Nickel-based alloy of high mechanical strength

Abstract

A nickel-based alloy of a specified composition of elements exhibits high mechanical strength with the sum of weight-% contents of titanium (Ti), aluminum (Al), niobium (Nb), tantalum (Ta) and vanadium (V) being at least 1.35-times the weight-% content of cobalt (Co).

Description

[0001] Nickel-based alloy of high mechanical strength

[0002] TECHNICAL FIELD

[0003] The present invention relates to a nickel-based alloy, a method of making a nickel-base alloy and an article 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, particularly their ability to maintain strength at high temperatures.

[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, morphology 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 grain boundaries, twin boundaries, or within grains. A small amount of delta phase is beneficial to control grain growth during solution annealing and ageing 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 aluminium, titanium and niobium in Alloy 718Plus® provide a thermally stable microstructure and advantageous high-temperature mechanical properties, including substantial rupture and creep strength. The aluminium 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 aluminium 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 aluminium 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] Nickel-based alloys are generally prepared by melting the alloy components and casting the melt into ingots. Ingots may also be formed into billets by hot working the ingots. Billets may further be processed by rolling or drawing. Final products may include a tube or pipe, a bloom, a strip, a bar, a wire, a powder and a plate. The alloys are usually applied in a heat-treated condition. Heat treatment includes solution annealing or solution annealing plus subsequent ageing. In addition to the chemical composition of the alloy, the heat treatment process is of importance as it significantly influences and determines the physical, chemical and microstructural properties of the alloy.

[0015] Solution annealing (or just “annealing”) is a process in which the alloy is heated to a temperature above its critical point (crystallization temperature), maintained at suitable temperature for an appropriate amount of time and then cooled either by air cooling or water quenching to recrystallize. In annealing, atoms migrate in the crystal lattice and the number of dislocations decreases, and grain size and phase composition may change. Annealing leads to a change in ductility and hardness of the alloy.

[0016] Ageing (precipitation hardening; age hardening) is a subsequent heat treatment used to increase the yield strength and in superalloys, it is applied to improve high-temperature strength. Ageing relies on changes in solid solubility with temperature to produce different intermetallic phases, which impede the movement of dislocations or defects in the crystal lattice. Since dislocations are often the dominant carriers of plasticity, this serves to harden the material. Unlike ordinary tempering, alloys often must be kept at elevated temperature for hours to allow precipitation to take place. Due to this time delay, the process is called "ageing". Solution treatment (annealing) and ageing is sometimes abbreviated "STA".

[0017] Thus, the final properties of the nickel-based alloys are determined by their chemical composition and the heat treatment applied. For example, a recommended heat treatment for Alloy 718 includes solution annealing at a temperature in the range from about 925°C to about 1050°C for a time from 0.5 to 8 hours, followed by a subsequent two-step ageing process with a first step at a temperature in the range from about 700°C to about 800°C for a time of about 6 to 8 hours, air cooling down to a temperature in the range from about 600°C to about 650°C and holding again for a time of about 6 to 8 hours as the second step.

[0018] For Alloy 718Plus, a recommended heat treatment process includes solution annealing at a temperature in the range from about 950°C to about 980°C for 1 hour, followed by a subsequent two-step ageing process with a first step at a temperature of about 720°C to about 788°C for a time of about 2 to 8 hours, air cooling down to a temperature of about 620°C to about 704°C and holding again for a time of about 8 hours as the second step.

[0019] Suitable annealing and ageing temperatures and times of alloys rely to a large extent on experience and empirical data. Even though phase diagrams of certain elements and knowledge about chemical and metallurgical behaviour of such elements may provide a rough hint towards suitable heat treatment conditions to obtain certain properties, due to the complexity of possible interactions in multi-element alloys, precise predictions are difficult or impossible to make.

[0020] There is thus still room for improvement of nickel-based alloy compositions and heat treatment processes. 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 superalloys, such as Alloy 718Plus®.

[0021] ASPECT OF THE INVENTION

[0022] 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, good hot workability.

[0023] It is another aspect of the present invention to provide a method for manufacturing such an alloy.

