Foundry core for manufacturing a hollow metal aeronautical part

Abstract

Casting core for the manufacture of hollow metal aeronautical parts, in particular high-pressure turbine parts by lost-wax casting, including a composite material including on the one hand a first phase of formula M.sub.n+1AlC.sub.n, 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 including on the other hand a second phase of formula Al.sub.4C.sub.3.

Claims

1. A casting core for the manufacture of hollow metal aeronautical parts comprising a composite material comprising on the one hand a first phase of formula M.sub.n+1AlC.sub.n, 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 Al.sub.4C.sub.3.

2. The casting core according to claim 1, wherein the first phase is of one of the formulae among Nb.sub.4AlC.sub.3, Nb.sub.2AlC, Mo.sub.2TiAlC.sub.2 or Ti.sub.2AlC.

3. The casting core according to claim 1, wherein the composite material comprises between 1 and 50% second phase by B volume of the composite material.

4. The casting core according to claim 1, wherein an outer surface of the casting core is covered by a layer of alumina.

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

6. The casting core according to claim 1, wherein the composite material comprises between 1 and 20% second phase by volume of the composite material.

7. A method of manufacturing a casting core for making a hollow metal aeronautical part the casting core comprising a composite material comprising, on the one hand, a first phase of the formula M.sub.n+1AlC.sub.n, 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 Al.sub.4C.sub.3, the casting core 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.

8. The method according to claim 7, 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 Al.sub.4C.sub.3 powder so as to obtain the second phase.

9. A The method according to claim 7, wherein the mixing step comprises mixing pure powders constituting the first phase with excess Al.sub.4C.sub.3 powder so as to form the composite material in a single operation.

10. The method according to claim 7, wherein the first phase is of the formula Ti.sub.2AlC, the method comprising, after the casting core shaping step, a core oxidation step enabling the formation of an alumina layer on a core surface.

11. The method according to claim 7, in which the first phase is of one of the formulae Nb.sub.4AlC.sub.3, Nb.sub.2AlC and Mo.sub.2TiAlC.sub.2, 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.

12. A lost-wax casting method for manufacturing a hollow metal aeronautical part, in particular a high-pressure turbine part, using a casting core obtained by the method according to claim 7 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.

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

14. The method according to claim 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.

15. A method of manufacturing a ceramic-matrix composite hollow aeronautical part using a core obtained by the method according to claim 7, the method comprising, after steps of inserting the core into a fibrous preform, impregnating a ceramic matrix into the fibrous preform and solidifying the matrix, a step of knockout the core by steaming.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention and its advantages will be better understood on reading the following detailed description of various embodiments of the invention given by way of non-limiting examples. This description refers to the attached pages of figures, on which:

(2) FIG. 1 shows a perspective view of a high-pressure turbine hollow metal blade,

(3) FIG. 2 shows a cross-section of the blade shown in FIG. 1,

(4) FIG. 3 is a perspective view of a casting core according to the present disclosure,

(5) FIG. 4 shows schematically the steps of a method for manufacturing a hollow metal part according to a first embodiment in accordance with the present disclosure,

(6) FIG. 5 shows schematically the steps of a method of manufacturing a hollow metal part according to a second embodiment as described herein.

DESCRIPTION OF THE EMBODIMENTS

(7) FIG. 1 shows a perspective view of a hollow high-pressure turbine blade 10, and FIG. 2 shows a cross-sectional view of said blade 10, showing the various cooling circuits 12 within said blade 10.

(8) Such a blade is obtained, according to the present disclosure, by a lost-wax casting method. In particular, the cooling circuits 12 are obtained by using, during the manufacturing method, a casting core 1, manufactured in a preliminary step of the method, and having a shape corresponding to that of the cooling circuits 12 to be formed.

(9) Such a casting core 1, according to the present disclosure, is shown in perspective on FIG. 3. Some portions 2 of this core 1, allowing to obtain the various cooling channels 12, are complex or thin. Nevertheless, the casting core 1 according to the present disclosure comprises a composite material to facilitate removal of this core 1, during the knockout step described later.

