Nickel-based alloy

Abstract

Nickel-based alloy having reduced density A nickel-based alloy of a specified composition of elements exhibits reduced density with the sum of weight-% of titanium (Ti), aluminum (Al) and vanadium (V) being at least 5.0 weight-%.

Description

[0001] Nickel-based alloy

[0002] TECHNICAL FIELD

[0003] The present invention relates to nickel-based alloys, a method of making nickel-base alloys and articles of manufacture including a nickel-base alloy.

[0004] BACKGROUND

[0005] Superalloys, or high-performance alloys, are alloys with the ability to operate in load-bearing and high temperature applications. Among these, nickel-based superalloys are widely used due to their superior properties including mechanical strength, thermal creep deformation resistance, surface stability, and corrosion and oxidation resistance. Among the most demanding applications are those in the hot sections of turbine engines, e.g. turbine blades. Nevertheless, their mechanical and microstructural stability at elevated temperature is limited.

[0006] Nickel-based superalloys develop high temperature strength through solid solution strengthening and precipitation strengthening from secondary phase precipitates. Gamma prime (y1), gamma double prime (y") and delta (6) precipitates play a crucial role in the mechanical performance of nickel-based superalloys.

[0007] Gamma prime (y1) is an intermetallic phase based on Ni3(Ti , Al) and has fee (face centred cubic) structure, which makes a coherent precipitate to the matrix of the superalloy and contributes to the alloy's high-temperature strength and creep resistance.

[0008] Gamma double prime (y"), on the other hand, is a phase that occurs in nickel superalloys with significant additions of niobium or vanadium. The composition of the y" phase is typically Ni3Nb or Ni3V, it has a bet (body centred tetragonal) structure (D022, with tetragonal structure with c / a=2.04) and appears as nanometer scale discs under the transmission electron microscope (TEM). The y" phase has larger lattice parameters compared to the solid-solution fee y’ phase, and the size, morpho logy and distribution of the y" precipitates are considered to induce a bit of strain in atomic level leading to a strengthening effect and contributing to the mechanical performance of some superalloys. However, it is important to note that y” is a metastable precipitate and has limited thermal stability up to about 649°C, after which it transforms into delta (6) phase. Delta (6) is a Nb-rich phase with an ordered orthorhombic structure, is incoherent with the austenite matrix and appears as long needles at the grain boundaries, twin boundaries, or within grains. A small amount of delta phase is beneficial to control grain growth during solution annealing and aging and can deliberately be precipitated during a heat treatment called “delta dump.” However, too much delta phase is detrimental and decreases the fracture toughness, strength, and creep resistance.

[0009] In addition to the formation of y’ and y” phases during the manufacturing of the alloys, especially during ageing, small secondary carbides precipitate and grow, which may increase hardness of the superalloy. Small secondary carbides are visible in SEM. In addition to the small secondary carbides, large blocky carbonitrides of Ti and Nb may be present in the microstructure, which can act as crack initiation sites and reduce fatigue performance. Under certain heat treatment conditions, these carbonitrides can precipitate as a grain boundary film that degrades ductility.

[0010] Alloy 718 (UNS N07718), developed in the 1950s, has been one of the most widely used nickel-based superalloys. Alloy 718 has high strength along with balanced creep and stress rupture properties up to about 649°C. While most high strength nickel-based superalloys derive their strength by the precipitation of y’ phase with aluminium and titanium being major strengthening elements, i.e. , Nis(AI ,Ti), Alloy 718 is strengthened mainly by y” phase (gamma double prime) with niobium, i.e. NisNb, being a major strengthening element and with a small amount of y’ phase playing a secondary strengthening role. Since the y” phase has a higher strengthening effect than y’ phase at the same volume fraction and particle size, Alloy 718 is generally stronger than most superalloys strengthened by y’ phase precipitation. In addition, y” phase precipitation in Alloy 718 results in good high temperature time-dependent mechanical properties such as creep and stress rupture properties. The processing characteristics of Alloy 718, such as castability, hot workability and weldability, are also good, thereby making fabrication of articles from Alloy 718 relatively easy. These processing characteristics are believed to be closely related to the lower precipitation temperature and the sluggish precipitation kinetics of the y” phase associated with Alloy 718.