[0024] SUMMARY

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

[0026] Chromium (Cr) 15.0 to 20.0 Iron (Fe) 8.0 to 16.0 Manganese (Mn) up to 2.0 Silicon (Si) up to 0.5 Aluminum (Al) 0.6 to 2.0 Titanium (Ti) 0.5 to 1.5 Carbon (C) 0.005 to 0.05 Niobium (Nb) 5.0 to 7.5 Tantalum (Ta) up to 1.5 Cobalt (Co) 4.5 to 7.0 Copper (Cu) up to 2.5 Tungsten (W) up to 0.8 Molybdenum (Mo) up to 2.7

[0027] Vanadium (V) up to 3.5 Boron (B) up to 0.01

[0028] Nickel (Ni) 47.0 to 57.0 and incidental impurities, wherein the sum of weight-% contents of titanium (Ti), aluminum (Al), niobium (Nb), tantalum (Ta) and vanadium (V), is at least 1.35-times the weight-% content of cobalt (Co).

[0029] The present invention also relates to a method for making a nickel-based alloy as defined hereinabove or hereinafter which is subjected to processing, including solution annealing, cooling and ageing.

[0030] 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, 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.

[0031] DETAILED DESCRIPTION

[0032] The present invention relates to a nickel-based alloy comprising the following contents of elements in weight-%:

[0033] Chromium (Cr) 15.0 to 20.0

[0034] Iron (Fe) 8.0 to 16.0

[0035] Manganese (Mn) up to 2.0

[0036] Silicon (Si) up to 0.5

[0037] Aluminum (Al) 0.6 to 2.0

[0038] Titanium (Ti) 0.5 to 1.5

[0039] Carbon (C) 0.005 to 0.05

[0040] Niobium (Nb) 5.0 to 7.5

[0041] Tantalum (Ta) up to 1.5

[0042] Cobalt (Co) 4.5 to 7.0

[0043] Copper (Cu) up to 2.5

[0044] Tungsten (W) up to 0.8

[0045] Molybdenum (Mo) up to 2.7

[0046] Vanadium (V) up to 3.5

[0047] Boron (B) up to 0.01 Nickel (Ni) 47.0 to 57.0 and incidental impurities, wherein the sum of weight-% contents of titanium (Ti), aluminum (Al), niobium (Nb), tantalum (Ta) and vanadium (V), is at least 1.35-times the weight-% content of cobalt (Co).

[0048] It has been found that the alloys according to the present invention have superior material properties, such as high mechanical strength, thermal creep deformation resistance, structural stability, and corrosion and oxidation resistance, similar or even improved compared to Alloy 718Plus®, also at elevated temperature of 650°C and even higher, and, at the same time, good hot-workability.

[0049] The requirement that the sum of weight-% contents of titanium (Ti), aluminum (Al), niobium (Nb), tantalum (Ta) and vanadium (V) is at least 1.35-times the weight-% content of cobalt (Co), may also be expressed as ([Ti]+[AI]+[Nb]+[Ta]+[V]) / [Co] > 1.35. Co generally contributes to solution hardening of the alloy. Therefore, the alloy of the present invention contains a certain amount of cobalt (Co) within the range defined herein. However, it has surprisingly been found that using a too high content of Co in the entire context of the amounts of elements in the nickel-based alloy according to the invention, which results in a ([Ti]+[AI]+[Nb]+[Ta]+[V]) / [Co] ratio lower than 1.35, a sufficient precipitation hardening may not be achieved for an alloy within the ranges of contents of elements of the inventive alloy. ([Ti]+[AI]+[Nb]+[Ta]+[V]) / [Co] > 1.35 ensures that the material will be properly precipitation hardened and thereby strengthening is ensured.

[0050] With respect to the indication of contents of alloy elements in weight-%, the term “up to x” means the same as “0 to x”, i. e. the respective element may not be present in the alloy (= “0” zero weight-%), except for being present as an incidental impurity, and the upper limit is “x” weight-%.

[0051] In an embodiment of the nickel-based alloy according to the invention ([Ti]+[AI]+[Nb]+[Ta]+[V]) / [Co] > 1.40. In another embodiment of the nickel-based alloy according to the invention ([Ti]+[AI]+[Nb]+[Ta]+[V]) / [Co] > 1.43. A ratio of ([Ti]+[AI]+[Nb]+[Ta]+[V]) / [Co] > 1.40 or even > 1.42 or even > 1.45 may further improve the precipitation hardening.

