Alloy powder, method for manufacturing a part based on said alloy and resulting part

Abstract

The invention relates to a nickel-based alloy powder, that comprises in weight percentages, 14.00 to 15.25% of chromium, 14.25 to 15.75% of cobalt, 4.00 to 4.60% of aluminium, 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 sulphur, 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 inevitable impurities, the rest being made up of nickel, and has a particle size D10 between 3 and 10 μm, a particle size D90 between 20 and 40 μm and a particle size D50 between 10 and 20 μm, the values of the particle sizes D10, D50 and D90 having been measured by laser diffraction according to standard ISO 13322-2. The invention also relates to a method for manufacturing a part using said powder and a resulting part.

Description

[0001] Alloy powder, process for manufacturing a part based on this alloy and part thus obtained.

[0002] TECHNICAL FIELD

[0003] The invention relates to a nickel-based alloy powder particularly intended for use in a metal injection molding manufacturing process.

[0004] 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.

[0005] STATE OF THE ART

[0006] 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 maintain their mechanical properties at these high temperatures.

[0007] For this purpose, it is known to manufacture certain parts of the turbojet engine from "superalloys". 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).

[0008] The René 77 intermetallic alloy from foundry was used for the manufacture of certain turbine parts. Indeed, René 77 parts can work up to 1000 °C while undergoing high fatigue, tensile and creep stresses. René 77 parts also have very good resistance to oxidation and corrosion up to 1100 °C.

[0009] 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.

[0010] 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 to the desired dimensions.

[0011] Several materials are commercially available for the manufacture of turbomachine parts using the MIM process.

[0012] 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 turbine.

[0013] 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. Therefore, there is a need to solve the above-mentioned problems.

[0014] BRIEF DESCRIPTION OF THE INVENTION

[0015] 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 resistance to traction, fatigue, creep and oxidation / corrosion up to a minimum of 1000°C and, which, moreover, can be used in a MIM molding process.

[0016] Another aim of the invention is to obtain parts for aeronautics with a good surface finish.

[0017] 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 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 in that it has:

[0018] - a D10 particle size between 3 and 10 pm,

[0019] - a D90 particle size between 20 and 40 pm and,

[0020] - a D50 particle size between 10 and 20 pm, the values ​​of the D10, D50 and D90 particle sizes having been measured by laser diffraction according to the ISO 13322-2 standard.

[0021] The chemical composition and 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, creep strength and good resistance to corrosion and oxidation up to 1000°C.

[0022] The invention also proposes a method for manufacturing a part, in particular for aeronautics, characterized in that it comprises the following steps:

[0023] - a step of mixing the nickel-based alloy powder as described above with at least one plastic binder,

[0024] - a step of granulating this mixture, so as to obtain granules of alloy and plastic mixture

[0025] - a step of injection molding the mixture granules into a mold, to obtain a raw part, - a debinding step to obtain a debinded part,

[0026] - a sintering step of the debinded part to obtain a sintered part.

[0027] This process makes it possible to obtain, from the alloy powder described above, complex parts, with controlled dimensions and a good surface finish.

[0028] This process also makes it possible to obtain parts with good tensile strength, fatigue strength, creep 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.

[0029] According to other advantageous and non-limiting characteristics of the invention, taken alone or in combination:

[0030] - 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,

[0031] - 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,

[0032] - the method further comprises a hot isostatic compacting 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,

[0033] - the method further comprises a high-temperature heat treatment step 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 optional hot isostatic compacting step, but before the optional heat treatment steps,

[0034] - the alloy volumetric loading rate of the alloy and plastic mixture granules is between 50% and 75% and the hot fluidity of said granules is between 60 cm 3 / 10min and 85 cm 3 / 10min 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 hot fluidity being carried out according to the ISO 1133-1 standard, - the diameter of the alloy and plastic mixture granules is between 1 mm and 5 mm,

[0035] - the debinding step itself comprises two successive steps: a first step of primary chemical debinding 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,

[0036] - 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,

[0037] - 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 duration of between 100 and 300 h,

[0038] - the thermal debinding step is carried out under argon at a pressure 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,

[0039] - the sintering step of the debinded part is carried out by applying a 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.

