Nickel-based superalloy, single-crystal blade and turbine engine

Abstract

The invention relates to a nickel-based superalloy comprising: 5.0 to 6.3 wt% aluminium; 0.50 to 2.0 wt% tantalum; 1.5 to 3.5 wt% titanium; 0 to 3.0 wt% cobalt; 9.5 to 12.5 wt% chromium; 0.50 to 2.5 wt% molybdenum; 0 to 2.0 wt% tungsten; 1.5 to 6.5 wt% iron; 0.05 to 0.15 wt% hafnium; 0 to 0.15 wt% silicon; the remainder consisting of nickel and unavoidable impurities. The invention also relates to a single-crystal blade (20A, 20B) comprising such an alloy and to a turbine engine (10) comprising such a blade (20A, 20B).

Description

NICKEL-BASED SUPERALLOY, MONOCRYSTALLINE BLADE AND TURBOMACHINE Technical field

[0001] This presentation concerns nickel-based superalloys for gas turbines, in particular for the fixed blades, also called distributors or rectifiers, or mobile blades of a gas turbine, for example in the field of aeronautics. Prior art

[0002] It is known to use nickel-based superalloys for the manufacture of fixed or moving single-crystal blades for gas turbines for aircraft or helicopter engines.

[0003] The main advantages of these materials are that they combine high creep resistance at high temperatures with resistance to oxidation and corrosion.

[0004] Over time, nickel-based superalloys for single-crystal blades have undergone significant changes in chemical composition, particularly with the aim of improving their high-temperature creep properties while maintaining resistance to the highly aggressive environment in which these superalloys are used.

[0005] Furthermore, metallic coatings suitable for these alloys have been developed to increase their resistance to the aggressive environment in which these alloys are used, including oxidation resistance and corrosion resistance. In addition, a low thermal conductivity ceramic coating, which acts as a thermal barrier, can be added to reduce the temperature at the metal surface.

[0006] Typically, a complete protection system has at least two layers.

[0007] The first layer, also called undercoat or bonding layer, is directly deposited on the part to be protected in nickel-based superalloy, also called substrate, for example a blade. The deposition step is followed by a step of diffusion of the sub-layer into the superalloy. Deposition and diffusion can also be carried out in a single step.

[0008] Materials generally used to make this undercoat include aluminoforming metal alloys of the MCrAlY type (M = Ni (nickel) or Co (cobalt)) or a mixture of Ni and Co, Cr = chromium, Al = aluminum and Y = yttrium, or nickel aluminide type alloys (NixAly), some also containing platinum (NixAlyPtz).

[0009] The second layer, generally referred to as a thermal barrier coating or "TBC", is a ceramic coating comprising, for example, yttria-containing zirconia, also referred to as "YSZ" or "YPSZ" and having a porous structure. This layer can be deposited by various processes, such as electron beam evaporation ("EB-PVD" or "Electron Beam Physical Vapor Deposition"), thermal spraying ("APS" or "SPS" or "Suspension Plasma Spraying"), or any other process for obtaining a porous ceramic coating with low thermal conductivity.

[0010] Due to the use of these materials at high temperatures, for example from 650°C to 1100°C, inter-diffusion phenomena occur at the microscopic scale between the nickel-based superalloy of the substrate and the metallic alloy of the underlayer. These inter-diffusion phenomena, 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 manufacturing of the coating, then during the use of 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. In superalloys highly loaded with refractory elements, in particular tungsten, molybdenum or rhenium, a secondary reaction zone (ZR) can thus form in the superalloy under the underlayer.S) over a depth of several tens, even hundreds, of micrometers. The mechanical characteristics of this ZRS are significantly inferior to those of the superalloy of. substrate. The formation of ZRS is undesirable because it leads to a significant reduction in the mechanical strength of the superalloy.

[0011] These developments in the bonding layer, combined with the stress fields related to the growth of the alumina layer that forms in service on the surface of this bonding layer, also called "TGO" in accordance with the English acronym for "Therally Grown Oxide", and the differences in thermal expansion coefficients between the different layers, generate decohesions in the interfacial zone between the underlayer and the ceramic coating, which can lead to partial or total flaking of the ceramic coating. The metal part (superalloy substrate and metal underlayer) is then exposed and directly exposed to the combustion gases, which increases the risks of damage to the blade and therefore to the gas turbine.

