Method for assembling parts made of sic-based materials by bonding and infiltration

Abstract

The invention relates to a method for assembling parts (11, 12) made of silicon carbide-based materials by bonding, pre-assembling with a mixture of a crosslinkable organic resin and SiC powder, then infiltration of liquid silicon or a liquid non-reactive alloy MSi.

Description

[0001] PROCESS FOR ASSEMBLING PARTS MADE OF SIC-BASED MATERIALS BY BONDING AND

[0002] INFILTRATION

[0003] TECHNICAL FIELD OF THE INVENTION

[0004] The present invention relates to a method of assembling parts made of silicon carbide-based materials by bonding and infiltration, in particular to produce silicon carbide-based components.

[0005] By “silicon carbide-based” materials, we generally mean a material whose SiC content is greater than or equal to 50% by mass, preferably greater than or equal to 80% by mass, more preferably 100% by mass, in the latter case, we can say that the material is made of or composed of silicon carbide.

[0006] Silicon carbide may be in the form of (i) silicon carbide fibers, (ii) sintered or ceramic-bonded silicon carbide powder, (iii) a monolithic silicon carbide part, or (iv) a silicon carbide composite prepared by chemical vapor deposition (CVD) or chemical vapor infiltration (CVI).

[0007] These silicon carbide-based materials may include pure silicon carbide such as pure silicon carbide a (SiCa) or P (SiCP), silicon-infiltrated silicon carbide substrates (SiSiC), or SiC-based composite materials such as silicon carbide fiber composite materials, and silicon carbide matrix composite materials, namely SiC-based ceramic matrix composites (CMCs).

[0008] The technical field of the invention can be generally defined as that of the assembly of parts based on silicon carbide SiC.

[0009] The assemblies prepared by the process according to the invention can be used in the manufacture of components with complex shapes requiring good mechanical strength between the silicon carbide-based substrates and, possibly, satisfactory sealing on either side of the joint. STATE OF THE ART

[0010] Silicon carbide-based materials, such as SiC ceramics and SiC-based ceramic matrix composites (CMCs), are materials with high wear and oxidation resistance at high temperatures.

[0011] However, the preparation processes for these materials such as sintering, chemical vapor deposition (CVD), chemical vapor infiltration (CVI), polymer infiltration and pyrolysis (PIP), and reactive melt infiltration (RMI) make it difficult to manufacture large and / or complex shaped parts from these materials.

[0012] At the end of these processes, a machining operation of the components obtained is necessary, but the high hardness of these materials makes them difficult to machine and the machining of these components is also unacceptable for cost reasons.

[0013] It is therefore often preferable to manufacture large and / or complex shaped parts or structures in these materials from simple and / or small shaped ceramic elements, then to assemble these elements to create the final structure.

[0014] Such a technique is particularly necessary for manufacturing heat exchanger-type structures and silicon carbide structural components with a working temperature of up to, for example, 900°C or even 1000°C and even 1200°C.

[0015] Due to the high temperatures, for example around 900°C to 1000°C or even 1200°C, used in ceramic and CMC applications, the assembly of these ceramics and CMC by bonding with organic adhesives is excluded, because the operating temperatures for this type of assembly cannot exceed a maximum of 200°C.

[0016] Purely mechanical joining techniques, such as stapling, riveting, or screwing, only provide partial and random contact between the parts. The resulting joints cannot be watertight. Mechanical strength is only provided by staples, rivets, and screws, which is limited. To ensure good mechanical strength of the joint, it is essential to create good adhesion between the parts to be joined, which is not possible with screws, rivets, or staples.

[0017] Furthermore, mechanical joining techniques such as riveting are not suitable for ceramic materials which are sensitive to cracking phenomena caused by localized stresses at the junction.

[0018] Furthermore, ceramic fusion only occurs at very high temperatures, and sometimes in a non-congruous manner, being associated with the volatilization of certain components. Such volatilization occurs in particular for SiC ceramics. Fusion welding is therefore not an option, especially in the presence of fibers that would be degraded during heating.

[0019] Accordingly, existing joining techniques for ceramic materials and their ceramic composites involve solid-state diffusion or wetting of a liquid-phase filler material.

[0020] A distinction is made between solid-state assembly techniques and liquid-state assembly techniques.

[0021] Solid-state joining techniques include techniques involving direct bonding, sintering techniques with the addition of a joining material, and diffusion reactive welding techniques.

