Classifications

• • 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
  • F01D5/00—Blades; Blade-carrying members; Heating, heat-insulating, cooling or antivibration means on the blades or the members
  • F01D5/12—Blades
  • F01D5/28—Selecting particular materials; Particular measures relating thereto; Measures against erosion or corrosion
• • 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
  • C22C19/057—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W with the maximum Cr content being less 10%
• • 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
  • F01D5/00—Blades; Blade-carrying members; Heating, heat-insulating, cooling or antivibration means on the blades or the members
  • F01D5/12—Blades
  • F01D5/28—Selecting particular materials; Particular measures relating thereto; Measures against erosion or corrosion
  • F01D5/288—Protective coatings for blades
• • 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
  • F05D2230/00—Manufacture
  • F05D2230/90—Coating; Surface treatment
• • 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
  • F05D2300/17—Alloys
  • F05D2300/175—Superalloys
• • 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
  • F05D2300/60—Properties or characteristics given to material by treatment or manufacturing
  • F05D2300/606—Directionally-solidified crystalline structures

Definitions

• this structure of the nickel-based superalloy allows the implementation of a heat treatment which redissolves the precipitates of phase Y' and the eutectic phases Y/Y' which form during solidification. superalloy. It is thus possible to obtain a single-crystal superalloy based on nickel containing y' precipitates of controlled size, and containing a small proportion of y/y' eutectic phases.
• the heat treatment also makes it possible to control the molar fraction of the y' phase precipitates present in the single-crystal nickel-based superalloy.
• a high proportion of y' phase precipitates hinders the movement of dislocations and promotes the hot flow resistance of the alloy. As the diffusion phenomena are less below 950 °C, the majority of damage then occurs by shearing of the y' phase precipitates - Thus, at these temperatures, the intrinsic resistance of the y' phase precipitates is a determining factor for the static or creep mechanical strength of the superalloy. However, redissolving the Y' phase precipitates at higher temperatures results in a reduction in the mechanical strength of the superalloy.
• a complete protection system comprises at least two layers.
• the first layer also called sub-layer or bonding layer
• the deposition step is followed by a diffusion step of the sublayer in the superalloy.
• Deposit and distribution can also be carried out in a single step.
• M Ni (nickel) or Co (cobalt)
• Cr chromium
• NiAlyPtz nickel aluminide type alloys
• the second layer is a ceramic coating comprising for example yttriated zirconia, also called “YSZ” in accordance with the English acronym for " Yttria Stabilized Zirconia” or “YPSZ” in accordance with the English acronym for “Yttria Partially Stabilized Zirconia” and having a porous structure.
• This layer can be deposited by different processes, such as electron beam evaporation (“EB-PVD” in accordance with the English acronym for “Electron Beam Physical Vapor Deposition”), thermal spraying (“APS” in accordance with the English acronym for “Atmospheric Plasma Spraying” or “SPS” in accordance with the English acronym for “Suspension Plasma Spraying”), or any other process making it possible to obtain a porous ceramic coating with low thermal conductivity.
• EB-PVD electron beam evaporation
• APS in accordance with the English acronym for “Atmospheric Plasma Spraying” or “SPS” in accordance with the English acronym for “Suspension Plasma Spraying”
• any other process making it possible to obtain a porous ceramic coating with low thermal conductivity.
• inter-diffusion phenomena occur on the microscopic scale between the nickel-based superalloy of the substrate and the metal alloy of the underlayer.
• These inter-diffusion phenomena associated with the oxidation of the undercoat, modify in particular the chemical composition, the microstructure and consequently the mechanical properties of the undercoat from the manufacture of the coating, then during the use of the coating. the blade in the turbine.
• These inter-diffusion phenomena also modify the chemical composition, the microstructure and consequently the mechanical properties of the superalloy of the substrate under the coating.
• a secondary reaction zone can thus form in the superalloy under the sub-layer to a depth of several tens, or even hundreds, of micrometers.
• the mechanical characteristics of this ZRS are significantly lower than those of the substrate superalloy.
• the formation of ZRS is undesirable because it leads to a significant reduction in the mechanical strength of the superalloy.
• foundry defects are likely to form in parts, such as blades, during their manufacture by directed solidification. These defects are generally parasitic grains of the “Freckle” type, the presence of which can cause premature failure of the part in service. The presence of these defects, linked to the chemical composition of the superalloy, generally leads to the rejection of the part, which results in an increase in production costs.
• the present presentation aims to propose nickel-based superalloy compositions for the manufacture of monocrystalline components, presenting increased performance in terms of lifespan and mechanical strength and making it possible to reduce the production costs of the part ( reduction in scrap rate) compared to existing alloys.
