NICKEL-BASED SUPERALLOY, MONOCRYSTALLINE BLADE

Abstract

The invention relates to a nickel-based superalloy comprising, by mass percentages, 5.0 to 6.3% aluminum, 0.50 to 2.0% 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, and 0 to 0.15% silicon, the remainder being nickel and unavoidable impurities. The invention also relates to a single-crystal blade (20A, 20B) comprising such an alloy and a turbomachine (10) comprising such a blade (20A, 20B). Figure for the abstract: Fig. 1

Description

Title of the invention: NICKEL-BASED SUPERALLOY, MONOCRYSTALLINE BLADE AND TURBOMACHINE technical field

[0001] The present disclosure relates to nickel-based superalloys for gas turbines, in particular for fixed blades, also called distributors or rectifiers, or moving 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] These materials have the main advantages of combining both high resistance to fining at high temperature and resistance to oxidation and corrosion.

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

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

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

[0007] The first layer, also called the sublayer or bonding layer, is directly The coating is deposited onto the part to be protected, which is a nickel-based superalloy, also called a substrate, such as a blade. The deposition step is followed by a diffusion step of the sub-layer into the superalloy. Deposition and diffusion can also be performed in a single step.

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

[0009] The second layer, generally called a thermal barrier or “TBC” Thermal Barrier Coating (TBC), as it is known in English, is a ceramic coating containing, for example, yttria-stabilized zirconia, also called YSZ (Yttria Stabilized Zirconia) or YPSZ (Yttria Partially Stabilized Zirconia), and exhibiting a porous structure. This layer can be deposited by various processes, such as electron beam physical vapor deposition (EB-PVD), atmospheric plasma spraying (APS or SPS), or any other process that produces 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, microscopic inter-diffusion phenomena occur between the nickel-based superalloy of the substrate and the metallic alloy of the sub-layer. These inter-diffusion phenomena, associated with the oxidation of the sub-layer, modify the chemical composition, microstructure, and consequently the mechanical properties of the sub-layer from the moment the coating is manufactured, and then during the use of the blade in the turbine. These inter-diffusion phenomena also modify the chemical composition, microstructure, and consequently the mechanical properties of the substrate superalloy beneath the coating.In superalloys with high refractory element content, particularly tungsten, molybdenum, or rhenium, a secondary reaction zone (SRT) can form within the superalloy beneath the sublayer, reaching depths of tens or even hundreds of micrometers. The mechanical properties of this SRT are significantly inferior to those of the substrate superalloy. SRT formation is undesirable because it leads to a substantial reduction in the superalloy's mechanical strength.

[0011] These changes 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" (Thermally Grown Oxide), and with the differences in coefficients of thermal expansion between the various layers, generate decohesion in the interfacial zone between the sub-layer and the ceramic coating, which can lead to partial or total spalling of the ceramic coating. The metallic part (superalloy substrate and metallic sub-layer) is then exposed and directly subjected to the combustion gases, which increases the risk of damage to the blade and therefore to the gas turbine.

[0012] Furthermore, the complexity of the chemistry of these alloys can lead to a destabilization of their optimal microstructure with the appearance of undesirable phase precipitates when parts formed from these alloys are held at high temperatures. This Destabilization has negative consequences on the mechanical properties of these alloys. These undesirable phases with complex crystalline structure and brittle nature are notably the phases called topologically close-packed ("TCP") phases.

[0013] Furthermore, 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, related to the chemical composition of the superalloy, generally leads to the rejection of the part, resulting in an increase in production costs. Description of the invention

[0014] The present exposition aims to propose nickel-based superalloy compositions for the manufacture of single-crystal components, exhibiting enhanced performance in terms of lifespan and mechanical strength, and enabling a reduction in part production costs (reduced scrap rate) compared to existing alloys. These superalloys exhibit a specific scour strength (scour strength per unit mass) at high temperature superior to that of existing alloys, while demonstrating good microstructural stability within the superalloy bulk (low susceptibility to PTC formation), good microstructural stability under the thermal barrier coating sublayer (low susceptibility to ZRS formation), good resistance to oxidation and corrosion, while avoiding the formation of parasitic grains of the "Freckle" type.

