Improved counter-form for the manufacture of a metal aeronautical part

Abstract

Disclosed is a counter-form (1) for producing metal aeronautical parts, in particular a turbine part, by solid-phase densification, comprising a composite material containing, on the one hand, a first phase having formula Mn+1AlCn, where n = 1 to 3 and M is a transition metal selected from the group consisting of titanium and / or molybdenum and / or niobium and / or chromium, and, on the other hand, a second phase having formula Al4C3.

Description

Technical Field

[0001] The invention relates to the manufacture of aeronautical parts, in particular blades or rectifiers of aeronautical turbomachines, by solid phase densification methods. More specifically, the invention relates to the counter-forms used in the manufacture of these aeronautical parts, to a method of manufacturing such a counter-form, and to a method of manufacturing such an aeronautical part. Prior art

[0002] Metal aeronautical parts, particularly turbine blades or rectifiers, are generally manufactured from nickel-, titanium-, or titanium aluminide-based alloys. To limit the risk of contamination of the materials constituting the parts linked to the use of liquid phases during foundry manufacturing processes, solid-phase densification manufacturing processes can be used.

[0003] Such solid-phase densification manufacturing processes include, for example, sintering under load, such as flash sintering or SPS (for Spark Plasma Sintering) or hot isostatic pressing (HIP for Hot Isostatic Pressing), or the injection of a mixture of metal powder and a thermoplastic polymer (known as the MIM process for Metal Injection Molding).

[0004] SPS sintering is a sintering method using the Joule effect to heat the pre-compacted powder, constituting the part to be manufactured (in the present application, a powder based on nickel, titanium, or titanium aluminide) in a hollow graphite tool between two electrodes, between which a pulsed current is applied, under an inert atmosphere or under vacuum, the tool being subjected to uni-axial pressure, for example under the action of a hydraulic press. The Joule effect heating of the powder thus allows the densification of the part.

[0005] In the case of HIP sintering, a preform of the part to be manufactured is placed in a vacuum-evacuated container before being hermetically sealed. A uniform pressure in all directions is thus applied to the part, via the container, by injecting a neutral gas under pressure (for example argon or nitrogen) into the container enclosure.

[0006] Furthermore, during powder injection mixing, known as the MIM process, a powder constituting the material to be manufactured is mixed with a polymer binder. The resulting mixture, known as "feedstock", is then injected into a tool to form the part to be manufactured. The binder is then removed during a debinding process. A sintering operation can then be carried out on the resulting part.

[0007] These types of processes allow the manufacture of demoldable parts, such as certain turbine blades. However, these processes have certain drawbacks. Indeed, for SPS sintering for example, after densification at high temperature, the current is cut and the part cools. During this cooling phase, the densified part is still contained by the graphite mold that gave it its shape, and undergoes a contraction linked to its coefficient of thermal expansion (approximately 10-12x10 -6 < / °C for metal parts). However, given its coefficient of thermal expansion (approximately 2-3x10 -6 < / °C), graphite tooling deforms only very little during cooling, which causes differential expansions and stresses that can lead either to the breakage of the tools or their premature wear, or to the breakage of the densified part.This is particularly the case for the geometries of blades with licks and feet, or even of straighteners.

[0008] To overcome this limitation, it is known to use so-called "drawer" molds, having different parts arranged with each other in such a way as to allow the densification of the part according to a predefined shape, but while allowing the mold to shrink during the cooling of the latter. The mechanical constraints applied by the part during its cooling cause in particular a movement of the different parts of the mold. Although this technique has advantages, it can cause local burrs, and requires a very strict adjustment of the parts of the mold which is difficult to maintain due to its repeated use at temperature and under load.

[0009] To overcome these drawbacks, it is also known to use counter-forms corresponding to the negative of the part to be manufactured, making it possible to produce complex parts, these counter-forms themselves being arranged in the aforementioned graphite tooling. A method using such counter-forms conventionally comprises the manufacture of a counter-form by additive manufacturing, the partial sintering of the counter-form to give it rigidity, the filling of the counter-form with a powder to be densified, the joint SPS sintering of the material constituting the counter-form and the powder present inside it, and finally the decoupling of the counter-form to release the sintered part.

