Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
  • B22F1/10—Metallic powder containing lubricating or binding agents; Metallic powder containing organic material
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/04—Making non-ferrous alloys by powder metallurgy
  • C22C1/0433—Nickel- or cobalt-based alloys
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
  • B22F3/22—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces for producing castings from a slip
  • B22F3/225—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces for producing castings from a slip by injection molding
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
  • B22F3/24—After-treatment of workpieces or articles
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F5/00—Manufacture of workpieces or articles from metallic powder characterised by the special shape of the product
  • B22F5/009—Manufacture of workpieces or articles from metallic powder characterised by the special shape of the product of turbine components other than turbine blades
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F5/00—Manufacture of workpieces or articles from metallic powder characterised by the special shape of the product
  • B22F5/04—Manufacture of workpieces or articles from metallic powder characterised by the special shape of the product of turbine blades
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C19/00—Alloys based on nickel or cobalt
  • C22C19/03—Alloys based on nickel or cobalt based on nickel
  • C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
  • C22C19/051—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W
  • C22C19/056—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W with the maximum Cr content being at least 10% but less than 20%
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/002—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working by rapid cooling or quenching; cooling agents used therefor
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/10—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of nickel or cobalt or alloys based thereon
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01D—NON-POSITIVE DISPLACEMENT MACHINES OR ENGINES, e.g. STEAM TURBINES
  • F01D25/00—Component parts, details, or accessories, not provided for in, or of interest apart from, other groups
  • F01D25/005—Selecting particular materials
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
  • B22F3/24—After-treatment of workpieces or articles
  • B22F2003/241—Chemical after-treatment on the surface
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
  • B22F3/24—After-treatment of workpieces or articles
  • B22F2003/248—Thermal after-treatment
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2201/00—Treatment under specific atmosphere
  • B22F2201/02—Nitrogen
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2301/00—Metallic composition of the powder or its coating
  • B22F2301/15—Nickel or cobalt
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2303/00—Functional details of metal or compound in the powder or product
  • B22F2303/01—Main component
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2304/00—Physical aspects of the powder
  • B22F2304/15—Millimeter size particles, i.e. above 500 micrometer
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
  • B22F2998/10—Processes characterised by the sequence of their steps
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
  • F05D—INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS
  • F05D2300/00—Materials; Properties thereof
  • F05D2300/10—Metals, alloys or intermetallic compounds
  • F05D2300/13—Refractory metals, i.e. Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W

Definitions

• the invention relates to a nickel base alloy powder particularly intended for use in a metal injection molding manufacturing process.
• the invention also relates to such a manufacturing process using this powder, as well as a part, in particular for aeronautics, manufactured by this process.
• the exhaust gases generated by the combustion chamber can reach high temperatures, above 1200°C, or even 1600°C.
• the parts of the turbojet, 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.
• Superalloys typically nickel-based, are 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).
• René 77 intermetallic alloy from casting was used to manufacture certain turbine parts.
• 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.
• nickel-based alloys withstanding such high temperatures for example above 900° C.
• metal powder injection molding (known under the English name of “MIM” for “Metal Injection Molding”). This method can be advantageously used for the manufacture of complex turbomachine parts with the desired dimensions.
• Nickel-based Inconel 718 for example, is commonly used, but the part obtained cannot work above 650°C, which is too low a temperature for use in the combustion chamber or at the level of the turbine.
• 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. There is therefore a need to solve the aforementioned problems.
• An object of the invention is therefore to propose a solution making it possible to obtain complex parts, such as, for example, turbine nozzles, turbine blades with internal channels, retaining rings or sealed sectors, of controlled dimensions, made of an alloy material which has good tensile, fatigue, creep and oxidation/corrosion resistance up to a minimum of 1000°C and which, moreover, can be used in a MIM molding process .
• Another object of the invention is to obtain parts for aeronautics having a good surface condition.
• the invention proposes 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, 4.00-4.60% aluminum, 0-0.50% iron, 0-0.15% manganese, 3.00-3.70% titanium, 3.90-4.50 % Molybdenum, 0-0.015% Sulfur, 0-0.06% Zirconium, 0.012-0.020% Boron, 0-0.20% Silicon, 0-0.10% Copper, 0-150 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 of nitrogen, 0 to 1000 ppm of rhenium, 0 to 410 ppm of oxygen and 0 to 500 ppm of unavoidable impurities, the remainder consisting of nickel,
• this alloy powder 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 resistance to traction, fatigue, creep and good resistance to corrosion and oxidation up to 1000°C.