[0022] • Direct connection

[0023] Without filler material, ceramic materials can be bonded by direct bonding. This type of technique mainly involves diffusion and plastic deformation phenomena due to the application of heat and pressure. This technique can be applied using a hot pressing process, or flash sintering (SPS).

[0024] • Sintering with addition of an assembly material

[0025] The sintering process is also applicable to the assembly of ceramics by adding a powder between the elements to be joined. To promote adhesion of the joint to the substrate, sintering can be reactive sintering using metallic elements.

[0026] A homogeneous assembly is also possible by using a joint composition identical to that of the ceramic substrate. For example, a silicon carbide joint can be created to achieve a SiC / SiC assembly. The homogeneity of composition between the substrate and the joint also prevents the formation of residual stresses due to a difference in thermomechanical properties.

[0027] • Reactive diffusion welding

[0028] Diffusion welding consists of bonding two elements with an intermediate metallic material remaining in the solid state. Under pressure (of the order of 0.1 MPa-100 MPa) and at temperatures of 50% to 90% of the melting temperature of the metal, it reacts with the ceramic substrate to form intermediate phases, such as silicides and carbides. The reactivity of the intermediate layers with the substrate allows good chemical adhesion between the materials, but can induce the formation of phases that weaken the joint, such as NiCr3Si2 and ClSiC for Ni-Cr layers.

[0029] The intermediate layer can also be composed of a low-melting alloy plated onto a more refractory metal core. During heat treatment, the alloy melts and wets the surface of the substrate, before diffusing into the metal core, which remains in the solid state. This variant of the diffusion reactive welding process has the advantage of producing a joint whose application temperature is higher than the assembly temperature. In addition, it involves the wetting phenomenon, and can thus reduce the assembly pressure to values ​​of the order of kPa.

[0030] Generally speaking, the various techniques based on diffusion, such as direct bonding, sintering or reactive welding require the application of pressure, which has many disadvantages, particularly when implemented on complex geometries. These techniques can mechanically damage the material, be difficult to apply uniformly, and require complex tools for applying pressure and holding the parts in position.

[0031] Liquid-state joining techniques include brazing, techniques using oxide joints, and techniques using SiC joints prepared by pyrolyzing a preceramic polymer.

[0032] • Soldering

[0033] The brazing process involves an intermediate layer, an interlayer, composed of metallic elements, which is heated above its melting point. This layer is chosen for the purpose of wetting the ceramic substrate. It can be non-reactive or, on the contrary, it can react with the ceramic substrate to form intermediate phases. This reactivity with the substrate further promotes the wetting of the brazing joint.

[0034] Reactive brazing has the advantage of generally not requiring the application of pressure. The presence in the joint of phases with coefficients of thermal expansion different from that of the substrate material, however, leads to the formation of residual stresses during cooling, which increase with the thickness of the joint. This results in a reduction in the strength of the joint due to these residual stresses.

[0035] A non-reactive brazing technique is described in documents [1-3] which describe a method of joining parts made of SiC-based materials by non-reactive brazing with a non-reactive brazing composition which is a binary alloy or a tertiary alloy comprising a high atomic percentage of silicon.

[0036] Silicon limits reactive attack of the solder on the substrate while allowing good wetting of the alloy on the SiC. In addition, silicon and SiC have similar coefficients of expansion, which limits the presence of residual stresses after assembly. These two phases are, moreover, in chemical equilibrium.

[0037] However, brazing techniques, and in particular the non-reactive brazing technique described above, are carried out at high temperatures and they have the disadvantage of requiring complex tooling, such as specific molds, to precisely position the parts, then to hold them in place during brazing at these high temperatures.

[0038] • Oxide seals

[0039] Patent application FR-A1-2 984 784 concerns the assembly of SiC-based parts by non-reactive brazing in an oxidizing atmosphere with a brazing composition consisting of oxides (Alumina, Silica, CaO, MgO) [4],

[0040] Glass or glass-ceramic joints are also used for the assembly of ceramic materials. These joints can be prepared, for example, from suspensions of powders in ethanol, and do not systematically require assembly pressure.

[0041] These seals have higher coefficients of expansion than silicon carbide, but they can also exhibit advantageous self-healing properties at temperatures above their curing temperature. However, the operating temperature of these seals is limited to a maximum of 800°C, which is very restrictive.

