The present disclosure relates to nickel base superalloys for gas turbines, especially for vanes, also called dispensers or rectifiers, or mobile gas turbine, for example in the field of aeronautics.
[0002] It is known to use nickel-based superalloys for the manufacture of monocrystalline blades fixed or mobile gas turbine engines for aircraft or helicopter.
[0003] These materials have the major advantages of combining both resistance to high temperature and a high creep resistance to oxidation and corrosion.
[0004] Over time, the nickel-based superalloys for monocrystalline blades have undergone significant changes in chemical composition, in order in particular to improve their high-temperature creep properties while retaining resistance to environmental very aggressive in which these superalloys are used.
[0005] Moreover, metallic coatings suitable for these alloys were developed in order to increase their resistance to the aggressive environment in which these alloys are used, in particular resistance to oxidation and corrosion resistance. In addition, a low thermal conductivity ceramic coating having a function as a thermal barrier may be added to reduce the surface temperature of the metal.
[0006] Typically, a complete protection system comprises at least two layers.
[0007] The first layer, also known as undercoat or bond layer is directly deposited on the part to be protected in superailiage based on nickel, also called substrate, eg a blade. The deposition step is followed by a diffusion step of the underlayer in the superalloy. The filing and dissemination can also be made in a single step.
[0008] generally the materials used to carry out this sub-layer include metal alloys aluminoformeurs type MCrAlY (M = Ni (nickle) or Co (cobalt) or a mixture of Ni and Co, Cr = chromium, Al = aluminum and Y = yttrium) or aluminide-type alloys of nickel (Ni x Al y ), some also containing platinum (NixAlyPy.
[0009] The second layer, generally referred to as thermal barrier or "TBC" according to the English acronym for "Thermal Barrier Coating" is a ceramic coating comprising for example yttria-stabilized zirconia, also referred to as "YSZ" in accordance with Acronym English for "Yttria Stabilized Zirconia" or "YPSZ" according to the English acronym for "Yttria Partially Stabilized Zirconia" and having a porous structure. This layer may be deposited by various methods, such as evaporation under electron beam ( "EB-PVD" according to the English acronym for "electron beam physical vapor deposition"), thermal spraying ( "APS" in accordance with the acronym for "Atmospheric Plasma Spraying"), "SPS" in accordance with
[0010] Due to the use of these materials at high temperatures, e.g. 650 ° C to 1150 ° C, there occurs the inter-diffusion phenomena at the microscopic level between the nickel-based superalloy substrate and the metal alloy of the underlayer. These inter-diffusion phenomena, associated with the oxidation of the undercoat, including changing the chemical composition, microstructure, and consequently the mechanical properties of the underlayer during manufacture of the coating, and during the use of the blade in the turbine. These inter-diffusion phenomena also change the chemical composition, microstructure and consequently the mechanical properties of the superalloy substrate. In superalloys highly charged with refractory elements, particularly rhenium, it can thus be formed in the superalloy in the underlayer a secondary reaction zone (ZRS) to a depth of several tens or even hundreds of micrometers. The mechanical characteristics of this ZRS are significantly lower than those of the superalloy substrate. The formation of ZRS is undesirable because it leads to a significant reduction in the strength of the superalloy.

[0011] These changes in the link layer associated with stress fields related to the growth of the alumina layer that forms in use on the surface of the binding layer, also called "TGO" under Acronym English for "thermally Grown Oxide", and differences in thermal expansion coefficients between different layers, generate decohesions in the interfacial region between the undercoat and the ceramic coating, which can lead to the partial or total coating flaking ceramic. The metal part (superalloy substrate and underlayer metal) is then laid bare and exposed directly to the combustion gases, which increases the risk of damage of the blade and thus of the gas turbine.

OBJECT AND SUMMARY OF THE INVENTION

[0012] The present disclosure aims to provide compositions of nickel-based superalloys for the fabrication of monocrystalline components, showing the mechanical characteristics at very high temperatures higher than those of existing alloys, and promoting resistance to flaking of the barrier thermal.

