Special nickel-based superalloy, and ingots and parts made from the superalloy

Abstract

The present invention relates to a nickel-based superalloy having the following composition, the contents of the various elements being expressed as percentages by weight: - 1.3% < Al < 2.8%; - trace < Co < 11%; - 14% < Cr < 17%; - trace < Fe < 12%; - 2.0% < Mo < 5.0%; - 0.5% < Nb + Ta < 2.5%; - 2.5% < Ti < 4.5%; - 1.0% < W< 4.0%; - 0.0030% < B < 0.030%; - trace < C < 0.018%; - 0.01% < Zr < 0.06%; - trace < N < 0.0047%; and - 0 < P < 0.03%, the remainder consisting of nickel and impurities resulting from production, and such that the composition satisfies the following equations, in which the contents are expressed in atomic percentages: 8.0 at% < Al at% + Ti at% + Nb at% + Ta at% < 11.0 at% 0.7 < (Ti at%+ Nb at% + Ta at%) / Al% at% < 1.3.

Description

[0001] Specific nickel-based superalloy, ingots and parts made from this superalloy

[0002] The present invention relates to the field of nickel-based superalloys, intended in particular for the manufacture of parts for land or aeronautical turbines, for example turbine discs.

[0003] Improving turbine performance requires, in particular, the development of alloys capable of withstanding operating temperatures of around 700°C. Superalloys have therefore been developed that can guarantee high mechanical properties at these temperatures (tensile strength, creep and oxidation resistance, crack propagation resistance) while maintaining good microstructural stability. These are in particular gamma / gamma' superalloys. Some of these superalloys are generally highly loaded with elements that promote the presence of the gamma' phase Ni3(AI,Ti), and therefore cannot be satisfactorily processed by the conventional route (ingot route), where the casting of an ingot from liquid metal is followed by a series of shaping and heat treatments.These alloys can only be obtained by powder metallurgy, with the major disadvantage of a very high production cost.

[0004] In particular, the nickel-based superalloy known under the name UDIMET 720 is distinguished, as described in particular in documents US-A-3,667,938 and US-A-4,083,734. This superalloy retains good mechanical properties at high temperatures, in particular because it comprises between 13% and 19% by mass of cobalt. However, this alloy, known to those skilled in the art to be at the limit of feasibility of the conventional route, presents a significant risk of freckle formation, which limits the size of the ingots obtainable from this alloy.

[0005] It is in this context that the Applicant has developed an alloy having a low production cost, i.e. with a lower cost in alloying elements than that of alloys of the UDIMET 720 type, and whose forging ability is increased compared to alloys of the UDIMET 720 type, while exhibiting high mechanical properties at high temperatures (700°C). Document WO 2011 / 20976 describes a nickel-based superalloy composition comprising (the contents of the various elements being expressed as weight percentages):

[0006] - 1.3% < Al < 2.8%;

[0007] - traces < Co < 11%;

[0008] - 14% < Cr < 17%; - traces < Fe < 12%;

[0009] - 2% < Mo < 5%;

[0010] - 0.5% < Nb + Ta < 2.5%;

[0011] - 2.5% < Ti < 4.5%;

[0012] - 1% < W < 4%;

[0013] - 0.0030% < B < 0.030%;

[0014] - traces < C < 0.1%;

[0015] - 0.01% < Zr < 0.06%; the remainder being made up of nickel and impurities resulting from the production, the composition satisfying the following equations, in which the contents are expressed in atomic percentages:

[0016] 8 at% < Al at% + Ti at% + N b at% + Ta at% < 11 at%

[0017] 0.7 < (Ti at% + Nb at% + Ta at%) / Al% at% < 1.3.

[0018] Although it has good mechanical properties, ease of forging and the lowest possible alloy material cost, this alloy is not always suitable for the preparation of ingots with a large diameter (typically with a diameter greater than 450 mm, preferably greater than 480 mm). Indeed, when the ingot diameter increases, the solidification time increases, as well as the number and / or size of defects, in particular alignments of endogenous particles (precipitates and non-metallic inclusions) of the "stringer" type, also increase, to the point of becoming prohibitive because they are too detrimental to the mechanical performance of the superalloy, in particular fatigue resistance. In addition, increasing the diameter of the ingots also increases the risk of forming freckles, the presence of which is also prohibitive for mechanical performance, in particular fatigue resistance."Stringers" is an anglicism commonly used by those skilled in the art to designate "alignments of carbonitrides", and "freckles" is an anglicism commonly used by those skilled in the art to designate "segregated veins" or "segregated channels".

[0019] There is therefore a need for new nickel-based superalloys that can be obtained in the form of large diameter ingots, typically ingots with a diameter greater than 450 mm, preferably greater than or equal to 480 mm.

[0020] In particular, there is a need for new nickel-based superalloys that can be obtained in the form of large diameter ingots with few or no defects, including few or no stringers and no freckles. In particular, there is a need for new nickel-based superalloys that can be obtained in the form of large diameter ingots that have good mechanical properties, for example, high fatigue strength, especially at high temperatures (typically around 700 °C), ease of forging, and as low a cost as possible.