[0040] 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.

[0041] According to other advantageous and non-limiting characteristics of the invention, taken alone or in combination:

[0042] - the part 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 to 1000 ppm of palladium, 0 at 50 ppm of hydrogen, 0 to 5 ppm of silver, 0 to 200 ppm of nitrogen, 0 to 1000 ppm of rhenium, 250 to 900 ppm of carbon, 0 to 500 ppm of oxygen and 0 to 500 ppm of unavoidable impurities, the remainder being constituted by nickel and in that it further has a microstructure having 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 E112 standard,

[0043] - the part is a turbine blade, a turbine nozzle, a retaining ring, a sealed sector or a trim part. BRIEF DESCRIPTION OF THE FIGURES

[0044] Other characteristics and advantages of the invention will emerge from the detailed description which follows, with reference to the appended drawings, in which:

[0045] - Figure 1 represents an electron microscope view of a René 77 piece from the foundry after a series of heat treatments.

[0046] - figure 2 schematically represents the different stages of the manufacturing process in accordance with the invention.

[0047] - Figures 3A and 3B respectively represent two optical microscope views, at two different scales, of a part obtained at the end of the sintering step of the manufacturing process according to the invention.

[0048] - Figures 4A and 4B represent two optical microscope views, 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.

[0049] - Figures 5A and 5B represent two optical microscope views, at two different scales, of a part obtained at the end of the high-temperature heat treatment step of the manufacturing method according to the invention, said high-temperature heat treatment step having been carried out after the hot isostatic compacting (HIC) step.

[0050] DETAILED DESCRIPTION OF EMBODIMENTS

[0051] 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 of bismuth, less than 5 ppm silver, less than 5 ppm lead, less than 25 ppm nitrogen, less than 1000 ppm platinum, less than 1000 ppm rhenium and less than 1000 ppm palladium, the remainder being nickel which is the base of the alloy and unavoidable impurities.

[0052] The microstructure of René 77 from the foundry has metallurgical grains whose size is less than or equal to 00 ASTM. Figure 1 is a representation of such a microstructure of René 77 from the foundry in which the grains measure 00 ASTM. In the bottom left of Figure 1, one of these metallurgical grains can be seen in darker gray. The measurement of the size of the metallurgical grains is carried out according to the ASTM E112 standard.

[0053] The René 77 intermetallic alloy has interesting mechanical and chemical properties for applications in the field of turbomachinery. Indeed, parts made of René 77 from the foundry maintain good mechanical resistance to creep, 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 R mof René 77 parts from foundry is greater than 650 MPa. Over the same temperature range, the elastic limit with 0.2% residual plastic deformation of said Rpo,2 parts is reached for a stress greater than 500 MPa and the elongation at break is greater than 2%.

[0054] On the other hand, metal powder injection molding makes it possible to obtain complex-shaped parts with an excellent surface finish and to finely control the dimensions of said parts. Metal powder injection molding is also a process that stands out for its rapid implementation.

[0055] 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.

[0056] The MIM process is a process for molding parts by injecting a mixture of metal powder and plastic binder into a mold. The plastic binder holds the injected part in place. The plastic binder is removed in subsequent steps, called debinding steps. The debinded part is fragile because it is very porous. An additional sintering step is required, during which the metal powder grains are bonded together.

[0057] Nickel-type alloy powder suitable for use in metal powder injection molding

[0058] The invention relates to a nickel-based metal alloy powder. The chemical composition and particle size of the alloy powder have been chosen 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 mechanical properties are close to those of the foundry René 77 alloy.

[0059] Chemical composition of the powder

[0060] Although the plastic binder is almost completely removed during the debinding steps described above, residues of this plastic binder impregnate the metal material. Nitrogen, oxygen and carbon levels are higher in the molded part resulting from the powder injection molding process than in the powder injected at the beginning of the process.

[0061] 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 tensile stress.

[0062] The levels of the various elements in the alloy powder of the invention, in particular the levels of nitrogen, oxygen and carbon, were therefore chosen accordingly.