[0052] In an embodiment of the nickel-based alloy according to the invention, the sum of weight-% contents of titanium (Ti), aluminum (Al), niobium (Nb) and vanadium (V), also expressed as [Ti]+[AI]+[Nb]+[V], is at least 7.80 weight-%, such as at least 8.00 weight-% or at least 8.10 weight-% or at least 8.20 weight-%.

[0053] It has been found that adjustment of [Ti]+[AI]+[N b]+[V] to at least 7.80 weight-% in the context of the amounts of elements in the nickel-based alloy according to the invention ensures that the hardening, solution plus precipitation hardening, will provide sufficient and satisfying strength to the alloy. The effect of the amounts of the combination of these four elements was unexpected. If the sum of weight-% amounts of these four elements is too low, satisfying strength to the alloy may not be achieved.

[0054] Chromium (Cr) 15.0 to 20.0 weight%

[0055] 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 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 20.0 weight%, the toughness of the alloy will decrease, and the hot workability deteriorate thereby making working difficult. Further, if the Cr content exceeds 20.0%, there is a risk of the formation of intermetallic phases, which may cause embrittlement. Thus, according to embodiments of the nickel-based alloy according to the invention, the content of Cr is from 15.5 to 20.0 weight%.

[0056] Iron (Fe) 8.0 to 16.0 weiqht%.

[0057] 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. The Fe content is therefore not more than 16.0 weight%. According to embodiments, the content of iron (Fe) is from 9.0 to 15.0 weight-%.

[0058] Manganese (Mn) up to 2.0 weight-%

[0059] 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 may be beneficial for deoxidation and / or desulfurisation during melting and provides improvement of the workability of the present alloy. However, an excessive high Mn may reduce corrosion resistance. Hence, the Mn content is up to 2.0 weight-%. According to embodiments, the nickel-based alloy as defined hereinabove or hereinafter, the content of Mn is from 0.01 to 2.7 weight-%, such as 0.01 to 1.5 weight-%. Silicon (Si) up to 0.5 weiqht-%

[0060] Si is frequently used as deoxidation agent and may therefore be added to the present alloy. However, weldability and structure stability may be affected negatively if the content of Si is more than 0.5 weight%. Hence, according to embodiments, the content of silicon is from 0.01 to 0.3 weight-%, such as from 0.1 to 0.3 weight-%.

[0061] Aluminum (Al) 0.6 to 2.0 weiqht-%

[0062] At least 0.6 weight% of Al is added to provide creep strength. Furthermore, in high temperature environments, Al may have a positive impact on the corrosion resistance by forming a stable passive layer on the surface. On the other hand, if the Al content exceeds 2.0 wt%, the weldability and hot workability may be negatively influenced. According to embodiments, the Al content is from 0.80 to 1 .75 weight-%, such as from 0.80 to 1.70.

[0063] Titanium (Ti) 0.5 to 1.5 weiqht-%

[0064] Ti is added to provide improved high temperature strength and creep strength. To obtain this effect, it is necessary that the content of Ti is at least 0.5 wt%. According to embodiments, the content of Ti is as at least 0.7 wt%. On the other hand, if the Ti content exceeds 1.5 wt%, the weldability and hot workability may be negatively influenced. According to embodiments, the content of Ti is 0.7 to 1.3 weight%.

[0065] Carbon (C) 0.005 to 0.05 weiqht%

[0066] 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-%.

[0067] Niobium (Nb) 5.0 to 7.5 weiqht%

[0068] Nb will provide high temperature strength and creep strength and is therefore added in an amount of at least 5.0 weight%. However, if the Nb content exceeds 7.5 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 is from 5.4 to 7.0 weight-%.

[0069] Tantalum (Ta) up to 1.5 weiqht%

[0070] Ta may be added up to 1.5 weight%. According to embodiments, Ta may be present in 0.005 to 1.5 weight%. According to embodiments, the content of Ta is at least 0.01 wt%. If the Ta content exceeds 1.5 wt%, the hot workability may be negatively affected and there may also be a risk for formation of unwanted Laves phases. According to embodiments, the content of Ta is from 0.01 to 1.3 weight%, such as from 0.01 to 1.2 weight-%.

[0071] Cobalt (Co) 4.5 to 7.0 weight-%

[0072] 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 Co content is from 5.0 to 7.0 weight- %.

