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

Abstract

The invention relates to a nickel-based alloy powder comprising, in mass percentages, 14.00 to 15.25% chromium, 14.25 to 15.75% cobalt, 4.00 to 4.60% aluminum, 0 to 0.50% iron, 0 to 0.15% manganese, 3.00 to 3.70% titanium, 3.90 to 4.50% molybdenum, 0 to 0.015% sulfur, 0 to 0.06% zirconium, 0.012 to 0.020% boron, 0 to 0.20% silicon, 0 to 0.10% copper, 0 to 150 ppm carbon, 0 to 0.5 ppm bismuth, 0 to 5 ppm lead, 0 to 1000 ppm of platinum, 0 to 1000 ppm palladium, 0 to 50 ppm hydrogen, 0 to 5 ppm silver, 0 to 120 ppm nitrogen, 0 to 1000 ppm rhenium, 0 to 410 ppm oxygen and 0 to 500 ppm unavoidable impurities, the remainder being nickel, and which has 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 20 µm, the values ​​of the D10, D50 and D90 particle sizes having been 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 nickel-based alloy powder particularly intended for use in a metal injection molding manufacturing process.

[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).

[0005] The René 77 intermetallic alloy from foundry has been used for the manufacture of certain turbine parts. Indeed, parts made from René 77 can work up to 1000 °C while undergoing high fatigue, tensile and fining stresses. Parts made from René 77 also have very good resistance to oxidation and corrosion up to 1100 °C.

[0006] However, nickel-based alloys that can withstand such high temperatures, for example above 900°C, are often refractory materials that have a strong tendency to crack.

[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 LTnconel 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.

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

[0012] An aim of the invention is therefore to propose a solution making it possible to obtain complex parts, such as, for example, turbine distributors, turbine blades with internal channels, retaining rings or sealed sectors, of controlled dimensions, made of an alloy material which has good tensile, fatigue, fining and oxidation / corrosion resistance up to a minimum of 1000°C and, which, moreover, can be used in a MIM molding process.

[0013] Another aim of the invention is to obtain parts for aeronautics having a good surface condition.

[0014] For this purpose, the invention provides a nickel-based alloy powder, characterized in that it comprises, in mass percentages, 14.00 to 15.25% of chromium, 14.25 to 15.75% of cobalt, 4.00 to 4.60% of aluminum, 0 to 0.50% of iron, 0 to 0.15% of manganese, 3.00 to 3.70% of titanium, 3.90 to 4.50% of molybdenum, 0 to 0.015% of sulfur, 0 to 0.06% of zirconium, 0.012 to 0.020% of boron, 0 to 0.20% of silicon, 0 to 0.10% of copper, 0 to 150 ppm of carbon, 0 to 0.5 ppm of bismuth, 0 to 5 ppm of lead, 0 to 1000 ppm of platinum, 0 to 1000 ppm of palladium, 0 to 50 ppm of hydrogen, 0 to 5 ppm of silver, 0 to 120 ppm of nitrogen, 0 to 1000 ppm of rhenium, 0 to 410 ppm of oxygen and 0 to 500 ppm of unavoidable impurities, the remainder being nickel, 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 20 pm, the values ​​of the D10, D50 and D90 granulometries having been measured by laser diffraction according to the ISO 13322-2 standard.

[0015] 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 1000°C.

[0016] The invention also proposes a method for manufacturing a part, in particular for aeronautics, characterized in that it comprises the following steps: - a step of mixing the nickel-based alloy powder as described above with at least one plastic binder, - a step of granulating this mixture, so as to obtain mixture granules alloy and plastic - 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.

[0017] This process makes it possible to obtain, from the alloy powder described above, complex parts, with controlled dimensions and having a good surface condition.

[0018] 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 1000°C, while being less massive than a part made from a nickel-based alloy.

