WO2001068560A1

WO2001068560A1 - Method for coating parts made of material based on sic, coating compositions, and resulting coated parts

Info

Publication number: WO2001068560A1
Application number: PCT/FR2001/000739
Authority: WO
Inventors: Adrien Gasse
Original assignee: Commissariat A L'energie Atomique
Priority date: 2000-03-14
Filing date: 2001-03-13
Publication date: 2001-09-20
Also published as: FR2806406A1; EP1263695A1; JP2003527294A; FR2806406B1

Abstract

The invention concerns a method for coating a part made of material based on silicon carbide, which consists in applying on at least a surface of said part a coating composition, and in heating the assembly formed by the part and the coating composition at a temperature sufficient to cause the surface of the coating composition to melt, so as to coat with a deposit said part made of material based on silicon carbide. Said coating composition is a non-reactive composition consisting, in atomic percentages, 40 to 97 % of silicon and 60 to 3 % of another element selected among chromium, rhenium, titanium, vanadium, ruthenium, iridium, rhodium, palladium, cobalt, platinum, cerium and zirconium, and, prior to heating a SiC and/or C reinforcement is added to the composition. The invention also concerns coating compositions and coated parts obtained by said method.

Description

METHOD FOR COVERING MATERIAL PARTS

SiC-BASED, COATING COMPOSITIONS, AND COATED PARTS OBTAINED BY THIS PROCESS

DESCRIPTION

The present invention relates to a method of covering parts made of materials based on silicon carbide with a non-reactive covering composition based on silicon and another element. The invention also relates to certain coating compositions, as well as to the coated parts obtained by this process.

By materials "based on silicon carbide" is generally meant all materials whose SiC content is greater than or equal to 80% by weight. The technical field of the invention can be defined, in general, as that of covering the surface of ceramics. The term “covering” is generally understood to mean providing the surface of a ceramic with a layer of a deposit or a coating.

A covering has, for example, the function of protecting the ceramic against a corrosive environment, whether it is gaseous or liquid, such as a strongly oxidizing, sulfurized, fluorinated medium, an acidic or basic medium, etc. Thus, no only the covering must generally be resistant to a corrosive environment, but above all, it must effectively protect the ceramic. In the case of porous ceramics, or of composites which are mostly porous, this covering can provide a sealing function with respect to different liquid or gaseous media. The coating modifying the surface of the ceramic can also bring an improvement in the resistance of the ceramic to wear, to friction, to erosion, etc.

In particular, the field of the invention is that of covering the surface of a ceramic based on silicon carbide, in order, in particular, to protect it, to make it waterproof or to improve its mechanical properties using an essentially metallic layer, deposit or coating.

Indeed, the field of use of ceramic products based on SiC is very varied. For reasons of the manufacturing process, but also to lighten the ceramic, we sometimes use products that are not dense and whose porosity can be very high, which can range, for example, up to 50%. These materials therefore pose significant sealing problems. In addition, despite the remarkable properties of SiC: hardness, low coefficient of expansion, high breaking strength, good resistance to thermal shock, chemical resistance to corrosion, and to oxidation, it is necessary to provide it with covering deposits, in particular to protect sintered SiC or SiC-based composites oxidation or any corrosive environment. In particular, the sensitivity to oxidation of C / SiC composites is very high.

The covering of components, both ceramic and other materials of the same type, is described in numerous documents.

Thus, for example, the document JP-A-111 087 describes a combustion chamber made of a carbon-based composite material consisting of a carbon matrix reinforced with carbon or graphite fibers, in which a layer of SiC overlay is formed on the inner surface of the composite and a chemically deposited carbon film is formed on the outer surface of the composite. The cracks in the layer are then impregnated. of covering in SiC with tetraethyl orthosilicate and a heat treatment is carried out at a temperature of 1400 to 2000 ° C.

This technique applies to carbon-carbon composite materials and not to SiC-based ceramics and, in addition, the coating process involves a large number of steps, such as CVD deposition, impregnation, heat treatment, etc., and is long and complicated. Finally, the material deposited is SiC, it therefore departs from the field of the invention, where it is, on the contrary the part to be covered, which is made of silicon carbide.

Document JP-B2-95 119079 describes a part for a rocket engine nozzle which comprises a basic composite layer of carbon fiber - carbon, an intermediate layer comprising long and short fibers of SiC or Si ₃ N ₄ , deposited by CVD, and finally a layer of ceramic powder and / or refractory metal powder and / or short fibers impregnated with SiC or Si ₃ N ₄ , filed by CVD.

Again, this process is long and complicated and it applies to carbon-carbon composite materials and not to SiC-based ceramics. Document JP-A-53 25857 relates to the protection of a resistive film the nature of which is not specified. The protective layer consists of at least one metal and silicon carbide and / or silicon nitride. The metal is chosen from Hf, Nb, Ta, Mo, W, Re, Ru, Rh and Ir. This system is reactive and, until proven otherwise, this document does not relate to the covering of ceramics.

Document US Pat. No. 5,294,489 describes a protective coating for the reinforcing phase, for example, in C or SiC, of a composite material with a silicon carbide matrix formed by infiltration of molten silicon. This protective coating comprises an internal layer of a material resistant to reaction with molten silicon, an intermediate layer of a material reacting with the compound infiltrating into the matrix, such as molten silicon, to form a compound having a temperature melting greater than that of the infiltrating compound, such as silicon, and an outer layer of material resistant to reaction with molten silicon. The materials of the external and / or internal layers may be made of carbides, nitrides, borides, oxides, metal silicides.

This document relates to the internal protection of a composite reinforcement and not to the protection by external covering of the surface of a body or of a ceramic part, as such. The formation of the deposit is also very difficult to control because it involves the use of three layers, one of which is obtained by a delicate reaction between liquid Si and a metal.

In general, the coating of ceramics by melting and cooling a metal alloy must overcome the fundamental problem of poor wettability of ceramics by liquid metals.

The essentially reactive coating, as described in the documents cited above, could be adapted to the coating of oxide ceramics such as alumina, since the reactivity is limited and the mechanical behavior of the oxides formed satisfactory.

In the case of non-oxide ceramics such as nitride or silicon carbide which interests us more particularly, the reactivity between the active elements of the metal alloy and the ceramic is particularly exacerbated; the latter induces the formation of fragile intermetallic compounds such as silicides and carbides in the case of SiC, large porosities and cracks extending into the ceramic, which seriously limits the mechanical resistance of the coatings thus formed.

Another important problem encountered during the covering of ceramics is that these ceramics are brittle and practically devoid of any deformability, even at high temperatures.

It is therefore essential, when making a deposit on a ceramic, to limit the residual stresses which develop during cooling, due to a differential of expansion coefficient between the deposit and between the ceramic and the deposit. These residual constraints have the effect that the deposit is poorly covering, non-homogeneous and inconsistent with the ceramic.

