Alloy powder, manufacturing process of a part based on this alloy and the part thus obtained.

Abstract

The invention relates to a titanium-based alloy powder, comprising, by mass percentages, 32.0 to 33.5% aluminum, 4.50 to 5.10% niobium, 2.40 to 2.70% chromium, 0 to 0.1% iron, 0 to 0.025% silicon, 0 to 100 ppm carbon, 0 to 100 ppm nitrogen, 0 to 1000 ppm dioxygen, 0 to 50 ppm dihydrogen, and 0 to 500 ppm unavoidable impurities, the remainder being titanium, and exhibiting a D10 particle size between 3 and 10 µm, a D90 particle size between 20 and 40 µm, and a D50 particle size between 10 and 25 µm, the D10 particle size values, D50 and D90 were measured by laser diffraction according to ISO 13322-2. The invention also relates to a method for manufacturing a part using this powder and to a part thus obtained. Figure for the abstract: 2

Description

Title of the invention: Alloy powder, method of manufacturing a part based on this alloy and part thus obtained. Technical field

[0001] The invention relates to a titanium-based alloy powder particularly intended for use in a manufacturing process by metal injection molding.

[0002] The invention also relates to such a manufacturing method using this powder, as well as a part, in particular for aeronautics, manufactured by this method. STATE OF THE ART

[0003] In a turbojet engine, the exhaust gases generated by the combustion chamber can reach high temperatures, above 1200°C, or even 1600°C. The parts of the turbojet engine, in contact with these exhaust gases, such as the turbine blades for example, must therefore be able to retain their mechanical properties at these high temperatures.

[0004] For this purpose, it is known to manufacture certain parts of the turbojet engine from “superalloy”. Superalloys, typically nickel-based, constitute a family of high-strength metal alloys that can work at temperatures relatively close to their melting points (typically 0.7 to 0.9 times their melting temperatures). However, these alloys are very dense, and their mass limits the efficiency of the turbines.

[0005] The intermetallic alloy TiAl 48-2-2 from foundry has been used for the manufacture of certain turbine parts. Indeed, TiAl parts can work up to 700 °C while maintaining good mechanical strength in terms of finishing, fatigue and traction, as well as good resistance to corrosion and oxidation. In addition, the intermetallic alloy TiAl has the advantage of being less dense than a nickel-based superalloy.

[0006] However, it remains difficult to obtain TiAl parts with the correct dimensions using traditional foundry processes, particularly when it comes to complex parts, such as a turbine distributor or turbine blades with internal channels or trim parts. The method, which consists of starting from a piece of TiAl, results in a significant loss of material and therefore an unnecessary additional cost.

[0007] Also known from the state of the art is metal powder injection molding (known under the English term "MIM" for "Metal Injection Molding"). This process can be advantageously used for the manufacture of complex turbomachine parts with the desired dimensions.

[0008] Several materials are commercially available for the manufacture of turbomachine parts by the MIM process.

[0009] Nickel-based Inconel 718, for example, is commonly used, but the resulting part cannot work above 650°C, which is too low a temperature for use in the combustion chamber or at the turbine level. In addition, this material is relatively massive.

[0010] Hastelloy X is another available material that allows the manufacture of parts that can work up to 950 °C. However, its mechanical properties are limited and it can only be used for very lightly loaded parts.

[0011] Finally, René 77 makes it possible to obtain parts that can work up to 1000°C while undergoing high fatigue and finishing constraints. However, this material is also a nickel-based alloy, so the part obtained is relatively massive.

[0012] There is therefore a need to resolve the above-mentioned problems. BRIEF DESCRIPTION OF THE INVENTION

[0013] An aim of the invention is therefore to propose a solution making it possible to obtain complex parts, such as, for example, turbine distributors or turbine blades with internal channels, of controlled dimensions, made of an alloy material which has the same properties as foundry TiAl, namely good resistance to traction, fatigue, fining and oxidation / corrosion up to 700°C, while being much less massive than nickel-based alloys and which, moreover, can be used in a MIM molding process.

[0014] Another aim of the invention is to obtain parts for aeronautics having a good surface condition.