[0019] According to other advantageous and non-limiting characteristics of the invention, taken alone or in combination:

[0020] - 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 1120°C and 1190°C, preferably a temperature between 1150°C and 1170°C for a duration between 1 hour and 3 hours, preferably for 2 hours at atmospheric pressure, this step being carried out after the sintering step,

[0021] - the method further comprises a tempering heat treatment step which consists of a heat treatment of the sintered part at a temperature between 720°C and 800°C, preferably a temperature between 750°C and 770°C for a duration between 3h30 and 4h30, preferably for 4 hours, this step being carried out after the sintering step and after the optional quenching step,

[0022] - the method further comprises a hot isostatic compaction step which consists of a heat treatment at a temperature between 1160°C and 1200°C, preferably a temperature of 1180°C, for 2 hours to 4 hours under a pressure greater than 100 MPa and less than 200 MPa, preferably a pressure between 110 MPa and 130 MPa, this step being carried out after the sintering step and before any quenching and tempering heat treatment steps,

[0023] - the method further comprises a high temperature heat treatment step temperature of the sintered part which consists of a heat treatment of the sintered part at a temperature between 1200°C and 1280°C, preferably a temperature between 1220°C and 1240°C for a duration between 2 hours and 6 hours, preferably for five hours at atmospheric pressure, this step being carried out after the sintering step and after the possible hot isostatic compacting step, but before the optional heat treatment steps,

[0024] - the volumetric alloy loading rate of the alloy mixture granules and plastic is between 50% and 75% and the melt flow rate of said granules is between 60 cmVIOmin and 85 cmVIOmin at a temperature between 190°C and 230°C, and the injection temperature during the molding step is between 170°C and 200°C, the measurement of the melt flow rate being carried out according to ISO 1133-1,

[0025] - the diameter of the granules of alloy and plastic mixture is between 1 mm and 5 mm,

[0026] - 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 debinded part to obtain a debinded part,

[0027] - 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 and 150 °C,

[0028] - the primary debinding step is debinding by solvent with demineralized water, with stirring of the water, the water temperature being between 20 and 100°C for a period of between 100 and 300 h,

[0029] - the thermal debinding step is carried out under argon at a pressure of between between 200 mbar and 500 mbar by two successive temperature stages, the first temperature stage being between 450°C and 550°C for 150 to 300 minutes, the second temperature stage being between 550°C and 650°C for 150 to 300 minutes,

[0030] - the sintering step of the debinded part is carried out by applying a temperature temperature between 1260 and 1300 °C for a period of between 4 and 8 hours under an argon atmosphere at a pressure between 20 mbar and 50 mbar.

[0031] The invention finally relates to a nickel-based alloy part, particularly for aeronautics, characterized in that it is manufactured by the manufacturing method as described above.

[0032] According to other advantageous and non-limiting characteristics of the invention, taken alone or in combination:

[0033] - the part comprises, in mass percentages, 14.00 to 15.25% of chromium, 14.25 to 15.75% cobalt, 4.00-4.60% aluminum, 0-0.50% iron, 0-0.150% manganese, 3.00-3.70% titanium, 3.90-4.50% molybdenum, 0-0.015% sulfur, 0-0.060% zirconium, 0.012-0.020% boron, 0-0.20% silicon, 0-0.100% copper, 0-0.5 ppm bismuth, 0-5 ppm lead, 0-1000 ppm platinum, 0 to 1000 ppm palladium, 0 to 50 ppm hydrogen, 0 to 5 ppm silver, 0 to 200 ppm nitrogen, 0 to 1000 ppm rhenium, 250 to 900 ppm carbon, 0 to 500 ppm oxygen and 0 to 500 ppm unavoidable impurities the remainder being nickel and in that it further has a micro structure with metallurgical grains of size between 00 ASTM and 9 ASTM, the measurement of the size of the metallurgical grains being carried out according to the ASTM El 12 standard,

[0034] - the part is a turbine blade, a turbine distributor, a retaining ring, a waterproof sector or a piece of cladding. BRIEF DESCRIPTION OF THE FIGURES

[0035] Other characteristics and advantages of the invention will emerge from the detailed description which follows, with reference to the appended drawings, in which:

[0036] - [Fig.l] [Fig.l] represents an electron microscope view of a part in René 77 from the foundry after a series of heat treatments.

[0037] - [Fig.2] [Fig.2] schematically represents the different stages of the manufacturing process according to the invention.

[0038] - [Fig.3A] and [Fig.3B] Figures 3A and 3B represent respectively, two views at optical microscope, at two different scales, of a part obtained at the end of the sintering step of the manufacturing process according to the invention.

[0039] - [Fig.4A] and [Fig.4B] Figures 4A and 4B represent two microscope views optical, at two different scales, of a part obtained at the end of the hot isostatic compaction (HIC) step of the manufacturing process according to the invention, said hot isostatic compaction step having been carried out after the sintering step.