• the invention also proposes a process for manufacturing a part, in particular for aeronautics, characterized in that it comprises the following steps:
• This process makes it possible to obtain, from the alloy powder described above, complex parts, with controlled dimensions and having a good surface finish.
• This process also makes it possible to obtain parts with good tensile, fatigue and creep resistance and good resistance to corrosion and oxidation up to 1000°C, while being less massive than a part made in a nickel-based alloy.
• 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 period of between 1 hour and 3 hours, preferably for 2 hours at atmospheric pressure, this step being carried out after the sintering step,
• the method further comprises a tempering heat treatment step which consists of a heat treatment of the sintered part at a temperature of between 720°C and 800°C, preferably a temperature of 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,
• 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 higher pressure at 100 MPa and less than 200 MPa, preferably a pressure of between 110 MPa and 130 MPa, this step being carried out after the sintering step and before any quenching and tempering heat treatment steps,
• the method further comprises a step of high temperature heat treatment 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 period of 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 steps of heat treatments,
• the alloy volume 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 standard ISO 1133-1 , - the diameter of the alloy and plastic mixture granules is between 1 mm and 5 mm,
• the debinding step itself comprises two successive steps: a first step of primary debinding 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 for the obtaining a debinded part,
• 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,
• the primary debinding step is solvent debinding with demineralised water, with water stirring, the water temperature being between 20 and 100°C for a period of between 100 and 300 hours,
• the thermal debinding step 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 level being between 550°C and 650°C for 150 to 300 minutes,
• the step 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.
• the invention finally relates to a nickel-based alloy part, in particular for aeronautics, characterized in that it is manufactured by the manufacturing process as described above.
• the part 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, 0-0.150% 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 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, 0-5 ppm silver, 0-200 ppm nitrogen, 0-1000 ppm rhenium, 250-900 ppm carbon, 0-500 ppm oxygen and 0-500 ppm unavoidable impurities the remainder being made up of nickel and in that it also has a microstructure having metallurgical grains of size between 00 ASTM and
• the part is a turbine blade, a turbine nozzle, a retaining ring, a sealed sector or a trim part.
• FIG. 1 shows an electron microscope view of a René 77 part from the foundry after a series of heat treatments.
• FIG. 3A and 3B represent respectively two views under an 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.
• FIGS. 4A and 4B show two views under an optical microscope, at two different scales, of a part obtained at the end of the hot isostatic compacting (CIC) step of the manufacturing method in accordance with the invention, said hot isostatic compacting step having been carried out after the sintering step.
• CIC hot isostatic compacting
• FIGS. 5A and 5B show two views under an optical microscope, 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 step of high temperature heat treatment having been carried out after the hot isostatic compaction (CIC) step.
• CIC hot isostatic compaction
• the René 77 alloy from foundry comprises, in mass percentage, between 0.05% and 0.09% carbon, between 14.25% and 15.75% cobalt, between 14.00% and 15.25% chromium, between 4.00% and 4.60% aluminium, between 3.90% and 4.50% molybdenum, between 3.00% and 3.70% titanium, less than 0.50% iron, between 0.012% and 0.020% boron, between 0 and 0.06% zirconium, between 0 and 0.15% manganese, between 0 and 0.20% silicon, between 0 and 0.10% copper , between 0 and 0.015% sulfur, less than 0.5 ppm 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 of rhenium and less than 1000 ppm of palladium, the remainder being constituted by nickel which is the base of the alloy and the inevitable impurities.
• the microstructure of René 77 from foundry has metallurgical grains whose size is less than or equal to 00 ASTM.
• Figure 1 is a representation of such a René 77 foundry microstructure in which the grains measure 00 ASTM. At the bottom left of Figure 1, one can distinguish in darker gray one of said metallurgical grains. The measurement of the size of the metallurgical grains is carried out according to the standard ASTM E112.
• the René 77 intermetallic alloy has interesting mechanical and chemical properties for applications in the field of turbomachines.
• the parts in René 77 foundry products retain good mechanical resistance in creep, fatigue and traction up to 1000°C, as well as good resistance to corrosion and oxidation up to 1100°C.
• the limit stress leading to tensile rupture R m of René 77 castings is greater than 650 MPa.
• the elastic limit with 0.2% residual plastic deformation of said parts Rpo,2 is reached for a stress greater than 500 MPa and the elongation at break is greater than 2%.
• 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 that is distinguished by its speed of implementation.
• 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 part of René 77 alloy and those of a part resulting from a metal powder injection molding process.