[0012] In addition, the complexity of the chemistry of these alloys can lead to a destabilization of their optimal microstructure with the appearance of precipitates of undesirable phases when parts formed from these alloys are maintained at high temperature. This destabilization has negative consequences on the mechanical properties of these alloys. These undesirable phases of complex crystalline structure and brittle nature are in particular the phases called topologically compact phases ("PTC") or "TCP" phases according to the English acronym for "Topologically Compact-Packed".

[0013] In addition, casting defects are likely to form in 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, linked to the chemical composition of the superalloy, generally leads to the rejection of the part, which results in an increase in the production cost. Statement of the invention

[0014] This presentation aims to propose nickel-based superalloy compositions for the manufacture of single-crystal components, exhibiting increased performance in terms of service life and mechanical resistance. and allowing to reduce the production costs of the part (reduction of the scrap rate) compared to existing alloys. These superalloys have a specific creep resistance (creep resistance related to the density) at high temperature higher than that of existing alloys while demonstrating good microstructural stability in the volume of the superalloy (low sensitivity to the formation of PTC), good microstructural stability under the sub-coating layer 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.

[0015] For this purpose, the present disclosure relates to a nickel-based superalloy comprising, in mass percentages, 5.0 to 6.3% of aluminum, 0.50 to 2.0% of tantalum, 1.5 to 3.5% of titanium, 0 to 3.0% of cobalt, 9.5 to 12.5% ​​of chromium, 0.50 to 2.5% of molybdenum, 0 to 2.0% of tungsten, 1.5 to 6.5% of iron, 0.05 to 0.15% of hafnium, 0 to 0.15% of silicon, preferably 0.05 to 0.15% of silicon, the remainder being constituted by nickel and unavoidable impurities.

[0016] This superalloy is intended for the manufacture of single-crystal gas turbine components, such as fixed or moving blades.

[0017] With this composition of the nickel (Ni)-based superalloy, the specific creep strength is improved compared to existing superalloys, particularly at temperatures up to 1100°C, and the thermal barrier adhesion is enhanced compared to that observed on existing superalloys of similar density.

[0018] This alloy therefore has improved high-temperature creep resistance. This alloy also has improved corrosion and oxidation resistance. This alloy can also have improved thermal fatigue resistance.

[0019] These superalloys have a density less than or equal to 8.00 g / cm 3 (gram per cubic centimeter).

[0020] A single-crystal nickel-based superalloy part is obtained by a directed solidification process under thermal gradient in a lost-wax casting process. The single-crystal nickel-based superalloy comprises an austenitic matrix of face-centered cubic structure, a nickel-based solid solution, called gamma ("y") phase. This matrix contains gamma prime (“y'”) hardening phase precipitates of L 12 ordered cubic structure of Ni3AI type. The whole (matrix and precipitates) is therefore described as a y / y' superalloy.

[0021] Furthermore, this composition of the nickel-based superalloy allows the implementation of a heat treatment which redissolves the y' phase precipitates and the y / y' eutectic phases which form during the solidification of the superalloy. It is thus possible to obtain a single-crystal nickel-based superalloy containing y' precipitates of controlled size, preferably between 300 and 500 nanometers (nm), and containing a small proportion of y / y' eutectic phases.

[0022] Heat treatment also allows the mole fraction of y'-phase precipitates present in the nickel-based monocrystalline superalloy to be controlled. The mole percentage of y'-phase precipitates may be greater than or equal to 50%, preferably greater than or equal to 60%, even more preferably equal to 70%.

[0023] Furthermore, a high fraction of y' phase precipitates hinders the movement of dislocations and promotes the hot creep resistance of the alloy. On the other hand, at lower temperatures (<950°C), diffusion phenomena are less and the majority of damage occurs by shearing of the y' phase precipitates. Thus, at lower temperatures, the intrinsic strength of the y' phase precipitates is a determining factor for the static or creep mechanical resistance of the alloys. The chemistry of the alloys of the invention has therefore been adjusted to ensure high creep mechanical resistance from 650° to 1100°C.