[0011] However, due to the rather rapid transformation of the y” phase into the more stable 5 phase at temperatures higher than 649°C, fracture toughness, strength, and creep resistance of Alloy 718 deteriorate rapidly at above this temperature, and the use of Alloy 718 is typically limited to applications below 649°C. Due to these limitations of Alloy 718, many attempts have been made to improve upon that superalloy. For example, Rene® 220 alloy is a nickel-based superalloy with the same processing advantages (castability, weldability, workability) as Alloy 718, but with temperature capabilities of up to 704°C. However, Rene® 220 alloy is very expensive, at least partly because it contains more than 2 percent, typically 3 percent, of tantalum, which can be from 10 to 50 times the cost of cobalt and niobium. In addition, Rene® 220 alloy has a relatively high 5 phase content, which decreases the fracture toughness, strength, and creep resistance.

[0012] Another nickel-based superalloy, known as Waspaloy® (UNS N07001), is also widely used for aerospace and gas turbine engine components. Waspaloy® has useful strength and good oxidation resistance in gas turbine engine atmospheres up to 870°C. Its creep rupture strength is superior to that of Alloy 718 at temperatures above 620-650°C. However, Waspaloy® is more expensive than Alloy 718, resulting, at least partly, from increased amounts of the alloying elements nickel, cobalt, and molybdenum. Also, processing characteristics, such as hot workability and weldability, are inferior to those of Alloy 718 due to strengthening by y’, which leads to higher manufacturing costs and more limited component repairability.

[0013] A great advance has been achieved by the development of Alloy 718Plus® (UNS N07818) in the early 2000s, another y’ phase strengthened nickel-base alloy, which is commercially available from ATI Allvac, Monroe, NC. It is assumed that the levels and ratios of aluminum, titanium and niobium in Alloy 718Plus® provide a thermally stable microstructure and advantageous high-temperature mechanical properties, including substantial rupture and creep strength. The aluminum and titanium contents of Alloy 718Plus® alloy, in conjunction with the niobium content, are considered to result in the alloy being strengthened by y’ phase and y” phase, with y’ phase being the predominant strengthening phase. Unlike the relatively high titanium and low aluminum composition typical of certain other nickel-base superalloys, such as in Alloy 718 or Waspaloy®, the composition of Alloy 718Plus® has a relatively large ratio of aluminum to titanium that is believed to increase thermal stability. Whereas Alloy 718 contains no cobalt, and Rene® 220 and Waspaloy® contain about 12- 15 weight percent of cobalt, Alloy 718Plus® has a cobalt level in the order of about 8 to 10 weight percent, which is assumed to contribute to improved stress rupture properties after long periods of exposure to high temperatures.

[0014] The above-mentioned nickel-based alloys 718, Rene® 220, Waspaloy® and Alloy 718Plus® have densities in the range of about 8.2 to 8.25 g / cm3, and in applications such as advanced aircraft engines, structures made of superalloys, such as the nickel-based superalloys discussed herein, make up to over 50% of the weight of the engines. However, weight is a key factor in aerospace engineering and other transportation applications, as each amount of additional weight increases fuel consumption and load bearing to structural parts.

[0015] Therefore, it would be desirous to provide an alloy having similar or even improved mechanical properties, also at elevated temperatures, compared to the superior properties of known superalloy, such as Alloy 718Plus®, and, at the same time, less weight or density, respectively. Also, the costs for manufacturing such an alloy should be competitive.

[0016] ASPECT OF THE INVENTION

[0017] It is an aspect of the present invention to provide an alloy having superior material properties, such as high mechanical strength, thermal creep deformation resistance, surface stability, and corrosion and oxidation resistance, similar or even improved compared to Alloy 718Plus® and, at the same time, less weight or density, respectively.

[0018] It is another aspect of the present invention to provide a method for manufacturing such an alloy.

