Nickel-Based Alloys

Abstract

In mass percent, it contains 9.5-14.4% chromium, 3.8-9.6% cobalt, 0.0-4.0% iron, 0.6-5.1% molybdenum, 0.7-6.2% tungsten, 2.6-3.3% aluminum, 2.3-5.6% titanium, 0.0-4.0% niobium, 0.0-2.4% tantalum, 0.01-0.1% carbon, 0.001-0.1% boron, 0.001-0.3% zirconium, and 0.0-0. 5% silicon, 0.0-0.1% yttrium, 0.0-0.1% lanthanum, 0.0-0.1% cerium, 0.0-0.003% sulfur, 0.0-0.25% manganese, 0.0-0.5% vanadium, 0.0-0.5% copper, and 0.0-0.5% hafnium, with the balance being nickel and unavoidable impurities, and the mass percentages of niobium, tantalum, titanium, and aluminum contained in the alloy are W, ... Nb , W Ta , W Ti and W Al Then, the nickel-based alloy composition satisfies the following formula: 0.6W Ti +0.31W Nb +0.27W Ta +0.12W Al ≧3.7

Description

[Technical field]

[0001] The present invention relates to nickel-base superalloy compositions for use as turbine disk components in gas turbine engines and other turbomachines. [Background technology]

[0002] Turbine disks are critical components in gas turbine engines, and improving the performance of turbine disk alloys in terms of maximum operating temperature and maximum service life can have a significant impact on the efficiency of the engine and the cost-effectiveness of its operation.

[0003] Examples of typical compositions of nickel-base superalloys used in turbine disk components are listed in Table 1. Referring to FIG. 1, there is a trend in the development of alloys with higher strength toward higher levels of cost. Table 1 shows the nominal compositions, in mass %, of commonly applied nickel-base superalloys used in powder metallurgy turbine disks.

[0004] [Table 1] Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention aims to provide very high strength combined with reduced cost and improved oxidation / corrosion resistance. The balance of properties of the new alloy allows for more cost-effective manufacture of components for high temperature applications, particularly for use as turbine disk applications where the component operating temperatures are above 800°C. [Means for solving the problem]

[0006] According to the present invention, the composition contains, in mass%, 9.5 to 14.4% chromium, 3.8 to 9.6% cobalt, 0.0 to 4.0% iron, 0.6 to 5.1% molybdenum, 0.7 to 6.2% tungsten, 2.6 to 3.3% aluminum, 2.3 to 5.6% titanium, 0.0 to 4.0% niobium, 0.0 to 2.4% tantalum, 0.01 to 0.1% carbon, 0.001 to 0.1% boron, 0.001 to 0.3% zirconium, 0. The alloy comprises 0-0.5% silicon, 0.0-0.1% yttrium, 0.0-0.1% lanthanum, 0.0-0.1% cerium, 0.0-0.003% sulfur, 0.0-0.25% manganese, 0.0-0.5% vanadium, 0.0-0.5% copper, and 0.0-0.5% hafnium, with the balance being nickel and unavoidable impurities; and the mass percentages of niobium, tantalum, titanium, and aluminum contained in the alloy are W, W+, and W+, respectively. Nb , W Ta , W Ti and W Al Then, a nickel-based alloy composition is provided that satisfies the following formula: 0.6W Ti +0.31W Nb +0.27W Ta +0.12W Al ≧3.7

[0007] This alloy represents a good compromise between high strength, cost, oxidation / corrosion resistance, and resistance to the formation of TCP.

[0008] In a preferred embodiment, the mass percentages of niobium, tantalum and cobalt contained in the alloy are W Nb , W Ta and W Co and Then, the following equation is satisfied. W Nb +1.53W Co + 3.7W Ta <= 14.7 Preferably, the following formula is satisfied: W Nb +1.53W Co + 3.7W Ta <= 12.4 Most preferably, the following formula is satisfied: W Nb +1.53W Co + 3.7W Ta <=9.5 Such alloys are optimized for cost reduction.

[0009] In a preferred embodiment, the mass percentages of niobium, tantalum, titanium and aluminum contained in the alloy are W. Nb , W Ta , W Ti and W Al Then, the following equation is satisfied: 0.6W Ti +0.31W Nb +0.27W Ta +0.12W Al ≧4.0 Such alloys have higher strength.

[0010] In one embodiment, the mass percentages of niobium, tantalum, titanium, and aluminum in the alloy are each W. Nb , W Ta , W Ti and W Al Then, the following formula is satisfied. (0.6W Ti +0.31W Nb +0.15W Ta ) / W Al ≦1.3 Such alloys have high gamma prime phase stability and are resistant to undesirable eta and delta phases, i.e., they have excellent ductility and fatigue resistance.

[0011] In one embodiment, the mass percentages of niobium, tantalum, titanium, and aluminum in the alloy are each W. Nb , W Ta , W Ti and W Al Then, the following formula is satisfied. 0.6W Ti +0.31W Nb +0.15W Ta +0.9W Al<= 6.3 Preferably, the following formula is satisfied: 0.6W Ti +0.31W Nb +0.15W Ta +0.9W Al <= 5.9 Such alloys have a solvus temperature of the gamma prime phase below 1180°C, which allows for heat treatment above the gamma prime solvus while reducing the alloy's susceptibility to cracking when cooled from a temperature above the gamma prime solvus temperature.

[0012] In one embodiment, the mass percentages of niobium, tantalum, titanium, and aluminum in the alloy are each W. Nb , W Ta , W Ti and W Al Then, the following formula is satisfied. 5.4≦0.6W Ti +0.31W Nb +0.15W Ta +0.8W Al <= 6.0 Such alloys have excellent strength properties.

[0013] In one embodiment, the mass percent of tungsten and tantalum in the alloy is W W and W Ta Then, the following formula is satisfied. W W +1.1W Ta ≦6.2 Preferably, the following formula is satisfied: W W +1.1W Ta ≦4.6 Most preferably, the following formula is satisfied: W W +1.1W Ta <= 2.9 Such alloys have limited density while maintaining high strength.

[0014] In one embodiment, the weight percent of tungsten, cobalt, and molybdenum in the alloy is W. W , WCo and W Mo Then, the following formula is satisfied. W W +0.96W Co +1.2W Mo ≧16.0 Such alloys have particularly high creep resistance.

[0015] In one embodiment, the nickel-based alloy composition has a chromium content, by weight percent, of at least 10.0%, more preferably at least 11.5%, such alloys have improved corrosion resistance.

[0016] In one embodiment, the nickel-base alloy composition comprises at least 5.5% cobalt, by weight, which provides an improved balance between creep resistance and alloy stability.

[0017] In one embodiment, the nickel-based alloy composition comprises, by weight percent, 8.1% or less of cobalt, preferably 8.0% or less of cobalt, and more preferably 6.0% or less of cobalt, such alloys provide reduced cost.

[0018] In one embodiment, the nickel-based alloy composition has an iron content, by weight percent, of 1.0% or more, such alloys offering the advantage of being cheaper and more easily recycled.

[0019] In one embodiment, the nickel-base alloy composition has an iron content of up to 2.0%, by weight, which provides a good balance of improved microstructural stability, low cost, and improved recyclability.