[0015] For this purpose, the invention provides a titanium-based alloy powder, characterized in that it comprises, in mass percentages, 32.0 to 33.5% of aluminum, 4.50 to 5.10% of niobium, 2.40 to 2.70% of chromium, 0 to 0.1% of iron, 0 to 0.025% of silicon, 0 to 100 ppm of carbon, 0 to 100 ppm of nitrogen, 0 to 1000 ppm of oxygen, 0 to 50 ppm of hydrogen and 0 to 500 ppm of unavoidable impurities, the remainder being constituted by titanium, and in that it has: - a D10 particle size between 3 and 10 pm, - a D90 particle size between 20 and 40 pm and, - a D50 particle size between 10 and 25 pm, the values ​​of the D10, D50 and D90 granulometries having been measured by laser diffraction according to the ISO 13322-2 standard.

[0016] The chemical composition and the particle size of this alloy powder are chosen so that said alloy powder can be used in a powder injection molding process and to obtain, at the end of the process, an alloy part having good tensile strength, fatigue strength, fining strength and good resistance to corrosion and oxidation up to 700°C while being less massive than a nickel-based alloy.

[0017] The invention also provides a method for manufacturing a part, in particular for aeronautics, characterized in that it comprises the following steps: - a step of mixing the titanium-based alloy powder according to the invention with at least one plastic binder, - a step of granulating this mixture, so as to obtain granules of alloy and plastic mixture - a step of injection molding the mixture granules into a mold, to obtain a raw part, - a debinding step to obtain a debinded part, - a sintering step of the debinded part to obtain a sintered part.

[0018] This process makes it possible to obtain, from the alloy powder described above, complex parts, with controlled dimensions and having a good surface condition.

[0019] This process also makes it possible to obtain parts with good tensile strength, fatigue strength, fining strength and good resistance to corrosion and oxidation up to 700°C, while being less massive than a part made from a nickel-based alloy.

[0020] According to other advantageous and non-limiting characteristics of the invention, taken alone or in combination:

[0021] - the method further comprises a hot isostatic compaction step which consists of a heat treatment at a temperature between 1175°C and 1195°C, preferably a temperature of 1185°C, for a duration between 1 hour and 5 hours, preferably for 3 hours under a pressure between 125 MPa and 150 MPa, this step being carried out after the sintering step E6,

[0022] - the method further comprises a step of quenching the sintered part which consists of a heat treatment of the sintered part at a temperature between 1140°C and 1160°C for 3 hours, under a pressure between 125 MPa and 150 MPa, during the first two hours then under a pressure between 100 MPa and 125 MPa during the last hour, this step being carried out after the sintering step or after the hot isostatic compacting step,

[0023] - the volumetric alloy loading rate of the alloy mixture granules and plastic is between 50% and 75% and the hot melt flow rate of said granules is between 60 cmVIOmin and 85 cmVIOmin at a temperature between 190°C and 230°C, and in that the injection temperature during the molding step is between 160°C and 200°C, the hot melt flow rate being measured according to ISO 1133-1,

[0024] - the diameter of the granules of alloy and plastic mixture is between 1 mm and 5 mm,

[0025] - the debinding step itself comprises two successive steps: a first primary debinding step of a chemical nature of the raw part so as to obtain a partially debinded part, and a second step of thermal debinding of the partially debound part to obtain a debound part,

[0026] - the primary debinding step is a catalytic debinding under nitrogen, in the presence of nitric acid vapors, for a period of between 2 and 10 hours, the flow rate of the nitric acid vapors being between 2 mL / min and 5 mL / min, the temperature being between 100 °C and 150 °C,

[0027] - the primary debinding step is debinding by solvent with demineralized water, with stirring of the water, the temperature of the water being between 20°C and 100°C for a period of between 100 h and 400 h,

[0028] - the thermal debinding step is carried out under argon by two temperature stages successive temperatures, the first temperature level being between 250°C and 450°C for 100 minutes to 300 minutes, the second temperature level being between 350°C and 550°C for 100 minutes to 300 minutes,

[0029] - the sintering step of the debinded part is carried out by applying a temperature temperature between 1400°C and 1450°C for a period of between 2 hours and 6 hours under an argon atmosphere.

