EP3710610B1 - Nickel-based superalloy, single-crystal blade and turbomachine - Google Patents

Description

Background of the invention

This presentation relates to nickel-based superalloys for gas turbines, in particular for stationary blades, also called distributors or rectifiers, or vanes of a gas turbine, for example in the field of aeronautics.

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

These materials have the main advantages of combining both high creep resistance at high temperature and resistance to oxidation and corrosion.

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

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

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

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

The materials generally used to produce this underlayer include aluminoforming metal alloys of the MCrAlY type (M = Ni (nickel) or Co (cobalt)) or a mixture of Ni and Co, Cr = chromium, Al = aluminum and Y = yttrium, or alloys of the nickel aluminide type (Ni _x Al _y ), some also containing platinum (Ni _x Al _y Pt _z ).

The second layer, generally called thermal barrier or "TBC" according to the English acronym for "Thermal Barrier Coating", is a ceramic coating comprising for example yttria zirconia, also called "YSZ" according to the English acronym for " Yttria Stabilized Zirconia” or “YPSZ” in accordance with the English acronym for “Yttria Partially Stabilized Zirconia” and having a porous structure. This layer can be deposited by various processes, such as evaporation under an electron beam ("EB-PVD" in accordance with the English acronym for "Electron Beam Physical Vapor Deposition"), thermal spraying ("APS" in accordance with the English acronym for “Atmospheric Plasma Spraying” or “SPS” in accordance with the English acronym for “Suspension Plasma Spraying”), or any other process making it possible to obtain a porous ceramic coating with low thermal conductivity.

Due to the use of these materials at high temperature, for example from 650° C. to 1150° C., inter-diffusion phenomena occur on a microscopic scale between the nickel-based superalloy of the substrate and the metal alloy of the underlayer. These phenomena of inter-diffusion, associated with the oxidation of the underlayer, modify in particular the chemical composition, the microstructure and consequently the mechanical properties of the underlayer from the manufacture of the coating, then during the use of dawn in the turbine. These inter-diffusion phenomena also modify the chemical composition, the microstructure and consequently the mechanical properties of the superalloy of the substrate under the coating. In superalloys highly loaded with refractory elements, in particular rhenium, a secondary reaction zone (ZRS) can thus form in the superalloy under the sub-layer to a depth of several tens, or even hundreds, of micrometers. The mechanical characteristics of this ZRS are clearly inferior to those of the superalloy of the substrate. There ZRS formation is undesirable because it leads to a significant reduction in the mechanical strength of the superalloy.

These evolutions of the bonding layer, associated with the stress fields related to the growth of the alumina layer which forms in service on the surface of this bonding layer, also called "TGO" according to the English acronym for " Thermally Grown Oxide”, and the differences in thermal expansion coefficients between the different layers, generate decohesions in the interfacial zone between the underlayer and the ceramic coating, which can lead to partial or total chipping of the ceramic coating. The metal part (superalloy substrate and metal sub-layer) is then exposed and exposed directly to the combustion gases, which increases the risk of damage to the blade and therefore to the gas turbine.

Moreover, the complexity of the chemistry of these alloys can lead to a destabilization of their optimal microstructure with the appearance of particles of undesirable phases when parts formed from these alloys are held at high temperature. This destabilization has negative consequences on the mechanical properties of these alloys. These undesirable phases of complex crystalline structure and of fragile nature are called topologically compact “PTC” phases or “TCP” phases in accordance with the English acronym for “Topologically Close-Packed”.

In addition, foundry defects are liable to form in the parts, such as blades, during their manufacture by directional solidification. These defects are generally parasitic grains of the "Freckle" type, the presence of which can cause premature failure of the part in service. The presence of these defects, related to the chemical composition of the superalloy, generally leads to the rejection of the part, which leads to an increase in the cost of production.
US5366695 describes superalloys not comprising ruthenium.

Subject matter and summary of the invention

This presentation aims to propose compositions of nickel-based superalloys for the manufacture of single-crystal components, presenting increased performance in terms of service life and mechanical resistance and making it possible to reduce the costs of production of the part (reduced scrap rate) compared to existing alloys. These superalloys exhibit superior high temperature creep resistance than existing alloys while showing good microstructural stability within the bulk of the superalloy (low susceptibility to PTC formation), good microstructural stability under the coating underlayer of the thermal barrier (low sensitivity to the formation of ZRS), good resistance to oxidation and corrosion while avoiding the formation of parasitic grains of the "Freckle" type.

To this end, the present disclosure relates to a nickel-based superalloy comprising, in mass percentages, 4.0 to 5.5% rhenium, 1.0 to 3.0 ruthenium, 2.0 to 14.0% cobalt, 0.30-1.00% molybdenum, 3.0-5.0% chromium, 2.5-4.0% tungsten, 4.5-6.5% aluminum, 0.50 to 1.50% titanium, 8.0 to 9.0% tantalum, 0.15 to 0.30% hafnium, preferably 0.16 to 0.30% hafnium, preferably 0.17 to 0 .30% hafnium, preferably 0.18 to 0.30% hafnium, preferably 0.08 to 0.12% silicon, even more preferably 0.10% silicon, even more preferably 0.20 to 0.30% hafnium, 0.05 to 0.15% silicon, the remainder consisting of nickel and inevitable impurities.