[0013] To this end, the present disclosure relates to a nickel-base superalloy comprising in percentages by weight, 4.0 to 6.0% chromium, 0.4 to 0.8% molybdenum, 2.5 to 3 , 5% rhenium, 6.2 to 6.6% tungsten, 5.2 to 5.7% aluminum, 0.0 to 1.6% titanium and 6 to 9.9% tantalum, 0 to 0.7% hafnium, 0.0 to 0.3% silicon, the balance being nickel and incidental impurities.

[0014] This superalloy is for the manufacture of single crystal gas turbine components, such as fixed or movable blades.

[0015] With this composition of the nickel-base superalloy (Ni), the creep strength is improved compared to existing superalloys, in particular at temperatures up to 1200 ° C and the adhesion of the thermal barrier is enhanced compared to that observed on existing superalloys.

[0016] The alloy therefore has a resistance to improved high temperature creep. The life of this alloy being so long, this alloy also exhibits corrosion resistance and improved oxidation. This alloy can also have improved thermal fatigue resistance.

[0017] A single crystal piece of nickel-base superalloy is obtained by a solidification process conducted under thermal gradient casting using the lost wax. Monocrystalline superalloy based on nickel comprises an austenitic matrix structure face-centered cubic, solid solution based on nickel, called gamma ( "γ"). This matrix contains the hardening gamma prime phase precipitates ( "γ '") in an ordered cubic structure Ll 2 type Ni 3 AI. The assembly (matrix and precipitates) is described as a superalloy γ / γ '.

[0018] Par ailleurs, this composition du superalliage made from nickel autorise the mise en oeuvre d'un traitement thermique here remet Totalement solution in les précipités of phase γ 'phases and eutectiques γ / γ' here if forment lors de la solidification du superalliage. On peut obtenir ainsi a superalliage Monocristallin made from nickel containing des précipités γ 'de taille contrôlée, de préférence comprise between 300 and 500 nanometers (nm), and exempts eutectiques phases of γ / γ'.

[0019] The heat treatment also can control the volume fraction of the γ phase precipitates' present in the monocrystalline superalloy based on nickel. The percentage by volume of phase precipitates γ 'may be greater than or equal to 50%, preferably greater than or equal to 60%, even more preferably equal to 70%.

[0020] The addition of tungsten (W), chromium (Cr), rhenium (Re) or molybdenum (Mo) is used primarily to enhance the γ austenitic matrix by solid solution hardening.

[0021] The addition of aluminum (Al), de titane (I) or of tantale (Ta) favorecedor the precipitation of the γ'-phase durcissante ΝΪ3 (ΑΙ, Ti, Ta).

[0022] The rhenium (Re) rallentare Permet de la diffusion des espèces Rooms au sein du superalliage limiter and the coalescence des précipités of phase γ 'en cours de service high-temperature, linguistic here entraîne une réduction de la résistance mécanique. The rhenium permet ainsi d'améliorer la résistance in high-temperature creep du superalliage made from nickel. Toutefois, a concentration of rhenium élevée trop peut entrainer the Precipitation of phases intermétalliques, par exemple σ phase, phase or phase P μ,

with a compact topology, also called TCP phases under the acronym for "Topologically Close-Packed", which have a negative effect on the mechanical properties of the superalloy. A too high concentration of rhenium may also cause the formation of a secondary reaction zone in the superalloy in the underlayer, which has a negative effect on the mechanical properties of the superalloy.

[0023] The simultaneous addition of silicon (Si) and hafnium (Hf) improves the resistance to hot oxidation of nickel-base superalloys by increasing the adhesion of the layer of alumina (Al 2 0 3 ) which forms the high-temperature superalloy surface. This alumina layer forms a passivation layer on the surface of nickel-base superalloy and a barrier to the diffusion of oxygen from the outside to the inside of the nickel-base superalloy. However, also can be added without adding hafnium silicon or conversely adding silicon without also adding hafnium and still improve the resistance to hot oxidation of the superalloy.

