Nickel-based alloy and part made from nickel-based alloy

Abstract

The invention relates to a γ / γ' nickel-based alloy comprising, in weight percentages, 16% to 18.5% chromium, 10% to 23% iron, 0% to 5% cobalt, 0.5% to 3% molybdenum, 1% to 2% titanium, 3% to 5% aluminum, 0% to 5% tungsten, 1% to 3.5% niobium, 0% to 0.5% hafnium, 0% to 0.03% carbon, 0% to 0.06% boron, 0% to 0.06% zirconium, 0% to 0.5% manganese, and 0% to 0.5% silicon, the remainder consisting of nickel and unavoidable impurities.

Description

[0001] DESCRIPTION

[0002] TITLE: Nickel-based alloy and nickel-based alloy part

[0003] TECHNICAL FIELD

[0004] The invention relates to a nickel-based alloy and a part, particularly for aeronautics, made of this nickel-based alloy.

[0005] STATE OF THE ART

[0006] Some components of the low-pressure turbines in civil and military aircraft engines are subjected to temperatures that can locally reach between 650°C and 750°C during operation. This is the case for certain turbine discs or casings. In addition, the atmosphere inside the turbine is rich in sulfur compounds such as SO2( g ) or SO 3(g) which are derived from fuel combustion products. Finally, particles ingested in flight by the turbojet (sea salts, ash, dust, etc.) as well as combustion products are likely to accumulate in the retention areas of the parts.

[0007] The nickel-based alloys used to manufacture these parts naturally form an oxide layer in air, primarily composed of chromium oxide. However, the combination of the three parameters mentioned above (temperature, sulfurous atmosphere, and pollutant accumulation) is highly conducive to the formation of agents, such as sodium sulfate, which destabilize the nickel-based alloy and the protective oxide layers, initiating hot corrosion of these parts, mainly of the so-called IL type. Indeed, the alloy reacts gradually with these agents to form other reaction products, notably a mixture of molten salts including metallic sulfates, such as NiSO4, which leads to the degradation of the parts.

[0008] More specifically, the hot corrosion phenomenon takes place in two stages: the first stage corresponds to an incubation period and is characterized by low attack rates, while the second stage is a propagation period which corresponds to significant damage to the alloy.

[0009] In addition to these hot corrosion phenomena, these components are subjected to significant mechanical stresses during operation. The alloy from which they are made must therefore be able to withstand these stresses, even at high temperatures ranging from 650°C to 750°C. The nickel-based alloy Inconel 718 exhibits excellent resistance to type II hot corrosion. However, above 650°C, it undergoes microstructural changes that make its use unsuitable for the hottest stages of high- and low-pressure turbines. Other nickel-based alloys must therefore be used, such as the AD730 alloy. However, this alloy has lower resistance to type II hot corrosion and may therefore require the application of an anti-corrosion coating.Such an anti-corrosion coating is not a completely satisfactory solution because, as it currently stands, it involves the use of chromium(VI), which is subject to strict regulations regarding its use in Europe to protect human health and the environment. Furthermore, anti-corrosion coatings can degrade the overall mechanical strength of the parts.

[0010] BRIEF DESCRIPTION OF THE INVENTION

[0011] One aim of the invention is to design a nickel-based alloy which, when subjected to temperatures between 650 °C and 750 °C, combines good mechanical strength with increased resistance to hot type II corrosion compared to current commercial alloys such as the AD730 alloy.

[0012] Another objective of the invention is to design a nickel-based alloy exhibiting type II hot corrosion resistance comparable to that of Inconel 718 and which is sufficiently mechanically strong to be used in the hottest stages of a high or low pressure turbine for turbomachinery equipping a civil or military aircraft or a land or gas turbine.

[0013] Another objective of the invention is to design an alloy usable for parts located in the hottest stages of high and low pressure turbines which makes it possible to avoid the application of anti-corrosion coatings.