This superalloy is intended for the manufacture of monocrystalline gas turbine components, such as fixed or moving blades.

Thanks to this composition of the nickel-based superalloy (Ni), the creep resistance is improved compared to existing superalloys, in particular at temperatures which can go up to 1200°C.

This alloy therefore has improved creep resistance at high temperature. This alloy also exhibits improved corrosion and oxidation resistance.

These superalloys have a density less than or equal to 9.00 g/cm ³ (gram per cubic centimeter).

A single-crystal nickel-based superalloy part is obtained by a process of directed solidification under a thermal gradient in the lost-wax foundry. The single-crystal nickel-based superalloy comprises an austenitic matrix with a face-centered cubic structure, nickel-based solid solution, known as the gamma (“γ”) phase. This matrix contains gamma prime hardening phase precipitates (“γ'”) of ordered cubic structure L1 ₂ of the Ni ₃ Al type. The assembly (matrix and precipitates) is therefore described as a γ/γ' superalloy.

Furthermore, this composition of the nickel-based superalloy allows the implementation of a heat treatment which redissolves the γ′ phase precipitates and the γ/γ′ eutectic phases which are formed during the solidification of the superalloy. It is thus possible to obtain a monocrystalline nickel-based superalloy containing γ′ precipitates of controlled size, preferably between 300 and 500 nanometers (nm), and containing a small proportion of γ/γ′ eutectic phases.

The heat treatment also makes it possible to control the volume fraction of the γ′ phase precipitates present in the single-crystal nickel-based superalloy. The percentage by volume of the γ' phase precipitates can be greater than or equal to 50%, preferably greater than or equal to 60%, even more preferably equal to 70%.

The major addition elements are cobalt (Co), chromium (Cr), molybdenum (Mo), rhenium (Re), ruthenium (Ru), tungsten (W), aluminum (Al), titanium (Ti) and tantalum (Ta).

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

Unavoidable impurities include sulfur (S), carbon (C), boron (B), yttrium (Y), lanthanum (La) and cerium (Ce). Unavoidable impurities are defined as those elements which are not intentionally added to the composition and which are added with other elements.

The addition of tungsten, chromium, cobalt, rhenium, ruthenium or molybdenum mainly makes it possible to reinforce the austenitic matrix γ of face-centered cubic crystal structure (fcc) by hardening in solid solution.

The addition of aluminum (Al), titanium (Ti) or tantalum (Ta) promotes the precipitation of the hardening phase γ′-Ni ₃ (Al, Ti, Ta).

Rhenium (Re) makes it possible to slow down the diffusion of chemical species within the superalloy and to limit the coalescence of γ' phase precipitates during service at high temperature, a phenomenon which leads to a reduction in mechanical strength. Rhenium thus makes it possible to improve the creep resistance at high temperature of the nickel base superalloy. However, too high a concentration of rhenium can lead to the precipitation of PTC intermetallic phases, for example σ phase, P phase or µ phase, which have a negative effect on the mechanical properties of the superalloy. Too high a rhenium concentration can also cause the formation of a secondary reaction zone in the superalloy under the underlayer, which has a negative effect on the mechanical properties of the superalloy. The addition of ruthenium makes it possible in particular to displace part of the rhenium in the γ' phase and to limit the formation of PTC.

The simultaneous addition of silicon and hafnium makes it possible to improve the resistance to hot oxidation of nickel-based superalloys by increasing the adhesion of the layer of alumina (Al ₂ O ₃ ) which forms on the surface. high temperature superalloy. This layer of alumina forms a passivation layer on the surface of the nickel-based superalloy and a barrier to the diffusion of oxygen coming from the exterior towards the interior of the nickel-based superalloy. However, it is possible to add hafnium without also adding silicon or conversely add silicon without also adding hafnium and still improve the resistance to hot oxidation of the superalloy.

Furthermore, the addition of chromium or aluminum makes it possible to improve the resistance to oxidation and to corrosion at high temperature of the superalloy. In particular, chromium is essential for increasing the hot corrosion resistance of nickel-based superalloys. However, too high a chromium content tends to reduce the solvus temperature of the γ' phase of the nickel-based superalloy, i.e. the temperature above which the γ' phase is completely dissolved in the γ matrix, which is undesirable. Also, the chromium concentration is between 3.0 to 5.0% by mass in order to maintain a high solvus temperature of the γ' phase of the nickel-based superalloy, for example greater than or equal to 1250° C. but also to avoid the formation of topologically compact phases in the γ matrix highly saturated with alloying elements such as rhenium, molybdenum or tungsten.

The addition of cobalt, which is an element close to nickel and which partially substitutes for nickel, forms a solid solution with the nickel in the γ matrix. Cobalt makes it possible to reinforce the γ matrix, to reduce susceptibility to PTC precipitation and ZRS formation in the superalloy under the protective coating. However, too high a cobalt content tends to reduce the solvus temperature of the γ' phase of the nickel-based superalloy, which is undesirable.