[0063] 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 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.

[0064] "Unavoidable impurities" are defined as elements that are not intentionally added to the composition of the powder and are brought in by other elements. Examples of unavoidable impurities include yttrium, which can come from the crucibles used for atomizing the powder.

[0065] 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.

[0066] Powder particle size

[0067] The particle size of the powder was chosen so that the powder could be used in the manufacturing process described below, particularly during the injection and sintering stages.

[0068] The implementation of the powder injection molding process requires control of the size of the powder grains to ensure proper injection of the alloy powder and plastic binder mixture into the part mold. Indeed, small alloy powder grains induce a large contact interface between the alloy powder and the plastic binder within the alloy powder and plastic binder mixture and therefore significant friction during the injection of said mixture into the part mold. Conversely, alloy powder grains that are too large are more difficult to carry away by the plastic binder during said injection and can therefore lead to an inhomogeneous injected part.

[0069] 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 powder grains will more strongly reduce their interfaces and their surfaces, significantly lowering their entropy. 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.

[0070] The D10 particle size corresponds to 10% passing. In other words, 10% of the grains in the alloy powder have a diameter smaller than D10. Similarly, the D50 and D90 particle sizes correspond to 50% and 90% passing respectively.

[0071] The D10 particle size of the alloy powder according to the invention is between 3 and 10 μm. The D50 particle size is between 10 and 20 μm. Finally, the D90 particle size is between 20 and 40 μm.

[0072] The values ​​of the D10, D50 and D90 particle sizes were measured according to ISO 13322-2. This standard provides for measurement by laser diffraction.

[0073] Preparation of the powder

[0074] The nickel-based alloy powder that 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 particle size of the alloy powder obtained. In addition, it ensures good morphology of the powder, which is predominantly spherical. Finally, it makes it possible to limit the risks of pollution.

[0075] Metal powder injection molding process

[0076] The invention also relates to a method for manufacturing a part, particularly for aeronautics, which uses the nickel-based alloy powder defined above.

[0077] Generally, this process comprises successive steps of mixing, granulation, injection molding, chemical debinding, thermal debinding, sintering and quenching. Optionally, the process may further comprise one or more additional heat treatment steps. These steps are described in more detail below with reference to Figure 2.

[0078] Blend.

[0079] 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 cm. 3 / 10min and 85 cm 3 / 10min at a temperature between 190°C and 230°C, the measurement of hot fluidity being carried out according to ISO 1133-1.

[0080] Granulation.

[0081] 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.

[0082] Molding.

[0083] 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. Other parameters, such as injection speed, injection pressure, holding time after injection or injection time depend on the part to be injected.

[0084] Following molding step E3, a raw part 4, also called a "green part", is obtained, which is a part made of mixed alloy powder and plastic (alloy grains suspended in the plastic). Adjusting the molding parameters allows for a part without porosity. The plastic binder ensures the part's hold.

[0085] Debinding.

[0086] “Debinding” allows the plastic binder to be removed from the raw part 4 obtained previously.

[0087] Two debinding stages are carried out successively, one chemical, the other thermal.

[0088] Primary debinding.

[0089] Primary debinding E4 is a chemical debinding process. Primary debinding E4 allows for a partially debinded part 5 to be obtained. This debinding can be either: debinding using a solvent E4B, or preferably catalytic debinding E4A. The latter has the advantage of being faster.

[0090] E4A catalytic debinding involves vaporizing and then burning the plastic binder by injecting acid vapors into a furnace.

[0091] 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 nitric acid flow preferably being between 2 and 5 mL / min.

[0092] E4B debinding using a solvent consists of bathing the raw part 4 in a bath of said solvent, so as to dissolve the plastic.

[0093] E4B debinding is, for example, 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 around 60°C.

[0094] 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.

[0095] Thermal debinding.

[0096] 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.

[0097] 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%).

[0098] 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 green part 4. However, unlike the green 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 held the part together has been removed.

[0099] Sintering.

[0100] 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 bind together. During sintering, the part shrinks and its density increases.

