FR2907448A1 - Soldering composition for assembling ceramic-based silicon carbide and/or carbon part and ceramic-based silicon carbide, carbon, aluminum nitride or mullite part in aeronautical field, comprises mixture of praseodymium silicide and silicon - Google Patents

Abstract

The soldering composition (6) for assembling ceramic-based silicon carbide and/or carbon part (7) and ceramic-based silicon carbide, carbon, aluminum nitride or mullite part (5) in aeronautical field, comprises a mixture of praseodymium silicide and silicon in which silicon contains 81-85 atomic percentage and praseodymium contains 19-15 atomic percentage. The mixture of praseodymium silicide and silicon is constituted by a eutectic mixture of praseodymium silicide and silicon. An independent claim is included for a process of assembling two parts using a soldering composition.

Description

The invention relates to an assembly between a metal part and

  a piece of ceramic material based on silicon carbide (SiC) and / or carbon (C). This invention finds a privileged application in the field of aeronautics, for assembling a piece of refractory metal alloy, such as a nickel-based alloy (Ni) or cobalt (Co), and a piece of ceramic matrix composite material, or CMC part. More particularly, the CMC parts concerned comprise a matrix based on SiC, C or a so-called "mixed" matrix of C and SiC, reinforced by SiC fibers and / or C. Said matrix may be single-phase (for example entirely in SiC) or multiphase (it may contain, for example, at least one other phase with self-healing property as described in the document FR 2 732 338). CMC parts are used in aircraft turbojets to replace the most thermomechanically exposed mechanical parts because they retain good mechanical properties at high temperatures, require less cooling, and are generally lighter. There is a problem, however, in attaching these ceramic pieces to the surrounding metal pieces. Among the assembly techniques used to date, there is the conventional mechanical assembly, riveting or bolting type. This type of assembly is often unsuitable for reasons of bulk, mass and / or poor dynamic behavior.

Brazing joining techniques are also known for joining two pieces of ceramic material together. However, these techniques are difficult to use for brazing together a piece of ceramic material and a metal part, because of the thermo-mechanical and physicochemical behaviors very different from ceramic and metal materials. In particular, there is a very large difference in expansion between the parts in the presence. Indeed, the coefficient of expansion of a metal alloy is often two to five times greater than that of the ceramic materials used. Thus, during the cooling subsequent to the melting of the solder composition, the relative shrinkage of the metal part generates an area in compression, respectively in tension, in the areas adjacent to the solder joint of the piece of ceramic material, respectively of the metal part. This results in a bending of the assembly which gives rise to stresses which may be at the origin of the breakage of one of the parts, generally the piece of ceramic material which is the most fragile, and a poor holding of the joint of solder because of its localized deformation. In addition, because of the high reactivity of C or SiC with metals (more particularly transition metals), there is generally the formation of fragile chemical compounds of the carbide or silicide type between the ceramic pieces and metallic. These fragile compounds increase the fragility of the assembly. The invention aims to overcome these drawbacks, or at least to mitigate them, by proposing an assembly that allows, on the one hand, to compensate for the expansion gap between a metal part and a piece of ceramic material to based on SiC and / or C and, on the other hand, to avoid or limit the formation of undesirable chemical compounds. This object is achieved by means of an assembly according to the invention comprising a stacked structure comprising the following elements assembled two by two, in this order, by brazing: said metal part; a first intermediate piece; a second intermediate piece; and said piece of ceramic material based on SiC and / or C, this assembly being such that: the second intermediate part is made of another ceramic material (ie a ceramic material different from that of said piece of ceramic material) this other ceramic material being chemically less reactive towards metals than SiC or C, and having a coefficient of expansion less than that of the material constituting said metal part; and the first intermediate part is metallic and able to deform to compensate for the expansion gap between said metal part and the second intermediate part. It should be noted that said ceramic piece may be a solid SiC piece 35 or a CMC piece of the type previously described.

The invention therefore proposes to interpose between the ceramic and metal parts two spacers having separate functions. The first intermediate part makes it possible to compensate, by deforming, the expansion gaps between the ceramic and metal parts.