[0014] In order to achieve one and / or the other of these goals, the invention proposes a nickel-based alloy of type y / y' comprising, in mass percentages, 16% to 18.5% chromium, 10% to 23% iron, 0% to 5% cobalt, 0.5% to 3% molybdenum, 1% to 2% titanium, 3% to 5% aluminium, 0% to 5% tungsten, 1% to 3.5% niobium, 0% to 0.5% hafnium, 0% to 0.03% carbon, 0% to 0.06% boron, 0% to 0.06% zirconium, 0% to 0.5% manganese, 0% to 0.5% silicon, the remainder being nickel and unavoidable impurities. The high iron content of the alloy according to the invention makes said alloy particularly resistant to hot type II corrosion when combined with other judiciously chosen elements, particularly at temperatures between 650°C and 750°C which are reached in the hottest parts of high and low pressure turbine discs.This type II hot corrosion resistance is at least comparable to that of Inconel 718. Furthermore, the higher and lower aluminum and niobium contents compared to Inconel 718 allow for the stabilization of a y / y' type microstructure even above 650 °C with a high y' precipitate content. This microstructure, with its high y' precipitate content, provides the alloy according to the invention with high mechanical strength that is maintained up to high temperatures (750 °C or even higher), thus making it suitable for use in the hottest stages of high- and low-pressure turbines.

[0015] Depending on other optional characteristics of the y / y' type nickel-based alloy, taken alone or in combination where technically feasible:

[0016] - The nickel-based alloy comprises, by mass percentages, 3% aluminium, 0.01% carbon, 0% cobalt, 16% chromium, 12% iron, 0.1% hafnium, 0.1% manganese, 0.5% molybdenum, 3.5% niobium, 0.1% silicon, 2% titanium and 1% tungsten, the remainder being nickel and unavoidable impurities,

[0017] - the nickel-based alloy comprises, by mass percentages, 3% aluminium, 0.01% carbon, 0% cobalt, 16% chromium, 12% iron, 0.1% hafnium, 0.1% manganese, 3% molybdenum, 1% niobium, 0.1% silicon, 2% titanium and 0% tungsten, the remainder being nickel and unavoidable impurities,

[0018] - The nickel-based alloy comprises, by mass percentages, 3% aluminium, 0.01% carbon, 0% cobalt, 18.5% chromium, 10% iron, 0.1% hafnium, 0.1% manganese, 3% molybdenum, 1% niobium, 0.1% silicon, 2% titanium and 0% tungsten, the remainder being nickel and unavoidable impurities,

[0019] - The nickel-based alloy comprises, by mass percentages, 3% aluminium, 0.01% carbon, 0% cobalt, 16% chromium, 12% iron, 0.1% hafnium, 0.1% manganese, 0.5% molybdenum, 1% niobium, 0.1% silicon, 2% titanium and 5% tungsten, the remainder being nickel and unavoidable impurities,

[0020] - The nickel-based alloy comprises, by mass percentages, 5% aluminium, 0.01% carbon, 5% cobalt, 16% chromium, 12% iron, 0.1% hafnium, 0.1% manganese, 0.5% molybdenum, 1% niobium, 0.1% silicon, 1% titanium and 1% tungsten, the remainder being nickel and unavoidable impurities,

[0021] - the nickel-based alloy comprises, by mass percentages, 2.5% aluminium, 0.01% carbon, 0% cobalt, 16% chromium, 23% iron, 0.1% hafnium, 0.1% manganese, 0.5% molybdenum, 1% niobium, 0.1% silicon, 2% titanium and 1% tungsten, the remainder being nickel and unavoidable impurities.

[0022] The invention also relates to a part made of nickel-based alloy, said nickel-based alloy having a composition and microstructure as previously described.

[0023] Depending on other optional characteristics of the nickel-based alloy part, taken alone or in combination where technically possible:

[0024] - the part is a component of a gas turbine, aeronautical or terrestrial;

[0025] - the part is a turbine disc, a compressor disc, a turbine ring, a flange and / or a turbine housing.

[0026] Other features and advantages of the invention will become apparent from the detailed description that follows.

[0027] DETAILED DESCRIPTION OF IMPLEMENTATION METHODS

[0028] The applicant believes that the chromium activity of a nickel-based alloy is directly related to the mass concentration of chromium in that alloy. Thus, the higher the chromium concentration in the alloy, the higher the chromium activity, and therefore the greater the chromium's ability to form a chromium oxide (Cr2O3) layer, which constitutes an effective protective barrier against IL-type hot corrosion. However, an excessively high chromium concentration risks altering the microstructural characteristics and therefore the mechanical properties of the alloy.