[0021] To this end, the invention relates to a nickel-based superalloy of the following composition, the contents of the various elements being expressed in mass percentages:

[0022] - 1.3% < Al < 2.8%;

[0023] - traces < Co < 11%;

[0024] - 14% < Cr < 17%;

[0025] - traces < Fe < 12%;

[0026] - 2.0% < Mo < 5.0%;

[0027] - 0.5% < Nb + Ta < 2.5%;

[0028] - 2.5% < Ti < 4.5%;

[0029] - 1.0% < W < 4.0%;

[0030] - 0.0030% < B < 0.030%;

[0031] - traces < C < 0.018%;

[0032] - 0.01% < Zr < 0.06%;

[0033] - traces < N < 0.0047%, and

[0034] - 0 < P < 0.03%, the remainder being made up of nickel and impurities resulting from the production, and such that the composition satisfies the following equations in which the contents are expressed in atomic percentages:

[0035] 8.0 at% < Al at% + Ti at% + Nb at% + Ta at% < 11.0 at%

[0036] 0.7 < (Ti% at%+ Nb% at% + Ta%at) / Al% at% < 1.3.

[0037] Preferably, the difference Ap between the density of the liquid phase at the point in the solidification process of the superalloy at which it is in the form of a mixture of 50% by mass of liquid phase and 50% by mass of solid phase, and the density of the liquid phase of the superalloy at the liquidus, is greater than or equal to -47 kg / m 3 , preferably greater than or equal to -42 kg / m 3 , preferably between -47 kg / m 3 and 0 kg / m 3 , preferably between -47 kg / m 3 and -5 kg / m 3 .

[0038] Preferably, the nickel-based superalloy has a mass fraction of carbides and carbonitrides in the solidus of less than or equal to 0.08%, preferably between 0.0001% and 0.08%. The carbides are in particular titanium and niobium carbides, and the carbonitrides are in particular titanium carbonitride. Such a low mass fraction of carbides and carbonitrides in the solidus makes it possible to limit the number of carbides and carbonitrides larger than 10 μm.

[0039] Preferably, the nickel-based superalloy comprises from 0.0001% to 0.0047% N, preferably from 0.0001% to 0.0040% N, preferably from 0.0001% to 0.0035% N, preferably from 0.0001% to 0.0030% N, preferably from 0.0001% to 0.0025% N.

[0040] Preferably, the nickel-based superalloy comprises from 0.0001% to 0.018% of C, preferably from 0.001% to 0.015%, preferably from 0.002% to 0.015%, preferably from 0.005% to 0.015%.

[0041] Preferably, the nickel-based superalloy comprises from 1.0% to 3.8% of W, preferably from 1.0% to 3.3%, preferably from 1.0% to 3.0%, preferably from 1.5% to 3.0%.

[0042] Preferably, the nickel-based superalloy comprises from 2.5% to 4.2% Ti, preferably from 2.5% to 4.0%, preferably from 2.7% to 3.8%, preferably from 2.8% to 3.8%, preferably from 3.0% to 3.8%.

[0043] Preferably, the nickel-based superalloy comprises from 0.6% to 2.5% of Nb + Ta, preferably from 0.7% to 2.5%, preferably from 0.8% to 2.0%, preferably from 0.8% to 1.8%, preferably from 0.8% to 1.6%.

[0044] Preferably, the nickel-based superalloy comprises from 2.2% to 5.0% of Mo, preferably from 2.5% to 5.0%, preferably from 2.7% to 4.5%, preferably from 2.7% to 4.1%, preferably from 2.7% to 4.0%.

[0045] Preferably, the nickel-based superalloy comprises from 1.5% to 2.8% of Al, preferably from 1.8% to 2.8%, preferably from 2.0% to 2.8%.

[0046] Preferably, the composition of the nickel-based superalloy satisfies the following equation, in which the contents are expressed in atomic percentages:

[0047] 8.5 at% < Al at% + Ti at% + Nb at% + Ta at% < 10.8 at%, preferably 8.8 at% < Al at% + Ti at% + Nb at% + Ta at% < 10.5 at%, preferably 9.2 at% < Al at% + Ti at% + Nb at% + Ta at% < 10.1 at%.

[0048] Indeed, the inventors surprisingly discovered that reducing the carbon and nitrogen content (below a certain threshold) makes it possible to increase the diameter of the ingots without any deleterious effect on the mechanical properties of the superalloy, in particular on its fatigue resistance. Without wishing to be bound by any theory, the inventors believe that this joint reduction in the carbon and nitrogen content makes it possible, on the one hand, to reduce the size and number of carbonitrides, and therefore to drastically reduce the size and number of stringers (large stringers being particularly harmful), and on the other hand to reduce or even eliminate the risk of freckles. Indeed, during the solidification of the ingot, the chemical elements of the composition are divided between the solid phase which progresses and the liquid phase which regresses.During solidification, the liquid phase therefore has a variable composition depending on its position in the pasty zone (mixed zone composed of liquid and solid), which leads to local differences in the density of the liquid constituting a driving force and causing the initiation of liquid movements in the pasty zone of the superalloy during solidification, and the appearance of privileged flow channels within the permeable dendritic structure forming the pasty zone. After complete solidification, this results in segregated veins, called "freckles" and formed by the localized flow of the segregated liquid in the pasty zone constituting marked chemical and therefore microstructural heterogeneities which are extremely detrimental to the targeted usage properties.According to the inventors, this effect is exacerbated by the presence of high levels of certain elements, particularly carbon, and on the contrary, is therefore reduced by reducing the level of these elements.