The addition of ruthenium makes it possible to reinforce the γ matrix and to reduce the sensitivity of the superalloy to the formation of PTC. The addition of ruthenium makes it possible in particular to displace part of the rhenium in the γ' phase and to limit the formation of PTC. The addition of ruthenium can also have a beneficial effect on the adhesion of the ceramic coating.

The addition of refractory elements, such as molybdenum, tungsten, rhenium or tantalum makes it possible to slow down the mechanisms controlling the creep of nickel-based superalloys and which depend on the diffusion of chemical elements in the superalloy.

A very low sulfur content in a nickel-based superalloy increases the 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 (part per million by mass), or even ideally less than 0.5 ppm by mass, makes it possible to optimize these properties. Such a mass content of sulfur can be obtained by producing a low-sulphur mother casting or by a desulfurization process carried out after casting. In particular, it is possible to maintain a low sulfur content by adapting the process for producing the superalloy.

Nickel-based superalloys are understood to mean superalloys in which the mass percentage of nickel is predominant. It is understood that nickel is therefore the element whose mass percentage in the alloy is the highest.

The superalloy may comprise, in mass percentages, 4.5 to 5.5% rhenium, 1.0 to 3.0 ruthenium, 3.0 to 5.0% cobalt, 0.30 to 0.80% molybdenum, 3.0-4.5% chromium, 2.5-4.0% tungsten, 4.5-6.5% aluminum, 0.50-1.50% titanium, 8.0 to 9.0% tantalum, 0.15 to 0.30% hafnium, preferably 0.17 to 0.30% hafnium, even more preferably 0.20 to 0.30% hafnium, 0.05 to 0.15% silicon, the balance consisting of nickel and inevitable impurities.

The superalloy may comprise, in mass percentages, 4.0 to 5.5% rhenium, 1.0 to 3.0 ruthenium, 3.0 to 13.0% cobalt, 0.40 to 1.00% molybdenum, 3.0-4.5% chromium, 2.5-4.0% tungsten, 4.5-6.5% aluminum, 0.50-1.50% titanium, 8.0 to 9.0% tantalum, 0.15 to 0.30% hafnium, preferably 0.17 to 0.30% hafnium, even more preferably 0.20 to 0.30% hafnium, 0.05 to 0.15% silicon, the balance consisting of nickel and inevitable impurities.

The superalloy may comprise, in mass percentages, 4.0 to 5.0% rhenium, 1.0 to 3.0 ruthenium, 11.0 to 13.0% cobalt, 0.40 to 1.00% molybdenum, 3.0-4.5% chromium, 2.5-4.0% tungsten, 4.5-6.5% aluminum, 0.50-1.50% titanium, 8.0 to 9.0% tantalum, 0.15 to 0.30% hafnium, preferably 0.17 to 0.30% hafnium, even more preferably 0.20 to 0.30% hafnium, 0.05 to 0.15% silicon, the balance consisting of nickel and inevitable impurities.

The superalloy may comprise, in mass percentages, 5.0% rhenium, 2.0 ruthenium, 4.0% cobalt, 0.50% molybdenum, 4.0% chromium, 3.0% tungsten, 5.4% aluminum, 1.00% titanium, 8.5% tantalum, 0.25% hafnium, 0.10% silicon, balance being nickel and unavoidable impurities.

The superalloy may comprise, in mass percentages, 5.0% rhenium, 2.0 ruthenium, 4.0% cobalt, 0.50% molybdenum, 4.0% chromium, 3.5% tungsten, 5.4% aluminum, 0.90% titanium, 8.5% tantalum, 0.25% hafnium, 0.10% silicon, the balance being made up of nickel and inevitable impurities.

The superalloy may comprise, in mass percentages, 4.4% rhenium, 2.0 ruthenium, 4.0% cobalt, 0.70% molybdenum, 4.0% chromium, 3.0% tungsten, 5.4% aluminum, 1.00% titanium, 8.5% tantalum, 0.25% hafnium, 0.10% silicon, balance being nickel and unavoidable impurities.

The superalloy may comprise, in mass percentages, 4.4% rhenium, 2.0 ruthenium, 12.0% cobalt, 0.70% molybdenum, 4.0% chromium, 3.0% tungsten, 5.4% aluminum, 1.00% titanium, 8.5% tantalum, 0.25% hafnium, 0.10% silicon, the balance consisting of nickel and inevitable impurities.

The superalloy may comprise, in mass percentages, 5.0% rhenium, 2.0 ruthenium, 4.0% cobalt, 0.50% molybdenum, 3.5% chromium, 3.5% tungsten, 5.4% aluminum, 0.90% titanium, 8.5% tantalum, 0.25% hafnium, 0.10% silicon, the balance being made up of nickel and inevitable impurities.

