed on sample B, following the oxyacetylene torch (OAT) test. The scale shown in this figure represents 200 pm.

[0137] [Fig. 13B] is a photograph taken with an SEM of the microstructure of the oxide layer formed on sample 2, following the oxyacetylene torch (OAT) test. The scale shown in this figure represents 200 pm.

[0138] DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

[0139] The invention will now be described with reference to the following examples, given for illustrative and non-limiting purposes.

[0140] EXAMPLES

[0141] Two examples which illustrate the preparation of two composite materials according to the invention are presented in the following.

[0142] 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.

[0143] 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.

[0144] 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 the company Schunk®.

[0145] Figures 2A and 2B show photographs of the CF 1227 / 2 carbon C / C preform used in the two examples.

[0146] The characteristics of this C / C preform are as follows: - Dimensions: 20 x 20 x 4 mm3 - Density: 1.33 g. cm3 - Weaving architecture: 2D - Porosity: 25% - Pore volume: 0.45 cm3 Example 1

[0147] 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. • In a first step, reactive melt infiltration (RMI) of HfSi2 is carried out in the C / C composite material preform.

[0148] The objective of this step is to obtain a matrix comprising or even composed of hafnium carbide and silicon.

[0149] This RMI step will allow the material to be densified by adding two new phases to the matrix, namely HfC and SiC.

[0150] For this, an alloy composed of HfxSiy with x and y as previously defined is used. The values ​​of x and y as previously defined make it possible to modify the quantity of HfC and SiC in the matrix.

[0151] In the present example, an alloy of HfSi2 is used.

[0152] 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.

[0153] In the present 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:

[0154] [Math.4] C(» + Si(l} - SiC(x} (Eq4)

[0155] [Math.5] Cœ+ (Eq 5)

[0156] 4.3 g of HfSi2 alloy are placed above the composite material preform C / C. This alloy mass corresponds to the pore volume. The HfSi2 alloy then undergoes heat treatment at 1950°C under argon.

[0157] [Fig.3] represents 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 here in dark gray and the pores of the preform are in black.

[0158] Table 1 below summarizes the characteristics of this composite preform before carbon / carbon and after infiltration of HfSi2. The liquid phase during the heat treatment consists of 0.18 cm3 of hafnium and 0.36 cm3 of silicon. Only 2.00 g infiltrated the preform, which corresponds to a volume of 0.247 cm3. This corresponds to 33% voi of hafnium and 66% voi of silicon.

[0159] [Tables 1] C / C preform dimensions Pore volume Mass before RMI Mass after RMI Infiltrated volume % infiltrated pore volume 20 x 20 x 4 mm3 0.45 cm3 2.27 g 4.26 g 0.247 cm3 55%

[0160] Table 1:

[0161] Characteristics of the preform before and after infiltration of HfSi2 in relation to [Fig.3]. • 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.

[0162] 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.

[0163] 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) which acts as a carbon supply source for obtaining silicon carbide.

[0164] Silicon is supplied in powder form (“grade AX 20”, d = 2.3 pm, from HC Starck).

[0165] The successive stages of preparation of the resin loaded with silicon powder are the following: - 10 g of Furolite® resin are weighed into a beaker, - 13 g of silicon powder are added, - 25 mL of ethanol are added to reduce the viscosity of the mixture. resin and powder, also facilitating the mixing and homogeneity of the loaded resin, - the charged resin is mixed with a glass rod to obtain a homogeneous mixture.

[0166] The silicon-loaded resin is applied with a brush to the preform.

[0167] A layer is deposited before being dried in an oven at 100°C for 1 hour.

[0168] This deposition operation is repeated twice, which makes it possible to increase the thickness of the coating. When the deposit is dry, it is placed in a heat treatment furnace.

[0169] The heat treatment is carried out according to the temperature profile shown in [Fig.4]. A primary vacuum is required during the heat treatment.

[0170] As described in [Fig.4], the heat treatment comprises the following successive steps - First rise from 25°C to 1000°C at a speed of 20°C / min, - 15 min stage at 1000°C maintained to pyrolyze the Furolite® resin in carbon, - Second rise 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] [Math.6] C(s) + Si(i) -> SiC(s) (Eq 6) - Temperature reduction to 25°C, at a speed of 20°C / min.

