alloy

Abstract

In atomic percent, aluminum: 20% to 35%, zirconium: 16.7%, vanadium: 7%, tungsten: 35%, chromium: 35%, iron: 10%, nickel: 5%, titanium: 40%, tantalum: 35%, niobium: 20%, molybdenum: 35%, cobalt: 5%, manganese: 10%, copper: 5%, hafnium: 10%, silicon: 5%, platinum: 5%, palladium: 5%, ruthenium: 10%, rhodium: 5%, iridium: 5%, rhenium: 35%, and the atomic percentages of rhenium, tantalum, tungsten, and niobium are A, respectively. Re , A Ta , A W and A Nb Then, A Re ≦(35-A Ta )+(35-A W )+(20-A Nb ) and the total amount of unavoidable impurities is 1 atomic % or less; [0010] JPEG2025506026000038.jpg34170 where x i is the atomic fraction of element i in the alloy, and VEC i is the number of valence electrons associated with an atom of element i and R is the universal gas constant for the alloy.

Description

[Technical field]

[0001] The present invention relates to composite concentrated alloys (CCAs) designed for high temperature applications that offer a unique combination of high ductility, high temperature mechanical strength, and oxidation resistance at high temperatures, which can be achieved in combination with low density and reasonable alloy cost. [Background technology]

[0002] Traditional alloys with high mechanical strength at high temperatures typically rely on major base elements. Alloys with very high melting points are often based on refractory elements such as molybdenum, tungsten, niobium, and tantalum. These alloys have very high melting points and strength, but are not resistant to environmental damage. These alloys are also often very dense, limiting their application in rotating machinery, especially aerospace applications where increased weight is undesirable. Alternatively, platinum group metal (PGM) alloys often combine high melting points with environmental resistance. However, the high cost of PGM alloys and the relative scarcity of the materials make them economically unfeasible to use in many commercial applications.

[0003] To address this challenge, there has been recent development activity in the areas of composite concentrated alloys (CCA) and refractory composite concentrated alloys (RCCA). However, currently proposed alloys do not achieve the combination of high melting points, high temperature strength, and high oxidation resistance at high temperatures with low density and reasonable cost required for commercial applications in fields such as gas turbine technology, jet turbine technology, and rocket propulsion. Examples of commonly studied alloys are shown in Table 1. (Cao et al. Effects of Al and Mo on high temperature oxidation behaviour of refractory high entropy alloys, Trans. Nonferrous Met. Soc. China 29(2019) 1476-1483; Gorr et al., High-Temperature Oxidation Behaviour of Refractory High-Entropy Alloys: Effect of Alloy Composition, Oxid. Met. (2017) 88: 339-349; Miracle et al., Mechanical Properties of Nb 25 Mo 25 Ta 25 W 25 and V 20 Nb 20 Mo 20 Ta 20 W 20 Refractory High-Entropy Alloys (PREPRINT), July 2011, Air Force Research Laboratory Materials and Manufacturing Directorate, Wright-Patterson Air Force Base, OH45433-7750 Air Force Materiel Command United States Air Force). [1]-[3]

[0004] Table 1 shows the atomic percentages of the nominal compositions of the high-temperature complex enriched alloys that have been studied to date. [Table 1]

[0005] The alloy according to the present invention contains, in atomic percent, aluminum: 20% to 35%, zirconium: 16.7%, vanadium: 7%, tungsten: 35%, chromium: 35%, iron: 10%, nickel: 5%, titanium: 40%, tantalum: 35%, niobium: 20%, molybdenum: 35%, cobalt: 5%, manganese: 10%, copper: 5%, hafnium: 10%, silicon: 5%, platinum: 5%, palladium: 5%, ruthenium: 10%, rhodium: 5%, iridium: 5%, and rhenium: 35%, with the atomic percents of rhenium, tantalum, tungsten, and niobium being A, B, C, D, E, F, H, and I, respectively. Re , A Ta , A W and A Nb Then, A Re ≦(35-A Ta )+(35-A W )+(20-A Nb ) and the total amount of unavoidable impurities is 1 atomic % or less;