The superalloy may comprise, in mass percentages, 4.4% rhenium, 2.0 ruthenium, 12.0% cobalt, 0.70% molybdenum, 3.5% chromium, 3.5% tungsten, 5.4% aluminum, 0.90% titanium, 8.5% tantalum, 0.25% hafnium, 0.10% silicon, the balance being made up of nickel and inevitable impurities.

This presentation also relates to a single-crystal blade for a turbomachine comprising a superalloy as defined above.

This blade therefore has an improved resistance to creep at high temperature.

The blade may include a protective coating comprising a metal underlayer deposited on the superalloy and a ceramic thermal barrier deposited on the metal underlayer.

Thanks to the composition of the nickel-based superalloy, the formation of a secondary reaction zone in the superalloy resulting from interdiffusion phenomena between the superalloy and the underlayer is avoided, or limited.

The metallic underlayer can be an alloy of the MCrAlY type or an alloy of the nickel aluminide type.

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

The dawn may have a structure oriented along a <001> crystallographic direction.

This orientation generally gives the blade the optimum mechanical properties.

This presentation also relates to a turbomachine comprising a blade as defined above.

Brief description of the drawings

• la figure 1 est une vue schématique en coupe longitudinale d'une turbomachine ;
• la figure 2 est un graphique représentant le paramètre NFP (No-Freckles Parameter) pour différents superalliages ;
• la figure 3 est un graphique représentant la fraction volumique de phase γ' à différentes températures et pour différents superalliages.

Other characteristics and advantages of the invention will emerge from the following description of embodiments of the invention, given by way of non-limiting examples, with reference to the single appended FIGURE, in which:

• there figure 1 is a schematic view in longitudinal section of a turbomachine;
• there picture 2 is a graph representing the NFP (No-Freckles Parameter) parameter for various superalloys;
• there picture 3 is a graph representing the volume fraction of γ' phase at different temperatures and for different superalloys.

Detailed description of the invention

Nickel-based superalloys are intended for the manufacture of single-crystal blades by a directed solidification process in a thermal gradient. The use of a monocrystalline seed or of a grain selector at the start of solidification makes it possible to obtain this monocrystalline structure. The structure is oriented for example along a crystallographic direction <001> which is the orientation which generally confers the optimum mechanical properties on the superalloys.

As-solidified nickel-based single-crystal superalloys have a dendritic structure and consist of γ' Ni ₃ (Al, Ti, Ta) precipitates dispersed in a γ matrix of face-centered cubic structure, nickel-based solid solution. These γ' phase precipitates are distributed heterogeneously in the volume of the single crystal due to chemical segregations resulting from the solidification process. Furthermore, γ/γ' eutectic phases are present in the inter-dendritic regions and constitute preferential crack initiation sites. These γ/γ' eutectic phases are formed at the end of solidification. In addition, the γ/γ' eutectic phases are formed to the detriment of the fine precipitates (size less than a micrometer) of the γ' hardening phase. These γ' phase precipitates constitute the main source of hardening of nickel-based superalloys. Also, the presence of residual γ/γ' eutectic phases does not make it possible to optimize the hot creep resistance of the nickel-based superalloy.

It has in fact been shown that the mechanical properties of superalloys, in particular the creep resistance, were optimal when the precipitation of the γ' precipitates was ordered, that is to say that the γ' phase precipitates are aligned in a manner regular, with a size ranging from 300 to 500 nm, and when all of the γ/γ' eutectic phases were returned to solution.

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 which aims to dissolve the γ′ phase precipitates and to eliminate the γ/γ′ eutectic phases or to significantly reduce their volume fraction. This treatment is carried out at a temperature above the solvus temperature of the γ' phase and below the starting melting temperature of the superalloy (T _solidus ). Quenching is then carried out at the end of this first heat treatment to obtain a fine and homogeneous dispersion of the γ' precipitates. Tempering heat treatments are then carried out in two stages, at temperatures below the solvus temperature of the γ' phase. During a first step, to make the γ′ precipitates grow and obtain the desired size, then during a second step, to increase the volume fraction of this phase to about 70% at room temperature.

There figure 1 represents, in section along a vertical plane passing through its main axis A, a turbofan engine 10. The turbofan engine 10 comprises, from upstream to downstream according to the circulation of the air flow, a fan 12, a compressor low pressure 14, a high pressure compressor 16, a combustion chamber 18, a high pressure turbine 20, and a low pressure turbine 22.

The high pressure turbine 20 comprises a plurality of moving vanes 20A rotating with the rotor and stator vanes 20B (fixed vanes) mounted on the stator. The stator of the turbine 20 comprises a plurality of stator rings 24 arranged opposite the moving blades 20A of the turbine 20.

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

It is therefore possible to manufacture a moving blade 20A or a stator 20B for a turbomachine comprising a superalloy as defined above.

It is also possible to manufacture a moving blade 20A or a stator 20B for a turbomachine comprising a superalloy as defined previously coated with a protective coating comprising a metal sub-layer

A turbomachine can in particular be a turbojet engine such as a turbofan engine 10. The turbomachine can also be a single-flow turbojet engine, a turboprop engine or a turboshaft engine.