[0019] SUMMARY

[0020] The present invention therefore provides a nickel-based alloy having the following composition

[0021] Chromium (Cr) 15.0 to 19.0 Iron (Fe) 7.0 to 11.0 Manganese (Mn) up to 4.0 Silicon (Si) up to 0.5 Aluminum (Al) 2.0 to 5.0 Titanium (Ti) 0.5 to 3.0 Carbon (C) 0.005 to 0.05 Niobium (Nb) 1.0 to 4.0 Cobalt (Co) 4.5 to 7.0 Copper (Cu) up to 1.0 Tungsten (W) up to 0.5 Molybdenum (Mo) up to 1.0

[0022] Vanadium (V) 1.5 to 4.0 Boron (B) up to 0.01 Nickel (Ni) 50.0 to 60.0 and incidental impurities and fulfilling the condition that the sum of weight-% of titanium (Ti), aluminum (Al) and vanadium (V) is at least 5.0 weight-%. The present invention also relates to a method for making a nickel-based alloy as defined hereinafter. In particular, according to such method of the present invention, a nickel-based alloy having a composition within the present invention as described herein is provided and is subject to processing, including solution annealing, cooling and aging.

[0023] The alloy may be further processed to an article of manufacture or into any other desired form, such as, for example, a disk, a blade, a fastener, a case, a tube or pipe, a bloom, a strip or bar, a wire, a powder, or a plate or a shaft fabricated from or including the nickel-based alloy of the present invention. The articles formed of the nickel-based alloy of the present invention may be particularly advantageous when intended for in load-bearing and high temperature applications, such as components in the hot sections of turbine engines, such as turbine blades.

[0024] DETAILED DESCRIPTION

[0025] The present invention relates to a nickel-based alloy comprising the following contents of elements, in weight-%:

[0026] Chromium (Cr) 15.0 to 19.0 Iron (Fe) 7.0 to 11.0

[0027] Manganese (Mn) up to 4.0 Silicon (Si) up to 0.5 Aluminum (Al) 2.0 to 5.0 Titanium (Ti) 0.5 to 3.0

[0028] Carbon (C) 0.005 to 0.05 Niobium (Nb) 1.0 to 4.0 Cobalt (Co) 4.5 to 7.0 Copper (Cu) up to 1.0

[0029] Tungsten (W) up to 0.5 Molybdenum (Mo) up to 1.0 Vanadium (V) 1.5 to 4.0 Boron (B) up to 0.01 Nickel (Ni) 50.0 to 60.0 and incidental impurities, and wherein the sum of weight-% of titanium (Ti), aluminum (Al) and vanadium (V) is at least 5.0 weight-%. It has been found that the alloys according to the present invention have an about 4-5% lower density than other known nickel-based superalloys, such as Alloy 718 and Alloy 718Plus, which means a significant weight reduce in application of the alloys. At the same time, the alloys of the present invention exhibit similar or even better mechanical strength, also at elevated temperature of 650°C and even higher. Furthermore, due to the costs of the elements of the alloy compositions, the costs of the alloys of the present invention may be up to about 10% lower than for Alloy 718Plus, which of course depends on and may vary due to actual market price conditions.

[0030] In an embodiment of the nickel-based alloy according to the invention, the sum of weight-% contents of titanium (Ti), aluminum (Al) and vanadium (V) is at least 6.0 weight-% or at least 6.5 weight-%.

[0031] It has been found that in the context of the amounts of elements in the nickel-based alloy according to the invention the sum of weight-% contents of titanium (Ti), aluminum (Al) and vanadium (V) need to be adjusted to be at least 5.0 weight-%, such as at least 6.0 weight-% or even at least 6.5 weight-% to ensure that the hardening, solution plus precipitation hardening, will provide sufficient and satisfying strength to the alloy. The importance of the combination and amounts of these three elements was unexpected. If the sum of weight-% contents of titanium (Ti), aluminum (Al) and vanadium (V) is too low, satisfying strength to the alloy may not be achieved.

[0032] In another embodiment of the nickel-based alloy according to the invention the sum of weight- % contents of titanium (Ti), aluminum (Al), , vanadium (V) and niobium (Nb) is at least 1.45- times, such as at least 1.5-times or at least 1.6-times, the weight-% content of cobalt (Co).

