Microalloyed superalloys and heat treatment

Abstract

The invention relates to a nickel-based superalloy comprising (in wt%): C: 0.05% to 0.16%, Cr: 8.0% to 9.5%, Co: 9.0% to 10.5%, W: 9.0% to 10.5%, Mo: 0.2% to 1.0%, Ta: 2.5% to 3.5%, Al: 5.0% to 6.0%, Ti: 0.5% to 1.5%, B: 0.01% to 0.025%, Hf: 1.0% to 2.0%, Zr: 0.004% to 0.06%, nickel (Ni) and unavoidable impurities.

Description

Technical Field

[0001] This application belongs to the technical field of superalloys and relates to a superalloy with good long-term stability and suitable for heat treatment. Background Art

[0002] Gas turbines not only have extremely high requirements for the initial machining accuracy and assembly accuracy of hot-end components, but also require no failure and fracture during long-term use. The alloys used for these components are required to have excellent high-temperature long-term stability and performance to avoid component failure before the overhaul period. Currently, there are few alloys among existing superalloys that can fully meet the above requirements. Generally, alloys that can achieve the above mechanical properties have poor long-term stability. Summary of the Invention

[0003] This application aims to solve at least some of the technical problems in the related art to some extent.

[0004] This problem is solved by the claims according to claim 1 and the heat treatment according to claim 11.

[0005] Other advantages are listed in the dependent claims, and these advantages can be combined arbitrarily with each other to produce other advantages.

[0006] The embodiments of this application propose a superalloy with good long-term stability. Such a superalloy with good long-term stability not only has excellent mechanical properties, but also has long-term stability and long life. It fully meets the design and use requirements of advanced aeroengines and gas turbines and is suitable for medium- and long-term working components such as turbine blades and hot-end components of aeroengines and gas turbines.

[0007] The superalloy with good long-term stability according to the embodiments of this application contains (by wt%): C: 0.05% - 0.16%, Cr: 8.0% - 9.5%, Co: 9.0% - 10.5%, W: 9.0% - 10.5%, Mo: 0.2% - 1.0%, Ta: 2.5% - 3.5%, Al: 5.0% - 6.0%, Ti: 0.5% - 1.5%, B: 0.01% - 0.025%, Hf: 1.0% - 2.0%, Zr: 0.004% - 0.06%, nickel (Ni) and inevitable impurities. Nickel is used as the balance in particular.

[0008] All percentages (%) throughout the specification are given or expressed as wt% unless ppm is mentioned.

[0009] A special contribution is given by magnesium (Mg), manganese (Mn), silicon (Si) and / or iron (Fe).

[0010] The superalloy according to the embodiments of the present application has good long-term stability. In the embodiments of the present application, a strengthening element design scheme of high Al, low Ti and high Ta is adopted. Detailed implementation manners

[0011] The embodiments described below with reference to the accompanying drawings are merely exemplary and are intended to explain the present application and should not be construed as limiting the present application.

[0012] The superalloy according to the embodiments of the present application comprises: C: 0.06% to 0.09%, Cr: 8.0% - 8.5%, Co: 9.0% - 9.5%, W: 9.1% - 9.8%, Mo: 0.3% - 0.7%, Ta: 3.0% - 3.5%, Al: 5.3% - 5.8%, Ti: 0.5% - 1.0%, B: 0.01% - 0.02%, Hf: 1.1% - 1.7%, Zr: 0.005% - 0.02%. Nickel is used as the balance in particular.

[0013] The functions of the main elements in the superalloy according to the embodiments of the present application are as follows:

[0014] Carbon: C mainly inhibits the growth of austenite grains during heating by forming MC-type carbides at the end of the solidification of the nickel-based superalloy and forms MC along the grain boundaries during the heat treatment process. Different types of carbides play a role in strengthening the grain boundaries, delaying the initiation, propagation and coalescence of microcracks, thereby improving the high-temperature durability life of the alloy. When the C content is less than 0.05%, it is not sufficient to form enough MC. When the C content is too high, the size of the formed MC is larger, and it will consume too much Mo, Cr, Ti and Ta in the alloy. On the one hand, it not only reduces the solid solution strengthening effect of Mo and Cr, on the other hand, the Ti and Ta used to form the Ni3(Al, Ti) and Ni3,(Al, Ti, Ta) composite strengthening phases will be reduced, which will adversely affect the high-temperature performance and durability of the alloy. Therefore, C should be controlled within 0.05% and 0.16%.

