EP4069872A1 - Alliage à base de nickel - Google Patents

Alliage à base de nickel

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Publication number
EP4069872A1
EP4069872A1 EP20825185.0A EP20825185A EP4069872A1 EP 4069872 A1 EP4069872 A1 EP 4069872A1 EP 20825185 A EP20825185 A EP 20825185A EP 4069872 A1 EP4069872 A1 EP 4069872A1
Authority
EP
European Patent Office
Prior art keywords
nickel
weight percent
alloy
based alloy
composition according
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP20825185.0A
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German (de)
English (en)
Inventor
Daniel BARBA CANCHO
Roger Charles REED
Enrique ALABORT MARTINEZ
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Alloyed Ltd
Original Assignee
Alloyed Ltd
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Filing date
Publication date
Application filed by Alloyed Ltd filed Critical Alloyed Ltd
Publication of EP4069872A1 publication Critical patent/EP4069872A1/fr
Pending legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C19/00—Alloys based on nickel or cobalt
    • C22C19/03—Alloys based on nickel or cobalt based on nickel
    • C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
    • C22C19/051—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W
    • C22C19/057—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W with the maximum Cr content being less 10%

Definitions

  • the present invention relates to a nickel-based single crystal superalloy composition designed for high performance jet propulsion applications.
  • the alloy - a third generation single crystal nickel-based superalloy - exhibits a combination of creep resistance and oxidation resistance and processability which is comparable to or better than equivalent grades of alloy.
  • the density, cost, yield strength and long-term stability of the alloy have also been considered in the design of the new alloy.
  • Table 1 Examples of typical compositions of third generation nickel-based single crystal superalloys are listed in Table 1. These alloys may be used for the manufacture of rotating/stationary turbine blades used in gas turbine engines. Figure 1 shows schematically the trade off between creep resistance and strength and oxidation resistance made in some prior art alloys.
  • the present invention provides a nickel-based alloy composition consisting, in weight percent, of: 1.6 to 5.0% chromium, 4.5 to 14.0% cobalt, 2.5 to 8.5% tungsten, 0.0 to 0.5% molybdenum, 5.0 to 8.5% rhenium, 5.5 to 7.3% aluminium, 3.7 to 9.5% tantalum, 0.0 to 0.5% hafnium, 0.0 to 0.5% niobium, 0.0 to 0.5% titanium, 0.0 to 0.5% vanadium, 0.0 to 1.0 platinum, 0.0 to 1.0 palladium, 0.0 to 1.0 iridium, 0.0 to 0.1% silicon, 0.0 to 0.1% yttrium, 0.0 to 0.1% lanthanum, 0.0 to 0.1% cerium, 0.0 to 0.1% magnesium, 0.0 to 0.003% sulphur, 0.0 to 0.05% manganese,
  • the nickel-based alloy composition provides a good balance of properties, particularly between creep, oxidation resistance and processability as well as cost, density, manufacturability and yield stress.
  • the nickel-based alloy composition consists, in weight percent, of between 2.0 and 4.5% chromium. Such an alloy is particularly resistant to TCP formation and presents a high strength at mid temperatures whilst still having good oxidation & corrosion resistance at higher temperatures.
  • the nickel-based alloy composition consists, in weight percent, of cobalt between 5.0% to 12.0% wt.
  • Such an alloy has improved environmental resistance to oxidation combined with an increased resistance to deformation at mid temperatures and a limit in cost.
  • the nickel-based alloy composition consists, in weight percent of, between 5.0 and 8.0% tungsten. This composition assures a good creep performance, high strength at low and mid temperatures while still achieving a light and stable alloy.
  • the nickel-based alloy composition consists, in weight percent, of between 5.7 or 5.9 and 7.0% aluminium. This composition achieves the correct ⁇ ' amount for high creep resistance and strength while keeping a reduced density alongside with an increased oxidation resistance.
  • the nickel-based alloy composition consists, in weight percent, of between 4.0 and 8.0% or 7.4% tantalum, preferably between 4.0 and 7.4% or 7.0% tantalum. This provides the optimal microstructure range with a good creep resistance, ease of manufacture (based upon solutioning window) and high strength at mid and low temperatures and reduces the cost and density of the alloy further and provides a superior strength up to higher temperatures, while keeping a good the solutioning window.
  • the nickel-based alloy composition consists, in weight percent, of 0.1% or more molybdenum. This is advantageous for improved creep resistance.
  • the nickel-based alloy composition consists, in weight percent of, between 5.5 and 7.0% rhenium, providing a good balance of creep resistance, density, resistance to TCP formation and cost.