[0033] Differently expressed, the amounts in terms of weight percentages of ([Al] + [Ti] + [V] + [Nb]) I [Co] should be greater than 1.45. It has been found that in the context of the amounts of elements in the nickel-based alloy according to the invention this ratio or relationship, respectively, ensures that the material will be properly precipitation hardened and thereby strengthening is ensured. Co generally contributes to solution hardening of the alloy, however, it has surprisingly been found that a too high content of Co, which results in a ([Al] + [Ti] + [V] + [Nb]) I [Co] less than 1.45, has a negative effect on the hardening in the context of the alloy compositions of the present invention. Chromium (Cr) 15.0 to 19.0 weiqht%

[0034] Cr is added to provide sufficient corrosion resistance in high temperatures as it will influence the corrosion resistance by forming a stable passive layer on the surface. In order to ensure this this effect, it is necessary that the content of Cr is at least 15.0 weight%. According to embodiments, to further ensure that this effect is obtained, the content of Cr is at least 15.5 wt%. However, if the Cr content exceeds 19.0 weight%, the toughness of the alloy will decrease, and the hot workability deteriorate thereby making working difficult. Further, if the Cr content exceeds 19.0%, there is a risk of the formation of intermetallic phases, which may cause embrittlement. Hence, the maximum content of Cr is 19.0 weight%. Further, according to embodiments, the content of Cr is from 15.0 to 18.0 weight-%.

[0035] Iron (Fe) 7.0 to 11.0 weight-%.

[0036] At least 7.0 weight% Fe is added for enhancing the mechanical properties, such as strength and ductility. However, it has been found that too high amounts of Fe may provide a detrimental effect to the mechanical properties and therefore the Fe content is not more than 11.0 weight%. According to embodiments, the content of iron (Fe) is from 8.0 to 10.5 weight-%.

[0037] Manganese (Mn) up to 4.0 weight-%

[0038] Mn may optionally be added since it is an austenitic structure stabilizer and may be used to replace some of content of the expensive alloying element Ni. In addition, Mn is beneficial for deoxidation and / or desulfidation during melting and provides improvement of the workability of the present alloy. However, an excessive high Mn will reduce the formation of the passive layer comprising Cr. Hence, the Mn content is up to 4.0 weight-%, such as uo to 3.5 weight-%-

[0039] Silicon (Si) up to 0.5 weight-%

[0040] Si is frequently used as deoxidation agent and may therefore be added to improve the hardness and strength. However, weldability and structure stability may be negatively affected if the content of Si is more than 0.5 weight%. According to embodiments, the content of silicon is from 0.001 to 0.3 weight-%, such as 0.01 to 0.3 weight-%.

[0041] Aluminum (Al) 2.0 to 5.0 weight- %

[0042] Al is added to provide creep strength and to provide reduced density. Furthermore, in high temperature environments, Al may have a positive impact on the corrosion resistance by forming a stable passive layer on the surface. To obtain these effects, it is necessary that the content of Al is at least 2.0 wt%. On the other hand, if the Al content exceeds 5.0 wt%, the weldability and hot workability may be negatively influenced. According to embodiments, the Al content is from 2.3 to 4.0 weight-%, or from 2.6 to 3.5 weight-%, or from 2.8 to 3.4 weight- %.

[0043] Titanium (Ti) 0.5 to 3.0 weight-%

[0044] Ti is added to provide improved high temperature strength and creep strength and to reduce density. To obtain these effects, it is necessary that the content of Ti is at least 0.5 wt%. On the other hand, if the Ti content exceeds 3.0 wt%, the weldability and hot workability may be negatively influenced. According to embodiments, the content of Ti may be from 0.8 to 2.8 weight-%, or from 0.9 to 2.5 weight-%, or from 1.0 to 2.3 weight-%.

[0045] Carbon (C) 0.005 to 0.05 weight%

[0046] The content of C should be as low as possible. C is an austenitic structure stabilizer and small addition of C may however increase high temperature strength. Too high amount of C will cause a poor toughness and for this reason, C should be less than 0.05 wt%. According to embodiments, the content of carbon (C) is from 0.005 to 0.03 weight-%.

[0047] Niobium (Nb) 1.0 to 4.0 weight%

[0048] Nb will provide high temperature strength and creep strength and is therefore added in an amout of at least from 1.0 weight-%. However, if the Nb content exceeds 4.0 wt%, the hot workability may be negatively affected and there may be a risk of formation of unwanted Laves phases. According to embodiments, the content of Nb may be from nickel-based alloy according to the from 1 .3 to 3.5 weight-%, or from 1.4 to 3.2 weight-%.