[0015] Chromium Cr: The main function of Cr is to improve the oxidation resistance of the alloy and has a certain solid solution strengthening effect. After the aging treatment, it can also combine with C to form granular MC distributed along the grain boundaries and play a role in strengthening the grain boundaries. However, when the Cr content is too high, it is easy to form the TCP phase, which reduces the long-term microstructure and performance stability of the alloy. Therefore, its content generally does not exceed 25%. In the embodiments of the present application, considering the corrosion resistance and the stability of the long-term microstructure and performance, the Cr content is controlled at 8.0% - 9.5%.

[0016] Cobalt: Co is an important solid-solution strengthening element and an important precipitation strengthening element. The Co element can dissolve in the matrix, providing good solid-solution strengthening for the alloy. It can significantly reduce the stacking fault energy of the matrix, broaden and expand the dislocation width, making it difficult for dislocations to cluster and undergo cross-slip, thereby improving the alloy's properties, creep resistance, and lifespan. Co can also partially replace the precipitation of Ni3Al-type elements in the strengthening phase, improving the stability of the phase during long-term use. Co can also reduce the solid solubility of Al and Ti elements in the matrix, promoting the precipitation of the γ' strengthening phase and increasing the quantity and temperature of precipitation and solid solution. When the Co content is less than 9%, the high-temperature strength is low. When the Co content is higher than 11%, the η phase that affects its long-term use performance is likely to form. Therefore, the Co content is controlled at 9.0% - 10.5%.

[0017] Tungsten and molybdenum: W and Mo: W and Mo are one of the main solid-solution strengthening elements. They can dissolve in the alloy matrix and the γ' strengthening phase, and at the same time increase the interatomic binding force, raise the diffusion activation energy and the recrystallization temperature, thereby effectively improving the high-temperature strength. However, when the Mo content is too high, the μ phase is likely to be produced during long-term high-temperature aging, reducing the alloy's toughness. Therefore, the Mo content is controlled at 0.2% - 1.0%. The atomic radius of W is relatively large, more than 10% larger than that of nickel, and the solid-solution strengthening effect is obvious. However, W is an element that accelerates high-temperature corrosion and will form the harmful δ phase during long-term use, reducing the strength and toughness of the alloy. Therefore, the W content is controlled at 9.0% - 10.5%.

[0018] Aluminum, titanium, and tantalum: Al, Ti, and Ta: These three elements are the forming elements of the strengthening phase γ' in nickel-based alloys. Generally, it is considered that as the content of the three increases, the amount of γ' increases, and the high-temperature creep and durability improve. However, too much γ' will lead to deteriorated workability. In addition, Ti and Ta will also combine with C to form MC-type carbides, which hinder the growth of grain boundaries and the slip of grain boundaries at high temperatures and play a role in improving high-temperature mechanical properties. However, too much Ti and Ta will form large-grained MC-type carbides. Carbides are harmful to the mechanical properties of the alloy. In this application, through research, it is found that the high-temperature mechanical properties of the alloy not only depend on the amount of the γ' phase but also on its composition and characteristics. Through optimization, the best γ' strengthening effect can be obtained. In the alloy of the embodiment of this application, a strengthening element design scheme of high Al, low Ti, and high Ta is adopted. The 3(Al, Ti) strengthening phase is modified to simultaneously form Ni3(Al, Ti, Ta) with a higher Al content and Ta. Compared with the conventional Ni3(Al, Ti) strengthening phase, it is more resistant to high temperatures, thereby improving the tensile properties and long lifespan of the alloy. The specific control ranges of the three are: Al: 5.0% - 6.0%, Ti: 0.5% - 1.5%, Ta: 2.5% - 3.5%.