  • the nickel-based alloy composition consists, in weight percent, of between 0.0 and 0.2% hafnium. This is optimum for tying up incidental impurities in the alloy, for example, carbon.
  • the nickel-based alloy composition is such that the following equation is satisfied in which W Ta and W Al are the weight percent of tantalum and aluminium in the alloy respectively 36 ⁇ W Ta + 5.0 W Al ⁇ 39. This is advantageous as it allows a suitable volume fraction ⁇ ' to be present (60-70%).
  • the nickel-based alloy composition is such that the following equation is satisfied in which W Ta and W Cr are the weight percent of tantalum and chromium in the alloy respectively -3.5 ⁇ W Cr - W Ta +0.44 W Co ; preferably -3.0 ⁇ W Cr - W Ta +0.44 W Co . This is advantageous as it allows a suitable solutioning window for the alloy to allow for heat- treatment processes.
  • the nickel-based alloy composition is such that the following equation is satisfied in which W Re is the weight percent of ruthenium and rhenium in the alloy respectively 252 ⁇ 10 + 30 W Re ; preferably 225 ⁇ 10 + 30 W Re . This is advantageous as it results in an alloy with a relatively low cost.
  • the nickel-based alloy composition is such that the following equation is satisfied in which W Re and W W are the weight percent of rhenium and tungsten in the alloy respectively 1.17 W Re + W W ⁇ 15.7; preferably 1.17 W Re + W W ⁇ 12.6. This is advantageous as it results in an alloy with a relatively low density.
  • the nickel-based alloy composition is such that the following equation is satisfied in which W Re , W Mo and W W are the weight percent of rhenium, molybdenum and tungsten in the alloy respectively 0.85W Re +0.47(W W + W Mo ) - W Cr ⁇ 5.0; preferably 0.85 W Re +0.47(W W + W Mo ) - W Cr ⁇ 6.0. This is advantageous as it results in an alloy with a high creep resistance.
  • the nickel-based alloy composition is such that the following equation is satisfied in which W Co , W W and are the weight percent of cobalt, chromium, tungsten and tantalum in the alloy respectively 0.61(W Co ) — W w ⁇ 0.325 This is advantageous as it results in an alloy with a mid-temperature strength.
  • the sum of the elements niobium, titanium and vanadium, in weight percent is less than 1%, preferably 0.5% or less. This means that those elements do not have too much of a deleterious effect on environmental resistance of the alloy.
  • the combination of W and Co following the relation 0.63W Co - W W > -6.5; preferably 0.63 W Co - W W > -3.5 to maintain a good oxidation resistance.
  • the nickel-based alloy composition has between 60 and 70% volume fraction ⁇ '.
  • a single crystal article is provided, formed of the nickel-based alloy composition of any of the previous embodiments.
  • a turbine blade for a gas turbine engine is provided, formed of an alloy according to any of the previous embodiments.
  • a gas turbine engine comprising the turbine blade of the previous embodiment is provided.
  • Figure 1 indicates in a triangular plot the performance of each of 3 example baselines alloys of each generation of yield strength, mid temperature creep resistance and high temperature creep resistance of examples of 3 rd Generation single crystal alloys and comparison with the performance of the example alloys proposed in this patent.
  • Figure 2 shows schematically the link between chemical elements and each of the alloy properties. For each element, the properties defining the upper and lower compositional limits are indicated.
  • Figure 3 is a contour plot showing the effect of ⁇ ' forming elements aluminium and tantalum on volume fraction of ⁇ ' for alloys within the alloy design space, determined from phase equilibrium calculations conducted at 900°C.;
  • Figure 4 is a contour plot showing the effect rhenium and tungsten on density, for alloys with a volume fraction of ⁇ ' between 60-70% at 900°C with tantalum between 3.7 - 9.5 wt.%;
  • Figure 5 is a contour plot showing the effect of rhenium content on raw elemental cost, for alloys with a volume fraction of ⁇ ' between 60-70% at 900°C with tantalum between 3.7- 9.5 wt.%;
  • Figures 6a-e are contour plots showing the effect of elements chromium and tungsten on microstructural stability, for alloys with a volume fraction of ⁇ ' between 60-70% at 900°C with tantalum between 3.7-9.5 wt.% which contain 2 wt.% rhenium, 4 wt.% rhenium, 6 wt.% rhenium, 8 wt.% rhenium, 10 wt.% rhenium, respectively;
  • Figure 7 is a contour plot showing the effect of elements Mo and tungsten on microstructural stability, for alloys with a volume fraction of ⁇ ' between 60-70% at 900°C with tantalum between 3.7-9.5 wt.%, 4.5% wt% Cr which contain 8.5 wt.% rhenium;
  • Figure 8 is a contour plot showing the effect of elements tantalum, cobalt and chromium on the solutioning window for alloys with a volume fraction of ⁇ ' between 60-70% at 900°C
  • Figure 9 is a contour plot showing the effect of elements tungsten and cobalt on the oxidation resistance for alloys with a volume fraction of ⁇ ' between 60-70% at 900°C with tantalum between 3.7-9.5 wt.%, and rhenium between 5-8.5wt.%
  • Figure 10 is a contour plot showing the effect of the elements aluminium and tantalum on the yield strength at room temperature for alloys with rhenium between 5.0-8.5wt.%.