[0073] Copper (Cu) up to 2.5 weight%

[0074] Cu may be added to provide additional stability of the austenite phase. However, if the Cu content exceeds 2.5 wt%, the weldability and hot workability may be negatively influenced. According to embodiments, the highest content of Cu is up to 2.5 weight-%, the highest content of Cu is up to 2.3 weight-%, such as up to 1 .5 weight-%.

[0075] Tungsten (W) up to 0.8 weight-%

[0076] 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 0.8 weight%. According to embodiments, the content of tungsten is up to 0.6 weight-%.

[0077] Molybdenum (Mo) up to 2.7 weight-%

[0078] Mo may be added to the nickel-based alloy since it increases the entropy value. According to embodiments, Mo content is from 0.01 to 2.7 weight-%.

[0079] Vanadium (V) up to 3.5 weight-%

[0080] A certain amount of vanadium (V), as described in the following, may be desirous to further improve the hardening effect. According to embodiments, the content of vanadium (V) is at least According to embodiments, the content of vanadium is from 0.001 to 3.5 weight%, such as the content of vanadium is at least 0.4 weight-%, or from 0.4 to 3.0 weight-%, or from 0.5 to 2.5 weight-%.

[0081] Boron up to 0.01 weight-%

[0082] 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%.

[0083] Calcium (Ca), Magnesium and Cerium (Ce) less than 0.4 weight-%

[0084] 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%.

[0085] 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 47.0 to 57.0 weight%, such 48 to 55 weight-%

[0086] 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 weight% as it is strongly detrimental to hot workability and weldability. Sulphur (S) may be present less than 0.03 weight% as it is strongly detrimental to hot workability and weldability.

[0087] 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

[0088] According to the present invention, the terms “weight-%”, “weight%” and “wt%” are used interchangeably and means weight per percentage.

[0089] In an embodiment of the nickel-based alloy according to the invention the alloy has a density of not more than 8.15 g / cm3. In another embodiment of the nickel-based alloy according to the invention the alloy has a density of not more than 8.12 g / cm3, such as 8.10, g / cm3. 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. The density can be adjusted by the proper choice of alloying elements within the ranges of the present invention.

[0090] 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 / (- ?) 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

[0091] 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).

[0092] With such a high configurational entropy value ASmiX / (- ?) 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, Nb 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.

[0093] 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. The present invention also relates to a method for making a nickel-based alloy, the method comprising:

[0094] - providing a nickel-based alloy of the composition of elements as defined hereinabove or hereinafter;

[0095] - solution annealing the alloy at a temperature of from 1050°C to 1300°C and for a time of from 15 minutes to 180 minutes,

[0096] - cooling the alloy; and

[0097] - ageing the alloy at a temperature of from 600 to 900°C and for a time of from 2 hours to 12 hours.

[0098] In an embodiment of the method according to the present invention the solution annealing is carried out at a temperature of from 1100°C to 1250°C, such as from 1100°C to 1200°C, and / or for a time of from 20 minutes to 120 minutes, such as from 30 minutes to 60 minutes.

[0099] The cooling after the solution annealing is preferably carried out by water cooling, air cooling or a combination of both. The cooling is carried out down to a temperature below 60°C, preferably down to about room temperature.

[0100] In an embodiment of the method according to the present invention the ageing is carried out in a two-step process comprising a first heat treatment step at a temperature of from 700°C to 900°C, such as from 750°C to 830°C, and for a time of from 2 hours to 8 hours, such as from 3 hours to 6 hours or from 3.5 hours to 4.5 hours, followed by water cooling down to below 60°C, and a second heat treatment step at a temperature of from 600°C to 800°C, such as from 650°C to 760°C, and for a time of from 4 hours to 12 hours, such as from 6 hours to 10 hours or from 7 hours to 9 hours, followed by water cooling or air cooling.

[0101] Advantageously, the nickel-based alloy is provided by melting the components, casting the melt into ingots, and optionally further hot working the ingots to bars or billets.

[0102] In an embodiment of the method according to the present invention, prior to the solution annealing, the nickel-based alloy is subjected to a hot-working step.

[0103] In another embodiment of the method according to the present invention, prior to the hot working step, the nickel-based alloy is subjected to a homogenization heat treatment step at a temperature of from 1050°C to 1300°C, such as from 1100°C to 1250°C or from 1150°C to 1200°C, and for a time of from 1 hour to 60 hours, such as from 1 hour to 30 hours, such as from 1 h to 20 hours. EXAMPLES

[0104] Alloy sample preparation

[0105] 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.