[0049] Optimally, preferred compositions of the invention have a difference Ap between the density of the liquid phase at the point in the solidification process of the superalloy at which it is in the form of a mixture of 50% by mass of liquid phase and 50% by mass of solid phase, and the density of the liquid phase of the superalloy at the liquidus, greater than or equal to -47 kg / m 3. The inventors have in fact discovered that this is a key parameter for determining the most optimal compositions for obtaining large diameter ingots, because the closer the Ap is to 0, the more the risk of forming freckles decreases, or even disappears. The inventors have also discovered that obtaining large diameter ingots is notably linked to the content of certain elements in the composition. The inventors believe that these elements have a more pronounced tendency than others to influence the value of the Ap. This is mainly linked to two parameters characterizing the alloying elements: their partition coefficient between the liquid and the solid k, and their solutal volume expansion coefficient. A partition coefficient k far from 1 greatly depletes or enriches the liquid during the solidification of the alloy and will therefore strongly influence the Ap.Two cases are particularly unfavorable because they lead to an increase in the absolute value of Ap: if k < 1, and the difference in density between the pure alloying element in the liquid state and that of the alloy at the liquidus temperature is high and negative (case of Al, Ti, C), and if k > 1, and the difference in density between the pure alloying element in the liquid state and that of the alloy at the liquidus temperature is high and positive (case of W, or Co to a lesser extent).

[0050] There are therefore in theory four types of alloying elements influencing the value of Ap: - elements which enrich the liquid and are less dense than the liquid and therefore lighten the liquid (examples: Al, Ti and C),

[0051] - elements which enrich the liquid and are denser than the liquid and therefore make the liquid heavier (examples: Nb, Ta, and Mo to a lesser extent),

[0052] - elements which impoverish the liquid and are less dense than the liquid and therefore make the liquid heavier, and

[0053] - elements which deplete the liquid and are denser than the liquid and therefore lighten the liquid (examples: W and Co).

[0054] The value of Ap can be calculated using the following method:

[0055] During solidification of the superalloy, it is possible to estimate the density of the interdendritic liquid at a given liquid fraction (p^p) as a function of temperature and liquid composition by applying the Boussinesq approximation: with

[0056] Pfe / and Pref, the densities, respectively of the interdendritic liquid at the liquid fraction gl and of the liquid at the reference state, p th and Psou, the coefficients of expansion, respectively thermal and solutal, of the liquid and T ref, the temperatures, respectively of the interdendritic liquid at the liquid fraction gl and of the liquid at the reference state, and M re fi , the mass fractions of solute i, respectively in the interdendritic liquid at the liquid fraction gl and in the liquid in the reference state.

[0057] In the following, the reference state will be defined as the liquid at the liquidus temperature (T ii? ), to the nominal composition (mass fraction ÙJ0, OR volume v O i of the solute i) and density pu q . The Boussinesq approximation is then written:

[0058] This expanded and simplified formula becomes:

[0059] P(gl) = Pliq + Pth (gl) + ^Psol gl)

[0060] Thus, the density of the liquid at a given liquid fraction, p toi) , can be evaluated by adding to the density of the reference state p tiq , the so-called thermal contributions toth (gi) - effect of temperature variation as a function of the liquid fraction - and solutales p so i (gi) - effect of variation of content of each solute i depending on the liquid fraction. The proposed formula for assessing the alloy's propensity to initiating freckles-type defects is the calculation of the difference between the density of the interdendritic liquid at a given liquid fraction gl and the density of the liquid at the liquidus temperature

[0061] The formula was applied to different superalloy compositions. For each alloy, a Thermo-Cale calculation (e.g. using Thermo-Cale software version 2023b and the TTNI8 database) determines the evolution of the liquid fraction (gl) and the composition of the liquid phase (mass fraction or volume v^ i of element i) as a function of temperature (T toi) ) during solidification.

[0062] Thermal contribution:

[0063] The thermal contribution is calculated as follows:

[0064] ^Pth gi) = Piiq-Pth Tigi) - Titq) with p th = obtained by linear regression of Thermo-Cale predictions (for example using version 2023b of the Thermo-Cale software and with the TTNI8 database) describing the evolution of liquid density for temperatures above the liquidus.

[0065] Solutal contribution:

[0066] Considering an ideal mixture, âp soi toi) can be written in the form: with v Wi and v O i , the volume fraction of element i, respectively at the liquid fraction gl and at the liquidus, and p 1 , the density of the pure liquid of each element taken at the melting point of the latter.

[0067] Throughout this application, unless otherwise specified, the contents are expressed as a percentage by mass relative to the total mass of the superalloy.

[0068] The expressions "from ... to ..." and "between ... and ..." include the limits.

[0069] Preferably, the composition of the nickel-based superalloy satisfies the following equation, in which the contents are expressed in atomic percentages:

[0070] 1.0 < (Ti% at%+ Nb%at% + Ta%at) I Al% at% < 1.3.

[0071] Preferably, the nickel-based superalloy comprises from 3% to 12% of Fe. Preferably, the nickel-based superalloy comprises, expressed in mass percentages:

[0072] - 1.3% < Al < 2.8%;

[0073] - 7% < Co < 11%;

[0074] - 14% < Cr < 17%;

[0075] - 3% < Fe < 9%;

[0076] - 2.0% < Mo < 5.0%;

[0077] - 0.5% < Nb + Ta < 2.5%;

[0078] - 2.5% < Ti < 4.5%;

[0079] - 1.0% < W < 4.0% ;

[0080] - 0.0030% < B < 0.030% ;

[0081] - traces < C < 0.018%;

[0082] - 0.01% < Zr < 0.06%;

[0083] - traces < N < 0.0047%, and

[0084] - 0 < P < 0.03%, preferably 0.005% < P < 0.02%, and its composition satisfies the following equations, in which the contents are expressed in atomic percentages:

[0085] 8.0 at% < Al at% + Ti at%+ Nb at% + Ta at% < 11.0 at%

[0086] 0.7 < (Ti at% + Nb at% + Ta at%) / Al at% < 1.3 the remainder being made up of nickel and impurities resulting from the production.