• 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 unbound part is fragile, because it is very porous. An additional sintering step is necessary during which the grains of metal powder are bonded together.
• Nickel-type alloy powder usable in metal powder injection molding
• a nickel-based metal alloy powder Disclosed is a nickel-based metal alloy powder.
• the chemical composition and the particle size of the alloy powder were chosen in order to allow its use in a metal injection molding (MIM) process and to obtain, at the end of the process, an alloy part with nickel base whose chemical composition and mechanical properties are close to those of the René 77 foundry alloy.
• MIM metal injection molding
• the carbon, nitrogen and dioxygen levels given in the René 77 specification are relatively low with regard to the expected mechanical properties.
• a high carbon content 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 it may break during use. High levels of oxygen and nitrogen also cause a drop in the ductility of the part and rapid failure in fatigue and in tension.
• the levels of the various elements of the alloy powder of the invention in particular the levels of nitrogen, oxygen and carbon, were therefore chosen accordingly.
• the alloy powder in accordance with the invention comprises, in mass percentages, 14.00 to 15.25% chromium, 14.25 to 15.75% cobalt, 4.00 to 4.60% aluminum, 0-0.50% Iron, 0-0.15% Manganese, 3.00-3.70% Titanium, 3.90-4.50% Molybdenum, 0-0.015% Sulfur, 0-0 .06% zirconium, 0.012-0.020% boron, 0-0.20% silicon, 0-0.10% copper, 0-150 ppm carbon, 0-0.5 ppm bismuth, 0-5 ppm lead, 0-1000 ppm platinum, 0-1000 ppm palladium, 0-50 ppm hydrogen, 0-5 ppm silver, 0-120 ppm nitrogen, 0-1000 ppm rhenium, 0 to 410 ppm oxygen and 0 to 500 ppm unavoidable impurities, the remainder being nickel.
• unavoidable impurities the elements which are not added intentionally in the composition of the powder and which are brought by other elements.
• unavoidable impurities mention may be made, for example, of yttrium which may come from the crucibles used for the atomization of the powder.
• 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.
• the particle size of the powder was chosen so that the powder can be used in the manufacturing process described below, in particular during the injection and sintering steps.
• the implementation of the powder injection molding process requires a control of the size of the powder grains to guarantee a good injection of the mixture of alloy powder and plastic binder into the mold of the part.
• grains of alloy powder of small size induce a large interface of contact 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.
• grains of alloy powder that are too large in size are more difficult to carry off by the plastic binder during said injection and can therefore lead to an inhomogeneous injected part.
• the particle size is important for obtaining 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 reduce their interfaces and their surfaces more strongly, significantly lowering their entropy.
• the size of the grains of the alloy powder of the invention has therefore been defined by a range of acceptable values for the grain sizes D10, D50 and D90 of said alloy powder.
• the D10 grain size corresponds to 10% passing. In other words, 10% by number of the grains of the alloy powder have a diameter less than D10. Similarly, the D50 and D90 grain sizes correspond respectively to 50% and 90% passing.
• the D10 particle size of the alloy powder in accordance with the invention is between 3 and 10 ⁇ m.
• the D50 particle size is itself between 10 and 20 ⁇ m.
• the D90 particle size is between 20 and 40 ⁇ m.
• the values of the grain sizes D10, D50 and D90 were measured according to the ISO 13322-2 standard. This standard provides for measurement by laser diffraction.
• 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 provides the chemical composition and particle size of the alloy powder obtained. In addition, it ensures a good morphology of the powder, mostly spherical. Finally, it limits the risk of pollution.
• the invention also relates to a process for manufacturing a part, in particular for aeronautics, which uses nickel-based alloy powder, defined above.
• this process includes successive stages of mixing, granulation, injection molding, chemical debinding, thermal debinding, sintering and quenching.
• the method may further comprise one or more additional heat treatment steps. These steps are described in more detail below with reference to Figure 2.
• the nickel-based alloy powder 1 in accordance with 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.
• 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.
• 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, alloy and plastic mixture pellets 3 exhibiting a hot fluidity guaranteeing effective injection of said granules 3 during 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 of between 190°C and 230°C, the measurement of the hot fluidity being carried out according to the ISO 1133 standard -1.
• step E2 of granulating the mixture of the alloy powder and the at least one plastic binder the mixture resulting 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 name of “feedstock”.
• the shape and size of the alloy and plastic mixture pellets 3 are fixed by the setting of the extruder.