[0040] - [Fig.5A] and [Fig.5B] Figures 5A and 5B represent two microscope views optical, at two different scales, of a part obtained at the end of the high temperature heat treatment step of the manufacturing process according to the invention, said high temperature heat treatment step having been carried out after the hot isostatic compacting (HIC) step. DETAILED DESCRIPTION OF EMBODIMENTS

[0041] The René 77 alloy from the foundry comprises, in mass percentage, between 0.05% and 0.09% of carbon, between 14.25% and 15.75% of cobalt, between 14.00% and 15.25% of chromium, between 4.00% and 4.60% of aluminum, between 3.90% and 4.50% of molybdenum, between 3.00% and 3.70% of titanium, less than 0.50% of iron, between 0.012% and 0.020% of boron, between 0 and 0.06% of zirconium, between 0 and 0.15% of manganese, between 0 and 0.20% of silicon, between 0 and 0.10% of copper, between 0 and 0.015% of sulfur, less than 0.5 ppm bismuth, less than 5 ppm silver, less than 5 ppm lead, less than 25 ppm dinitrogen, less than 1000 ppm platinum, less than 1000 ppm rhenium and less than 1000 ppm palladium, the remainder being nickel which is the basis of the alloy and unavoidable impurities.

[0042] The microstructure of René 77 from the foundry has metallurgical grains whose size is less than or equal to 00 ASTM. [Fig.l] is a representation of such a microstructure of René 77 from the foundry in which the grains measure 00 ASTM. At the bottom left of [Fig.l], one of said metallurgical grains can be seen in darker gray. The measurement of the size of the metallurgical grains is carried out according to the ASTM El 12 standard.

[0043] The René 77 intermetallic alloy has interesting mechanical and chemical properties for applications in the field of turbomachinery. Indeed, the René 77 parts from the foundry maintain good mechanical strength in terms of finishing, fatigue and traction up to 1000 °C, as well as good resistance to corrosion and oxidation up to 1100 °C. For example, for temperatures below 800 °C, the ultimate stress leading to tensile failure Rm of the René 77 parts from the foundry is greater than 650 MPa. Over the same temperature range, the elastic limit with 0.2% residual plastic deformation of said parts Rp0>2 is reached for a stress greater than 500 MPa and the elongation at break is greater than 2%.

[0044] 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.

[0045] 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 René 77 alloy part and those of a part resulting from a metal powder injection molding process.

[0046] 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.

[0047] Nickel type alloy powder usable in metal powder injection molding

[0048] The invention relates to a nickel-based metal alloy powder. The chemical composition and particle size of the alloy powder have been chosen in order to allow its use in a metal injection molding (MIM) process and to obtain, at the end of the process, a nickel-based alloy part whose chemical composition and the mechanical properties are close to those of the foundry René 77 alloy.

[0049] Chemical composition of the powder

[0050] 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.

[0051] However, the carbon, nitrogen and oxygen levels given in the René 77 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 traction.

[0052] 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.

[0053] The alloy powder according to the invention comprises, in mass percentages, 14.00 to 15.25% of chromium, 14.25 to 15.75% of cobalt, 4.00 to 4.60% of aluminum, 0 to 0.50% of iron, 0 to 0.15% of manganese, 3.00 to 3.70% of titanium, 3.90 to 4.50% of molybdenum, 0 to 0.015% of sulfur, 0 to 0.06% of zirconium, 0.012 to 0.020% of boron, 0 to 0.20% of silicon, 0 to 0.10% of copper, 0 to 150 ppm of carbon, 0 to 0.5 ppm of bismuth, 0 to 5 ppm of lead, 0 to 1000 ppm platinum, 0 to 1000 ppm palladium, 0 to 50 ppm hydrogen, 0 to 5 ppm silver, 0 to 120 ppm nitrogen, 0 to 1000 ppm rhenium, 0 to 410 ppm oxygen and 0 to 500 ppm unavoidable impurities, the remainder being nickel.

[0054] "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.

[0055] The alloy powder in accordance with the invention comprises, in mass percentages, between 0 and 50 ppm of each element considered to constitute an unavoidable impurity.

[0056] Powder particle size

[0057] 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.

[0058] 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 in the mold of the part. Indeed, small grains of alloy powder 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.