[0049] Cobalt (Co) 4.5 to 7.0 weight-%

[0050] Co is an effective austenitic structure stabilizer and is added to provide increased entropy value, high temperature strength, creep strength and solution hardening. In order to ensure this effect, it is necessary that the content of Co is at least 4.5 wt%. On the other hand, if the Co content exceeds 7.0 wt%, the hot workability may be negatively affected, thus the maximum content of Co is 7.0 wt%. According to embodiments, the content of Co is from 5.0 to 6.5 weight-%, or from 5.4 to 6.1 weight-%.

[0051] Copper (Cu) up to 1.0 weight%

[0052] Cu may be added to provide additional stability of the austenite phase. However, if Cu content exceeds 1.0 wt% the weldability and hot workability may be negatively influenced. According to embodiments the content of copper (Cu) is up to 0.5 weight-%. Tungsten (W) up to 0.5 weight-%

[0053] W may optionally be added to the nickel-based alloy since it increases the entropy value. Thus, if added, the W content is up to 0.5 weight%.

[0054] Molybdenum (Mo) up to 1.0 weight-%

[0055] Mo is added to the nickel-based alloy since it increases the entropy value. Thus, if added, the Mo content is up to 1.0 weight-%.

[0056] Vanadium (V) 1.5 to 4.0 weight-%

[0057] V is added to further improve the hardening effect. In order to achieve this effect in the present alloy, the content of V is from 1.5 weight-%. However, if V is higher than 4.0 weight%, there will be a problem with thermal stability. Therefore, the content of V is at most 4.0 weight%. According to embodiments, the content of V is from 2.0 to 3.5 weight-%, or from 2.3 to 3.2 weight-%.

[0058] Boron up to 0.01 weight-%

[0059] B is an element that may be added to provide improved hot workability and creep strength. However, if the B content exceeds 0.01 weight%, the weldability may be negatively affected, thus, B is present up to 0.01 weight-%. According to embodiments, the content of boron (B) is from 0.0001 to 0.0075 weight-%, such as 0.001 to 0.0075 weight%.

[0060] Calcium (Ca), Magnesium (Mg) and Cerium (Ce) less than 0.4 weight-%

[0061] Ca, Mg and Ce are elements that may be added to provide improved hot workability. Either Ca or Mg may be added in an amount less than 0.02 weight%. Ce may be added alone or in combination with Ca or Mg. If Ce is added it is added in a content less than 0.3 weight%.

[0062] The present nickel-based alloy also contains incidental impurities. These substances may contaminate the nickel-based alloy when it is industrially produced, due to the raw materials, such as ores and scraps, and due to various other factors in the production process and are allowed to contaminate within the ranges not adversely affecting the properties of the nickel- based alloy as defined hereinabove or hereinafter Examples of these include phosphorus (P) and sulfur (S). Phosphorus (P) may be present less than 0.03 wt% as it is strongly detrimental to hot workability and weldability. Sulphur (S) may be present less than 0.03 wt% as it is strongly detrimental to hot workability and weldability. According to embodiments of the nickel-based alloy according to the invention the content of nickel (Ni) is balance, thus Ni is present in a content of 50.0 to 60.0 weight%, such as in a content of 50 to 59.0 weight%, such as of 50 to 57 weight%.

[0063] According to the present invention, the terms “weight-%”, “weight%” and “wt%” are used interchangeably and means weight per percentage.

[0064] According to embodiments of the present invention the contents of the alloying elements as mentioned hereinabove or hereinafter may individually or in combination be further limited as outlined hereinabove or hereinafter. Further, according to embodiments, the nickel-based alloy comprises or consists of the elements mentioned hereinabove or hereinafter in the ranges mentioned hereinabove or hereinafter. According to embodiments, an object of said nickel- based alloy may comprise or consist of elements mentioned hereinabove or hereinafter in the ranges mentioned hereinabove or hereinafter.

[0065] In an embodiment of the nickel-based alloy according to the invention the alloy has a density of not more than 8.1 g / cm3. In an embodiment of the nickel-based alloy according to the invention, the alloy has a density of not more than 8.0 g / cm3or not more than 7.9 g / cm3.

[0066] The advantage of a low density is a reduction in weight of parts prepared of the inventive nickel-based alloy compared to the same parts made of conventional nickel-based alloys, such as Alloy 718, Alloy 718Plus, Waspaloy® or Rene® 220, which in turn can reduce fuel consumption and load-bearing to structural parts, such as turbine blades in aircraft engines.

