IMPROVED CAST CORE FOR THE MANUFACTURING OF A HOLLOW AERONAUTIC METAL PART

Description

Technical Field

[0001] The invention relates to the manufacture of hollow metal aeronautical parts, in particular aeronautical turbomachine blades, by lost wax casting methods. More specifically, the invention relates to the foundry core used in the manufacture of hollow aeronautical parts, to a method of manufacturing such a foundry core, and to a method of manufacturing such an aeronautical part. Prior art

[0002] Metal aircraft parts, particularly nickel-based high-pressure turbine blades, typically have internal cooling channels, making these parts hollow.

[0003] As is known, these hollow parts are produced by so-called "lost wax" casting processes, using ceramic cores to form the internal cavities that form the cooling channels on the final part. These processes generally include the following steps: manufacturing of ceramic cores, for example by ceramic injection and sintering, injection of wax models (injection of wax around the core), assembly of the models and manufacturing of the shell mold, dewaxing to remove the wax and make way for the alloy, followed by a firing step of the shell mold, vacuum casting of nickel-based alloys and controlled solidification, mechanical de-coating of the shell and chemical de-coating of the cores, for example by dissolution, to obtain the final blade with an internal cavity.

[0004] Current research and development efforts aim to increase the performance of aircraft engines and reduce CO2 emissions and specific fuel consumption. To achieve this, it is necessary to develop high-pressure turbine blade technologies that can increase the turbine inlet temperature (TET). To achieve a higher TET, new technologies are being implemented, including new higher-temperature monocrystalline materials, new protective coatings compatible with new alloys, or new thermal barriers with reduced thermal conductivity and resistant to environmental aggression.

[0005] Cooling circuits in particular play a major role in achieving these objectives. As a result, the complexity of these circuits tends to increase, integrating very thin and long sections. As a result, these circuits can be difficult to manufacture. Indeed, given the fragility of the ceramic composition used and the need to use demouldable shapes, the development of such circuits by ceramic injection into a mould, which represents the process generally used for the manufacture of foundry cores, can be laborious and expensive, notably presenting a high reject rate.

[0006] On the other hand, chemical decoupling of these complex circuits also presents disadvantages both from an environmental and industrial point of view (handling of very dangerous solvents), and from the point of view of the efficiency of this step of the process, which can in particular be limited by the complexity and / or accessibility by chemical etching fluids. In addition, the increasing complexity of the cooling channels leads to an increase in decoupling time as well as processing temperatures and pressures, which can ultimately increase the risk of chemical interaction between the superalloy and the bases / acids used. Finally, the material used to produce these cores is not reusable and cannot be regenerated at the end of the process.

[0007] Currently, various solutions exist to partially overcome some of these drawbacks. In particular, it is known to use refractory metal cores instead of ceramic cores, particularly based on alloys containing molybdenum. Although this technology makes it possible to reduce the fineness of the cooling channels and to obtain more complex shapes, it does not offer a solution to the other problems mentioned above, particularly those related to recycling, the environment and the de-moulding of complex circuits. Furthermore, molybdenum and its alloys oxidize at high temperatures and become brittle. These metals are therefore sensitive to the core firing, shell annealing and superalloy casting stages.This degradation can lead to erosion of the material in contact with the superalloy, thus creating asperities on the internal surface of the blade and consequently undesirable fluid disturbances, which can lead to a reduction in the efficiency of the cooling circuits. These metals are also soluble in the superalloy. Documents US 4,187,266 A and EP 1,764,170 A1 also refer to the manufacture of a hollow metal aeronautical part casting core.

[0008] This disadvantage can be overcome by applying coatings to the refractory metal. However, in order to meet certain properties, including chemical compatibility with the refractory metal, good adhesion to the latter, being detachable and having a coefficient of thermal expansion close to that of the refractory metal, these coatings must be composed of several layers, and the processes for producing these coatings remain complex.