[0059] 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.

[0060] The grain size of the alloy powder of the invention has therefore been defined by a range of acceptable values ​​for the particle sizes D10, D50 and D90 of said alloy powder.

[0061] 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.

[0062] 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 20 μm. Finally, the particle size D90 is between 20 and 40 μm.

[0063] 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.

[0064] Preparation of the powder

[0065] The nickel-based alloy powder which is the subject of the invention can, for example, be obtained from the basic elements of the René 77 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 ensures a good morphology of the powder, which is predominantly spherical. Finally, it makes it possible to limit the risks of pollution.

[0066] Metal powder injection molding process

[0067] The invention also relates to a method for manufacturing a part, particularly for aeronautics, which uses the nickel-based alloy powder defined above.

[0068] Generally, this process comprises successive steps of mixing, granulation, injection molding, chemical debinding, thermal debinding, sintering and quenching. Optionally, the process can further comprise one or more additional heat treatment steps. These steps are described in more detail below with reference to [Fig.2].

[0069] Mixing.

[0070] In a first mixing step E1, the nickel-based alloy powder 1 according to the invention is mixed 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.

[0071] Granulation.

[0072] 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.

[0073] 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 170 and 200 °C. Below 170 °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.

[0074] 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.

[0075] “Debinding” makes it possible to remove the plastic binder from the raw part 4 obtained previously.

[0076] Two debinding stages are carried out successively, one chemical, the other thermal. Primary debinding.

[0077] Primary debinding E4 is a chemical debinding process. Primary debinding E4 makes it possible to obtain a partially debinded part 5.

[0078] This debinding can be either: debinding using an E4B solvent, or preferably catalytic debinding E4A. The latter has the advantage of being faster.

[0079] E4A catalytic debinding consists of vaporizing and then burning the plastic binder by injecting acid vapors into a furnace.

[0080] 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 and 5 mL / min.

[0081] Debinding E4B using a solvent consists of bathing the raw part 4 in a bath of said solvent, so as to dissolve the plastic.

[0082] The E4B debinding is for example a water debinding, the green part 4 being immersed for 100 to 300 hours in a bath of demineralized water with stirring at a temperature between 20 and 100°C, preferably of the order of 60°C.

[0083] 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.

[0084] Thermal debinding E5 is preferably carried out under an argon atmosphere at a pressure of between 200 mbar and 500 mbar by successively applying two temperature stages to the partially debinded part 5. During the first stage, a temperature of between 450°C and 550°C is applied for 150 minutes to 300 minutes. During the second stage, a temperature of between 550°C and 650°C is applied for 150 minutes to 300 minutes.

[0085] At the end of the thermal debinding step (E5), a debinded part is obtained or “brown part” 6, thermal debinding having removed the remaining plastic binder (i.e. the remaining less than 5%).

[0086] 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 debinded part 6 is very porous because the plastic binder has been removed, the density of the debinded part 6 is between 50% and 75% of the density of a part of René 77 alloy from the foundry. In addition, the debinded part 6 is very fragile because the plastic binder which ensured the holding of the part has been removed. Sintering.

[0087] 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.

[0088] Sintering is carried out in a furnace, preferably at a temperature between 1260 and 1300°C for 4 hours to 6 hours under an argon atmosphere at a pressure between 20 mbar and 50 mbar.

[0089] 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.

[0090] 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 René 77 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.

[0091] The sintered part made of nickel-based alloy 7 comprises, in mass percentages, 14.00 to 15.25% of chromium, 14.25 to 15.75% of cobalt, 4.00 to 4.60% of aluminum, 0 to 0.50% of iron, 0 to 0.150% of manganese, 3.00 to 3.70% of titanium, 3.90 to 4.50% of molybdenum, 0 to 0.015% of sulfur, 0 to 0.060% of zirconium, 0.012 to 0.020% of boron, 0 to 0.20% of silicon, 0 to 0.100% of copper, 0 to 0.5 ppm of bismuth, 0 to 5 ppm of lead, 0 to 1000 ppm of platinum, 0 at 1000 ppm palladium, 0 to 50 ppm hydrogen, 0 to 5 ppm silver, 0 to 200 ppm nitrogen, 0 to 1000 ppm rhenium, 250 to 900 ppm carbon, 0 to 500 ppm oxygen and 0 to 500 ppm unavoidable impurities, the remainder being nickel. In particular, the sintered part made of nickel-based alloy 7 comprises, in mass percentages, between 0 and 50 ppm of each element considered to constitute an unavoidable impurity.