[0024] Furthermore, the addition of chromium or aluminum improves the resistance to oxidation and corrosion at high temperature of the superalloy. In particular, chromium is essential for increasing the resistance to hot corrosion of nickel-base superalloys. However, an excessively high chromium content tends to reduce the solvus temperature of the gamma prime phase nickel base superalloy, that is to say the temperature above which the gamma prime phase is completely dissolved in the y matrix, which is undesirable. Also, the chromium concentration is between 4.0 to 6.0 mass% in order to maintain a high solvus temperature of the gamma prime phase nickel base superalloy,

[0025] The addition of refractory elements such as molybdenum, tungsten, rhenium or tantalum slows the mechanisms controlling the flow of nickel-based superalloys and which depend on the diffusion of chemical elements in the superalloy .

[0026] Note also that the nickel-base superalloy includes no cobalt (Co) element that has the effect of reducing the solvus temperature of the γ-phase.

[0027] By impurities is meant chemical elements present in the undesirably metal and in small quantities, for example, elements having a lower mass concentration or equal to 0.05%.

[0028] The term superalloys based on nickel, superalloys which the percentage by mass of nickel is majority. It is understood that the nickel is the element whose weight percentage in the alloy is the highest.

[0029] The superalloy may comprise, in percentages by weight, 4.8 to 5.2% chromium, 0.4 to 0.8% molybdenum, 2.8 to 3.2% rhenium, 6.2 to 6 , 6% tungsten, 5.2 to 5.7% aluminum, 0.8 to 1.2% titanium, 6.3 to 9.2% tantalum, 0.3 to 0.7% of hafnium , 0.0 to 0.3% silicon, the balance being nickel and incidental impurities.

[0030] The superalloy may comprise, in percentages by weight, 4.8 to 5.2% chromium, 0.4 to 0.8% molybdenum, 2.8 to 3.2% rhenium, 6.2 to 6 , 6% tungsten, 5.2 to 5.7% aluminum, 0.0 to 1.5% titanium, 6.3 to 6.7% tantalum, 0.3 to 0.7% of hafnium , 0.0 to 0.3% silicon, the balance being nickel and incidental impurities.

[0031] The superalloy may comprise, in percentages by weight, 4.8 to 5.2% chromium, 0.4 to 0.8% molybdenum, 2.8 to 3.2% rhenium, 6.2 to 6 , 6% tungsten, 5.2 to 5.7% aluminum, 0.0 to 0.5% titanium, 8.8 to 9.2% tantalum, 0.3 to 0.7% of hafnium , 0.0 to 0.3% silicon, the balance being nickel and incidental impurities.

[0032] The superalloy may comprise, in percentages by weight, 5% chromium, 0.6% molybdenum, 3% rhenium, 6.4% tungsten, 5.5% aluminum, 1% titanium, 6 , 5% tantalum, 0.5% hafnium, 0.0 to 0.1% silicon, the balance being nickel and incidental impurities.

[0033] The superalloy may comprise, in percentages by weight, 5% chromium, 0.6% molybdenum, 3% rhenium, 6.4%

tungsten, 5.5% aluminum, 9% tantalum, 0.5% hafnium, 0.0 to 0.1% silicon, the balance being nickel and incidental impurities.

[0034] The present disclosure also relates to a single crystal blade for a turbomachine comprising a superalloy as defined above.

[0035] The vane therefore has an improved resistance to high temperature creep.

[0036] The blade may comprise a protective coating comprising a metallic sub-layer deposited on the superalloy article and a ceramic thermal barrier deposited on the metal underlayer.

[0037] Thanks to the composition of the nickel-base superalloy, the inter-diffusion phenomena between the superalloy and the underlayer reduces or do not lead to the formation of a secondary reaction zone in the superalloy.