[0009] There is therefore a need for a solution to at least partially overcome the aforementioned drawbacks. Statement of the invention

[0010] The present disclosure relates to a foundry core for the manufacture of a hollow metal aeronautical part, in particular a high-pressure turbine part by lost wax casting, comprising a composite material comprising on the one hand a first phase of formula M n+1 AlC n , where n = 1 to 3 and M being a transition metal chosen from the group consisting of titanium and / or niobium and / or molybdenum, the composite material comprising on the other hand a second phase of formula Al 4 C 3 .

[0011] It is understood that the first phase is of the “MAX phase” type, a crystalline structure of generic formula M n+1 AX n , combining characteristics of both metals and ceramics, and in particular having good thermal and electrical conductivity, good machinability, as well as damage tolerance and resistance to oxidation at high temperature. It is further understood that the expression “for the manufacture of hollow metal aeronautical parts” means that the core is adapted and suitable for the manufacture of such metal parts. However, it is understood that this application is not limiting, a core having the same composition may also be suitable for the manufacture of ceramic matrix composite (CMC) parts, in particular.

[0012] In the present disclosure, the use of aluminum on site A makes it possible to ensure either the formation of a protective alumina layer by oxidation of the core, or compatibility with aluminoforming coatings possibly deposited on the core. In addition, the use of carbon on site X is advantageous in that the carbide-type phases thus formed have a melting temperature greater than 1500°C, and therefore greater than the melting temperature of the metal used during the casting of the molten metal into the shell mold. Carbon also makes it possible to form phases chemically compatible with Al 4 C 3 . Furthermore, titanium and / or niobium and / or molybdenum, used on site M, make it possible, in coordination with the use of carbon, to obtain phases having melting temperatures higher than that of the metal used during casting, and also having good mechanical properties up to at least 1500°C.

[0013] Furthermore, the association of this first phase with a second phase of formula Al 4 C 3 is particularly advantageous. Indeed, aluminum carbide (Al 4 C 3 ) is an inorganic compound, whose melting temperature is very high (2200°C), and which can easily hydrolyze at room temperature, in the presence of a water-rich atmosphere. Thus, the composite material used for the foundry core of the present presentation integrates this second phase of aluminum carbide into the grain boundaries of the first phase. This makes the composite material particularly reactive to atmospheres containing water. The degradation of the aluminum carbide is accompanied by a variation in volume and a release of gas, capable of fragmenting the grain boundary and propagating cracks in the first initial phase.It is thus possible to propagate the hydrolysis phenomenon over relatively large distances, and thus facilitate the fragmentation and detachment of the core. In other words, the composite material forming the core can be initially dense and massive, and be reduced to powder by hydrolysis.

[0014] Furthermore, the chemical gradient between the aluminum carbide and the first phase containing aluminum and carbon is very limited, which limits the interdiffusion between the different chemical elements during the core shaping and casting stages. In addition, once the core has been shaken out, a fragmented material, composed of grains of the first phase and hydrated aluminum, can be recovered. After drying, this material can be "recharged" with Al 4 C 3 and reused to manufacture new foundry cores.

[0015] The composite material of the foundry core according to the present disclosure thus combines the aforementioned advantages linked to the refractory compounds of the first phase, with the use of a second phase of formula Al 4 C 3 , allowing the production of hollow structures of complex shapes, while allowing easy and rapid decoupling of fine cores, without having to resort to chemical solutions potentially harmful to the part subsequently manufactured and to the environment, and which can be recycled.

[0016] In some embodiments, the first phase is of one of the formulas Nb 4 AlC 3 , Nb 2 AlC, Mo 2 TiAlC 2 or Ti 2 AlC.

[0017] The Ti 2 AlC phase is aluminoforming and therefore does not require the addition of a coating to allow the formation of this protective layer. Its coefficient of thermal expansion is of the order of 7-9x10 -6< K -1< , which is close to alumina, and prevents flaking of the oxide formed at high temperature.