[0024] The major addition elements are cobalt (Co), chromium (Cr), molybdenum (Mo), iron (Fe), tungsten (W), aluminum (Al), titanium (Ti), and tantalum (Ta).

[0025] The minor addition elements are hafnium (Hf) and silicon (Si), for which the maximum mass content is less than 1% by mass.

[0026] Examples of unavoidable impurities include sulfur (S), carbon (C), boron (B), yttrium (Y), lanthanum (La), and cerium (Ce). Unavoidable impurities are defined as elements that are not intentionally added to the composition and are introduced with other elements. For example, the superalloy may contain 0.005% carbon by mass.

[0027] The addition of tungsten, chromium, cobalt, iron or molybdenum mainly serves to strengthen the austenitic matrix y of face-centered cubic (fcc) crystal structure by solid solution hardening.

[0028] The addition of aluminum (Al), titanium (Ti) or tantalum (Ta) promotes the precipitation of the hardening phase y'-Ni3(Al, Ti, Ta).

[0029] The simultaneous addition of silicon and hafnium improves the hot oxidation resistance of nickel-based superalloys by increasing the adhesion of the alumina layer (AI2O3) that forms on the surface of the superalloy at high temperature. This alumina layer forms a passivation layer on the surface of the nickel-based superalloy and a barrier to the diffusion of oxygen from the outside to the inside of the nickel-based superalloy. However, hafnium can be added without also adding silicon or conversely silicon can be added without also adding hafnium and still improve the hot oxidation resistance of the superalloy.

[0030] Furthermore, the addition of chromium or aluminum improves the oxidation and high-temperature corrosion resistance of the superalloy. In particular, chromium is essential for increasing the hot corrosion resistance of nickel-based superalloys. However, 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. Also, the chromium concentration is between 9.5 and 12.5% ​​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 while maintaining good corrosion resistance and avoiding the formation of topologically compact phases in the y matrix highly saturated with alloying elements such as molybdenum or tungsten.

[0031] The addition of cobalt, which is an element close to nickel and partially substitutes for nickel, forms a solid solution with nickel in the y-matrix. Cobalt helps strengthen the y-matrix, reducing the sensitivity to PTC precipitation and ZRS formation in the superalloy under the protective coating. However, too high a cobalt content tends to reduce the solvus temperature of the y' phase of the nickel-based superalloy, which is undesirable.

[0032] Also, the chromium and cobalt content is optimized to obtain adequate solvus temperatures with the intended 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 that is sufficiently wide.

[0033] The addition of 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.

[0034] A very low sulfur content in a nickel-based superalloy increases the resistance to oxidation and hot corrosion, as well as the resistance to spalling of the thermal barrier. Thus, a low sulfur content, less than 2 ppm by mass (parts per million by mass), or ideally less than 0.5 ppm by mass, optimizes these properties. Such a mass sulfur content can be achieved by producing a low-sulfur master cast or by a desulfurization process carried out after casting. In particular, it is possible to maintain a low sulfur level by adapting the superalloy production process.

[0035] Iron addition is rare in superalloys intended for single-crystal casting. Iron partitions predominantly into the y phase, where iron replaces nickel. The cost of iron is much lower than that of nickel, and its addition therefore reduces the price of the superalloy. The density of iron is lower than that of nickel, and therefore reduces the density of the superalloy. Iron addition can be beneficial for the environmental resistance of the superalloy.

[0036] The addition of iron also makes the superalloy more tolerant from the point of view of using recycled superalloys when developing a superalloy containing iron. Indeed, iron is contained in some of the most widely used superalloys of the Inconel® (718) or Incoloy® (909) families.

[0037] Excessive additions of iron can, however, induce inhibition of the precipitation of the hardening phase y' essential for mechanical strength and the potential precipitation of the TCP phase which is deleterious to the mechanical properties of the superalloy.

[0038] Superalloys have thus seen their compositions optimized in order to present compromises between mechanical resistance, microstructural stability, cost and density.

