Micro alloyed superalloy and heat treatment

Abstract

A nickel based superalloy, which includes (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.

Description

CROSS REFERENCE TO RELATED APPLICATIONSThis application is the US National Stage of International Application No. PCT / EP2023 / 082688 filed 22 Nov. 2023, and claims the benefit thereof, which is incorporated by reference herein in its entirety. The International Application claims the benefit of European Application No. EP22214482 filed 19 Dec. 2022.FIELD OF INVENTIONThe application belongs to the technical field of superalloys and relates to a superalloy with good long-term stability and suitable heat treatments.BACKGROUND OF INVENTIONGas turbines not only have extremely high requirements on the initial machining accuracy and assembly accuracy hot-end components, but also require that failure and fracture cannot occur during long-term service. Alloys for such components are required to have excellent high-temperature long-term stability and performance to avoid part failure before the overhaul period. At present, there are almost no alloys that can fully meet the above requirements in the existing superalloys. Generally, the alloys that can achieve the above mechanical properties have poor long-term stability.SUMMARY OF INVENTIONThe present application aims to solve some of the technical problems in the related art at least to a certain extent.The problem is solved by a superalloy and a heat treatment according to the claims.In the dependent claims further advantages are listed which can be combined arbitrarily with each other to yield further advantages.Embodiments of the present application propose a superalloy with good long-term stability. This superalloy with good long-term stability not only has excellent mechanical properties, but also has long-term stability and long-lasting life. It fully meets the requirements for the design and use of advanced aero-engines and gas turbines and is suitable for medium-and long-term service parts such as turbine blades, hot-end components of aero-engines and gas turbines.The superalloy with good long-term stability according to the embodiment of the present application comprises (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. Nickel is especially used for balancing.All percentages (%) in the whole description are given or meant in wt % except if ppm is mentioned.A special contribution is given by Magnesium (Mg), Manganese (Mn), Silicon (Si) and / or Iron (Fe).The superalloys according to the embodiments of the present application have good long-term stability. In the examples of this application, the strengthening element design scheme of high Al, low Ti, and high Ta is adopted.DETAILED DESCRIPTION OF INVENTIONThe embodiments described below are only exemplary and are intended to be used to explain the present application, but should not be construed as a limitation to the present application.

[0013] The superalloy according to the embodiment 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 especially used for balancing.

[0014] The role of each main element in the superalloy of the embodiment of the present application is as follows:

[0015] Carbon: C mainly suppresses the growth of austenite grains during heating by forming MC-type carbides at the end of solidification in nickel-based superalloys and forms MC along grain boundaries during heat treatment. Various types of carbides, which play a role in strengthening grain boundaries, delaying the initiation, expansion and merging of microcracks, thereby improving the high-temperature durable life of the alloy. When the C content is less than 0.05%, it is not enough to form enough MC. When the C content is too high, the size of MC formed 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, it is used to form Ni3(Al, Ti) and Ni3 The Ti and Ta of the (Al, Ti, Ta) composite strengthening phase will be reduced, which will adversely affect the high temperature performance and durability of the alloy, so C should be controlled within 0.05% and 0.16%.

[0016] 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 aging treatment, it can also combine with C to form granular MC distributed along the grain boundaries and plays 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 examples of this application, considering the stability of corrosion resistance and long-term microstructure and properties, the Cr content is controlled at 8.0%-9.5%.

[0017] Cobalt: Co is both an important solid solution strengthening element and an important precipitation strengthening element. Co element can be dissolved in the matrix to provide a good solid solution strengthening effect for the alloy, which can significantly reduce the stacking fault energy of the matrix, widen and expand the dislocation width, so that the dislocation is not easy to bunch up and cross-slip occurs, thereby improving the alloy. creep resistance and longevity. Co can also partially replace Ni3Al-type precipitation of elements in the strengthening phase improves the stability of the phase in long-term service; Co can also reduce the solid solubility of Al and Ti elements in the matrix, promote the precipitation of γ′ strengthening phase and increase the number of precipitation and solid solution. temperature. When the Co content is lower than 9%, the high temperature strength is low. When the Co content is higher than 11%, it is easy to form an n phase that affects its performance in long-term service, so the Co content is controlled at 9.0%-10.5%.