• these superalloys With a contained density, these superalloys have greater resistance to creep at high temperatures than the previous ones while continuing to allow heat treatment thanks to a wide difference between the solvus temperatures of the y' phase and the solidus.
• these superalloys exhibit good microstructural stability in the volume of the superalloy (low sensitivity to PTC formation), good microstructural stability under the metal coating underlayer (low sensitivity to ZRS formation), and good resistance to oxidation and corrosion while avoiding the formation of parasitic grains such as “Freckles”.
• the present presentation concerns a nickel-based superalloy comprising, in percentages by weight, 5.0 to 6.0% of aluminum, 6.5 to 8.5% of tantalum, 0 to 1, 0% titanium, 1.0 to 4.0% cobalt, 5.0 to 8.0% chromium, 0 to 0.5% molybdenum, 3.0 to 4.0% tungsten, 3.75 at 5.75% rhenium, 3.5 to 5.0 platinum, 0.05 to 0.25% hafnium, 0 to 0.15% silicon, the remainder consisting of nickel and inevitable impurities.
• this superalloy may in particular comprise at least 3.75%, preferably at least 4.0%, of platinum and at least 4.0% of rhenium, in percentages by weight.
• platinum content may in particular not exceed 4.75%, preferably 4.5%, and that of rhenium 5.25%, preferably 4.75%, in percentages by weight.
• the silicon content may be greater than or equal to 0.05%, as a mass percentage.
• rhenium makes it possible to reinforce the y phase by solid solution and to slow down, due to its low diffusion kinetics, the degradation of the y/y' microstructure by limiting the coalescence of the y' phase precipitates. during service at high temperatures, a phenomenon which leads to a reduction in mechanical resistance. Rhenium thus makes it possible to improve the creep resistance at high temperatures of the nickel-based superalloy. Although rhenium also normally tends to promote the precipitation of PTC, e.g.
• the platinum contents are beneficial with respect to resistance to oxidation and corrosion.
• the addition of platinum in the superalloy thus makes it possible to improve the lifespan of the system comprising a superalloy covered with a metallic coating and a thermal barrier.
• the addition of platinum to the chemical composition of the superalloy makes it possible to reduce, or eliminate, the addition of platinum in the coating.
• the superalloy can thus have a temperature difference [solidus - solvus y 7 ] of at least 10°C, preferably at least 12°C, and a phase fraction y' at 1250°C of at least 20 mol%, preferably at least 23 mol%, thus combining the maintenance of a significant fraction of phase y' at high temperatures and therefore close to the solvus temperature of this phase y', with a deviation sufficient between this solvus temperature and a higher solidus temperature to allow heat treatment of the superalloy in the range between these two temperatures.
• the superalloy may have a density less than or equal to 9.05 g/cm 3 .
• the other major addition elements apart from platinum (Pt) and rhenium (Re), are cobalt (Co), chromium (Cr), tungsten (W), aluminum (Al) and tantalum (Ta).
• the minor addition elements are titanium (Ti), molybdenum (Mo), hafnium (Hf), and silicon (Si), for which the maximum mass content is equal to or less than 1% by mass. .
• unavoidable impurities we can cite, for example, sulfur (S), carbon (C), boron (B), yttrium (Y), lanthanum (La) and cerium (Ce ).
• Unavoidable impurities are defined as those elements which are not intentionally added to the composition and which are brought with other elements.
• the superalloy may include 0.005% by mass of carbon.
• tungsten, chromium, cobalt or molybdenum mainly makes it possible to reinforce the austenitic matrix y with a face-centered cubic (cfc) crystal structure by solid solution hardening.
• chromium or aluminum makes it possible to improve the resistance to oxidation and corrosion at high temperatures of the superalloy.
• chromium is essential for increasing the hot corrosion resistance of nickel-based superalloys.
• too high a chromium content tends to reduce the solvus temperature of the y' phase of the nickel-based superalloy, that is to say the temperature above which the y' phase is completely dissolved in the y matrix, which is undesirable. Too high a chromium content also causes the precipitation of harmful PTCs.
• cobalt which is an element close to nickel and which partially replaces nickel, forms a solid solution with nickel in the matrix y.
• Cobalt helps strengthen the y-matrix, reducing susceptibility to PTC precipitation and ZRS formation in the superalloy under the protective coating.
• too high a cobalt content also tends to reduce the solvus temperature of the y' phase of the nickel-based superalloy, which is undesirable.