[0020] In one embodiment, the nickel-based alloy composition comprises at least 2.2% molybdenum, preferably at least 3.6% molybdenum, by weight, which provides a better balance between creep resistance and density. In one embodiment, the nickel-based alloy composition comprises at most 4.1% molybdenum, by weight, which provides further improved alloy stability.

[0021] In one embodiment, the nickel-based alloy composition comprises 1.9% or more tungsten by weight, providing a better balance between creep resistance and alloy stability.

[0022] In one embodiment, the nickel-based alloy composition comprises no more than 4.6% tungsten, preferably no more than 2.9% tungsten, by weight, resulting in an even less dense alloy.

[0023] In one embodiment, the nickel-base alloy composition comprises aluminum, by weight, greater than or equal to 2.6%, which provides an improved combination of strength, gamma-prime solvus, and gamma-prime stability.

[0024] In one embodiment, the nickel-base alloy composition has an aluminum content of 3.0% or less by weight, which allows the alloy to reach the gamma prime solvus at a lower temperature.

[0025] In one embodiment, the nickel-base alloy composition comprises, by weight, at least 2.6% titanium, preferably at least 3.0%, more preferably at least 3.5%, and most preferably at least 4.1% titanium. By increasing the titanium content, the amount of tantalum required to provide an alloy with a given strength can be reduced, thereby reducing the cost of the alloy.

[0026] In one embodiment, the nickel-based alloy composition comprises, by weight, tantalum in an amount of 1.8% or less, preferably 1.0% or less, such alloys provide reduced cost and density.

[0027] In one embodiment, the nickel-base alloy composition comprises 2.7% or less niobium, by weight, which provides an alloy with improved creep properties at a low cost.

[0028] In one embodiment, the nickel-base alloy composition comprises a volume fraction of gamma prime between 51 and 58% at 850° C. This results in a high strength alloy combined with a low gamma prime solvus.

[0029] In one embodiment of the present invention, a turbine disk is provided that is formed from the nickel-base alloy composition according to the present invention.

[0030] In one embodiment of the present invention, a gas turbine engine includes a turbine disk formed from the nickel-base alloy composition according to the present invention.

[0031] The term "comprising" is used herein to indicate that the composition is 100% and to the exclusion of the presence of additional components, making the percentage 100%. Unless otherwise stated, % is expressed as % by weight.

[0032] The present invention will now be more fully described, by way of example only, with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0033] [Figure 1] FIG. 1 shows the calculated tradeoff between element cost and yield strength (in terms of strength figure of merit) for the alloys listed in Table 1 and for alloys that fall within the alloy design domain listed in Table 2. [Diagram 2] Figure 2 is a contour plot showing the effect of cobalt and niobium on the elemental cost of the alloy, where the tantalum content is fixed at 0.0 wt.%. [Diagram 3] Figure 3 is a contour plot showing the effect of cobalt and niobium on the elemental cost of an alloy in which the tantalum content is fixed at 1.0 wt%. [Figure 4] Figure 4 is a contour plot showing the effect of cobalt and niobium on the elemental cost of the alloy, where the tantalum content is fixed at 2.0 wt%. [Diagram 5]Figure 5 is a contour plot showing the effect of cobalt and niobium on the elemental cost of the alloy, where the tantalum content is fixed at 3.0 wt%. [Figure 6] Figure 6 is a contour plot showing the effect of cobalt and niobium on the elemental cost of the alloy, where the tantalum content is fixed at 4.0 wt%. [Figure 7] Figure 7 is a contour plot showing the effect of the elements Aluminum and Titanium on the yield strength (in terms of strength figure of merit) for an alloy with a preferred elemental cost (<14.7$ / kg), in which the niobium content is fixed at 0.0% by weight and the tantalum content is fixed at 0.0% by weight. Preferred limits for the proportions of the elements Titanium, Niobium and Aluminum based on the relationship (0.6WTi+0.31WNb) / WAl are superimposed. [Figure 8] Figure 8 is a contour plot showing the effect of the elements Aluminum and Titanium on the yield strength (in terms of strength figure of merit) for an alloy with a preferred elemental cost (<14.7$ / kg), in which the Niobium content is fixed at 1.0% by weight and the Tantalum content is fixed at 0.0% by weight. Preferred limits for the proportions of the elements Titanium, Niobium and Aluminum based on the relationship (0.6WTi+0.31WNb) / WAl are superimposed. [Figure 9] Figure 9 is a contour plot showing the effect of the elements Aluminum and Titanium on the yield strength (in terms of strength figure of merit) for an alloy with a preferred elemental cost (<14.7$ / kg), in which the Niobium content is fixed at 2.0% by weight and the Tantalum content is fixed at 0.0% by weight. Preferred limits for the proportions of the elements Titanium, Niobium and Aluminum based on the relationship (0.6WTi+0.31WNb) / WAl are superimposed. [Figure 10]Figure 10 is a contour plot showing the effect of the elements Aluminum and Titanium on the yield strength (in terms of strength figure of merit) for an alloy with a preferred elemental cost (<14.7$ / kg), in which the Niobium content is fixed at 3.0% by weight and the Tantalum content is fixed at 0.0% by weight. Preferred limits for the proportions of the elements Titanium, Niobium and Aluminum based on the relationship (0.6WTi+0.31WNb) / WAl are superimposed. [Figure 11] Figure 11 is a contour plot showing the effect of the elements Aluminum and Titanium on the yield strength (in terms of strength figure of merit) for an alloy with a preferred elemental cost (<14.7$ / kg), in which the niobium content is fixed at 4.0% by weight and the tantalum content is fixed at 0.0% by weight. Preferred limits for the proportions of the elements Titanium, Niobium and Aluminum based on the relationship (0.6WTi+0.31WNb) / WAl are superimposed. [Figure 12] Figure 12 is a contour plot showing the effect of the elements Aluminum and Niobium + Titanium (based on the 0.6WTi + 0.3WNb relationship) on the gamma prime solvus temperature for an alloy with a preferred elemental cost (<14.7$ / kg). In this alloy, the tantalum content is fixed at 0.0% by weight. Superimposed are preferred limits for the elemental titanium, niobium and aluminum ratios based on the (0.6WTi + 0.31WNb) / WAl relationship and preferred concentrations of Aluminum, Titanium and Niobium based on the (0.6WTi + 0.3WNb + 0.12WAl = 3.7) relationship. [Figure 13]Figure 13 is a contour plot showing the effect of the elements Aluminum and Niobium + Titanium (based on the 0.6WTi + 0.3WNb relationship) on the gamma prime volume fraction at 900°C for an alloy with a preferred elemental cost (<14.7$ / kg). In this alloy, the tantalum content is fixed at 0.0 wt.%. Superimposed are preferred limits for the elemental titanium, niobium and aluminum ratios based on the relationship (0.6WTi + 0.31WNb) / WAl and preferred concentrations of Aluminum, Titanium and Niobium based on the relationship (0.6WTi + 0.3WNb + 0.12WAl = 3.7). [Figure 14] FIG. 14 is a contour plot showing the effect of elemental tungsten and tantalum on alloy density. [Figure 15] 15 is a contour plot showing the effect of the elements tungsten and molybdenum on creep resistance (in terms of creep figure of merit), in which the tantalum content is fixed at 0.0 wt. %. [Figure 16] 16 is a contour plot illustrating the effect of the elements tungsten and molybdenum on creep resistance (in terms of creep figure of merit), in which the tantalum content is fixed at 1.0 wt.%. [Figure 17] 17 is a contour plot showing the effect of the elements tungsten and molybdenum on creep resistance (in terms of creep figure of merit). In this alloy, the tantalum content is fixed at 2.0 wt.%. [Figure 18] 18 is a contour plot illustrating the effect of the elements tungsten and molybdenum on creep resistance (in terms of creep figure of merit). In this alloy, the tantalum content is fixed at 3.0 wt.%. [Figure 19] 19 is a contour plot illustrating the effect of the elements tungsten and molybdenum on creep resistance (in terms of creep figure of merit). In this alloy, the tantalum content is fixed at 4.0 wt.%. [Figure 20]20 is a contour plot showing the effect of the elements tungsten and molybdenum on creep resistance (in terms of creep figure of merit), in which the tantalum content is fixed at 5.0 wt.%. [Figure 21] FIG. 21 is a contour plot showing the effect of the elements chromium and tungsten plus molybdenum (based on the relationship WMo+0.5WW) on the stability number Md. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] Traditionally, nickel-base superalloys have been designed on an empirical basis. Thus, the chemical composition of a nickel-base superalloy has been identified through time-consuming and expensive experimental development involving small-scale processing of limited amounts of material and subsequent characterization of behavior. The alloy composition found to exhibit the best, or most desirable, combination of properties is then adopted. The large number of alloying element families that can achieve this combination indicates that these alloys are not fully optimized and that improved alloys are likely to exist.