[0039] Nickel-based superalloys are superalloys whose mass percentage is predominantly nickel. It is understood that nickel is therefore the element whose mass percentage in the alloy is the highest.

[0040] The superalloy may comprise, in mass percentages, 6.0% aluminum, 1.0% tantalum, 2.0% titanium, 10.0% chromium, 1.0% molybdenum, 3.0% iron, 0.10% hafnium, 0.10% silicon, the remainder being nickel and unavoidable impurities.

[0041] The superalloy may comprise, in mass percentages, 6.0% aluminum, 1.0% tantalum, 2.0% titanium, 12.0% chromium, 2.0% molybdenum, 2.0% iron, 0.10% hafnium, 0.10% silicon, the remainder being nickel and unavoidable impurities.

[0042] The superalloy may include, in mass percentages, 5.75% aluminum, 1.0% tantalum, 3.0% titanium, 2.0% cobalt, 11.0% chromium, 1.0% molybdenum, 6.0% iron, 0.10% hafnium, 0.10% silicon, the remainder being nickel and unavoidable impurities.

[0043] The superalloy may include, in mass percentages, 5.75% aluminum, 1.0% tantalum, 3.0% titanium, 11.0% chromium, 1.0% molybdenum, 6.0% iron, 0.10% hafnium, 0.10% silicon, the remainder being nickel and unavoidable impurities.

[0044] The superalloy may include, in mass percentages, 5.75% aluminum, 1.5% tantalum, 3.0% titanium, 11.0% chromium, 1.0% molybdenum, 1.0% tungsten, 6.0% iron, 0.10% hafnium, 0.10% silicon, the remainder being nickel and unavoidable impurities.

[0045] The superalloy may include, in mass percentages, 5.75% aluminum, 1.0% tantalum, 3.0% titanium, 12.0% chromium, 1.0% molybdenum, 3.0% iron, 0.10% hafnium, 0.10% silicon, the remainder being nickel and unavoidable impurities.

[0046] The superalloy may comprise, in mass percentages, 5.75% aluminum, 1.5% tantalum, 3.0% titanium, 12.0% chromium, 1.0% molybdenum, 1.0% tungsten, 3.0% iron, 0.10% hafnium, 0.10% silicon, the remainder being nickel and unavoidable impurities.

[0047] This disclosure also relates to a single-crystal blade for a turbomachine comprising a superalloy as defined previously.

[0048] This blade therefore has improved high temperature creep resistance. This blade therefore has improved oxidation and corrosion resistance.

[0049] In some embodiments, the blade may include a protective coating comprising a metallic undercoat deposited over the superalloy and a ceramic thermal barrier deposited over the metallic undercoat.

[0050] 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 is avoided, or limited.

[0051] In some embodiments, the metallic underlayer may be an MCrAlY type alloy or a nickel aluminide type alloy.

[0052] In some embodiments, the ceramic thermal barrier may be a yttria-based zirconia material or any other low thermal conductivity ceramic (zirconia-based) coating.

[0053] In some embodiments, the blade may have a structure oriented along a crystallographic direction <001>.

[0054] This orientation generally gives the blade the optimal mechanical properties.

[0055] This disclosure also relates to a turbomachine comprising a blade as defined previously. Brief description of the drawings

[0056] Other characteristics and advantages of the subject of the present disclosure will emerge from the following description of embodiments, given as non-limiting examples, with reference to the appended figures.

[0057] [Fig. 1] Figure 1 is a schematic longitudinal sectional view of a turbomachine. Detailed description

[0058] Nickel-based superalloys are intended for the manufacture of single-crystal blades using a directed solidification process in a thermal gradient. The use of a single-crystal seed or a grain selector at the beginning of solidification makes it possible to obtain this single-crystal structure. The structure is oriented, for example, along a crystallographic direction. <001> which is the orientation that generally gives the optimal mechanical properties to superalloys.