• the chromium and cobalt content is optimized to obtain adequate solvus temperatures with the targeted applications both for the desired mechanical properties and for the heat treatment capacity of the superalloy with a heat treatment window compatible with industrial needs, that is to say a difference between the solvus temperature and the solidus temperature of the superalloy which is sufficiently wide.
• rhenium, molybdenum, tungsten or tantalum which are refractory elements, makes it possible to slow down the mechanisms controlling the creep of nickel-based superalloys and which depend on the diffusion of chemical elements in the superalloy. .
• This superalloy may in particular be intended for the manufacture of single-crystal gas turbine components, such as fixed or mobile blades.
• Such a monocrystalline part made of nickel-based superalloy can in particular be obtained by a directed solidification process under thermal gradient in lost wax foundry.
• the present presentation also relates in particular to a single-crystalline blade for a turbomachine comprising a superalloy as defined above.
• This blade therefore has resistance to creep at high temperatures and improved resistance to oxidation and corrosion.
• the blade may comprise a protective coating comprising a metallic underlayer deposited on the superalloy and a ceramic thermal barrier deposited on the metallic underlayer. Thanks to the composition of the nickel-based superalloy, the formation of a secondary reaction zone in the superalloy resulting from inter-diffusion phenomena between the superalloy and the sub-layer can be avoided, or limited.
• the metallic underlayer may be an MCrAlY type alloy or a nickel aluminide type alloy.
• the ceramic thermal barrier may be a material based on yttriated zirconia or any other ceramic coating (based on zirconia) with low thermal conductivity.
• the blade may have a structure oriented in a crystallographic direction ⁇ 001>.
• This presentation also concerns a turbomachine comprising a blade as defined above.
• Figure 1 is a schematic view in longitudinal section of a turbomachine.
• Nickel-based superalloys are intended for the manufacture of single-crystal blades by a directed solidification process in a thermal gradient.
• the use of a single crystal seed or a grain selector at the start of solidification makes it possible to obtain this single crystal structure.
• the structure is oriented for example in a crystallographic direction ⁇ 001> which is the orientation which generally confers optimal mechanical properties to superalloys.
• the raw solidified single-crystal nickel-based superalloys have a dendritic structure and are made up of precipitates y' - Ni, Pt)3 AI, Ti, Ta) dispersed in a matrix y of face-centered cubic structure, solid solution nickel-based. These y' phase precipitates are heterogeneously distributed in the volume of the single crystal due to chemical segregations resulting from the solidification process. Furthermore, y/y' eutectic phases are present in the inter-dendritic regions and constitute preferential sites for crack initiation. These y/y' eutectic phases form at the end of solidification.
• the eutectic phases y/y' are formed to the detriment of the fine precipitates (size less than a micrometer) of the hardening phase y'.
• These y' phase precipitates constitute the main source of hardening of nickel-based superalloys.
• the presence of residual y/y' eutectic phases does not make it possible to optimize the hot creep resistance of the nickel-based superalloy.
• the raw solidified nickel-based superalloys are therefore heat treated to obtain the desired distribution of the different phases.
• the first heat treatment is a microstructure homogenization treatment which aims to dissolve the y' phase precipitates and eliminate the Y/Y' eutectic phases OR to significantly reduce their mole fraction. This treatment is carried out at a temperature higher than the solvus temperature of the y' phase and lower than the starting melting temperature of the superalloy (solidus temperature). Quenching is then carried out at the end of this first heat treatment to obtain a fine and homogeneous dispersion of the precipitates y'. Tempering heat treatments are then carried out in two stages, at temperatures lower than the solvus temperature of the y' phase. During a first step, to increase the precipitates y' and obtain the desired size, then during a second step, to increase the mole fraction of this phase to approximately 70% at room temperature.
• Figure 1 represents, in section along a vertical plane passing through its main axis A, a dual-flow turbojet 10.
• the dual-flow turbojet 10 comprises, from upstream to downstream depending on the circulation of the air flow, a blower 12, a low pressure compressor 14, a high pressure compressor 16, a combustion chamber 18, a high pressure turbine 20, and a low pressure turbine 22.
• the high pressure turbine 20 comprises a plurality of moving blades 20A rotating with the rotor and rectifiers 20B (fixed blades) mounted on the stator.
• the stator of the turbine 20 comprises a plurality of stator rings 24 arranged opposite the moving blades 20A of the turbine 20.
• a movable blade 20A or a rectifier 20B for a turbomachine comprising a superalloy as defined previously coated with a protective coating comprising a metallic undercoat
• a turbomachine can in particular be a turbojet such as a double-flow turbojet 10.
• the turbomachine can also be a single-flow turbojet, a turboprop or a turboshaft engine.