[0018] Tungsten and Molybdenum: W and Mo: W and Mo are one of the main solid-solution strengthening elements, which can be solid-dissolved in the alloy matrix and in the γ′ strengthening phase and at the same time can improve the bonding force between atoms, increase the diffusion activation energy and recrystallization temperature, so as to effectively improve the high temperature strength. However, when Mo is too high, long-term high temperature aging is easy to generate u phase and reduce alloy toughness. Therefore, the Mo content is controlled at 0.2%-1.0%. The atomic radius of W is relatively large, more than ten percent larger than the atomic radius of nickel, and the solid solution strengthening effect is obvious. However, W is an element that accelerates high-temperature corrosion, and will form a harmful delta phase during long-term service, reducing the strength and toughness of the alloy. Therefore, the W content is controlled at 9.0%-10.5%.

[0019] Aluminum, Titanium and Tantalum: Al, Ti and Ta: The three are the forming elements of the strengthening phase γ′ in nickel-based alloys. It is generally believed that with the increase of the content of the three, the amount of γ′ increases, and the high-temperature creep and durability improve, but too much γ′ will cause Deterioration of processability. In addition, Ti and Ta will also combine with C to form MC-type carbides, which hinder the growth of grain boundaries and the sliding of grain boundaries at high temperatures and play a role in improving high-temperature mechanical properties, but too much Ti and Ta will form large-grained MC-type carbides. Carbides are detrimental to the mechanical properties of the alloy. Through research in this application, it is found that the high-temperature mechanical properties of the alloy depend not only on the amount of γ′ phase, but also on its composition and characteristics. optimization, the best γ′ strengthening effect can be obtained. In the alloys of the examples of the present application, the strengthening element design scheme of high Al, low Ti and high Ta is adopted. 3(Al, Ti) strengthening phase was modified to form Ni with higher Al content and Ta at the same time 3(Al, Ti, Ta), compared to conventional Ni3 The (Al, Ti) strengthening phase is more resistant to high temperatures, thereby improving the tensile properties and long-lasting life of the alloy. The specific control range of the three is: Al: 5.0%-6.0%, Ti: 0.5%-1.5%, Ta: 2.5%-3.5%.

[0020] Boron: The role of B is mainly manifested in two aspects. First, because the atomic radius of B is very small, so B atoms are easily enriched at the grain boundaries. The low melting point elements cannot segregate at the grain boundary, which improves the bonding force of the grain boundary; the second is that the boride on the grain boundary can prevent the grain boundary from slipping, the initiation and expansion of voids, and improve the creep resistance and lasting life of the alloy. favorable. However, too much B will deteriorate the hot workability and welding performance of the alloy, so the suitable B content of the alloy in the embodiment of the present application is 0.01%-0.025%.

[0021] Zirconium: Zr helps to purify the grain boundary and enhance the bonding force of the grain boundary. The compound addition of Zr and B helps to maintain the high temperature strength and long-lasting life of the alloy, but excessive Zr easily reduces the processing performance. The alloys in the examples of this application control Zr at 0.004%-0.06%.

[0022] Mg, Mn, Si, Fe: the superalloy is micro-alloyed with Mg, Mn, Si and / or Fe. The key point to achieve improvement in mechanical high temperature properties and long lifetime are the grain boundaries, phases, and therefore the atoms which segregate there. Fe is quite close in the PSE (Periodic system of the elements) to Ni and next to Co. Mn is next to Fe in the PSE. Therefore, these elements Fe, Mn should be controlled. Si is next to Al in the PSE and should be controlled, too.