• the alloy and plastic mixture granules 3 are, for example, cylinders whose base diameter is preferably between 1 mm and 5 mm.
• 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 it does not fit into the mould. Above 200°C, the mixture is too liquid, the alloy powder and the plastic binder separate and the alloy powder is not washed away. Other parameters, such as injection speed, injection pressure, dwell time after injection or injection time depend on the part to be injected.
• a raw part 4 is obtained, also called a “green part”, which is a part of alloy powder and mixed plastic (alloy grains suspended in the plastic). Adjusting the molding parameters makes it possible to obtain a part without porosity. The plastic binder holds the part together.
• E4 primary debinding is chemical debinding.
• Primary debinding E4 makes it possible to obtain a partially debinded part 5.
• This debinding can be either: debinding using an E4B solvent, or preferably catalytic E4A debinding. The latter has the advantage of being faster.
• E4A catalytic debinding consists of vaporizing then burning the plastic binder by injecting acid vapors into an oven.
• the catalytic debinding is carried out, for example, at a temperature of between 100° C. and 150° C. for 2 to 10 hours, under a nitrogen atmosphere, in the presence of nitric acid vapours, the nitric acid flow being comprised of preferably between 2 and 5 mL/min.
• E4B debinding using a solvent consists of bathing the green part 4 in a bath of said solvent, so as to dissolve the plastic.
• the E4B debinding is for example a water debinding, the green part 4 being immersed for 100 to 300 hours in a bath of demineralised water with stirring at a temperature of between 20 and 100° C., preferably of the order of 60°C.
• the chemical debinding step E4 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.
• the thermal debinding E5 is preferably carried out under an argon atmosphere at a pressure of between 200 mbar and 500 mbar by the successive application of two temperature stages to the partially debinded part 5.
• a temperature between 450°C and 550°C for 150 minutes to 300 minutes.
• a temperature of between 550° C. and 650° C. is applied for 150 minutes to 300 minutes.
• a debinding part or "brown part” 6 is obtained, the thermal debinding having made it possible to remove the remaining plastic binder (that is to say the less than 5 remaining).
• the debinded part 6 resulting from the primary E4 and thermal E5 debinding steps is a part of the same dimensions as 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 René 77 alloy part from the foundry.
• the debinded part 6 is very fragile because the plastic binder which held the part together has been removed.
• the debinded part 6 is sintered.
• the sintering consists in subjecting the debinded part 6 to a temperature close to the melting point of the powder of alloy so that the grains of powder bind together. During sintering, the part shrinks and its density increases.
• the sintering is carried out in an oven, preferably at a temperature of between 1260 and 1300° C. for 4 hours to 6 hours under an argon atmosphere at a pressure of between 20 mbar and 50 mbar.
• the thermal debinding step E5 and the sintering step E6 are carried out in the same oven, because the debinded part 6 is fragile.
• 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.
• the sintered nickel-base alloy part 7 comprises, in mass percentages, 14.00 to 15.25% chromium, 14.25 to 15.75% cobalt, 4.00 to 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 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, 0-50 ppm hydrogen, 0-5 ppm silver, 0-200 ppm nitrogen, 0-1000 ppm rhenium, 250-900 ppm carbon, 0-500 ppm oxygen and 0 to 500 ppm of unavoidable impurities, the remainder consisting of nickel.
• the sintered part made of nickel-based alloy 7 comprises,
• 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.
• 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 in accordance with the invention from the Alloy powder 1 comprises 270 ppm oxygen, 100 ppm nitrogen and 1100 ppm carbon.
• the additional elements carbon, oxygen and nitrogen are residues of the plastic binder which has impregnated the metallic material.
• excessively high levels of said elements can have a negative impact on the mechanical properties of the alloy part resulting from the MIM process.
• the alloy powder 1 must have much lower levels of carbon, oxygen and nitrogen. to those of the René 77 in question.
• FIGS. 3A and 3B are reported two views under an optical microscope, at two different scales, of a sintered part 7 obtained at the end of the sintering step of the method in accordance with the invention.
• FIG. 3A and in 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 as gray areas whose contrast varies from grain to grain, are bonded and the material is relatively dense.
• the material also includes porosity residues (see small round and black spots) which can affect the mechanical properties of the final part. Heat treatments, for example hot isostatic compacting, can be implemented to remove said porosity residues.
• 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 metallurgical grains is carried out according to the ASTM E112 standard.
• 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.
• 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 in accordance with the intended application.
• a step E7 of hot isostatic compacting of the sintered part 7 in order to fill in the residual porosities, in particular if the density of the sintered part is less than 95% of the density of the René 77 foundry alloy.