[0067] In an embodiment of the nickel-based alloy according to the invention the components and amounts of components are selected within the herein described ranges such that the alloy has a configurational entropy value ASmiX / (-7?) of more than or equal to 1.45, such as more than or equal to 1.50, with the configurational entropy Smixbeing defined by the following formula (1) mix= -R ^XilnXi (1), wherein

[0068] R is the ideal gas constant [J / K.mol], n is the number of components of the alloy,

[0069] Xi is the atomic fraction of component i (with Xt = 1).

[0070] With such a high configurational entropy value ASmiX / (-7?) of more than or equal to 1.45 or even more than or equal to 1 .50, in combination with the amounts of Ni, Cr, Fe, Al and Co, the nickel-based alloys of the present invention are close to or within the features of high entropy alloys (HEA), a concept in metallic alloy design with improving the thermal stability of alloys by increasing their configuration entropy. HEAs are defined as a group of multi-component crystalline alloys composed of five or more principal elements in amounts of 5 or more atomic percent and with a configurational entropy higher than 1.50xR (R is the ideal gas constant) in an ideal solid solution. Due to their unique multi-principal and super-saturated solid solution structure, HEAs possess outstanding properties such as a good combination of high strength and toughness, exceptional high-temperature resistances etc. They usually also have considerably better strength-to-weight ratios, than conventional alloys.

[0071] Compared to conventional nickel-based superalloys, such as Alloy 718, Alloy 718Plus, Waspaloy® or Rene® 220, it is assumed that approaching the criteria of HEAs provides improved properties to the nickel-based alloy of the present invention, which are otherwise rather known from HEAs, such as good mechanical properties at room temperature and high temperature and, at the same time a density, which is lower than for the conventional nickel-based alloys, i. e. a better strength-to-weight ratio.

[0072] The present invention relates to a method for making a nickel-based alloy, the method comprising: providing a nickel-based alloy of the composition of elements as defined hereinabove or hereinafter; solution annealing the alloy, cooling the alloy; and ageing the alloy.

[0073] In an embodiment of the method for making a nickel-based alloy according to the invention, the solution annealing is carried out at a temperature of from 950°C to 1200°C, such as from 1000°C to 1170°C or from 1050°C to 1150°C, and for a time of from 20 minutes to 300 minutes, such as from 25 minutes to 240 minutes or from 30 minutes to 180 minutes or from 40 minutes to 120 minutes.

[0074] In an embodiment of the method for making a nickel-based alloy according to the invention the cooling of the alloy comprises water cooling and air cooling. Preferably, after annealing, the alloy is cooled by water quenching down to about room temperature.

[0075] In an embodiment of the method for making a nickel-based according to the invention the ageing is carried out in a one-step process at a temperature of from 700°C to 900°C, such as from 750°C to 850°C or from 780°C to 820°C, and for a time of from 1 hour to 10 hours, such as from 2 hours to 9 hours or from 3 hours to 6 hours. In an alternative embodiment of the method for making a nickel-based alloy according to the invention the ageing is carried out in a two-step process with a first heating step, followed by a cooling of the alloy, followed by a second heating step, wherein the heating steps are carried out at a temperature of from 650°C to 900°C, such as from 700°C to 850°C or from 700°C to 800°C or from 700°C to 750°C, and for a time of from 1 hour to 10 hours, such as from 2 hours to 9 hours or from 3 hours to 8 hours.

[0076] Examples

[0077] Alloy sample preparation

[0078] All of the alloys were made by vacuum induction melting (VIM) techniques that are well known to those of ordinary skill in the art. The melt was cast into ingots of about 2 kg each. For hot rolling, each ingot was machined into three rolling billets with a diameter of about 20 mm and a length of about 60 mm. The billets were then heated up to 1170-1190°C for about 4 hours for a homogenization treatment before the hot-rolling. All billets of the alloys could be hot rolled into 10 mm x 10 mm or 7 mm x 7 mm squared bars.

[0079] Heat treatment

[0080] All hot-rolled samples were subjected to a solution annealing at 1150°C for 30 minutes and then water quenching down to about room temperature was done.

[0081] Since mechanical tests of the alloy compositions were made in an as-annealed condition (without subsequent ageing) and also in an annealed plus aged condition, samples of the alloy compositions were taken after the annealing and quenching treatment, and further samples of the alloy compositions were subjected to an ageing process.