  • Figure 11 is a contour plot showing the effect of the combined elements cobalt and tungsten on the resistance to plastic deformation at mid temperatures (600-800 °C) for alloys with a volume fraction of ⁇ ' between 60-70% at 900°C with rhenium 5.0-8.5 wt%.
  • Figure 12 has contour plots showing the effect of elements rhenium, chromium and tungsten on the creep resistance, for alloys with a volume fraction of ⁇ ' between 60-70% at 900°C with tantalum between 3.7-9.5 wt, which contain, 4 wt.% ruthenium, 5 wt.% ruthenium, 6 wt.% ruthenium, 8 wt.% ruthenium, 10 wt.% ruthenium, respectively;
  • aluminium (Al), tantalum (Ta) and titanium (Ti) are introduced as these promote the formation of the precipitate hardening phase gamma-prime ( ⁇ ').
  • This precipitate phase is coherent with the face-centered cubic (FCC) matrix phase which is referred to as gamma ( ⁇ ).
  • FCC face-centered cubic
  • ABS Alloys-By-Design
  • This approach utilises a framework of computational materials models combined with machine learning to estimate design relevant properties across a very broad compositional space.
  • this alloy design tool allows the so called inverse problem to be solved; identifying optimum alloy compositions that best satisfy a specified set of design constraints.
  • the first step in the design process is the definition of an elemental list along with the associated upper and lower compositional limits.
  • the compositional limits for each of the elemental additions considered in this invention - referred to as the “alloy design space” - are detailed in Table 2.
  • the connection between each property and the affecting elemental limit is presented in Fig. 3 as a summary of the invention process.
  • the second step relies upon thermodynamic calculations used to calculate the phase diagram and thermodynamic properties for a specific alloy composition. Often this is referred to as the CALPHAD method (CALculate PHAse Diagram). These calculations are conducted at the service temperature for the new alloy (900°C), providing information about the phase equilibrium (microstructure).
  • CALPHAD method CALculate PHAse Diagram
  • a third stage involves isolating alloy compositions which have the desired microstructural architecture.
  • the creep rupture life is maximised when the volume fraction of the precipitate hardening phase ⁇ ' lies between 60%-70%.
  • Rejection of alloy on the basis of unsuitable microstructural architecture is also made from estimates of susceptibility to topologically close-packed (TCP) phases based on the effective valence number of the ⁇ phase (Md ⁇ ).
  • TCP topologically close-packed
  • Md ⁇ effective valence number of the ⁇ phase
  • the present calculations predict the formation of the deleterious TCP phases (sigma ( ⁇ ), P and mu ( ⁇ )) using CALPHAD modelling.
  • the model isolates all compositions in the design space which are calculated to result in (1) a volume fraction of ⁇ ' of between 60 and 70.
  • merit indices are estimated for the remaining isolated alloy compositions in the dataset based on physical models combined with machine learning tools using an extensive experimental alloy performance database. Examples of these include: (2) density, (3) cost, (4) solutioning window, (5) microstructural stability, (6) oxidation resistance, (7) yield strength of the alloy at room temperature, (8) Larson Miller parameter (LMP) for mid temperature resistance and (9) LMP for high temperature creep (which describes an alloy’s creep resistance based solely on mean composition). These indexes and how each of the main elemental components affects them are indicated in Fig. 2.
  • the calculated merit indices are compared with limits for the required requirements, these design constraints are considered to be the boundary conditions to the problem. All compositions which do not fulfil the boundary conditions are excluded and the preferred compositional ranges are delimited.
  • the final, sixth stage involves analysing the dataset of remaining compositions. This can be done in various ways. One can sort through the database for alloys which exhibit maximal values of the merit indices - the lightest, the most creep resistant, the most oxidation resistant, and the cheapest for example. Or alternatively, one can use the database to determine the relative trade-offs in performance which arise from different combination of properties. In this patent a combination of both procedures is used. First, the critical microstructural and physical requirements are imposed (1-6). Then, for the suitable alloys, a multitarget optimisation on the performance of the alloy at room, mid and high temperatures (7-9) is performed to rank the alloys.