Examples

Six nickel-based monocrystalline superalloys of this presentation (Ex 1 to Ex 6) were studied and compared to six commercial monocrystalline superalloys CMSX-4 (Ex 7), CMSX-4PlusC (Ex 8), René N6 (Ex 9), CMSX-10 (Ex 10), MC-NG (Ex 11) and TMS-138 (Ex 12). The chemical composition of each of the single-crystal superalloys is given in table 1, the Ex 9 composition also comprising 0.05% by mass of carbon (C) and 0.004% by mass of boron (B), the Ex 10 composition also comprising in addition to 0.10% by mass of niobium (Nb). All these superalloys are nickel-based superalloys, that is to say that 100% of the compositions presented consist of nickel and inevitable impurities. Table 1 D Ru Co MB CR W Al You Your Off Whether Ex 1 5.0 2.0 4.0 0.50 4.0 3.0 5.4 1.00 8.5 0.25 0.10 Ex 2 5.0 2.0 4.0 0.50 4.0 3.5 5.4 0.90 8.5 0.25 0.10 Ex 3 4.4 2.0 4.0 0.70 4.0 3.0 5.4 1.00 8.5 0.25 0.10 Ex 4 4.4 2.0 12.0 0.70 4.0 3.0 5.4 1.00 8.5 0.25 0.10 Ex 5 5.0 2.0 4.0 0.50 3.5 3.5 5.4 0.90 8.5 0.25 0.10 Ex 6 4.4 2.0 12.0 0.70 3.5 3.5 5.4 0.90 8.5 0.25 0.10 Ex 7 3.0 0.0 9.6 0.60 6.6 6.4 5.6 1.00 6.5 0.10 0.00 Ex 8 4.8 0.0 10.0 0.60 3.5 6.0 5.7 0.85 8.0 0.10 0.00 Ex 9 5.3 0.0 12.2 1.10 4.4 5.7 6.0 0.00 7.5 0.15 0.00 Ex 10 6.0 0.0 3.0 0.40 2.0 5.0 5.7 0.20 8.0 0.03 0.00 Ex 11 4.0 4.0 0.0 1.00 4.0 5.0 6.0 0.50 5.0 0.10 0.10 Ex 12 4.9 2.0 5.9 2.9 2.9 5.9 5.9 0.00 5.5 0.10 0.00

Volumic mass

• où D₁ = 100/[(%Cr/D_Cr) + (%Ni/D_Ni)+ .... + (%X/D_X)]
• où D_Cr, D_Ni,..., D_X sont les masses volumiques des éléments Cr, Ni, ..., X exprimées en Ib/in³ (livre par pouce cube) et D est la masse volumique du superalliage exprimé en g/cm³.
• où %Cr, %Ni, ...%X sont les teneurs, exprimées en pourcentages massiques, des éléments du superalliage Cr, Ni, ..., X.

The room temperature density of each superalloy was estimated using a modified version of Hull's formula ( FC Hull, Metal Progress, November 1969, pp139-140 ). This empirical equation was proposed by Hull. The empirical equation is based on the law of mixtures and includes corrective terms deduced from a linear regression analysis of experimental data (chemical compositions and measured densities) concerning 235 superalloys and stainless steels. This Hull formula has been modified, in particular to take into account elements such as rhenium and ruthenium. The modified Hull formula is: $$\mathrm{D}=27.68\times \left[\begin{array}{l}{\mathrm{<figure-callout\; id="1"\; label="D"\; filenames="imgf0002.png"\; state="\{\{state\}\}">D</figure-callout>}}_1+0.14037-0.00137\%\mathrm{CR}-0.00139\%\mathrm{Neither}-\\ 0.00142\%\mathrm{Co}-0.00140\%\mathrm{Fe}-0.00186\%\mathrm{Mo}-0.00125\%\mathrm{W}-0.00134\\ \%\mathrm{V}-0.00119\%\mathrm{Number}-0.00113\%\mathrm{Your}+0.0004\%\mathrm{You}+0.00388\%\mathrm{VS}+\\ 0.0000187{\left(\mathrm{<figure-callout\; id="2"\; label="\%\; Mo"\; filenames="imgf0002.png"\; state="\{\{state\}\}">\%</figure-callout>}\mathrm{Mo}\right)}^2-0.0000506\left(\%\mathrm{Co}\right)\times \left(\%\mathrm{You}\right)-0.00096\%D-0.001131\\ \%\mathrm{Ru}\end{array}\right]$$

• where D ₁ = 100/[(%Cr/D _Cr ) + (%Ni/D _Ni )+ .... + (%X/D _X )]
• where D _Cr , D _Ni ,..., D _X are the densities of the elements Cr, Ni, ..., X expressed in Ib/in ³ (pounds per cubic inch) and D is the density of the superalloy expressed in g/cm ³ .
• where %Cr, %Ni, ...%X are the contents, expressed in mass percentages, of the superalloy elements Cr, Ni, ..., X.

The densities calculated for the alloys of the disclosure and for the reference alloys are less than 9.00 g/cm ³ (see table 2).