[0082] The alloy compositions of the present invention were subjected to a one-step ageing process of 805°C for 3 to 7 hours (as indicated below) and subsequent water quenching to room temperature. The one-step ageing process turned out to be suitable for the alloy compositions of the present invention. However, it should be acknowledged that solution annealing and ageing temperatures and times may be adjusted to optimize the mechanical properties of the alloys depending on their composition.

[0083] Alloy 718 and Alloy 718Plus (referred to as “Alloy 718+” in the tables) compositions were prepared and tested as reference alloys in an as-annealed condition and also in an annealed plus aged condition. The ageing of the samples of Alloy 718 and Alloy 718Plus compositions was carried out according to a standard two-step ageing process as it is described in the literature and recommended by manufacturers for these alloys to obtain improved mechanical properties (788°C for 4 hours I water quenching to about room temperature I 704°C for 8 hours I air quenching). In addition, for comparison, a sample of Alloy 718Plus composition was also subjected to the one step ageing process of 805°C for 7 hours, as it was applied to inventive samples, however, compared to the samples treated by the standard two-step ageing process the mechanical properties dropped drastically (data not shown).

[0084] Density measurement

[0085] The densities of the samples were measured in the as-annealed condition according to the standard ISO 3369-2006. During measurement the material is weighted, first in air and then in water. Applying the Archimedes principle, the density of the material is calculated with high accuracy.

[0086] Mechanical tests

[0087] The mechanical properties tensile strength (Rm), offset yield of 0.2 % (Rp0,2) and elongation at break (At) were determined for each alloy composition i) in as-annealed condition (without subsequent ageing) at room temperature (RT), ii) in annealed and aged condition at room temperature (RT), and iii) in annealed and aged condition at elevated temperature of 650°C.

[0088] The mechanical tests i) and ii) at room temperature were made according to standard ISO 6892-1 :2019 using an Instron 4505 testing system, and the tests iii) at 650°C were made according to standard ISO 6892-2:2018 using a servohydraulic testing system of MTS Landmark® Modell 370.10. In then tests, a high strain rate of 3,0x10'4 / s - 8,04x10'3 / s (but within the standard ISO 6892-2:2018) was applied.

[0089] The following table 1 shows the chemical compositions of the alloy compositions prepared according to the present invention and according to Alloy 718 and Alloy 718Plus.

[0090] T able 2 shows for each alloy the configurational entropy in terms of , the measured density [g / cm3], the sum of [Ti]+[AI]+[V] and ([Ti]+[AI]+[V]+[Nb]) / [Co] in terms of weight percentages are indicated.

[0091] Table 3 shows the mechanical properties of the hot-rolled alloy samples according to the present invention and according to Alloy 718 and Alloy 718Plus in the conditions i), ii) and iii). All alloys according to the present invention have an about 4-5% lower density than Alloy 718 and Alloy 718Plus, which means a significantly reduced weight in application of the alloys. At the same time, the alloys of the present invention exhibit similar or even better mechanical strength compared to Alloy 718 and Alloy 718Plus at RT and also at elevated temperature of 650°C. Furthermore, due to the costs of the elements of the alloy compositions, the costs of the alloys of the present invention may be up to about 10% lower than for the reference alloys, of course depending on actual market price conditions.

[0092] Furthermore, all alloys according to the present invention exhibit high configurational entropy values of more than or equal to 1.45, most samples even show configurational entropy values of more than 1.50, i.e. values of high entropy alloys (HEA).

[0093] Table 1 - Alloy Compositions

[0094] Table 2 - Alloy Properties

[0095] Table 3 - Mechanical Properties of hot-rolled Alloy Samples

[0096] *low strain rate 10'4-10'5 / s, others: 10'3-10'4 / s

Claims

CLAIMS1 . A nickel-based alloy comprising the following contents of elements, in weight-%:Chromium (Cr) 15.0 to 19.0 Iron (Fe) 7.0 to 11.0Manganese (Mn) up to 4.0 Silicon (Si) up to 0.5 Aluminum (Al) 2.0 to 5.0 Titanium (Ti) 0.5 to 3.0 Carbon (C) 0.005 to 0.05 Niobium (Nb) 1.0 to 4.0Cobalt (Co) 4.5 to 7.0Copper (Cu) up to 1.0Tungsten (W) up to 0.5Molybdenum (Mo) up to 1.0Vanadium (V) 1.5 to 4.0Boron (B) up to 0.01Nickel (Ni) 50.0 to 60.0 and incidental impurities, wherein the sum of weight-% of titanium (Ti), aluminum (Al) and vanadium (V) is at least 5.0 weight-%.