[0015] To this end, the present disclosure relates to a nickel-based superalloy comprising, in mass percentages, 5.0 to 6.3% aluminium, 0.50 to 2.0% 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, preferably 0.05 to 0.15% silicon, the remainder being 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] Thanks to this composition of the nickel (Ni) based superalloy, the specific fining resistance is improved compared to existing superalloys, in particular at temperatures up to 1100°C and the adhesion of the thermal barrier is strengthened compared to that observed on existing superalloys of similar density.

[0018] This alloy therefore exhibits improved resistance to high-temperature machining. This This alloy also exhibits improved corrosion and oxidation resistance. It may also demonstrate improved thermal fatigue resistance.

[0019] These superalloys have a density less than or equal to 8.00 g / cm3 (gram per cubic centimeter).

[0020] A single-crystal nickel-based superalloy is obtained by a thermal gradient directional solidification process in a lost-wax casting. The single-crystal nickel-based superalloy comprises a face-centered cubic austenitic matrix, a nickel-based solid solution, referred to as the gamma phase ("y"). This matrix contains precipitates of the gamma prime hardening phase ("y'") with an ordered cubic Ll2 structure of the Ni3Al type. The assembly (matrix and precipitates) is therefore described as a y / y' superalloy.

[0021] Furthermore, this nickel-based superalloy composition allows for a heat treatment that resuspends the y' phase precipitates and the y / y' eutectic phases that form during the solidification of the superalloy. This makes it 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 low proportion of y / y' eutectic phases.

[0022] The heat treatment also allows control of the mole fraction of the y' phase precipitates present in the single-crystal nickel-based superalloy. The mole percentage of the y' phase precipitates can be greater than or equal to 50%, preferably greater than or equal to 60%, and even more preferably equal to 70%.

[0023] Furthermore, a high fraction of y' phase precipitates hinders dislocation movement and promotes the alloy's hot finishing strength. On the other hand, at lower temperatures (<950°C), diffusion phenomena are less pronounced, and the majority of damage occurs through 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 finishing mechanical strength of the alloys. The alloy chemistry of the invention has therefore been adjusted to ensure high finishing mechanical strength from 650° to 1100°C.

[0024] The major addition elements are cobalt (Co), chromium (Cr), molybdenum (Mo), iron (Fe), tungsten (W), aluminium (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] Among the unavoidable impurities, examples 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 along 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 allows the austenitic matrix y with face-centered cubic (fcc) crystal structure to be strengthened by hardening in solid solution.

[0028] The addition of aluminium (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 high-temperature oxidation resistance of nickel-based superalloys by increasing the adhesion of the alumina (Al₂O₃) layer that forms on the surface of the superalloy at high temperatures. This alumina layer acts as a passivation layer on the surface of the nickel-based superalloy and a barrier to oxygen diffusion 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 the high-temperature oxidation resistance of the superalloy can still be improved.

[0030] Furthermore, the addition of chromium or aluminum improves the high-temperature oxidation and corrosion resistance of the superalloy. In particular, chromium is essential for increasing the hot corrosion resistance of nickel-based superalloys. However, an excessively high chromium content tends to lower 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. Therefore, 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 preserving good corrosion resistance and preventing the formation of topologically compact phases in the y matrix, which is highly saturated with alloying elements such as molybdenum or tungsten.

[0031] The addition of cobalt, an element closely related to nickel and which partially substitutes for nickel, forms a solid solution with the nickel in the y matrix. The cobalt strengthens the y matrix and reduces the susceptibility to PTC precipitation and ZRS formation in the superalloy under the protective coating. However, an excessively high cobalt content tends to lower 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 for 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 sufficiently wide difference between the solvus temperature and the solidus temperature of the superalloy.

[0033] The addition of molybdenum, tungsten or tantalum, which are refractory elements, makes it possible to slow down the mechanisms controlling the refining 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 resistance to oxidation and hot corrosion, as well as the spalling resistance 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 low sulfur content can be achieved by producing a low-sulfur master casting or by a desulfurization process carried out after casting. In particular, it is possible to maintain a low sulfur content by adapting the superalloy manufacturing process.

[0035] The addition of iron is rare in superalloys intended for single-crystal casting. Iron partitions mainly in the γ phase, where it substitutes for nickel. The cost of iron is much lower than the cost of nickel, and its addition therefore reduces the price of the superalloy. The density of iron is lower than the density of nickel, thus reducing the density of the superalloy. The addition of iron can be beneficial for the environmental resistance of the superalloy.