[0042] Finally, just like brazing, this technique has the disadvantage of requiring complex tools, such as specific molds, to precisely position the parts and then hold them in place at high temperature.

[0043] • SiC seals prepared by pyrolyzing a preceramic polymer

[0044] Silicon carbide components can also be joined using ceramic precursor polymers or preceramic polymers. The polymer is first coated between SiC components, then the polymer is crosslinked and pyrolyzed to obtain a ceramic joint between the components.

[0045] This technique allows for joint compositions close to the ceramic materials to be assembled and thus implies satisfactory thermal and chemical compatibility. Unlike homogeneous assemblies by direct bonding or sintering, this technique can also be carried out without assembly pressure.

[0046] The joints thus formed, however, have low mechanical resistance due to the formation of porosities and cracks during the contraction of the material during pyrolysis.

[0047] These performances can be improved but this then requires the application of pressure during assembly or the implementation of successive re-infiltrations and pyrolysis which makes the process complex and expensive.

[0048] • RMI process

[0049] A technique for joining SiC or SiC-based composites by reactive melt infiltration (RMI) has also been developed [5]. A suspension of carbon powder in a phenolic resin is first cured at 110-120°C to obtain a porous network. This is then infiltrated at 1250-1425°C by a liquid phase of silicon or silicon alloy, whereby a reaction between the carbon and the silicon occurs, leading to the formation of silicon carbide SiC.

[0050] This technique is carried out without pressure and allows the pre-assembly of parts at low temperature during the curing of the carbon powder and resin suspension [6], which avoids the use of tooling for holding parts at high temperature. However, this technique has the disadvantage of being a reactive technique.

[0051] Indeed, the carbon powder and the carbon obtained via the pyrolysis of the resin which are used during the porous network formation step then react with the silicon, during the infiltration step, in an exothermic reaction, thus causing heating of the parts. This exothermicity can create a runaway reaction and further promote the creation of a plug and therefore poor infiltration, this phenomenon is known as "shocking-off".

[0052] Furthermore, the width of the joint that can be obtained by this technique is limited, because the reaction that occurs during the infiltration step leads to the precipitation of carbides such as SiC along the infiltration path, which can lead to the obstruction of the network pores and the blocking of the liquid propagation.

[0053] The aim of the present invention is, among other things, to provide a method for assembling at least two parts made of a silicon carbide-based material, which does not have the drawbacks, defects, limitations and disadvantages of the assembly methods of the prior art, as described in particular above, and which solves the problems which arise in the methods of the prior art.

[0054] STATEMENT OF THE INVENTION

[0055] This aim, and others, are achieved, in accordance with the invention, by a method for assembling at least two parts made of a silicon carbide-based material, each of the parts comprising a surface to be assembled, in which the following successive steps are carried out: a) A silicon carbide powder and a crosslinkable organic resin are interposed between the surfaces to be assembled of the parts and in contact with said surfaces to be assembled; b) The mixture of silicon carbide powder and crosslinkable organic resin and the parts placed in position are heated to a temperature below 200°C, preferably below 100°C, to crosslink the crosslinkable organic resin, and to create, between the surfaces to be assembled, a network formed by the crosslinked organic resin in which silicon carbide particles are distributed;c) The network created in step b) is brought into contact, without applying pressure, with silicon or a non-reactive alloy MSi containing silicon and at least one metal M, and the parts, the network formed by the crosslinked organic resin in which silicon carbide particles are distributed, and the silicon or the non-reactive alloy MSi are heated to carry out: the pyrolysis of the crosslinked organic resin and the formation of a porous network essentially comprising silicon carbide; then the deoxidation of the silicon carbide; then the melting of the silicon or the non-reactive alloy MSi and the infiltration of the liquid silicon or the non-reactive alloy MSi into the porous silicon carbide network; d) The parts are cooled, whereby a joint is obtained between the surfaces to be joined and the joining of the two parts.;

[0056] The method according to the invention comprises a specific series of specific steps which has never been described or suggested in the prior art, in particular as set out above.

[0057] The method according to the invention can be defined as a non-reactive assembly method which notably comprises two successive and obligatory steps, namely steps b) and c), namely:

[0058] In the method according to the invention, step b) can be described as a pre-assembly, or bonding, step at low temperature, during which the parts to be assembled are bonded using a mixture of a silicon carbide powder and a crosslinkable organic resin, creating, between the surfaces to be assembled, a network formed by the crosslinked crosslinkable organic resin in which silicon carbide particles are distributed.