[0035] In superalloys, chromium (Cr) and aluminum (Al) are typically added to provide oxidation / corrosion resistance, and cobalt (Co) is added to improve resistance to sulfidation. For creep resistance, molybdenum (Mo), tungsten (W) and cobalt (Co) are added because they inhibit thermally activated processes (e.g., dislocation climb) that determine the rate of creep deformation. For static and cyclic strength, aluminum (Al), tantalum (Ta), niobium (Nb) and titanium (Ti) are added because they promote the formation of a precipitation hardening phase, gamma prime (γ´), which is coherent with the face-centered cubic (FCC) matrix phase, called gamma (γ).

[0036] The model-based approach used to identify new grades of nickel-base superalloys is described herein by the term "Alloy Design" (ABD) methodology. This approach utilizes a framework of computational materials models to estimate design-relevant properties over a very wide compositional range. In principle, this alloy design tool allows the so-called inverse problem to be solved; that is, the optimum alloy composition that best satisfies specified design constraints can be identified.

[0037] The first step in the design process is to define the table of elements and the associated upper and lower compositional limitations. In the present invention, the compositional limitations for each element are considered when adding each element, called the "alloy design space." These compositional limitations are detailed in Table 2. Table 2 shows the alloy design space that was studied.

[0038] [Table 2]

[0039] The second step is based on thermodynamic calculations to calculate the phase diagram and thermodynamic properties of a particular alloy composition. This is often called the CALculate PHAse Diagram (CALPHAD) method. These calculations are performed at the typical service temperature of the new alloy (900°C) to obtain information about the phase equilibria (microstructure).

[0040] The third step involves identifying an alloy composition with the desired microstructure. For nickel-base superalloys that require superior resistance to creep deformation, creep rupture life improves gradually as the volume fraction of the precipitation-hardening phase gamma-minus increases. The range of gamma-minus volume fraction at 900°C where creep rupture life is most beneficial is 60-70% (although other design constraints often limit the volume fraction to lower values, so alloys with gamma-minus volume fractions of 50-60% are included). A decrease in creep resistance is observed above 70% gamma-minus volume fraction.

[0041] Also, the gamma / gamma' lattice mismatch must be positive or negative, whichever is smaller, to lose coherency. Therefore, the limit depends on the absolute value. The lattice mismatch δ is defined as the mismatch between the gamma and gamma' phases and is given by the following formula:

[0042]

number

[0043] Here, α γ and α γ´ are the lattice constants of the γ and γ′ phases.

[0044] The model therefore identifies all compositions within the design space that have a desired calculated volume fraction of γ′, where the lattice mismatch of γ′ is less than a given absolute value.

[0045] In the fourth step, figures of merit are estimated for the identified alloy compositions remaining in the data set, including creep figure of merit (which indicates an alloy's creep resistance based on average composition only), strength figure of merit (which indicates an alloy's precipitation yield strength based on average composition only), density, cost, microstructural stability, and gamma prime solvus temperature.

[0046] In the fifth stage, the calculated figures of merit are compared to constraints on the desired behavior, and these design constraints are considered as boundary conditions for the problem. All compositions that do not satisfy the boundary conditions are rejected. At this stage, the size of the test data set is made very small.

[0047] The sixth and final step involves analyzing the remaining composition dataset. This can be done in a variety of ways. One way is to sort through the database for alloys with the highest figures of merit, such as the lightest alloys, the most creep resistant alloys, the most oxidation resistant alloys, and the least expensive alloys. Alternatively, the database can be used to determine the relative tradeoffs in performance that result from different combinations of properties.

[0048] Explain the six merit indices.

[0049] The first figure of merit is the creep figure of merit. The most important observation is that the time-dependent deformation (i.e. creep) of nickel-base superalloys occurs by dislocation creep with initial activity limited to the gamma phase. Thus, dislocation segments are rapidly pinned at the gamma / gamma interface due to the large fraction of gamma' phase. The rate-limiting step is the escape of the trapped configuration of dislocations from the gamma / gamma' interface. It depends on the local chemistry (in this case the composition of the gamma phase) which causes the critical effect of the alloy composition on the creep properties.

[0050] The physics-based microstructural model assumes that the loading is uniaxial. <001> In the case where the creep strain ε is along the crystallographic direction, · The set equation is:

[0051]

number

[0052] Here, ρ m is the mobile dislocation density, φ p is the volume fraction of the γ´ phase, and ω is the width of the matrix channel. The terms σ and T are the applied stress and temperature, respectively. The terms b and k are the Burgers vector and the Boltzmann constant, respectively. The term K CF is the constraint coefficient.

[0053]

number

[0054] term K CF describes the proximity of cubic grains in these alloys. Equation 3 describes the dislocation multiplication process, which requires an estimate of the multiplication parameter C and the initial dislocation density. The term D eff is the effective diffusivity that controls the ascending process at the particle / matrix interface.

[0055] In the above, the composition dependence is expressed by two terms φ p and D eff Therefore, assuming the microstructure is constant (the microstructure is largely controlled by heat treatment), φ p Since is fixed, the dependence on chemical composition is D eff For the purposes of the alloy design modeling described herein, it can be appreciated that it is not necessary to perform a full integration of Equations 2 and 3 for each prototype alloy composition. Instead, the first order figure of merit M creep is used. creep is calculated using the following formula:

[0056]

number

[0057] where x i is the atomic fraction of solute i in the γ phase. D i ~ is the appropriate interdiffusion coefficient.