[0010] This process nevertheless involves several disadvantages. On the one hand, the materials used for the counterforms are ceramics, or a composite thereof, such as yttria-stabilized zirconia (YSZ), alumina-reinforced zirconia (ATZ), or zirconia-reinforced alumina (ZTA). These materials have the disadvantage of not being electrically conductive, which, particularly in the context of SPS sintering, limits the generation of the Joule effect in the sintering powder, and can lead to local densification defects due to inhomogeneity of the induced thermal field.

[0011] On the other hand, the titanium or titanium aluminide alloys used to manufacture the blades or the straighteners are conventionally sintered by SPS at temperatures above 1350°C. However, at these temperatures, the above ceramic materials used for the counter-forms have a density above 80%, which makes them difficult to shake out and requires a specific step involving chemical or mechanical shake out, potentially harmful to the part subsequently manufactured and to the environment, since the counter-form cannot be recycled. Documents US 4,187,266 A and US 2007 / 056709 A1 also refer to a counter-form for the manufacture of metal aeronautical parts.

[0012] In addition, the materials used for the part to be manufactured and the counter-form have different coefficients of thermal expansion, which can cause the part to deform in the finest areas such as the trailing edges, break the parts, or lead to the recrystallization of certain areas under stress, inducing mechanical deformation.

[0013] There is therefore a need for a solution to at least partially overcome the aforementioned drawbacks. Statement of the invention

[0014] The present disclosure relates to a counter-form for the manufacture of a metallic aeronautical part, in particular a turbine part by solid phase densification, 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 molybdenum, and / or niobium and / or chromium, the composite material comprising on the other hand a second phase of formula Al 4 C 3 .

[0015] It is understood that the first phase is of the "MAX phase" type, a crystalline structure with the generic formula M n+1 AX n , combining characteristics of both metals and ceramics, and notably presenting good thermal and electrical conductivity, good machinability, as well as tolerance to damage and resistance to oxidation at high temperature.

[0016] In the present presentation, the use of aluminum on the A site and carbon on the X site ensures good chemical compatibility with the Al 4 C 3 phase. Furthermore, the use of aluminum on the A site ensures the formation of a protective alumina layer by oxidation of the counter-form. In addition, the use of carbon on the X site is advantageous in that it does not present the risk of contaminating the materials present, nor of reacting negatively with the Al 4 C 3 phase, unlike nitrogen.

[0017] Furthermore, titanium or chromium, used on site M, have melting temperatures higher than the temperatures used during sintering of the part to be manufactured, allowing their structure and stability to be preserved during sintering. Furthermore, they have coefficients of thermal expansion compatible with those of the materials to be densified, in particular alloys based on nickel, titanium, or titanium aluminide, and good thermal conductivity.

[0018] 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 counter-form 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 counter-form. In other words, the composite material forming the counter-form can be initially dense and massive, and be reduced to powder by hydrolysis.

[0019] On the other hand, 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 counter-form shaping and casting stages. In addition, once the counter-form 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 counter-forms.

[0020] The composite material of the counter-form according to the present disclosure thus combines the aforementioned advantages linked to the first phase, with the use of a second phase of formula Al 4 C 3 , allowing the production of parts with complex shapes without having to resort to complex graphite tools, while allowing easy and rapid detachment of the counter-form not requiring chemical solutions potentially harmful to the part subsequently manufactured and to the environment, and which can be recycled.

[0021] In some embodiments, the first phase is of one of Cr 2 AlC, Ti 3 AlC 2 , Ti 2 AlC, Nb 4 AlC 3 , Nb 2 AlC or Mo 2 TiAlC 2 .

[0022] These phases have good chemical compatibility with the second phase Al 4 C 3 and make it possible to obtain a thermodynamically stable composite at high temperature, during the sintering phase. The Cr 2 AlC, Ti 3 AlC 2 , Ti 2 AlC phases also have the advantage of covering the densification temperature ranges and thermal expansion coefficients of the materials considered and used to manufacture the part. In addition, the Cr 2 AlC, Ti 3 AlC 2 , Ti 2 AlC phases are aluminoforming. Since the other phases are not aluminoforming, it is preferable to add a coating allowing the formation of a protective layer. This addition is however not essential, other oxides having a similar function to alumina, although less adherent than the latter, can form on the counter-form when it is subjected to an oxidation step.

[0023] 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.

[0024] In some embodiments, an inner surface of the counterform is covered with a layer of alumina.

[0025] The degradation of the counterform, by hydrolysis of the aluminum carbide in an atmosphere containing water, should only occur when the counterform is shaken out. Thus, the presence of a dense, adherent alumina layer on the internal surface of the counterform protects the composite material from degradation during the other stages of manufacturing a part prior to shakeout of the counterform.