[0023] Mg, Mn, Si, Fe as well as B, C atoms are segregated at grain boundaries, and this segregation is a balanced segregation. The segregation of these atoms at the grain boundary improves the bonding force of the grain boundary and increases the strength of the grain boundary. Mg, Mn, Fe atoms are not only segregated at grain boundaries, but also at carbide phase boundaries, γ′ phase boundaries. Mg atoms also enter into γ′ and carbides, which have a favorable effect on the mechanical properties. The segregation of a small amount of Mg, Mn, Fe at the grain boundary reduces the grain boundary energy and phase boundary energy, and improves and refines the morphology of other grain boundary precipitation phases at the grain boundary carbide level. For example, carbides can be lumped or spheroidized, effectively inhibiting grain boundary sliding, reducing grain boundary stress concentration, and eliminating notch sensitivity. Mg, Mn, Fe and Sulfur and other harmful impurities form high melting point compounds such as MgS, which purifies the grain boundary, so that the concentration of S, O, P and other impurity elements in the grain boundary is significantly reduced, and the harmful effects of S, O, P and other impurities are reduced.

[0024] A small amount of Mg, Mn, Fe increases durability and plasticity, improves creep properties and high-temperature tensile plasticity, increases impact toughness and fatigue strength, and can also improve hot workability and yield for some alloys. But the content should not be too high, too high will deteriorate the performance.

[0025] Boron and Silicon have the similar effect (melting depressant) and should be controlled.

[0026] Therefore, the contents of this microalloying elements are given by:

[0027] Mg: 10 ppm-70 ppm,and / or

[0028] Si: 20 ppm-300 ppm,especially 30 ppm-300 ppmand / or

[0029] Fe: 20 ppm-400 ppm,and / or

[0030] Mn: 10 ppm-200 ppm;or more preferably:

[0031] Mg: 20 ppm-60 ppmand / 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] Purity of bar or billets of the superalloy are achieved by carefully choosing the raw material of the alloying elements. Some of the raw material comprises all microalloying elements, some raw material only a part of them.

[0036] Regarding the costs of the alloy not every possible purest raw material can be used and should not as these microalloying elements provide also positive effects at a ppm level.

[0037] A special contribution is given by Magnesium (Mg), Manganese (Mn), Silicon (Si) and / or Iron (Fe) especially in combination with Boron (B) and / or Carbon (C): (in wt %).

[0038] Amounts of this microalloying elements are preferably chosen by:

[0039] B and Mg are given by 250 ppm≤B+10Mg≤750 ppmand / or

[0040] Fe and Si are given by 400 ppm≤Fe+Si≤550 ppmand / or

[0041] Mn and Si are given by 400 ppm≤Si+2Mn≤500 ppmand / or

[0042] C and Si are given by 1000 ppm≤C+2Si≤1200 ppmand / or

[0043] Fe and C are given by 950 ppm≤C+2Fe≤1200 ppmand / or

[0044] Si and Mg are given by 250 ppm≤Si+10Mg≤750 ppm.

[0045] In alloys impurities (Sn, Sb, As, Zn, Hg, U, Th, Ce, Ge, Y, Pt, Au, In, Na, K, La, Ce, Pd, Ba) are generally unavoidable.

[0046] In the Ni superalloy of the present application, the unavoidable impurities like Phosphorus (P), Sulfur(S), Copper (Cu), Niobium (Nb), Lead (Pb), Selenium (Se), Wismut (Bi), Tellurium (Te), Thallium (Tl), Nitrogen (N), Oxygen (O), Silver (Ag), Vanadium (V), Gallium (Ga), Rhenium (Re), Ruthenium (Ru) are very small, usually below 0.01%, 0.001% or 0.001% or below, or even undetectable.

[0047] Preferably is V≤500 ppm and / or Nb<500 ppm and / or Cu<100 ppm. More preferably is V: 20 ppm≤V≤200 ppm and / or Nb<50 ppm and / or Cu<50 ppm.

[0048] Furthermore, the particular features, structures, materials or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, those skilled in the art may combine and combine the different embodiments or examples described in this specification, as well as the features of the different embodiments or examples, without conflicting each other.

[0049] The alloy can also only reveal his best properties with an appropriate heat treatment.

[0050] A heat treatment is preferably performed at four different temperatures levels, especially at three different temperature levels, very especially only at three different temperature levels. Different temperature levels means at least a difference of 10° C.

[0051] Each temperature level is characterized by increasing the temperature to his desired temperature, holding time and decreasing the temperature, especially near or to room temperature.

[0052] Active cooling can or must be performed depending on the height of the temperature.

[0053] Controlled heating and cooling rates are also needed.