[0038] Thanks to the composition of the nickel-base superalloy, the chipping resistance of the thermal barrier to the blade is enhanced compared with the case of nickel-based superalloys vanes of the prior art.

[0039] The metallic sub-layer may be a MCrAlY type alloy or aluminide type alloys of nickel.

[0040] The ceramic thermal barrier can be a zirconia-based material or any other yttria ceramic coating (zirconia-based) low thermal conductivity.

[0041] The blade may have an oriented structure according to a crystallographic direction <001>.

[0042] This approach generally provides optimum mechanical properties at dawn.

[0043] The present disclosure also relates to a turbomachine including a blade as defined above.

Brief Description of Drawings

[0044] Other features and advantages of the invention will become apparent from the following description of embodiments of the invention, given as non-limiting examples, in reference to the single appended figure, in which:

- Figure 1 is a schematic view in longitudinal section of a turbomachine.

Detailed Description of the Invention

[0045] nickel-based superalloys are designed for the manufacture of monocrystalline blades with a solidification process conducted in a thermal gradient. The use of a monocrystalline seed or a grain selector at the beginning of solidification allows to obtain the single crystal structure. The structure is oriented for example in a crystallographic direction <001> direction which is the orientation which gives, in general, optimum mechanical properties superalloys.

[0046] The monocrystalline superalloys based on nickel raw solidification have a dendritic structure and are constituted by precipitated γ 'Ni 3(AI, Ti, Ta) disperses in a matrix structure of γ cubique to centrées faces, solid solution made from nickel. Ces précipités of phase γ 'sont toujours répartis heterogeneous in the volume of monocristal respecting ségrégations Rooms résultant du procédé de solidification. Par ailleurs, des phases eutectiques γ / γ 'PRESENTES sont dans les régions inter-dendritiques et des sites préférentiels constituent of amorçage of fissures. De plus, les phases eutectiques γ / γ 'sont au formées van des fins précipités (taille au inférieure micrometre) durcissante of phase γ'. Ces précipités of phase γ 'constituent the main source of Durchziehen des superalliages made from nickel. Aussi, la présence de phases eutectiques γ / γ 'résiduelles it Permet no'

[0047] The tidiness été montre que les properties mécaniques des superalliages, en particulier la résistance au creep, étaient optimales lorsque the prekipevatiti des précipités γ 'was ordonnée, avec une taille below 300 to 500 nm, and lorsque the totality des eutectiques phases γ / γ 'was remise en solution.

[0048] The base superalloys crude solidification nickel are thus heat-treated to obtain the desired distribution of the various phases. The first heat treatment is a treatment

homogenization of the microstructure which aims to dissolve the precipitated phase γ 'and eutectic phases γ / γ'. This treatment is carried out at a temperature above the phase solvus temperature of γ '. Quenching is then performed at the end of this first heat treatment to obtain a fine and homogeneous dispersion of the precipitated γ '. Thermal tempering treatments are then carried out in two stages, at temperatures below the solvus temperature of the γ-phase. During a first step for growing the precipitated γ 'and obtain the desired size, and then in a second step, to increase the volume fraction of this phase up to about 70%.

[0049] Examples

[0050] Two single-crystal superalloys based on nickel of the present disclosure (Example 1 and Example 2) were studied and compared to three superalloys commercial single crystal CMSX-4 (Ex 3), AMI (Ex 4) and MC2 (Example 5). The chemical composition of each of single crystal superalloys is given in Table 1. All these superalloys are nickel-based superalloys, that is to say, the complement to 100% of the concentrations shown in Table 1 is constituted by nickel and incidental impurities.

[0051] Table 1

[0052] creep

[0053] Table 2 shows the results of a creep resistance test under argon (Ar) at 1200 ° C by applying a stress of 80 MPa, performed on superalloys Ex 1 to Ex 5. The creep resistance is quantified by the lifetime expressed in hours (h) of the test piece, that is to say the time between the start of turning on the load at 1200 ° C and the rupture of the specimen.