There is therefore currently a need for a process which makes it possible in particular to achieve the covering of SiC-based ceramics with a very adherent, very homogeneous, very consistent, but also very refractory deposit, that is to say which can in particular resist temperatures up to 1600 ° C and even beyond.

None of the covering methods and covering compositions described in the documents of the prior art meets this need.

In particular, none of the methods and compositions of the prior art simultaneously meet the following criteria, highlighted by the inventors, and which are fundamental for achieving the recovery of ceramics, such as SiC, the deposits and covered parts, being preferably very refractory:

- 1. The covering composition must make it possible to produce a strong bond between the deposit and the ceramic part such as silicon carbide.

- 2. The covering composition must thoroughly wet the silicon carbide and adhere well thereto. - 3. The covering composition must have a coefficient of expansion adapted to the SiC, that is to say close to the coefficient of expansion of the latter to remove any residual stress which may appear within the coating or deposit during cooling. and guarantee that there is no crack initiation, which would be damaging to the mechanical strength of the deposit and of the coated coated part.

- 4. The recovery composition must be made up of a limited number of elements, in order to facilitate its preparation and implementation.

- 5. The deposit must be very refractory, making it possible to withstand usage temperatures of 1600 ° C and above. - 6. In addition, the deposit or coating must be covering, homogeneous and consistent with the ceramic, in order to protect the latter against corrosive environments of all kinds, and in addition ensure its tightness with respect to all environments. liquids or gases, possibly at high temperature, with which the ceramic is in contact with, and to improve its properties, such as resistance to wear, to erosion, to friction, etc.

In addition, the method must allow the covering of any type of ceramic, in particular of high porosity, and must be able to easily adapt to any specific ceramic based on silicon carbide.

The process must be simple, reliable, reproducible, short, easy to implement, include a limited number of steps.

The object of the invention is therefore to provide a method of covering parts or components made of materials based on silicon carbide which meets, inter alia, the needs mentioned above, which satisfies, inter alia, all of the requirements and criteria mentioned above, which eliminates the drawbacks, defects, limitations encountered with the processes of the prior art, and which makes it possible to produce overlays or deposits, among others, very refractory, very adherent, with high tenacity, very homogeneous, very covering and very consistent with the ceramic and free from cracking both during the preparation of the covering and in the operating conditions.

This object, and others still, are achieved according to the invention by a method of covering a part made of material based on silicon carbide, in which a covering composition is applied to at least one surface of this part, and we heat the assembly formed by the part and the covering composition at a temperature (so-called “covering” temperature) sufficient to melt the covering composition in order to cover said surface of the part in material based on SiC with a deposit, in which the covering composition is a non-reactive composition consisting, in atomic percentages, of 40 to 97% of silicon and from 60 to 3% of another element chosen from chromium, rhenium, titanium, vanadium, ruthenium, iridium, rhodium, palladium, cobalt, platinum, cerium and zirconium and in which, prior to heating, an addition of a reinforcement of SiC and / or C is carried out. The process according to the invention meets the needs, satisfies all the requirements and criteria, mentioned above, and does not have the drawbacks of the processes of the prior art and thus makes it possible to prepare coatings which are very adherent and very r refractories.

The inventors have shown, surprisingly, that for the criteria mentioned above are met, and in particular so that the covering composition, while being very refractory allows to achieve a strong bond between the deposit (coating, covering ) and the part, it was necessary that this coating composition is not reactive with SiC, that is to say is chemically compatible with SiC. In addition, it was again and again surprisingly demonstrated that for the covering composition not to be reactive with SiC, one had to place oneself in the specific range of atomic percentages mentioned above.

The very refractory specific silicides used in the. process of the invention have, in general, a higher coefficient of expansion than SiC, and their range of non-reactive composition is absolutely not predictable a priori.

These silicides are simple, since they are binary and non-tertiary silicides, or even more complex. The method according to the invention has the advantage of leading to very refractory deposits (coatings, coatings) which can withstand high temperatures which can go in air up to 1600 ° C. or beyond because the temperature at which it is carried out the overlap is also from 950 to 1,850 ° C., and the melting point of the compositions (solidus) generally varies from 900 to 1,820 ° C.

According to the invention, the coating compositions used must generally have a silicon content greater than or equal to 40 atom% so as not to be reactive with SiC.

In order for the coefficient of expansion of the covering composition to be close to, but greater than, that of silicon carbide, the percentage of silicon should preferably not exceed 97 atomic%.

A process using the coating compositions, the atomic percentages of which are situated in the range mentioned above, is simple to implement, since these compositions are non-reactive, on a submicron scale and have very good wettability properties. and adhesion to SiC. The covering composition, in itself, is inexpensive because it contains only elements of low cost.

Given the non-reactive nature of the coating composition of the invention, it is possible to dissolve the coating composition if necessary and to carry out a coating operation again. Since there is no reaction of the coating composition on the SiC, a further, subsequent coating operation, such as repair is possible. In addition to the use of a specific, non-reactive coating composition, the second essential characteristic of the process of the invention is the addition of a reinforcement of SiC and / or C before the heating of the coating composition.

It should first of all be noted that the use of such a reinforcement, which moreover is in conjunction with a covering composition, a fortiori a non-reactive covering composition, is neither disclosed nor suggested in the art. prior. The addition of a reinforcement of SiC and / or C makes it possible to perfectly adapt the coefficient of the covering including the reinforcement plus the covering alloy to the material based on SiC. It is possible, thanks to the process of the invention, to cover all known SiC-based materials.

Thus the method according to the invention allows, for example, to cover ceramics and composites based on SiC. The covering compositions, implemented in the method according to the invention, generally have an intrinsic expansion coefficient which is not adapted to the SiC-based material and it is precisely the addition of a reinforcement of SiC and / or C which makes it possible to adapt the overall expansion of the covering to that of the SiC-based material to be covered.

The reinforcement, by exactly adapting the expansion, makes it possible not only to eliminate any possible cracking consecutive to the residual thermomechanical stresses during the preparation of the overlays, but also to obtain a covering whose toughness is reinforced and is extremely high.

In other words, on the one hand, the non-reactive coating compositions, used in the process according to the invention, ensure excellent chemical compatibility with the SiC-based material, wet it well and adhere well to that -this ; on the other hand, in order to limit the residual stresses, which appear during the cooling, following the difference in expansion coefficient between the SiC-based material and the coating composition, the overall composition in the coating includes, according to the invention, a metal-silicon alloy and a reinforcement of SiC and / or C, whose coefficient of expansion is close to that of the SiC-based material. This is all the more true when the thickness of the covering is high, or when the mechanical stress is high. Thanks to the method according to the invention, which avoids any cracking induced either during the preparation of the covering, or during an operation in service of the covered part, which would be very damaging to the life of the part or component. In other words, the very good adhesion of the deposit, the lack of reactivity and the mechanical compatibility of the composition with the ceramic does not damage the deposit / SiC interface. Thus, again, the coefficient of expansion of the composition is close to SiC, which, upon cooling, generates only very little residual stress and leads to a covering deposit, homogeneous and consistent with the ceramic. This covering has, for example, the function of protecting the ceramic from various corrosions and oxidations, as described above, but it also makes it possible, in the case of porous ceramics or composites, to seal the porous body. vis-à-vis any liquid or gaseous medium. Depending on the operating conditions, this covering is strictly limited to the surface of the SiC or enters the internal porosities of the ceramic to a greater or lesser depth, as demonstrated by observation with an electron microscope. As the coating modifies the surface of the ceramic, it can also bring ^• an improvement in resistance to wear, friction, erosion, etc.