[0059] As-solidified single-crystal nickel-based superalloys have a dendritic structure and consist of y' Ni3(Al, Ti, Ta) precipitates dispersed in a y matrix of face-centered cubic structure, a nickel-based solid solution. 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. In addition, the y / y' eutectic phases are formed at the expense of fine precipitates (sub-micrometer size) of the hardening y' phase. These y' phase precipitates constitute the main source of hardening of nickel-based superalloys.Also, the presence of residual y / y' eutectic phases does not allow the hot creep resistance of the nickel-based superalloy to be optimized.

[0060] It has indeed been shown that the mechanical properties of superalloys, in particular creep resistance, were optimal when the precipitation of the y' precipitates was ordered, i.e. the y' phase precipitates were aligned regularly, with a size ranging from 300 to 500 nm, and when all the y / y' eutectic phases were put back into solution.

[0061] The as-solidified nickel-based superalloys are then heat-treated to obtain the desired distribution of the different phases. The first heat treatment is a homogenization treatment. of the microstructure which aims to dissolve the y' phase precipitates and to eliminate the y / y' eutectic phases or to significantly reduce their molar fraction. This treatment is carried out at a temperature higher than the solvus temperature of the y' phase and lower than the incipient melting temperature of the superalloy (T solidus ). A quench is then carried out at the end of this first heat treatment to obtain a fine and homogeneous dispersion of the y' precipitates. Tempering heat treatments are then carried out in two stages, at temperatures lower than the solvus temperature of the y' phase. In a first stage, to enlarge the y' precipitates and obtain the desired size, then in a second stage, to increase the molar fraction of this phase to approximately 70% at room temperature.

[0062] Figure 1 represents, in section along a vertical plane passing through its main axis A, a double-flow turbojet engine 10. The double-flow turbojet 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.

[0063] 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.

[0064] These properties make these superalloys interesting candidates for the manufacture of single-crystal parts intended for the hot parts of turbojets.

[0065] It is therefore possible to manufacture a moving blade 20A or a rectifier 20B for a turbomachine comprising a superalloy as defined previously.

[0066] It is also possible to manufacture a moving blade 20A or a rectifier 20B for a turbomachine comprising a superalloy as defined previously coated with a protective coating comprising a metallic underlayer.

[0067] A turbomachine may in particular be a turbojet such as a double-flow turbojet 10. The turbomachine may also be a single-flow turbojet, a turboprop or a turboshaft engine. Examples

[0068] Seven nickel-based single-crystal superalloys of the present disclosure (Ex 1 to Ex 7) were studied and compared with four commercial or experimental single-crystal superalloys (CEx 1 to CEx 4). The two commercial single-crystal superalloys are: IN-738® (CEx 3) and RR2000® (CEx 4). The chemical composition of each of the single-crystal superalloys is given in Table 1, with composition CEx 3 further comprising 0.17% by mass of carbon (C) and 0.9% by mass of niobium (Nb) and composition CEx 4 further comprising 1.0% by mass of vanadium (V). All these superalloys are nickel-based superalloys, i.e. the remainder of the compositions presented to 100% is nickel and unavoidable impurities.

[0069] [Table 1]

[0070] Table 2 shows different parameters for superalloys Ex 1 to Ex 7 and CEx 1 to CEx 4.

[0071] Density

[0072] The room temperature density of each superalloy was estimated using a modified version of Hull's formula (FC Hull, Metal Progress, November 1969, ppl39-140). This empirical equation was proposed by Hull. The empirical equation is based on a law of mixtures and includes correction terms derived from a linear regression analysis of experimental data (chemical compositions and measured densities) concerning 235 superalloys and stainless steels.

[0073] This Hull formula has been modified, in particular to take into account elements such as rhenium, and this, from 272 nickel-based, cobalt-based and iron-based superalloys. The modified Hull formula is as follows: [Math 1] D = 100 / [Σ (%X / D x )] + 2 A x x %X where D x are the densities of the elements Cr, Ni, ..., X and D is the density of the superalloy, the densities being expressed in g / cm 3 , where Ax is a coefficient expressed in g / cm 3 elements Cr, Ni, X and are as follows: A Ni = -0.0011 ; A AI = 0.0622; A Ta = 0.0121; A Ti = 0.0317; A Co = -0.0001; Ac, = -0.0034; A Mo = 0.0033; Aw = 0.0033; A Re = 0.0036; A Hf = 0.0156. where %X are the contents, expressed as mass percentages, of the elements of the superalloy Cr, Ni, ..., X.