[0054] Table 2

Superalloys life (h)

Ex 1 90

Ex 2 50

Ex 3 25

Ex 4 4

Ex 5 3

[0055] As can be seen, superalloys Ex 1 and Ex 2 show a lifetime creep rupture, much higher than that of the CMSX-4 compared to superalloys (Ex 3), AMI (Ex 4) and MC2 ( ex 5). Superalloys Ex 1 and Ex 2 can therefore be operated withstand stresses greater than those superalloys can withstand comparison for comparable lifetimes or show superior lifetimes under similar constraints.

[0056] Protective coating jersey

[0057] To investigate the compatibility of superalloys Ex 1 to Ex 5 with the coating (metal underlayer and ceramic thermal barrier) holding tests of the thermal barrier in cyclic oxidation were performed.

[0058] These tests, performed in air are constituted by the repetition of an elementary heat cycle comprising a step of heating up to 1100 ° C for ten minutes followed by a hold at 1100 ° C, the duration cumulative of these two steps being 1 h, and a forced cooling during a dozen of minutes to a temperature below 100 ° C.

[0059] The test is stopped when the test specimen has a chipping of the ceramic thermal barrier on at least 20% of the surface of the specimen, that is to say when the ceramic thermal barrier is present over less than 80% of the surface of the specimen. This measurement can be performed by image analysis.

[0060] Superalloys Ex 1 to Ex 5 were coated with a metallic undercoating NiPtAI type and a type of ceramic thermal barrier yttria-stabilized zirconia deposited by EB-PVD. The yttria stabilized zirconia is the 8YPSZ type which is a yttria-stabilized zirconia containing 8% by mass of yttrium oxide (Y 2 0 3 ).

[0061] The results of these tests are reported in Table 3 which shows the number of cycles at 1100 ° C carried out on each test piece before the test is stopped.

[0062] The dispersion of the results of various tests carried out on a type of superalloy is represented by the uncertainty expressed in number of cycles that can be added or subtracted from the value of the number of column cycles 2 of Table 3. For each alloy , the test was carried out on at least three separate test tubes.

[0063] Table 3

[0064] It is found that the specimens having the substrate Ex 1 and Ex 2 compositions may undergo a number of cycles between 1100 ° C and the temperature lower than 100 ° C much higher oxidizing atmosphere after the test pieces having the substrate the compositions ex 3 ex 4 and before the thermal barrier peeling over 20% of the surface of the specimen.

[0065] The microstructure of the coated specimens having substrate for Ex 1 and Ex 2 compositions was monitored at the end of thermal cycling test between 1100 ° C and the temperature lower than 100 ° C. Observations by light microscopy demonstrate the absence of a secondary reaction zone in the superalloy substrate as NiPtAI type metal underlayer.

[0066] In conclusion, the superalloys of the present disclosure exhibit on the one hand, the creep properties than commercial alloys CMSX-4, AMI and MC2 (Ex 3 Ex 5) at very high temperature (1200 ° C ). Moreover, these superalloys can improve the life of the thermal barrier. Finally, these alloys are not susceptible to the formation of a secondary reaction zone in the coating of the thermal barrier. These superalloys thus possible to increase the life of the parts (e.g. turbine blades) High

temperature which are made from such superalloys, particularly where these parts comprise a protective coating.

[0067] Figure 1 shows, in section along a vertical plane passing through the major axis A, a turbofan 10. The turbofan 10 includes, from upstream to downstream according to the flow of the airflow, a fan 12, a low pressure compressor 14, a high pressure compressor 16, a combustor 18, a high pressure turbine 20 and a low pressure turbine 22.

[0068] The high pressure turbine 20 includes a plurality of moving blades rotating with the rotor 20A and 20B rectifiers (stator blades) mounted on the stator. The stator of the turbine 20 comprises a plurality of rings 24 of stator disposed vis-à-vis the blades 20A of the turbine 20.