In addition to the advantages, already mentioned above, it may be indicated that the coating composition used in the invention is a silicide whose high Si content strengthens its resistance to oxidation by forming a surface layer of silica .

The composition of the coating used according to the invention also has the advantage of being not very sensitive to corrosion, for example by oleum, nitric acid and to oxidation.

In addition, since the covering composition is not reactive, the quality of the atmosphere of the furnace is less critical, thus wetting is immediate and this even with atmospheres having a non-negligible partial pressure of oxygen, such as for example, with commercial grade argon, so the recovery operation can be carried out under vacuum or under simple protection of neutral gas, but also using reducing gases, such as hydrogen.

Other advantages of the process of the invention include: - short durations of recovery operations, thanks to the absence of reaction, for example, only 5 to 15 minutes. In addition, the parameter of the duration of the covering operation is no longer critical, and if necessary, for example, in the case of covering large pieces, with thermal inertia in the oven, the holding time in temperature can be easily extended or adapted; great simplicity inducing low overall costs of the process, in fact, the covering operation is simply carried out in one go, by heating and melting the alloy composition on the surface of the ceramic;

- the very wide range of compositions and reinforcements allows easy adaptation, depending on the desired properties: such as protection against corrosion and / or oxidation of the material to be covered, sealing, resistance to wear, etc.

The preferred coating compositions for use in the process according to the invention are as follows:

- 50 to 97 at% of silicon, 50 to 3 at% of chromium (including the composition CrSi ₂ ), which corresponds for these compositions in mass quantities to 34 to 94.5% by weight of silicon and 66 to 5, 5% by weight of chromium, the covering temperature of these compositions is generally more than 1,400 ° C. up to 1,550 ° C .;

- 40 to 97 at% of silicon and 60 to 3 at% of rhenium, which corresponds for these compositions in mass quantities at 9 to 82.5% by weight of Si at 91 to 17.5% by weight of rhenium;

- 60 to 97 at% of silicon and 40 to 3 at% of titanium (including the composition TiSi ₂ ), which corresponds for these compositions in mass quantities to 46 to 95% by weight of silicon and to 54 to 5% in by weight of titanium, the coating temperature of these compositions is generally more than 1,400 ° C. up to 1,600 ° C .; - 55 to 97 at% of silicon, 45 to 3 at% of vanadium, which corresponds for these compositions in mass quantities to 40 to 95% by weight of silicon and 60 to 5% by weight of vanadium;

- 60 to 97 at% of silicon and 40 to 3 at% of zirconium (including the composition ZrSi ₂ ), which corresponds for these compositions in mass quantities to 31 to 95% by weight of silicon and 69 to 5% by weight zirconium;

- 45 to 97 at% of silicon and 55 to 3 at% of ruthenium, which corresponds for these compositions in mass quantities to 20 to 90% by weight of silicon and 80 to 10% by weight of ruthenium;

- 48 to 97 at% of silicon, 52 to 3 at% of iridium, which corresponds for these compositions in mass quantities to 12 to 82.5% by weight of silicon and 88 to 17.5% by weight of iridium ;

- 50 to 97 at% of sicilium, 50 to 3 at% of rhodium, which corresponds for these compositions in mass quantities to 21.5 to 90% by weight of silicon and 78.5 to 10% by weight of rhodium; - 50 to 97 at% of silicon, 50 to 3 at% of palladium, which corresponds for these compositions in mass quantities to 21 to 89.5% by weight of silicon and 21 to 10.5% by weight of palladium; - 58 to 97 at% of silicon, 42 to 3 at% of cobalt, which corresponds for these compositions in mass quantities to 40 to 95% by weight of silicon and 60 to 5% by weight of cobalt;

- 50 to 97 at% of silicon, 50 to 3 at% of platinum, which corresponds for these compositions in mass quantities to 12.5 to 82% by weight of silicon and 87.5% to 18% by weight of platinum;

- 53 to 97 at% of silicon and 47 to 3 at% of cerium, which corresponds for these compositions in mass quantities to 18 to 90% by weight of silicon and 82 to 10% by weight of cerium.

The method according to the invention is generally carried out by forming a powder of the covering composition, by suspending this powder in an organic binder, by applying the suspension obtained on the surface of the part to be covered, and by performing a addition of a reinforcement of SiC and / or C, prior to heating to melt said covering composition. The covering composition can be applied to a surface of the part to be covered, but preferably it is applied to the entire surface of this part.

The addition of SiC and / or of C is, as indicated above, in particular, to increase the tenacity of the deposit and to adapt the coefficient of expansion of the covering composition to that of the SiC to be covered, generally by reducing the coefficient of expansion of the covering composition. This addition of SiC and / or C is generally carried out in an amount of 3 to 60% by weight of SiC and / or C relative to the weight of the covering composition (i.e. (Si + metal) described above. It will be noted that the lower the proportion of Si in the covering composition, the greater the proportion of the reinforcement must be to compensate for the increase in the coefficient of expansion linked to the metal. Thus, depending on the coefficient of expansion of the various Si and metal alloys, it is necessary to have a greater or lesser proportion of reinforcement, with generally a minimum of 3% by weight.

This addition of a reinforcement of SiC and / or of C can be done in different ways, by adding the reinforcement of SiC and / or of C to the covering composition, before heating, in order to melt the composition, or by placing the reinforcement on the surface of the part to be covered. The reinforcement may be in any suitable form chosen from: powder, grains, pieces and particles of various shapes, fabric, nonwoven, felt, foam, etc.

More specifically: - It is possible to mix SiC and / or C powder directly with the covering composition;

- The SiC and / or C powder can be suspended in an organic binder and coat the surface of the part to be covered with the suspension obtained;

- SiC and / or C particles can be added to the coating composition;

- Finally, the reinforcement can be applied, for example in the form of a fabric, a nonwoven, a felt or a foam of silicon carbide and / or carbon on the surface of the part to be cover.

This application is carried out prior to application to the surface to be covered with the covering composition (Si + metal).

The addition of SiC and / or C (particles, tissue, etc.) makes it possible to obtain high tenacity recoveries due to the presence of particles of SiC and / or C or a tissue of SiC and / or C in the covering (coating).