[0036] The addition of iron also makes the superalloy more tolerant with regard to the use of recycled superalloys when preparing a superalloy containing iron. Indeed, iron is contained in some of the most widely used superalloys in the Inconel® (718) or Incoloy® (909) families.

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

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

[0039] Nickel-based superalloys are defined as superalloys in which nickel constitutes the majority by mass. It is understood that nickel is therefore the element present in the highest mass percentage in the alloy.

[0040] The superalloy may comprise, by mass percentages, 6.0% aluminium, 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, by 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 made up of nickel and unavoidable impurities.

[0042] The superalloy may comprise, in mass percentages, 5.75% aluminium, 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 comprise, by mass percentages, 5.75% aluminium, 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 comprise, by mass percentages, 5.75% aluminium, 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 comprise, by mass percentages, 5.75% aluminium, 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, by mass percentages, 5.75% aluminium, 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] The present disclosure also relates to a single-crystal turbine blade for a turbomachine comprising a superalloy as defined above.

[0048] This blade therefore exhibits improved resistance to high-temperature sagging. This blade therefore exhibits improved resistance to oxidation and corrosion.

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

[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 sublayer 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 can be a yttria-based zirconia material or any other ceramic (zirconia-based) coating with low thermal conductivity.

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

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

[0055] The present exposition also relates to a turbomachine comprising a blade as defined above. Brief description of the drawings

[0056] Other features and advantages of the subject matter of this presentation will become apparent from the following description of embodiments, given by way of non-limiting examples, with reference to the attached figures.

[0057] [Fig-1] Fig. 1 is a schematic longitudinal cross-sectional view of a tower bomachine. Detailed description

[0058] Nickel-based superalloys are intended for the manufacture of single-crystal blades by a directional 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 which generally gives superalloys their optimal mechanical properties.

[0059] As-solidified, single-crystal nickel-based superalloys have a dendritic structure and consist of Ni3(Al, Ti, Ta) precipitates y' dispersed in a face-centered cubic matrix y, a nickel-based solid solution. These y' phase precipitates are heterogeneously distributed throughout the single crystal due to chemical segregation resulting from the solidification process. Furthermore, eutectic phases y / y' are present in the interdendritic regions and constitute preferential crack initiation sites. These y / y' phase eutectic phases form at the end of solidification. Moreover, the y / y' phase eutectic phases are formed at the expense of fine precipitates (smaller than one micrometer) of the hardening phase y'. These y' phase precipitates constitute the main source of hardening in nickel-based superalloys.Also, the presence of residual eutectic phases y / y' prevents optimization of the hot finishing performance of the nickel-based superalloy.

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

[0061] As-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 aimed at dissolving the y' phase precipitates and eliminating the eu- phases The y / y' precipitates are then treated at a temperature above the solvus temperature of the y' phase and below the initial melting temperature of the superalloy (TsoUdus). Quenching is then performed 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 below the solvus temperature of the y' phase. The first stage is used to enlarge the y' precipitates to the desired size, and the second stage is used to increase the mole fraction of this phase to approximately 70% at room temperature.

[0062] Fig. 1 represents, in cross-section along a vertical plane passing through its main axis A, a turbofan engine 10. The turbofan engine 10 comprises, from upstream to downstream along the airflow circulation, 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 movable blades 20A rotating with the rotor and of stators 20B (fixed blades) mounted on the stator. The stator of the turbine 20 comprises a plurality of stator rings 24 arranged opposite the movable blades 20A of the turbine 20.

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

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

[0066] A moving blade 20A or a rectifier 20B for a turbine can also be manufactured comprising a superalloy as defined above coated with a protective coating comprising a metallic underlayer

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

[0068] Seven nickel-based single-crystal superalloys of this 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 the CEx 3 composition further comprising 0.17 wt% carbon (C) and 0.9 wt% niobium (Nb), and the CEx 4 composition further comprising 1.0 wt% vanadium (V). All of these superalloys are nickel-based superalloys, i.e., the The remaining 100% of the compositions presented consists of nickel and unavoidable impurities.