  • the first merit index is density (2).
  • the second merit index was cost (3).
  • x i was multiplied by the current raw material cost for the alloying element, c i .
  • a third merit index is the solutioning window (4).
  • CALPHAD thermodynamic modelling
  • the temperature at which completed dissolution of the ⁇ ' phase (known as the ⁇ ' solvus temperature) occurs must be known, as must the solidus temperature.
  • the difference between the solidus temperature and the ⁇ ' solvus temperature will give the solutioning window. So the solutioning window index calculates as the difference between the solidus temperature and the ⁇ ' solvus temperature.
  • TCP phases ( ⁇ , ⁇ & P) is detrimental for long term mechanical properties in Ni-based superalloys. Their appeared is caused by long high temperature exposition and they are greatly influenced by the alloy chemistry. It has been found that the propensity of forming TCP phases is directly linked with the d-orbital energy levels of the ⁇ composition in the alloy (Md Y ). From experimental observation it has been observed that alloys with Md Y ⁇ 0.93 do not form TCP phases. In this invention, the Md Y values (5) for each alloy composition has been calculated using thermodynamical databases.
  • Md d-orbital energy levels of the alloying elements
  • Oxidation of superalloys depends strongly on the oxides layers form on their surface. Chromia and Alumina ( AI 2 O 3 ) layer has been proved to be beneficial for the oxidation resistance of the alloy. Chromia is formed when sufficient amount of chromium is achieved in the alloy. However, for SX this amount is not sufficient due to the creep requirement. On the other side, alumina formation, which is the main barrier in most commercial SX alloys, is promoted when low effective valences of AI 2 O 3 (Val eff ) and low formation energies of this compound ( ⁇ G f ) are combined together.
  • the seventh merit index (7) is the yield strength. This yield strength is derived from a physical based model combining the amount of ⁇ ' fraction (f ⁇ ' ) and the strength of these precipitates. (3)
  • T is the Taylor factor (for SX ⁇ 001> is 1/0.41)
  • b is the burger vector
  • ⁇ APB is the antiphase boundary (APB) energy.
  • the ⁇ ' fraction is obtained as stated before from thermodynamic databases.
  • the fault energies in the ⁇ ' phase - for example, including ⁇ APB- have a significant influence on the deformation behaviour of nickel-based superalloys.
  • Increasing the APB energy has been found to improve mechanical properties including, tensile strength and resistance to creep deformation.
  • the APB energy was studied for a number of Ni-Al-X systems using density functional theory.
  • ⁇ APB 195 — 1.7x Cr — 1.7x Mo + 4.6x W + 27.1x Ta + 21.4x Nb + 15x Ti (4)
  • x Cr , x Mo , x W , x Ta , x Nb and x Ti represent the concentrations, in atomic percent, of Cr, Mo, W, Ta, Nb and Ti in the ⁇ ' phase, respectively.
  • the composition of the ⁇ ' phase is determined from phase equilibrium calculations.
  • the eigth merit index (8) is the mid-temperature Larson Miller Parameter (LMP Mid ) and define the resistance of the alloy to mid-temperature deformation (600-800°C).
  • LMP Mid mid-temperature Larson Miller Parameter
  • the definition of the LMP is: 151
  • the last merit index is the creep-merit index (9).
  • the overarching observation is that creep deformation of a single crystal superalloy above 800°C occurs by dislocation climb of the ⁇ ' which is highly dependent on the alloy chemistry. Because of this change of mechanistic above 800°C a new chemical composition dependence is being calculated for LMP Creep .
  • a database of 1314 experimental datapoints and 120 alloys is used to train the linear model using machine learning.
  • the chemical linear relation found for LMP Creep is
  • the ABD method described above was used to isolate the inventive alloy composition.
  • the design intent for this alloy was to isolate the composition of a third-generation single crystal (SX) nickel-based superalloy that exhibits a better balance of creep resistance, oxidation and corrosion resistance and heat treatment window than existing alloys.
  • SX third-generation single crystal
  • One of the best performing third-generation single crystal alloys in terms of creep resistance is CMSX-10N and a desirable property is to achieve a creep resistance which is comparable or better than CMSX-10N but keeping the oxidation and corrosion resistance similar to Rene N6 and a heat treatment window closer to that of TMS-75.