[0087] Preferably, for this superalloy, 1.0 < (Ti at% + Nb at% + Ta at%) / Al at% < 1.3.

[0088] More preferably, the nickel-based superalloy comprises, expressed in mass percentages:

[0089] - 1.8% < Al < 2.8%;

[0090] - 7% < Co < 10.5%;

[0091] - 14% < Cr < 17%;

[0092] - 3.6% < Fe < 7%;

[0093] - 2.0% < Mo < 4.0%;

[0094] - 0.5% < Nb + Ta < 2.0%;

[0095] - 2.8% < Ti < 4.2%;

[0096] - 1.5% < W < 3.5%;

[0097] - 0.0030% < B < 0.030% ;

[0098] - traces < C < 0.018%;

[0099] - 0.01% < Zr < 0.06%; - traces < N < 0.0047%, and

[0100] - 0 < P < 0.03%, preferably 0.005% < P < 0.02%, and its composition satisfies the following equations, in which the contents are expressed in atomic percentages:

[0101] 8.0 at% < Al at% + Ti at%+ N b at% + Ta at% < 11.0 at%

[0102] 0.7 < (Ti at% + Nb at% + Ta at%) / Al at% < 1.3 the remainder being made up of nickel and impurities resulting from the production.

[0103] In some cases, for this superalloy, 0.7 < (Ti at% + Nb at% + Ta at%) / Al at% < 1.15

[0104] In some cases, for this superalloy, 1.0 < (Ti at% + Nb at% + Ta at%) / Al at% < 1.3.

[0105] Preferably, the nickel-based superalloy according to any one of the above embodiments comprises a gamma' phase fraction of between 30% and 45%, preferably between 32% and 42%, and the solvus of the gamma' phase of the superalloy is less than 1145°C.

[0106] Preferably, the nickel-based superalloy according to any one of the above embodiments has a Cr content (expressed as atomic percentage) in the gamma matrix at 700°C, greater than 24 at%.

[0107] Preferably, the nickel-based superalloy according to any one of the above embodiments has a Mo + W content (expressed as atomic percentage) > 2.8 at% in the gamma matrix.

[0108] Preferably, the nickel-based superalloy according to any one of the above embodiments has:

[0109] - from 0.0001% to 0.0047% of N, from 0.0001% to 0.0040% of N, preferably from 0.0001% to 0.0035%, preferably from 0.0001% to 0.0030%, preferably from 0.0001% to 0.0025%; and / or

[0110] - from 0.0001% to 0.018% of C, preferably from 0.001% to 0.015% of C, preferably from 0.002% to 0.015%, preferably from 0.005% to 0.015%; and / or

[0111] - from 1.0% to 3.8% of W, preferably from 1.0% to 3.3%, preferably from 1.0% to 3.0%, preferably from 1.5% to 3.0%; and / or

[0112] - from 2.5% to 4.2% of Ti, preferably from 2.5% to 4.0%, preferably from 2.7% to 3.8%, preferably from 2.8% to 3.8%, preferably from 3.0% to 3.8%; and / or

[0113] - from 0.6% to 2.5% of Nb + Ta, preferably from 0.7% to 2.5%, preferably from 0.8% to 2.0%, preferably from 0.8% to 1.8%, preferably from 0.8% to 1.6%; and / or - from 2.2% to 5.0% of Mo, preferably from 2.5% to 5.0%, preferably from 2.7% to 4.5%, preferably from 2.7% to 4.1%, preferably from 2.7% to 4.0%; and / or

[0114] - optionally P, in a content ranging from 0% to 0.03%, preferably from 0.005% to 0.02%, and / or

[0115] - a composition satisfying the following equations, in which the contents are expressed in atomic percentages:

[0116] 8.5 at% < Al at% + Ti at% + Nb at% + Ta at% < 10.8 at%, preferably 8.8 at% < Al at% + Ti at% + Nb at% + Ta at% < 10.5 at%, preferably 9.2 at% < Al at% + Ti at% + Nb at% + Ta at% < 10.1 at%.

[0117] The present invention also relates to a nickel-based superalloy ingot according to the invention. Preferably, the ingot is in the form of a cylinder, generally having a height ranging from 2 to 6 times its diameter.

[0118] Preferably, the ingot has a diameter greater than or equal to 450 mm, preferably greater than or equal to 480 mm, preferably greater than or equal to 490 mm, preferably greater than or equal to 570 mm, preferably between 450 mm and 800 mm.

[0119] In fact, the limiting dimension for the cooling of the ingot and therefore the defects is its diameter, while its height allows the weight of the ingot to be adjusted.

[0120] The present invention further relates to a nickel superalloy part, characterized in that its composition is according to the invention. Preferably, the part is an aeronautical or land-based gas turbine component.

[0121] In addition to the main advantage of being able to produce large diameter ingots, the superalloy according to the invention has good forging properties, thanks to the limited contents of elements generating the gamma' phase, and in particular Nb, to also avoid segregation problems during production. An alloy according to the invention is for example forgeable in the supersolvus domain of the alloy, which makes it possible to ensure better homogeneity of the metal and to significantly reduce the costs related to the forging process. In addition, the superalloy according to the invention makes it possible to reduce the costs relating to the production processes and the thermomechanical treatment processes (forging and die-stamping) of a part made from this superalloy.

[0122] For example, lowering the Co content to a value less than or equal to 11% makes it possible to considerably reduce the cost of the alloy, Co being, among the elements significantly present in the composition of the superalloy, the most expensive. To maintain good mechanical properties in creep and traction, the lowering of the Co content is, on the one hand, compensated by an adjustment of the contents of Ti, Nb, and Al forming the hardening phase gamma' and, on the other hand, compensated by an adjustment of the contents of W and Mo which harden the gamma matrix of the alloy. The inventors were able to observe that a part of the Co can be substituted by Fe, which significantly lowers the cost of the superalloy.