[0030] The invention finally relates to a titanium-based alloy part, in particular for aeronautics, characterized in that it is manufactured by the manufacturing method as described above.

[0031] According to other advantageous and non-limiting characteristics of the invention, taken alone or in combination:

[0032] - the part comprises in mass percentages, between 32.0 and 33.5% of aluminum, between 4.50 and 5.10% niobium, between 2.40 and 2.70% chromium, less than 0.1% iron, less than 2000 ppm oxygen, less than 0.025% silicon, less than 350 ppm carbon, less than 200 ppm nitrogen, less than 100 ppm hydrogen and less than 500 ppm unavoidable impurities, the remainder being titanium, and in that it further has a duplex to weakly duplex microstructure with between 10% and 60% multiphase lamellar grains and between 90% and 40% gamma grains.

[0033] - the part is a turbine blade or a turbine nozzle. BRIEF DESCRIPTION OF THE FIGURES

[0034] Other characteristics and advantages of the invention will emerge from the detailed description which follows, with reference to the appended drawings, in which:

[0035] - [Fig.l] [Fig.l] represents an electron microscope view of a part in TiAl 48-2-2 from the foundry after a series of heat treatments.

[0036] - [Fig.2] [Fig.2] schematically represents the different stages of the manufacturing process according to the invention.

[0037] - [Fig.3] [Fig.3] is an electron microscope view of a part obtained from the outcome of the sintering step of the manufacturing process according to the invention.

[0038] - [Fig.4] [Fig.4] is an electron microscope view of a part obtained from the outcome of the hot isostatic compacting (HIC) step and the quenching step of the manufacturing process according to the invention. DETAILED DESCRIPTION OF EMBODIMENTS

[0039] The TiAl 48-2-2 alloy from the foundry comprises, in mass percentage, between 32.0% and 33.5% of aluminum, between 4.50% and 5.10% of niobium, between 2.40% and 2.70% of chromium, less than 0.10% of iron, less than 0.015% of carbon, less than 0.02% of nitrogen, less than 0.01% of hydrogen, between 0.04% and 0.13% of oxygen, less than 0.05% of other elements which constitute unavoidable impurities, the remainder being constituted by titanium which is the base of the alloy.

[0040] [Fig.l] is a representation of a microstructure of TiAl 48-2-2 from foundry, of duplex micro structure, obtained after a series of heat treatments, on which we can see, in gray, two-phase lamellar grains and, in white, single-phase gamma grains. The term "duplex" means that the micro structure comprises two types of phases.

[0041] The intermetallic alloy TiAl 48-2-2 has interesting mechanical and chemical properties for applications in the field of turbomachinery. Parts made of TiAl 48-2-2 maintain good mechanical strength in terms of finishing, fatigue and traction, as well as good resistance to corrosion and oxidation up to 700 °C. In addition, the TiAl alloy is less dense than a nickel-based superalloy.

[0042] On the other hand, metal powder injection molding makes it possible to obtain parts of complex shape with an excellent surface finish and to finely control the dimensions of said parts. Metal powder injection molding is also a process which is distinguished by its speed of implementation.

[0043] The invention relates to an alloy powder and to a process whose parameters have been chosen to obtain, from the alloy powder and at the end of the process, parts which advantageously combine the properties of a TiAl 48-2-2 alloy part and those of a part resulting from a metal powder injection molding process.

[0044] The MIM process is a process for molding parts by injection into a mold of a mixture of metal powder and plastic binder. The hold of the injected part is ensured by the plastic binder. The plastic binder is removed during subsequent steps, called debinding steps. The debinded part is fragile, because it is very porous. An additional sintering step is necessary during which the grains of metal powder are bound together.

[0045] Titanium Aluminum type alloy powder usable in injection molding of metal powder

[0046] The invention relates to a titanium-based metal alloy powder. The composition The chemical composition and particle size of the alloy powder were chosen to allow its use in a metal injection molding (MIM) process and to obtain, at the end of the process, a titanium-based alloy part whose chemical composition is close to that of the TiAl 48-2-2 foundry alloy and whose mechanical properties are improved.