[0029] An example of Inconel 718 alloy comprises, by mass percentage, between 50.00% and 55.00% nickel plus cobalt (cobalt being present in trace amounts), between 17.00% and 21.00% chromium, between 4.75% and 5.50% niobium plus tantalum (of which less than 0.1% tantalum), between 2.80% and 3.30% molybdenum, between 0.65% and 1.15% titanium, between 0.20% and 0.80% aluminum, a maximum of 1.00% cobalt, a maximum of 0.08% carbon, a maximum of 0.35% manganese, a maximum of 0.35% silicon, a maximum of 0.015% phosphorus, a maximum of 0.015% sulfur, a maximum of 0.006% boron and a maximum of 0.30% copper, the balance being ensured by iron (for example between 15% and 21% iron) and other trace elements such as calcium, magnesium, silver, bismuth, lead, selenium, oxygen and nitrogen.Elements are said to be present in trace amounts when they are impurities whose presence is unavoidable due to the extraction and processing stages of the material. The applicant notes that Inconel 718 offers excellent resistance to hot corrosion (Type II) because it naturally forms the aforementioned chromium oxide (Cr2O3) layer on its surface. In particular, the hot corrosion resistance (Type II) of Inconel 718 is significantly better than that of other industrial alloys such as AD730. The applicant attributes this excellent corrosion resistance of Inconel 718 to the high chromium activity in this alloy, despite a chromium content almost identical to that of AD730. The applicant further believes that it is the high iron content of the Inconel 718 alloy that enables such chromium activity within the alloy.

[0030] However, the high iron and niobium content of Inconel 718 has the disadvantage of stabilizing a microstructure comprising an austenitic matrix with a face-centered cubic crystal structure, known as the γ phase, and Ni3(Ti,Nb) precipitates, which constitute a so-called γₓ phase. The γₓ phase is the hardening phase of the alloy and gives it its mechanical properties. Above approximately 650 °C, this structure is not stable: the γₓ phase transforms into the γₓNi3(Ti,Nb) phase, which has a different crystallographic structure than the γₓ phase, resulting in a sharp decrease in the alloy's mechanical strength. Such microstructural changes make it impossible to use Inconel 718 for the hottest stages of high- and low-pressure turbine disks.

[0031] Other industrial alloys exist that exhibit a microstructure comprising a y phase (the matrix) and a so-called y' phase consisting of Ni3(Al, Ti, Ta) precipitates with an L12 ordered cubic structure. In this case, the y' precipitates constitute the hardening phase. They impart high mechanical strength to such alloys. Furthermore, the y' precipitates are stable up to sufficiently high temperatures to allow the use of such alloys in the hottest stages of high- and low-pressure turbine disks. In the following text, a y / y' type nickel-based alloy refers to a nickel-based alloy with a primary y-type phase and a secondary phase in the form of y'-type precipitates.

[0032] The AD730 alloy is an example of a nickel-based alloy with a y / Y'-type microstructure. An example of AD730 alloy comprises, by mass percentage, between 15% and 17% chromium, between 3.6% and 5% iron, between 8% and 10% cobalt, between 2.5% and 3.5% molybdenum, between 3.3% and 3.9% titanium, between 2.0% and 2.5% aluminum, between 2% and 3% tungsten, between 0.8% and 1.4% niobium, less than 0.02% carbon, between 0.005% and 0.02% boron, between 0.01% and 0.05% zirconium, and other trace elements considered impurities whose unavoidable presence results from extraction and material processing. On the other hand, these y / y' microstructure alloys are much less resistant to corrosion, particularly to hot type II corrosion, than Inconel 718 alloy. Although they do form an external chromium layer (Cr2O3), this offers limited protection against type II corrosion phenomena.The inventors attribute the lower resistance of industrial alloys with a y / y' microstructure to type II hot corrosion to lower chromium activity within these alloys. The inventors suspect that this lower activity is related to the content of certain other elements in the alloy. In particular, they highlighted the role of iron in these forged Y / Y' microstructured turbine disk alloys.