[0018] The Nb 4 AlC 3 , Nb 2 AlC, Mo 2 TiAlC 2 phases are not aluminoforming. It is preferable to add a coating allowing the formation of this protective layer. However, their coefficient of thermal expansion is also of the order of 7-9x10 -6< K -1< , close to alumina, and therefore allows the direct deposition of an alumina layer or an aluminoforming coating.

[0019] These phases thus make it possible to avoid the need for a multi-layer deposit that takes a very long time to implement. They are also refractory phases which have a mechanical resistance close to that of the ceramics used, but with better ductility than the latter, which makes their use easier.

[0020] In certain embodiments, the composite material comprises between 1 and 50% of second phase by volume of the composite material, preferably between 1 and 20%. These values ​​make it possible to ensure the fragmentation of the composite material by hydrolysis, while leaving a sufficient volume of first phase in the composite material, making it possible to retain the technical advantages linked to this first phase. In addition, this fraction of Al 4 C 3 phase makes it possible to ensure the chemical stability of the material at high temperature, while making it possible to induce a hydrolysis phenomenon facilitating debonding.

[0021] In some embodiments, an outer surface of the foundry core is covered with a layer of alumina.

[0022] Degradation of the core, by hydrolysis of the aluminum carbide in an atmosphere containing water, should only occur during core shakeout. Thus, the presence of a dense, adherent alumina layer on the surface of the core protects the composite material from degradation during the other stages of manufacturing a casting prior to core shakeout, particularly during the wax removal stage.

[0023] In some embodiments, the alumina layer has a thickness of between 1 and 50 µm. This thickness ensures protection of the core during the manufacture of a casting. More specifically, the alumina layer thus formed is thin enough not to have an impact on the removal of the core by shakeout, but chemically isolates the core from the outside.

[0024] The present disclosure also relates to a method for manufacturing a foundry core for the manufacture of a hollow metal aeronautical part, in particular a high-pressure turbine part by lost wax casting, the foundry core comprising a composite material comprising on the one hand a first phase of formula M n+1 AlC n , where n = 1 to 3 and M being a transition metal chosen from the group consisting of titanium and / or niobium and / or molybdenum, the composite material comprising on the other hand a second phase of formula Al 4 C 3 , the foundry core being obtained by a powder metallurgy method comprising a mixing step in which powders making it possible to obtain the composite material are mixed, and a shaping step.

[0025] The mixture of powders used to obtain the composite material may comprise the mixture of pure powders of carbon, aluminum, titanium and / or titanium carbide, and / or niobium, and / or niobium carbide and / or molybdenum and / or aluminum carbide Al 4 C 3 . In other words, the composite material constituting the foundry core is obtained by reacting the different powders of the constituent elements of this material at high temperature. This process has the advantage of involving, in the production of the composite material, the Al 4 C 3 phase, making it possible to provide the necessary elements AI and C, thus providing the aforementioned advantages.

[0026] Furthermore, the shaping step may comprise the injection of a binder onto a powder (called “binder jetting” in English), the injection of a mixture of metal powder and a thermoplastic polymer (or MIM process for “Metal Injection Molding” in English) or any other suitable known 3D printing process, preferably followed by conventional debinding and / or sintering, or unconventional debinding and / or sintering such as “flash sintering” (or SPS sintering for “Spark Plasma Sintering” in English), for example.

[0027] In some embodiments, the mixing step comprises mixing pure powders constituting the first phase so as to obtain the first phase in powder form, then mixing said first phase in powder form with an Al 4 C 3 powder so as to obtain the second phase.

[0028] In other words, the pure powders of carbon, aluminum, titanium and / or titanium carbide, and / or niobium, and / or niobium carbide, and / or molybdenum, and / or aluminum carbide are mixed first, so as to obtain the first phase in a first step, then the first phase obtained is mixed with an aluminum carbide powder in a second step, so as to obtain the second phase. This makes it possible to improve the control of the proportions of each phase.