[0047] Chemical composition of the powder

[0048] Even if the plastic binder is almost entirely removed during the debinding steps described above, residues of this plastic binder impregnate the metallic material. The levels of nitrogen, oxygen and carbon are higher in the molded part resulting from the powder injection molding process than in the powder injected at the beginning of the process.

[0049] However, the carbon, nitrogen and oxygen levels given in the TiAl 48-2-2 specification are relatively low compared to the expected mechanical properties. A high carbon level leads, for example, to the formation of carbides at the grain boundaries which block the growth and movement of said grains. The part is then less ductile and risks breaking during use. High levels of oxygen and nitrogen also lead to a reduction in the ductility of the part and rapid failure in fatigue and tension.

[0050] The levels of the different elements of the alloy powder of the invention, in particular the levels of nitrogen, oxygen and carbon, were therefore chosen accordingly.

[0051] The alloy powder according to the invention comprises, in mass percentages, 32.0 to 33.5% of aluminum, 4.50 to 5.10% of niobium, 2.40 to 2.70% of chromium, 0 to 0.1% of iron, 0 to 0.025% of silicon, 0 to 100 ppm of carbon, 0 to 100 ppm of nitrogen, 0 to 1000 ppm of oxygen, 0 to 50 ppm of hydrogen, 0 to 500 ppm of unavoidable impurities, the remainder being constituted by titanium.

[0052] "Unavoidable impurities" are defined as elements that are not intentionally added to the composition of the powder and which are provided by other elements. Examples of unavoidable impurities include yttrium, which may come from the crucibles used for atomizing the powder.

[0053] Powder particle size

[0054] The particle size of the powder was chosen so that the powder could be used in the manufacturing process described below, in particular during the injection and sintering steps.

[0055] The implementation of the powder injection molding process requires control of the size of the powder grains to ensure good injection of the mixture of alloy powder and plastic binder into the mold of the part. Indeed, small alloy powder grains induce a large contact interface between the alloy powder and the plastic binder within the mixture of alloy powder and plastic binder and therefore significant friction during the injection of said mixture into the mold of the part. Conversely, grains of alloy powder that are too large are more difficult to carry away by the plastic binder during said injection and can therefore lead to a non-homogeneous injected part.

[0056] Furthermore, the particle size is important to obtain good sintering, a step during which the grains will diffuse and bind to each other so as to eliminate their interfaces and thus lower their entropy. Fine powder will thus be more easily sinterable because by grouping together, the small grains of powder will more strongly reduce their interfaces and their surfaces, significantly lowering their entropy.

[0057] The grain size of the alloy powder of the invention was therefore defined by a range of acceptable values ​​for the particle sizes D10, D50 and D90 of said alloy powder.

[0058] The particle size D10 corresponds to 10% passing. In other words, 10% by number of the grains of the alloy powder have a diameter less than D10. In the same way, the particle sizes D50 and D90 correspond respectively to 50% and 90% passing.

[0059] The particle size D10 of the alloy powder according to the invention is between 3 and 10 μm. The particle size D50 is between 10 and 25 μm. Finally, the particle size D90 is between 20 and 40 μm.

[0060] The values ​​of the particle sizes D10, D50 and D90 were measured according to the ISO 13322-2 standard. This standard provides for measurement by laser diffraction.

[0061] Preparation of the powder

[0062] The titanium-based alloy powder which is the subject of the invention can, for example, be obtained from the basic elements of the TiAl 48-2-2 alloy, by a powder atomization process. The atomization process makes it possible to provide the chemical composition and the particle size of the alloy powder obtained. In addition, it makes it possible to ensure a good morphology of the powder, which is predominantly spherical. Finally, it makes it possible to limit the risks of pollution.

[0063] Metal powder injection molding process

[0064] The invention also relates to a method for manufacturing a part, particularly for aeronautics, which uses the titanium-based alloy powder defined above.

[0065] Generally, this process comprises successive steps of mixing, granulation, injection molding, chemical debinding, thermal debinding, sintering and quenching. These steps are described in more detail below with reference to [Fig.2].