[0172] [Fig.5] shows the microstructure of the C / HfC - SiC / SiC composite material obtained at the end of 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 is ​​continuous within the material. This synergy provided by the excess silicon within the resin allows for strong chemical intimacy between the core and the surface of the material. Example 2

[0174] 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 a HfB2 / SiC / HfC matrix, and SiC at the periphery with the “matrix continuum” already described above. • In a first step, an HfB2 boride powder is inserted into the C / C composite material preform.

[0175] 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.

[0176] This process makes it possible to fill part of the porosity with boride powders, the particle size of which is close to 1 μm. For this, the powder is suspended in a solvent, which makes it possible to obtain a slip. 7 mL of slip are necessary in order to infiltrate 25% of the pore volume of the C / C composite material preform, the dimensions of which have already been given above.

[0177] The successive stages of preparation of the slip are as follows: 1. Mix 1.7 mL of water with 4.0 mL of ethanol, 2. Stirring with a magnetic bar, 3. Addition of 0.13 g of branched polyethyleneimine (PEI) (32,000 molar mass), 4. Stirring for 15 minutes, 5. Addition of 13 g of HfB2 (Hafnium boride, 99.5%, d50= 0.8 pm, available from Neyco®), 6. Stirring for 30 minutes, 7. Subjecting the mixture to the action of a sonotrode for 2 minutes, 8. Repeating steps 7) and 8).

[0178] Simultaneously with the preparation of the slip, the preform made of C / C composite material is placed in the APS system. This APS system includes a steel jacket which will allow the vacuum and then the pressure to be applied. A Teflon® mold is placed inside this steel jacket. The composite made of C / C material 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 in order 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 then placed in an oven at 100°C in order to evaporate the solvent consisting of water and ethanol.

[0179] 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.

[0180] [Fig.6] shows the microstructure of the infiltrated C / C composite material composite by HfB2 using the APS process.

[0181] 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 over the entire thickness of the preform. However, the closed porosities are not accessible and therefore are not infiltrated.

[0182] Table 2 summarizes the amounts of powder infiltrated into the C / C composite. Only 26% of the pores are infiltrated by hafnium boride.

[0183] [Tables2] C / C preform dimensions Pore volume Mass before infiltration Mass after infiltration Infiltrated volume % infiltrated pore volume 20 x 20 x 4 mm3 0.45 cm3 2.27 g 3.59 g 0.125 cm3 26%

[0184] Table 2: Characteristics of the composite infiltrated by HfB2 using the APS process. • In a second step, reactive melt infiltration (RMI) of HfSi2 is carried out in the HfB2-infiltrated C / C composite material preform that was prepared in the first step of this Example 2, using the APS process.

[0185] 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 necessary.

[0186] [Fig.7] shows the microstructure of a carbon / carbon composite preform infiltrated with HfB2 using an APS process, then infiltrated with a molten alloy of HfSi2 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 here in very dark gray and the pores of the preform in black. • In a third step, the infiltrated preform obtained at the end of the second step is treated with a resin loaded with Si powder.

[0187] This step is identical to the second step of the process carried out in Example 1 described above.

[0188] [Fig.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 SiC surface matrix prepared from Furolite® resin loaded with silicon powder.

[0189] The white areas represent HfC and HfB2 (not dissociable at this magnification), while the dark gray areas represent SiC. In [Fig.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 up of HfB2 - HfC - SiC resulting from the APS of HfB2 then from the RMI of HfSi2. On the surface, the matrix is ​​only made up of SiC resulting from the pyrolysis of the resin loaded with silicon powder. Example 3

[0190] 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.

[0191] 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.

[0192] These comparative composite materials according to the prior art are: - a HfC-SiC composite material prepared only by RMI of HfSi2 according to document [1]. This comparative composite material is referred to as sample A. - 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.

[0193] The behaviors of samples 1 and A are compared, as well as the behaviors of samples 2 and B.

[0194] 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.

[0195] Atmospheric re-entries present extreme conditions for materials used as heat shields. Many physicochemical phenomena appear given the very high temperatures (above 2000°C), the oxidizing species (dissociated oxygen) as well as the ablation phenomena.

[0196] 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 the present example.

[0197] The flame produced by this type of torch reaches 3000°C and can heat the materials at 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.

[0198] The bench is equipped with numerous measuring devices allowing several parameters to be monitored during the test. The surface temperatures on the front and back faces 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 allowing the appearance of different phenomena to be monitored during the test.

[0199] During 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.