[0058] The second figure of merit is the strength figure of merit. For high nickel-base superalloys, most of the strength comes from the precipitate phases. Therefore, optimizing the alloy composition to maximize the precipitation strength is an important design consideration. Based on hardening theory, the strength figure of merit M strengthis proposed. This index takes into account the maximum possible precipitation strength (determined as the point at which the transition of dislocation shear from weak to strong bonds occurs) and is approximated using the following equation:

[0059]

number

[0060] where M- is the Taylor coefficient, γ APB is the antiphase boundary (APB) energy, φ p is the volume fraction of the γ´ phase and b is the Burgers vector.

[0061] From equation (5), it is clear that the defect energy in the gamma-phase (e.g., the antiphase boundary APB energy) has a significant effect on the deformation behavior of nickel-base superalloys. Increasing the APB energy was found to improve the mechanical properties, including tensile strength and resistance to creep deformation. A study of the APB energy was carried out for a number of Ni-Al-X systems using density functional theory. The study calculated the effect of ternary elements on the APB energy of the gamma-phase and assumed a linear superposition of the effects of each ternary element addition when considering complex multicomponent systems. This resulted in the following equation:

[0062]

number

[0063] where x Cr , x Mo , x W , x Ta , x Nb and x Ti are the atomic percentages of chromium, molybdenum, tungsten, tantalum, niobium, and titanium in the gamma prime phase. The composition in the gamma prime phase is determined by phase equilibrium calculations.

[0064] The third figure of merit is density. Density ρ was calculated using a simple rule of mixtures and correction factors, where ρ i is the density of a given element, and x i is the atomic fraction of the alloying element.

[0065]

number

[0066] The fourth figure of merit is cost. To estimate the cost of each alloy, we applied the simple rule of mixtures, where the cost of each alloy is the mass fraction of the alloying element x i 2. Current (2017) raw material costs of alloying elements i The value multiplied by was used.

[0067]

number

[0068] This estimate assumes that processing costs are the same for all alloys, i.e. product yields are not affected by composition.

[0069] The fifth figure of merit is based on the elimination of alloy candidates based on unsuitable microstructures made based on susceptibility to TCP phases. To do this, the d-orbital energy levels (designated Md) of the alloying elements are used to determine the total effective Md level according to the following formula:

[0070]

number

[0071] where x i represents the mole fraction of element i in the alloy. A higher value of Md indicates a higher possibility of TCP formation.

[0072] The sixth figure of merit is the gamma prime solvus temperature. The gamma prime solvus is defined as the temperature at which the volume fraction of gamma prime tends to zero. This is determined using thermodynamic calculations as described above in the second step of the alloy design method. The phase diagram and thermodynamic properties of a particular alloy composition are calculated and used to find the temperature at which the phase transition occurs.

[0073] Using the ABD methodology described above, the alloy composition of the present invention was identified. The design intent of this alloy is to provide substantially higher strength combined with reduced alloy cost and improved oxidation / corrosion resistance. The balance of properties of the new alloy allows for more cost-effective manufacture of components for high temperature applications, particularly for use as turbine disk applications where the component operating temperature is 800 degrees or higher.

[0074] The material properties (determined using the ABD method) of nominal compositions of commonly applied / investigated alloys (listed in Table 1) used for powder metallurgy (PM) turbine disk applications are listed in Table 3. In relation to the predicted properties listed for these alloys, the design of new alloys was considered. Table 3 shows the calculated phase fractions, mismatches and figures of merit generated by the "Alloy Design" software. This is the result for the nickel-base superalloys listed in Table 1.

[0075] The design principles of the new alloy are explained below.

[0076] [Table 3]

[0077] FIG. 1 shows the calculation of the cost and strength figures of merit for the nominal compositions of commonly applied / investigated alloys (listed in Table 1) used for powder metallurgy (PM) turbine disk applications. FIG. 1 also shows the calculation of the cost and strength figures of merit for millions of alloys that fall within the compositional design space listed in Table 2 (shaded area). For a given alloy cost, there is an upper limit to the maximum strength that can be achieved (FIG. 1). The dotted line in FIG. 1 represents the maximum strength that can be achieved for a given alloy cost. It can be seen that it is possible to achieve high strength levels (comparable to or higher than the prior art) while reducing the elemental cost of the alloy. The hatched area in FIG. 1 shows the performance criteria targeted by the present invention in terms of alloy cost and strength figures of merit. The identification of alloy compositions that have a combination of high strength and low cost is discussed in the next section.

[0078] Figures 2-6 show the effect of the elements tantalum, cobalt and niobium on the cost of the alloy. These elements have a significantly higher cost than the base element nickel, which significantly increases the price of the alloy (based on September 2017 metal prices). Normalized to the price of nickel, the costs of tantalum, cobalt and niobium are 11.93, 5.45 and 3.82, respectively. As will be explained below in connection with Figures 15-20, a minimum level of cobalt of 3.8 wt.% is preferred to provide an alloy with sufficient creep strength (in terms of creep figure of merit).

[0079] The cost target in the present invention is 14.7$ / kg or less, i.e. a 10% reduction in element cost compared to the lowest cost alloy listed in Table 1 (Alloy N19, 16.4$ / kg). From Figures 2-6, a relationship between elemental additions (based on niobium, cobalt and tantalum) and the target alloy cost was derived. The relationship representing the three-dimensional surface was determined in the following way. From Figures 2-6, the relationship between alloy cost and niobium and cobalt was determined for a cost target of 14.7$ / kg and preferred cost targets of 14.0$ / kg and 13.1$ / kg. This was determined from the contour lines at these values. The transformation of the lines as a function of different tantalum contents was determined from Figures 2-6. From the above process, the additions of tantalum, cobalt and niobium were identified to comply with the following formula:

[0080]

number

[0081] where f(cost) is a number and W Nb , W Co and W Taand f(cost) denote the mass% of niobium, cobalt and tantalum, respectively, contained in the alloy. For example, to produce an alloy with a cost of 14.7$ / kg or less, the value of f(cost) should be 14.7 or less. Based on the minimum level of cobalt (3.8% by weight) and the minimum concentration of niobium (0.0% by weight) in the present invention, the maximum content of tantalum in the alloy should be 2.4% by weight or less, referring to f(cost). To achieve the cost target, the maximum content of cobalt should be limited to 9.6% by weight (see FIG. 2). Preferably, to achieve a cost of 14.0$ / kg or less (i.e., a 15% reduction in elemental cost compared to the lowest cost alloy (Alloy N19, 16.4$ / kg)), the value of f(cost) should be 12.4 or less. In this case, based on the minimum concentration of cobalt (3.8% by weight) and the minimum concentration of niobium (0.0% by weight), the maximum content of tantalum in the alloy should be 1.8% by weight or less. Due to cost considerations, the maximum cobalt content is preferably limited to 8.1 wt.% or less (see FIG. 2). Most preferably, the value of f(cost) should be 9.5 or less to achieve a cost of 13.1 $ / kg or less (i.e., a 20% reduction in elemental costs compared to the lowest cost alloy (Alloy N19, 16.4 $ / kg)). In this case, based on the minimum concentration of cobalt (3.8 wt.%) and the minimum concentration of niobium (0.0 wt.%), the maximum amount of tantalum contained in the alloy should be 1.0 wt.% or less. Most preferably, the maximum cobalt content is limited to 6.0 wt.% to achieve a cost of 13.1 $ / kg or less (see FIG. 2).