[0123] The inventors were able to observe that an optimal Co content was between 7% and 11%, better 7% to 10%, to achieve a significant increase in mechanical properties such as creep resistance while maintaining a low cost of raw materials, preferably by adding 3% to 9% of Fe, better 3.6% to 7%, in the composition. Beyond 11% of Co the inventors were able to observe that the performances of the alloy were not significantly improved.

[0124] The ratio of the sum of the atomic contents of Ti, Nb and Ta and the atomic content of Al required for the superalloy composition of the invention makes it possible to ensure solid solution hardening of the gamma phase while avoiding the risk of the appearance of a needle phase in the alloy which could alter its ductility.

[0125] A minimum fraction of gamma' phase (preferably 30%, better 32%) is desired to obtain very good creep and tensile strength at 700°C. The fraction and solvus of the gamma' phase must, however, preferably be respectively less than 45% (better 42%) and 1145°C so that the alloy retains good forgeability, and also so that the alloy can be partly forged in the supersolvus range, i.e. at a temperature between the gamma' solvus and the melting onset temperature.

[0126] The proportions of the phases present in the alloy, such as the volume fractions of gamma' phases and the molar concentrations of the TCP phases (the definition of which will be given later), were determined by the inventors and as a function of the composition, using phase diagrams obtained by thermodynamic calculations (using the THERMOCALC software commonly used by metallurgists).

[0127] The above conditions on the Mo + W content in the gamma matrix are justified to avoid the precipitation of brittle intermetallic compounds of the sigma or mu type. The sigma and mu phases, when developed in excessive quantities, lead to a significant reduction in the ductility and mechanical strength of the alloys. It has also been observed that excessive Mo and W contents significantly impair the forgeability of the alloy and considerably reduce the forgeability range, i.e. the temperature range where the alloy tolerates significant deformations for hot forming. These elements also have high atomic masses, and their presence results in a significant increase in the density of the alloy, which for aeronautical applications is a predominant criterion.

[0128] The composition of the superalloy according to the invention makes it possible to maintain a TCP value ("Topologically close-packed" = topologically compact phases such as the mu + sigma phases whose content is expressed as a molar percentage of phase) of less than 6% at 700°C in the alloy. This value confirms that the superalloy according to the invention has very good microstructural stability at high temperatures.

[0129] In summary, the equations that must be or optimally respected by the composition of the superalloy according to the invention are:

[0130] (1) (optimally) Cr > 24 at% in the gamma matrix at 700°C to optimize oxidation resistance (optimization resulting from thermodynamic calculations).

[0131] (2) (mandatory) 0.7 < (Ti at% + Nb at% + Ta at%) / Al at% < 1.3 to ensure hardening of the y' phase and limit the risk of the appearance of a needle phase, and optimally 1 < (%Ti + %Nb + %Ta) / %AI < 1.3 for better hardening, and optimally 0.7 < (Ti at% + Nb at% + Ta at%) / Al at% < 1.15 to avoid the risk of the appearance of a needle phase.

[0132] (3) (mandatory) 8.0 at% < Al at% + Ti at% + Nb at% + Ta at% < 11.0 at% to ensure an adequate fraction of gamma' phase, and optimally 8.5 at% < Al at% + Ti at% + Nb at% + Ta at% < 10.8 at%, preferably 8.8 at% < Al at% + Ti at% + Nb at% + Ta at% < 10.5 at%, preferably 9.2 at% < Al at% + Ti at% + Nb at% + Ta at% < 10.1 at% to further enhance the possibility of forming large ingots, in particular large diameter ingots.

[0133] (4) (optimally) 30% < fraction y' < 45% and solvus y' < 1145°C (optimization resulting from thermodynamic calculations); better: 32% < fraction y' < 42%; it is in this interval that the best compromise is obtained between, on the one hand, creep resistance and tensile strength, and, on the other hand, forgeability; the optimal value is approximately 37%.

[0134] (5) (optimally) mol% of TCP phases < 6% at 700°C to ensure good microstructural stability at high temperatures (optimization resulting from thermodynamic calculations).

[0135] (6) (optimally) Mo at% + W at% in the gamma phase at 700°C > 2.8 at% to ensure good hardening of the gamma matrix (optimization resulting from thermodynamic calculations), but without exceeding Mo mass contents of 5% and W of 4% to avoid the precipitation of fragile intermetallic compounds of the sigma or mu type. (7) (optimally) the mass content of Nb + Ta ranges from 0.6% to 2.5%, preferably from 0.7% to 2.5%, preferably from 0.8% to 2.0%, preferably from 0.8% to 1.8%, preferably from 0.8% to 1.6%, to optimize the possibility of forming large ingots, in particular large diameters.

[0136] (8) (optimally) the mass content of Ti ranges from 2.5% to 4.2%, preferably from 2.5% to 4.0%, preferably from 2.7% to 3.8%, preferably from 2.8% to 3.8%, preferably from 3.0% to 3.8%, to optimize the possibility of forming large ingots, in particular large diameter ingots.

[0137] (9) (optimally) the mass content of W ranges from 1.0% to 3.8%, preferably from 1.0% to 3.3%, preferably from 1.0% to 3.0%, preferably from 1.5% to 3.0% to optimize the possibility of forming large ingots, in particular large diameter ingots.