• the hot isostatic compacting step E7 makes it possible to increase the density of part 7 resulting from sintering to 100% of the density of foundry René 77 and to improve the mechanical properties of said part.
• the hot isostatic compaction step E7 makes it possible to reduce the dimensional dispersion of parts resulting from the metal powder injection molding process.
• high pressure and high temperature are jointly applied under an inert atmosphere.
• a temperature of between 1160° C. and 1200° C., preferably a temperature of 1180° C., and a pressure greater than 100 MPa and less than 200 MPa, preferably between 110 MPa and 130 MPa are applied for 2 hours at 4 hours under an inert atmosphere, for example a helium atmosphere or under vacuum, preferably an argon atmosphere.
• FIGS. 4A and 4B are two views under an optical microscope, at two different scales, of a part obtained at the end of steps E6 and E7 of the process according to the invention.
• Step E7 of hot isostatic compacting therefore made it possible to fill in the last porosities and to obtain a completely healthy material.
• High temperature heat treatment It is optionally possible to implement a step E8 of high temperature heat treatment of the sintered part. If a hot isostatic compacting step E7 is implemented, the high temperature heat treatment step E8 is preferably carried out after said step E7.
• E8 high temperature heat treatment involves 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 so 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: the application of a high temperature makes it possible to increase the speed of grain groupings.
• the high temperature heat treatment step E8 is advantageously implemented for the manufacture of parts which 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.
• 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 time of between 2 hours and 6 hours, more preferably for 5 hours at atmospheric pressure, under an inert atmosphere, for example an argon atmosphere.
• FIGS. 5A and 5B are two views under an optical microscope, at two different scales, of a part obtained at the end of steps E6, E7 then E8 of the process in accordance with the invention. If the microstructure in FIGS. 5A and 5B is compared with that, in FIGS.
• the size of the grains has actually increased during of step E8 of high temperature heat treatment.
• the grain size of the microstructure shown in Figures 4A and 4B is 2 ASTM.
• step E8 makes it possible to improve the creep resistance of the part, while guaranteeing said part good fatigue and tensile strength.
• a quenching heat treatment step E9 is implemented.
• the quenching heat treatment consists in heating the part to a solution temperature of the good alloying elements that constitute the nickel long enough to allow the re-dissolving of said elements and their diffusion in the crystalline solid. The part is then cooled relatively quickly so that said good alloying elements re-precipitate. This step makes it possible to obtain a part with the expected mechanical and chemical properties.
• 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 it reaches a temperature of between 1070°C and 1090°C, preferably a temperature of 1080°C, then at a speed average greater than or equal to 16°C/min.
• an inert atmosphere is maintained, for example an argon atmosphere, at atmospheric pressure, or said step is carried out under vacuum.
• a tempering heat treatment step E10 is implemented. During the E10 tempering heat treatment, certain alloying 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 makes it possible in particular to improve the tensile strength of said manufactured part.
• the tempering heat treatment step E10 comprises the application of a temperature comprised between 720°C and 800°C, preferentially comprised between 750°C and 770°C for a duration comprised between 3h30 and 4h30, preferentially 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.
• the invention also relates to parts obtained from the manufacturing process using the alloy powder 1 in accordance with the invention.
• 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.
• FIG. 1 which represents a part made of René 77 from the foundry, it can be seen, as stated previously, that the latter has a microstructure with grains of size 00 ASTM.
• the size of the metallurgical grains of a René 77 alloy part 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 alloy powder 1 conforming to the invention is between 00 ASTM and 9 ASTM.
• said grain size is 6 ASTM.
• the part obtained at the end of the high temperature heat treatment step E8 of FIGS. 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 René 77 casting.
• R m the value of the limit stress leading to rupture in tension
• R m , Rpo,2 the value of the stress at which the elastic limit is reached with 0.2% of residual plastic deformation
• A% the value of the elongation at break.
• the gain in fatigue is of the order of 20%.
• the values R m , Rpo,2 and A% of a part manufactured according to the process using the alloy powder 1 in accordance with the invention, said process further comprising an E8 tape as previously described, is of the order 15% compared to a René 77 casting.
• the gain in fatigue is in this case of the order of 10%.
• the invention finds particular application in the manufacture of parts for aeronautics, such as for example turbine blades, including blades with internal channels, turbine nozzles, 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.
• parts for aeronautics such as for example turbine blades, including blades with internal channels, turbine nozzles, 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.

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• 2022
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