[0033] The invention therefore relates to a new nickel-based alloy comprising, in mass percentages: 16% to 18.5% chromium, 10% to 23% iron, 0% to 5% cobalt, 0.5% to 3% molybdenum, 1% to 2% titanium, 3% to 5% aluminium, 0% to 5% tungsten, 1% to 3.5% niobium, 0% to 0.5% hafnium, 0% to 0.03% carbon, 0% to 0.06% boron, 0% to 0.06% zirconium, 0% to 0.5% manganese, 0% to 0.5% silicon, the remainder being nickel and unavoidable impurities.

[0034] The alloy according to the invention does not, in particular, comprise any elements other than vanadium, sulfur, phosphorus, copper, lead, iron, bismuth, nitrogen, oxygen, hydrogen, or mixtures thereof, except as unavoidable impurities. These unavoidable impurities in the alloy according to the invention originate from the manufacturing steps of said alloy or from impurities present in the raw materials used to manufacture the alloy. They may constitute up to 1% by mass of the alloy and each may not represent more than 0.5% by weight of the total composition. The impurity content in the alloy is measured with an uncertainty of 10%.

[0035] The limits of the mass content ranges for each of the elements in the alloy according to the invention should not be interpreted strictly, but with a certain tolerance taking into account the experimental uncertainty in the evaluation of said contents. These contents are typically evaluated, for major elements, by inductively coupled plasma optical emission spectroscopy (ICP-OES), for minor elements, by glow discharge mass spectrometry (GDMS), and for gas-generating elements such as carbon, hydrogen, and oxygen, by instrumentation gas analysis (IGA). More specifically, the alloy according to the invention may include, without departing from the scope of the invention,between 15.8% and 18.7%, preferably between 15.85% and 18.75%, of chromium, between 9.8% and 23.2%, preferably between 9.85% and 23.15%, of iron, between 0% and 5.3%, preferably between 0% and 5.2%, of cobalt, between 0.46% and 3.04%, preferably between 0.48% and 3.02%, more preferably between 0.49% and 3.01%, of molybdenum, between 0.8% and 2.2%, preferably between 0.9% and 2.1%, of titanium, between 2.96% and 5.04%, preferably between 2.98% and 5.02%, even more preferably between 2.99% and 5.01%, of aluminum, between 0% and 5.04%, preferably between 0% and 5.02%, even more preferably between 0% and 5.01% of tungsten, between 0.96% and 3.54%, preferably between 0.98% and 3.52%, of niobium, between 0% and 0.033%, preferably between 0% and 0.032%, of carbon, 0% to 0.061% of boron, 0% to 0.061% of zirconium, 0% to 0.51% of manganese, 0% to 0.51% of silicon and 0% to 0,51% hafnium. The widest permissible tolerances for each element are summarized in Table 0.

[0036] Table 0

[0037] Furthermore, the alloy according to the invention has a microstructure comprising a Y phase and a y'- phase

[0038] Thus, the alloy according to the invention comprises iron and chromium contents comparable to those of Inconel 718, so as to promote high chromium activity. Conversely, it comprises a lower niobium content and a higher aluminum content. A niobium content of less than 3.5% advantageously avoids stabilizing the "y" phase. Indeed, the "y" phase would be detrimental because it would transform into phase 5 above approximately 650 °C, thus abruptly reducing the mechanical strength of the alloy. When the temperature of a y / y' type alloy increases, the proportion of the y' phase decreases due to the redissolution of the y' precipitates in the y matrix, which leads to a reduction in the mechanical strength of said alloy.An aluminum content exceeding 3% allows for strong stabilization of the y' structure, essential for the alloy's hardening, even at high temperatures despite the high iron content; in other words, it maintains a non-zero proportion of y' precipitates even at high temperatures. A high aluminum content is important because the high iron content of the alloy according to the invention tends, conversely, to lower the fraction of y' precipitates. Compared to nickel-based alloys with a y / y' structure, such as TAD730, the alloy according to the invention advantageously exhibits a comparable chromium content but a higher iron content. Indeed, an iron content exceeding 10% allows for higher chromium activity compared to said nickel-based alloys with a y / y' microstructure, without requiring the chromium content to be higher than that of said alloys.Such chromium activity advantageously allows the formation of the protective chromium oxide layer which effectively limits the formation of nickel oxide (NiO), said nickel oxide being able to cause the appearance of type II hot corrosion phenomena. Indeed, in the presence of an atmosphere rich in sulfur trioxide (SO₄). 3(g ), nickel oxide reacts with said sulfur trioxide to form nickel sulfate NiSO₄ 4(s) Nickel sulfate then reacts with sodium sulfate (Na2SO4). 4(s) originating from pollutants ingested by the engine to form low melting point eutectics which are liquid at the operating temperatures of the alloy.