[0019] Boron: The role of B is mainly manifested in two aspects. First, because the atomic radius of B is very small, B atoms are prone to enrichment at grain boundaries. Low-melting-point elements cannot segregate at grain boundaries, which improves the binding force of grain boundaries; second, borides on grain boundaries can prevent grain boundary slip, the initiation and expansion of voids, and improve the creep resistance and creep rupture life of the alloy, which is beneficial. However, too much B will deteriorate the hot workability and welding performance of the alloy. Therefore, the appropriate B content of the alloy in the embodiments of this application is 0.01% - 0.025%.

[0020] Zirconium: Zr helps to purify grain boundaries and enhance the binding force of grain boundaries. The combined addition of Zr and B helps to maintain the high-temperature strength and long life of the alloy, but excessive Zr is likely to reduce the processing performance. The alloy in the embodiments of this application controls Zr at 0.004% - 0.06%.

[0021] Mg, Mn, Si, Fe: The superalloy is microalloyed with Mg, Mn, Si, and / or Fe. The key points for the improvements achieved in mechanical high-temperature performance and long life are grain boundaries, phases, and thus the atoms segregating here.

[0022] In the PSE (Periodic Table of Elements), Fe is very close to Ni and adjacent to Co. In the PSE, Mn is adjacent to Fe. Therefore, these elements, Fe and Mn, should be controlled. In the PSE, Si is adjacent to Al and should also be controlled.

[0023] Mg, Mn, Si, Fe, as well as B and C atoms segregate at grain boundaries, and this segregation is equilibrium segregation. The segregation of these atoms at grain boundaries improves the binding force of grain boundaries and increases the strength of grain boundaries. Mg, Mn, and Fe atoms not only segregate at grain boundaries but also at carbide phase boundaries and γ'-phase boundaries. Mg atoms also enter γ' and carbides, which has a beneficial effect on mechanical properties. The segregation of a small amount of Mg, Mn, and Fe at grain boundaries reduces the grain boundary energy and phase boundary energy and improves and refines the morphology of other grain boundary precipitates at the grain boundary carbide level. For example, carbides can agglomerate or spheroidize, effectively inhibiting grain boundary slip, reducing grain boundary stress concentration, and eliminating notch sensitivity. Mg, Mn, Fe, and other harmful impurities such as sulfur form high-melting-point compounds such as MgS, which purify grain boundaries, significantly reducing the concentration of other impurity elements such as S, O, and P in grain boundaries and reducing the harmful effects of other impurities such as S, O, and P. A small amount of Mg, Mn, and Fe increases durability and plasticity, improves creep characteristics and high-temperature tensile plasticity, increases impact toughness and fatigue strength, and for some alloys, it can also improve hot workability and yield. However, the content should not be too high, as too high a content will deteriorate the performance.

[0024] Boron and silicon have similar effects (melting inhibitors) and should be controlled.

[0025] Therefore, the content of the microalloying elements is given by:

[0026] Mg: 10 ppm - 70 ppm, and / or

[0027] Si: 20 ppm - 300 ppm, especially 30 ppm - 300 ppm, and / or

[0028] Fe: 20 ppm - 400 ppm, and / or

[0029] Mn: 10 ppm - 200 ppm;

[0030] Or, more preferably:

[0031] Mg: 20 ppm - 60 ppm, and / or

[0032] Si: 30 ppm - 200 ppm, especially 40 ppm - 200 ppm, and / or

[0033] Fe: 30 ppm - 300 ppm, especially 40 ppm ≤ Fe ≤ 300 ppm, and / or

[0034] Mn: 10 ppm ≤ Mn ≤ 200 ppm.

[0035] The purity of the superalloy bar or billet is obtained by carefully selecting the raw materials of the alloying elements. Some raw materials contain all the microalloying elements, and some raw materials only include a part of them. Regarding the cost of the alloy, the purest possible raw materials for each one cannot be used, nor should they be used, because these microalloying elements can also provide positive effects at the ppm level.

[0036] The special contributions are given by: magnesium (Mg), manganese (Mn), silicon (Si) and / or iron (Fe), especially in combination with boron (B) and / or carbon (C): (in wt%).