[0106] Heat treatment

[0107] If not otherwise indicated, the solution annealing step (or only referred to as “annealing”) of the hot-rolled samples included heating at 1150°C for 30 minutes and then water quenching down to about room temperature.

[0108] Since mechanical tests of the alloy compositions were either made in an as-annealed condition (without subsequent ageing) or in an annealed plus aged condition, samples of the alloy compositions were taken after the annealing treatment, as described before, and further samples of the alloy compositions were subjected to a subsequent ageing process.

[0109] Ageing of the annealed plus aged alloy compositions of the present invention was done in a two-step process including a first heating step at 788°C for 4 hours and water quenching to about room temperature, and a second heating step at 704°C for 8 hours and air cooling. 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.

[0110] Alloy 718 and Alloy 718Plus compositions were prepared and tested as reference alloys in an as-annealed condition and also in an annealed plus aged condition. The annealing and ageing of the samples of Alloy 718 and Alloy 718Plus compositions was carried out as described above for the alloy compositions of the present invention.

[0111] Density measurement

[0112] 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. Mechanical tests

[0113] 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.

[0114] 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 the tests, a high strain rate of 3,0x10-4 / s - 8,04x10'3 / s (but within the standard ISO 6892-2:2018) was applied.

[0115] Results

[0116] Table 1 shows the chemical compositions of the alloy samples prepared according to the present invention and according to Alloy 718 and Alloy 718Plus.

[0117] Table 2 shows for each alloy the configurational entropy in terms of ASmiX / (- ?) , the measured density [g / cm3], the sum of [Ti]+[AI]+[Nb]+[V] and ([Ti]+[AI]+[Nb]+[Ta] +[V]) / [Co] in terms of weight percentages are indicated.

[0118] Table 3 shows the mechanical properties of alloy samples, which were subjected to the heat treatment (annealing or annealing plus ageing) in the as-cast condition, i. e. without hot-rolling subsequent to the casting, in the conditions i), ii) and iii), wherein ageing was carried out according to the standard two-step ageing process (788°C for 4 hours I water quenching to about room temperature 1704°C for 8 hours I air quenching).

[0119] In the as-cast and solution-annealed condition, the as-cast alloys according to the invention show higher strength compared to Alloy 718Plus, except inventive alloy no. 5 that shows similar strength as Alloy 718Plus. In the aged condition, all of the as-cast alloys according to the invention show much higher strength than Alloy 718Plus, including inventive alloy no. 5 that shows the highest strength.

[0120] Table 4 shows the mechanical properties of alloy samples, which were subjected to the heat treatment (annealing and annealing + ageing) in the hot-rolled condition in the conditions i), ii) and iii), wherein ageing was carried out according to the two-step ageing process, 788°C for 4 hours, water quenching to about room temperature, 704°C for 8 hours I air quenching.

[0121] In the as-annealed condition, the mechanical properties of the alloys according to the invention are similar or even better than the mechanical properties of comparative Alloy 718 and Alloy 718Plus. In the annealed plus aged condition, the alloys according to the invention show both higher Rp0.2 and higher Rm, but in some cases lower elongation, than Alloy 718 and Alloy 718Plus at RT and 650°C.

[0122] Table 1 - Alloy Compositions

[0123] Table 2 - Alloy Properties

[0124] Table 3 - Mechanical Properties of as-cast Alloy Samples

[0125] Table 4 - Mechanical Properties of hot-rolled Alloy Samples

Claims

CLAIMS1 . A nickel-based alloy comprising the following contents of elements, in weight-%:Chromium (Cr) 15.0 to 20.0 Iron (Fe) 8.0 to 16.0 Manganese (Mn) up to 2.0 Silicon (Si) up to 0.5 Aluminum (Al) 0.6 to 2.0 Titanium (Ti) 0.5 to 1.5 Carbon (C) 0.005 to 0.05 Niobium (Nb) 5.0 to 7.5 Tantalum (Ta) up to 1.5 Cobalt (Co) 4.5 to 7.0 Copper (Cu) up to 2.5 Tungsten (W) up to 0.8 Molybdenum (Mo) up to 2.7 Vanadium (V) up to 3.5 Boron (B) up to 0.01 Nickel (Ni) 47.0 to 57.0 and incidental impurities, wherein the sum of weight-% contents of titanium (Ti), aluminum (Al), niobium (Nb), tantalum (Ta) and vanadium (V), is at least 1.35-times the weight-% content of cobalt (Co).