[0039] An iron content between 10% and 23% maximizes chromium activity and thus achieves a type II hot corrosion resistance at least equivalent to or greater than that of Inconel 718. Indeed, an iron content greater than 23% would risk the formation of an oxide layer comprising mixed oxides (Cr,Fe)2O3 and / or iron oxide (Fe2O3) which is less effective in corrosion protection than the chromium oxide layer. In addition, too high an iron content could lead to the formation of fragile phases of the TCP type (according to the Anglo-Saxon acronym "topologically close packed"), q-Ni3Ti or y' and / or lower the temperature of the solvus of the y' phase (temperature beyond which the y' precipitates begin to redissolve), in other words lower the stability of said y' phase with temperature.The inventors' choice to limit the molybdenum content of the alloy to 3% also helps to avoid the formation of previously mentioned TCP-type phases, such as the o phase.

[0040] Since chromium directly participates in the formation of the protective oxide layer, increasing the chromium content advantageously improves corrosion resistance. Conversely, an excessively high chromium content would lead to the precipitation of the β phase, which is detrimental to the alloy's mechanical properties, a precipitation exacerbated by the alloy's high iron content. The chromium and iron content ranges of the alloy according to the invention are therefore optimized to obtain the best corrosion protection while preventing the precipitation of the β phase. In an alloy according to the invention with a high chromium content (for example, 18.5%), it is preferable to reduce the iron content (for example, 10%). Conversely, in an alloy according to the invention with a lower chromium content (for example, 16%), those skilled in the art could choose a higher iron content to improve corrosion resistance (for example, 12% or 23%).However, an iron content of 23% may have the effect of decreasing the fraction of phase y'.

[0041] However, the titanium and cobalt contents of the alloy according to the invention are chosen to be lower than those of TAD730. Indeed, as previously mentioned, the addition of iron as a substitute for nickel in significant quantities in y / y' type alloys can lead to two detrimental phenomena:

[0042] - the stabilization of a q-Ni3Ti phase which alters the hot ductility of the alloy by precipitating in the form of needles at grain boundaries,

[0043] - lowering the solvus temperature of phase y' leads to low y' phase contents within the alloy's service range. Indeed, the higher the solvus temperature of phase y', the higher the fraction of phase y' remains at high temperatures.

[0044] A cobalt content of less than 5% combined with a niobium content greater than 1% advantageously prevents the solvus of the y' phase from falling below 1000 °C, thus maintaining a significant proportion of the y' phase even at high temperatures (still 29% of the y' phase at 700 °C). A titanium content of 2% or less advantageously prevents the formation of the q phase. However, the titanium content is chosen to be greater than 1% to ensure solid solution strengthening of the y' phase and improve the mechanical properties of the alloy.

[0045] Consequently, the proportion of the y' phase in the alloy according to the invention is at least equivalent to that of currently used y / y' microstructure alloys such as AD730, so that the alloy according to the invention exhibits mechanical characteristics close to the best performing among them. Furthermore, the y' phase remains stable in a significant proportion up to high temperatures, in particular up to the maximum service temperatures of the components located in the hottest stages of the low-pressure turbine (i.e., 700 °C or more), ensuring the maintenance of mechanical characteristics up to these temperatures. For example, the y' phase is still present at 900 °C in the alloy of the invention.

[0046] It is noteworthy that the alloy according to the invention advantageously has a high iron content, which, from an economic point of view, reduces its cost price compared to another alloy which would include a higher content of more expensive elements such as nickel or cobalt.

[0047] An example of an Inco718Plus alloy comprises 53% nickel, 9% cobalt, 19% chromium, 9% iron, 0.75% titanium, 2.8% molybdenum, 1.6% aluminum, 1% tungsten, 0.06% carbon, 0.35% manganese, 0.2% phosphorus, 0.01% silicon, and 0.01% sulfur. The alloy according to the invention is therefore distinguished from the Inco718Plus alloy, at least in that the Inco718Plus alloy comprises a higher content of cobalt and chromium, but a lower content of iron than the alloy according to the invention. The alloy according to the invention has the advantage of not stabilizing the QN i3Ti phase, unlike the Inco718Plus alloy.