[0082] In one embodiment of the present invention, instead of including nickel, it is desirable to include iron, which has the advantage of reducing the cost of the alloy and increasing the recyclability of the alloy. The addition of iron can compromise microstructural stability. Limiting the iron addition to a level of 4.0 wt. % provides a good balance between low cost, improved recyclability and microstructural stability. More preferably, the iron content ranges from 1.0 wt. % to 2.0 wt. %.

[0083] In combination with low cost, the present invention relates to a high strength alloy. The goal of the present invention is to have a strength figure of merit of 1700 MPa or more. Having this target strength figure of merit provides an alloy with a maximum operating temperature comparable to the highest strength alloys listed in Table 1 (the three highest strength alloys, ranging between 1719 MPa and 1854 MPa), but with significantly reduced elemental costs (30-45% compared to alloys with strength figures of merit above 1700 MPa). Thus, a significantly improved combination of strength and cost is achieved.

[0084] The gamma-prime (γ´) former elements, aluminum, titanium, niobium and tantalum, are the primary metals added to increase the strength figure of merit. Figures 7-11 show the effect of aluminum, titanium and niobium on strength in alloys that meet cost targets. Note that the results (Figures 7-11) do not include tantalum-containing metals. Titanium, niobium and tantalum additions are given coefficients to convert the weight % added to "aluminum equivalent". The effect of elements with widely differing densities can be directly compared. For example, aluminum has a density of 2.7 g / cm 3 whereas titanium has a density of 4.5 g / cm 3 4.5 = 0.6) Similar to titanium, the element niobium (8.57 g / cm 3 ) and elemental tantalum (16.4 g / cm 3In order to convert the amount of addition of niobium (Ti, Al, and Ni) to "aluminum equivalent", a constant is added. That is, the correction factors for niobium and tantalum are determined from the density of those elements relative to aluminum, which are 0.3 and 0.15, respectively. Based on Figures 7-11, the relationship between the amount of element addition (based on titanium, aluminum, and niobium) and the target metal strength was obtained. The relationship (drawing a three-dimensional surface) was determined by the following method. The relationship between the metal strength and aluminum and titanium at a target strength of 1700 MPa was determined from Figures 7-11, which was determined in the isopleth of these values. The conversion of the line as a function of different niobium contents was determined based on Figures 7-11. Based on the above process, it can be seen that the amount of addition of aluminum, titanium, and niobium follows the following formula:

[0085]

number

[0086] where f(strength) is a number and W Ti , W Nb and W Al are the mass percent of titanium, niobium, and aluminum contained in the alloy, respectively. To produce an alloy with a strength figure of merit of 1700 MPa or more, the value of f(strength) must be 3.7 or more.

[0087] Tantalum is an added element present in an amount of up to 2.4% by weight. In one embodiment of the present invention, tantalum can be added by atomic substitution of titanium and niobium up to a level of 2.4% by weight, i.e., for every atom of tantalum added, the maximum allowable level of at least one of titanium and niobium is reduced so that the sum of the maximum atomic percentages of titanium, tantalum, and niobium is equal to the atomic percentage corresponding to the sum of the maximum allowable levels of titanium and niobium.

[0088] The amounts of aluminum, titanium, niobium, and tantalum added follow the formula below. Note that a factor of 0.27 is applied to tantalum, rather than 0.15, which is determined based on its effect on gamma prime formation. This is because tantalum has a large effect on APB energy intensity, as shown in formula (6). Based on formula (6), the APB strength factor for tantalum is 27.1, and a factor of 15 is applied to titanium, meaning that tantalum is 1.8 times more effective in terms of strength. This factor was multiplied by the aluminum equivalent of tantalum (0.15) to arrive at a factor of 0.27 (i.e., 0.15 x 1.80 = 0.27).

[0089]

number

[0090] To produce an alloy with a strength figure of merit of 1700 MPa or more, the value of f(strength) must be 3.7 or more. To further increase the strength, the value of f(strength) is preferably 4.0 or more, or 4.1 or more.

[0091] To achieve a good balance between strength and ability to process the alloy, the gamma prime solvus should be below 1180°C. A gamma prime solvus below 1180°C is preferred because it reduces the alloy's susceptibility to cracking on cooling from above the gamma prime solvus while still allowing heat treatment above the gamma prime solvus. Heat treatment above the gamma prime solvus is desirable because it promotes coarse grain growth and improves resistance to dwell fatigue. This damage mechanism is often the life limiting factor in this class of alloys. Based on Figure 12, the gamma prime solvus of the alloy, aluminum, and (0.6W Ti +0.31W Nb The relationship between the total amount of titanium and niobium elements and the amount of aluminum, titanium and niobium added is as follows:

[0092]

number

[0093] where f(solvus) is a numerical value. In one embodiment of the present invention, tantalum can be added as a replacement for titanium and niobium up to a level of 2.4 wt. %, where the function f(solvus) is:

[0094]

number

[0095] To produce alloys with a solvus below 1180°C, the value of f(solvus) should be less than 6.3. To produce alloys with a solvus below 1170°C, the value of f(solvus) is preferably less than 5.9. If the solvus is less than 1170°C, the ability to process the alloy can be improved.

[0096] Based on the formula for f(strength) and the need to keep the γ' solvus below 1180°C, the maximum aluminum content is limited to 3.3 wt.% (FIG. 12). In order to keep the γ' solvus below 1170°C, the aluminum content is preferably limited to 3.0 wt.% (FIG. 12). Ti +0.31W Nb ) / W AlA ratio of elements based on NiO ≦1.3 is desirable (see DJ Crudden, N. Warnken, A. Mottura, and RC Reed. Modelling of the influence of alloy composition on flow stress in high-strength nickel-based superalloys. Acta Materialia, 7:356-370, 2014). This is necessary to maintain the stability of the gamma-phase, and above this value the alloy is prone to the formation of undesirable eta (Ni3Ti) and delta (Ni3Nb) phases, which reduce the alloy's ductility and fatigue resistance. Niobium should be limited to less than 4.0 wt. % because higher concentrations of niobium tend to stabilize the niobium-rich delta phase Ni3Nb. Niobium need not be present in the alloy because of its detrimental effect on stability.

[0097] In one embodiment of the present invention, tantalum can be added as a replacement for titanium and niobium up to a level of 2.4% by weight. In this embodiment, the proportion of the element is (0.6W Ti +0.31W Nb +0.15W Ta ) / W Al The relationship is ≦1.3.

[0098] Based on the maximum elemental niobium content (4%, by weight), the maximum elemental aluminum content (3.3%, by weight), and the maximum elemental tantalum content (2.4%, by weight), the minimum level of titanium required is 2.3%, by weight (see formula for f(strength)). To achieve the preferred tantalum content (1.8%, by weight), the titanium content is preferably 2.6% or more. To achieve the more preferred tantalum content (1.0%, by weight), the titanium content is more preferably 3.0% or more. Most preferably, the titanium content is 3.5% or more. By achieving 3.5% or more, by weight, the alloy can be substantially free of tantalum, which improves the combination of cost and strength. Even more preferably, the titanium content is 4.1% or more, by weight. By achieving 4.1% or more, by weight, the alloy can be substantially free of tantalum, and niobium can be used at a preferred level (2.7% or less, by weight) as described below in the relationship between creep figure of merit and alloy cost. Based on maximum solvus temperature (1180°C), 0.6W Ti +0.31W Nb +0.15W Ta The total amount of elements derived from the relationship between the elements and the maximum aluminum content (3.3% by weight) and the minimum niobium and tantalum contents (0.0% by weight) must not exceed 3.33 (see the formula for f(solvus)). The maximum allowable titanium content is therefore 5.6% by weight (3.33 / 0.6=5.6). To ensure the desired combination of strength, gamma-prime solvus and gamma-prime stability is achieved, the aluminum content must be greater than or equal to 2.6% by weight (i.e., (0.6W Ti +0.31W Nb +0.15W Ta ) / W Al ≦1.3) (see FIG. 12). It is more preferable to limit the aluminum content to 3 mass % in order to lower the γ′ solvus (see FIG. 12).