[0029] In some embodiments, the mixing step comprises mixing pure powders constituting the first phase with excess Al 4 C 3 powder so as to form the composite material in one operation.

[0030] In other words, according to this configuration, the mixing of the powders is not carried out in two stages (manufacturing of the first phase in the first stage, then mixing with an aluminum carbide powder), but the aforementioned pure powders are mixed in the same operation with an excess Al 4 C 3 powder, i.e. in over-stoichiometry, thus allowing the formation of the composite material "in situ". The fact of reacting the Al 4 C 3 powder in over-stoichiometry with respect to the first desired phase makes it possible to maintain a controlled volume fraction of this phase in the final material.

[0031] In some embodiments, the first phase is of formula Ti 2 AlC, the method comprising, after the step of shaping the foundry core, a step of oxidizing the core allowing the formation of an alumina layer on a surface of the core.

[0032] As mentioned previously, the Ti 2 AlC formula phase is aluminoforming, and thus allows the formation of an alumina layer by simple oxidation of the core, without requiring the addition of a complex multi-layer coating allowing the formation of this protective layer. However, this core degradation step must only be able to be activated after the casting has been carried out. This oxidation step makes it possible to produce an adherent and dense alumina layer on the surface of the core capable of protecting the composite material from degradation, in particular during the dewaxing step. It should also be noted that since the subsequent metal casting step is carried out under vacuum, the latter does not pose any particular problem with these materials.

[0033] In some embodiments, the first phase is of one of the formulas Nb 4 AlC 3 , Nb 2 AlC, Mo 2 TiAlC 2 , the method comprising, after the step of shaping the foundry core, a step of depositing an aluminoforming coating, then a step of oxidizing the coating allowing the formation of an alumina layer on a surface of the core.

[0034] As mentioned previously, these phases are not aluminoforming, and therefore require the addition of a coating to allow the formation of this protective layer. However, these phases are compatible with aluminoforming coatings capable of forming an alumina layer by oxidation. It is thus possible to form a protective alumina layer in a simple manner, without requiring the addition of a complex multi-layer coating to form this protective layer.

[0035] In some embodiments, the oxidation step is carried out by placing the core in an enclosure under air between 1000°C and 1400°C.

[0036] The present disclosure also relates to a method of manufacturing by lost wax casting a hollow metal aeronautical part, in particular a high-pressure turbine part, using a foundry core obtained by a method according to any one of the preceding embodiments, the method comprising, after steps of casting a molten metal around the foundry core and solidifying said metal, a step of detaching the foundry core by baking.

[0037] In other words, after solidification of the metal in a ceramic mold and around the foundry core, the assembly is placed in a device, for example an oven, preferably with controlled humidity. As mentioned previously, the presence of the Al 4 C 3 phase between the grain boundaries allows, in air laden with water, the disintegration of the foundry core. This thus facilitates shakeout, and in particular improves shakeout of very fine channels, while avoiding the use of chemical solutions, such as acids, which are potentially harmful to the manufactured part.

[0038] In some embodiments, the method comprises, before the knockout step, a step in which an opening is made in the part.

[0039] More specifically, the casting devices are eliminated and an opening is made in the part without the alumina layer. This makes it possible to further facilitate the detachment of the core, the composite material thus degraded being able to be evacuated via this opening.

[0040] In some embodiments, the method comprises, after the shakeout step, a recovery step, in which the material shaken out by baking is recovered so as to be reused for the manufacture of another foundry core starting from the mixing step.

[0041] In other words, once the core has degraded, a fragmented material composed of grains from the first phase and hydrated aluminum can be recovered. After drying, this material can be "recharged" with Al 4 C 3 during the mixing step and thus be reused to manufacture new cores. It is thus possible to recycle the de-molded foundry core, thus making it possible to respond at least in part to the aforementioned environmental issues.