[0069] [Tables 1] Al Ta Ti Co Cr Mo W Fe Hf Si Ex 1 6.0 1.0 2.0 0 10.0 1.0 0 3.0 0.10 0.10 Ex 2 6.0 1.0 2.0 0 12.0 2.0 0 2.0 0.10 0.10 Ex 3 5.75 1.0 3.0 2.0 11.0 1.0 0 6.0 0.10 0.10 Ex 4 5.75 1.0 3.0 0 11.0 1.0 0 6.0 0.10 0.10 Ex 5 5.75 1.5 3.0 0 11.0 1.0 1.0 6.0 0.10 0.10 Ex 6 5.75 1.0 3.0 0 12.0 1.0 0 3.0 0.10 0.10 Ex 7 5.75 1.5 3.0 0 12.0 1.0 1.0 3.0 0.10 0.10 CEx 1 5.5 1.0 3.0 0 14.0 2.0 0 0 0.10 0.10 CEx 2 5.5 1.75 2.5 0 15.0 1.0 0.50 0 0.10 0.10 CEx 3 3.4 1.75 3.4 8.5 16.0 1.75 2.6 0 0 0 CEx 4 5.5 0 4.0 15.0 10.0 3.0 0 0 0 0

[0070] Table 2 presents 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, pp. 39-140). This empirical equation was proposed by Hull. The empirical equation is based on a law of mixtures and includes corrective terms derived from a linear regression analysis of experimental data (chemical compositions and measured densities) for 235 superalloys and stainless steels.

[0073] This Hull formula has been modified, notably to take into account elements such as rhenium, and based on 272 nickel-based, cobalt-based, and iron-based superalloys. The modified Hull formula is as follows: [Math 1] D = 100 / [E (%X / Dx)] + E Ax x %X where Dx are the densities of the elements Cr, Ni, ..., X and D is the density of the superalloy, the densities being expressed in g / cm3, where Ax is a coefficient expressed in g / cm3 of the elements Cr, Ni, ..., X and are as follows: ANi = -0.0011 ; AAi = 0.0622 ; ATa = 0.0121 ; ATi = 0.0317 ; ACo = -0.0001 ; A Cr = -0.0034 ; AMo = 0.0033 ; Aw = 0.0033 ; ARe = 0.0036 ; AHf = 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 / cm3 (see Table 2).

[0075] Density is of primary importance for rotating component applications such as turbine blades. Indeed, increasing the density of the superalloy used for the blades necessitates strengthening the disc supporting them, and therefore adds further weight. It is observed that superalloys Ex 1 to Ex 7 exhibit densities similar to the comparison superalloys. It should be noted that the density range of nickel-based superalloys for single-crystal casting can reach over 9.0 g / cm³; this similarity demonstrates a significant reduction that can have substantial beneficial effects for turned parts.

[0076] Cost of superalloys

[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 about $25 / kg which is 20% lower than the cost of the reference superalloys CEx 3 and CEx 4.

[0079] Sensitivity to the formation of ZRS

[0080] To estimate the sensitivity of rhenium-containing nickel-based superalloys to the formation of ZRS, Walston (US document 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 where 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 from the René N6® alloy family under a NiPtAl coating.

[0082] The higher the value of the parameter [ZRS(%)]1 / 2, the more sensitive the superalloy is to the formation of ZRS. In particular, negative values ​​are representative of 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 re NitPtAl garment, coating which is often present for turbine nozzle applications (rotating blade and / or distributor).

[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 quantifies the sensitivity to the formation of parasitic grains of the "Freckles" type during the directional solidification of the part (US patent 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 superalloys Ex 5 and Ex 7 have an NFP parameter of 0.7. The commercial superalloy CEx 3 exhibits a higher sensitivity to the formation of this type of defect, as shown in Table 2. Low sensitivity to this type of defect is an important parameter because it implies a low scrap rate related to this defect during the manufacture of parts.

[0088] Gamma Resistance Prime fRGP)

[0089] The intrinsic mechanical strength of phase y' increases with the content of elements substituting for aluminum in the Ni3Al compound, such as titanium, tantalum, and a portion of the tungsten. The stoichiometry of phase y' can therefore be written as Ni3(Al, Ti, Ta, W). The RGP parameter allows for estimating the level of hardening of phase y': [Math 4] RGP = [CTi + CTa + (Cw / 2)] / CAi where CTi, CTa, Cw and Cai are the nominal concentrations, expressed as atomic percentages, of the elements Ti, Ta, W and Al in the superalloy.

[0090] A higher RGP parameter is favorable to improved mechanical strength of the superalloy. Table 2 shows that the RGP parameter calculated for superalloys Ex 1 to Ex 7 averages 0.28.