To differentiate the particles from the powder, it can be indicated that the particle size of the latter is smaller. The invention also relates to a non-reactive refractory covering composition chosen from: a covering composition consisting, in atomic percentages, of 50 to 97% of silicon and 50 to 3% chromium, the composition CrSi ₂ being excluded; a coating composition made up, in atomic percentages, of 40 to 97% of silicon and 60 to 3% of rhenium;

a covering composition consisting, in atomic percentages, of 60 to 97% of silicon and 40 to 3% of titanium, the composition TiSi ₂ being excluded; - a covering composition made up, in atomic percentages, of 55 to 97% of silicon and of 45 to 3% of vanadium;

- a covering composition consisting, in atomic percentages, of 60 to 97% of silicon and 40 to 3% of zirconium, the composition ZrSi ₂ being excluded;

a covering composition made up, in atomic percentages, of 45 to 97% of silicon and 55 to 3% of ruthenium; - a covering composition consisting, in atomic percentages, of 48 to 97% of silicon and of 52 to 3% of iridium;

a covering composition made up, in atomic percentages, of 50 to 97% of silicon and of 50 to 3% of rhodium;

- a covering composition consisting, in atomic percentages, of 50 to 97% of silicon and of 50 to 3% of palladium; - a covering composition made up, in atomic percentages, of 58 to 97% of silicon and of 42 to 3% of cobalt; a coating composition consisting, in atomic percentages, of 50 to 97% of silicon and of 50 to 3% of platinum; a covering composition made up, in atomic percentages, of 53 to 97% of silicon and of 47 to 3% of cerium. The invention also relates to a composition for the non-reactive refractory coating of parts made of materials based on silicon carbide comprising a non-reactive coating composition, as defined above, and, in addition, an addition of a SiC reinforcement. and / or C.

The invention further relates to the covering, deposit or refractory lining, and the covered part, obtained by the method described above. Other characteristics and advantages of the invention will emerge more clearly on reading the description which follows, given by way of nonlimiting illustration, with reference to the accompanying drawings, in which: - Figures 1 to 10 are micrographs produced in cross section showing deposits, or overlays, made on SiC-based ceramics, by the method of the invention. These figures also show the deposit - ceramic interface and the infiltration of the ceramic by the covering which thus ensures its sealing.

The process of the invention consists, first of all, in preparing a coating composition containing silicon and, chromium, rhenium, titanium, vanadium, zirconium, ruthenium, iridium, rhodium, palladium, cobalt, platinum or cerium, in the desired proportions indicated above.

The coating composition is generally a pulverulent composition which can be prepared, for example, by first synthesizing, from the pure elements, an intermetallic compound containing silicon and chromium, rhenium, titanium, vanadium , zirconium, ruthenium, iridium, rhodium, palladium, cobalt, platinum or cerium.

The synthesis of such an intermetallic composition is done, for example, by introducing silicon - for example, in the form of pieces - and chromium, rhenium, titanium, vanadium, zirconium, ruthenium, iridium , rhodium, palladium, cobalt, platinum or cerium - for example, in the form of wire, pieces, or the like - in an alumina refractory crucible, by heating, for example, to a temperature of 1250 at 1850 ° C., to melt the various constituents of said composition and to obtain the desired final, homogeneous intermetallic compound. The intermetallic compound obtained is then ground in any suitable device, for example, in a mortar to obtain a powder of adequate particle size, that is to say, the grains have, for example, a diameter of 1 to 250 μm. Instead of being synthesized, said intermetallic compound may also be a commercial compound in the form of a powder of intermetallic compound of known particle size and purity. Among these commercial powders include, for example: the powder of the compound CrSi ₂ ^® brand CERAC, of 99.5% and particle size less than 10 microns; powder TiSi ₂ compound, GOODFELLO ^® brand, purity 99.9% and particle size less than 45 microns; the powder VSi ₂ compound, CERAC ^® brand, purity 99.5% and particle size less than 45 microns; the powder of ZrSi ₂ compound, CERAC ^® brand, purity 99.5% and particle size less than 45 microns; powder CESI ₂ compound, CERAC ^® brand, purity 99.5% and particle size less than 10 microns; and Re powder composition ₅ Si _3, Goodfellow ^® brand, purity 99.5%, and particle size smaller than 40 .mu.m. This powder consisting of two intermetallic compounds can be used as such as a coating composition.

However, in order to adjust the Si content of the coating composition, it may be necessary to mix one of the powders of intermetallic compound mentioned above with silicon powder. pure. This pure silicon powder can be prepared from pieces of pure silicon ground in any suitable device, for example, in a mortar, to obtain a powder of adequate particle size whose grains have, for example, a diameter of 1 to 250 μm .

Instead of being thus prepared, said pure silicon powder can also be a commercial powder of known particle size and purity. Among these commercial powders include, for example: pure Si powder, brand CERAC ^®, purity of 99.5% or 99.99% and a particle size less than 10 micrometres.

The powder composed of the mixture of powders of intermetallic compound and Si constitutes, in this case, the covering composition.

According to the invention, an addition of a reinforcement of SiC and / or C is carried out before heating the covering composition in order to make it melt. This addition of a SiC and / or C reinforcement can be carried out, as indicated above, in various ways.

For example, since the covering composition has a high coefficient of expansion, SiC and / or C powder is added thereto, in particular in order to reduce the coefficient of expansion and to adjust the toughness of the deposit and of the covered part, this is in particular the case when the Si content of the covering composition is not large enough for the coefficient of expansion of the deposit to be adapted to that of the SiC of the part to be covered. The SiC and / or C added represents, generally, from 3 to 60% by weight of the covering composition. The SiC powder may be, for example, a commercially available powder, such as Starck ^® brand powder, purity 98.5% and particle size less than 10 micrometres.

The coating composition powder, (Si and metal) optionally supplemented with pure SiC and / or pure C powder, is conventionally suspended in a liquid organic binder, preferably relatively viscous, which decomposes for example between 100 and 300 ° C without leaving traces. It may for example be a cement of the NICROBRAZ ^* type.

The surface of the part made of SiC-based material to be covered is degreased in an organic solvent, for example of the ketone, ester, ether, alcohol type, or a mixture of these, etc. a preferred solvent being acetone or an acetone-ethyl alcohol-ether mixture, for example in the proportions 1/3, 1/3, 1/3; then dried. The term "surface" can relate to only part of the total surface of the part, but preferably, it is the whole surface of the part.

The part made of SiC material to be covered may be alone, but it is also possible to simultaneously cover a larger number of parts up to 100.

