Classifications

• • 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%
• • 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
• • 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

Definitions

• This presentation relates to nickel-based superalloys for gas turbines, in particular for stationary blades, also called distributors or rectifiers, or mobiles of a gas turbine, for example in the field of aeronautics.
• nickel-based superalloys for single-crystal blades have undergone significant changes in chemical composition, with the particular aim of improving their creep properties at high temperature while maintaining resistance to the environment. very aggressive in which these superalloys are used.
• metal coatings adapted to these alloys have been developed in order to increase their resistance to the aggressive environment in which these alloys are used, in particular the resistance to oxidation and the resistance to corrosion.
• a ceramic coating of low thermal conductivity, performing a thermal barrier function can be added to reduce the temperature at the surface of the metal.
• a complete protection system comprises at least two layers.
• the first layer also called sub-layer or bonding layer
• the first layer is directly deposited on the part to be protected in nickel-based superalloy, also called substrate, for example a blade.
• the deposit step is followed by a step of diffusion of the underlayer in the superalloy.
• the deposition and the diffusion can also be carried out during 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 yttria zirconia, also called “YSZ” in accordance with the acronym English for “Yttria Stabilized Zirconia” or “YPSZ” in accordance with the English acronym for “Yttria Partially Stabilized Zirconia” and having a porous structure.
• yttria zirconia also called “YSZ” in accordance with the acronym English 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 various processes, such as evaporation under an electron beam (“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
• 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 a microscopic scale between the nickel-based superalloy of the substrate and the metal alloy of the underlayer.
• These phenomena of inter-diffusion, associated with the oxidation of the underlayer modify in particular the chemical composition, the microstructure and consequently the mechanical properties of the underlayer from the manufacture of the coating, then during the use of dawn 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 clearly inferior to those of the superalloy of the substrate.
• 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 the parts, such as blades, during their manufacture by directional 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, related to the chemical composition of the superalloy, generally leads to the rejection of the part, which leads to an increase in the cost of production.
• the present presentation aims to propose compositions of nickel-based superalloys for the manufacture of single-crystal components, presenting increased performance in terms of service life and mechanical strength and making it possible to reduce the production costs of the part ( decrease in scrap rate) compared to existing alloys.
• These superalloys exhibit higher high temperature creep resistance than existing alloys while demonstrating good microstructural stability within the bulk of the superalloy (low susceptibility to PTC formation), good microstructural stability under the coating underlayer of the thermal barrier (low sensitivity to the formation of ZRS), good resistance to oxidation and corrosion while avoiding the formation of parasitic grains of the "Freckle" type.
• the present presentation relates to a nickel-based superalloy comprising, in mass percentages, 5.0 to 6.5% aluminum, 0.50 to 2.5% tantalum, 1.50 to 4.0% Titanium, 0-7.0% Cobalt, 12.0-16.0% Chromium, 0.50-2.5% Molybdenum, 0-2.0% Tungsten, 0.05 to 0.15% hafnium, 0 to 0.15% silicon, preferably 0.05 to 0.15 silicon, the remainder consisting of nickel and inevitable impurities.
• This superalloy is intended for the manufacture of monocrystalline gas turbine components, such as fixed or moving blades.
• the creep resistance is improved compared to existing superalloys, in particular at temperatures which can go up to 1100° C. and the adhesion of the thermal barrier is reinforced compared to that observed on existing superalloys.
• This alloy therefore has improved creep resistance at high temperature. As the service life of this alloy is thus long, this alloy also has improved resistance to corrosion and oxidation. This alloy may also exhibit improved thermal fatigue resistance.
• a monocrystalline nickel-based superalloy part is obtained by a process of directed solidification under a thermal gradient in a lost-wax casting.
• the single-crystal nickel-based superalloy comprises an austenitic matrix of face-centered cubic structure, nickel-based solid solution, known as the gamma (“y”) phase.
• This matrix contains gamma prime (“y'") hardening phase precipitates of structure ordered cubic l_l 2 of Ni 3 AI type. The whole (matrix and precipitates) is therefore described as a g/g′ superalloy.
• this composition of the nickel-based superalloy allows the implementation of a heat treatment which redissolves the phase precipitates g′ and the eutectic phases g/g′ which form during the solidification of the superalloy. It is thus possible to obtain a monocrystalline nickel-based superalloy containing precipitates g' of controlled size, preferably between 300 and 500 nanometers (nm), and containing a low proportion of eutectic phases g/g'.