According to a first embodiment of the first intermediate part, the latter is composed of a layer of ductile metallic material. In this case, the piece generally has a massive structure and forms a cushion of material capable of deforming by shearing. Among the ductile materials that may be used are nickel, palladium, gold, or alloys comprising these different metals. Advantageously, for aeronautical applications that require refractory assemblies, the nickel-based alloys are chosen, these having a good resistance to high temperature and a limited cost. According to a second embodiment of the first intermediate part, said deformation is obtained by choosing a deformable structure for this part. This structure may, for example, be spiral spring or bellows. The part is not necessarily made of ductile material. To ensure good mechanical properties and good temperature resistance, this part can be made of Ni alloy or Co.

The second spacer is intended to chemically protect said piece of ceramic material by preventing the attack thereof by the liquid solder used, which generally comprises SiC or C reactive metals. between the piece of ceramic material and the metal parts of the assembly the second intermediate part, made of another ceramic material, less reactive with respect to metals (more particularly transition metals), such as an oxide or a nitride. Advantageously, the second insert has a stiffness and / or a higher tensile strength than that of the piece of ceramic material. The rigidity of the second intermediate part makes it possible to form a rigid support for the first intermediate part, which ensures the deformation of the latter, and makes it possible to attenuate the mechanical stresses exerted on the piece of ceramic material. Its resistance to breakage ensures the good mechanical strength of the assembly. The second spacer thus makes it possible to mechanically protect the piece of ceramic material which, by nature, is generally fragile.

Advantageously, the second spacer has a coefficient of expansion sufficiently close to that of the piece of ceramic material, in order to limit the expansion gaps between these parts. Advantageously, taking into account the mechanical and chemical conditions which the second intermediate part must check, the latter is made of mullite (an oxide) or of aluminum nitride AlN (a nitride). Mullite is an alumina silicate, a defined compound of formula (3Al 2 O 3, 2SiO 2) obtainable by heating silica in the presence of alumina. For aeronautical applications that require refractory assemblies, mullite and AIN 10 are particularly interesting because of their good temperature resistance and good resistance to oxidation. For other applications, alumina (AI203) can be used. Advantageously, the first solder composition used to assemble the first intermediate part to the metal part and / or to the second intermediate part, is based on Ni and comprises an atomic proportion of Ti less than or on the order of 10%. . Preferably, this first composition also comprises the following elements: Fe, Cr and Si. The solder compositions comprising the elements Ni, Fe, Cr, Si and Ti will be noted hereinafter NiFeCrSiTi.

Various Ni-based solder compositions, which are said to be reactive (because they give rise to new intermetallic chemical compounds), are already known, but in this case the proportion of Ti must be limited because this element has a high reactivity. vis-à-vis the second insert, which would lead to the birth of fragile intermetallic phases. Thus, said first solder composition preferably comprises, in atomic percentages: between 3 and 6% (preferentially between 3.5 and 5.5%) of Ti when the second insert is in AlN, and between 6 and 10% Ti when the second insert is in mullite.

Advantageously, the second braze composition used to assemble the second AlIN or mullite spacer part to the ceramic material part based on SiC and / or C is an Si-based alloy. According to a first alternative, this second brazing composition essentially comprises, in atomic percentages: 60% to 97% of Si and 40 to 3% of zirconium zirconium Zr and, preferably, it is a eutectic mixture of zirconium silicide ZrSi2 and Si. The use of a ZrSi2-Si mixture for brazing an SiC ceramic material part with a mullite part is known and described in WO 03/037823. The use of ZrSi2-Si has the following disadvantage: the liquidus temperature of a eutectic mixture ZrSi2-Si is about 1370 C, a temperature generally higher than the melting start temperature to aeronautical metal alloys used for metal piece and / or the first insert (for example, the melting start temperature of the "Hastelloy X" alloy, described later, is 1310 C). To achieve the assembly of the invention it is therefore necessary to perform two successive thermal cycles of rise and fall in temperature: a first cycle typically performed up to 1400 C to achieve the assembly 15 of the piece of ceramic material to the second intermediate part; and a second cycle typically performed up to 1250 C, higher than the liquidus temperature of the first solder composition, but to which said aeronautical metal alloys do not degrade. This second cycle makes it possible to perform the final assembly by assembling the metal parts together, that is to say the metal base part and the first metal spacer part, and with the pieces made of ceramic materials, that is to say the that is to say the second intermediate part and the piece of ceramic material based on SiC and / or C. According to a second alternative, the second solder composition consists essentially of a mixture of praseodymium silicide (PrSi 2) and Si , in which the silicon (Si) is the majority and the praseodymium (Pr) is a minority, in atomic proportions. Such a solder composition is new and can be used more generally for the brazed joining of two pieces, one of the pieces being ceramic based on SiC 30 and / or C and the other piece being ceramic with SiC, C, AIN or mullite. Advantageously, said mixture of PrSi 2 and Si comprises, in atomic percentages 78% to 97% Si and 22 to 3% Pr, and preferably consists of a eutectic mixture of PrSi 2 and Si.