number

[0006] In one embodiment, to reduce the variation in intermetallic phase formation, the following equation is satisfied:

number

[0007] In one embodiment, to reduce spalling and thereby increase oxidation resistance, the following formula is satisfied:

number

[0008] In one embodiment, to reduce the density of the alloy, the following equation is satisfied:

number

[0009] In one embodiment, the following equation is satisfied to enhance the high temperature strength of the alloy:

number

[0010] In one embodiment, to enhance the stability of the solid solution, the following formula is satisfied:

number

[0011] In one embodiment, to reduce the cost of the alloy, the following formula is satisfied:

number

[0012] In one embodiment, to reduce the cost of the alloy, the following formula is satisfied: 75≧A V +3A Ta Preferably, 64≧A V +3A Ta More preferably, 53≧A V +3A Ta Even more preferably, 42≧A V +3A Ta Even more preferably, 34≧A V +3A Ta Most preferably, 26≧A V +3A Ta Here, A V and A Ta are the atomic percentages of vanadium and tantalum, respectively.

[0013] In one embodiment, the alloy comprises between 21 and 35 atomic % aluminum, preferably between 22 and 35 atomic % aluminum, and more preferably between 23 and 35 atomic % aluminum, such alloys having excellent oxidation resistance.

[0014] In one embodiment, the alloy contains up to 33 atomic percent aluminum, preferably up to 31 atomic percent aluminum, which provides improved high temperature strength.

[0015] In one embodiment, the alloy contains up to 11.1 atomic % zirconium, preferably up to 10 atomic % zirconium, and most preferably up to 9 atomic % zirconium, which reduces the likelihood of intermetallic phases forming.

[0016] In one embodiment, the alloy comprises at least 2 atomic % zirconium, preferably at least 4 atomic % zirconium, more preferably at least 6 atomic % zirconium, even more preferably at least 8 atomic % zirconium, and most preferably at least 10 atomic % zirconium. Such alloys have reduced VEC, which increases ductility and reduces the likelihood of spalling, which can lead to reduced oxidation resistance.

[0017] In one embodiment, the alloy contains up to 5.1 atomic percent vanadium, preferably up to 3 atomic percent vanadium. Such alloys have excellent corrosion resistance.

[0018] In one embodiment, the alloy includes at least 2 atomic % vanadium, preferably at least 5 atomic % vanadium, such alloys have reduced density and improved high temperature strength.

[0019] In one embodiment, the alloy comprises up to 26.8 atomic % tungsten, preferably up to 25.1 atomic % tungsten, more preferably up to 20.0 atomic % tungsten, preferably up to 19.0 atomic % tungsten, preferably up to 10 atomic % tungsten. Such alloys have a low density.

[0020] In one embodiment, the alloy comprises at least 2 atomic % tungsten, preferably at least 5 atomic % tungsten, preferably at least 8 atomic % tungsten, more preferably at least 11 atomic % tungsten, such alloys have improved high temperature strength.

[0021] In one embodiment, the alloy contains 25 atomic % or less chromium, preferably 20 atomic % or less chromium, most preferably 15 atomic % or less chromium, and even more preferably 10 atomic % or less chromium, which reduces the likelihood of harmful Laves phases and other Cr-rich phases.

[0022] In one embodiment, the alloy contains up to 7 atomic % iron, preferably up to 5 atomic % iron. Such alloys have reduced VEC and improved ductility.

[0023] In one embodiment, the alloy comprises at least 0.5 atomic % iron, preferably at least 2 atomic % iron, more preferably at least 4 atomic % iron. Such alloys have excellent printability.

[0024] In one embodiment, the alloy comprises up to 4 atomic % nickel, preferably up to 3 atomic % nickel, and more preferably up to 1 atomic % nickel. Such alloys have a lower VEC and therefore improved ductility.

[0025] In one embodiment, the alloy includes at least 0.5 atomic % nickel, preferably at least 1 atomic % nickel, and more preferably at least 2 atomic % nickel, such alloys have a reduced tendency to spall and therefore improved oxidation resistance.