[0066] Mixture.

[0067] In a first mixing step E1, the alloy powder based on titanium 1 according to the invention with at least one plastic binder 2, preferably two plastic binders. This binder 2 is for example polyethylene (PE) or polyethylene glycol (PEG) or a mixture of the two. During the mixing step E1, the temperature is set at a value such that the plastic is pasty to allow good mixing. The temperature depends on the composition of the plastic, it is for example between 50 °C and 150 °C. During the mixing step E1, the titanium-based alloy powder 1 and the plastic binder 2 are mixed in proportions chosen so as to obtain, at the end of the granulation step E2 described below, granules of alloy and plastic mixture 3 having a hot fluidity guaranteeing effective injection of said granules 3 during the molding step E3.The mixture of alloy powder 1 and at least one plastic binder 2 preferably comprises, in volume percentage, between 50% and 75% of alloy powder 1 and between 50% and 25% of plastic binder 2, so that the mixture granules 3 have a hot fluidity of between 60 cmVIOmin and 85 cm3 / 10min at a temperature of between 190°C and 230°C, the measurement of the hot fluidity being carried out according to the ISO 1133-1 standard.

[0068] Granulation.

[0069] In a second step E2 of granulating the mixture of the alloy powder and at least one plastic binder, the mixture from step E1 is passed through an extruder to obtain granules 3 of alloy and plastic mixture, known to those skilled in the art under the English term “feedstock”. The shape and size of the granules of alloy and plastic mixture 3 are fixed by the parameterization of the extruder. The granules of alloy and plastic mixture 3 are for example cylinders whose base diameter is preferably between 1 mm and 5 mm. Molding.

[0070] In a third molding step E3, the granules 3 of alloy and plastic mixture are injected into the mold of the part to be manufactured, the injection temperature being between 160°C and 200°C. Below 160°C, the mixture is too solid and does not enter the mold. Above 200°C, the mixture is too liquid, the alloy powder and the plastic binder separate and the alloy powder is not carried away. The other parameters, such as the injection speed, the injection pressure, the holding time after injection or the injection time depend on the part to be injected.

[0071] Following molding step E3, a raw part 4 is obtained, also called a “green part”, which is a part of mixed alloy powder and plastic (alloy grains suspended in the plastic). Adjusting the molding parameters makes it possible to obtain a part without porosity. The plastic binder ensures the part holds. Debinding.

[0072] “Debinding” makes it possible to remove the plastic binder from the raw part 4 obtained previously.

[0073] Two debinding stages are carried out successively, one chemical, the other thermal. Primary debinding.

[0074] Primary debinding E4 is a chemical debinding process. Primary debinding E4 makes it possible to obtain a partially debinded part 5.

[0075] This debinding can be either: debinding using an E4B solvent, or preferably catalytic debinding E4A. The latter has the advantage of being faster.

[0076] E4A catalytic debinding consists of vaporizing and then burning the plastic binder by injecting acid vapors into a furnace.

[0077] The catalytic debinding is carried out for example at a temperature between 100°C and 150°C for 2 to 10 hours, under a nitrogen atmosphere, in the presence of nitric acid vapors, the flow of nitric acid preferably being between 2 mL / min and 5 mL / min.

[0078] Debinding E4B using a solvent consists of bathing the raw part 4 in a bath of said solvent, so as to dissolve the plastic.

[0079] The E4B debinding is for example a water debinding, the green part 4 being immersed for 100 hours to 400 hours in a bath of demineralized water with stirring at a temperature between 20°C and 100°C, preferably of the order of 60°C.

[0080] At the end of the chemical debinding step E4, the partially debinded part 5 is obtained, the chemical debinding having made it possible to remove more than 95% of the plastic binder. Thermal debinding.

[0081] Thermal debinding E5 is preferably carried out by the successive application of two temperature stages, under an argon atmosphere, to the partially debinded part. During the first stage, a temperature of between 250°C and 450°C is applied for 100 minutes to 300 minutes. During the second stage, a temperature of between 350°C and 550°C is applied for 100 to 300 minutes.