[0099] The addition of aluminum, niobium, and titanium affects the proportion of precipitation hardening γ´ phase. The point at which the strength figure of merit must be greater than 1700 MPa (determined as a function of f(strength)) and the proportion of elements (0.6W Ti +0.31W Nb ) / W Al ≦1.3), the gamma prime volume fraction of the alloy should be in the range of 51%-58% at a temperature of 850°C (see Figure 13). The gamma prime volume fraction is experimentally determined by the following procedure: After aging heat treatment at 850°C, a portion of the material is cut and polished using conventional / standard metallurgical preparation techniques with a scanning electron microscope. The microstructure of the prepared gamma / gamma prime should be visible with a scanning electron microscope and grains of 30 μm or less in diameter should be visible. Ten images are taken that provide a statistically representative data set. The images are at least 1 mm in diameter. 2 The 2D images revealing the gamma / gamma prime microstructure must be processed to identify the gamma prime phase and the area fraction of the gamma prime phase must be calculated. The area fraction of this phase is taken as the volume fraction of gamma prime and must be between 51-58%. Based on FIG. 13, the γ´ fraction of the alloy and the aluminum and (0.6W Ti +0.31W Nb To achieve an alloy with a γ´ fraction between 51 and 58%, the amounts of aluminum, titanium and niobium added should follow the formula:

[0100]

number

[0101] Here, f(γ´) is a value in the range of 5.4 to 6.0.

[0102] In one embodiment of the present invention, tantalum may be added as an alternative to titanium and niobium up to a level of 2.4 wt. %. In this embodiment, the amounts of aluminum, titanium, niobium and tantalum added preferably follow the formula:

[0103]

number

[0104] The addition of tantalum increases the strength of the alloy (in terms of strength figure of merit) by increasing the gamma prime volume fraction and by increasing the antiphase boundary energy. The addition of tungsten to the alloy increases the creep strength in the alloy (in terms of creep figure of merit) by making diffusion in the gamma matrix very slow. The addition of tungsten to the alloy also increases the gamma matrix phase's solid solution strengthening. The strength is improved due to the addition of tungsten and tantalum, which acts as a strengthening agent. However, tungsten and tantalum are the heaviest alloying elements listed in the design region of Table 2, and are significantly denser than nickel. Therefore, the contribution of tungsten and tantalum to strength must be balanced against their detrimental effect on alloy density. The target density in this invention is 8.4 g / cm3. 3 This makes the alloy lighter than other alloys (Table 3) that have strength figures of merit above 1700 MPa. Figure 14 shows the effect of tantalum and tungsten elements on the alloy density. The density is 8.4 g / cm 3 14, the amount of tantalum and tungsten added satisfies the following formula:

[0105]

number

[0106] Here, f(density) is 8.4g / cm 3A value of 6.2 or less is required to achieve a density of 8.3 g / cm. 3 To produce an alloy with a density of less than 8.2 g / cm, the value of f(density) is less than 4.6. More preferably, it is less than 8.2 g / cm. 3 In order to produce an alloy with a density of 2.9 or less, the value of f(density) is 2.9 or less. Therefore, tungsten is preferably 4.6% by mass or less, and more preferably 2.9% by mass or less.

[0107] To provide creep strength equivalent to alloy N19 at a lower cost, the target creep figure of merit for the alloy is 2.4 x 10 -15 m -2 The target density is 8.4g / cm 3 Therefore, tungsten is limited to 6.2 mass% or less (FIG. 14). The roles of tungsten, cobalt and molybdenum are shown in FIGS. 15 to 20. From FIGS. 15 to 20, the relationship between the amount of elemental addition (based on cobalt, molybdenum and tungsten) and the target alloy creep figure of merit is obtained. The relationship (drawing a three-dimensional surface) is determined by the following method. The relationship between the alloy creep figure of merit, cobalt and tungsten is obtained when the target creep figure of merit is 2.4×10 -15 m -2 s was determined from Figures 15-20, and the relationship was determined in the contour lines of these values. The transformation of the lines as a function of different molybdenum contents was determined based on Figures 15-20. Based on the above process, in order to improve creep resistance (in terms of creep figure of merit), the addition of tungsten, cobalt and molybdenum follows the following formula:

[0108]

number

[0109] Here, f(creep) is 2.4×10 -15 m -2In order to achieve a creep figure of merit of .s or more, a value of 16.0 or more is required. Therefore, based on the maximum level of tungsten (6.2%, by weight) and the maximum level of cobalt (9.6%, by weight), a molybdenum content of at least 0.6%, by weight, is required to achieve sufficient creep resistance. To reduce the alloy density, tungsten is preferably limited to 4.6%, by weight, with molybdenum being increased accordingly to 2.2%, by weight or more. To reduce both the density and the cost of the alloy, it is more preferable to limit tungsten to 4.6%, by weight, and cobalt to 8.1%, by weight or less, with molybdenum being preferably 3.6%, by weight or more. As will be explained later with reference to FIG. 21, stability requirements limit the maximum molybdenum content to 5.1%, by weight or less.

[0110] The minimum creep figure of merit is 2.4 x 10 -15 m -2 To achieve s, at a maximum cobalt of 9.6% by weight, a minimum tungsten content of 0.7% by weight is required (see FIG. 20). Since it is preferred to limit molybdenum to 4.1% to improve the alloy stability (see below), the tungsten content is preferably 1.9% by weight or more to obtain a better balance between creep resistance and alloy stability. Based on the maximum tungsten level (6.2% by weight) and the maximum molybdenum level (5.1% by weight), a minimum concentration of cobalt of 3.8% by weight is desirable to obtain a good level of creep resistance (FIG. 20). Since tungsten is preferably limited to 4.6% by weight, the cobalt level is preferably 5.5% by weight or more accordingly, and more preferably tungsten is limited to 2.9% by weight, the cobalt content is preferably 8.0% by weight or more accordingly (FIG. 20). This balances creep resistance and alloy stability. Based on the preferred cobalt content of 8.0 wt.% or more, niobium is preferably limited to 2.7 wt.% or less to improve the balance between creep resistance and density (FIG. 2).