[0138] (10) (optimally) the mass content of Mo ranges from 2.2% to 5.0%, preferably from 2.5% to 5.0%, preferably from 2.7% to 4.5%, preferably from 2.7% to 4.1%, preferably from 2.7% to 4.0%, to optimize the possibility of forming large ingots, in particular large diameter ingots.

[0139] (11) (mandatory) the carbon mass content ranging from traces to 0.018% of C, and optimally ranging from 0.0001% to 0.018%, preferably from 0.001% to 0.015%, preferably from 0.002% to 0.015%, preferably from 0.005% to 0.015%, and the nitrogen content ranging from traces to 0.0047% of N, and optimally from 0.0001% to 0.0047%, preferably from 0.0001% to 0.0040%, preferably from 0.0001% to 0.0035%, preferably from 0.0001% to 0.0030%, preferably from 0.0001% to 0.0025%, to reduce or even eliminate the presence of defects which limit the diameter of the ingots.

[0140] (12) (optimally) the difference Ap between the density of the liquid phase at the point in the solidification process of the superalloy at which it is in the form of a mixture of 50% by mass of liquid phase and 50% by mass of solid phase, and the density of the liquid phase of the superalloy at the liquidus, is greater than or equal to -47 kg / m 3 , preferably greater than or equal to -42 kg / m3 , preferably between -47 kg / m 3 and 0 kg / m 3 , preferably between -47 kg / m 3 and -5 kg / m 3 , to enhance the possibility of forming large ingots, particularly those with a large diameter.

[0141] Details of the elements and their content in the composition of the nickel-based superalloy

[0142] Cobalt

[0143] The cobalt content has been limited to contents less than or equal to 11%, preferably less than 10%, for economic reasons, since this element is one of the most expensive of those used in the composition of the alloy. Advantageously, a minimum content of 7% is desired in order to maintain very good creep resistance.

[0144] Iron

[0145] Substituting nickel or cobalt with iron has the advantage of significantly reducing the cost of the alloy. However, the addition of iron promotes the precipitation of the sigma phase, which is detrimental to ductility and notch sensitivity. The iron content of the alloy must therefore be adjusted to achieve a significant cost reduction while ensuring a very stable alloy at high temperatures. The Fe content is generally between traces and 12%, but is preferably between 3% and 12%, better between 3% and 9%, and best between 3.6% and 7%.

[0146] Aluminum, Titanium, Niobium, Tantalum

[0147] The weight contents of these elements are:

[0148] - from 1.3% to 2.8%, better from 1.8% to 2.8%, preferably from 2.0% to 2.8% for Al,

[0149] - from 2.5% to 4.5%, preferably from 2.5% to 4.2%, preferably from 2.5% to 4.0%, preferably from 2.7% to 3.8%, preferably from 2.8% to 3.8%, preferably from 3.0% to 3.8% for Ti,

[0150] - from 0.5 to 2.5%, preferably from 0.6% to 2.5%, preferably from 0.7% to 2.5%, preferably from 0.8% to 2.0%, preferably from 0.8% to 1.8%, preferably from 0.8% to 1.6% for the sum Nb + Ta.

[0151] Although the precipitation of the gamma' phase in nickel-based alloys is essentially due to the presence of aluminum in sufficient concentration, the elements Ti, Nb and Ta can favor the appearance of this phase if they are present in the alloy in sufficient concentration: the elements aluminum, titanium, niobium and tantalum are so-called "gamma'-gene" elements. The stability domain of the gamma' phase (of which the gamma' solvus of the alloy is representative) and the gamma' phase fraction are therefore a function of the sum of the atomic concentrations at% of aluminum, titanium, niobium and tantalum. These elements have thus been adjusted so as to obtain, optimally, a fraction of the y' phase between 30% and 45%, better between 32% and 42%, and a gamma' phase solvus below 1145°C.

[0152] An adequate fraction of gamma' phase in the alloys of the invention is obtained with a sum of the Al, Ti, Nb and Ta contents greater than or equal to 8.0 at% and less than or equal to 11.0 at%. A minimum fraction of gamma' phase is desired to obtain very good creep and tensile strength at 700°C. The fraction and solvus of the gamma' phase must, however, preferably be less than 45% and 1145°C respectively so that the alloy retains good forgeability, and also can be partly forged in the supersolvus range, i.e. at a temperature between the gamma' solvus and the melting onset temperature. A fraction of y' phase and a solvus temperature exceeding the previously mentioned upper limits would make it more difficult to process the alloy by the conventional ingot method, which would risk reducing one of the advantages of the invention.Within this range of 8.0 at% to 11.0 at%, the sum of the contents of Al, Ti, Nb and Ta can be further optimized between 8.5 at% and 10.8 at%, preferably between 8.8 at% and 10.5 at%, preferably between 9.2 at% and 10.1 at%, in order to optimize the compromise between good mechanical properties at 700°C and forgeability. The same applies to the mass content of Nb + Ta, which can preferably be from 0.6% to 2.5%, preferably from 0.7% to 2.5%, preferably from 0.8% to 2.0%, preferably from 0.8% to 1.8%, preferably from 0.8% to 1.6% to optimize the compromise between good mechanical properties at 700°C and forgeability.