[0059] This network formed by the crosslinked organic resin in which silicon carbide particles are distributed, forms a joint between the parts to be assembled, which are thus glued, pre-assembled, provisionally assembled, held in place, by means of this joint with a view to the final definitive assembly which is carried out during step c) which follows.

[0060] Step c) can be described as an infiltration step, by Si or by a non-reactive silicon-based alloy (MSi), of the network formed by the crosslinked organic resin and the silicon carbide powder, obtained at the end of step b). In other words, in the method according to the invention, the parts made of a silicon carbide-based material are first pre-assembled and bonded at low temperature, then a final assembly of these parts is carried out by a non-reactive liquid infiltration process.

[0061] Unlike the method according to the invention, the brazing techniques do not include a pre-assembly step b). This step b) of the method according to the invention allows the precise positioning of the parts together at low temperature and their holding in place without tools during infiltration. Thus, the method according to the invention does not require the use of specific molds for positioning the parts at high temperature since this crosslinking is done with the parts to be assembled placed in position and the mixture of silicon carbide powder and crosslinkable organic resin at the interface of these parts to be assembled.

[0062] According to an important characteristic of the method according to the invention, which distinguishes it in particular from solid state assembly techniques, no pressure is applied during step c) of the method according to the invention.

[0063] As a result, the method according to the invention is greatly simplified and does not require the use of complex, energy-consuming equipment to apply pressure to the parts.

[0064] Furthermore, step a) and / or step b) and / or step d) of the method according to the invention can also be carried out without applying pressure to the parts and in particular to the surfaces to be assembled. It should be noted, however, that it may be necessary to apply moderate pressure to hold the parts together, particularly during pre-assembly (step b)). By "moderate pressure" is meant a pressure of less than 20 MPa and, preferably, between 5 MPa and 15 MPa. Such pressure is very low, unlike high-temperature pressure as implemented in the prior art.

[0065] According to yet another important characteristic, the method according to the invention is a non-reactive method.

[0066] First of all, the process according to the invention is a non-reactive process because it does not use carbon powder to produce the porous network mainly composed of SiC powder. The process according to the invention is non-reactive, so nothing other than the SiC and Si / MSi already present is formed, no new carbide or ternary component being formed. Furthermore, the crosslinkable organic resin used has a very low carbon yield after pyrolysis, i.e. a yield of less than 5%, in particular less than 4%, in particular less than 3%, more particularly less than 2% and even more particularly less than 1% by mass relative to the initial mass of resin. During the deoxidation sub-step in step c), the small amount of residual carbon resulting from the pyrolysis of the crosslinked resin reacts with oxygen and is eliminated in gaseous form.It therefore does not participate in any reaction with the molten compounds used, justifying the name of a non-reactive process. It should be noted that the absence of SiC on the surface of the joint and obstructing the pores of the latter is indirect proof of the absence of any reaction between carbon and molten silicon.

[0067] The absence of reaction avoids the risk of heating by exothermicity during infiltration.

[0068] This absence of reaction also has the advantage that the width of the joint that can be prepared by the method according to the invention is not limited, which is not the case with the reactive melt infiltration (RMI) joining technique described above. Indeed, the reaction with the carbon / carbon pre-joint mixture used in the reactive melt infiltration (RMI) joining technique described in documents [5] and [6] leads to the precipitation of carbides such as SiC along the infiltration path, which can lead to the obstruction of the pores of the network and the blocking of the propagation of the liquid.

[0069] Then, the method according to the invention is a non-reactive method also because, during step c), it can use a non-reactive alloy MSi containing silicon and at least one metal M.

[0070] By "non-reactive alloy" is meant that this alloy does not react with the silicon carbide-based material of the parts to be assembled and does not react with the network formed by the crosslinked organic resin and the SiC powder. This alloy therefore does not have the disadvantages associated with reactive alloys which react with the material of the parts. As previously explained, the carbon resulting from the pyrolysis of the crosslinked organic resin is eliminated during the deoxidation step. For this reason, the infiltrate (Si or SiM) used in the invention does not react with carbon resulting from the pyrolysis of the crosslinked organic resin. Prior to the silicon carbide deoxidation step, the porous network comprises a small amount of carbon resulting from the pyrolysis of the crosslinked organic resin.By "small quantity" is meant a quantity of carbon less than 10% by mass relative to the total mass of the porous network, the remainder being constituted by SiC, hence the expressions "porous network essentially / mainly constituted of SiC (or SiC powder)" and "porous network essentially / mainly composed of SiC (or SiC powder)".