2. The nickel-based alloy according to claim 1 , wherein the content of Ta is 0.005 up to 1.5 weight%.

3. The nickel-based alloy according to claim 1 or 2, wherein the Mo content is from 0.01 to 2.7 weight-%.

4. The nickel-based alloy according to any one of claims 1 to 3, wherein the sum of weight- % contents of titanium (Ti), aluminum (Al), niobium (Nb) and vanadium (V) is at least 7.80 weight-%.

5. The nickel-based alloy according to any one of the preceding claims, wherein the sum of weight-% contents of titanium (Ti), aluminum (Al), niobium (Nb), vanadium (V) andtantalum (Ta) is at least 1.40-times, such as at least 1.45-times, the weight-% content of cobalt (Co).

6. The nickel-based alloy according to any one of the preceding claims, wherein the content of vanadium (V) is from 0.4 to 3.0 weight-%, or from 0.5 to 2.5 weight-%.

7. The nickel-based alloy according to any one of the preceding claims, wherein the content of niobium (Nb) is from 5.4 to 7.0 weight-% and / or the content of tantalum (Ta) is from 0.01 to 1.2 weight-% and / or the content of chromium (Cr) is from 15.5 to 20.0 weight-% and / or the content of manganese (Mn) is from 0.01 to 1.5 weight-% and / or the content of iron (Fe) is from 9.0 to 15.0 weight-% and / or the content of silicon (Si) is from 0.1 to 0.3 weight-% and / or the content of copper (Cu) is up to 1.5 weight-% and / or the content of carbon (C) is from 0.005 to 0.03 weight-% and / or the content of tungsten (W) is up to 0.6 weight-% and / or the content of boron (B) is from 0.0001 to 0.0075 weight-%.

8. The nickel-based alloy according to any one of the preceding claims, wherein the alloy has a density of not more than 8.15 g / cm3.

9. 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 1.45, with the configurational entropy Smixbeing defined by the following formula (1) a.mix= -R ^XilnXi (1), whereinR 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 X = 1).

10. A method for making a nickel-based alloy, the method comprising: a. providing a nickel-based alloy of the composition of elements as defined in any of claims 1 to 7; b. solution annealing the alloy at a temperature of from 1050°C to 1300°C and for a time of from 15 minutes to 180 minutes, c. cooling the alloy; and d. ageing the alloy at a temperature of from 600°C to 900°C and for a time of from 2 hours to 12 hours.

11. The method for making a nickel-based alloy according to claim 10, wherein the solution annealing is carried out at a temperature of from 1100°C to 1250°C, such as from 1100°C to 1200°C, and / or for a time of from 20 minutes to 120 minutes, such as from 30 minutes to 60 minutes.

12. The method for making a nickel-based alloy according to claim 10 or claim 11 wherein the cooling of the alloy comprises water cooling and / or air cooling down to below 60°C.

13. The method for making a nickel-based alloy according to any of claims 10 to 12, wherein the ageing is carried out in a two-step process comprising a first heat treatment step at a temperature of from 700°C to 900°C, such as from 750°C to 830°C, and for a time of from 2 hours to 8 hours, such as from 3 hours to 6 hours or from 3.5 hours to 4.5 hours, followed by water cooling down to below 60°C, and a second heat treatment step at a temperature of from 600°C to 800°C, such as from 650°C to 760°C, and for a time of from 4 hours to 12 hours, such as from 6 hours to 10 hours or from 7 hours to 9 hours, followed by water cooling or air cooling.

14. The method for making a nickel-based alloy according to any of claims 10 to 13, wherein the nickel-based alloy is provided by melting the components and then casting the melt into ingots.

15. The method for making a nickel-based alloy according to any of claims 10 to 14, wherein, prior to the solution annealing, the nickel-based alloy is subjected to a hot- working step.

16. The method for making a nickel-based alloy according to claim 15, wherein, prior to the hot-working step, the nickel-based alloy is subjected to a homogenization heat treatment step at a temperature of from 1050°C to 1300°C, such as from 1100°C to 1250°C or from 1150°C to 1200°C, and for a time of from 1 hour to 60 hours, such as from 1 hour to 30 hours, such as from 1 h to 20 hours.

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