[0026] In some embodiments, the alumina layer has a thickness of between 1 and 50 µm. This thickness ensures protection of the counterform during the manufacture of a part. More specifically, the alumina layer thus formed is thin enough not to have an impact on the mechanical shrinkage of the part during cooling, but chemically insulates the powder and the counterform.

[0027] The present disclosure also relates to a method for manufacturing a counter-form for the manufacture of a hollow metal aeronautical part, in particular a turbine part by solid phase densification, the counter-form 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 and / or chromium, the composite material comprising on the other hand a second phase of formula Al 4 C 3 , the counter-form 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.

[0028] The mixture of powders used to obtain the first phase may in particular comprise the mixture of pure powders of carbon, aluminum, titanium and / or chromium, and / or chromium carbide, and / or chromium carbide, and / or titanium carbide, and / or aluminum carbide. In other words, the composite material constituting the counter-form 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.

[0029] Furthermore, the shaping step may include 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 sintering, or sintering under load called "flash sintering" (or SPS sintering for "Spark Plasma Sintering" in English), for example.

[0030] In some embodiments, the mixing step comprises mixing the 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.

[0031] In other words, pure powders of carbon, aluminum, titanium and / or chromium and / or chromium carbide, and / or chromium carbide, and / or titanium carbide, and / or aluminum carbide for example 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.

[0032] 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.

[0033] 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.

[0034] In certain embodiments, during the step of shaping the counter-form, a supply channel configured to allow the supply of powder constituting the part to be manufactured, is provided in the counter-form.

[0035] In other words, when shaping the counter-form using one of the 3D printing techniques mentioned above, a supply channel is provided in the structure of the counter-form, so as to put the internal cavity of the counter-form forming the negative of the part to be manufactured, in fluid communication with the exterior of the counter-form. This channel makes it easier to supply powder of the material constituting the part to be manufactured and densified.

[0036] In certain embodiments, the first phase is of formula Cr 2 AlC, Ti 3 AlC 2 or Ti 2 AlC, the method comprising, after the step of shaping the counter-form, an oxidation step allowing the formation of an alumina layer on an internal surface of the counter-form.

[0037] As mentioned previously, the phases of formula Cr 2 AlC, Ti 3 AlC 2 or Ti 2 AlC are aluminoforming, and thus allow the formation of an alumina layer by simple oxidation of the counter-form, without requiring the addition of a complex multi-layer coating allowing the formation of this protective layer. This oxidation step makes it possible to produce an adherent and dense alumina layer on a wall of the internal cavity of the counter-form forming the negative of the part to be manufactured, capable of protecting the composite material, further improving the densified part debonding and limiting the risks of interdiffusion between the densified powder and the composite material constituting the counter-form. It should also be noted that since the subsequent densification step is carried out under vacuum, the latter does not pose any particular problem with respect to the composite material.

[0038] In certain embodiments, the oxidation step is carried out by placing the counter-form in an enclosure under air between 1000°C and 1400°C.

[0039] The present disclosure also relates to a method for manufacturing a metal aeronautical part, in particular a turbine part by solid phase densification, using a counter-form obtained by a method according to any one of the preceding embodiments, the method comprising, after steps of filling the counter-form with a powder constituting the part to be manufactured and of densifying said powder in the counter-form, a step of unmolding the counter-form by baking.

[0040] In other words, after densification of the powder by SPS sintering, for example, in the counter-form, 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 core of the counter-form. This thus facilitates the demoulding and therefore the demoulding of the part, while avoiding the use of chemical solutions, such as acids, which are potentially harmful to the manufactured part.

[0041] In some embodiments, the method comprises, after the demoulding step, a recovery step, in which the material demoulded by baking is recovered so as to be reused for the manufacture of another counter-form starting from the mixing step.

[0042] In other words, once the counterform 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 counterforms. It is thus possible to recycle the detached counterform, thus making it possible to respond at least in part to the aforementioned environmental issues. 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 metal turbine blade comprising wipers, [ Fig. 2 ] There figure 2 schematically represents the dawn of the figure 1 , and a counter-form according to the present presentation, in two parts, [ Fig. 3 ] There figure 3 is a perspective view of a counter-form according to the present disclosure, in one part, [ Fig. 4 ] There figure 4 schematically represents the steps of a method of manufacturing a 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 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 turbine blade 10 comprising an aerodynamic profile 12 having a lower surface 13 and an upper surface 14, a blade root 15 at its lower end, and a heel 16 at its upper end. The blade 10 further comprises two sealing lips 17 and 18 formed on the upper face of the heel 16 arranged transversely to the lower surface 13 and upper surface 14 sides.