[0111] FIG. 21 shows the effect of chromium content and the sum of the elements molybdenum and tungsten (based on the relationship Mo+0.5W) on the stability number. The higher the stability number, the more likely the alloy is to form TCP phases. It is beneficial to limit or stop the precipitation of TCP phase formation, since TCP phases lead to degradation of material properties. Tungsten has about twice the density of molybdenum, so a correction factor of 0.5 is applied. This factor accounts for the large difference in density of the elements. To achieve a good level of oxidation resistance, a chromium level of 9.5 wt.% or more is desirable. To avoid TCP formation while ensuring microstructural stability, the target stability is 0.91 or less. Therefore, the molybdenum content is desirably 5.1 wt.% or less (md≦0.91), and preferably 4.1 wt.% or less (md≦0.90) (FIG. 21). Based on the creep requirement determined by f(creep), the minimum sum of molybdenum and tungsten according to the relationship Mo+0.5W is 3.7% by weight (maximum tungsten content is 6.1% by weight and minimum molybdenum content is 0.6% by weight). Therefore, the maximum level of chromium should be 14.4% by weight. To improve oxidation resistance, the chromium content is preferably 10.0% or more. To improve oxidation resistance (higher Cr content) over other alloys with strength figure of merit of 1700 MPa or more, the chromium content should be 11.5% by weight or more, and more preferably 12.0% by weight or more. Based on FIG. 21, it was found that the addition amounts of the elements molybdenum, tungsten and chromium follow the formula:

[0112]

number

[0113] Here, f(stability) is a value of 15.5 or less in order to maintain alloy stability.

[0114] The addition of carbon, boron and zirconium is necessary to provide strength to the grain boundaries. This is particularly beneficial to the creep and fatigue properties of the alloy. Carbon is added to act as grain boundary pinning particles. Carbon is required when heat treating above the gamma prime solvus temperature to inhibit excessive grain growth. The carbon concentration should be in the range of 0.01% to 0.1% by weight. The carbon level is preferably between 0.2 and 0.06 to provide better distribution of the carbide phase to control the alloy microstructure, especially grain size.

[0115] The boron concentration should be in the range of 0.001-0.1 wt.%. The addition of boron can improve creep ductility and grain boundary strength through the formation of boride phases. To achieve the desired level of boride phases, the boron content in the alloy is preferably 0.01-0.05 wt.%.

[0116] The zirconium concentration should be in the range of 0.001% to 0.3% by weight, preferably 0.02 to 0.1% by weight. Zirconium serves to expel undesirable impurities (e.g. oxygen and sulfur) contained in the alloy, which may cause embrittlement of the alloy, especially due to grain boundary embrittlement.

[0117] When the alloy is produced, it is beneficial for it to be substantially free of unavoidable impurities. These impurities may include elemental sulfur (S), elemental manganese (Mn) and elemental copper (Cu). Elemental sulfur should be lower than 0.003% by weight (30 PPM by weight). Manganese is an unavoidable impurity limited to 0.25% by weight, and preferably limited to less than 0.1% by weight. Copper (Cu) is an unavoidable impurity preferably limited to 0.5% by weight. The presence of more than 0.003% by weight of sulfur can cause embrittlement of the alloy, and sulfur also segregates to the alloy / oxide interface formed during oxidation. For this reason, the level of sulfur is preferably less than 0.001% by weight. Vanadium, an unavoidable impurity, adversely affects the oxidation behavior of the alloy and is therefore preferably limited to 0.5% by weight, and preferably less than 0.3% by weight, and most preferably less than 0.1% by weight. This segregation can lead to increased spalling of the protective oxide scale. When the concentrations of these unavoidable impurities exceed specified levels, problems with product yield and degradation of the material properties of the alloy are expected.

[0118] Hafnium (Hf) can be beneficially added up to 0.5 wt. % to tie up unavoidable impurities in the alloy and to provide strength. Hafnium is a strong carbide former and can provide additional grain boundary strengthening. Due to the high elemental cost and the detrimental effect of its addition on the alloy cost, hafnium is preferably limited to 0.2 wt. %, and more preferably to less than 0.1 wt. %.

[0119] The so-called "reactive elements" (yttrium (Y), lanthanum (La) and cerium (Ce)) are added at levels up to 0.1 wt. %. This is beneficial in improving the adhesion of protective oxide layers such as Cr2O3. These reactive elements can "sweep" harmful elements such as sulfur, which segregates at the alloy-oxide interface and weakens the bond between the oxide and the substrate, leading to oxide spalling. Silicon (Si) can be added beneficially at levels up to 0.5 wt. %. The addition of silicon to nickel-base superalloys at levels up to 0.5 wt. % has been shown to be beneficial for oxidation properties. In particular, silicon segregates at the alloy / oxide interface and improves the bond of the oxide to the substrate. This reduces oxide spalling, resulting in improved oxidation resistance.

[0120] Based on the description of the invention in this section, broad ranges of the invention are listed in Table 4. Table 4 also provides preferred ranges.

[0121] [Table 4]

[0122] In the next section, exemplary compositions of the present invention are described. Calculated properties of these new alloys are listed. The rationale for the design of these alloys is next described. EXAMPLES

[0123] An inventive example of the composition (exemplary LCPM-1) is listed in Table 5. The listed alloy has several advantages over the high strength alloys (Table 3) listed in Table 1, which have strength figures of merit of 1700 MPa or more. In particular, the cost is significantly reduced (14.5 $ / kg) compared to these alloys (which have costs of 21.6-28.6 $ / kg), reducing element costs by at least 32% while retaining comparable strength. The LCPM alloys further have the advantage that they are less expensive than these alloys (8.5-8.7 g / cm 3 It has a low density (8.3 g / cm3) compared to 3LCPM alloy has a chromium content (11.8% by weight) similar to these alloys (10.0-13.4% by weight chromium content).

[0124] In Table 5, (0.6W Ti +0.31W Nb +0.15W Ta ) / W Al The ratio of elements based on the relationship between the alloy and the alloy was revised to a range of 1.13 to 1.28. This was shown to further increase the strength of the alloy (Table 6). Table 5 shows the results for the alloy with a 0.6W Ti +0.31W Nb +0.15W Ta ) / W Al The following shows an example of a composition in which the ratio of (0.6W) is modified between 1.13 and 1.28. Table 6 shows the calculated phase fractions and figures of merit generated by the "Alloy Design" software. This is because, in the example alloy LCPM-1, Ti +0.31W Nb +0.15W Ta ) / W Al The results are for compositions in which the ratio was modified between 1.13 and 1.28 (Table 5).

[0125] [Table 5]

[0126] [Table 6]

[0127] In Table 7, the composition of the exemplary alloy LCPM-1 is modified to provide a lower cost alloy. The cobalt content of the alloy is reduced to reduce alloy cost. Cobalt provides creep resistance to the alloy, necessitating the use of molybdenum and tungsten as substitutes for cobalt, based on the relationship defined by f(creep). To manage the stability of the alloy, the levels of molybdenum and tungsten are increased with the reduction of chromium, based on the relationship of f(stability). Alloys LCPM6-8 are beneficial when there is a strong desire to reduce alloy cost, and where a reduction in alloy density (Table 8) and a lesser increase in alloy corrosion resistance are desired (i.e., lower chromium levels). Table 7 shows an example where the composition of chromium, cobalt, molybdenum, and tungsten is modified in the exemplary alloy LCPM-1 to maintain the creep resistance of the alloy at a lower cost. Table 8 shows the calculated phase fractions and figures of merit generated by the "Alloy Design" software. This is the result of modified compositions of chromium, cobalt, molybdenum and tungsten in the exemplary alloy LCPM-1 (Table 7) to maintain the creep resistance of the alloy at a lower cost.