[0042] The present disclosure also relates to a method for manufacturing a hollow aeronautical part made of ceramic matrix composite using a core obtained by a method according to any one of the preceding embodiments, the method comprising, after steps of inserting the core into a fiber preform, impregnating a ceramic matrix into the fiber preform and solidifying the matrix, a step of demoulding the core by baking. It will be noted that the foundry core obtained by a method according to the present disclosure is more simply called a “core” when it is used for the manufacture of ceramic matrix composite (CMC) parts. Brief description of the drawings

[0043] The invention and its advantages will be better understood upon reading the detailed description given below of different embodiments of the invention given as non-limiting examples. This description refers to the appended pages of figures, in which: [ Fig. 1 ] There figure 1 represents a perspective view of a hollow metal blade of a high-pressure turbine, [ Fig. 2 ] There figure 2 represents a cross-section of the blade of the figure 1 , [ Fig. 3 ] There figure 3 is a perspective view of a foundry core according to the present disclosure, [ Fig. 4 ] There figure 4 schematically represents the steps of a method of manufacturing a hollow metal part according to a first embodiment in accordance with the description, [ Fig. 5 ] There figure 5 schematically represents the steps of a method of manufacturing a hollow metal part according to a second embodiment in accordance with the description. Description of the embodiments

[0044] There figure 1 represents a perspective view of a hollow blade 10 of a high pressure turbine, and the figure 2 represents a sectional view of said blade 10, showing the different cooling circuits 12 within this blade 10.

[0045] Such a blade is obtained, according to the present disclosure, by a lost wax casting process. In particular, the cooling circuits 12 are obtained by using, during the manufacturing process, a foundry core 1, manufactured during a preliminary step of the process, and the shape of which corresponds to the shape of the cooling circuits 12 intended to be formed.

[0046] Such a foundry core 1, in accordance with the present disclosure, is shown in perspective on the figure 3 . Certain portions 2 of this core 1, making it possible to obtain the different cooling channels 12, are complex or thin. Nevertheless, the foundry core 1 according to the present disclosure comprises a composite material making it easier to remove this core 1, during the shake-out step described later.

[0047] In fact, the composite material comprises two phases: a first phase called the “MAX phase”, and a second phase with the formula Al 4 C 3 , in other words aluminium carbide.

[0048] MAX phases are so-called stoichiometric materials, known per se, with the formula: M n+1 AX n , with n=1 to 3, M being a transition metal, A an element from group A and X carbon and / or nitrogen.

[0049] In this presentation, the element used in group A is aluminum (Al) in order to ensure either the formation of an alumina layer when aluminoforming phases are used, or compatibility with subsequently deposited aluminoforming coatings. The element used at site X is carbon (C). Indeed, phases containing nitrogen (N) often have lower melting temperatures than their carbon-containing counterparts and chemical compatibility with the Al 4 C 3 phase is not ensured. Finally, the element used at site M is determined such that the resulting material has a melting point above 1500°C. Chromium (Cr)-based MAX phases, such as Cr 2 AlC for example, are not suitable for the present application because they begin to decompose around 1500°C. Similarly, zirconium (Zr)-based MAX phases have too low a melting temperature, notably below 1500°C.

[0050] Thus, in the application of the present disclosure, the first phase used may be of formula Nb 4 AlC 3 , Nb 2 AlC, Mo 2 TiAlC 2 or Ti 2 AlC.

[0051] The second phase of formula Al 4 C 3 is a known carbide with a very high melting temperature (2200°C). It is also aluminoforming at high temperature. However, the particularly advantageous property in the context of the invention is the ease with which this phase hydrolyses at room temperature in the presence of a water-rich atmosphere. The decomposition of this phase follows the following reaction: Al 4 C 3 + 12 H 2 O → 4 Al(OH) 3 + 3 CH 4

[0052] This reaction can be catalyzed by optimizing the humidity level but also the temperature.