[0092] 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. For example, if the alloy powder 1 comprises 250 ppm of oxygen, 20 ppm of nitrogen and 700 ppm of carbon, the part sintered 7 obtained at the end of the process according to the invention from the alloy powder 1 comprises 270 ppm of dioxygen, 100 ppm of nitrogen and 1100 ppm of carbon.

[0093] 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. Alloy 1 powder must have carbon, oxygen and nitrogen levels much lower than those of the targeted René 77.

[0094] Figures 3A and 3B show two optical microscope views, at two different scales, of a sintered part 7 obtained at the end of the sintering step of the process according to the invention. In [Fig.3A] and [Fig.3B] recorded after chemical etching aimed at improving the phase contrast, a microstructure characteristic of a nickel-based alloy is observed. The metallurgical grains, which appear in the form of gray areas whose contrast varies from one grain to another, 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, for example hot isostatic compacting, can be implemented to eliminate said porosity residues.

[0095] Furthermore, the size of the metallurgical grains within the sintered part 7 is relatively small, it is between 5 ASTM and 9 ASTM. The measurement of the metallurgical grains is carried out according to the ASTM El 12 standard. For example, the grain size of the microstructure in Figures 3A and 3B is 6 ASTM. A part composed of small metallurgical grains has good fatigue strength, but poor finishing strength. Depending on the intended application for the manufactured part, a high-temperature heat treatment can be implemented to increase the size of the metallurgical grains of said part. The conditions of said treatment are chosen to guarantee fatigue, finishing and tensile properties consistent with the intended application. Hot isostatic compaction.

[0096] It is optionally possible to implement a step E7 of hot isostatic compaction of the sintered part 7 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 René 77 alloy. The hot isostatic compaction step E7 makes it possible to increase the density of the part 7 resulting from sintering up to 100% of the density of the foundry René 77 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.

[0097] 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 1160°C and 1200°C, preferably a temperature of 1180°C, and a pressure of more than 100 MPa and less than 200 MPa, preferably between 110 MPa and 130 MPa, are applied for 2 hours to 4 hours under an inert atmosphere, for example a helium atmosphere or under vacuum, preferably an argon atmosphere.

[0098] Figures 4A and 4B are two optical microscope views, at two different scales, of a part obtained at the end of steps E6 and E7 of the process according to the invention. The microstructure of the nickel alloy is recognizable, but no more spots can be seen. Step E7 of hot isostatic compacting therefore made it possible to fill the last porosities and to obtain a completely healthy material. High temperature heat treatment

[0099] It is optionally possible to implement a step E8 of high-temperature heat treatment of the sintered part. If a step E7 of hot isostatic compacting is implemented, the step E8 of high-temperature heat treatment is preferably carried out after said step E7.

[0100] High temperature heat treatment E8 consists of heating the part to a temperature high enough to cause the metallurgical grains to grow. Indeed, under the action of temperature, the grains will group together in such a way as to limit their interface and thus lower their potential energy. The grouping of the initial metallurgical grains results in larger metallurgical grains. Temperature is a kinetic factor: applying a high temperature increases the speed of grain grouping.

[0101] Step E8 of high temperature heat treatment is advantageously implemented for the manufacture of parts which will be subjected to high finishing stresses such as, for example, turbine blades and turbine distributors. Indeed, the larger the metallurgical grains, the easier the sliding between said grains under the effect of finishing stresses and therefore the better the resistance of the part to said stresses.

[0102] Step E8 of high temperature heat treatment preferably comprises the application of a temperature between 1200°C and 1280°C, more preferably at a temperature between 1220°C and 1240°C for a duration between 2 hours and 6 hours, more preferably for 5 hours at atmospheric pressure, under an inert atmosphere, for example an argon atmosphere.