[0026] In one embodiment, the alloy comprises up to 35 atomic % titanium, preferably up to 33 atomic % titanium, more preferably up to 30 atomic % titanium, more preferably up to 25 atomic % titanium, and even more preferably up to 20 atomic % titanium. Such alloys have improved oxidation resistance.

[0027] In one embodiment, the alloy comprises at least 5 atomic percent titanium, preferably at least 8 atomic percent titanium, more preferably at least 13 atomic percent titanium, and most preferably at least 20 atomic percent titanium. Such alloys have improved high temperature strength.

[0028] In one embodiment, the alloy comprises up to 33.3 atomic % tantalum, preferably up to 25 atomic % tantalum, more preferably up to 21.3 atomic % tantalum, even more preferably up to 17.7 atomic % tantalum, more preferably up to 14 atomic % tantalum, more preferably up to 11.3 atomic % tantalum, and most preferably up to 8.7 atomic % tantalum. Such alloys have reduced density and cost.

[0029] In one embodiment, the alloy comprises at least 2 atomic % tantalum, preferably at least 5 atomic % tantalum, preferably at least 10 atomic % tantalum, more preferably at least 15 atomic % tantalum, and most preferably at least 20 atomic % tantalum, such alloys have improved high temperature strength.

[0030] In one embodiment, the alloy contains up to 16 atomic % niobium, preferably up to 13 atomic % niobium, which reduces the likelihood of plaging.

[0031] In one embodiment, the alloy comprises at least 5 atomic % niobium, preferably at least 8 atomic % niobium, and more preferably at least 10 atomic % niobium. Such alloys have increased strength.

[0032] In one embodiment, the alloy contains up to 20 atomic % molybdenum, preferably up to 15 atomic % molybdenum, more preferably up to 12 atomic % molybdenum, and even more preferably up to 7 atomic % molybdenum, which provides improved oxidation resistance.

[0033] In one embodiment, the alloy includes at least 2 atomic % molybdenum, preferably at least 4 atomic % molybdenum, and more preferably at least 6 atomic % molybdenum, which promotes improved high temperature strength.

[0034] In one embodiment, the alloy contains up to 3 atomic % cobalt, preferably up to 2 atomic % cobalt, which reduces the VEC and improves ductility.

[0035] In one embodiment, the alloy includes at least 0.5 atomic % cobalt, preferably at least 1 atomic % cobalt, more preferably at least 2 atomic % cobalt, even more preferably at least 3 atomic % cobalt, and most preferably at least 4 atomic % cobalt, which provides reduced density and cost, as well as improved oxidation resistance through reduced spalling.

[0036] In one embodiment, the alloy contains up to 4 atomic % copper, preferably up to 3 atomic % copper, which reduces VEC and improves ductility.

[0037] In one embodiment, the alloy includes at least 0.5 atomic percent copper, preferably at least 1 atomic percent copper, and more preferably at least 2 atomic percent copper, which helps reduce spalling and improve oxidation resistance.

[0038] In one embodiment, the alloy contains up to 7 atomic % manganese, preferably up to 5 atomic % manganese, which reduces the VEC and improves ductility as well as improves oxidation performance.

[0039] In one embodiment, the alloy includes at least 0.5 atomic % manganese, preferably at least 2 atomic % manganese, and more preferably at least 4 atomic % manganese, which helps reduce the density of the alloy.

[0040] In one embodiment, the alloy comprises up to 20 atomic % Re, preferably up to 15 atomic % Re, more preferably up to 10 atomic % Re, and most preferably up to 5 atomic % Re, which reduces cost, reduces spalling, and improves oxidation resistance.

[0041] In one embodiment, the alloy includes at least 3 atomic % rhenium, preferably at least 5 atomic % rhenium, which provides improved high temperature strength.