• the heat treatment also makes it possible to control the molar fraction of the g′ phase precipitates present in the single-crystal nickel-based superalloy.
• the molar percentage of the precipitates of phase g′ may be greater than or equal to 50%, preferably greater than or equal to 60%, even more preferably equal to 70%.
• the major addition elements are cobalt (Co), chromium (Cr), molybdenum (Mo), tungsten (W), aluminum (Al), titanium (Ti) and tantalum ( Your).
• the minor addition elements are hafnium (Hf) and silicon (Si), for which the maximum mass content is less than 1% by mass.
• Hf hafnium
• Si silicon
• Unavoidable impurities mention may be made, for example, of 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 added with other elements.
• the superalloy may comprise 0.005% by mass of carbon.
• tungsten, chromium, cobalt or molybdenum mainly makes it possible to reinforce the austenitic matrix y of face-centered cubic crystal structure (fcc) by hardening in solid solution.
• the addition of aluminum (Al), titanium (Ti) or tantalum (Ta) promotes the precipitation of the hardening phase y′-Ni 3 (Al, Ti, Ta).
• the simultaneous addition of silicon and hafnium makes it possible to improve the resistance to hot oxidation of nickel-based superalloys by increasing the adhesion of the layer of alumina (Al 2 O 3 ) which forms on the surface of the superalloy at high temperature.
• This layer of alumina forms a passivation layer on the surface of the nickel-based superalloy and a barrier to the diffusion of oxygen coming from the exterior towards the interior of the nickel-based superalloy.
• hafnium without also adding silicon or conversely add silicon without also adding hafnium and still improve the resistance to hot oxidation of the superalloy.
• chromium or aluminum makes it possible to improve the resistance to oxidation and to corrosion at high temperature 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, i.e. the temperature above which the y' phase is completely dissolved in the y matrix, which is undesirable.
• the chromium content is between 12.0 to 16.0% by mass in order to maintain a high solvus temperature of the y′ phase of the nickel-based superalloy, for example greater than or equal to 1200° C. but also to avoid the formation of topologically compact phases in the matrix y highly saturated with alloying elements such as molybdenum or tungsten.
• cobalt which is an element close to nickel and which partially replaces nickel, forms a solid solution with the nickel in the y matrix.
• Cobalt makes it possible to strengthen the matrix y, to reduce the sensitivity to the precipitation of PTC and to the formation of ZRS in the superalloy under the protective coating.
• too high a cobalt content tends to reduce the solvus temperature of the y' phase of the nickel base superalloy, which is undesirable.
• the chromium and cobalt content is optimized to obtain suitable 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. , i.e. a difference between the solvus temperature and the solidus temperature of the superalloy which is large enough.
• refractory elements such as molybdenum, tungsten or tantalum 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.
• a very low sulfur content in a nickel-based superalloy makes it possible to increase the resistance to oxidation and to hot corrosion as well as the spalling resistance of the thermal barrier.
• a low sulfur content less than 2 ppm by mass (part per million by mass), or even ideally less than 0.5 ppm by mass, makes it possible to optimize these properties.
• Such a mass content of sulfur can be obtained by producing a low-sulphur mother casting or by a desulfurization process carried out after casting. In particular, it is possible to maintain a low sulfur content by adapting the process for producing the superalloy.
• nickel-based superalloys means superalloys in which the mass percentage of nickel is predominant. It is understood that nickel is therefore the element whose mass percentage in the alloy is the highest.
• the superalloy may comprise, in mass percentages, 5.25 to 6.25% aluminum, 0.50 to 2.25% tantalum, 2.0 to 3.5% titanium, 0 to 7, 0% Cobalt, 12.5-15.5% Chromium, 0.50-2.5% Molybdenum, 0-1.5% Tungsten, 0.05-0.15% Hafnium, 0-0 1.15% silicon, preferably 0.05 to 0.15 silicon, the balance being made up of nickel and inevitable impurities.
• the superalloy may comprise, in mass percentages, 5.25 to 6.25% aluminum, 0.50 to 2.0% tantalum, 2.5 to 3.5% titanium, 0 to 7, 0% cobalt, 12.5-15.5% chromium, 0.50-2.5% molybdenum, 0.05-0.15% hafnium, 0-0.15% silicon, preferably 0 0.05 to 0.15 of silicon, the balance being made up of nickel and inevitable impurities.