[0069] These properties make these superalloys so interesting candidates for the production of monocrystalline parts for hot sections of jet engines.

[0070] We can make a moving blade 20A or 20B rectifier for a turbomachine comprising a superalloy as previously defined.
[0071] One can also manufacture a blade 20A or 20B rectifier for a turbomachine comprising a superalloy as defined (e) previously coated (e) a protective coating comprising a metal sublayer
[0072] A turbine engine may especially be a turbojet engine such as a turbofan engine 10. The turbine engine may be a jet engine single-flow, a turboprop or turboshaft engine.
[0073] Although the present disclosure has been described with reference to a specific embodiment, it is obvious that various modifications and changes can be made to these examples without departing from the general scope of the invention as defined by the claims. In addition, individual features of the different embodiments discussed can be combined into additional embodiments. Therefore, the description and drawings should be considered illustrative rather than restrictive sense.

WE CLAIMS

1. Nickel-base superalloy comprising in percentages by weight, 4.0 to 6.0% chromium, 0.4 to 0.8% molybdenum, 2.5 to 3.5% rhenium, 6.2 to 6.6% tungsten, 5.2 to 5.7% aluminum, 0.0 to 1.6% titanium, 6.0 to 9.9% tantalum, 0.0 to 0.7% hafnium, 0.0 to 0.3% silicon, the balance being nickel and incidental impurities.
2. A superalloy according to claim 1, comprising, in percentages by weight, 4.8 to 5.2% chromium, 0.4 to 0.8% molybdenum, 2.8 to 3.2% rhenium, 6.2 to 6.6% tungsten, 5.2 to 5.7% aluminum, 0.8 to 1.2% titanium, 6.3 to 9.2% tantalum, 0.3 to 0.7% hafnium, 0.0 to 0.3% silicon, the balance being nickel and incidental impurities.
3. A superalloy according to claim 1, comprising, in percentages by weight, 4.8 to 5.2% chromium, 0.4 to 0.8% molybdenum, 2.8 to 3.2% rhenium, 6.2 to 6.6% tungsten, 5.2 to 5.7% aluminum, 0.0 to 1.5% titanium, 6.3 to 6.7% tantalum, 0.3 to 0.7% hafnium, 0.0 to 0.3% silicon, the balance being nickel and incidental impurities.
4. A superalloy according to claim 1, comprising, in percentages by weight, 4.8 to 5.2% chromium, 0.4 to 0.8% molybdenum, 2.8 to 3.2% rhenium, 6.2 to 6.6% tungsten, 5.2 to 5.7% aluminum, 0.0 to 0.5% titanium, 8.8 to 9.2% tantalum, 0.3 to 0.7% hafnium, 0.0 to 0.3% silicon, the balance being nickel and incidental impurities.
5. superalloy according to claim 1, comprising, in percentages by weight, 5% chromium, 0.6% molybdenum, 3% rhenium, 6.4% tungsten, 5.5% aluminum, 1% titanium , 6.5% tantalum, 0.5% hafnium, 0.0 to 0.1% silicon, the balance being nickel and incidental impurities.
6. The superalloy of Claim 1 comprising, in percentages by weight, 5% chromium, 0.6% molybdenum, 3% rhenium, 6.4% tungsten, 5.5% aluminum, 9% tantalum , 0.5% hafnium, 0.0 to 0.1% silicon, the balance being nickel and incidental impurities.
7. blade (20A, 20B) for a turbomachine comprising a single crystal superalloy according to any one of claims 1 to 6.
8. blade (20A, 20B) according to claim 7, comprising a protective coating comprising a metallic sub-layer deposited on the superalloy article and a ceramic thermal barrier deposited on the metal underlayer.
9. blade (20A, 20B) according to claim 7 or 8, having an oriented structure according to a crystallographic direction <001>.
10. A turbomachine including a blade (20A, 20B) according to any one of claims 7 to 9.