The comparison between the estimated and measured densities (see table 2) makes it possible to validate the modified Hull model (equation (1)). Estimated and measured densities are consistent.

Table 2 presents different parameters for Ex 1 to Ex 12 superalloys. Table 2 Estimated density (1) (g/cm ³ ) Measured density (g/cm ³ ) NFP RGP M d Ex 1 8.89 - 0.96 0.380 0.98 Ex 2 - - 0.91 0.376 - Ex 3 8.85 - 1.05 0.380 0.98 Ex 4 8.83 - 1.05 0.380 0.98 Ex 5 8.91 8.8 0.91 0.376 0.98 Ex 6 8.86 - 1.00 0.376 0.98 Ex 7 8.71 - 0.65 0.358 0.99 Ex 8 8.91 - 0.68 0.371 0.99 Ex 9 8.87 - 0.69 0.256 0.98 Ex 10 8.99 - 0.67 0.299 0.96 Ex 11 8.75 8.75 0.55 0.232 0.97 Ex 12 8.88 - 0.61 0.215 0.97

No-Freckles Parameter (NFP)

où %Cr, %Ni, ...%X sont les teneurs, exprimées en pourcentages massiques, des éléments du superalliage Cr, Ni, ..., X. $$\mathrm{NFP}=\left[\%\mathrm{Your}+1.5\%\mathrm{Off}+0.5\mathrm{\%MB}-0.5\%\%\mathrm{You})\right]/\left[\begin{array}{l}\%\mathrm{W}+1.2\\ \%D)\end{array}\right]$$

where %Cr, %Ni, ...%X are the contents, expressed in mass percentages, of the superalloy elements Cr, Ni, ..., X.

The NFP parameter makes it possible to quantify the sensitivity to the formation of parasitic grains of the "Freckles" type during the directed solidification of the part (document US 5,888,451 ). To avoid the formation of “Freckles” type faults, the NFP parameter must be greater than or equal to 0.7.

As can be seen in Table 2 and in the figure 2 , the Ex 1 to Ex 6 superalloys all have an NFP parameter greater than or equal to 0.7, whereas commercial superalloys Ex 7 to Ex 12 have an NFP parameter of less than 0.7.

Resistance Gamma Prime (RGP)

où C_Ti, C_Ta, C_W et C_Al sont les concentrations, exprimées en pourcentage atomique, respectives des éléments Ti, Ta, W et AI dans le superalliage.The intrinsic mechanical strength of the γ' phase increases with the content of elements replacing the aluminum in the Ni ₃ Al compound, such as titanium, tantalum and part of the tungsten. The γ' phase compound can therefore be written as Ni ₃ (Al, Ti, Ta, W). The RGP parameter makes it possible to estimate the level of hardening of the γ' phase: $$\mathrm{RGP}=\left[{\mathrm{VS}}_{\mathrm{You}}+{\mathrm{VS}}_{\mathrm{Your}}+\left({\mathrm{VS}}_{\mathrm{W}}/2\right)\right]/{\mathrm{VS}}_{\mathrm{Al}}$$

where C _Ti , C _Ta , C _W and C _Al are the respective concentrations, expressed in atomic percentages, of the elements Ti, Ta, W and Al in the superalloy.

A higher RGP parameter is favorable to a better mechanical strength of the superalloy. It can be seen in Table 2 that the calculated RGP parameter for Ex 1 to Ex 6 superalloys is higher than the calculated RGP parameter for Ex 7 to Ex 12 commercial superalloys.

Susceptibility to PTC formation ( M̅ d)

où X_i est la fraction de l'élément i dans le superalliage exprimée en pourcentage atomique, (Md)_i est la valeur du paramètre Md pour l'élément i.The parameter M d is defined as if: $$\bar{M}d={\displaystyle {\sum }_{I=1}^{\mathrm{not}}{X}_I}{\left(\mathit{md}\right)}_I$$

where X _i is the fraction of element i in the superalloy expressed in atomic percentage, (Md) _i is the value of the Md parameter for element i.

Table 3 presents the Md values for the different elements of the superalloys. Table 3 Element md Element md You 2,271 Off 3.02 CR 1,142 Your 2,224 Co 0.777 W 1,655 Neither 0.717 D 1,267 Number 2,117 HAVE 1.9 Mo 1.55 Whether 1.9 Ru 1.006

The sensitivity to PTC formation is determined by the parameter M d, according to the New PHACOMP method which was developed by Morinaga et al. ( Morinaga et al., New PHACOMP and its application to alloy design, Superalloys 1984, edited by M Gell et al., The Metallurgical Society of AIME, Warrendale, PA, USA (1984) pp. 523-532 ). According to this model, the sensitivity of superalloys to the formation of PTC increases with the value of the parameter M d.

As can be seen in table 2, the superalloys Ex 1 to Ex 12 present values of the parameter M d substantially equal. These superalloys therefore exhibit similar sensitivities to the formation of PTC, sensitivities which are relatively low.