[0042] In one embodiment, to improve ductility, the following equation is satisfied:

number

[0043] In one embodiment, to reduce density, the following equation is satisfied: A W +0.8A Ta <=37.8 Preferably, A W+0.72A Ta <=26.8 More preferably, A W +0.6A Ta <= 20 Here, A Ta and A W are the atomic percentages of tantalum and tungsten, respectively, in the alloy.

[0044] In one embodiment, to improve ductility, the following equation is satisfied: A Al +A Zr +A Ti ≧41 Preferably, A Al +A Zr +A Ti ≧60 Here, A Al , A Zr and A Ti are the atomic percentages of aluminum, zirconium, and titanium, respectively, in the alloy.

[0045] In one embodiment, to improve ductility, the following equation is satisfied: A Zr +A Ti ≧6 Here, A Zr and A Ti are the atomic percentages of zirconium and titanium, respectively.

[0046] In one embodiment, to improve high temperature oxidation resistance, the following formula is satisfied: A V +1.15A W <=28.9 Here, A V and A W are the atomic percent amounts of vanadium and tungsten, respectively.

[0047] In one embodiment, to improve high temperature oxidation resistance, the following formula is satisfied: A Nb +0.83ATa <= 42.5 Here, A Nb and A Ta are the atomic percentages of niobium and tantalum, respectively.

[0048] In one embodiment, the alloy comprises 1 atomic % chromium or more, preferably 2 atomic % chromium or more, more preferably 3 atomic % chromium or more, even more preferably 5 atomic % chromium or more, and most preferably 10 atomic % chromium or more. Such alloys provide excellent corrosion resistance.

[0049] In one embodiment, to improve high temperature strength, the following formula is satisfied: 10≦A W +A Ta +A Mo +A Nb Preferably, 13≦A W +A Ta +A Mo +A Nb More preferably, 26≦A W +A Ta +A Mo +A Nb Even more preferably, 39≦A W +A Ta +A Mo +A Nb Most preferably, 50≦A W +A Ta +A Mo +A Nb Here, A W , A Ta , A Mo and A Nb are the atomic percentages of tungsten, tantalum, molybdenum and niobium, respectively.

[0050] In one embodiment, to improve high temperature strength, the following formula is satisfied: A W+A Ta +A Mo +A Nb ≧10 Preferably, A W +A Ta +A Mo +A Nb ≧0.75A Al -4.75 More preferably, A W +A Ta +A Mo +A Nb ≧0.75A Al +8.75 Even more preferably, A W +A Ta +A Mo +A Nb ≧0.8A Al +23 Most preferably, A W +A Ta +A Mo +A Nb ≧1.25A Al +21.25 Here, A Al , A W , A Ta , A Mo and A Nb are the atomic percentages of aluminum, tungsten, tantalum, molybdenum and niobium, respectively.

[0051] The term "comprising" is used herein to indicate that the composition is 100% and that the percentage is made to the exclusion of the presence of additional components. Unless otherwise stated, all amounts are expressed as atomic % (at %). i is the atomic percentage of element i in the alloy, and x i is the atomic fraction of element i in the alloy.