When the atomic proportion of the mixture of PrSi 2 and Si is close to the eutectic, that is to say of the order of 81 to 85% of Si and 19 to 15% of Pr, the melting temperature PrSi2-Si solder composition is relatively low and the assembly can be accomplished by brazing all the parts of the assembly in a single step. It will be noted that the liquidus temperature of a eutectic mixture of PrSi2 and Si is approximately 1212 ° C., and therefore about 158 ° C. lower than the liquidus temperature of a eutectic mixture of ZrSi2 and Si. where the atomic proportion of the mixture of PrSi2 and Si is less close to the eutectic, especially between 78 and 81% of Si and 22 to 19% of Pr, or between 85 and 97% of Si and 15 to 3% Pr, it will then proceed in two stages, as detailed above, to avoid the melting of metal parts. Owing to the solder composition PrSi2-Si, it is therefore possible to braze together all the parts of the assembly, in a single step, at a temperature above the liquidus temperatures of said first and second solder compositions, but which remains low enough not to degrade the alloys present. The invention also relates to a method of assembly by brazing with the aid of such a composition.

The invention will be better understood and its advantages will appear better on reading the detailed description which follows, of an embodiment shown by way of non-limiting example. The description refers to the accompanying drawings in which: - Figure 1 schematically shows an assembly according to a first embodiment of the invention; FIG. 2 diagrammatically represents an assembly according to a second embodiment of the invention; and - Figure 3 shows schematically an assembly according to a third embodiment of the invention.

According to a first exemplary assembly according to the invention, represented in FIG. 1, this comprises: a metal part 1 made of a Ni base alloy such as the one sold under the trademark "Hastelloy X", comprising, percentages by weight: not more than 0.5% Al; not more than 0.008% of B; 0.05% to 0.15% C; 20.5% to 23% Cr; 0.5% to 2.5% Co; at most 0, 5% 2907448 7 deCu; 17 to 20% Fe, at most 1% Mn, 8 to 10% Mo, at most 0.04% P; not more than 1% of Si; not more than 0.03% of S; not more than 0.15% Ti; 0.2 to 1% of W and a balance in Ni; a first intermediate piece 3 made of Ni-based alloy, for example an alloy marketed under the trademark "Inconel 600", "Inconel 601", "Inconel 625" or "Nimonic 80A". An "Inconel 625" type alloy typically comprises, in percentages by weight: at most 0.4% Al; not more than 0.1% of C; 20 to 23% Cr; not more than 1% of Co; not more than 5% Fe; not more than 0,5% of Mn; 8 to 10% Mo; 3.15 to 4.15% Niobium io Nb; not more than 0.015% of P; not more than 0.5% Si; not more than 0.015% of S; not more than 0,4% of Ti; and a balance in Ni. a second intermediate part 5 made of AlN; and - a ceramic matrix composite part 7 (CMC) based on SiC. The first solder composition 2 used for soldering the metal part 1 to the first intermediate part 3 and for brazing the first intermediate part 3 to the second intermediate part 5 is of the NiFeCrSiTi type and essentially comprises (ie with impurities), in percentages. Mass: 2.8% Fe; 7% Cr; 6.2% Si; 4.5% Ti and a balance in Ni.