• the superalloy may comprise, in mass percentages, 5.5% aluminum, 1.0% tantalum, 3.0% titanium, 14.0% chromium, 2.0% molybdenum, 0, 10% hafnium, 0.10% silicon, the balance consisting of nickel and inevitable impurities.
• the superalloy may comprise, in mass percentages, 5.75% aluminum, 1.5% tantalum, 3.0% titanium, 4.0% cobalt, 14.0% chromium, 1, 5% molybdenum, 0.10% hafnium, 0.10% silicon, the balance consisting of nickel and inevitable impurities.
• the superalloy may comprise, in mass percentages, 6.0% aluminum, 1.0% tantalum, 3.0% titanium, 6.0% cobalt, 14.0% chromium, 1, 0% molybdenum, 0.10% hafnium, 0.10% silicon, the balance consisting of nickel and inevitable impurities.
• the superalloy may comprise, in mass percentages, 5.5% aluminum, 1.5% tantalum, 3.0% titanium, 15.0% chromium, 1.0% molybdenum, 0, 10% hafnium, 0.10% silicon, the balance consisting of nickel and inevitable impurities.
• the superalloy may comprise, in mass percentages, 5.5% aluminum, 1.0% tantalum, 3.0% titanium, 13.0% chromium, 2.0% molybdenum, 0, 10% hafnium, 0.10% silicon, the balance consisting of nickel and inevitable impurities.
• the superalloy may comprise, in mass percentages, 5.75% aluminum, 1.5% tantalum, 3.0% titanium, 4.0% cobalt, 13.0% chromium, 1, 5% molybdenum, 1.0% tungsten, 0.10% hafnium, 0.10% silicon, balance being nickel and unavoidable impurities.
• the superalloy may comprise, in mass percentages, 5.5% aluminum, 1.75% tantalum, 2.5% titanium, 15.0% chromium, 1.0% molybdenum, 0, 50% tungsten, 0.10% hafnium, 0.10% silicon, balance consisting of nickel and unavoidable impurities.
• the superalloy may comprise, in mass percentages, 5.5% aluminum, 1.5% tantalum, 3.0% titanium, 15.0% chromium, 1.0% molybdenum, 0, 50% tungsten, 0.10% hafnium, 0.10% silicon, balance consisting of nickel and unavoidable impurities.
• This presentation also relates to a monocrystalline blade for a turbomachine comprising a superalloy as defined previously. [0047] This blade therefore has improved creep resistance at high temperature. This blade therefore has improved resistance to oxidation and corrosion.
• the blade may comprise a protective coating comprising a metal underlayer deposited on the superalloy and a ceramic thermal barrier deposited on the metal underlayer.
• the composition of the nickel-based superalloy 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 underlayer is avoided or limited.
• the metal underlayer can be an alloy of the MCrAlY type or an alloy of the nickel aluminide type.
• the ceramic thermal barrier can be a material based on yttria-zirconia or any other ceramic coating (based on zirconia) with low thermal conductivity.
• the blade may have a structure oriented along a ⁇ 001> crystallographic direction.
• This orientation generally confers optimum mechanical properties at dawn.
• This presentation also relates to a turbine engine comprising a blade as defined previously.
• Figure 1 is a schematic view in longitudinal section of a turbine engine.
• 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 monocrystalline seed or of a grain selector at the start of solidification makes it possible to obtain this monocrystalline structure.
• the structure is oriented for example along a crystallographic direction ⁇ 001> which is the orientation which generally confers the optimum mechanical properties on the superalloys.
• Single-crystal superalloys based on nickel as they solidified have a dendritic structure and consist of precipitates g′ Ni 3 (Al, Ti, Ta) dispersed in a matrix g of face-centered cubic structure, solid solution based on nickel. These g' phase precipitates are distributed heterogeneously in the volume of the single crystal due to chemical segregations resulting from the solidification process. Furthermore, g/g' eutectic phases are present in the inter-dendritic regions and constitute preferential crack initiation sites. These g/g' eutectic phases are formed at the end of solidification.
• the g/g' eutectic phases are formed to the detriment of the fine precipitates (size less than a micrometer) of the hardening phase g'. These g' phase precipitates constitute the main source of hardening of nickel-based superalloys. Also, the presence of residual g/g' eutectic phases does not make it possible to optimize the hot creep resistance of the nickel-based superalloy.
• the as-solidified nickel-based superalloys are therefore heat-treated to obtain the desired distribution of the different phases.