2. The nickel-based alloy according to claim 1 , wherein the sum of weight-% contents of titanium (Ti), aluminum (Al) and vanadium (V) is at least 6.0 weight-% or at least 6.5 weight-%.

3. The nickel-based alloy according to any one of the preceding claims, wherein the sum of weight-% contents of titanium (Ti), aluminum (Al), vanadium (V) and niobium (Nb) is at least 1.45-times, the weight-% content of cobalt (Co).

4. The nickel-based alloy according to any one of the preceding claims, wherein the content of vanadium (V) is from 2.0 to 3.5 weight-%, or from 2.3 to 3.2 weight-%.

5. The nickel-based alloy according to any one of the preceding claims, wherein the content of aluminum (Al) is from 2.3 to 4.0 weight-%, or from 2.6 to 3.5 weight-%, or from 2.8 to 3.4 weight-%, and / or the content of titanium (Ti) is from 0.8 to 2.8 weight-%, or from 0.9 to 2.5 weight-%, or from 1.0 to 2.3 weight-%, and / or the content of niobium (Nb) is from 1.3 to 3.5 weight-%, or from 1.4 to 3.2 weight-%, and / or the content of cobalt (Co) is from 5.0 to 6.5 weight-%, or from 5.4 to 6.1 weight-% and / or the content of chromium (Cr) is from 15 to 18 weight-% and / or the content of iron (Fe) is from 8.0 to 10.5 weight-% and / or the content of silicon (Si) is from 0.001 to 0.3 weight-% and / or the content of copper (Cu) is up to 0.5 weight-% and / or the content of boron (B) is from 0.0001 to 0.0075 weight-% and / or the content of nickel (Ni) is balance.

6. The nickel-based alloy according to any one of the preceding claims, wherein the alloy has a density of not more than 8.1 g / cm3, such as not more than 8.0 g / cm3or not more than 7.9 g / cm3.

7. The nickel-based alloy according to any one of the preceding claims, wherein the alloy has a configurational entropy value ASmiX / (-7?) of more than or equal to 1.45with the configurational entropy Smixbeing defined by the following formula (1) mix= -R ^XilnXi (1), wherein R is the ideal gas constant [J / K.mol], n is the number of components of the alloy, Xi is the atomic fraction of component i (with Xt = 1).

8. A method for making a nickel-based alloy, the method comprising: providing a nickel-based alloy of the composition of elements as defined in any one of claims 1 to 5; solution annealing the alloy, cooling the alloy; and ageing the alloy.

9. The method for making a nickel-based alloy according to claim 8, wherein the solution annealing is carried out at a temperature of from 950°C to 1200°C, such as from 1000°C to 1170°C or from 1050°C to 1150°C, and for a time of from 20 minutes to 300 minutes, such as from 25 minutes to 240 minutes or from 30 minutes to 180 minutes or from 40 minutes to 120 minutes.

10. The method for making a nickel-based alloy according to claim 8 or claim 9, wherein the cooling of the alloy comprises water cooling and air cooling.11 . The method for making a nickel-based alloy according to any of claims 8 to 10, wherein the ageing is carried out in a one-step process at a temperature of from 700°C to 900°C, such as from 750°C to 850°C or from 780°C to 820°C, and for a time of from 1 hour to 10 hours, such as from 2 hours to 9 hours or from 3 hours to 6 hours.

12. The method for making a nickel-based alloy according to any of claims 8 to 10, wherein the ageing is carried out in a two-step process with a first heating step, followed by a cooling of the alloy, followed by a second heating step, wherein the heating steps are carried out at a temperature of from 650°C to 900°C, such as from 700°C to 850°C or from 700°C to 800°C or from 700°C to 750°C, and for a time of from 1 hour to 10 hours, such as from 2 hours to 9 hours or from 3 hours to 8 hours.

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