[0037] The amount of the microalloying elements is preferably selected by:

[0038] B and Mg are given by 250 ppm ≤ B + 10Mg ≤ 750 ppm, and / or

[0039] Fe and Si are given by 400 ppm ≤ Fe + Si ≤ 550 ppm, and / or

[0040] Mn and Si are given by 400 ppm ≤ Si + 2Mn ≤ 500 ppm, and / or

[0041] C and Si are given by 1000 ppm ≤ C + 2Si ≤ 1200 ppm, and / or

[0042] Fe and C are given by 950 ppm ≤ C + 2Fe ≤ 1200 ppm, and / or

[0043] Si and Mg are given by 250 ppm ≤ Si + 10Mg ≤ 750 ppm.

[0044] In the alloy, impurities (Sn, Sb, As, Zn, Hg, U, Th, Ce, Ge, Y, Pt, Au, In, Na, K, La, Ce, Pd, Ba) are usually inevitable. In the Ni superalloy of the present application, inevitable impurities such as phosphorus (P), sulfur (S), copper (Cu), niobium (Nb), lead (Pb), selenium (Se), bismuth (Bi), tellurium (Te), thallium (Tl), nitrogen (N), oxygen (O), silver (Ag), vanadium (V), gallium (Ga), rhenium (Re), ruthenium (Ru) are very few, usually less than 0.01%, 0.001% or 0.001% or lower, or even undetectable.

[0045] Preferably, V ≤ 500 ppm and / or Nb < 500 ppm and / or Cu < 100 ppm. More preferably, V: 20 ppm ≤ V ≤ 200 ppm and / or Nb < 50 ppm and / or Cu < 50 ppm.

[0046] In addition, the specific features, structures, materials or properties described can be combined in any one or more embodiments or examples in any suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples without conflicting with each other.

[0047] The alloy can also only exhibit its optimal performance through appropriate heat treatment.

[0048] The heat treatment is preferably carried out at four different temperature levels, especially at three different temperature levels, very particularly only at three different temperature levels. Different temperature levels mean a difference of at least 10 °C.

[0049] Each temperature level is characterized by raising the temperature to its desired temperature, holding for a certain time and then lowering the temperature, especially lowering it to near room temperature or to room temperature.

[0050] Active cooling can or must be carried out according to the height of the temperature. Controlled heating and cooling rates are also required.

[0051] Higher temperature levels require careful ramping up, which means that the heating rate can be higher at the beginning, but will be reduced when the desired temperature is reached.

[0052] Gas or vacuum cooling is required at higher temperatures.

[0053] In particular, the temperature level of each subsequent level is reduced.

[0054] First, solution treatment is carried out. The solution temperature depends on the actual composition, but for the claimed narrow range of the superalloys of the present invention, the solution temperature will be between 1220 °C and 1250 °C.

[0055] Second, stabilization treatment is carried out at a temperature that is at least 130 °C lower, especially at least 140 °C lower, than the solution treatment temperature. However, preferably, the difference is not greater than 250 °C, especially not greater than 200 °C.

[0056] In particular, for the first level to the second level, the difference is not greater than 190 °C.

[0057] The holding time at the stabilization temperature level of the stabilization treatment (preferably 100 minutes to 140 minutes) is at least 40% less than the holding time at the first temperature level which is the solution treatment temperature (preferably 220 minutes to 260 minutes).

[0058] Third, aging treatment is carried out at a temperature that is at least 170 °C lower, especially 180 °C lower, than the stabilization treatment temperature. However, preferably, the difference is not greater than 250 °C.

[0059] Between the first level and the second level, another level can be carried out as an intermediate treatment (as a "super-solution" treatment) which has a temperature higher than the solution treatment temperature, which means at least 10 °C higher but not higher than 50 °C, but preferably only three levels are used.

[0060] An exemplary embodiment of the present invention:

[0061] C: 0.072%, Cr: 8.1%, Co: 9.2%, W: 9.5%, Mo: 0.5%, Ta: 3.3%, Al: 5.4%, Ti: 0.5%, B: 0.015%, Hf: 1.2%, Zr: 0.01%. Heat treatment is carried out at 1239 °C for 250 minutes, at 1085 °C for 175 minutes, and at 880 °C for 1 day.