  • FIG 1 much of the inventive alloy space achieves all three of these desirable characteristics, whereas other areas of the alloy are focused at one or more specific properties, whilst leaving other properties at acceptable levels.
  • the density, cost, stability and mid temperatures strength of the alloy have also been considered in the design of the new alloy with similar values to the ones obtained for 4 th generation SX.
  • the material properties - determined using the ABD method - for the commercially used third generation single crystal turbine blade alloys are listed in Table 3.
  • the design constrains of the new alloy were established by the predicted values of baselines alloys (HT creep, cost, density, HT window, MT strength) and 2 nd generation alloys (yield strength, oxidation and corrosion resistance, stability) as stated in the sixth row of Table 3.
  • the alloys falling in the scope of the invention meet all of the criteria set in the sixth row of table 3, whereas each of the prior art alloys does not meet at least at least two criteria.
  • the alloys of the present invention achieve good creep resistance at high temperatures and mid-temperatures in combination with a high yield stress and high yield stress in combination with a solutioning window exceeding 50 °C.
  • the calculated material properties for a set of example alloys in accordance with the present invention are also given.
  • the composition for the example set of alloys are stated in Table 5.
  • the results of table 3 are plotted for some of the examples in Figure 1 showing how the alloys achieve a better balance of properties than prior art alloys.
  • the shaded area in each triangle indicates the properties exhibited by an alloy so the closer a triangle goes to an apex, the higher the property defined at that apex.
  • Table 3 Calculated phase ⁇ ractions and merit indices made with the “Alloys-by-Design ” so ⁇ tware. Results ⁇ or third generation single crystal turbine blades listed in Table 1 and the proposed compositions in the current invention listed in Table 5.
  • Optimisation of the alloy’s microstructure - primarily comprised of an austenitic face centre cubic (FCC) gamma phase (g) and the ordered L1 2 precipitate phase ( ⁇ ') - was required to maximise creep resistance.
  • a volume fraction of the ⁇ ' phase between 60-70% is generally regarded as optimum as this microstructure is known to provide the maximum level of creep resistance in single crystal blade alloys.
  • a volume fraction ⁇ ' of between 60 and 70% was the target for the present alloy but the inventive alloy may deviate from this target.
  • Aluminium and tantalum are well known to be the primary ⁇ ' formers. Hence, the levels of these elements were controlled to produce the desired ⁇ ' volume fraction.
  • Figure 3 shows the effect the elements which are added to form the ⁇ ' phase - predominantly aluminium and tantalum - have on the fraction of ⁇ ' phase in the alloy at the operation temperature, 900°C in this instance.
  • this alloy compositions which result in a volume fraction of ⁇ ' between 60-70% were considered because this matches the ⁇ ' content in the third generation alloys.
  • wt.% weight percent of aluminium was required based on a tantalum required content of 3.7 - 9.5 wt% (described with reference to Figures 8 and 10).
  • the alloy contains 5.9 wt% or more aluminium as this increases strength to 1100 MPa for the minimum amount of ⁇ ' of 60% as stated in Figure 10
  • FIG. 10 shows the influence of aluminium and tantalum on the yield strength of the alloy for rhenium 5.0 to 8.5% (described elsewhere). If the yield strength of third generation alloys is too low it can lead to low cycle fatigue problems. A yield strength of 1000 MPa is aimed at in the present invention combined with a third-generation creep resistance. Compositions where the yield strength achieves the strength of third generation single crystal alloys ( ⁇ 1000 MPa) are indicated in the graph. Modelling calculations showed that tantalum levels in the alloy greater than 3.7 wt.% easily produce an alloy with a yield strength of above 1000MPa at the lowest level of aluminium allowable and of nearly 1000MPa at the highest aluminium content.
  • the alloy has at least 4.0 wt% tantalum so that even at the highest aluminium levels allowable the yield stress is comparable to the 3 rd generation alloys.
  • the maximum tantalum content will be explained below with reference to Figure 8 and results in a tantalum range of 3.7 - 9.5 wt.%.
  • a maximum amount of tantalum of 7.4% is particularly preferred because of the good balance between yield strength and HT window.
  • Niobium, titanium and vanadium behave in a similar way to that of tantalum i.e. they are gamma prime forming elements which increase anti-phase boundary energy. These elements can optionally be added to the alloy. The benefits of this may include lower cost and density in comparison to tantalum. However, additions of these elements must be limited as they can have a negative impact on the environmental resistance of the alloy. Therefore, those elements can each be present in an amount of up to 0.5 wt.%.