[0048] The molybdenum and tungsten concentrations in the alloy according to the invention are optimized to promote solid solution hardening of the γ phase and thus improve the mechanical strength of said alloy. The niobium concentration is optimized to increase the creep life of said alloy, as well as its yield strength and tensile strength. The presence of carbon in the alloy according to the invention advantageously allows for good precipitation of said carbon into primary and secondary carbides, thereby positively influencing the mechanical properties of the alloy. However, an excessive amount of carbon could lead to the precipitation of an excessive fraction of carbides, which could weaken the alloy. Finally, boron and zirconium can improve creep resistance and limit crack propagation at high temperatures.However, their concentration must remain less than or equal to 0.03% and 0.06% respectively to avoid obtaining the opposite effect to that expected.

[0049] The hafnium content is advantageously chosen to be less than or equal to 0.5%. Indeed, a higher content would lead both to a decrease in the alloy's oxidation resistance and to excessive precipitation of hafnium carbides, which can degrade the alloy's mechanical properties. Manganese plays a role similar to hafnium but has the advantage of being less expensive. However, an excessive concentration of manganese would degrade the alloy's corrosion resistance. As for silicon, it improves the adhesion of the protective oxide layer. The silicon concentration of the alloy according to the invention is optimized so as not to degrade the corrosion resistance of said alloy.

[0050] Advantageously, the alloy according to the invention is free of tantalum, cobalt, and / or tungsten (the mass content of any of these elements is strictly 0%). These elements are expensive and their prices fluctuate, so being able to do without them is a significant industrial advantage. In particular, the alloy according to the invention exhibits very good resistance to hot corrosion even though it does not contain tantalum, which is a real advantage of the alloy. The alloy according to one embodiment of the invention can be prepared by casting, for example, in the form of ingots. Alternatively, the alloy according to the invention can be prepared in powder form, using powder metallurgy, for example, by atomizing ingots. The ingot can then be shaped, for example, by forging or die-casting. A series of heat treatments then stabilizes the microstructure y / y'.

[0051] The invention also relates to a nickel-based alloy part, said nickel-based alloy having a composition and microstructure as previously described. The part is, for example, a component of an aeronautical or land-based gas turbine, more particularly a turbine disc, a compressor disc, a ring, a flange, and / or a turbine housing.

[0052] The part according to an embodiment of the invention can be formed from an ingot or a powder of the alloy according to an embodiment of the invention, the y / y' type microstructure of the part then being stabilized by a series of thermomechanical treatments so as to obtain the fraction of phases y' and the grain sizes necessary to achieve the mechanical characteristics for the desired application.

[0053] Examples

[0054] Six alloys (Ex 1 to Ex 6) according to the invention were studied in simulation and compared with two industrial reference alloys: Inconel 718 (CEx 1), TAD730 (CEx 2) and Inco718Plus (CEx 3). The composition of each of the six alloys according to the invention is shown in Table 1.

[0055] Table 1

[0056] More specifically, certain characteristics of the example alloys of the invention Ex 1 to Ex 6 and the reference alloys CEx 1, CEx 2, and CEx 3 were estimated using various methods, such as models derived from multiple linear regressions or thermodynamic calculations using the CALPHAD (CALculation of PHAse Diagrams) method for calculating phase diagrams via the Thermo-Cale software (Thermo-Cale Software AB, Sweden) associated with the TCNI9 thermodynamic database. The characteristics concerned (and their method of determination) are as follows:

[0057] - the transformation temperatures: solvus y', solvus 5 and solidus (Thermo-Cale software);

[0058] - the volume fraction of precipitates of phase y', 5 and TCP at 700 °C (Thermo-Cale software);

[0059] - the activity of nickel and chromium (Thermo-Cale software);

[0060] - the mass density (modified Hull formula);

[0061] - the propensity to form TCP phase by destabilization of the y matrix, called Md (NEW PHACOMP formula, Morinaga, Superalloys 1984).

[0062] Hull's formula is based on a law of mixtures and includes corrective terms derived from a linear regression analysis of experimental data (measured chemical compositions and densities) for 272 nickel-, cobalt-, or iron-based superalloys. The formula has been modified to account for additional elements such as rhenium, or for supplementary data on alloys developed after the formula's invention.