[0062] Although the embodiments of the present application have been shown and described above, it should be understood that the above embodiments are exemplary and should not be construed as a limitation to the present application. The embodiments can be varied, modified, substituted, and changed.

Claims

1. A nickel-based superalloy, comprising (in wt%): C：0.05％-0.16％， Cr：8.0％-9.5％， Co: 9.0% - 10.5%, W：9.0％-10.5％， Mo: 0.2% - 1.0%, Ta: 2.5% - 3.5%, Al：5.0％-6.0％， Ti: 0.5% - 1.5%, B：0.01％-0.025％， Hf: 1.0% - 2.0%; Zr：0.004％-0.06％， Nickel (Ni) and inevitable impurities, In particular, the balance is nickel, Optionally Mg: 10 ppm - 70 ppm, and / or Si: 20 ppm - 300 ppm, and / or Fe: 20 ppm - 400 ppm, and / or Mn: 10 ppm - 200 ppm, and / or V ≤ 500 ppm, and / or Nb < 500 ppm, and / or Cu < 100 ppm.

2. The alloy according to claim 1, comprising (in wt%): C: 0.06% - 0.09%, Cr：8.0％-8.5％， Co: 9.0% - 9.5%, W：9.1％-9.8％， Mo: 0.3% - 0.7%, Ta: 3.0% - 3.5%, Al：5.3％-5.8％， Ti: 0.5% - 1.0%, B：0.01％-0.02％， Hf: 1.1% - 1.7%, Zr：0.005％-0.02％。 3. The alloy according to one of claims 1 or 2, comprising: Mg: 20 ppm - 60 ppm, and / or Si: 30 ppm - 200 ppm, in particular 40 ppm - 200 ppm, and / or Fe: 30 ppm - 300 ppm, in particular 40 ppm ≤ Fe ≤ 300 ppm, and / or Mn: 10 ppm ≤ Mn ≤ 100 ppm, and / or V: 20 ppm ≤ V ≤ 200 ppm, and / or Nb < 50 ppm, and / or Cu < 50 ppm.

4. The alloy according to any one of the preceding claims, wherein, B and Mg are given by 250 ppm ≤ B + 10Mg ≤ 750 ppm.

5. The alloy according to any one of the preceding claims, wherein, Fe and Si are given by 400 ppm ≤ Fe + Si ≤ 550 ppm.

6. The alloy according to any one of the preceding claims, wherein, Mn and Si are given by 400 ppm ≤ Si + 2Mn ≤ 500 ppm.

7. The alloy according to any one of the preceding claims, wherein, C and Si are given by 1000 ppm ≤ C + 2Si ≤ 1200 ppm.

8. The alloy according to any one of the preceding claims, wherein, Fe and C are given by 950 ppm ≤ C + 2Fe ≤ 1200 ppm.

9. The alloy according to any one of the preceding claims, wherein, Si and Mg are given by 250 ppm ≤ Si + 10Mg ≤ 750 ppm.

10. The alloy according to any one of the preceding claims, which does not contain rhenium (Re) and / or does not contain ruthenium (Ru) and does not contain yttrium (Y).

11. A method for heat-treating an alloy according to any one of the preceding claims, wherein, The temperature level is characterized in particular by raising the temperature to its desired temperature, holding for a certain time, and lowering the temperature, in particular lowering it to near room temperature or lowering it to room temperature, wherein four different temperature levels are used, in particular three different temperature levels are used.

12. The method according to claim 11, wherein, Only three different temperature levels are used.

13. The method according to any one of the preceding claims 11 or 12, wherein The temperature lowered for each subsequent temperature level is in particular at least 130 °C.

14. The method according to any one of the preceding claims 11, 12 or 13, wherein, The temperature drop from the first level to the second level is at most 190 °C.

15. The method according to any one of the preceding claims 11, 12, 13 or 14, wherein, The temperature drop from the second level to the third level is at least 170 °C and preferably at most 250 °C.

16. The method according to any one of the preceding claims 11, 12, 13, 14 or 15, wherein, The duration held at the stable temperature level for stabilization treatment is preferably 100 minutes to 140 minutes, which is at least 40% shorter than the duration held at the first temperature level for solution treatment and preferably 220 minutes to 260 minutes.