  • those elements are substituted for tantalum meaning that the sum of the elements consisting of niobium, titanium, vanadium and tantalum is preferably limited to 3.7-9.5 or 7.4% wt.%, more preferably 4.0-8.0 or 7.4% wt.% which is the preferred range for tantalum.
  • the sum of the elements consisting of niobium, titanium and vanadium is preferably limited to below 1.0 wt.% and preferably below 0.5 wt.% so as to avoid reduction in environmental resistance of the alloy.
  • the elements platinum and palladium behave in a similar way to that of tantalum, titanium and niobium i.e. they are ⁇ ' forming elements which increase anti-phase boundary energy.
  • These elements can optionally be added to the alloy for example in substitution for the elements tantalum, titanium, vanadium and niobium.
  • the benefits of this may include an improvement in resistance to high temperature corrosion.
  • additions of these elements can be limited due to the high cost of these elemental additions. Therefore, those elements can each be present in an amount of up to 1.0 wt% or less and most preferably 0.5 wt% or less as this range provides the best balance of cost and improvement to corrosion resistance.
  • the element iridium behaves in a similar way to that of tungsten i.e. it is a gamma forming element which improves the creep merit index.
  • Iridium can optionally be added to the alloy. Additions of iridium will significantly increase the creep response of the alloy in comparison to tungsten (as it has much slower diffusivity), however this is achieved with substantial increases in cost due to the high cost of iridium. Preferably the addition of iridium is limited to 1.0 wt% or less and even more preferably to 0.5 wt% or less.
  • the balance of aluminium and tantalum can be adjusted such that there is a balance between desired target volume fraction of ⁇ ' as well as a sufficiently high yield strength as described above.
  • consideration must also be given to the processing of the alloy.
  • One such consideration is the solutioning window; there should exist a sufficient temperature range window, below the melting temperature of the alloy, across which only the ⁇ phase is stable.
  • the solutioning window depends upon the dissolution of the ⁇ ' phase it is strongly influenced by alloy chemistry, specially by tantalum and chromium content. This solutioning heat treatment is used to remove any residual microsegregation and eutectic mixtures rich in ⁇ ' which might occur during the casting processes used to produce the single crystal alloy.
  • the solutioning window is greater than 50°C to allow for conventional processing methods.
  • Figure 8 shows the solutioning window magnitude (in °C) for varying wt% Cr and Ta with a volume fraction ⁇ ' of 60-70%.
  • the minimum chromium content for the present invention is greater than or equal to 1.6 wt.% and preferably greater than or equal to 2.0 wt.% in order to attain oxidation resistance which comparable to current third generation single crystal alloys which have Cr contents ranging between 1.6-4.0 wt.%. That is, equal to a higher weight percent of chromium is provided than in most of third generation alloys on the basis that this will match or improve oxidation resistance compared to those alloys.
  • the chromium content is limited to 5.0 wt.% to reduce the propensity for the alloy to form the deleterious TCP phases which will be explained later ( Figure 6). That is, within the limits for tungsten of 2.5-8.5wt.% and rhenium 5.0-8.5wt.% the Md ⁇ can be kept low whilst achieving desirable physical properties. At levels of higher chromium than 5.0%, microstructural stability starts to be deleteriously affected.
  • the chromium content in the alloy is limited to 4.5 wt.% or even 4.0wt.% or less chromium as this produces an alloy with the best balance between oxidation resistance and microstructural stability.
  • the tantalum content is limited to 8.0 wt.% as this produces an alloy with a solutioning window greater than 50°C even at lower levels of Cr. Limiting tantalum even further to say 7.4% or even 7.0% or 6.5 wt.% or less may be beneficial for further increasing the solutioning window.
  • elements such as rhenium, tungsten and chromium (chromium is added for oxidation resistance as stated before) must be suitably balanced such that a balance between creep resistance and oxidation is achieved without resulting in a microstructurally unstable alloy which is prone to the formation of deleterious TCP phases, Figure 6.
  • FIG. 5 shows the effect which levels of rhenium has on alloy cost for an alloy of 60-70% ⁇ ' volume fraction at 900°C.
  • the rhenium content in the alloy is limited to 8.5 wt.% ensuring that the cost of the alloy of the present invention is equivalent to or no more than 10% higher than current grades of third generation alloy (about 252 $/kg).
  • ⁇ (Cost) 10 + 30 ⁇ W Re
  • ⁇ (Cost) is a numerical value which is less than or equal to 252 to produce an alloy with a cost of 252$/kg or less
  • W Re is the weight percent of rhenium in the alloy and so this is a preferable feature.
  • the numerical value for ⁇ (Cost) is less than or equal to 225 as this produces an alloy with a lower cost of 225$/lb or less.