[0091] [Tables2] Density (1) (g / cm3) Cost ($ / kg) [ZRS(%)]1 / 2 (2) NFP (3) RGP (4) Ex 1 7.89 24.5 -63.5 0.21 Ex 2 7.88 24.8 -80.1 0.21 Ex 3 7.85 25.0 -71.3 0.32 Ex 4 7.85 23.7 -70.7 0.32 Ex 5 7.91 25.0 -70.3 0.7 0.35 Ex 6 7.85 24.3 -78.1 0.32 Ex 7 7.91 25.6 -77.7 0.7 0.35 CEx 1 7.87 25.2 -95.1 0.33 CEx 2 7.91 26.7 -100.7 2.3 0.31 CEx 3 8.17 31.8 -113.7 0.4 0.7 CEx 4 7.82 31.0 -71.6 0.41

[0092] Table 3 presents 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 phase y' at equilibrium.

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

[0096] Heat treatment interval (HTI)

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

[0098] The manufacturability of the alloys of the invention was also estimated based on the possibility of industrially resuspending the y' phase precipitates to optimize the mechanical properties of the alloys. The heat treatment range was estimated based on the calculation of the solidus and solvus temperatures of the y' phase precipitates of the alloys. The superalloys Ex 1 to Ex 7 have wide heat treatment windows, exceeding 50°C, which is compatible with industrial ovens.

[0099] Mole fraction of phase y'

[0100] The CALPHAD method was used to calculate the mole fraction (in mole percent) of phase y' 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, the superalloys Ex 1 to Ex 7 contain phase mole fractions similar to superalloys CEx 1 and CEx 2 and much higher similar to superalloys CEx 3 and CEx 4.

[0102] Mole fraction of PTC

[0103] The CALPHAD method was used to calculate the mole fraction (in mole percent) of PCT phases at equilibrium 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 small, which reflects a low sensitivity to PTC precipitation.

[0105] The 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] [Tables3] Transformation temperature (°C) Mole fraction of phase y' (mol%) Mole fraction of PTC (mol%) Solvus TTH 750°C 900°C 750°C Ex 1 1220 103 65 55 0 Ex 2 1219 91 66 55 2.9 Ex 3 1203 82 60 53 1.8 Ex 4 1211 74 61 52 1.9 Ex 5 1224 55 62 54 2.8 Ex 6 1224 70 64 56 1.5 Ex 7 1236 51 65 57 1.8 CEx 1 1223 72 66 56 3.5 CEx 2 1227 73 65 55 0.3 CEx 3 1136 161 48 42 0.2 CEx 4 1208 92 69 62 4.8

[0107] According to the various criteria taken into account, the alloys exemplifying the invention thus present a strong potential for high-temperature applications, particularly for the manufacture of turbine blades, combining a suitable compromise with low density, high mechanical strength, low sensitivity to defect formation (PTC, ZRS, casting defects), while maintaining 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 laden with products that 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 compounds (always present regardless of the fuel's cleanliness). Thus, on the one hand, the alloys oxidize under the operating conditions imposed by the engines (temperature, pressure) through reactions with the various gases contained (O2(g), COX, NOX, H2O, etc.) in the engine environment.On the other hand, they can undergo accelerated corrosion (known as hot corrosion) through reaction with liquid alkali sulfates M2SO4 (M = Na, K, Ca) at around 900°C, which may be present in the deposits that form on the surface of the parts. To improve resistance to these two phenomena, oxidation and corrosion, the aim is to form protective oxides such as alumina (Al2O3) for oxidation and chromium (Cr2O3) for corrosion. Thus, the corrosion and oxidation properties of the superalloys of the invention were estimated based on the chromium and aluminum content of the superalloys, which are necessary for the formation of these protective oxides.

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

[0110] The superalloys Ex 1 to Ex 7 were developed taking into account a compromise between the mechanical strength and the environmental resistance of the superalloys.

[0111] Although the present description has been made with reference to a specific embodiment, it is evident that various modifications and changes can 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 mentioned can be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than restrictive sense.

Claims

Claims

1. 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, 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. Superalloy according to claim 1, comprising, in mass percentages, 5.75% of aluminum, 1.0% of tantalum, 3.0% of titanium, 12.0% 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.

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

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

Images