[0103] Following the performance of said step E8 under the conditions thus described, the size of the metallurgical grains is between 00 ASTM and 5 ASTM, on average it is 2 ASTM. As mentioned previously, the size of the grains was between 5 ASTM and 9 ASTM at the end of sintering step E6. The grain size has therefore increased. Figures 5A and 5B are two optical microscope views, at two different scales, of a part obtained at the end of steps E6, E7 and then E8 of the process according to the invention. If we compare the microstructure in Figures 5A and 5B with that, in Figures 4A and 4B, of the part after step E7 and before step E8 of said process, we see that the grain size has actually increased during step E8 of high-temperature heat treatment. For example, the grain size of the microstructure shown in Figures 4A and 4B is 2 ASTM.

[0104] Increasing the grain size when carrying out step E8 makes it possible to improve the resistance of the part in finishing, while guaranteeing said part good fatigue and tensile strength.

[0105] Quenching.

[0106] In addition, a quenching heat treatment step E9 is implemented. The quenching heat treatment consists of heating the part to a temperature for dissolving the good alloying elements that constitute nickel 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 part with the expected mechanical and chemical properties.

[0107] The quenching heat treatment step E9 is preferably carried out at a temperature of between 1120°C and 1190°C, more preferably at a temperature of between 1150°C and 1170°C for a period of between 1 hour and 3 hours, more preferably for 2 hours. The part is finally cooled at an average rate of between 47°C / hour and 67°C / hour until a temperature of between 1070°C and 1090°C is reached, preferably a temperature of 1080°C, then at an average rate greater than or equal to 16°C / min. Throughout the quenching heat treatment step E9, which comprises heating and then cooling the part, an inert atmosphere, for example an argon atmosphere, is maintained at atmospheric pressure, or said step is carried out under vacuum. Tempering heat treatment

[0108] Finally, a tempering heat treatment step E10 is implemented. During the tempering heat treatment E10, certain alloy elements precipitate at the grain boundaries. The tempering heat treatment E10 makes it possible to obtain the expected mechanical properties for the manufactured alloy part. The E10 treatment makes it possible in particular to improve the tensile strength of said manufactured part.

[0109] The tempering heat treatment step E10 comprises the application of a temperature of between 720°C and 800°C, preferably of between 750°C and 770°C for a duration of between 3h30 and 4h30, preferably a duration 4 hours in air. For example, under such conditions of execution of the E10 tempering heat treatment, a 20% improvement in stress resistance can be observed. Parts obtained by the process

[0110] The invention also relates to parts obtained from the manufacturing process using the alloy 1 powder in accordance with the invention.

[0111] Said parts are nickel-based alloy parts comprising in particular, in mass percentages, between 250 ppm and 900 ppm of carbon, less than 200 ppm of nitrogen and less than 500 ppm of oxygen, the chemical compositions being measured by elemental analysis, for example by inductively coupled plasma spectrometry.

[0112] In [Fig. 1] which represents a part made of René 77 from a foundry, it can be seen, as stated previously, that it has a microstructure with grains of size 00 ASTM. If the size of the metallurgical grains of a part of René 77 alloy from a foundry is less than or equal to 00 ASTM, the size of the metallurgical grains of a part obtained from the manufacturing process using the alloy powder 1 in accordance with the invention is between 00 ASTM and 9 ASTM. For example, for the part obtained at the end of the sintering step E6 and whose microstructure is visible in Figures 3A and 3B, said grain size is 6 ASTM. For the part obtained at the end of the high-temperature heat treatment step E8 of Figures 5A and 5B, it is 2 ASTM.The parts obtained from the manufacturing process using the alloy powder in accordance with the invention therefore have a microstructure with metallurgical grains smaller than the grains within the foundry René 77 alloy, which gives them better tensile and fatigue resistance than a part made from foundry René 77.

[0113] Rm is the value of the limit stress leading to tensile failure Rm, Rpo,2 is the value of the stress at which the elastic limit is reached with 0.2% residual plastic deformation and A% is the value of the elongation at break. The values ​​Rm, Rp0>2 and A% of a part manufactured according to the process using the alloy 1 powder in accordance with the invention, said process comprising steps E1 to E7 then E9 and E10 as previously described, increase by around 30% compared to the values ​​Rm, Rp0>2 and A% of a part made of René 77 from the foundry. In addition, the fatigue gain is around 20%.

[0114] The values ​​Rm, Rp0>2 and A% of a part manufactured according to the process using the alloy 1 powder in accordance with the invention, said process further comprising an E8 tape as previously described, is of the order of 15% compared to a part made of René 77 from a foundry. The fatigue gain is in this case of the order of 10%.