[0071] The method according to the invention finally has the advantage of including the heat treatments for preparing the porous network and infiltration in the same cycle carried out during step c).

[0072] Finally, it can be estimated that the method according to the invention has the significant advantage, compared to the prior art, of allowing the non-reactive assembly of parts, including parts of complex shapes with pre-bonding at a low temperature.

[0073] Advantageously, the silicon carbide-based material may be chosen from pure silicon carbides such as pure silicon carbide a (SiCa) or P (SiCP) and SiC-based composite materials such as silicon carbide fiber and / or matrix composites.

[0074] Advantageously, the silicon carbide-based material may be selected from pressureless sintered silicon carbide (“PLS-SiC”); Si-infiltrated silicon carbide (“SiSiC” or “RBSC”); 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”; SiC / SiC composites with a self-healing matrix; C / SiC composites, for example, with carbon fibers or “whiskers” and with a SiC matrix; SiC single crystals; and SiC composites with a SiC matrix or coated with SiC.

[0075] By “silicon carbide-based material” is generally meant a material having a silicon carbide content of at least 50% by mass, preferably at least 80% by mass, and more preferably 100% by mass.

[0076] Advantageously, the parts can be parts of complex geometry and / or large parts.

[0077] Those skilled in the art in this field of technology will know that the terms "complex geometry" and "large size" have recognized and established meanings and are widely used. "Complex geometry parts" generally mean parts that have one or more of recesses, indentations, overhangs, angles, concavities, convexities, etc.

[0078] "Large rooms" generally means rooms with a size (defined by their largest dimension) greater than 20 cm, preferably 1 m to 4 m, or with a volume greater than 1 m 3 , preferably 1.5 m 3 at 15 m 3 .

[0079] By "crosslinkable organic resin" is meant a resin comprising groups capable of reacting with each other to form several three-dimensional networks by chemical or physical means, for example, by heating with the creation of chemical bonds between the macromolecular chains of the resin. In addition, as previously indicated, the crosslinkable organic resin used has a very low carbon yield, after pyrolysis.

[0080] The crosslinkable organic resin used in the invention may be chosen from furfuryl alcohol, a phenolic resin and an epoxy resin.

[0081] The crosslinkable organic resin used in the invention is also a pyrolyzable resin, which during its pyrolysis gives carbon.

[0082] In step a) of the method according to the invention, the silicon carbide powder and the crosslinkable organic resin can be interposed between the faces to be assembled simultaneously or one after the other. When applied simultaneously, the silicon carbide powder and the crosslinkable organic resin can be mixed beforehand and then be in the form of a paste.

[0083] The definition and characteristics of a paste are well known to those skilled in the art. Alternatively, they can be deposited successively at the interface between the parts in the form of a powder suspension which will be dried before being impregnated with the crosslinkable organic resin.

[0084] Advantageously, during step b) the mixture and the parts are heated to a temperature of 50°C to 150°C, for example, 100°C.

[0085] Advantageously, during step b) the mixture and the parts are heated for a sufficient time to crosslink the crosslinkable organic resin, for example, furfuryl alcohol, this time can be in particular from 15 minutes to 24 hours, for example, 1 hour. In a particular embodiment, prior to step c), it is possible to deposit an anti-wetting compound, such as boron nitride, on the surfaces not involved in the assembly to limit the wetting of the Si or MSi to the area to be assembled.

[0086] Advantageously, during step c):

[0087] The parts, the network formed by the crosslinked organic resin in which silicon carbide particles are distributed, and the silicon or the non-reactive alloy MSi are heated to a temperature of 700°C to 1000°C, for example 800°C, and a first stage is observed at this temperature for a period of 5 minutes to 200 minutes, for example 10 minutes, to achieve the pyrolysis of the crosslinked organic resin and the formation of a porous network; then

[0088] Heating continues, up to a temperature of 1100 C to 1400 C, for example 1300°C, and a second stage is observed at this temperature for a period of 10 minutes to 200 minutes, for example 30 minutes to achieve deoxidation of the silicon carbide; then

[0089] Heating is continued to a temperature above the melting temperature of silicon, preferably from 1420 C to 1700 C, for example 1500°C, and a third stage is observed at this temperature for a period of 1 minute to 120 minutes, for example 15 minutes to 30 minutes to achieve the melting of the silicon or the non-reactive alloy MSi, the infiltration of the liquid silicon or the non-reactive alloy MSi liquid into the porous silicon carbide network.