[0063] The modified Hull formula is as follows:

[0064] D = 27.68 x [Ü! + 0.14037 - 0.00137% Cr - 0.00139% Ni - 0.00142% Co - 0.00140% Fe - 0.00186% M o - 0.00125% w - 0.00134% v - 0.00119% Nb - 0.00113% Ta + 0.0004% Ti + 0.00388 %c + 0.0000187 (% Mo ) 2 - 0.0000506 (% C o)x(% T i) - 0.00096% Re where D-, = 100 / [(% Cr / D Cr) + (% Ni / D Ni )+ .... + (%x / D x )l where D Cr , D Ni ,..., D x are the densities of the elements Cr, Ni, ..., X expressed in g / cm³ 3 and D is the density of the superalloy expressed in g / cm³ 3 , Or % Cr , % Ni , ...% x are the contents, expressed as mass percentages, of the elements of the superalloy Cr, Ni, ..., X.

[0065] The densities of the example and reference alloys, as well as the metallurgical properties determined by CALPHAD, are reported in Table 2. The phase fractions y', 5, and TCP, and the reported Cr activities, are those calculated at 700 °C. The ATTH quantity represents the difference between the alloy solidus and the highest dissolution temperature of the hardening precipitates (y' or 5).

[0066] Table 2

[0067] Simulations show that the example alloys of the invention have predicted densities less than or equal to those of the commercial reference alloys CEx 1 and CEx 2. The inventors attribute these relatively low alloy densities, with a maximum of 8.17 g / cm³. 3 , with significant additions of iron and chromium. This parameter is of primary importance when alloys are used for the manufacture of rotating components such as turbine discs.

[0068] The Md criterion is calculated from the composition of matrix y at 700 °C, a composition determined using CALPHAD calculations. This Md criterion is compared, at a given temperature, to a threshold below which the risk of TCP phase formation is reduced. This threshold is 0.895 at 700 °C. With the exception of alloy Ex 5, all the alloys of the invention have a value below this threshold, identical to the reference commercial alloys CEx 1 and CEx 2. Alloy Ex 5, on the other hand, has the highest y' phase fraction of the exemplary alloys of the invention and the reference commercial alloys, as well as one of the highest solvus values ​​of this y' phase among the exemplary alloys of the invention. The TCP phase fraction at 700 °C, determined at thermodynamic equilibrium by the CALPHAD method, complements the Md criterion and is inherently more stringent.All the alloys of the invention have a predicted TCP phase fraction lower (Ex 1, 2, 4, 6) or equal (Ex 3, 5) to that of the commercial reference alloys CEx 1 and CEx 2, indicating a suitability of the microstructure for the intended applications. In particular, the alloys Ex 1, Ex 4, and Ex 6 have a very low predicted TCP phase fraction, which should translate into good microstructural stability during service life.

[0069] The chromium activity of the alloys of the invention at 700 °C is at least equal to that of the commercial reference alloy CEx 1, already known to exhibit good corrosion resistance, and at least 14% higher than that of the commercial reference alloy CEx 2. These observations confirm that the compositions according to the invention would exhibit increased corrosion resistance at high temperature.

[0070] The phase fraction y' of the alloys of the invention at 700 °C is between the phase fraction 5 of alloy CEx 1 and the phase fraction y' of alloy CEx 2 at 700 °C, with the exception of alloy Ex 5 where it is even greater than the phase fraction y' of alloy CEx 2 at 700 °C. Combined with the previously mentioned limited TCP phase fraction values, these values ​​demonstrate a certain suitability of the microstructure for the intended applications, particularly with regard to mechanical properties.

[0071] The solvus of phase y' in the alloys of the invention is, with the exception of alloy Ex 6, similar to or greater than the solvus of phase 5 in alloy CEx 1, ensuring (1) a certain capacity to use the alloys at at least similar temperatures, and (2) a certain feasibility of the resolution heat treatment of phase y'. This heat treatment advantageously allows control of the effective fraction and distribution of phase y', two factors that greatly influence the mechanical properties of the alloy. The feasibility of said heat treatment in the alloys according to the invention is also illustrated by the resolution heat treatment range (RHT) of at least 187 °C.