• Example 1 to Ex 7 Seven nickel-based monocrystalline superalloys of the present presentation (Ex 1 to Ex 7) were studied and compared to four commercial monocrystalline superalloys (reference alloys CEx 1 to CEx 4) and to three experimental monocrystalline superalloys (CEx 5 to CEx 7).
• the four commercial monocrystalline superalloys are: CMSX-4® (CEx 1), CMSX-4 Plus Mod C® (CEx 2), CMSX-10K® (CEx 3), René N6® (CEx 4).
• the experimental single-crystal superalloy CEx 5 is cited under the name “PX5” in the publication by J. S. Van Sluytman, C. J. Moceri, and T. M.
• the density is of primary importance for applications for rotating components such as turbine blades. Indeed, an increase in the density of the superalloy of the blades imposes a reinforcement of the disk carrying them, and therefore another additional cost in weight.
• the density at room temperature of each superalloy of examples Ex 1 to Ex 7 and comparative examples CEx 1 to CEx 7 was estimated using a modified version of the Hull formula (F.C. Hull, Metal Progress, November 1969, ppl39-140).
• This equation (2) was obtained by multiple linear regression analysis from observations made after aging for 400 hours at 1093°C (degree centigrade) of samples of various nickel-based superalloys from the d family. René N6® alloys under a NiPtAI coating.
• alloys Ex 1 to Ex 7 are largely due to the significant additions of the platinum element. These costs are thus located between those of CEx 6/7 and CEx 5 alloys, respectively half as much and twice as much loaded with platinum. The costs of the alloys of the invention are thus higher than those of the commercial alloys CEx 1 to CEx 4.
• the characteristics of the alloys Ex 1 to Ex 7 can make it possible to reduce the additions of platinum in metallic coatings of the NiPtAI type by compared to commercial alloys, so that the saving of platinum in the coatings exceeds the cost of adding platinum in the proportions considered in the alloys of the invention. Additionally, reducing platinum additions in coatings would limit repair costs of coated components.
• the CALPHAD method was used to calculate the solvus temperature of the phase y' at equilibrium.
• the superalloys Ex 1 to Ex 7 have a solvus temperature y' greater than 1320°C.
• the manufacturability of the alloys of the invention was also estimated based on the possibility of industrially resolving the y' phase precipitates to optimize the mechanical properties of the alloys.
• the interval between the solvus temperature of the y' phase at equilibrium and the solidus temperature at equilibrium, as they can be calculated by the CALPHAD method, represents the ATTH heat treatment interval of the superalloys.
• the CALPHAD method was used to calculate the mole fraction (in mole percentage) of phase y' at equilibrium in the superalloys Ex 1 to Ex7 and CEx 1 to CEx 7 at 900°C, 1100°C and 1250 °C.
• the alloys of the invention (Ex 1 to Ex 7) have phase fractions y' at very high temperature (1250°C) of 23% mol or more, this which should ensure strong mechanical strength of the alloy at these temperatures.
• the y' phase fractions are higher than those of the CEx 1 and CEx 4 superalloys, and similar to those of the CEx 2 and CEx 6 superalloys whose mechanical strength at high temperatures has been demonstrated experimentally.
• the comparative alloys CEx 3, CEx 5 and CEx 6 have phase fractions y' equal to or greater than the alloys of the invention at 900, 1100 and 1250 ° C, the maintenance of these high fractions is done to the detriment of the heat treatment window for redissolving phase y'.
• the superalloys Ex 1 to Ex 7 have proportions of phases other than y and y' at 750 °C lower than those of each of the reference superalloys CEx 1, CEx 2 and CEx 4 to CEx 6, which reflects the high stability of their microstructure. These fractions at 900 °C remain low, and in particular lower than those predicted for the reference superalloys CEx 2, CEx 3 and CEx 5.
• No alloy of the invention has a phase other than the phases y and y' at l equilibrates at 1100°C, unlike the commercial CEx 3 alloy.
• the exemplary superalloys Ex 1 to Ex 7 thus present a strong potential for applications at high, or even very high, temperatures, in particular for the manufacture of turbine blades, because they combine a contained density, low sensitivity to the formation of defects (PTC, ZRS), good microstructural stability, high mechanical strength and satisfactory resistance to oxidation and corrosion.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Turbine Rotor Nozzle Sealing (AREA)

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• 2022
  • 2022-09-02 FR FR2208815A patent/FR3139347B1/fr active Active
• 2023
  • 2023-08-30 EP EP23772915.7A patent/EP4581183A1/de active Pending
  • 2023-08-30 WO PCT/FR2023/051315 patent/WO2024047315A1/fr not_active Ceased

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