[0090] The MSi alloy can be a binary or ternary alloy.

[0091] Advantageously, M is chosen from metals which do not form carbides and can therefore be chosen from cobalt (Co), nickel (Ni), iridium (Ir), ruthenium (Ru), rhenium (Re), rhodium (Rh), palladium (Pd), platinum (Pt) and mixtures thereof.

[0092] The non-reactive alloys may in particular be chosen from alloys containing, in atomic percentages, more than 50% silicon, preferably more than 65% silicon. Examples of such alloys are described in documents [1] and [2]. It may be a binary alloy, consisting, in atomic percentages, of 60 to 66% silicon and 34% to 40% nickel, or a ternary alloy, consisting of atomic percentages of 45% to 65% silicon, 28% to 45% nickel, and 5% to 15% cobalt.

[0093] The invention will be better understood upon reading the following description, given for illustrative and non-limiting purposes, of embodiments of the invention given in the form of examples.

[0094] This description is made in relation to the attached drawings.

[0095] BRIEF DESCRIPTION OF THE FIGURES

[0096] Figure 1 is a schematic vertical sectional view of a test piece prepared by the method according to the invention.

[0097] Figure 2 is a photograph showing an aluminum tool or assembly for positioning the parts to be assembled using the method according to the invention.

[0098] Figure 3 is a schematic front view illustrating the placement of the parts during the infiltration step of the process according to the invention.

[0099] Figure 4 is a graph showing the thermal cycle implemented during the infiltration step of the process according to the invention.

[0100] Figure 5 is a sectional view in the plane of the joint, obtained by X-ray tomography of the joint obtained by assembling two monolithic SiC parts using the method according to the invention (Example 1).

[0101] Figure 6 is a cross-sectional view, obtained by optical microscopy, of the joint obtained by assembling two monolithic SiC parts (Example 1).

[0102] The scale in Figure 6 represents 20 pm.

[0103] Figure 7 is a sectional view in the plane of the joint, obtained by X-ray tomography of the joint obtained by assembling two Cf / SiC n parts implementing the method according to the invention (Example 2).

[0104] Figure 8 is a cross-sectional view, obtained by optical microscopy, of the joint obtained by assembling two pieces of a composite material called Cf / SiC with a silicon matrix reinforced by carbon fibers. (Example 2).

[0105] The scale shown in Figure 8 represents 100 pm. DETAILED DESCRIPTION OF THE INVENTION

[0106] The invention will now be described with reference to the following examples given by way of illustration and not limitation.

[0107] In the following examples, the assembly of parts is carried out using the method according to the invention, which comprises a pre-assembly step followed by an infiltration step.

[0108] In example 1, two parts are assembled from sintered monolithic silicon carbide SiC.

[0109] In example 2, two parts are assembled from a composite material called Cf / SiC with a silicon matrix reinforced by Cf carbon fibers.

[0110] • Geometry of the test pieces

[0111] In both examples, the method according to the invention is used to assemble two parts and thus form a test piece having a particular geometry.

[0112] This test piece is in fact in the form of a small structure with an inverted “T” shaped geometry.

[0113] This inverted "T" shaped geometry, shown in Figure 1, is composed of two parts (11, 12) having dimensions of 10 mm x 10 mm x 4 mm and 15 mm x 10 mm x 4 mm respectively, and a gasket (13) in contact with the assembled surfaces (14, 15) of the two parts.

[0114] This particular shape of the test piece involves constraints such as the need to precisely position the parts in their place, a small contact surface available for assembly (approximately 40 mm 2 ) as well as difficulty applying pressure during assembly.

[0115] • Assembly process

[0116] We begin by carrying out a pre-assembly of the parts ((step b) of the process according to the invention) using aluminum tools or mountings for positioning the parts (Figure 2).

[0117] The parts are arranged in this assembly according to the inverted "T" shaped geometry, shown in Figure 1, and a mixture of SiC powder (beta-phase, 1 pm powder, 99% purity, Alfa Aesar) and furfuryl alcohol (Aldrich), is placed between the surfaces to be joined (14, 15) of the two parts. This tooling includes holding screws to hold the parts to be joined in place.