As examples of materials based on SiC, mention may be made of pure dense silicon carbide or pressureless sintered silicon carbide ("PLS-SiC", know PressureLess Sintered SiC, Si infiltrated silicon carbide (called SiSiC or RBSC containing 5 to 20% Si); porous recrystallized silicon carbide (called RSiC); silicon graphite (C-SiC) consisting of graphite and covered by a layer of SiC, for example 0.1 to 1 mm thick; as well as SiC / SiC composites, for example, fibers or "Whiskers"; C / SiC composites, for example, with carbon fibers or “Whiskers” of carbon and SiC matrix; and again the SiC single crystals; and SiC composites with another ceramic, for example, SiC / Si ₃ N ₄ and SiC / TiN composites. It has been found, surprisingly, that the process of the invention notably allows recovery of composites based on SiC or sintered SiC with excellent results, in particular in terms of protection against oxidation and corrosion. The process of the invention is also particularly advantageous when it is applied to materials based on SiC (for example composites) of high porosity, for example, from 0 to 50%, of which it allows, in addition to protection, sealing against any gaseous or liquid medium.

The term “material based on silicon carbide” generally means here all the materials whose SiC content is greater than or equal to 80% by weight. However, certain materials to which the invention can apply and which are cited as an example above may have a silicon carbide content of less than 80%. To add the SiC and / or C reinforcement, it is also possible, for example, to previously coat the two surfaces of the parts with SiC-based materials using a pure SiC powder and / or Pure C, of the type described above, suspended in an organic binder similar to that mentioned above. It can be, for example, a solvent NICROBRAZ ^®.

The surface of the part to be covered is then coated with the suspension of the covering composition (Si and metal).

Another way of making the contribution, the addition of reinforcement of SiC and / or C is to add particles of SiC and / or C in the covering composition.

The addition of reinforcement can also be done by applying said reinforcement of SiC and / or C on the surface of the part to be covered.

In this case, the reinforcement is preferably in the form of a fabric, a nonwoven, a felt, or a foam of SiC and / or C.

Examples of such tissues include brand carbon fabrics Hexcel ^®. The thickness of such reinforcements, for example of fabric, is generally from 100 to 500 μm, and their specific mass is generally from 100 to 700 g / m ² . This thickness and this specific mass are chosen so that the mass proportion, indicated above, between the covering composition (Si and metal) and the reinforcement of SiC and / or C. is respected. The part then ready to be covered is then placed in an oven, under vacuum or under an atmosphere of neutral gas.

Generally, the vacuum is a secondary vacuum, that is to say that the pressure is 10 ^"3 to 10 ^{" 5} Pa, for example, 10 ^"4 Pa.

Preferably, the neutral gas is argon.

The invention even allows the use of commercial grade argon having a significant partial pressure of oxygen.

First of all, a first temperature level is carried out which allows degassing of the assembly and evaporation of the binder also called "debinding"; while a second temperature level allows the recovery itself.

The first stage is carried out for example at a temperature of 200 to 300 ° C, preferably 300 ° C for a period for example of 0.5 to 1 hour. The second level is carried out at a temperature corresponding to the melting temperature of the chosen covering composition, but this temperature is preferably a temperature at least 25 ° C. higher than the liquidus temperature of the composition.

Depending on the composition, this liquidus temperature varies from 900 to 1,820 ° C. The heating temperature (or temperature of the covering operation) will therefore vary, for example, from 950 ° C. to 1,850 ° C., preferably from 1,200 to 1,850 ° C. The covering is therefore carried out simply by melting and spreading said covering composition on the surface of the part.

Such a melting temperature of the compositions allows, according to another advantage of the process of the invention, use of the coated part, in particular, in air up to 1000 ° C. and even up to

1600 ° C.

The duration of the covering operation, that is to say the thermal cycle for producing the covering, according to the invention, is generally short-lived: the required landing time is for example less than 10 min. and preferably from 5 to 10 min. The covered part is then cooled to ambient temperature at the rate of, for example, 5 ° C. per minute.

The coating or deposit obtained generally has a thickness of 1 to 50 μm on the surface of the part. The covering or coating is not only covering, but sometimes penetrates into the open porosity of the room.

The parts covered with silicon carbide comprising a covering or deposit prepared by the method according to the invention can be used directly as such, but more generally they can be included in larger assemblies and allow structures, devices, components of complex shapes having high operating temperatures of up to 1600 ° C.

We know that the mechanical properties of silicon carbide: - high hardness;

- low coefficient of expansion;

- high breaking strength;

- good resistance to thermal shock;

- as well as its very good conductivity make it an essential material for present ^" and future industrial applications at high temperature.

In addition, SiC has very good chemical resistance to various acids, including hydrofluoric acid and very good resistance to oxidation in air at high temperature up to 1300 ° C.

All these properties make SiC a material of choice, in particular for the production of ceramic exchangers for thermal engineering and chemical engineering. Thus, among the applications of the covered parts obtained by the process according to the invention, mention may also be made, for example, of heat exchangers, burners, reactors, pump linings, furnace resistances in medium temperature air, but also combustion chambers for the automotive industry, composites for the aeronautical industry and all structures intended for corrosive environments at temperatures up to 1600 ° C. The high rigidity of SiC and its low density is also advantageous for applications in the space field.

The use of ceramic SiC products, in particular in sintered or composite form, is therefore very varied. For reasons of the manufacturing process, but also to lighten the ceramic, we sometimes use products that are not dense and whose porosity can be very high. The problem of the tightness of these materials "is advantageously solved by the covering process according to the invention. In addition and despite all the remarkable properties of SiC, the use of covering deposits, such as those prepared according to the invention, is necessary to protect the sintered SiC or the SiC-based composite from any oxidizing or corrosive environment (gaseous, liquid, acid, basic, sulphurized, fluorinated, and possibly at high temperature, etc.). Sensitivity to oxidation of C of C / SiC composites being very high, the use of the present process for covering parts made of these materials is particularly suitable.

Finally, in applications, such as braking systems or mechanical parts for the automobile or aeronautics, the covering according to the invention makes it possible to further improve the resistance to wear, to erosion, to abrasion, friction, etc., of SiC-based parts. The invention will now be described by means of the following examples, of course given by way of illustration and not limitation.

The examples which follow are not exhaustive, they only aim to illustrate the process of the invention by using various coating compositions with a reinforcement, different ceramics containing SiC and different thicknesses. Thus, the families of metals which have similar behaviors are Ru and Ir; Pd, Pt and Rh; Co, Ti and Cr; V and Zr; Re; And this.

The micrographs of Figures 1 to 10 attached make it possible to visualize the deposit (covering) and the infiltration of the latter into the ceramic which provides the seal.

Example 1:

This example relates to the covering of a part in "PLS α-SiC (PressureLess Sintered cc-SiC)", that is to say in silicon carbide α sintered without - pressure, by the process of the invention, in using a covering composition consisting of 90% by weight of Re and 10% by weight of Si with the addition of a reinforcement in SiC powder representing 3% by weight of the covering composition. a) Preparation of the covering composition and the piece to be covered:

Has a commercial powder of composition Re 90% by weight and Si 10% by weight, of brand

GOODFELLOW ^® , with a purity of 99.9% and a particle size of less than 20 μm, is added 3% by weight of pure SiC powder.