[0052] The present invention will now be more fully described, by way of example only, with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0053] [Figure 1a] % and there are no further restrictions. [Figure 1b] % and there are no further restrictions. [Figure 1c] Plot of Fe on the y-axis versus VEC on the x-axis for all alloys within the region defined in Table 2, except that zirconium may be present up to 35 atomic % and there are no further restrictions. [Figure 1d] % and there are no further restrictions. [Figure 1e] % and there are no further restrictions. [Figure 1f] % and there are no further restrictions. [Figure 1g] Plot of Pd on the y-axis versus VEC on the x-axis for all alloys within the region defined in Table 2, except that zirconium may be present up to 35 atomic % and there are no further restrictions. [Figure 1h] % and there are no further restrictions. [Figure 1i]% and there are no further restrictions. [Figure 1j] % and there are no further restrictions. [Diagram 2] 1 is a SEM micrograph of the surface layer of an experimental sample, along with contained V and O in the EDS map. [Diagram 3] It indicates the vanadium concentration of a given alloy and whether a mixed oxide or pure vanadium oxide outer layer is formed. [Figure 4a] Pilling-Bedworth ratios of alloys with varying W and V are plotted for the entire alloy range in Table 2, excluding hafnium, silicon, platinum, palladium, ruthenium, iridium and rhodium. [Figure 4b] Pilling-Bedworth ratios of alloys with varying Ta and Nb are plotted for the entire alloy range in Table 2, excluding hafnium, silicon, platinum, palladium, ruthenium, iridium and rhodium. [Figure 5a] 1 is a plot of the density of the alloy as a function of W and Ta content. A line is drawn for density ≦10 g / cm3. The alloy region is the elemental region defined in claim 1, excluding hafnium, silicon, platinum, palladium, ruthenium, iridium and rhodium, and including the constraints VEC≦4.6 and entropy ≧13.38. [Figure 5b] 1 is a plot of the density of the alloy as a function of W and Ta content. A line is drawn for density ≦9 g / cm3. The alloy region is the elemental region defined in claim 1, excluding hafnium, silicon, platinum, palladium, ruthenium, iridium and rhodium, and includes the constraints VEC≦4.6 and entropy ≧13.38. [Figure 5c]1 is a plot of the density of the alloy as a function of W and Ta content. A line is drawn for density ≦8 g / cm3. The alloy region is the elemental region defined in claim 1, excluding hafnium, silicon, platinum, palladium, ruthenium, iridium and rhodium, and includes the constraints VEC≦4.6 and entropy ≧13.38. [Figure 6] The VEC is plotted on the y-axis against Al equivalent (the sum of Al, Zr and Ti). The alloys plotted are within the scope of claim 1 and also include the constraints VEC≦4.6, entropy ≧13.38, Pilling-Bedworth ratio<2, density<10, and exclude hafnium, silicon, platinum, palladium, ruthenium, iridium and rhodium. [Figure 7] The zirconium concentration and the presence or absence of Al-Zr intermetallic compounds are shown. [Figure 8] SEM and EDS images of samples 2D and 2E are shown, demonstrating the absence of Zr-Al precipitates. [Figure 9a] 9a plots melting points as a function of tungsten equivalent (Weq, the sum of tungsten, tantalum, molybdenum and niobium) and aluminum atomic %. The alloy region is the elemental region defined in claim 1, which also includes the constraints VEC≦4.6 and entropy≧13.38, and excludes hafnium, silicon, platinum, palladium, ruthenium, iridium and rhodium. In FIG. 9a, alloys with melting points above 1800K are plotted. [Figure 9b] 9b plots melting points as a function of tungsten equivalent (Weq, the sum of tungsten, tantalum, molybdenum and niobium) and aluminum atomic %. The alloy region is the elemental region defined in claim 1, which also includes the constraints VEC≦4.6 and entropy≧13.38, and excludes hafnium, silicon, platinum, palladium, ruthenium, iridium and rhodium. In FIG. 9b, alloys with melting points above 2000 K are plotted. [Figure 9c]9 shows a plot of melting point as a function of tungsten equivalent (Weq, the sum of tungsten, tantalum, molybdenum and niobium) and aluminum atomic %. The alloy region is the elemental region defined in claim 1, which also includes the constraints VEC≦4.6 and entropy≧13.38, and excludes hafnium, silicon, platinum, palladium, ruthenium, iridium and rhodium. In FIG. 9c, alloys with melting points above 2200 K are plotted. [Figure 9d] 9 shows a plot of melting point as a function of tungsten equivalent (Weq, the sum of tungsten, tantalum, molybdenum and niobium) and aluminum atomic %. The alloy region is the elemental region defined in claim 1, which also includes the constraints VEC≦4.6 and entropy≧13.38, and excludes hafnium, silicon, platinum, palladium, ruthenium, iridium and rhodium. In FIG. 9d, alloys with melting points above 2400 K are plotted. [Figure 9e] Figure 9e plots melting points as a function of tungsten equivalent (Weq, the sum of tungsten, tantalum, molybdenum and niobium) and aluminum atomic %. The alloy region is the elemental region defined in claim 1, which also includes the constraints VEC≦4.6 and entropy≧13.38, and excludes hafnium, silicon, platinum, palladium, ruthenium, iridium and rhodium. Figure 9e plots alloys with melting points above 2500K. [Figure 10] A trade-off between density and melting point is shown for all alloys defined in claim 1, including the constraints VEC≦4.6 and entropy≧13.38. [Figure 11a] The relationship between cost and the concentrations of Ta and V is shown. The alloy region is the element region defined in claim 1, which includes the constraints VEC≦4.6 and entropy≧13.38, and excludes hafnium, silicon, platinum, palladium, ruthenium, iridium, and rhodium. [Figure 11b]The relationship between cost and the concentrations of Ta and V is shown. The alloy region is the element region defined in claim 1, which includes the constraints VEC≦4.6 and entropy≧13.38, and excludes hafnium, silicon, platinum, palladium, ruthenium, iridium, and rhodium. [Figure 11c] The relationship between cost and the concentrations of Ta and V is shown. The alloy region is the element region defined in claim 1, which includes the constraints VEC≦4.6 and entropy≧13.38, and excludes hafnium, silicon, platinum, palladium, ruthenium, iridium, and rhodium. [Figure 11d] The relationship between cost and the concentrations of Ta and V is shown. The alloy region is the element region defined in claim 1, which includes the constraints VEC≦4.6 and entropy≧13.38, and excludes hafnium, silicon, platinum, palladium, ruthenium, iridium, and rhodium. [Figure 11e] The relationship between cost and the concentrations of Ta and V is shown. The alloy region is the element region defined in claim 1, which includes the constraints VEC≦4.6 and entropy≧13.38, and excludes hafnium, silicon, platinum, palladium, ruthenium, iridium, and rhodium. [Figure 11f] The relationship between cost and the concentrations of Ta and V is shown. The alloy region is the element region defined in claim 1, which includes the constraints VEC≦4.6 and entropy≧13.38, and excludes hafnium, silicon, platinum, palladium, ruthenium, iridium, and rhodium. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0054] ABD Design Steps Traditionally, high performance alloy materials have been designed empirically, whereby their chemical compositions have been identified using time-consuming and costly experimental development involving small-scale processing of limited quantities of material followed by operational characterization. The alloy composition adopted is the one found to exhibit the best or most desirable combination of properties.