  • Ruthenium additions are known to be beneficial for the same reasons as rhenium additions. However ruthenium is even more expensive than rhenium and so in this alloy ruthenium is not present. It is surprising that the alloy achieves such good physical properties without the use of ruthenium in addition to rhenium.
  • the additions of the elements tungsten, rhenium and chromium are optimised in order to design an alloy which is highly resistant to creep deformation.
  • the high temperature creep resistance was determined by using the LMP creep model developed described above. It is desirable to maximise the LMP creep as this is associated with an improved high temperature (HT) creep resistance.
  • HT high temperature
  • the influence which tungsten, rhenium and chromium have on the HT creep resistance is presented in Figure 12.
  • the calculations to produce the graphs of Figures 4 and 12 are with the limitation that the ⁇ ' volume fraction at 900°C is between 60 and 70% enforced. It is seen that increasing the levels of rhenium and tungsten improve creep resistance, by this order of effectiveness, while chromium contents deteriorate the creep resistance.
  • the quantities of tungsten and rhenium required mean that this has a strong influence on alloy density, Figure 4. Therefore, the trade-off between creep resistance and alloy density must be balanced.
  • the alloy contains at least 5.0 wt.% of rhenium.
  • the rhenium content is greater as this clearly increases LMP creep , so that preferably rhenium is present in an amount of 5.5wt% or more, more preferably 6.0 wt.% or greater or even 6.1wt% or greater as this produces even higher creep resistance, i.e. LMP creep > 25.45 even at lower levels of tungsten.
  • the tungsten content is limited to 8.5 wt.% or less to keep the density as low as possible. At this level with levels of chromium and rhenium at their lower ends, a density of 9.0g/cm 3 or less is achievable. Preferably the tungsten content is limited to 8.0 wt% or less or even 7.0 wt.% or less as this produces an alloy with an even lower density (dashes lines in Figures 4 and 11). Lower levels of tungsten also ensure microstructural stability (Figure 8).
  • tungsten of 2.5 wt.% or more is shown to produce a LMP creep of nearly 25.3 at the maximum allowable amounts of rhenium of 8.5wt% for costing and at the maximum amount of chromium allowable of 5.0% for HT window.
  • the tungsten content is greater than 5.0 wt.% as this produces an alloy with higher creep resistance (Figure 12) whilst maintaining reasonable oxidation resistance particularly at higher cobalt levels (figure 4). In such an alloy cost can also be reduced as lower levels of rhenium may be required ( Figure 12).
  • a critical threshold of the oxidation index of -0.1 can be imposed to have a similar good oxidation resistance than 2 nd generation SX alloys (better than 3 th generation). From this figure, for the minimum amount of tungsten (W W >2.5%) the minimum value of cobalt for a good oxidation resistance is set to 4.5%. Preferably, alloys with cobalt higher than 5.0% present a better oxidation resistance.
  • a relationship between cobalt and tungsten content in the alloy and oxidation index can be derived from Figure 9 and results in the following two formulae which predict oxidation indexes of -0.1 or lower and -0.05 respectively.
  • the function ⁇ is preferably lower than 0.325 to predict a good strength at mid temperature with a LMP Mid of 21.0 or greater.
  • the maximum cobalt level to keep a good strength at mid temperatures is 14.0% or 12.0%.
  • impurities may include the elements carbon (C), boron (B), sulphur (S), zirconium (Zr) and manganese (Mn). If concentrations of carbon remain at 100 PPM or below (in terms of mass) the formation of unwanted carbide phases will not occur. Boron content is desirably limited to 50 PPM or less (in terms of mass) so that formation of unwanted boride phases will not occur. Carbide and boride phases tie up elements such as tungsten or tantalum which are added to provide strength to the ⁇ and ⁇ ' phases. Hence, mechanical properties including creep resistance are reduced if carbon and boron are present in greater amounts.
  • the elements Sulphur (S) and Zirconium (Zr) preferably remain below 30 and 500 PPM (in terms of mass), respectively.
  • Manganese (Mn) is an incidental impurity which is preferably limited to 0.05wt% (500PPM in terms of mass).
  • Sulphur above 0.003 wt.% can lead to embrittlement of the alloy and sulphur also segregates to alloy/oxide interfaces formed during oxidation. This segregation may lead to increased spallation of protective oxide scales.
  • the levels of zirconium and manganese must be controlled as these may create casting defects during the casting process, for example freckling. If the concentrations of these incidental impurities exceed the specified levels, issues surround product yield and deterioration of the material properties of the alloy is expected.