[0115] 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, retaining rings, sealed sectors or cladding parts which are subject to high tensile, fatigue and fining stresses, which must resist corrosion and oxidation, and which are used at high temperatures above 1000°C.

Claims

Claims

1. Nickel-based alloy powder (1), characterized in that it comprises, in mass percentages, 14.00 to 15.25% of chromium, 14.25 to 15.75% of cobalt, 4.00 to 4.60% of aluminum, 0 to 0.50% of iron, 0 to 0.15% of manganese, 3.00 to 3.70% of titanium, 3.90 to 4.50% of molybdenum, 0 to 0.015% of sulfur, 0 to 0.06% of zirconium, 0.012 to 0.020% of boron, 0 to 0.20% of silicon, 0 to 0.10% of copper, 0 to 150 ppm of carbon, 0 to 0.5 ppm of bismuth, 0 to 5 ppm of lead, 0 to 1000 ppm of platinum, 0 to 1000 ppm of palladium, 0 to 50 ppm of hydrogen, 0 to 5 ppm of silver, 0 to 120 ppm of nitrogen, 0 to 1000 ppm of rhenium, 0 to 410 ppm of oxygen and 0 to 500 ppm of unavoidable impurities, the remainder being constituted by nickel, and in that it has: - a D10 particle size of between 3 and 10 pm, - a D90 particle size of between 20 and 40 pm and, - a D50 particle size of between 10 and 20 pm, the values ​​of the D10 particle sizes,D50 and D90 having been measured by laser diffraction according to ISO 13322-2.,

2. Method for manufacturing a part, in particular for aeronautics, characterized in that it comprises the following steps: - a step (El) of mixing the nickel-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 (E9) of quenching the sintered part (7) which consists of a heat treatment of the sintered part (7) at a temperature between 1120°C and 1190°C, preferably a temperature between 1150°C and 1170°C for a duration between 1 hour and 3 hours, preferably for 2 hours at atmospheric pressure, 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 tempering heat treatment step (E10) which consists of a heat treatment of the sintered part (7) at a temperature between 720°C and 800°C, preferably a temperature between 750°C and 770°C for a duration between 3h30 and 4h30, preferably a duration of 4 hours, this step being carried out after the sintering step (E6) and after the optional quenching step (E9).

5. Method according to any one of claims 2 to 4, characterized in that it further comprises a step (E7) of hot isostatic compaction which consists of a heat treatment at a temperature between 1160 °C and 1200 °C, preferably a temperature of 1180 °C, for 2 hours to 4 hours under a pressure greater than 100 MPa and less than 200 MPa, preferably a pressure between 110 MPa and 130 MPa, this step being carried out after the sintering step (E6) and before the possible steps of quenching (E9) and tempering heat treatment (E10).

6. Method according to any one of claims 2 to 5, characterized in that it further comprises a step (E8) of high temperature heat treatment of the sintered part (7) which consists of a heat treatment of the sintered part (7) at a temperature between 1200°C and 1280°C, preferably a temperature between 1220°C and 1240°C for a duration between 2 hours and 6 hours, preferably for five hours at atmospheric pressure, this step being carried out after the sintering step (E6) and after the optional hot isostatic compacting step (E7), but before the optional heat treatment steps (E9) and (E10).

7. Method according to any one of claims 2 to 6 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 170 °C and 200 °C, the measurement of the hot fluidity being carried out according to the ISO 1133-1 standard.

8. Method according to any one of claims 2 to 7 characterized in that the diameter of the granules of mixture of alloy and plastic is between 1 mm and 5 mm.

9. Method according to any one of claims 2 to 8 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,

10. Method according to claim 9, 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.

11. V-. Method according to claim 9, 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 300 h.

12. Method according to any one of claims 9 to 11, characterized in that the thermal debinding step (E5) is carried out under argon at a pressure of between 200 mbar and 500 mbar by two successive temperature stages, the first temperature stage being between 450°C and 550°C for 150 to 300 minutes, the second temperature stage being between 550°C and 650°C for 150 to 300 minutes.

13. Method according to any one of claims 2 to 12, characterized in that the step (E6) of sintering the debinded part is carried out by applying a temperature of between 1260 and 1300°C for a period of between 4 and 8 hours under an argon atmosphere at a pressure of between 20 mbar and 50 mbar.

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