[0153] According to a remarkably advantageous aspect of the invention, the contents of aluminum, titanium, niobium and tantalum are such that the ratio between the sum of the atomic percentages of titanium, niobium and tantalum, and the atomic percentage of aluminum, is greater than or equal to 0.7 and less than or equal to 1.3. Indeed, the solid solution hardening in the gamma' phase provided by Ti, Nb and Ta is all the higher as the ratio (Ti at% + Nb at% + Ta at%) / Al at% is high. A ratio greater than or equal to 1.0 will be preferred to guarantee better hardening. However, for the same aluminium content, excessively high contents of Ti, Nb or Ta promote the precipitation of needle-like phases of the eta (Ni3Ti) or delta (Ni3(Nb,Ta)) type which are not desired in the context of the invention: these phases, if present in excessively large quantities, can alter the hot ductility of the alloy by precipitating in the form of needles at the grain boundaries.The ratio (Ti at% + Nb at% + Ta at%) / Al at% must therefore not exceed 1.3, and preferably 1.15 to prevent the precipitation of these harmful phases. The Nb + Ta content is, on the other hand, less than or equal to the titanium content so that the density of the alloy remains acceptable (less than 8.35), in particular for aeronautical applications. It is also known to those skilled in the art that excessively high niobium contents are detrimental to resistance to hot crack propagation (650-700°C).

[0154] Equations (2), (3), (7) and (8) account for these conditions.

[0155] Molybdenum and Tungsten The Mo content should be between 2.0% and 5.0% and the W content between 1.0% and 4.0%. Optimally, the Mo content is from 2.2% to 5.0%, preferably from 2.5% to 5.0%, preferably from 2.7% to 4.5%, preferably from 2.7% to 4.1%, preferably from 2.7% to 4.0%, and optimally the W content is from 1.0% to 3.8%, preferably from 1.0% to 3.3%, preferably from 1.0% to 3.0%, preferably from 1.5% to 3.0%.

[0156] Optimizing Mo and W contents helps to maximize the diameter of obtainable ingots.

[0157] Furthermore, molybdenum and tungsten provide strong hardening of the gamma matrix by solid solution effect. The Mo and W contents must be carefully adjusted to obtain optimal hardening without causing the precipitation of brittle intermetallic compounds of the sigma or mu type. These phases, when developed in excessive quantities, lead to a significant reduction in the ductility and mechanical strength of the alloys. It has also been observed that excessive Mo and W contents significantly impair the forgeability of the alloy and considerably reduce the forgeability range, i.e. the temperature range where the alloy tolerates significant deformations for hot forming. These elements also have high atomic masses, and their presence results in a significant increase in the density of the alloy, which is not desirable for aeronautical applications in particular.

[0158] Equations (5), (6), (9) and (10) account for these conditions.

[0159] Chromium

[0160] Chromium is essential for the oxidation and corrosion resistance of the alloy and thus plays an essential role in the resistance of the alloy to the effects of the high-temperature environment. The chromium content (14% to 17% by mass) of the alloys of the invention was determined so as to introduce a minimum concentration of 24 at% of Cr in the gamma phase at 700°C, taking into account the fact that too high a chromium content promotes the precipitation of harmful phases such as the sigma phase and therefore deteriorates the hot stability.

[0161] Equations (1) and (5) account for these conditions.

[0162] Boron, Zirconium, Carbon and Nitrogen

[0163] The B content is between 0.0030% and 0.030%. The Zr content is between 0.01% and 0.06%. The C content is between traces and 0.018%, preferably between 0.0001% and 0.018%, preferably between 0.001% and 0.015%, preferably between 0.002% and 0.015%, preferably between 0.005% and 0.015%. The N content ranges from trace to 0.0047%, preferably from 0.0001% to 0.0047%, preferably from 0.0001% to 0.0040%, preferably from 0.0001% to 0.0035%, preferably from 0.0001% to 0.0030%, preferably from 0.0001% to 0.0025%.

[0164] It is essential for the present invention that the carbon content does not exceed 0.018% by mass and that the nitrogen content does not exceed 0.0047% by mass, in order, as explained above, to promote the manufacture or production of large diameter ingots by limiting or even eliminating the appearance of defects, in particular stringers, and by reducing or even eliminating the risk of freckles.

[0165] In addition, the so-called minor elements carbon, boron, and zirconium form segregations at grain boundaries, for example in the form of borides or carbides. They contribute to increasing the strength and ductility of alloys by trapping harmful elements such as sulfur and modifying the chemical composition at the grain boundaries. Their absence would be detrimental. However, excessive contents lead to a reduction in the melting temperature and significantly impair forgeability.

[0166] Phosphorus

[0167] The superalloy composition according to the invention may, according to certain embodiments, comprise phosphorus, in a mass percentage content ranging from 0% to 0.03%, preferably from 0.005% to 0.02%.

[0168] The presence or addition of phosphorus can improve creep resistance and reduce sensitivity to creep notch effect.

[0169] The notch effect corresponds to premature failure in the notch on creep tests with mixed specimen (smooth and notched part).

[0170] The present invention will now be described by non-limiting examples.

[0171] EXAMPLES

[0172] Tables 1 and 2 below show the compositions of various nickel-based superalloys. The contents of the various elements are expressed as mass percentages, except where it is specified that they are expressed as atomic percentages.

[0173] [Table 1]

[0174] *: comparative

[0175] **: content of each element being considered in atomic percentage

[0176] [Table 2]

[0177] : comparative

[0178] **: content of each element being considered in atomic percentage

[0179] The Ap and the mass fraction of carbonitrides of each composition were determined using the Thermo-Cale software (calculations carried out with version 2023b of the Thermo-Cale software and with the TTNI8 database for the Ap and carried out with version 2023b of the Thermo-Cale software and with the equivalent of the TCNI9 commercial database for the mass fraction of carbonitrides).

[0180] Examples 1 to 4, 7 and 8 correspond to compositions according to the invention.

[0181] Examples 5, 6 and 9 are comparative compositions.