[0101] Sintering is carried out in a furnace, preferably at a temperature between 1260 and 1300°C for 4 to 6 hours under an argon atmosphere at a pressure between 20 mbar and 50 mbar.

[0102] 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.

[0103] 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.

[0104] The sintered part 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 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. In particular, the sintered part of nickel-based alloy 7 comprises, in mass percentages, between 0 and 50 ppm of each element considered to constitute an unavoidable impurity.

[0105] 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 sintered part 7 obtained at the end of the process according to the invention from the alloy powder 1 comprises 270 ppm of oxygen, 100 ppm of nitrogen and 1100 ppm of carbon.

[0106] The additional carbon, oxygen, and nitrogen elements are residues of the plastic binder that has impregnated the metallic material. However, excessively high levels of these 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.

[0107] 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. Figure 3A and Figure 3B recorded after chemical etching aimed at improving the phase contrast show a microstructure characteristic of a nickel-based alloy. 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 used to eliminate said porosity residues.

[0108] 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 E112 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 resistance, but poor creep resistance. 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, creep and tensile properties consistent with the intended application.

[0109] Hot isostatic compaction.

[0110] Optionally, a step E7 of hot isostatic compaction of the sintered part 7 can be implemented 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.

[0111] During the hot isostatic compaction 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.

[0112] 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.

[0113] High temperature heat treatment A high temperature heat treatment step E8 of the sintered part can optionally be implemented. If a hot isostatic compaction step E7 is implemented, the high temperature heat treatment step E8 is preferably carried out after said step E7.

[0114] E8 high-temperature heat treatment involves heating the part to a temperature high enough to cause the metallurgical grains to grow. Under the influence 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.

[0115] The high-temperature heat treatment step E8 is advantageously implemented for the manufacture of parts that will be subjected to high creep stresses, such as, for example, turbine blades and turbine nozzles. Indeed, the larger the metallurgical grains, the easier the sliding between said grains under the effect of creep stresses and therefore the better the resistance of the part to said stresses.

[0116] The high temperature heat treatment step E8 preferably comprises the application of a temperature of between 1200°C and 1280°C, more preferably at a temperature of between 1220°C and 1240°C for a duration of between 2 hours and 6 hours, more preferably for 5 hours at atmospheric pressure, under an inert atmosphere, for example an argon atmosphere.

[0117] 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 grain size was between 5 ASTM and 9 ASTM at the end of the 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 the microstructure in Figures 5A and 5B is compared with that, in Figures 4A and 4B, of the part after step E7 and before step E8 of said process, it can be seen that the grain size has actually increased during the high-temperature heat treatment step E8. For example, the grain size of the microstructure shown in Figures 4A and 4B is 2 ASTM.

[0118] Increasing the grain size during step E8 improves the creep resistance of the part, while ensuring good fatigue and tensile strength.

[0119] Quenching. In addition, a quenching heat treatment step E9 is implemented. The quenching heat treatment consists of heating the part to a temperature at which the good alloying elements, which are nickel, are dissolved, for a sufficient time to allow the said elements to be re-dissolved and diffused into the crystalline solid. The part is then cooled relatively quickly so that the said good alloying elements reprecipitate. This step produces a part with the expected mechanical and chemical properties.

[0120] The quenching heat treatment step E9 is preferably carried out at a temperature between 1120°C and 1190°C, more preferably at a temperature between 1150°C and 1170°C for a duration between 1 hour and 3 hours, more preferably for 2 hours. The part is finally cooled at an average rate between 47°C / hour and 67°C / hour until reaching a temperature between 1070°C and 1090°C, 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.

[0121] Tempering heat treatment

[0122] Finally, an E10 tempering heat treatment step is implemented. During the E10 tempering heat treatment, certain alloy elements precipitate at the grain boundaries. The E10 tempering heat treatment makes it possible to obtain the expected mechanical properties for the manufactured alloy part. The E10 treatment notably makes it possible to improve the tensile strength of the said manufactured part.