The SiC surface to be covered is degreased in an organic solvent, then dried. The assembly formed of the alloy composition and the SiC powder is mixed with an organic binder which is a type of cement NICROBRAZ ^® and applied over the entire surface of the SiC coating.

b) Recovery

The prepared SiC part is placed in the oven. A first level at 300 ° C for 1 hour is carried out to remove the organic binder, then the actual recovery is carried out under the following conditions:

- temperature: 1,800 ° C;

- duration of the stage: 10 min. ; - atmosphere: atmospheric pressure of argon.

The covered part obtained is then cooled to room temperature, at the rate of

5 ° C per minute. c) Observation of the deposit:

On leaving the oven, the molten composition forms a thick, dense and covering deposit on the ceramic. A micrograph, taken in cross section, shows the deposit protecting the ceramic

(cf. figure 1).

Example 2:

This example relates to the covering of a part in “PLS α-SiC (PressureLess Sintered α-SiC)”, that is to say in pressureless sintered α silicon carbide, by the process of the invention, using a covering composition consisting of VSi ₂ , with the addition of a SiC powder reinforcement representing 50% by weight of the covering composition.

a) Preparation of the covering composition and the piece to be covered:

A commercial powder of compound VSi ₂ CERAC ^® brand, with a purity of 99.5% and a particle size less than 45 microns, is added 50% by weight of SiC powder, SiC surface to be covered is degreased in an organic solvent, then dried. The composition formed of VSi ₂ and SiC powder is mixed with an organic binder which is a cement of the type NICROBRAZ ^® and applied to the surface of the SiC to be covered.

b) Recovery:

The prepared SiC part is placed in the furnace under secondary vacuum. A first level at 300 ° C for 1 hour is carried out to remove the organic binder, then the actual recovery is carried out under the following conditions:

- temperature: 1,700 ° C;

- duration of the stage: 5 min. ;

- atmosphere: argon with 1 atmosphere.

c) Observation of the deposit

On leaving the oven, the melted composition forms a dense dense covering covering the ceramic. A micrograph carried out in cross section shows the deposit composed of VSi ₂ and SiC protecting the ceramic and the infiltration of the ceramic ensuring the seal (cf. FIG. 2).

Example 3

This example relates to the covering of a part in “PLS α-SiC (PressureLess Sintered α-SiC)”, that is to say in pressureless sintered α silicon carbide, by the process of the invention, using a covering composition consisting of 29% by weight of chromium and 71% by weight of silicon, with the addition of a reinforcement in SiC powder representing 5% by weight of the covering composition.

a) Preparation of the covering composition and the piece to be covered:

A commercial powder of CrSi ₂ CERAC compound ^® brand, purity 99.5% and particle size less than 10 microns, is mixed with an Si powder of pure CERAC ^® brand of purity 99.5% and particle size less than 10 μm, in the following mass proportions: 60.4% by weight of CrSi ₂ and 39.6% by weight of Si. This mixture corresponds to an overall composition of 29% by weight of Cr and 71% by weight of Si. To this composition is added 5% by weight of SiC. The SiC surface is degreased in an organic solvent, then dried. The formed composition of the alloy and SiC powder is mixed with an organic binder, which is cementum NICROBRAZ ^® type and applied uniformly over the SiC surface to be covered.

b) Recovery:

The prepared SiC part is placed in the oven. A first plateau at 300 ° C for 1 hour is carried out to remove the organic binder, then the actual recovery is carried out under the following conditions:

- temperature: 1360 ° C;

- stop time: 5 min. ; - secondary vacuum: 10 ^"5 mbar.

The covered part obtained is then cooled to room temperature, at a rate of 5 ° C per minute.

c) Observation of the deposit:

On leaving the oven, the melted composition forms a dense dense covering covering the ceramic. A micrograph carried out in cross section shows the deposit protecting the ceramic and the infiltration of the ceramic ensuring the seal (see Figure 3).

Example 4:

This example relates to the covering of a part in “PLS α-SiC (PressureLess Sintered α-SiC)”, that is to say in pressureless sintered α silicon carbide, by the process of the invention, using a coating composition consisting of 25% by weight of titanium and 75% by weight of silicon, with the addition of a reinforcement of SiC powder representing 5% by weight of the coating composition. a) Preparation of the covering composition and the piece to be covered:

A commercial powder of the TiSi ₂ compound of GOODFELLOW ^® brand, of purity 99.9%, and of particle size less than 45 μm is mixed with a powder of pure Si, of CERAC ^® brand, of purity 99.99%, and of granulometry less than 10 μm, in the following mass proportions: 54.3% by weight of TiSi ₂ and 45.6% by weight of Si. This mixture corresponds to an overall composition of 25% by weight of Ti and 75% by weight of Si. To this composition is added 5% by weight of SiC powder. The Sic surface to be covered is degreased in an organic solvent, then dried. The formed composition of the alloy and the SiC powder is mixed with an organic binder, which is a type of cement NICROBRAZ ^® and applied to the SiC surface to be covered.

b) Recovery:

- temperature: 1360 ° C;

- stop time: 5 min. ;

- secondary vacuum: 10 ^"5 mbar. The covered part obtained is then cooled to room temperature, at a rate of 5 ° C per minute.

c) Observation of the deposit:

On leaving the oven, the melted composition forms a dense dense covering covering the ceramic. A micrograph carried out in cross section shows the deposit protecting the ceramic and the infiltration of the ceramic ensuring the seal (see Figure 4).

Example 5:

This example relates to the covering of a part in “PLS α-SiC (PressureLess Sintered α-SiC)”, that is to say in pressureless sintered α silicon carbide, by the process of the invention, using a covering composition consisting of 50% by weight of TiSi ₂ , with the addition of a reinforcement in SiC powder representing 50% by weight of the covering composition. a) Preparation of the covering composition and the piece to be covered:

A commercial powder of Goodfellow mark TiSi compound ₂ ^®, purity 99.9% and particle size less than 45 microns, is mixed with SiC powder in the following mass proportions: 54% by weight of TiSi _2, and 50 % by weight of SiC. The SiC surface to be covered is degreased in an organic solvent, then dried. The formed alloy composition and SiC powder is mixed with an organic binder which is a type of cement NICROBRAZ ^® and applied to the SiC surface to be coated.

b) Recovery:

- temperature: 1,530 ° C;

- duration of the stage: 5 min. ;

- atmosphere: argon with 1 atmosphere. The covered part obtained is then cooled to room temperature, at a rate of 5 ° C per minute. c) Observation of the deposit:

On leaving the oven, the melted composition forms a dense dense covering covering the ceramic. A micrograph carried out in transverse section shows the deposit composed of SiC and TiSi ₂ protecting the ceramic and the infiltration of the ceramic ensuring the seal (cf. FIG. 5).