[0055] In the field of CCA and RCCA, where the removal of key elements allows for a very large number of alloy combinations, modeling techniques provide new insights that can be applied to identify improved alloys.

[0056] Here we describe a modeling-based approach used to identify optimized CCAs, which we refer to as the "Alloys-By-Design" (ABD) method. This approach uses a computational materials model framework to estimate design-relevant properties over a very wide compositional range. In principle, this alloy design tool allows one to solve a so-called inverse problem: identifying the optimal alloy composition that best satisfies a specified set of design constraints.

[0057] The first step in the design process is to define the element list and associated upper and lower compositional limits. The compositional limits of each elemental addition (called the "alloy design space") contemplated in this invention are detailed in Table 2.

[0058] The starting point is that at least three different elements must be present (although at least four elements may be needed to ensure sufficient entropy), i.e. each element can be present up to 35 atomic %. Titanium can be increased up to 40 atomic % because it is important in reducing VEC. The only elements that reduce VEC are aluminum, zirconium and titanium. However, aluminum has a much lower melting point than the other two alloys, so too much aluminum can reduce high temperature strength. Zirconium is limited to reduce the chance of intermetallic phases forming. Thus, of these elements, titanium is the only one that can be used in very large quantities to reduce VEC. If a very high entropy alloy is required, the amount of titanium can be reduced to 35 atomic % or less.