[0118] Once the parts are arranged in the assembly with the SiC powder and the furfuryl alcohol placed between the surfaces to be assembled (14, 15), the assembly is then introduced into an oven at 100°C (which is a low temperature) for 1 hour in order to crosslink the furfuryl alcohol.

[0119] At the end of this step, a network (or interface) of crosslinked furfuryl alcohol is formed between the surfaces to be assembled (14, 15) of the two parts. In this network, SiC particles from the powder are distributed.

[0120] Step c) of the process according to the invention is then carried out, during which the infiltration of the crosslinked furfuryl alcohol network obtained at the end of step b) is carried out.

[0121] To implement this infiltration step c), boron nitride (Boron Nitride Spray (HeBoCoat® SL-E 200), henze Boron Nitride Products AG), which is an anti-wetting compound, is first deposited, prior to this step c), around the area of ​​the joint between the two surfaces (14, 15) to be assembled, to limit the wetting of the liquid silicon on the pre-assembled parts (11, 12) obtained at the end of the first step (Figure 3). In other words, boron nitride is deposited on an area (16) of the surface of the parts (11, 12) to be assembled, around the network (17) formed by the crosslinked organic resin in which silicon carbide particles are distributed (Figure 3).

[0122] Silicon chips (strem Chemicals 93-1496 chips of 99+% purity) (infiltrate (18)) are then deposited along the joint area, in contact with the crosslinked furfuryl alcohol network and silicon carbide powder obtained at the end of step b) (Figure 3).

[0123] The parts thus treated with the anti-wetting compound and provided with the infiltrate (18) are placed in a graphite crucible placed in a furnace heated by high frequency induction and capable of reaching 2000°C.

[0124] A thermal cycle reaching 1500°C (Figure 4) allows the silicon to melt and then infiltrate the porous network.

[0125] This thermal cycle comprises a first temperature rise up to a first plateau at a temperature of 800°C which is observed for 10 minutes in order to allow the pyrolysis of the furfuryl alcohol and thus form a porous network composed essentially of silicon carbide and comprising less than 10% by mass of carbon. Then, a second temperature rise is carried out up to a second plateau at a temperature of 1300°C, which is observed for 30 minutes to ensure deoxidation of the SiC powder. Finally, a third temperature rise is carried out up to a temperature of 1500°C which is maintained for 15 minutes (example 1, monolithic SiC for thin joint) or 30 minutes (example 2, Cf / SiC for thick joint) so that the silicon melts and infiltrates the porous SiC network.

[0126] Example 1

[0127] In this example, the assembly of two monolithic parts of sintered silicon carbide (Boostec®, 1.5% porosity, available from MERSEN®) is carried out using the process according to the invention described above, with the thermal cycle described above and in Figure 4.

[0128] The joint obtained in this example by implementing the method according to the invention is dense, as shown by the sectional view in the plane of the joint, obtained by X-ray tomography (Figure 5), and the cross-sectional view of the joint, obtained by optical microscopy (Figure 6).

[0129] The resulting assembly was also mechanically characterized in tension and demonstrated a breaking strength of 76.4 MPa. An identical sample was tested in shear and demonstrated a breaking strength of 88.2 MPa.

[0130] Example 2

[0131] In this example, two parts made of Cf / SiC composite material (BJS Ceramics) with a thickness of around 4 mm are assembled using the process according to the invention described above, with the thermal cycle described above and in Figure 4.

[0132] The joint obtained in this example by implementing the method according to the invention is dense, as shown by the sectional view in the plane of the joint, obtained by X-ray tomography (Figure 7), and the cross-sectional view of the joint, obtained by optical microscopy (Figure 8).

[0133] An identical sample was tested in tension and the joint demonstrated a higher breaking strength than the composite T-base stressed out of plane. The examples provided above demonstrate that the method according to the invention can be effectively implemented to produce the assembly of ceramics or ceramic matrix composites based on SiC.

[0134] REFERENCES

[0135] [1] FR-A1-2 957 543.

[0136] [2] FR-A1-2 957 544.

[0137] [3] US-A1-20140186102.

[0138] [4] FR-A1-2 984 784.

[0139] [5] Singh, 1998, Journal of Materials Science, vol. 33, pages 5781-5787.