[0074] The calculated densities for the alloys of the invention are less than 8.00 g / cm 3 (see Table 2).

[0075] Density is of prime importance for rotating component applications such as turbine blades. Indeed, an increase in the density of the superalloy of the blades requires reinforcement of the disc carrying them, and therefore a further weight increase. It is noted that superalloys Ex 1 to Ex 7 have densities similar to the comparison superalloys. It should be noted that the density range of nickel-based superalloys for single-crystal casting can reach more than 9.0 g / cm 3 , this similarity demonstrates a significant reduction that can have significant beneficial effects for turned parts.

[0076] Cost of suoeralliaqes

[0077] The cost per kilogram of superalloys Ex 1 to Ex 7 and CEx 1 to CEx 4 is calculated based on the composition of the superalloy and the costs of each element (updated July 2022). This cost is given for information purposes only.

[0078] The alloys of the invention are competitive given their positioning with respect to the reference alloys with a cost of approximately $25 / kg which is 20% lower than the cost of the CEx 3 and CEx 4 reference superalloys.

[0079] Sensitivity to ZRS formation

[0080] To estimate the sensitivity of nickel-based superalloys containing rhenium to ZRS formation, Walston (US 5,270,123) established the following equation: [Math 2] [ZRS(%)] 1 / 2 = 13.88 (%Re) + 4.10 (%W) - 7.07 (%Cr) - 2.94 (%Mo) 0.33 (%Co) + 12.13 where ZRS(%) is the linear percentage of ZRS in the superalloy under the coating and the concentrations of the alloying elements are in atomic percentages.

[0081] 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 of the René N6® alloy family under a NiPtAI coating.

[0082] The higher the value of the parameter [ZRS(%)] 1 / 2 The higher the value, the more sensitive the superalloy is to the formation of ZRS. In particular, negative values ​​are representative of a low sensitivity to this defect.

[0083] Thus, as can be seen in Table 2, for superalloys Ex 1 to Ex 7, the values ​​of the parameter [ZRS(%)] 1 / 2 are all significantly negative and these superalloys therefore exhibit low sensitivity to the formation of ZRS under a NitPtAI coating, a coating which is often present for turbine blade applications (rotating blade and / or nozzle).

[0084] No-Freckles Parameter (NFP)

[0085] [Math 3] NFP = [%Ta + 1.5 %Hf + 0.5 %Mo - 0.5% %Ti)] / [%W + 1.2 %Re)] where %Cr, %Ni, ...%X are the contents, expressed as mass percentages, of the elements of the superalloy Cr, Ni, ..., X.

[0086] The NFP parameter is used to quantify the sensitivity to the formation of parasitic grains of the “Freckles” type during the directional solidification of the part (document US 5,888,451). To avoid the formation of “Freckles” type defects, the NFP parameter must be greater than or equal to 0.7.

[0087] As can be seen in Table 2, the Ex 5 and Ex 7 superalloys have an NFP parameter equal to 0.7. The commercial CEx 3 superalloy has a higher sensitivity to the formation of this type of defects as indicated in the Error! Reference source not found.2. A low Sensitivity to this type of defect is an important parameter because it implies a low rate of rejection linked to this defect during the manufacture of parts.

[0088] Prime Gamma Resistance (PGR)

[0089] The intrinsic mechanical strength of the y' phase increases with the content of elements that replace aluminum in the Ni3AI compound, such as titanium, tantalum, and part of the tungsten. The stoichiometry of the y' phase can therefore be written as Ni3(AI, Ti, Ta, W). The RGP parameter allows the level of hardening of the y' phase to be estimated: where C Ti , C Ta , C w and CAI are the nominal concentrations, expressed in atomic percentage, of the elements Ti, Ta, W and Al respectively in the superalloy.