Example 6:

This example relates to the covering of a part in “PLS α-SiC (PressureLess Sintered α-SiC)”, that is to say in pressureless sintered α silicon carbide, by the process of the invention, using a covering composition consisting of 43% by weight of cerium and 57% by weight of silicon, with the addition of a reinforcement of SiC powder representing 5% by weight of the covering composition.

a) Preparation of the covering composition and the piece to be covered:

A commercial powder of CESI ₂ CERAC compound ^® brand, purity 99.5% and particle size less than 10 microns is mixed with a pure Si powder brand CERAC ^* of 99.5% and particle size less than 10 μm in the following mass proportions: 59.3% by weight of CeSi ₂ , and 40.7% by weight of Si. This mixture corresponds to an overall composition of 43% by weight of Ce and 57% by weight of Si. To this composition is added 3% by weight of SiC powder. The surface of the SiC to be covered is cleaned in an organic solvent, then dried. The formed composition of the alloy and the SiC powder is mixed with an organic binder which is a type of cement NICROBRAZ ^® and applied over the entire surface of the SiC coating.

b) Recovery

- temperature: 1300 ° C;

- stop time: 5 min. ; - secondary vacuum: 10 ^"4 mbar.

The . covered part obtained is then cooled to room temperature, at a rate of 5 ° C per minute.

c) Observation of the deposit:

On leaving the oven, the molten composition forms a thick, dense and covering deposit on the ceramic. A micrograph performed in transverse function shows the deposit protecting the ceramic and the infiltration of the ceramic ensuring the tightness (cf. figure 6).

Example 7:

This example relates to the covering of a part in “PLS α-SiC (PressureLess Sintered α-SiC)”, that is to say in pressureless sintered α silicon carbide, by the process of the invention, using a covering composition consisting of 63% by weight of rhodium and 37% by weight of silicon, with the addition of a reinforcement in SiC powder representing 3% by weight of the covering composition.

a) Preparation of the covering composition and the piece to be covered:

To a commercial powder of composition Rh 63% by weight - Si 37% by weight of GOODFELLOW ^® brand with purity 99.9% and particle size less than 20 μm, is added 3% by weight of SiC powder. The SiC surface to be covered is degreased in an organic solvent, then dried. The formed composition of the alloy and the SiC powder is mixed with an organic binder which is a type of cement NICROBRAZ ^® and applied over the entire surface of the SiC coating. b) Recovery:

The prepared SiC part is placed in the oven. A first level at 300 ° C for 1 hour is carried out to remove the organic binder, then the actual brazing is carried out under the following conditions:

- temperature: 1200 ° C;

- stop time: 5 min. ; - secondary vacuum: 10 ^"4 mbar.

c) Observation of the deposit:

On leaving the oven, the molten composition forms a thick, dense and covering deposit on the ceramic. A micrograph carried out in cross section shows the deposit protecting the ceramic and the infiltration of the ceramic ensuring the seal (see Figure 7).

Example 8

This example relates to the covering of a part in “PLS α-SiC (PressureLess Sintered α-SiC)”, that is to say in pressureless sintered α silicon carbide, by the process of the invention, using a recovery composition made up of 26.5% in weight of zirconium and 73.5% by weight of silicon, with the addition of a SiC powder reinforcement representing 3% by weight of the covering composition.

a) Preparation of the covering composition and the piece to be covered:

A commercial powder of ZrSi ₂ CERAC compound ^® brand, purity 99.5% and particle size less than 45 microns was mixed with a Si powder de- pure ^® brand CERAC, of 99.5% purity and particle size less than 10 μm, in the following mass proportions: 43% by weight of ZrSi ₂ and 57% by weight of Si. This mixture corresponds to an overall composition of 26.5% by weight of Zr and 73.5% by weight of Si. To this latter composition is added 3% by weight of SiC powder. The surface of the SiC to be covered is cleaned in an organic solvent, then dried. The formed composition of the alloy and the SiC powder is mixed with an organic binder which is a type of cement NICROBRAZ ^® and applied over the entire surface of the SiC coating.

b) Recovery:

The ready-to-cover SiC part is placed in the oven. A first level at 300 ° C for 1 hour is carried out to remove the binder organic, then the actual soldering is carried out under the following conditions:

- covering temperature: 1400 ° C;

- stop time: 5 min. ; - secondary vacuum: 10 ^"5 mbar.

c) Observation of the deposit:

On leaving the oven, the molten composition forms a thick, dense and covering deposit on the ceramic. A micrograph carried out in cross section shows the deposit protecting the ceramic and the infiltration of the ceramic ensuring the seal (see Figure 8).

Example 9:

This example relates to the covering of a C / SiC composite part, by the method of the invention, using a covering composition consisting of 26.5% by weight of zirconium and 73.5% by weight of silicon, with the addition of a SiC powder reinforcement representing 3% by weight of the covering composition. a) Preparation of the covering composition and the piece to be covered:

A commercial powder of CERAC mark ZrSi compound ₂ ^®, purity of 99.5% and particle size less than 45 microns was mixed with a Si powder of pure CERAC ^® brand of purity 99.5% and particle size less than at 10 μm in the following mass proportions: 43% by weight of ZrSi ₂ and 57% by weight of Si. This mixture corresponds to an overall composition of 26.5% by weight of Zr and 73.5% by weight of Si. To this composition is added 3% by weight of SiC powder. The surface of the composite to be covered is cleaned in an organic solvent, then dried. The formed composition of the alloy and the SiC powder is mixed with an organic binder which is a type of cement NICROBRAZ ^® and applied over the entire surface of the composite to be coated.

b) Recovery:

The ready-to-cover C / SiC composite part is placed in the oven. A first level at 300 ° C for 1 hour is carried out to remove the organic binder, then the soldering itself is carried out under the following conditions:

- covering temperature: 1400 ° C;

- duration of the stage: 5 min. ;

c) Observation of the deposit:

On leaving the oven, the molten composition forms a thick, dense and covering deposit on the composite. A micrograph carried out in transverse section shows the deposit protecting the composite ^" and the infiltration of the composite ensuring the seal (cf. FIG. 9).

Example 10

This example relates to the covering of a very porous sintered SiC part, by the process of the invention, using a covering composition consisting of 26.5% by weight of zirconium and 72.5% by weight of silicon, with the addition of a SiC powder reinforcement representing 3% by weight of the covering composition.

a) Preparation of the covering composition and the piece to be covered:

A commercial powder of CERAC mark ZrSi compound ₂ ^® of 99.5% and particle size less than 45 microns was mixed with a pure Si powder of CERAC ^® brand, purity 99.5%, and particle size less than 10 μm in the following mass proportions: 43% by weight of ZrSi ₂ and 57% by weight of Si. This mixture corresponds to an overall composition of 26.5% by weight of Zr and 73.5% by weight of Si. To this latter composition is added 3% by weight of the SiC powder. The piece of porous SiC to be covered is cleaned in an organic solvent, then dried.

Note that the porosity of this ceramic is very high, around 40%.