[0053] Thus, given the presence of the second phase of formula Al 4 C 3 , between the grain boundaries of the first phase, the foundry core 1 comprising this composite material can be easily removed by being degraded by hydrolysis, at the end of the blade manufacturing process.

[0054] In this respect, the method of manufacturing blades according to the present disclosure is a lost wax casting method. The different stages of this method, according to a first embodiment, are presented on the figure 4 .

[0055] The first step S100 of this method consists of manufacturing the casting core 1 described above, intended to be subsequently used in the manufacture of hollow turbomachine blades using the lost wax casting technique. The casting core 1 thus manufactured in step S100 is placed in a wax mold, being held in a predetermined position, so as to inject wax around the core to form the wax model having the shape of the final part (step S200). After demolding from the wax mold, the wax model is then repeatedly dipped into a slip in order to form a ceramic mold (step S300).After removal of the wax (step S400), obtained by placing the assembly in an autoclave furnace, for example, the molten metal, for example nickel-based alloys, is poured into the ceramic mold and around the ceramic core, the latter being again held in a fixed position inside the ceramic mold, and the metal is then solidified by controlled solidification (step S500). Finally, the ceramic mold and the foundry core 1 are removed by demoulding, in order to obtain the final part (step S600).

[0056] According to the present disclosure, step S100 of manufacturing the foundry core 1 is divided into several steps. Firstly, metal powders are mixed together, so as to obtain a composite powder comprising the first and second phases (step S110). According to the first embodiment, pure powders of aluminum (Al), carbon (C), niobium (Nb), and / or niobium carbide (NbC) and / or molybdenum (Mo) and / or titanium (Ti), and / or titanium carbide (TiC), are mixed with an excess Al 4 C 3 aluminum carbide powder, so as to form in situ a composite material comprising the first phase and the second phase, such that the second phase represents between 1 and 50%, preferably between 1 and 20% of the total volume of the composite material.

[0057] Once the mixing step has been carried out, the foundry core 1 is shaped (step S120), so that the latter takes the desired shape. This step can be carried out by various known methods such as the injection of a binder onto a powder (called "binder jetting" in English), the injection of a mixture of metal powder and a thermoplastic polymer (or MIM process for "Metal Injection Molding" in English) or any other suitable known 3D printing process, preferably followed by conventional debinding and / or sintering, or by unconventional debinding and / or sintering such as for example "flash sintering" (or SPS sintering for "Spark Plasma Sintering" in English), or any other suitable known process, or a combination of these different processes.

[0058] Then, a step of forming an alumina layer, making it possible to form an alumina layer with a thickness of between 1 and 50 µm is carried out (step S140). This step is carried out by oxidation of the foundry core 1 by bringing the latter to a temperature of between 1000 and 1400°C. However, depending on the first phase used in the composite material, a preliminary step to this oxidation step may be necessary. Indeed, as mentioned previously, the phases of formula Nb 4 AlC 3 , Nb 2 AlC, Mo 2 TiAlC 2 are not aluminoforming, so that bringing a core 1 comprising a composite material having one of these first phases to a temperature of between 1000 and 1400°C will not allow the formation of an alumina layer. Therefore, in this case, step S120 of shaping the core is followed by a step of depositing an aluminoforming coating (step S130).

[0059] For example, a layer of molybdenum (Mo) can be deposited directly onto the core by thermal spraying. Silicon (Si) and aluminum are then deposited by pack-cementation at 1100°C. A few hours of treatment in air at 1200°C allows the formation of an alumina layer on the surface. Direct deposition of aluminum by cementation or sol-gel, followed by oxidation in air at 1100°C is also possible. This aluminoforming coating can also be deposited by known techniques such as chemical vapor deposition (CVD), physical vapor deposition (PVD), or dip coating, for example. Once the deposition of the aluminoforming coating has been carried out, step S140 of forming the alumina layer by oxidation can be carried out, under the aforementioned conditions.