[0082] At the end of the thermal debinding step (E5), a debinded part or “brown part” 6 is obtained, the thermal debinding having made it possible to remove the remaining plastic binder (i.e. the remaining less than 5%).

[0083] The debinded part 6 resulting from the primary debinding steps E4 and thermal debinding steps E5 is a part of the same dimensions as the raw part 4. However, unlike the raw part 4, the debound part 6 is very porous because the plastic binder has been removed, the density of the debound part 6 is between 50% and 75% of the density of a TiAl alloy part from the foundry. In addition, the debound part 6 is very fragile because the plastic binder which held the part together has been removed. Sintering.

[0084] During a step E6, the debinded part 6 is sintered. Sintering consists of subjecting the debinded part 6 to a temperature close to the melting point of the alloy powder so that the powder grains bond together. During sintering, the part shrinks and its density increases.

[0085] Sintering is carried out in a furnace, preferably at a temperature between 1400°C and 1450°C for 2 to 6 hours under an argon atmosphere.

[0086] Preferably, the thermal debinding step E5 and the sintering step E6 are carried out in the same furnace, because the debinded part 6 is fragile.

[0087] At the end of the sintering step E6, a more compact sintered part 7 is obtained, the density of which is preferably greater than 95% of the density of a conventional foundry TiAl alloy. The dimensions of the sintered part 7 are smaller than those of the debinded part or brown part 6. A reduction in size of between 14 and 18% is typically observed.

[0088] [Fig. 3] is an electron microscope view of a part obtained at the end of the sintering step of the process according to the invention. A needle-shaped microstructure characteristic of a titanium-based alloy is observed, the grains are linked and the material is relatively dense. However, the material also includes porosity residues (see the small round black spots) which can harm the mechanical properties of the final part. Heat treatments can be implemented to eliminate said porosity residues.

[0089] Furthermore, the sintered part made of titanium-based alloy 7 comprises, in mass percentages, between 32.0% and 33.5% of aluminum, between 4.50% and 5.10% of niobium, between 2.40% and 2.70% of chromium, less than 0.1% of iron, less than 2000 ppm of oxygen, less than 0.025% of silicon, less than 350 ppm of carbon, less than 200 ppm of nitrogen, less than 100 ppm of hydrogen and less than 500 ppm of unavoidable impurities.

[0090] The chemical composition of the sintered part 7 is very close to that of the initial alloy powder. Only the carbon, oxygen and nitrogen levels increase significantly during the MIM process.

[0091] By way of example, if the alloy powder 1 comprises 970 ppm of oxygen, 90 ppm of nitrogen and 70 ppm of carbon, the sintered part 7 obtained at the end of the process according to the invention from the alloy powder 1 comprises 1600 ppm of oxygen, 120 ppm of nitrogen and 340 ppm of carbon.

[0092] The additional carbon, oxygen and nitrogen elements are residues of the plastic binder that has impregnated the metallic material. However, excessively high levels of said elements can have a negative impact on the mechanical properties of the alloy part resulting from the MIM process. The alloy 1 powder must have carbon, oxygen and nitrogen levels much lower than those of the targeted TiAl 48-2-2. Hot isostatic compaction.

[0093] It is optionally possible to implement a step E7 of hot isostatic compaction of the sintered part in order to fill the residual porosities, in particular if the density of the sintered part is less than 95% of the density of the foundry TiAl alloy. The hot isostatic compaction step E7 makes it possible to increase the density of the part 7 resulting from the sintering up to 100% of the density of the foundry TiAl and to improve the mechanical properties of said part. In addition, the hot isostatic compaction step E7 makes it possible to reduce the dimensional dispersion of the parts resulting from the metal powder injection molding process.

[0094] During the hot isostatic compacting step E7, high pressure and high temperature are applied together under an inert atmosphere. For example, a temperature of between 1175°C and 1195°C, preferably a temperature of 1185°C, and a pressure of between 125 MPa and 150 MPa, preferably between 132 and 140 MPa, are applied for a period of between 1 hour and 5 hours, preferably for 3 hours, under an inert atmosphere, for example a helium atmosphere or under vacuum, preferably an argon atmosphere.