  • Copper is an incidental impurity which is preferably limited to 0.5 wt%.
  • hafnium of up to 0.5 wt.%, or more preferably up to 0.2wt.% are beneficial for tying up incidental impurities in the alloy, in particular carbon.
  • Hafnium is a strong carbide former, so addition of this element is beneficial as it will tie up any residual carbon impurities which may be in the alloy. It can also provide additional grain boundary strengthening, which is beneficial when low angle boundaries are introduced in the alloy.
  • Iron behaves in a similar way to nickel and can be added as a low-cost alternative to nickel. Moreover, tolerance to iron additions improves the ability of the alloy to be manufactured from recycled materials. Therefore, it is preferred that iron is present in an amount of at least 0.1 wt%.
  • additions of iron up to 4.0 wt% can be made in order to substantially reduce the cost.
  • the additions of iron are 2.0 wt% or less in order to reduce the propensity to form the unwanted Laves phase which degrades the mechanical properties of the alloy.
  • iron additions are limited to 1.0 wt% as this produces an alloy which has good ability to be recycled with no loss in material performance.
  • Additions of the so called ‘reactive-elements’, Silicon (Si), Yttrium(Y), Lanthanum (La) and Cerium (Ce) may be beneficial up to levels of 0.1 wt.% to improve the adhesion of protective oxide layers, such as AI 2 O 3 .
  • These reactive elements can ‘mop-up’ tramp elements, for example sulphur, which segregates to the alloy oxide interface weakening the bond between oxide and substrate leading to oxide spallation.
  • additions of silicon to nickel based superalloys at levels up to 0.1 wt.% are beneficial for oxidation properties.
  • silicon segregates to the alloy/oxide interface and improves cohesion of the oxide to the substrate. This reduces spallation of the oxide, hence, improving oxidation resistance.
  • Magnesium (Mg) likewise may act to ‘mop up’ tramp elements, and can have beneficial effects on mechanical properties, so may be added up to 0.1%.
  • Table 5 Compositions o ⁇ the example alloys proposed in this invention n wt. %.

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Abstract

La présente invention concerne une composition d'alliage à base de nickel constituée, en pourcentage en poids, de : 1,6 à 5,0 % de chrome, 4,5 à 14,0 % de cobalt, 2,5 à 8,5 % de tungstène, 0,0 à 0,5 % de molybdène, 5,0 à 8,5 % de rhénium, 5,5 à 7,3 % d'aluminium, 3,7 à 9,5 % de tantale, 0,0 à 0,5 % de hafnium, 0,0 à 0,5 % de niobium, 0,0 à 0,5 % de titane, 0,0 à 0,5 % de vanadium, 0,0 à 1,0 % de platine, 0,0 à 1,0 % de palladium, 0,0 à 1,0 % d'iridium, 0,0 à 0,1 % de silicium, 0,0 à 0,1 % d'yttrium, 0,0 à 0,1 % de lanthane, 0,0 à 0,1 % de cérium, 0,0 à 0,1 % de magnésium, 0,0 à 0,003 % de soufre, 0,0 à 0,05 % de manganèse, 0,0 à 0,05 % de zirconium, 0,0 à 0,005 % de bore, 0,0 à 0,01 % de carbone, 0,0 à 0,5 % de cuivre, 0,0 à 4,0 % de fer, le reste étant du nickel et des impuretés inévitables.
EP20825185.0A 2019-12-04 2020-12-01 Alliage à base de nickel Pending EP4069872A1 (fr)

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GB1917717.9A GB2592182B (en) 2019-12-04 2019-12-04 A nickel-based alloy
PCT/GB2020/053074 WO2021111117A1 (fr) 2019-12-04 2020-12-01 Alliage à base de nickel

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US5151249A (en) * 1989-12-29 1992-09-29 General Electric Company Nickel-based single crystal superalloy and method of making
US5482789A (en) * 1994-01-03 1996-01-09 General Electric Company Nickel base superalloy and article
US5925198A (en) * 1997-03-07 1999-07-20 The Chief Controller, Research And Developement Organization Ministry Of Defence, Technical Coordination Nickel-based superalloy
GB0513121D0 (en) * 2005-06-28 2005-10-26 Rolls Royce Plc A nickel based superalloy
CN109576532A (zh) * 2018-12-10 2019-04-05 中国科学院金属研究所 持久强度高且抗氧化性优良的第三代单晶高温合金及制备
CN109797433B (zh) * 2019-01-23 2021-05-25 深圳市万泽中南研究院有限公司 单晶高温合金、热端部件及设备

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