[0072] The carbides MC and M23C6, where M represents one or more carbide-forming elements chosen, for example, from Cr, Fe, Mo, Nb, Ti, and W, play a key role in strengthening grain boundaries and thus increasing mechanical properties. Table 3 shows the simulated fractions of MC and M23C6 carbides in the example alloys of the invention, Ex 1 to Ex 6, determined using CALPHAD calculations. These fractions are compared to the simulated fractions of the reference commercial alloys, CEx 1, CEx 2, and CEx 3, determined using the same method. The carbide fractions are given at 700 °C. Table 3

[0073] The results presented in Table 3 show that, with the exception of alloy Ex 6, the fraction of M23C6 carbides in the alloys of the invention at 700 °C varies little and remains of the same order of magnitude as that of alloy CEx 2. Alloy Ex 6 also contains MC carbides, similarly to alloy CEx 1, although in a smaller proportion. For alloy Ex 6, the total fraction of carbides at 700 °C remains close to that of alloy CEx 2. These observations confirm that the compositions according to the invention would exhibit mechanical strength compatible with the intended applications.

Claims

DEMANDS 1. Nickel-based alloy of type y / y', comprising, by mass percentages, 16% to 18.5% chromium, 10% to 23% iron, 0% to 5% cobalt, 0.5% to 3% molybdenum, 1 2% to 3% titanium, 3% to 5% aluminum, 0% to 5% tungsten, 1% to 3.5% niobium, 0% to 0.5% hafnium, 0% to 0.03% carbon, 0% to 0.06% boron, 0% to 0.06% zirconium, 0% to 0.5% manganese, 0% to 0.5% silicon, the remainder being nickel and unavoidable impurities.

2. Nickel-based alloy according to claim 1, comprising, by mass percentages, 3% aluminium, 0.01% carbon, 0% cobalt, 16% chromium, 12% iron, 0.1% hafnium, 0.1% manganese, 0.5% molybdenum, 3.5% niobium, 0.1% silicon, 2% titanium and 1% tungsten, the remainder being nickel and unavoidable impurities.

3. Nickel-based alloy according to claim 1, comprising in mass percentages, 3% aluminium, 0.01% carbon, 0% cobalt, 16% chromium, 12% iron, 0.1% hafnium, 0.1% manganese, 3% molybdenum, 1% niobium, 0.1% silicon, 2% titanium and 0% tungsten, the remainder being nickel and unavoidable impurities.

4. Nickel-based alloy according to claim 1, comprising, by mass percentages, 3% aluminium, 0.01% carbon, 0% cobalt, 18.5% chromium, 10% iron, 0.1% hafnium, 0.1% manganese, 3% molybdenum, 1% niobium, 0.1% silicon, 2% titanium and 0% tungsten, the remainder being nickel and unavoidable impurities.

5. Nickel-based alloy according to claim 1, comprising, by mass percentages, 3% aluminium, 0.01% carbon, 0% cobalt, 16% chromium, 12% iron, 0.1% hafnium, 0.1% manganese, 0.5% molybdenum, 1% niobium, 0.1% silicon, 2% titanium and 5% tungsten, the remainder being nickel and unavoidable impurities.

6. Nickel-based alloy according to claim 1, comprising, by mass percentages, 5% aluminum, 0.01% carbon, 5% cobalt, 16% chromium, 12% iron, 0.1% hafnium, 0.1% manganese, 0.5% molybdenum, 1% niobium, 0.1% of silicon, 1% titanium and 1% tungsten, the remainder being nickel and unavoidable impurities.

7. Nickel-based alloy according to claim 1, comprising, by mass percentages, 2.5% aluminium, 0.01% carbon, 0% cobalt, 16% chromium, 23% iron, 0.1% hafnium, 0.1% manganese, 0.5% molybdenum, 1% niobium, 0.1% silicon, 2% titanium and 1% tungsten, the remainder being nickel and unavoidable impurities.

8. Nickel-based alloy part, said nickel-based alloy having a composition and microstructure according to any one of claims 1 to 7.

9. Part according to the preceding claim, characterized in that it is a component of a gas turbine, aeronautical or terrestrial.

10. Part according to the preceding claim, characterized in that it is a turbine disc, a compressor disc, a turbine ring, a flange and / or a turbine housing.

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