Solvus temperature of the γ' phase

The ThermoCalc software (Ni25 database) based on the CALPHAD method was used to calculate the solvus temperature of the γ' phase at equilibrium.

As can be seen in Table 4, the Ex 1 to Ex 6 superalloys exhibit a high γ' solvus temperature, comparable to the γ' solvus temperature of commercial superalloys Ex 7 to Ex 12.

Phase volume fraction γ'

The ThermoCalc software (Ni25 database) based on the CALPHAD method was used to calculate the volume fraction (in volume percentage) of γ' phase at equilibrium in Ex 1 to Ex 12 superalloys at 950°C, 1050° C and 1200°C.

As can be seen in Table 4 and in the picture 3 , Ex 1 to Ex 6 superalloys contain volume fractions of γ' phase greater than or comparable to the volume fractions of γ' phase of commercial superalloys Ex 7 to Ex 12.

Thus, the combination of a high γ' solvus temperature and high γ' phase volume fractions for Ex 1 to Ex 6 superalloys is favorable to good creep resistance at high temperature and very high temperature, for example at 1200 °C. This resistance must therefore be greater than the creep resistance of commercial superalloys Ex 7 to Ex 12. Table 4 T _solvus γ' (°C) Volume fraction of γ' phase (% vol) 950°C 1050°C 1200°C Ex 1 1338 67.0 62.0 46.0 Ex 2 1335 67.6 62.4 45.9 Ex 3 1337 66.6 61.1 43.2 Ex 4 1276 60.0 51.2 22.7 Ex 5 1344 65.0 60.0 46.0 Ex 6 1295 58.0 50.0 38.0 Ex 7 1290 58.0 48.0 25.0 Ex 8 1320 63.0 57.0 36.0 Ex 9 1283 60.0 51.0 24.0 Ex 10 1374 65.0 60.0 46.0 Ex 11 1348 68.0 62.0 45.0 Ex 12 1321 67.0 58.0 35.0

Volume fraction of σ-type PTC

The ThermoCalc software (Ni25 database) based on the CALPHAD method was used to calculate the volume fraction (in volume percentage) of phase σ at equilibrium in Ex 1 to Ex 12 superalloys at 950°C and 1050°C (see Table 5).

The calculated phase volume fractions σ are zero at 950°C for the Ex 3, Ex 4 and Ex 6 superalloys, and relatively low for the Ex 1 and Ex 5 superalloys, which reflects a low sensitivity to PTC precipitation. These results therefore corroborate the results obtained with the New PHACOMP method (parameter M d).

Mass concentration of chromium dissolved in the matrix γ

The ThermoCalc software (Ni25 database) based on the CALPHAD method was used to calculate chromium content (in mass percentage) in the equilibrium γ phase in Ex 1 to Ex 12 superalloys at 950°C, 1050° C and 1200°C.

As can be seen in Table 5, the chromium concentrations in the γ phase for the Ex 1 to Ex 6 superalloys are comparable to the chromium concentrations in the γ phase for the commercial superalloys Ex 7 to Ex 12, which is favorable good resistance to corrosion and hot oxidation. Table 5 Volume fraction of σ-type PTC (in % vol) Chromium content in the γ phase (in % by mass) 950°C 1050°C 950°C 1050°C 1200°C Ex 1 0.4 0.00 8.80 7.80 6.00 Ex 2 0.00 0.00 11.30 9.90 7.30 Ex 3 0.0 0.00 8.50 7.60 5.80 Ex 4 0.0 0.00 8.10 5.50 4.80 Ex 5 0.7 0.05 8.70 7.90 6.30 Ex 6 0.0 0.00 8.10 7.00 5.20 Ex 7 0.7 0.00 12.80 10.90 7.84 Ex 8 1.2 0.50 7.40 6.43 4.82 Ex 9 1.0 0.25 8.37 7.10 5.25 Ex 10 0.9 0.40 3.62 3.36 2.77 Ex 11 0.8 0.20 7.83 7.10 5.70 Ex 12 0.4 0.60 5.60 4.80 3.70

Creep property at very high temperature

Creep tests were carried out on Ex 2, Ex 7, Ex 9 and Ex 10 superalloys. Creep tests are carried out at 1200°C and 80 MPa according to standard NF EN ISO 204 of August 2009 (Guide U125_J) .

Table 6 presents the results of the creep tests in which the superalloys were loaded (80 MPa) at 1200°C. The results represent the time in hours (h) to the rupture of the specimen. Table 6 Breaking time (hour) Ex 2 63 Ex 7 7 Ex 9 9 Ex 10 59

The Ex 2 superalloy exhibits better creep behavior than the Ex 7 and Ex 9 superalloys. The Ex 10 superalloy also exhibits good creep properties.

Property in cyclic oxidation at 1150°C

Superalloys are subjected to one of the thermal cycles as described in INS-TTH-001 and INS-TTH-002: Oxidative Cycling Test Method (Mass Loss Test and Thermal Barrier).