[0140] [6] Singh & Lara-Curzio, 2001, J. Eng. Gas Turbines Power, vol. 123, pages 288-292.

Claims

CLAIMS 1. Method for assembling at least two parts made of a silicon carbide-based material, each of the parts comprising a surface to be assembled, in which the following successive steps are carried out: a) A silicon carbide powder and a crosslinkable organic resin are interposed between the surfaces to be assembled of the parts and in contact with said surfaces to be assembled; b) The mixture of silicon carbide powder and crosslinkable organic resin and the parts placed in position are heated to a temperature below 200°C, preferably below 100°C, to crosslink the crosslinkable organic resin, and to create between the surfaces to be assembled, a network formed by the crosslinked organic resin in which silicon carbide particles are distributed; c) The network created in step b) is brought into contact, without applying pressure, with silicon or a non-reactive alloy MSi containing silicon and at least one metal M, and: The parts, the network formed by the crosslinked organic resin in which silicon carbide particles are distributed, and the silicon or the non-reactive alloy MSi are heated to a temperature of 700°C to 1000°C and a first stage is observed at this temperature for a period of 5 minutes to 200°minutes, to carry out the pyrolysis of the crosslinked organic resin and the formation of a porous network essentially comprising silicon carbide; then Heating continues up to a temperature of 1100 C to 1400 C and a second stage is observed at this temperature for a period of 10 minutes to 200 minutes to achieve deoxidation of the silicon carbide; then Heating is continued to a temperature above the melting temperature of silicon and a third stage is observed at this temperature for a period of 1 minute to 120 minutes to achieve the melting of the silicon or the non-reactive alloy MSi, the infiltration of the silicon liquid or liquid non-reactive MSi alloy in the porous silicon carbide network; d) The parts are cooled, whereby a joint is obtained between the surfaces to be joined and the assembly of the two parts.

2. Method according to claim 1 in which the silicon carbide-based material is chosen from pure silicon carbides such as pure a or P silicon carbide and SiC-based composite materials such as silicon carbide fiber and / or matrix composites.

3. The method of claim 1 or 2, wherein the silicon carbide-based material is selected from pressureless sintered silicon carbide; Si-infiltrated silicon carbide; porous recrystallized silicon carbide; silicon graphite made of graphite and coated with a layer of SiC; SiC / SiC composites, for example, with fibers or whiskers; SiC / SiC composites with a self-healing matrix; C / SiC composites, for example, with carbon fibers or whiskers and a SiC matrix; SiC single crystals; and SiC composites with a SiC matrix or coated with SiC.

4. Method according to any one of the preceding claims, in which the silicon carbide-based material has a silicon carbide content of at least 50% by mass, preferably at least 80% by mass, and more preferably 100% by mass.

5. Method according to any one of the preceding claims, in which the parts are parts of complex geometry and / or large parts.

6. Method according to any one of the preceding claims, in which the crosslinkable organic resin is chosen from furfuryl alcohol, a phenolic resin and an epoxy resin.

7. Method according to any one of the preceding claims, in which, prior to step c), an anti-wetting compound is deposited on the non- involved in the assembly to limit the wetting of Si or MSi to the area to be assembled.

8. Method according to any one of the preceding claims, in which, during step c): - The parts, the network formed by the crosslinked organic resin in which silicon carbide particles are distributed, and the silicon or the non-reactive alloy MSi are heated to a temperature of 800°C, and a first stage is observed at this temperature for a period of 10 minutes, to achieve the pyrolysis of the crosslinked organic resin and the formation of a porous network; then - Heating continues up to a temperature of 1300°C, and a second stage is observed at this temperature for a period of 30 minutes to achieve deoxidation of the silicon carbide; then - Heating is continued to a temperature higher than the melting temperature of silicon, from 1420 C to 1700 C, for example 1500°C, and a third stage is observed at this temperature for a period of 15 minutes to 30 minutes to achieve the melting of the silicon or the non-reactive MSi alloy, the infiltration of the liquid silicon or the non-reactive MSi liquid alloy into the porous silicon carbide network.

9. Method according to any one of the preceding claims, in which M is chosen from cobalt (Co), nickel (Ni), iridium (Ir), ruthenium (Ru), rhenium (Re), rhodium (Rh), palladium (Pd), platinum (Pt) and mixtures thereof.

Images