(10) The composite material comprises two phases: a first phase known as the MAX phase, and a second phase with the formula Al.sub.4C.sub.3, i.e., aluminum carbide

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

(12) In the present disclosure, the element used in group A is aluminum (Al) 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). Phases containing nitrogen (N) often have lower melting temperatures than their carbon-containing counterparts, and chemical compatibility with the Al.sub.4C.sub.3 phase is not guaranteed. Finally, the element used at site M is determined so that the resulting material has a melting point above 1500 C. MAX phases based on chromium (Cr), such as Cr.sub.2AlC for example, are not suitable for the present application, as they start to decompose around 1500 C. Similarly, zirconium (Zr)-based MAX phases have too low a melting point, notably below 1500 C.

(13) Thus, in the application of the present disclosure, the first phase used can be of formula Nb.sub.4AlC.sub.3, Nb.sub.2AlC, Mo.sub.2TiAlC.sub.2 or Ti.sub.2AlC.

(14) The second phase, of formula Al.sub.4C.sub.3 is a well-known carbide with a very high melting point (2200 C.). It is also aluminoforming at high temperatures. However, a particularly advantageous property of the invention is the ease with which this phase hydrolyzes at room temperature in the presence of a water-rich atmosphere. The decomposition of this phase proceeds according to the following reaction: Al.sub.4C.sub.3+12H.sub.2O.fwdarw.4Al(OH).sub.3+3CH.sub.4

(15) This reaction can be catalyzed by optimizing both hygrometry and temperature.

(16) Thus, given the presence of the second phase of formula Al.sub.4C.sub.3, between the grain boundaries of the first phase, the casting core 1 comprising this composite material can be easily eliminated by being degraded by hydrolysis, at the end of the blade manufacturing method.

(17) In this respect, the blade manufacturing method according to the present disclosure is a lost-wax casting method. The various steps of this method, according to a first embodiment, are shown in FIG. 4.

(18) The first step S100 of this method consists in manufacturing the casting core 1 described above, intended for subsequent use in the manufacture of hollow turbomachine blades using the lost-wax casting technique. The casting core 1 thus produced in step S100 is placed in a wax mold, held in a predetermined position, so as to inject wax around the core to form the wax pattern having the shape of the final part (step S200). After removal from the wax mold, the wax pattern is then dipped several times in a slurry-cast to form a ceramic mold (step S300). Once the wax has been removed (step S400), e.g., by placing the assembly in an autoclave oven, the molten metal, e.g., nickel-based alloys, is poured into the ceramic mold and around the ceramic core, the latter again being 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 casting core 1 are removed by knockout, to obtain the final part (step S600).

(19) In accordance with the present disclosure, step S100 for manufacturing the casting core 1 is divided into several steps. Firstly, metal powders are mixed together to form a composite powder comprising the first and second phases (step S110). In the first step, pure aluminum (Al), carbon (C), niobium (Nb) and/or niobium carbide (NbC) and/or molybdenum (Mo) and/or titanium (Ti) and/or titanium carbide (TiC) powders are mixed with excess Al.sub.4C.sub.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.

(20) Once the mixing step has been completed, the casting core 1 is shaped (step S120) to the desired form. This step can be carried out by various known methods, such as binder jetting, injection of a mixture of metal powder and a thermoplastic polymer, (also known as Metal Injection Molding or MIM), or any other suitable known 3D printing process, preferably followed by conventional debinding and/or sintering, or non-conventional debinding and/or sintering such as SPS (Spark Plasma Sintering), or any other suitable known method, or a combination of these methods.

(21) This is followed by an alumina layer formation step, to form an alumina layer with a thickness of between 1 and 50 m (step S140). This step is carried out by oxidizing the casting core 1 by heating it to a temperature of between 100 and 1400 C. However, depending on the first phase used in the composite material, a preliminary step to this oxidation step may be necessary. As previously mentioned, phases of the formulae Nb.sub.4AlC.sub.3, Nb.sub.2AlC and Mo.sub.2TiAlC.sub.2 are not aluminoforming, so that heating a core 1 comprising a composite material with one of these first phases to a temperature of between 100 and 1400 C. will not result in the formation of an alumina layer. Consequently, in this case, core shaping step S120 is followed by an alumina-forming coating deposition step (step S130).