[0128] [Table 7]

[0129] [Table 8]

[0130] In Table 9, the exemplary alloy LCPM-7 was modified to include an additional element, tantalum. It is shown that tantalum can substitute for titanium (LCPM13-14) and tantalum can substitute for niobium (LCPM15-18). It can be seen that the addition of tantalum in atomic substitution for titanium or niobium increases the alloy cost. As shown in the examples, the addition of tantalum is beneficial when increased alloy strength is desired over reduced alloy cost. Table 9 shows examples of compositions in which the contents of niobium, titanium, and tantalum are modified in the exemplary alloy LCPM-7. Table 10 shows the calculated phase fractions and figures of merit generated by the "Alloy Design" software. This is the result of compositions in which the contents of niobium, titanium, and tantalum are modified in the exemplary alloy LCPM-7 (Table 9).

[0131] [Table 9]

[0132] [Table 10]

[0133] In Table 11, the balance of molybdenum and tungsten in the alloy is changed for the example alloy LCPM-1. It is shown that if molybdenum is reduced and tungsten is increased based on the f(creep) relationship, the chromium level in the alloy can be further increased based on the f(stability) relationship. As the elemental ratio of tungsten to molybdenum increases, the associated tradeoff in alloy density is shown in the example (Table 8) when there is an improvement in corrosion resistance due to the increase in chromium level. Table 11 shows an example of a composition in which the chromium, molybdenum, and tungsten contents are changed in the example alloy LCPM-1 to adjust the balance between creep resistance and corrosion resistance. Table 12 shows the calculated phase fractions and figures of merit created by the "Alloy Design" software. This is the result of a composition (Table 11) in which the chromium, molybdenum, and tungsten contents are changed in the example alloy LCPM-1 to adjust the balance between creep resistance and corrosion resistance.

[0134] [Table 11]

[0135] [Table 12]

Claims

1. In mass percent, 9.5 to 14.4% chromium, 3.8 to 9.6% cobalt, 0.0 to 4.0% iron, 0.6 to 5.1% molybdenum, 0.7 to 6.2% tungsten, 2.6 to 3.3% aluminum, 2.3 to 5.6% titanium, 0.0 to 4.0% niobium, 0.0 to 2.4% tantalum, 0.01 to 0.1% carbon, 0.001 to 0.1% boron, 0.001 0.0-0.5% hafnium, the balance consisting of nickel and unavoidable impurities; The mass percentages of niobium, tantalum, titanium and aluminum contained in the alloy are W Ｎｂ , W Ｔａ , W Ｔｉ and W Ａｌ Then, 0.6W Ｔｉ +0.31W Ｎｂ +0.27W Ｔａ +0.12W Ａｌ ≧3.7 The formula is satisfied. A nickel-base alloy composition, where the weight percent of niobium, tantalum and cobalt in the alloy are WNb, WTa and WCo, respectively, such that: WNb=WTa / WCo / Co. W Nb +1.53W Co +3.7W Ta ≦14.7

2. The mass percentages of niobium, tantalum, titanium and aluminum contained in the alloy are W Ｎｂ , W Ｔａ , W Ｔｉ and W Ａｌ The nickel-based alloy composition according to claim 1, which satisfies the following formula: 0.6W Ｔｉ +0.31W Ｎｂ +0.27W Ｔａ +0.12W Ａｌ ≧4.0

3. The mass percentages of niobium, tantalum, titanium and aluminum contained in the alloy are W Ｎｂ , W Ｔａ , W Ｔｉ and W Ａｌ The nickel-based alloy composition according to claim 1 or 2, which satisfies the following formula: (0.6W Ｔｉ +0.31W Ｎｂ +0.15W Ｔａ ) / W Ａｌ ≦1.3

4. The mass percentages of niobium, tantalum, titanium and aluminum contained in the alloy are W Ｎｂ , W Ｔａ , W Ｔｉ and W Ａｌ The nickel-based alloy composition according to any one of claims 1 to 3, which satisfies the following formula: 0.6W Ｔｉ +0.31W Ｎｂ +0.15W Ｔａ +0.9W Ａｌ ≦6.3

5. The mass percentages of niobium, tantalum, titanium and aluminum contained in the alloy are W Ｎｂ , W Ｔａ , W Ｔｉ and W Ａｌ The nickel-based alloy composition according to any one of claims 1 to 4, which satisfies the following formula: 5.4≦0.6W Ｔｉ +0.31W Ｎｂ +0.15W Ｔａ +0.8W Ａｌ ≦6.0

6. The mass percentages of tungsten and tantalum contained in the alloy are W Ｗ and W Ｔａ The nickel-based alloy composition according to any one of claims 1 to 5, which satisfies the following formula: W Ｗ +1.1W Ｔａ ≦6.2

7. The mass percentages of tungsten, cobalt, and molybdenum contained in the alloy are W Ｗ , W Ｃｏ and W Ｍｏ The nickel-based alloy composition according to any one of claims 1 to 6, which satisfies the following formula: <h2 style=";text-align:left;direction:ltr">W<h2 style=";text-align:left;direction:ltr"> Ｗ <h2 style=";text-align:left;direction:ltr"> +0.96W<h2 style=";text-align:left;direction:ltr"> Ｃｏ <h2 style=";text-align:left;direction:ltr"> 1225<h2 style=";text-align:left;direction:ltr"> Ｍｏ <h2 style=";text-align:left;direction:ltr"> ≧165.0

8. The nickel-based alloy composition according to claim 1 , containing, by mass %, 10.0% or more of chromium.

9. 9. The nickel-based alloy composition according to claim 1, further comprising, by mass%, 5.5% or more of cobalt.

10. 10. The nickel-based alloy composition according to claim 1, further comprising, by weight percent, up to 8.1% cobalt.

11. The nickel-based alloy composition according to claim 1 , comprising, by mass%, 1.0% or more of iron.

12. 12. The nickel-based alloy composition according to claim 1, comprising, by weight percent, up to 2.0% iron.

13. 13. The nickel-based alloy composition according to claim 1, comprising, by weight percent, at least 2.2% molybdenum.

14. 14. The nickel-based alloy composition of claim 1, further comprising, by weight, up to 4.1% molybdenum.

15. 15. The nickel-based alloy composition according to claim 1, containing, by mass%, 1.9% or more of tungsten.

16. 16. The nickel-based alloy composition of claim 1, comprising up to 4.6% tungsten, by weight.

17. 17. The nickel-based alloy composition according to claim 1, comprising, by mass%, 2.6% or more of aluminum.

18. 17. The nickel-based alloy composition of claim 1, further comprising, by weight percent, 3.0% or less of aluminum.

19. 19. The nickel-based alloy composition according to claim 1, comprising, by weight percent, at least 2.6% titanium.

20. 20. The nickel-based alloy composition of claim 1, comprising up to 1.8% tantalum, by weight.

21. 21. The nickel-based alloy composition of claim 1, containing up to 2.7% niobium, by weight.

22. 22. The nickel-base alloy composition of any one of the preceding claims, comprising a volume fraction of 51-58% gamma prime at 850°C.

23. 23. A turbine disk formed from the nickel-base alloy composition of any one of claims 1 to 22.

24. A gas turbine engine comprising a turbine disk according to claim 23.

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