[0123] The E10 tempering heat treatment step comprises the application of a temperature between 720°C and 800°C, preferably between 750°C and 770°C for a duration between 3h30 and 4h30, preferably a duration of 4 hours in air. For example, under such conditions of execution of the E10 tempering heat treatment, a 20% improvement in the stress resistance can be observed.

[0124] Parts obtained by the process

[0125] The invention also relates to parts obtained from the manufacturing process using the alloy 1 powder according to the invention.

[0126] 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. In Figure 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 1 powder 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 strength than a foundry René 77 part.

[0127] We call R m the value of the limit stress leading to tensile failure R m , Rpo,2 the value of the stress at which the elastic limit is reached with 0.2% residual plastic deformation and A% the value of the elongation at break. The values ​​R m, Rpo,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 ​​R m , Rpo,2 and A% of a René 77 part from the foundry. In addition, the fatigue gain is around 20%.

[0128] R values m , Rpo,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%.

[0129] The invention finds 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 trim parts which are subjected to high tensile, fatigue and creep stresses, which must resist corrosion and oxidation, and which are used at high temperatures above 1000°C.

Claims

DEMANDS 1. Nickel-based alloy powder (1), characterized in that it comprises, 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 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 in that it presents: - 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 pm, the values ​​of the D10, D50 and D90 particle sizes having been measured by laser diffraction according to the ISO 13322-2 standard.

2. A method for manufacturing a part, particularly for the aeronautical industry, characterized in that it comprises the following steps: - a step (E1) 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 of the mixture granules (3) into a mold, to obtain a raw part (4), - a debinding step (E4A, E4B, E5) to obtain a debinded part (6), - a step (E6) of sintering the debound part to obtain a sintered part (7).

3. The method according to claim 2, characterized in that it further comprises a quenching step (E9) of 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 period of between 1 hour and 3 hours, preferably for 2 hours at atmospheric pressure, this step being carried out after the sintering step (E6).

4. A method according to any one of claims 2 or 3, characterized in that it further comprises a tempering heat treatment step (E10) consisting of 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 of 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. A process according to any one of claims 2 to 4, characterized in that it further comprises a hot isostatic compaction step (E7) consisting of a heat treatment at a temperature between 1160 °C and 1200 °C, preferably a temperature of 1180 °C, for 2 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 any quenching (E9) and tempering heat treatment (E10) steps.

6. A method according to any one of claims 2 to 5, characterized in that it further comprises a high-temperature heat treatment step (E8) of the sintered part (7) which consists of heat treating the sintered part (7) at a temperature between 1200 °C and 1280 °C, preferably between 1220 °C and 1240 °C for a period of 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 compaction step (E7), but before the optional heat treatment steps (E9) and (E10).

7. A method according to any one of claims 2 to 6, characterized in that the volumetric alloy content of the alloy-plastic mixture granules (3) is between 50% and 75% and the hot flowability of said granules (3) is between 60 cm 3 / 10 min and 85 cm 3 / 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 hot flow measurement being carried out according to ISO 1133-1.

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

9. A 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 chemical debinding 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. The process 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 2mL / min and 5 mL / min, the temperature being between 100 and 150 °C.

11. Process according to claim 9, characterized in that the primary debinding step is a solvent debinding with demineralized water (E4B), under agitation of the water, the temperature of the water being between 20 and 100 °C for a duration of between 100 and 300 h.

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

13. A 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 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.

14. Nickel-based alloy part, particularly for aeronautics, characterized in that it is manufactured by the manufacturing process according to any one of claims 2 to 13.

15. Part according to claim 14, characterized in that it comprises, 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 0.150% manganese, 3.00 to 3.70% titanium, 3.90 to 4.50% molybdenum, 0 to 0.015% sulfur, 0 to 0.060% zirconium, 0.012 to 0.020% boron, 0 to 0.20% silicon, 0 to 0.100% copper, 0 to 0.5 ppm bismuth, 0 to 5 ppm lead, 0 to 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 furthermore exhibiting a microstructure 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 ASTM E112.

16. Part according to claim 14 or 15, characterized in that it is a turbine blade, a turbine distributor, a retaining ring, a sealing sector or a housing part.

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