[0200] 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:

[0201] [Math.7] CAM — (Eql)

[0202] [Math. 8] CAL= (Eq 8)

[0203] where: - CAM is the Mass Ablation Coefficient, in mg / s. - CAL is the Linear Ablation Coefficient, in pm / s. - t is the flame exposure time, in seconds. - mo and m; are respectively the masses of the sample at the initial instant (start of flame exposure) and after t seconds of flame exposure, in mg. - e0 and ej are respectively thicknesses at the initial instant and after t seconds, in pm. • Test results. - Behavior on the macroscopic scale. Surface temperature.

[0204] 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 by the

[0205]

[0206]

[0207]

[0208]

[0209]

[0210]

[0211] 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 necessary to reach 2500°C. - Result of the oxidation tests carried out on comparative sample A and on sample 1 according to the invention. 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 1 IA and 1 IB) of the oxide layer, following the torch test, provide information on the behavior of the samples during the OAT torch test. [Fig. 11 A] shows the microstructure of the oxide layer formed on sample A. [Fig. 11 B] shows the microstructure of the oxide layer formed on sample 1. The microstructure shown in [Fig.l 1 A] comprises a two-phase oxide layer, namely a liquid phase of frozen silicon oxide SiO2 and a solid phase of hafnium oxide HfO2. This solid phase of HfO2 is in dendritic form. This architecture is identical throughout the oxidized layer. The microstructure of sample 1 after the OAT torch test is very different ( [Fig.l IB]). 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. - Result of the oxidation tests carried out on comparative sample B and on sample 2 according to the invention. The two oxyacetylene torch ablation coefficients obtained for the two materials are shown in Figures 12A and 12B. These coefficients also show a clear improvement in ablation resistance for sample 2. In a similar way 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.

[0212] From a microstructural point of view, the structure of the oxide layer of the material without matrix continuum (sample B, [Fig.l3A]) shows similarities with the HfC - SiC structure (sample A, [Fig. 11 A]). The oxide layer is biphasic with a liquid ex-phase of SiO2 as well as a solid phase of dendritic HfO2.

[0213] The oxide layer of the material exhibiting the extreme surface gradient (sample 2 according to the present invention) has a completely different architecture ([Fig.l3B]). As in the case of the microstructure of the oxide layer of the HfC - SiC / SiC material ([Fig.llB]), the structure is organized in three parts with an ex-liquid phase mainly composed of frozen liquid SiO2, a layer of dense HfO2 and finally the healthy material. • Conclusion of the tests.

[0214] 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.

[0215] The explanation for this better behavior comes from the better organization of the oxide layer. Indeed, in the case of a composite produced 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 HfO2 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 HfO2 layer on 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. REFERENCES

[0216] [1] FR-A-3 002 952.

[0217] [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.

[0218] [3] JP Zhang, QG Fu, L. Wang, Preparation, "Ablation behavior and thermal retardant ability of C / C-HfB2-SiC composites", Mater. Des. 132 (2017) 552-558. https: / / doi.Org / 10.1016 / j.matdes.2017.07.041.

[0219] [4] P. Wang, S. Zhou, P. Hu, G. Chen, X. Zhang, W. Han, "Ablation résistance of ZrB2-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.

[0220] [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.

[0221] [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.

[0222] [7] FR-A1-2 843 109.

Claims

Claims

1. A method of preparing a composite material comprising an Ultra High Temperature ceramic matrix reinforced (containing) 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 by carbon fibers, during which at least one solid metal silicide MxSiy is deposited on a surface of the substrate, 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 at the temperature TP is observed 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 a suspension or slip of at least one submicron powder of boride or carbide of transition metal M' is infiltrated into the C / C composite material, whereby, after drying, a C / C composite material loaded with powder of boride or carbide of transition metal M' is obtained.

3. A method according to claim 2, wherein said transition metal M and said transition metal M', identical or different, are selected from Hafnium, Titanium, Zirconium and Tantalum, and preferably are Hafnium.

4. A method according to any preceding claim, wherein the metal silicide MxSiy is a disilicide of a transition metal M (MSi2).

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 preceding claim, wherein the deposition of the solid MxSiy metal silicide on the surface is carried out by depositing the MxSiy metal silicide on the surface or by depositing the substrate and MxSiy in a crucible.

8. A method according to claim 7, wherein the metal silicide MxSiy 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 MxSiy 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 chosen from Ta4HfC5, HfO2 and their mixtures.

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