• the first heat treatment is a treatment for homogenizing the microstructure, the purpose of which is to dissolve the g′ phase precipitates and to eliminate the g/g′ eutectic phases or to significantly reduce their molar fraction. This treatment is carried out at a temperature above the solvus temperature of the g' phase and below the starting melting temperature of the superalloy (T SO iidus) A quenching is then carried out at the end of this first heat treatment to obtain a fine and homogeneous dispersion of the precipitates g′. Tempering heat treatments are then carried out in two stages, at temperatures below the solvus temperature of phase g′. During a first stage, to make the precipitates g′ grow and obtain the desired size, then during a second stage, to make the molar fraction of this phase grow to about 70% at room temperature.
• FIG. 1 shows, in section along a vertical plane passing through its main axis A, a turbofan engine 10.
• the turbofan engine 10 comprises, from upstream to downstream according to the circulation of the air flow, a fan 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 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 turbomachine can in particular be a turbojet engine such as a turbofan engine 10.
• the turbomachine can also be a single-flow turbojet engine, a turboprop engine or a turboshaft engine.
• Example 1 and Ex 8 Eight nickel-based monocrystalline superalloys of the present presentation (Ex 1 and Ex 8) were studied and compared with two commercial monocrystalline superalloys (reference alloys).
• the two commercial monocrystalline superalloys are: RR2000® (CEx 1) and Inconel 738® (CEx 2).
• the chemical composition of each single crystal superalloy is given in the Table 1, composition CEx 1 additionally comprising 1.0% by mass of vanadium (V) and composition CEx 2 additionally comprising 0.90% by mass of niobium (Nb) and 0.17% by mass of carbon ( VS). All these superalloys are nickel-based superalloys, that is to say that 100% of the compositions presented consist of nickel and inevitable impurities.
• This Hull formula has been modified, in particular to take account of elements such as rhenium and this, from 272 nickel-based, cobalt-based and iron-based superalloys.
• the densities calculated for the Ex 1 to Ex 8 alloys are greater than or equal to 7.80 and less than 7.95 g/cm 3 (see Table 2).
• Density is of primary importance for applications of rotating components such as turbine blades. Indeed, an increase in the density of the superalloy of the blades imposes a reinforcement of the disc carrying them, and therefore another additional cost in weight.
• Commercial alloys of similar density such as CEx 1 and CEx 2 do not meet current superalloy development standards for blades. Indeed, CEx 1 and CEx 2 come from development for traditional foundry.
• This equation (2) was obtained by analysis by multiple linear regression from observations made after aging for 400 hours at 1093° C. (degree centigrade) of samples of various nickel-based superalloys of the family d of René N6® alloys under a NiPtAI coating.
• NFP [%Ta + 1.5%Hf + 0.5%Mo - 0.5%%Ti)]/[%W + 1.2%Re)] where %Cr, %Ni, .. .%X are the contents, expressed in mass percentages, of the superalloy elements Cr, Ni, ..., X.
• the NFP parameter makes it possible to quantify the sensitivity to the formation of parasitic grains of the “Freckles” type during the directed solidification of the part (document US Pat. No. 5,888,451). To avoid the formation of “Freckles” type faults, the NFP parameter must be greater than or equal to 0.7. A low sensitivity to this type of defect is an important parameter because it implies a low scrap rate linked to this defect during the manufacture of parts.
• the superalloys Ex 1 to Ex 8 and CEX 1 and CEx 2 have an NFP parameter greater than or equal to 0.7.
• the Ex 1 to Ex 5 and CEx 1 superalloys have an infinite value, these compositions comprising neither rhenium nor tungsten.
• the intrinsic mechanical strength of the y' phase increases with the content of elements replacing the aluminum in the Ni 3 Al compound, such as titanium, tantalum and some tungsten.
• the compound of phase y' can therefore be written Ni 3 (Al, Ti, Ta, W).
• the RGP parameter is used to estimate the level of hardening of the y' phase:
• RGP [Cri + Cia + (CW/2)]/C A I
• C Ti , C Ta , C w and C Ai are the respective concentrations, expressed in atomic percentage, of the elements Ti, Ta, W and Al in the superalloy.
• the superalloys Ex 1 to Ex 8 include tantalum, even tungsten, which contribute to the reinforcement of phase g′ and therefore to compensation, at least partially, of the reduction in the titanium content.