[0045] Such a blade is obtained, according to the present disclosure, by densification of a powder of the material constituting the blade, in particular alloys based on nickel (Ni), titanium (Ti), or titanium aluminide (TiAl), in a counter-form corresponding to the negative of the part to be manufactured, that is to say of the blade 10 in the present example.

[0046] Such a counter-form 1, in accordance with the present presentation, is represented in perspective on the figure 2 , with the blade 10 shown schematically in this figure. In this example, the counter-form 1 comprises two parts 1a and 1b arranged on either side of the blade 10, each comprising a half cavity, and intended to be assembled to form a counter-form 1 containing a complete cavity corresponding to the negative of the blade 10. Each half cavity respectively comprises a first portion 2a, 2b, a second portion 5a, 5b, a third portion 6a, 6b and locations 7a, 7b and 8a, 8b. These different portions together form, when the two parts 1a and 1b of the counter-form 1 are assembled (as illustrated in the figure 3 ), a first portion 2 corresponding to the negative of the aerodynamic profile 12 of the blade, a second portion 5 corresponding to the negative of the blade root 15, and a third portion 6 corresponding to the negative of the heel 16, and locations 7 and 8 intended to form the wipers 17 and 18.

[0047] A passage 9a, 9b is also provided in each part 1a, 1b respectively of the counter-form 1 so as to form a supply channel 9 in the counter-form 1 after assembly of the two parts 1a and 1b, and to allow the supply of the aforementioned powder constituting the blade to be manufactured, when the parts 1a and 1b are assembled.

[0048] There figure 3 shows the counter-form 1 after assembly of the two parts 1a and 1b. It should be noted, however, that this example is not limiting, the counter-form 1 being able to be manufactured in a single piece in a single operation by a method described in more detail in the remainder of the description, so as to form a cavity comprising the different portions 2, 5, 6, 7, 8 and 9 mentioned above.

[0049] Furthermore, the counter-form 1 comprises a composite material making it possible in particular to facilitate its removal, during the unsticking step described later.

[0050] 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.

[0051] 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.

[0052] In this presentation, the element used in group A is aluminum (Al) to ensure the formation of an alumina layer when aluminoforming phases are used. 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 assured.Finally, the element used on site M is determined so that the melting temperature and the coefficient of thermal expansion of the MAX phases considered are compatible with the constituent materials of the part to be sintered, in particular nickel-based alloys (Ni), having a coefficient of thermal expansion between 14 and 16x10 -6 < / °C, titanium (Ti), having a coefficient of thermal expansion between 10 and 13x10 -6 < / °C, or titanium aluminide (TiAl), having a coefficient of thermal expansion between 10 and 13x10 -6 < / °C. The sintering temperatures of these materials are also higher than 1350°C.

[0053] Thus, in the application of the present disclosure, the first phases retained may be of formula Cr 2 AlC, having a melting temperature greater than 1500°C and a coefficient of thermal expansion of approximately 13x10 -6 < / °C, Ti 3 AlC 2 having a melting temperature greater than 1550°C and a coefficient of thermal expansion of between 9 and 12x10 -6 < / °C, or Ti 2 AlC having a melting temperature greater than 1550°C and a coefficient of thermal expansion of between 7 and 10x10 -6 < / °C.

[0054] 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 hydrolyzes 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

[0055] This reaction can be catalyzed by optimizing the humidity level but also the temperature.

[0056] Thus, taking into account the presence of the second phase of formula Al 4 C 3 , between the grain boundaries of the first phase, the counter-form 1 comprising this composite material can be easily eliminated by being degraded by hydrolysis, at the end of the manufacturing process of the blade or the rectifier.

[0057] In this regard, a first example of a method for manufacturing blades according to the present disclosure is a process by sintering under load, called SPS sintering (for “Spark Plasma Sintering” in English) in the remainder of the description. The different steps of this method, according to a first embodiment, are presented on the figure 4 .

[0058] The first step S100 of this process consists of manufacturing the counter-form 1 described above, in one or two parts.