The second solder composition 6 used for brazing the second spacer 5 to the ceramic material part 7 is a eutectic mixture of ZrzSi and Si. The method of assembling the metal parts 1 and ceramic 7 comprises two thermal rise cycles. and lowering temperature, and essentially comprises the following steps: - the second solder composition 6 is disposed on the surfaces to be joined of the piece of ceramic material 7 and the second intermediate part 5; the assembly thus formed (parts 5 and 7 and composition 6) is mounted at a temperature above the liquidus temperature of the second solder composition 6, and then cooled; - The first solder composition 2 is disposed on the surfaces to be assembled of the first and second intermediate parts 3 and 5 and the metal part 1; and 2907448 8 - the new assembly thus formed (parts 5, 7, 3 and 1, compositions 2 and 6) is raised in temperature beyond the liquidus temperature of the first solder composition 2, and then cooled. Here is a detailed example of such a process: the surfaces of the parts of parts 5 and 7 to be assembled, respectively in AIN and CMC, are degreased in an organic solvent, for example of the acetone, ester, ether, alcohol or a mixture type. of these. The surfaces of the parts of the parts 7 and 5 are coated with the suspension of the second solder composition 6, formed of a eutectic mixture of ZrSi2 and Si. The parts in the vicinity of the CMC / AIN seal are covered with a suspension said anti-wetting agent non-wettable by said composition. This suspension avoids the flow of solder composition out of the CMC / AIN gasket. The assembly thus formed, ready to be brazed, is placed in a vacuum oven or under a neutral gas atmosphere. A first thermal cycle with a temperature plateau is typically performed at 1400 C for 5 to 10 minutes. This temperature is higher than the liquidus temperature of the composition of the solder (at least 25 C above). The whole is then cooled to room temperature at, for example, 5 ° C. per minute. The CMC / AIN assembly is removed from the oven. A continuous solder bead is observed between the CMC and AIN. The assembly is cleaned with acetone and then ethanol before the second soldering with the first intermediate part 3 and the metal part 1. The first intermediate part 3 is made of Ni base alloy of the "Inconel 625" type. metal part 1 is base alloy Ni type "Hastelloy X". The CMC part 7, the bead of the second solder composition 6 and the edges 25 of the AIN part 5 are covered with a so-called anti-wetting suspension, non-wettable by the first NiFeCrSiTi solder composition. The latter is applied as a ribbon on the AIN. On top of this solder ribbon, the first intermediate part 3 is deposited. This piece 3 is then covered with a NiFeCrSiTi solder tape and then with the metal part 1. The edges of the parts 1 and 3 can be coated with non-wetting anti-wetting agent by the NiFeCrSiTi solder composition. For the first insert 3, this anti-wetting coating depends on the shape of this piece. The CMC / ZrSi2-Si / AIN / NiFeCrSiTi solder / Ni base alloy / NiFeCrSiTi solder / Ni base alloy braze ready assembly is disposed in a vacuum oven or in a neutral gas atmosphere. A second thermal cycle is performed with a temperature plateau at 1100 C for 30 minutes followed by a second plateau at 1250 C for 15 minutes. This temperature of 1250 ° C. is greater than the liquidus temperature of the NiFeCrSiTi solder composition (at least 25 ° C. above). The whole is then cooled to room temperature at, for example, 5 C per minute. According to a second example of assembly according to the invention, the second solder composition 6 used in the first example given above is replaced by a eutectic mixture of PrSi2 and Si. In this case, the assembly process metal parts 1 and ceramic 7 comprises a single thermal rise and fall temperature cycle, which essentially comprises the following steps: the second solder composition 6 is disposed on the surfaces to be assembled of the piece of ceramic material 7 and the second insert 5; and the first solder composition 2 is disposed on the surfaces to be joined with first and second intermediate pieces 3 and 5 and the metal part 1; and the assembly thus formed (parts 5, 7, 3 and 1, compositions 2 and 6) is raised in temperature beyond the liquidus temperatures of the first and second solder compositions 6 and 2, and then the whole is cooled. Here is a detailed example of such a process: The surfaces of the parts 1, 3, 5 and 7 to be assembled are defatted in an organic solvent, for example of the acetone, ester, ether or alcohol type, or a mixture of these. The surfaces of the parts of the CMC 7 and AIN 5 parts facing each other are coated with carbon necessary for the good wetting of these surfaces by the solder composition PrSi2-Si. The carbon may be applied: 1) in the form of a graphite powder mixed or not with an organic binder, 2) by chemical vapor deposition (CVD) or physical deposition techniques. vapor phase or PVD (for "physical vapor deposition"), 3) simply by rubbing the surfaces with a graphite lead (eg a pencil lead). The recommended carbon thickness is of the order of 1 micron. Once the carbon layer has been applied to all these surfaces, the suspension of the second solder composition formed of the eutectic mixture PrSi2-Si 35 is placed between the CMC 7 piece and the piece AIN 5. The parts in the vicinity of the joint are covered with a so-called anti-wetting suspension that can not be wetted by said composition. This suspension prevents the flow of solder from the CMC / AIN seal. The AIN is covered with NiFeCrSiTi solder tape. On top of this brazing ribbon, the first intermediate piece 3 made of base alloy Ni is put in place. This piece 3 is then covered with a solder strip NiFeCrSiTi type and the metal piece "Hastelloy X" massive. The edges of the metal alloy parts 1 and 3 may be coated with anti-wetting, non-wettable by NiFeCrSiTi composition. For the first insert 3, this anti-wetting coating depends on the shape of this part. The CMC / PrSi2-Si / AIN / NiFeCrSiTi solder / Ni base alloy / NiFeCrSiTi solder / Ni base alloy, ready for brazing, is placed in a vacuum oven (or in a neutral gas atmosphere). A single thermal cycle is performed with a temperature step at 1100 C for 30 min. then a second plateau at 1250 C for 15 min. This temperature of 1250 ° C. is greater than the liquidus temperature of the NiFeCrSiTi solder and that of the second solder composition PrSi2-Si (at least 25 ° C. above). The whole is then cooled to room temperature at, for example, 5 C per minute.