[0054] Higher temperature levels need a careful ramp up, which means that in the beginning the heating rates can be higher, but will be lowered when reaching the desired temperature.

[0055] Gas or vacuum cooling is needed at higher temperature.

[0056] Especially the temperature levels of each subsequent level is decreased.

[0057] First, a solution treatment is performed. The solution temperature depends on the actual composition, but for this claimed small ranges of the inventive superalloy this solution temperature will between 1220° C. and 1250° C.

[0058] Secondly a stabilization treatment is performed at a temperature which is at least 130° C., especially at least 140° C. lower than the solution treatment temperature. But preferably the difference should not be bigger than 250° C., especially not bigger than 200° C. Especially for the first level to the second level this difference is not bigger than 190° C.

[0059] Holding time (preferably 100 min to 140 min) at the stabilization temperature level for the stabilization treatment is at least 40% smaller than the holding time at the first temperature level (preferably 220 min to 260 min) which is the solution treatment temperature.

[0060] Thirdly, an aging treatment is performed at a temperature which is at least 170° C., especially 180° C. lower than the temperature of the stabilization treatment temperature. But preferably this difference is not bigger than 250° C.

[0061] Between a first and a second level another level can be performed as an intermediate treatment as an “oversolution” treatment, which has a higher temperature 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.

[0062] One exemplary embodiment of the invention: 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%.

[0063] Heat treatment at 1239° C. for 250 min, 1085° C. for 175 min, 880° C. for 1 day.

[0064] 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 limitations to the present application. Embodiments are subject to variations, modifications, substitutions and variations.

Claims

1. A nickel based superalloy, which comprises (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,especially the balance is Nickel,optionallyMg: 10 ppm-70 ppm,and / orSi: 20 ppm-300 ppm,and / orFe: 20 ppm-400 ppm,and / orMn: 10 ppm-200 ppmand / orV≤500 ppmand / orNb<500 ppmand / orCu<100 ppm.

2. The superalloy according to claim 1, which comprises (in wt %),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%.

3. The superalloy according to claim 1, which comprisesMg: 20 ppm-60 ppmand / orSi: 30 ppm-200 ppm,especially 40 ppm-200 ppm,and / orFe: 30 ppm-300 ppm,especially 40 ppm≤Fe≤300 ppm,and / orMn: 10 ppm≤Mn≤100 ppmand / orV: 20 ppm≤V≤200 ppmand / orNb<50 ppmand / orCu<50 ppm.

4. The superalloy according to claim 1, claims,wherein B and Mg are given by 250 ppm≤B+10Mg≤750 ppm.

5. The superalloy according to claim 1,wherein Fe and Si are given by 400 ppm≤Fe+Si≤550 ppm.

6. The superalloy according to claim 1,wherein Mn and Si are given by 400 ppm≤Si+2Mn≤500 ppm.

7. The superalloy according to claim 1,wherein C and Si are given by 1000 ppm≤C+2Si≤1200 ppm.

8. The superalloy according to claim 1,wherein Fe and C are given by 950 ppm≤C+2Fe≤1200 ppm.

9. The superalloy according to claim 1,wherein Si and Mg are given by 250 ppm≤Si+10Mg≤750 ppm.

10. The superalloy according to claim 1, claims, comprisingno Rhenium (Re) and / or no Ruthenium (Ru) and no Yttrium (Y).

11. A method to heat treat an alloy according to claim 1, comprising:heat treating at a temperature level which is especially characterized by increasing the temperature to a desired temperature, a holding time, and decreasing the temperature, especially near or to room temperature,wherein four different temperature levels, especially 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 claim 11,wherein the temperature of each subsequent temperature level is decreased, especially by at least 130° C.

14. The method according to claim 11,wherein the temperature of first level to second level is decreased, by at maximum 190° C.

15. The method according to claim 11,wherein the temperature of a second level to third level is decreased at least by 170° C. and preferably at maximum 250° C.

16. The method according to claim 11,wherein the holding time at a stabilization temperature level for a stabilization treatment, which is preferably 100 min to 140 min, is least 40% shorter than the holding time at a first temperature level, which is preferably 220 min to 260 min, which is a solution treatment.