[0090] A higher RGP parameter is favorable for better mechanical strength of the superalloy. It can be seen in Table 2 that the calculated RGP parameter for superalloys Ex 1 to Ex 7 is on average 0.28.

[0091] [Table 2]

[0092] Table 3 shows other parameters for superalloys Ex 1 to Ex 7 and CEx 1 to CEx 4.

[0093] Solvus temperature of phase y'

[0094] The CALPHAD method was used to calculate the solvus temperature of the y' phase at equilibrium.

[0095] As can be seen in Table 3, superalloys Ex 1, Ex 2, Ex 4 to Ex 7 have a higher y' solvus temperature than superalloys CEx 3 and CEx 4 and a similar y' solvus temperature to superalloys CEx 1 and CEx 2. Although having a similar lower y' solvus temperature, superalloy Ex 3 has a relatively high cobalt and iron content. The iron content of Ex 3 increases the recyclability of the superalloy in return.

[0096] Heat Treatment Interval (TTH)

[0097] The CALPHAD method was used to calculate the heat treatment interval of superalloys.

[0098] The manufacturability of the alloys of the invention was also estimated from the possibility of industrially resolving the y' phase precipitates to optimize the mechanical properties of the alloys. The heat treatment interval was estimated from the calculation of the solidus temperature and the solvus temperature of the y' phase precipitates of the alloys. Superalloys Ex 1 to Ex 7 have wide heat treatment windows, above 50°C, which is compatible with industrial furnaces.

[0099] Mole fraction of phase y'

[0100] The CALPHAD method was used to calculate the mole fraction (in mole percentage) of y' phase at equilibrium in superalloys Ex 1, Ex 2 and CEx 1 to CEx 4 at 750°C and 900°C.

[0101] As can be seen in Table 3, superalloys Ex 1 to Ex 7 contain phase mole fractions similar to superalloys CEx 1 and CEx 2 and much higher than superalloys CEx 3 and CEx 4.

[0102] Mole fraction of PTC

[0103] The CALPHAD method was used to calculate the mole fraction (in mole percentage) of equilibrium PCT phases in superalloys Ex 1 to Ex 7 and CEx 1 to CEx 4 at 750°C (see Table 3).

[0104] The calculated mole fractions of PCT phases are relatively low, reflecting low sensitivity to PTC precipitation.

[0105] Superalloys Ex 1 to Ex 7 have low proportions of PTC phases at these temperatures, which reflects a high microstructural stability of these superalloys.

[0106] [Table 3]

[0107] According to the various criteria taken into account, the example alloys of the invention thus present a strong potential for high temperature applications, in particular for the manufacture of turbine blades, combining an adequate compromise combining low density, high mechanical strength, low sensitivity to the formation of defects (PTC, ZR.S, casting defects), while retaining high resistance to oxidation and corrosion.

[0108] The superalloys of the invention have been designed to maintain high corrosion resistance (~900°C) and oxidation resistance (~1100°C) at high temperatures. The flow circulating through the turbines of turbojet engines is loaded with products which are generally a result of the fuel combustion reaction, but which also include water, sand, and salts contained in the incoming air ingested by the turbomachine. The fuel also contains impurities and sulfur products (always existing regardless of the cleanliness of the fuel). Thus, on the one hand the alloys oxidize under the operating conditions imposed by the engines (temperature, pressure) by reactions with the various gases contained (O2(g), CO X , NO X, H2O, etc.) in the engine environment. On the other hand, they can undergo accelerated corrosion phenomena (called hot corrosion) by reaction with alkali sulfates M2SO4 (M = Na, K, Ca) liquid at around 900°C which may be present in the deposits that form on the surface of the parts. For better resistance to these two phenomena, oxidation and corrosion, we seek to form protective oxides such as alumina (AI2O3) for oxidation and chromia (Cr2O3) for corrosion. Thus, the corrosion and oxidation properties of the superalloys of the invention were estimated from the chromium and aluminum content of the superalloys, necessary for the formation of these protective oxides.