• CEx 2 has a value of the RGP parameter approximately double that of the superalloys Ex 1 to Ex 8, this is in particular due to the fact that CEx 2 comprises less phase g' in order to ensure its flowability and its setting. subsequent implementation. Furthermore, this value is also due to the lower aluminum content of CEx 2 compared to superalloys Ex 1 to Ex 8.
• the cost per kilogram of Ex 1 to Ex 8 and CEx 1 and CEx 2 superalloys is calculated based on the composition of the superalloy and the costs of each compound (updated April 2020). This cost is given as an indication.
• the Ex 1 to Ex 8 superalloys have a cost of approximately $60/kg which is of the same order of magnitude as the cost of the CEx 1 and CEx 2 alloys.
• Table 2 presents different parameters for Ex 1 to Ex 8 and CEx 1 and CEx 2 superalloys.
• the CALPHAD method was used to calculate the solvus temperature of the g' phase at equilibrium of the superalloys Ex 1 to Ex 8 and CEx 1 and CEx 2. As can be seen in Table 3, the superalloys Ex 1 to Ex 2 have a solvus temperature y′ greater than 1200°C.
• the CALPHAD method was used to calculate the heat treatment range for Ex 1 to Ex 8 and CEx 1 and CEx 2 superalloys.
• the manufacturability of the alloys of the invention was also estimated on the basis of the possibility of re-dissolving the g′ phase precipitates industrially in order to optimize the mechanical properties of the alloys.
• the heat treatment range was estimated from the calculation of the solidus temperature and the solvus temperature of the g' phase precipitates of the alloys.
• Ex 1 to Ex 8 superalloys have wide heat treatment windows, above 60°C, which is compatible with industrial furnaces.
• the CALPHAD method was used to calculate the molar fraction (in molar percentage) of phase g′ at equilibrium in the superalloys of the superalloys Ex 1 to Ex 8 and CEx 1 and CEx 2 at 750° C. and 1100° C. vs.
• the CALPHAD method was used to calculate the molar fraction (in molar percentage) of phase o at equilibrium in the superalloys Ex 1 to Ex 8 and CEx 1 and CEx 2 at 750° C. (see Table 3).
• the calculated mole fractions of phase o are relatively low, which reflects a low sensitivity to the precipitation of PTC.
• the total quantity of PTC phase includes the content of the BCC/B2 phase rich in chromium, the potentially deleterious nature of which with respect to the mechanical properties can approach that of the topologically compact phases.
• the Ex 1 to Ex 8 superalloys have solvus y' temperatures higher than those of the reference alloys, 7 to 21°C compared to CEx 1 and almost 80°C compared to CEx 1.
• the precipitate fractions g' of the Ex 1 to Ex 8 superalloys are similar to those of CEx 1 and much higher than those of CEx 2 (approximately +37% at 750°C and +200% at 1100°C).
• the density of Ex 1 to Ex 8 superalloys is of the same order of magnitude as that of CEx 1. Given that the range of density variation of nickel-based superalloys for single-crystal casting can reach more than 9 g/cm 3 , this similarity testifies to a significant reduction which can have significant beneficial effects for rotating parts.
• the superalloys of the invention have a chemical composition and a microstructure which makes it possible to envisage a mechanical strength superior to that of the reference alloys CEx 1 and CEx 2 while having a density lower than that from the first.
• the superalloys of the invention have been designed so as to maintain resistance to corrosion ( ⁇ 900° C.) and oxidation ( ⁇ 1100° C.) high at high temperature.
• the flow that circulates through the turbines of turbojet engines is loaded with products that are generally a result of the fuel combustion reaction, but which also include water, sands, and salts contained in the incoming air ingested by the turbomachine.
• the fuel also contains impurities and sulfur products (always present regardless of the cleanliness of the fuel).
• the alloys oxidize under the operating conditions imposed by the engines (temperature, pressure) by reactions with the various gases contained (0 2 (g), CO x , NO x , H 2 0, etc.) in the engine environment.
• the alloys of the invention have chromium contents higher than that of CEx 1 and lower than that of CEx 2.
• the aluminum contents of the alloys of the invention are greater than or equal to those of the reference alloys, in particular that of CEx 2.
• the resistance to oxidation and corrosion of these alloys is assumed to be similar or superior to that of the reference alloys CEx 1 and CEx 2.
• the example alloys of the invention thus have a high potential for high temperature applications, in particular for the manufacture of turbine blades, combining low density, high mechanical strength, low sensitivity to the formation of defects (PTC, Z RS, foundry defects), while maintaining high resistance to oxidation and corrosion.

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