(22) For example, a layer of molybdenum (Mo) can be deposited directly on the core by thermal spraying. Silicon (Si) and aluminum are then deposited by pack-cementation at 1100 C. After a treatment in air at 1200 C. for a few hours, an alumina layer is formed on the surface. Alternatively, aluminum can be deposited directly by cementation or sol-gel, followed by oxidation under air at 1100 C. This alumina-forming 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 alumina-forming coating has been deposited, step S140, which forms the alumina layer by oxidation, can be carried out under the aforementioned conditions.

(23) In contrast, the Ti.sub.2AlC phase is aluminoforming. Consequently, when the latter is used for the first phase of the composite material, step S120 for shaping the core 1 can be followed immediately by step S140 for forming the alumina layer by oxidation, without the need for a prior coating deposition step.

(24) The casting core 1 thus obtained, comprising an alumina layer on its outer surface, can then be used in the lost-wax casting method for manufacturing parts described above, in particular in step S200 for injecting wax around core 1 to form the wax pattern. The internal structure of core 1 will not be affected by the wax removal step (step S400), due to the presence of the alumina layer on its outer surface.

(25) Alternatively, the above-mentioned step S600, comprising the knockout of the casting core 1, can be carried out by placing the assembly in a humidity-controlled oven (relative humidity RH>50%) or preferably in a steam autoclave, at temperatures of between 10 and 180 C., and pressures of between 6 and 12 bar. Applying pressure accelerates the knockout kinetics, while facilitating access of vapors to the thin sections. This step is preferably preceded by a step to form an opening in the part, to facilitate evacuation of the core 1 degraded by hydrolysis in the aforementioned oven. It should be noted that during this step, the alumina layer may be evacuated along with the degrading composite, or may also remain adhered to the nickel-base superalloy, offering protection against internal oxidation of the cooling channels.

(26) Finally, knockout step S600 can be followed by a recovery step (step S700), or recycling, in which the composite material knocked out by steaming, then in powder form, is recovered so as to be reused for the manufacture of another casting core 1, starting again from mixing step S110. More precisely, once the core has been degraded, a fragmented material composed of grains of the first phase and hydrated aluminum is recovered. After drying, this material can be recharged with Al.sub.4C.sub.3 and reused to manufacture new casting cores 1.

(27) The various steps in a lost wax casting method for manufacturing blades, according to a second embodiment of the present disclosure, are shown in FIG. 5.

(28) The method according to the second embodiment differs from the method according to the first embodiment in that powder mixing step S110 is divided into two sub-steps. Whereas in the first embodiment, the mixing step is carried out in a single operation, in which the composite material is formed in situ by the presence of excess Al.sub.4C.sub.3, phase, the S110 powder mixing step in the second embodiment comprises firstly mixing the pure powders making up the first phase to obtain the first phase (step S111), then mixing the first phase thus obtained with an Al.sub.4C.sub.3 powder to obtain the composite material ex situ (step S112).

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

(30) By way of further example, in step S111, a first phase of formula Ti.sub.3AlC.sub.2 can be obtained by mixing pure titanium, aluminum and titanium carbide powders (Ti:Al:TiC) in molar proportions of 1:1.05:1.9 respectively. In this case, the titanium grains have a diameter of less than 45 m and a purity of 99.5%. The aluminum grains have a diameter of between 45 and 150 m, a purity of 99.5% and the titanium carbide grains have a diameter of 2 m, a purity of 99.5%, and a density of 7.82 g/cm.sup.3. These different powders can be mixed in a ball mill, then subjected to reactive sintering up to 1450 C. The resulting porous mass is ground to powder.

(31) It should also be noted that, in step S111, the pure powders can also be mixed with Al.sub.4C.sub.3 powder. In this case, the Al.sub.4C.sub.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.sub.4C.sub.3, powder, making it possible to obtain the previously mentioned proportions of Al.sub.4C.sub.3 in the composite material.

(32) Even though the present invention has been described with reference to specific embodiments, it is obvious that modifications and changes can be made to these embodiments without departing from the general scope of the invention as defined by the claims. In particular, individual features of the various illustrated/mentioned embodiments may be combined in additional embodiments. Consequently, the description and drawings are to be considered in an illustrative rather than restrictive sense.

(33) It is also clear that all features described with reference to a method are transposable, alone or in combination, to a device, and conversely, all features described with reference to a device are transposable, alone or in combination, to a method.