A specimen of the superalloy tested (pawn having a diameter of 20 mm and a height of 1 mm) is subjected to thermal cycling, each cycle of which includes a rise to 1150°C in less than 15 min (minutes), a plateau at 1150° C for 60 min and turbine cooling of the specimen for 15 min.

The thermal cycle is repeated until a loss in mass of the specimen equal to 20 mg/cm ² (milligrams per square centimeters) is observed.

The service life of the superalloys tested is presented in Table 7. Table 7 Lifespan (hours) Ex 2 > 1700 Ex 7 ∼ 230 Ex 8 ∼ 480 Ex 10 ∼ 100

It can be seen that the Ex 2 superalloy has a much longer service life than that of the Ex 7, Ex 8 and Ex 9 superalloys. It will be noted that the oxidation properties of the Ex 10 superalloy are much worse than those of the Ex 2 superalloy.

Microstructural stability

After aging for 300 hours at 1050° C., no PTC phase is observed for the Ex 2 superalloy by scanning electron microscopy image analysis.

Sensitivity to the formation of foundry defects

After shaping by the lost wax type process and controlled solidification in a Bidgman furnace, no defects resulting from the foundry process, in particular of the "Freckles" type, were observed in the Ex 2 superalloy. » are observed after immersion of the specimen in a solution based on HNO ₃ /H ₂ SO ₄ .

Although the present disclosure has been described with reference to a specific embodiment, it is obvious that different modifications and changes can be made to these examples without departing from the general scope of the invention as defined by the claims. Further, individual features of the various embodiments discussed may be combined in additional embodiments. Accordingly, the description and the drawings should be considered in an illustrative rather than restrictive sense.

Claims (14)

1. A nickel-based superalloy comprising, in percentages by mass, 4.0 to 5.5% rhenium, 1.0 to 3.0% ruthenium, 2.0 to 14.0% cobalt, 0.30 to 1.00% molybdenum, 3.0 to 5.0% chromium, 2.5 to 4.0% tungsten, 4.5 to 6.5% aluminum, 0.50 to 1.50% titanium, 8.0 to 9.0% tantalum, 0.15 to 0.30% hafnium, 0.05 to 0.15% silicon, the balance being nickel and unavoidable impurities.
2. The superalloy according to claim 1, comprising, 4.5 to 5.5% rhenium, 3.0 to 5.0% cobalt, 0.30 to 0.80% molybdenum and 3.0 to 4.5% chromium.
3. The superalloy according to claim 1, comprising, 3.0 to 13.0% cobalt, 0.40 to 1.00% molybdenum et 3.0 to 4.5% chromium.
4. The superalloy according to claim 3, comprising, 4.0 to 5.0% rhenium et 11.0 to 13.0% cobalt.
5. The superalloy according to claim 3, comprising, 5.0% rhenium, 2.0% ruthenium, 4.0% cobalt, 0.50% molybdenum, 4.0% chromium, 3.0% tungsten, 5.4% aluminum, 1.00% titanium, 8.5% tantalum, 0.25% hafnium et 0.10% silicon.
6. The superalloy according to claim 3, comprising, 4.4% rhenium, 2.0% ruthenium, 4.0% cobalt, 0.70% molybdenum, 4.0% chromium, 3.0% tungsten, 5.4% aluminum, 1.00% titanium, 8.5% tantalum, 0.25% hafnium et 0.10% silicon.
7. The superalloy according to claim 4, comprising, 4.4% rhenium, 2.0% ruthenium, 12.0% cobalt, 0.70% molybdenum, 4.0% chromium, 3.0% tungsten, 5.4% aluminum, 1.00% titanium, 8.5% tantalum, 0.25% hafnium et 0.10% silicon.
8. The superalloy according to claim 3, comprising, 5.0% rhenium, 2.0% ruthenium, 4.0% cobalt, 0.50% molybdenum, 3.5% chromium, 3.5% tungsten, 5.4% aluminum, 0.90% titanium, 8.5% tantalum, 0.25% hafnium et 0.10% silicon.
9. The superalloy according to claim 3, comprising, 5.0% rhenium, 2.0% ruthenium, 4.0% cobalt, 0.50% molybdenum, 4.0% chromium, 3.5% tungsten, 5.4% aluminum, 0.90% titanium, 8.5% tantalum, 0.25% hafnium et 0.10% silicon.
10. The superalloy according to claim 4, comprising, 4.4% rhenium, 2.0% ruthenium, 12.0% cobalt, 0.70% molybdenum, 3.5% chromium, 3.5% tungsten, 5.4% aluminum, 0.90% titanium, 8.5% tantalum, 0.25% hafnium et 0.10% silicon.
11. A single-crystal blade (20A, 20B) for a turbomachine comprising a superalloy according to any one of claims 1 to 10.
12. The blade (20A, 20B) according to claim 11, comprising a protective coating comprising a metallic bond coat deposited on the superalloy and a ceramic thermal barrier deposited on the metallic bond coat.
13. The blade (20A, 20B) according to claim 11 or 12, having a structure oriented in a <001> crystallographic direction.
14. A turbomachine comprising a blade (20A, 20B) according to any one of claims 11 to 13.

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