[0059] According to the present disclosure, step S100 of manufacturing the counter-form 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), chromium (Cr) and / or titanium (Ti), and / or chromium carbide (CrC), and / or chromium carbide (Cr 7 C 3 ), and / or titanium carbide (TiC) are mixed with an excess powder of aluminum carbide Al 4 C 3, 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.

[0060] Once the mixing step has been carried out, the counter-form 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 method, preferably followed by sintering, or SPS sintering, for example, or any other suitable known method, or a combination of these different methods. During this shaping step, in particular 3D printing by one of the aforementioned techniques, a supply channel 9 is provided, allowing the subsequent injection of metal powder.

[0061] Then, a step of forming an alumina layer, making it possible to form a protective alumina layer with a thickness of between 1 and 50 µm can be carried out (step S130). This step is carried out by oxidizing the counter-form 1 by bringing the latter to a temperature of between 1000 and 1400°C. This step is made possible by the fact that the phases of formula Cr 2 AlC, Ti 3 AlC 2 or Ti 2 AlC are aluminoform.

[0062] The counter-form 1 thus manufactured in step S100, and comprising the cavity described above corresponding to the negative of the blade, is then filled with a powder constituting the blade to be manufactured (step S200), in particular a powder based on titanium (Ti), a nickel-based superalloy (Ni), or an intermetallic alloy such as titanium aluminide (TiAl), via the supply channel 9. An ultrasonic table can be used to facilitate the flow of the powder into the counter-form and its filling.

[0063] It should be noted that for the densification of nickel-based materials, the use of a first phase of formula Cr 2 AlC is preferred, and for the densification of materials based on titanium or titanium aluminide, the use of a first phase of formula Ti 2 AlC or Ti 3 AlC 2 is preferred. These choices are based on the compatibilities of these different materials in terms of thermal expansion, but also chemical compatibility between the first phase and the alloy to be densified. Indeed, titanium presents a greater risk of diffusing at high temperature with nickel, and chromium presents the risk of forming embrittling phases with titanium.

[0064] The counter-form 1 containing the powder to be densified is then placed in a tool (not shown), preferably made of graphite, configured to carry out SPS sintering (step S300).

[0065] SPS sintering is then carried out (step S400). During SPS sintering, the counter-form 1 is placed in a press exerting axial pressure on the counter-form 1. A pulsed current is then applied to the counter-form 1, so as to heat the powder present in it by the Joule effect, allowing the densification of the powder.

[0066] When the densification of the part is complete, the counter-form 1 is extracted from the graphite tooling, and eliminated by detachment in order to obtain the final part (step S500). Step S500 of detachment of the counter-form 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 detachment kinetics while facilitating the access of the vapors to the thin sections. This step allows the disintegration of the counter-form 1, taking into account the presence of the second phase of formula Al 4 C 3 between the grain boundaries of the first phase. A cleaning and finishing step of the blade obtained can also be carried out.

[0067] Finally, the demoulding step S500 may be followed by a recovery step (step S600), or recycling, in which the composite material demoulded by baking, then in powder form, is recovered so as to be reused for the manufacture of another counter-form 1, starting again from the mixing step S110. More precisely, once the degradation of the counter-form 1 has been carried out, a fragmented material composed of grains of the first phase and hydrated aluminum is recovered. After drying, this material may be “recharged” with Al 4 C 3 and reused in order to manufacture new counter-forms 1.

[0068] The different stages of a process for manufacturing turbine blades or rectifiers by densification according to a second embodiment of the present presentation are presented on the figure 5 .

[0069] 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 making it possible to obtain the first phase (step S111), the grinding in powder form of this first phase, 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).

[0070] For 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.

[0071] In this case, during step S600 in which the composite material detached by baking is recovered so as to be reused for the manufacture of another counter-form 1, the material can be "recharged" with Al 4 C 3 starting again from step S112. It will also 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, such 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 previously in the composite material.

[0072] The first and second embodiments above have been described with reference to a first application example, in which the solid densification process of the powder contained in the counterform 1, comprising steps S200 to S400, is carried out by SPS sintering. This example is however not limiting, other solid densification methods may be used.

[0073] For example, instead of SPS sintering, hot isostatic pressing (HIP) can be used. In this case, step S200 of filling the counter-form 1 with a powder constituting the blade to be manufactured is also carried out, then, in step S300, the counter-form 1 containing said powder is placed in a deformable container. HIP densification is carried out in step S400, in which a neutral gas (for example argon or nitrogen) is injected into the pressure chamber, then applying a uniform pressure in all directions on the container containing the counter-form 1. Once the densification is complete, and the container removed by mechanical or chemical machining, the counter-form 1 is then demolished under the conditions described above in step S500, then the material is recovered in step S600.