[0095] Quenching.

[0096] Finally, a quenching heat treatment step E8 is implemented. The quenching heat treatment consists of heating the part to a temperature for dissolving the good alloying elements, which are titanium and aluminum, for a sufficiently long time to allow the said elements to be re-dissolved and to diffuse into the crystalline solid. The part is then cooled relatively quickly so that the said good alloying elements reprecipitate. This step makes it possible to obtain a final part with the expected mechanical and chemical properties.

[0097] The quenching heat treatment step E8 is preferably carried out at a temperature of 1150°C for 3 hours. If the hot isostatic compacting step (E7) has previously been carried out, the temperature is lowered from 1185°C to 1150°C while maintaining an inert atmosphere. In parallel with the application of this temperature, a pressure of between 125 MPa and 150 MPa, preferably between 132 and 140 MPa, is applied for two hours, then a pressure of between 100 and 125 MPa, preferably between 115 MPa and 125 MPa for one hour. The part is finally cooled at a rate of between 11 °C / min and 70 °C / min until reaching the temperature between 690 °C and 710 °C, preferably a temperature of 700 °C. During the entire heat treatment step of E8, which includes heating and then cooling the part, an inert atmosphere is maintained, for example an argon atmosphere, with cooling being carried out at atmospheric pressure.

[0098] [Fig. 4] is an electron microscope view of a part obtained at the end of steps E7 and E8 of the process according to the invention. The needle-like microstructure can be seen, but no more spots can be seen. Step E7 of hot isostatic compacting therefore made it possible to fill the last porosities and obtain a completely healthy material. Parts obtained by the process

[0099] The invention also relates to parts obtained from the manufacturing process using the alloy powder in accordance with the invention.

[0100] Said parts are titanium-based alloy parts comprising in particular, in mass percentages, less than 350 ppm of carbon, less than 200 ppm of nitrogen and less than 2000 ppm of oxygen, the chemical compositions being measured by elemental analysis, for example by inductively coupled plasma spectrometry. The properties of the parts having said carbon, nitrogen and oxygen compositions are comparable or even superior to those of TiAl parts from foundries.

[0101] In [Fig. 1] which represents a part made of TiAl from a foundry, we can see that it has a duplex microstructure with two-phase lamellar grains and single-phase gamma grains.

[0102] On the contrary and as can be seen in [Fig.4], the parts obtained from the manufacturing process using the alloy powder according to the invention have a duplex to low duplex multiphase microstructure with between 10% and 60% of multiphase lamellar grains and between 90% and 40% of gamma grains which gives them better tensile and fatigue strength than a TiAl part from a foundry. Indeed, for temperatures between 0 °C and 800 °C, the limit stress leading to tensile failure Rm of the parts obtained from the manufacturing process using said powder is greater than 250 MPa. The elastic limit with 0.2% residual plastic deformation of said parts Rp0j2 is reached for a stress greater than 150 MPa. The gain in fatigue and elasticity (with 0.2% plastic deformation) is at least 10% compared to a TiAl part from a foundry up to 700°C.

[0103] The invention finds a particular application in the manufacture of parts for aeronautics, such as for example turbine blades, including blades with internal channels, turbine distributors or trim parts which are subjected to high stresses, must resist corrosion, and are used at high temperatures above 600°C.

Claims

Claims

1. Titanium-based alloy powder (1), characterized in that it comprises, in mass percentages, 32.0 to 33.5% of aluminum, 4.50 to 5.10% of niobium, 2.40 to 2.70% of chromium, 0 to 0.1% of iron, 0 to 0.025% of silicon, 0 to 100 ppm of carbon, 0 to 100 ppm of nitrogen, 0 to 1000 ppm of oxygen, 0 to 50 ppm of hydrogen and 0 to 500 ppm of unavoidable impurities, the remainder being constituted by titanium, and in that it has: - a particle size D10 of between 3 and 10 pm, - a particle size D90 of between 20 and 40 pm and, - a particle size D50 of between 10 and 25 pm, the values of the D10, D50 and D90 granulometries having been measured by laser diffraction according to the ISO 13322-2 standard.