The formed composition of the alloy and the SiC powder is mixed with an organic binder which is a type of cement NICROBRAZ ^® and applied over the entire surface of the SiC coating.

b) Recovery

The SiC part, ready to cover, is placed in the oven. A first level at 300 ° C for 1 hour is carried out to remove the organic binder, then the soldering itself is carried out under the following conditions:

- covering temperature: 1400 ° C;

- stop time: 5 min. ; - secondary vacuum: 10 ^"5 mbar.

The covered part obtained is then cooled to room temperature, at a rate of 5 ° C per minute. c) Observation of the deposit:

On leaving the oven, the melted composition forms a dense dense covering covering the very porous ceramic. A micrograph carried out in transverse section shows the deposit protecting the ceramic and the infiltration of very porous ceramic ensuring sealing (cf. FIG. 10).

Claims

1. Method for covering a part made of material based on silicon carbide, in which a covering composition is applied to at least one surface of this part, and the assembly formed by the part and the covering composition is heated at a temperature sufficient to melt the surface of the covering composition, in order to cover with a deposit said piece of material based on silicon carbide, in which the covering composition is a non-reactive composition made up, in atomic percentages, from 40 to 97% of silicon and from 60 to 3% of another element chosen from chromium, rhenium, titanium, vanadium, ruthenium, iridium, rhodium, palladium, cobalt, platinum , cerium and zirconium, and in which, before heating, an addition of SiC and / or C is made.

2. Method according to claim 1, wherein the recovery is carried out at a temperature of 950 to 1850 ° C.

3. The method of claim 2, wherein said coating composition consists, in atomic percentages, of 50 to 97% silicon and 50 to 3% chromium.

4. The method of claim 2, wherein said coating composition consists, in atomic percentages, of 40 to 97% of silicon and 60 to 3% of rhenium.

5. The method of claim 2, wherein said coating composition consists, in atomic percentages, of 60 to 97% of silicon and 40 to 3% of titanium.

6. The method of claim 2, wherein said coating composition consists, in atomic percentages, of 55 to 97% silicon and 45 to 3% vanadium.

7. The method of claim 2, wherein said coating composition ^" consists, in atomic percentages, of 60 to 97% of silicon and 40 to 3% of zirconium.

8. The method of claim 2, wherein said coating composition consists, in atomic percentages, of 45 to 97% of silicon and 55 to 3% of ruthenium.

9. The method of claim 2, wherein said coating composition consists, in atomic percentages, of 48 to 97% of silicon and of 52 to 3% of iridium.

10. The method of claim 2, wherein said coating composition consists, in atomic percentages, of 50 to 97% of silicon and of 50 to 3% of rhodium.

11. The method of claim 2, wherein said coating composition consists, in atomic percentages, of 50 to 97% of silicon and of 50 to 3% of palladium.

12. The method of claim 2, wherein said coating composition is made up, in atomic percentages, of 58 to 97% of silicon and of 42 to 3% of cobalt.

13. The method of claim 2, wherein said coating composition consists, in atomic percentages, of 50 to 97% of silicon and of 50 to 3% of platinum.

14. The method of claim 2, wherein said coating composition consists, in atomic percentages, of 53 to 97% of silicon and of 47 to 3% of cerium.

15. Method according to any one of claims 1 to 14, in which a powder of covering composition is formed, this powder is suspended in an organic binder, the suspension obtained is applied to the surface of the part to be covered, and adding a reinforcement of SiC and / or C prior to heating.

16. Method according to any one of claims 1 to 15, wherein said addition of a reinforcement of SiC and / or C is carried out in an amount of 3 to 60% by weight of SiC and / or C relative to the weight of the covering composition.

17. Method according to any one of claims 1 to 16, in which said addition of a reinforcement of SiC and / or of C is carried out by adding said reinforcement of SiC and / or of C to the covering composition, before the heating, or by placing the reinforcement on the surface of the part to be covered.

18. A method according to any one of claims 1 to 17, wherein said SiC reinforcement and / or C is in a form chosen from a powder, grains, pieces, particles, a fabric, a nonwoven, a felt and a foam.

19. Method according to any one of claims 16 to 18, in which said addition of SiC and / or C is carried out by directly mixing SiC and / or C powder with the coating composition.

20. Method according to any one of claims 16 and 18 in which said addition of a reinforcement of SiC and / or C is carried out by placing the powder of SiC and / or C in suspension in an organic binder and by coating the surface of the part to be covered with the suspension obtained.

21. Method according to any one of claims 16 to 18, in which said addition of a reinforcement of SiC and / or C is carried out by adding particles of SiC and / or C to the coating composition.

22. Method according to any one of claims 16 to 18, in which said addition of a reinforcement of SiC and / or C is carried out by applying a fabric, nonwoven, felt or foam, of silicon carbide and / or carbon on the surface of the part to be covered.

23. Method according to any one of claims 1 to 22, in which the materials based on silicon carbide are chosen from pressurized sintered silicon carbide ("PLS-SiC"); Si infiltrated silicon carbide ("SiSiC" or "RBSC"); the porous recrystallized silicon carbide ("RSiC"); silicon graphite ("C-SiC") consisting of graphite and covered by a layer of SiC; SiC / SiC composites; for example, with fibers or "whiskers"; C / SiC composites, for example, with carbon fibers or “whiskers” and with an SiC matrix; single crystals of SiC; SiC composites with another ceramic, for example SiC / Si ₃ N ₄ and SiC / TiN composites.

24. The method as claimed in any one of claims 1 to 23, in which said materials based on silicon carbide have a silicon carbide content greater than or equal to 80% by weight.

25. Method according to any one of claims 1 to 24, in which said material based on silicon carbide has a porosity of 0 to 50%.

26. Non-reactive refractory covering composition chosen from: a covering composition consisting, in atomic percentages, of 50 to 97% of silicon and of 50 to 3% of chromium, the composition CrSi ₂ being excluded;

- a covering composition made up, in atomic percentages, of 40 to 97% of silicon and of 60 to 3% of rhenium;

- a covering composition consisting, in atomic percentages, of 60 to 97% of silicon and 40 to 3% of zirconium, the composition ZrSi ₂ being excluded; a coating composition made up, in atomic percentages, of 45 to 97% of silicon and 55 to 3% of ruthenium;

- a covering composition consisting, in atomic percentages, of 48 to 97% of silicon and of 52 to 3% of iridium;

- a covering composition consisting, in atomic percentages, of 50 to 97% of silicon and of 50 to 3% of palladium; - a covering composition made up, in atomic percentages, of 58 to 97% of silicon and of 42 to 3% of cobalt;

- a covering composition made up, in atomic percentages, of 50 to 97% of silicon and of 50 to 3% of platinum;

a covering composition made up, in atomic percentages, of 53 to 97% of silicon and of 47 to 3% of cerium.

27. Composition for the non-reactive refractory covering of parts made from base materials of silicon carbide comprising a non-reactive coating composition according to claim 26 and, in addition, an addition of a reinforcement of SiC and / or C.

28. A refractory covering, deposit or coating capable of being obtained by the process according to any one of claims 1 to 25.