[0060] On the other hand, the phase of formula Ti 2 AlC is aluminoforming. Consequently, when the latter is used for the first phase of the composite material, step S120 of shaping the core 1 can be followed immediately by step S140 of forming the alumina layer by oxidation, without requiring a prior step of depositing a coating.

[0061] The foundry core 1 thus obtained, comprising an alumina layer on its external surface, can then be used in the process for manufacturing parts by lost wax casting described above, in particular in step S200 of injecting the wax around the core 1 to form the wax model. The internal structure of the core 1 will not be affected by the step of removing the wax (step S400), due to the presence of the alumina layer on its external surface.

[0062] Furthermore, the above-mentioned step S600, comprising the shake-out of the foundry core 1, can be carried out by placing the assembly in a hygrometry-controlled oven (relative humidity RH >50%) or preferably in a steam autoclave, at temperatures between 100 and 180°C, and pressures between 6 and 12 bars. The application of pressure makes it possible to accelerate the shake-out kinetics while facilitating access of the vapors to the thin sections. This step is preferably preceded by a step of forming an opening in the part, making it possible to facilitate the evacuation of the core 1 degraded by hydrolysis in the aforementioned oven. It will be noted that during this step, the alumina layer can be evacuated at the same time as the degrading composite, or can also remain adherent to the nickel-based superalloy, providing protection against internal oxidation of the cooling channels.

[0063] Finally, the shake-out step S600 may be followed by a recovery step (step S700), or recycling, in which the composite material shaken out by baking, then in powder form, is recovered so as to be reused for the manufacture of another foundry core 1, starting again from the mixing step S110. More precisely, once the core has degraded, a fragmented material composed of grains from the first phase and hydrated aluminum is recovered. After drying, this material may be “recharged” with Al 4 C 3 and reused to manufacture new foundry cores 1.

[0064] The different stages of a process for manufacturing blades by lost wax casting according to a second embodiment of the present presentation are presented on the figure 5 .

[0065] The method according to the second embodiment differs from the method according to the first embodiment in that step S110 of mixing the powders is broken down into two sub-steps. Indeed, whereas in the context of the first embodiment, the mixing step is carried out in a single operation, in which the composite material is formed in situ due to the excess presence of the Al 4 C 3 phase, step S110 of mixing the powders in the context of the second embodiment comprises, firstly, the mixing of pure powders constituting the first phase making it possible to obtain the first phase (step S111), then the mixing of the first phase thus obtained with an Al 4 C 3 powder making it possible to obtain the composite material ex situ (step S112).

[0066] For example, in step S111, a first phase of formula Nb 4 AlC 3 can be obtained by mixing pure powders of niobium, aluminum and niobium carbide (Nb: Al: NbC) in the molar proportions 1.2: 1.1: 2.8 respectively. In this case, the niobium grains have a diameter of less than 44 µm, a purity of 99.8%, and a density of 8.57 g / cm 3< . The aluminum grains have a diameter of less than 44 µm, a purity of 99.5%, and a density of 2.70 g / cm 3< , and the niobium carbide grains have a diameter of less than 10 µm, a purity of 99%, and a density of 7.82 g / cm 3< . These different powders can be mixed in an attritor and in a solvent (for example ethanol), then subjected to drying and reactive sintering up to 1700°C. The porous mass thus obtained is ground to be reduced to powder.

[0067] Also by way of example, during step S111, a first phase of formula Ti 3 AlC 2 can be obtained by mixing pure powders of titanium, aluminum and titanium carbide (Ti: Al: TiC) according to the molar proportions 1: 1.05: 1.9 respectively. In this case, the titanium grains have a diameter of less than 45 µm, a purity of 99.5%. The aluminum grains have a diameter between 45 and 150 µm, a purity of 99.5% and the titanium carbide grains have a diameter of 2 µm, a purity of 99.5%, and a density of 7.82 g / cm3. These different powders can be mixed in a ball mixer, then subjected to reactive sintering up to 1450°C. The porous mass thus obtained is ground to be reduced to powder.