According to a third example of an assembly according to the invention, the second interlayer piece made of AlN brazed either with ZrSi2-Si (in the first example) or with PrSi2-Si (in the second example), is replaced by a part 5 made of mullite. According to a fourth example of an assembly according to the invention, the second spacer part made of AlN of the previous examples is replaced by a piece 5 made of mullite and metallization of the face of this part 5 is turned towards the piece 3. This metallization is made with a solder composition known under the trademark "TiCuSil" comprising in percentages by weight about 68.8% Ag, 26.7% Cu and 4.5% Ti. Another Pd-based solder composition of Pd and Ni, preferably comprising, in atomic proportions, between 35 and 55% of Pd and a balance of Ni (that is, between 50 and 69% of Pd). and between 50 and 31% Ni in percentages by weight), can then be used to join together the first and second intermediate pieces 3 and 5 and also to assemble the metal part with the first intermediate part. In this case, the method for assembling metal parts 1 and ceramic 7 comprises two thermal cycles and an additional metallization step between the first soldering of the piece of ceramic material 7 with the second intermediate part 5 and the complete brazing of assembly.

According to a fifth example of an assembly according to the invention, the Ni-based alloy metal part used in the first example given above is replaced by a metal part 1 made of a Co alloy, for example alloy known under the trademark "Haynes 188" and typically comprising, in percentages by weight: 20 to 24% of Ni, 20 to 24% of Cr, 13 to 15% of W, at most 3% of Fe, O, 2 to 0.5% of Si, at most 1.25% of Mn, 0.5 to 0.15% of C, at least 0.015% of B, 0.02 to 0.12% of La, and a balance of In this case, the assembly method of the metal parts 1 and ceramic 7 comprises two thermal cycles with a first temperature rise and fall cycle with a bearing at 1400 C for 5 to 15 min. and a second cycle with a plateau at 1250 C for 15 min. In the aforementioned examples, the first insert 3 may have a massive structure, as shown in Figure 1. This part 3 is then sufficiently ductile material to deform and compensate for the expansion gap between the metal and ceramic parts.

Of course, the dimensions of this first intermediate part 3 and, in particular, its thickness, must be sufficient for this part to play its role. By way of example, for a piece of ceramic material 7 and a metal part 1 both cylindrical in revolution, 10 mm in diameter and 5 mm in thickness, the first intermediate part 3 25 is chosen with a cylindrical shape of revolution. 10 mm in diameter and 2 mm thick and the first spacer also cylindrical in shape of revolution of 10 mm in diameter and 1 mm thick. According to another embodiment of the first intermediate part 3, it is made with a deformable structure. In this case, this piece 3 is not necessarily made of ductile alloy. By way of example, it is possible to make this piece 3 made of alloy of the "Inconel 601" type (registered trademark) typically comprising, in percentages by weight, 1 to 1.7% of Al, at most 0.1% of C , 21 to 25% of Cr, not more than 1% of Cu, not more than 1% of Mn, 58 to 63% of Ni, not more than 0.5% of Si, not more than 0.015% of S, and a balance of Fe .