2. Method for manufacturing a part, in particular for aeronautics, characterized in that it comprises the following steps: - a step (El) of mixing the titanium-based alloy powder according to claim 1 with at least one plastic binder (2), - a step (E2) of granulating this mixture, so as to obtain granules (3) of alloy and plastic mixture - a step (E3) of injection molding the mixture granules (3) in a mold, to obtain a green part (4), - a step (E4A, E4B, E5) of debinding to obtain a debinded part (6), - a step (E6) of sintering the debinded part to obtain a sintered part (7).

3. Method according to claim 2, characterized in that it further comprises a step (E7) of hot isostatic compaction which consists of a heat treatment at a temperature between 1175°C and 1195°C, preferably at a temperature of 1185°C for a duration between 1 hour and 5 hours, preferably for 3 hours under a pressure between 125 MPa and 150 MPa, this step being carried out after the sintering step (E6).

4. Method according to any one of claims 2 or 3, characterized in that it further comprises a step (E8) of quenching the sintered part (7) which consists of a heat treatment of the sintered part (7) at a temperature between 1140°C and 1160°C for 3 hours, under a pressure between 125 and 150 MPa, during the two first hours then under a pressure of between 100 and 125 MPa during the last hour, this step being carried out after the sintering step (E6) or after the hot isostatic compaction step (E7).

5. Method according to any one of claims 2 to 4 characterized in that the alloy volume loading rate of the granules of alloy and plastic mixture (3) is between 50% and 75% and the hot fluidity of said granules (3) is between 60 cmVIOmin and 85 cm3 / 10min at a temperature between 190 °C and 230 °C, and in that the injection temperature during the molding step (E3) is between 160 °C and 200 °C, the measurement of the hot fluidity being carried out according to the ISO 1133-1 standard.

6. Method according to any one of claims 2 to 5 characterized in that the diameter of the granules of mixture of alloy and plastic is between 1 mm and 5 mm.

7. Method according to any one of claims 2 to 6 characterized in that the debinding step (E4A, E4B, E5) itself comprises two successive steps: a first step (E4A, E4B) of primary debinding of a chemical nature of the raw part (4) so as to obtain a partially debinded part (5), and a second step (E5) of thermal debinding of the partially debinded part (5) to obtain a debinded part,

8. Method according to claim 7, characterized in that the primary debinding step is a catalytic debinding (E4A) under nitrogen, in the presence of nitric acid vapors, for a period of between 2 and 10 hours, the flow rate of the nitric acid vapors being between 2 mL / min and 5 mL / min, the temperature being between 100 and 150 °C.

9. V-. Method according to claim 7, characterized in that the primary debinding step is a debinding by solvent with demineralized water (E4B), with stirring of the water, the temperature of the water being between 20 and 100 °C for a duration between 100 and 400 h.

10. Method according to any one of claims 7 to 9, characterized in that the thermal debinding step (E5) is carried out under argon by two successive temperature stages, the first temperature stage being between 250°C and 450°C for 100 to 300 minutes, the second temperature stage being between 350°C and 550°C for 100 to 300 minutes.

11. Method according to any one of claims 2 to 10, characterized in that the step (E6) of sintering the debinded part is carried out by applying a temperature of between 1400 and 1450°C for a period of between 2 and 6 hours under an argon atmosphere.

12. Titanium-based alloy part, in particular for aeronautics, characterized in that it is manufactured by the manufacturing method according to any one of claims 2 to 11, in that it comprises, in mass percentages, between 32.0 and 33.5% of aluminum, between 4.50 and 5.10% of niobium, between 2.40 and 2.70% of chromium, less than 0.1% of iron, less than 2000 ppm of oxygen, less than 0.025% of silicon, less than 350 ppm of carbon, less than 200 ppm of nitrogen, less than 100 ppm of hydrogen and less than 500 ppm of unavoidable impurities, the remainder being constituted by titanium, and in that it further has a duplex to weakly duplex microstructure with between 10% and 60% of multiphase lamellar grains and between 90% and 40% gamma grains.

13. Part according to claim 12, characterized in that it is a turbine blade or a turbine distributor.

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