[0074] Alternatively, instead of SPS sintering, an injection of a mixture of metal powder and a thermoplastic polymer (called MIM process for "Metal Injection Molding" in English) can be carried out. In this case, during step S200, the counter-form 1 is inserted into a MIM injection press and a powder constituting the material to be manufactured, mixed with a polymer binder, is injected into the counter-form 1. The polymer binder is then removed during a debinding process. Natural sintering without pressure on the part obtained can then be carried out. If the latter allows the part to be sufficiently densified, in particular if the relative density is greater than 99%, the counter-form 1 can be debonded, in accordance with step S500.However, if it is necessary to further densify the part, natural sintering can be supplemented by a pressurized SPS or HIP densification cycle, by repeating steps S300 and S400 described above. Alternatively, the above-mentioned debinding can be immediately followed by SPS or HIP densification according to steps S300 and S400, without going through natural sintering.

[0075] Thus, either of the densification modes (SPS, HIP or MIM), or a combination thereof, may be used for the manufacture of the metal part, and apply to both embodiments described previously and described with reference to figures 4 And 5 It should be noted in particular that steps S100 for manufacturing counter-form 1, S500 for unsticking and S600 for recovering the material are common to all the densification methods (SPS, HIP or MIM) used.

[0076] Although the present invention has been described with reference to specific exemplary embodiments, it is obvious that modifications and changes may be made to these examples 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. Therefore, the description and drawings should be considered in an illustrative rather than restrictive sense.

[0077] It is also obvious that all the characteristics described with reference to a method are transposable, alone or in combination, to a device, and conversely, all the characteristics described with reference to a device are transposable, alone or in combination, to a method.

Claims

1. A counter-form (1) for producing metal aeronautical parts, in particular a turbine part by solid-phase densification, comprising a composite material comprising, on the one hand, a first phase having formula Mn+1AlCn, where n = 1 to 3 and M is a transition metal selected from the group consisting of titanium and / or molybdenum and / or niobium and / or chromium and, on the other hand, the composite material comprising a second phase having formula Al4C3.

2. The counter-form (1) according to claim 1, wherein the first phase is of one of the formulas among Cr2AlC, Ti3AlC2, Ti2AlC, Nb4AlC3, Nb2AlC or Mo2TiAlC2.

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

4. The counter-form (1) according to any one of claims 1 to 3, wherein an internal surface of the counter-form (1) is covered by a layer of alumina.

5. The counter-form (1) according to claim 4, wherein the alumina layer has a thickness comprised between 1 and 50 µm.

6. A process for manufacturing a counter-form (1) for producing a hollow metal aeronautical part, in particular a turbine part by solid-phase densification, the counter-form (1) comprising a composite material comprising, on the one hand, a first phase having formula Mn+1AlCn, where n = 1 to 3 and M is a transition metal selected from the group consisting of titanium and / or molybdenum and / or niobium and / or chromium, on the other hand, the composite material comprising a second phase having formula Al4C3, the counter-form (1) being obtained by a powder metallurgy process comprising a mixing step in which powders allowing to obtain the composite material are mixed, and a shaping step.

7. The process according to claim 6, wherein the mixing step comprises mixing the 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 a powder of Al4C3 so as to obtain the second phase.

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

9. The process according to any one of claims 6 to 8, wherein, during the step of shaping the counter-form, a supply channel configured to allow the supply of powder constituting the part to be manufactured, is provided in the counter-form.

10. The process according to any one of claims 6 to 9, wherein the first phase is of formula Cr2AlC, Ti3AlC2 or Ti2AlC, the process comprising, after the step of shaping the counter-form, an oxidation step allowing the formation of a layer of alumina on an internal surface of the counter-form.

11. A process for manufacturing a metal aeronautical part, in particular a turbine part by solid-phase densification, using a counter-form (1) obtained by a process according to any one of claims 6 to 10, the process comprising, after steps of filling the counter-form with a powder constituting the part to be manufactured and densifying said powder in the counter-form, a step of shaking the counter-form out by steaming.

12. The process according to claim 11, comprising, after the shakeout step, a recovery step, in which the material shaken out by steaming is recovered so as to be reused for the manufacture of another counter-form starting from the mixing step.

Images