An example of a first intercalary piece 3 with deformable structure is shown in FIG. 2. This part is formed of a deformable sheet 3 having flattened zones 11, 15 brazed and inclined zones 10 which succeed each other to form corrugations. concentric. The ply 35 comprises an inner flat area 11 substantially circular about an axis A, a substantially annular outer flat area coaxial with the inner area 11, and of inner diameter greater than the diameter of said inner area, and at least one annular intermediate flat zone 13 situated between zones 11 and 15 and coaxial therewith.

These zones 11, 13, 15 are interconnected by inclined zones 10 having a symmetry of revolution with respect to the axis A. The inner flat area 11 is brazed to the metal part 1 while the outer flat area 15 is brazed to the second spacer 5 or vice versa. The intermediate corrugations (formed by zones 10 and 13) remain free. According to another embodiment, not shown, the insert 3 is formed by a plurality of accordion folded ribbons and arranged radially around a fixed point, preferably center. These ribbons are arranged in a plurality of radial directions around said fixed point, which constitutes an arrangement of concentric corrugations. According to another example shown in FIG. 3, the deformable structure consists of several parts including a spiral spring 3 arranged in a circle whose main plane is substantially parallel to the surfaces of the parts 1 and 5 to be assembled, so that these surfaces rest on the 25 lateral faces of the spring. This structure may also comprise at least one spiral spring of rectilinear shape, disposed in the center of the circular spring 3 (not visible in Figure 3), whose axis is parallel to said surfaces. The assembly of the invention can be implemented in a turbomachine and, more particularly, in a turbojet engine. Thus, the invention may relate to a turbomachine nozzle comprising at least one assembly as mentioned above, wherein the metal part is a housing or a lever of this nozzle and the piece of ceramic material is a flap of this nozzle.

The invention also relates to a turbomachine combustion chamber comprising at least one assembly as mentioned above, wherein said metal part is a housing, a seal or, in general, a constituent part of this chamber, and said piece of ceramic material is another constituent part of this chamber. The invention also relates to a post-combustion equipment of a turbomachine comprising at least one assembly as mentioned above, in which the metal part is an afterburner or a platform, and the piece of ceramic material is a flameholder arm.

Claims (10)

  Solder composition (6) for soldering two pieces (5, 7), the first (7) of these pieces being made of SiC and / or C ceramic, and the second (5) of these parts being ceramics based on SiC, C, AlN or mullite, characterized in that it consists essentially of a mixture of PrSi2 and Si, in which Si is in the majority and Pr is a minority, in proportions atomic.   The solder composition (6) of claim 1, wherein said mixture of PrSi 2 and Si comprises, in atomic percentages, 78% to 97% Si and 22 to 3% Pr.   The solder composition (6) of claim 2, wherein said mixture of PrSi 2 and Si comprises, in atomic percentages, 81 to 85% Si and 19 to 15% Pr.   The solder composition (6) of claim 3, wherein said mixture of PrSi 2 and Si consists of a eutectic mixture of PrSi 2 and Si.   A brazed joining method using a solder composition according to any one of claims 1 to 4 for joining two pieces (5, 7), the first (7) of these pieces being made of SiC ceramic. and / or C, and the second (5) of these pieces being ceramic based on SiC, C, AlN or mullite.   6. The brazed joining method according to claim 5, wherein said second piece (5) is ceramic based on AlN or mullite.   The brazed joining method according to claim 6, wherein a third metal piece (3) is soldered to said second piece (5) using another solder composition. 2907448   The braze joining method according to claim 7, wherein said other solder composition is Ni-based and comprises an atomic proportion of Ti less than, or in the order of, 10%. 5   The brazed joining method according to claim 8, wherein said other solder composition (2) comprises, in atomic percentages: between 3 and 6% of Ti when said second piece (5) is in AlN, and between 6 and 10% Ti when said second piece (5) is in mullite. 10   The brazed joining method according to any one of claims 7 to 9, wherein a solder composition according to claim 3 or 4 is used, and in which a single thermal rise and fall cycle is carried out for assembling said first (7), second (5) and third (3) pieces. 15