[0109] The superalloys of the invention have chromium contents greater than or equal to that of the CEx 4 superalloy and less than that of the CEx 1 to CEx 3 superalloys. The aluminum contents of the superalloys of the invention are greater than or equal to those of the reference superalloys, in particular that of the CEx 3 superalloy. In addition, the reduction in the cobalt and titanium contents should improve the environmental resistance of the superalloys of the invention compared to the CEx 4 superalloy.

[0110] Superalloys Ex 1 to Ex 7 were developed taking into account a compromise between the mechanical strength and environmental resistance of the superalloys. [YES] Although the present disclosure has been described with reference to a specific exemplary embodiment, it is obvious that various modifications and changes may be made to these examples without departing from the general scope of the invention as defined by the claims. Furthermore, individual features of the various embodiments recited may be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than restrictive sense.

Claims

CLAIMS

1. Nickel-based superalloy comprising, in mass percentages, 5.0 to 6.3% of aluminum, 0.50 to 2.0% of tantalum, 1.5 to 3.5% titanium, 0 to 3.0% cobalt, 9.5 to 12.5% ​​chromium, 0.50 to 2.5% molybdenum, 0 to 2.0% tungsten, 1.5 to 6.5% iron, 0.05 to 0.15% hafnium, 0 to 0.15% silicon, the remainder being nickel and unavoidable impurities.

2. Superalloy according to claim 1, comprising, in mass percentages, 6.0% of aluminum, 1.0% of tantalum, 2.0% of titanium, 10.0% of chromium, 1.0% of molybdenum, 3.0% of iron, 0.10% of hafnium, 0.10% of silicon, the remainder being constituted by nickel and unavoidable impurities.

3. Superalloy according to claim 1, comprising, in mass percentages, 6.0% of aluminum, 1.0% of tantalum, 2.0% of titanium, 12.0% of chromium, 2.0% of molybdenum, 2.0% of iron, 0.10% of hafnium, 0.10% of silicon, the remainder being constituted by nickel and unavoidable impurities.

4. Superalloy according to claim 1, comprising, in mass percentages, 5.75% of aluminum, 1.0% of tantalum, 3.0% of titanium, 2.0% of cobalt, 11.0% of chromium, 1.0% of molybdenum, 6.0% of iron, 0.10% of hafnium, 0.10% of silicon, the remainder being constituted by nickel and unavoidable impurities.

5. Superalloy according to claim 1, comprising, in mass percentages, 5.75% of aluminum, 1.0% of tantalum, 3.0% of titanium, 11.0% of chromium, 1.0% of molybdenum, 6.0% of iron, 0.10% of hafnium, 0.10% of silicon, the remainder being constituted by nickel and unavoidable impurities.

6. Superalloy according to claim 1, comprising, in mass percentages, 5.75% of aluminum, 1.5% of tantalum, 3.0% of titanium, 11.0% of chromium, 1.0% of molybdenum, 1.0% of tungsten, 6.0% of iron, 0.10% of hafnium, 0.10% of silicon, the remainder being constituted by nickel and unavoidable impurities.

7. A superalloy according to claim 1, comprising, in mass percentages, 5.75% aluminum, 1.0% tantalum, 3.0% titanium, 12.0% chromium, 1.0% molybdenum, 3.0% iron, 0.10% hafnium, 0.10% silicon, the remainder being nickel and unavoidable impurities.

8. Superalloy according to claim 1, comprising, in mass percentages, 5.75% of aluminum, 1.5% of tantalum, 3.0% of titanium, 12.0% of chromium, 1.0% of molybdenum, 1.0% of tungsten, 3.0% of iron, 0.10% of hafnium, 0.10% of silicon, the remainder being constituted by nickel and unavoidable impurities.

9. Monocrystalline blade (20A, 20B) for a turbomachine comprising a superalloy according to any one of claims 1 to 8.

10. A blade (20A, 20B) according to claim 9, comprising a protective coating comprising a metallic underlayer deposited on the superalloy and a ceramic thermal barrier deposited on the metallic underlayer.

11. A blade (20A, 20B) according to claim 9 or 10, having a structure oriented along a crystallographic direction <001> .

12. Turbomachine comprising a blade (20A, 20B) according to any one of claims 9 to 11.

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