[0182] These results show that a C content less than or equal to 0.018% by mass, and a nitrogen content less than or equal to 0.0047% are necessary to obtain ingots with a diameter greater than 450 mm, preferably greater than 480 mm, which are compliant, i.e. having a size and / or a number of stringers sufficiently low so as not to significantly alter their mechanical properties. We therefore seek to limit the density of coarse (Ti,Nb)C carbides and Ti(C,N) carbonitrides (equivalent diameter > 10 pm), i.e. to limit the mass % of carbides / carbonitrides which precipitate above the solidus. An acceptable limit of carbides + carbonitrides content is 0.08% by mass at T = T so ii dus- In particular, the comparison between composition 8 according to the invention and comparative 9* shows that a C content less than or equal to 0.018% by mass, and a nitrogen content less than or equal to 47 ppm make it possible to obtain a mass fraction of carbides and carbonitrides at the solidus below 0.08% by mass. In an optimized manner, it is also preferable that the Ap is greater than or equal to -47 kg / m 3 , and / or that the Nb + Ta content is greater than or equal to 0.8%, and / or that the W content is less than or equal to 3.0%, and / or that the Ti content is less than or equal to 3.8%, and / or that the Mo content is greater than or equal to 2.5%, in order to further limit the presence of “freckles”, which are also detrimental to the mechanical properties, in particular those of large diameter ingots.

Claims

CLAIMS 1. Nickel-based superalloy of the following composition, the contents of the various elements being expressed in mass percentages: - 1.3% < Al < 2.8%; - traces < Co < 11%; - 14% < Cr < 17%; - traces < Fe < 12%; - 2.0% < Mo < 5.0%; - 0.5% < Nb + Ta < 2.5%; - 2.5% < Ti < 4.5%; - 1.0% < W < 4.0% ; - 0.0030% < B < 0.030% ; - traces < C < 0.018%; - 0.01% < Zr < 0.06%; - traces < N < 0.0047%, and - 0 < P < 0.03%, the remainder being made up of nickel and impurities resulting from the production, and such that the composition satisfies the following equations, in which the contents are expressed in atomic percentages: 8.0 at% < Al at% + Ti at% + Nb at% + Ta at% < 11.0 at% 0.7 < (Ti at% + Nb at% + Ta at%) / Al% at% < 1.

3.

2. Nickel-based superalloy according to claim 1, wherein the difference Ap between the density of the liquid phase at the point in the solidification process of the superalloy at which it is in the form of a mixture of 50% by mass of liquid phase and 50% by mass of solid phase, and the density of the liquid phase of the superalloy at the liquidus, is greater than or equal to -47 kg / m 3 , preferably greater than or equal to -42 kg / m 3 , preferably between -47 kg / m 3 and 0 kg / m 3 , preferably between -47 kg / m 3 and -5 kg / m 3 .

3. Nickel-based superalloy according to claim 1 or 2, having a mass fraction of carbides and carbonitrides in the solidus of less than or equal to 0.08%.

4. Nickel-based superalloy according to any one of the preceding claims, comprising from 0.0001% to 0.0047% of N, preferably from 0.0001% to 0.0040%, preferably from 0.0001% to 0.0035%, preferably from 0.0001% to 0.0030%, preferably from 0.0001% to 0.0025%.

5. Nickel-based superalloy according to any one of the preceding claims, comprising from 0.0001% to 0.018% of C, preferably from 0.001% to 0.015%, preferably from 0.002% to 0.015%, preferably from 0.005% to 0.015%.

6. Nickel-based superalloy according to any one of the preceding claims, comprising from 1.0% to 3.8% of W, preferably from 1.0% to 3.3%, preferably from 1.0% to 3.0%, preferably from 1.5% to 3.0%.

7. Nickel-based superalloy according to any one of the preceding claims, comprising from 2.5% to 4.2% of Ti, preferably from 2.5% to 4.0%, preferably from 2.7% to 3.8%, preferably from 2.8% to 3.8%, preferably from 3.0% to 3.8%.

8. Nickel-based superalloy according to any one of the preceding claims, comprising from 0.6% to 2.5% of Nb + Ta, preferably from 0.7% to 2.5%, preferably from 0.8% to 2.0%, preferably from 0.8% to 1.8%, preferably from 0.8% to 1.6%.

9. Nickel-based superalloy according to any one of the preceding claims, comprising from 2.2% to 5.0% of Mo, preferably from 2.5% to 5.0%, preferably from 2.7% to 4.5%, preferably from 2.7% to 4.1%, preferably from 2.7% to 4.0%.

10. Nickel-based superalloy according to any one of the preceding claims, comprising from 1.5% to 2.8% of Al, preferably from 1.8% to 2.8%, preferably from 2.0% to 2.8%.

11. Nickel-based superalloy according to any one of the preceding claims, the composition of which satisfies the following equation, in which the contents are expressed in atomic percentages: 8.5 at% < Al at% + Ti at% + Nb at% + Ta at% < 10.8 at%, preferably 8.8 at% < Al at% + Ti at% + Nb at% + Ta at% < 10.5 at%, preferably 9.2 at% < Al at% + Ti at% + Nb at% + Ta at% < 10.1 at%.

12. Nickel-based superalloy ingot according to any one of claims 1 to 11.

13. Ingot according to claim 12, having a diameter greater than or equal to 450 mm, preferably greater than or equal to 480 mm, preferably greater than or equal to 490 mm, preferably greater than or equal to 570 mm.

14. Part made of nickel superalloy, its composition being according to any one of claims 1 to 11.

15. Nickel superalloy part according to claim 14, being a component of an aeronautical or terrestrial gas turbine.

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