[0068] It will further be noted that, during step S111, the pure powders can also be mixed with an Al 4 C 3 powder. In this case, the Al 4 C 3 powder contributes to the formation of the first phase, but is not in sufficient quantity to form the composite material in situ, so that the second step S112 is necessary, and makes it possible to add a necessary quantity of Al 4 C 3 powder, making it possible to obtain the proportions of Al 4 C 3 mentioned above in the composite material.

Claims

1. A casting core (1) for the manufacture of hollow metal aeronautical parts, in particular high-pressure turbine parts by lost-wax casting, comprising a composite material comprising on the one hand a first phase of formula Mn+1AlCn, where n = 1 to 3 and M being a transition metal selected from the group consisting of titanium and / or niobium and / or molybdenum, the composite material comprising on the other hand a second phase of formula Al4C3.

2. The casting core (1) according to claim 1, wherein the first phase is of one of the formulae among Nb4AlC3, Nb2AlC, Mo2TiAlC2 or Ti2AlC.

3. The casting core (1) according to claim 1 or 2, wherein the composite material comprises between 1 and 50% second phase by volume of the composite material, preferably between 1 and 20%.

4. The casting core (1) according to any one of claims 1 to 3, wherein an outer surface of the casting core (1) is covered by a layer of alumina.

5. The casting core (1) according to claim 4, wherein the alumina layer has a thickness of between 1 and 50 µm.

6. A method of manufacturing a casting core (1) for making a hollow metal aeronautical part, in particular a high-pressure turbine part, by lost-wax casting, the casting core (1) comprising a composite material comprising, on the one hand, a first phase of the formula Mn+1AlCn, where n = 1 to 3 and M being a transition metal selected from the group consisting of titanium and / or niobium and / or molybdenum, the composite material also comprising a second phase of formula Al4C3, the casting core (1) being obtained by a powder metallurgy process comprising a mixing step in which powders for obtaining the composite material are mixed, and a shaping step.

7. The method according to claim 6, wherein the mixing step comprises mixing pure powders constituting the first phase so as to obtain the first phase in powder form, then mixing said first phase in powder form with an Al4C3 powder so as to obtain the second phase.

8. The method according to claim 6, wherein the mixing step comprises mixing pure powders constituting the first phase with excess Al4C3 powder so as to form the composite material in a single operation.

9. The method according to any one of claims 6 to 8, wherein the first phase is of the formula Ti2AlC, the method comprising, after the casting core shaping step, a core oxidation step enabling the formation of an alumina layer on a core surface.

10. The method according to any one of claims 6 to 8, in which the first phase is of one of the formulae Nb4AlC3, Nb2AlC and Mo2TiAlC2, the method comprising, after the step of shaping the casting core, a step of depositing an aluminoforming coating, followed by a step of oxidizing the coating to form a layer of alumina on a surface of the core.

11. A lost-wax casting method for manufacturing a hollow metal aeronautical part, in particular a high-pressure turbine part, using a casting core (1) obtained by the method according to any one of claims 6 to 10, the method comprising, after steps of casting a molten metal around the casting core and solidifying said metal, a step of knockout the casting core by steaming.

12. The method according to claim 11, comprising, prior to the knockout step, a step in which an opening is made in the part.

13. The method according to claim 11 or 12, comprising, after the knockout step, a recovery step, in which the material knocked out by steaming is recovered so as to be reused for the manufacture of another casting core starting again from the mixing step.

14. A method of manufacturing a ceramic-matrix composite hollow aeronautical part using a core (1) obtained by the method according to any one of claims 6 to 10, the method comprising, after steps of inserting the core (1) into a fibrous preform, impregnating a ceramic matrix into the fibrous preform and solidifying the matrix, a step of knockout the core (1) by steaming.