[0059] Certain elements are limited to 35 atomic % or less based on an understanding of the effects they may have, particularly oxidation behavior. A significant amount of aluminum is used in the alloy to produce a continuous alumina scale. Based on the known properties of conventional alloys, the minimum aluminum content used is 20 atomic %. This provides oxidation resistance equivalent to the alloys described by Gorr et al. in High-Temperature Oxidation Behaviour of Refractory High-Entropy Alloys: Effect of Alloy Composition, Oxid. Met. (2017) 88: 339-349. Increasing the aluminum content beyond this level is desirable, in order to increase the supply of aluminum atoms for scale formation and minimize the length of the vulnerable transient period during which oxides form. To further increase oxidation resistance, it is preferable to increase the aluminum content to 21 atomic % or more, or even 22 atomic % or more. More preferably, the minimum aluminum content of the present invention is 23 atomic %, since this provides excellent oxidation resistance, exceeding the levels described by Cao et al. in Effects of Al and Mo on high temperature oxidation behaviour of refractory high entropy alloys, Trans. Nonferrous Met. Soc. China 29(2019) 1476-1483.

[0060] High levels of niobium have been observed to correlate with severe plague oxidation in the Al-Nb-Ti ternary system, which is representative of the broader RCCA design space. Severe plague oxidation has been reported to occur when the niobium content is 42 mass% or more (Chen et al., Oxidation of Intermetallic Alloys in Ti-Al-Nb Ternary System, Corrosion-Vo.48, No.11, 1992, National Association of Corrosion Engineers). This corresponds to 20 atomic% for these alloys. The present invention encompasses alloys with 20 atomic% niobium or less. Reducing the amount of niobium to 16 atomic% or less further reduces the likelihood of plague occurrence. It has been reported that the mass gain due to plague oxidation is significantly reduced at niobium as low as 30 mass% (corresponding to 13 atomic%). For this reason, niobium levels of 13 atomic% or less are preferred.

[0061] The present invention includes alloys that, in addition to inherent ductility, have a low volume fraction of deleterious intermetallic compounds. It is known that the presence of zirconium leads to the formation of intermetallic compounds with aluminum (Soni et al., Phase stable as a function of Temperature in a refractory high-entropy aluminum, J. Mater, Res., 2018; Tsai et al., Intermetallic Phases in High-Entropy Alloys: Statistical Analysis of their Prevalence and Structural Inheritance, Metals 2019, 9, 247). Based on this, the present invention sets an upper limit of 16.7 atomic percent zirconium content.

[0062] Hafnium is not a major element in the compositional region due to its difficulty in sourcing, but its ability to scavenge oxygen and lower the ductile-to-brittle transition temperature can provide useful properties for RCCA (Tsakiropoulos, 2022). Based on the Hf-Nb phase diagram, hafnium above 10.0 atomic % promotes the formation of a second hafnium-rich phase. Therefore, hafnium must be present at a level of 10.0 atomic % or less. C103, a high-temperature niobium alloy, has a composition of Nb-10Hf-1Ti (by mass %), which corresponds to 5.5 atomic % hafnium. Therefore, it is preferred that hafnium be present at a level of 5.5 atomic % or less. Preferably, hafnium is present at a level of 1.0 atomic % or less. In one embodiment, it is preferred that no hafnium is present (e.g., at the level of unavoidable impurities).

[0063] The main refractory elements in the present invention (Mo, Nb, Re, Ta, Ti, V, W and Zr) have low solubility in silicon (3, 5, 10, 5, 5, 7, 4 and 0 atomic %, respectively). Beyond the solubility limit, silicide phases such as M3Si can form. At low volume fractions, these silicide phases can significantly increase the yield strength. However, silicides fracture brittle, so at high volume fractions or a continuous network of phases through the microstructure has a significant negative effect on fracture toughness. To avoid excessive silicide formation, the Si concentration must be kept below 5.0 atomic %, which corresponds to the limit for Nb, Ta and Ti. Preferably, silicon is below 3.0 atomic %, more preferably below 1.0 atomic %, and most preferably 0 atomic % (e.g., the level of unavoidable impurities), which eliminates the possibility of the formation of very brittle silicides.

[0064] Table 2 shows the alloy design space, in atomic percent, searched using the "Alloys-by-Design" method. [Table 2]

[0065] The selection of alloys depends on the calculation of the alloy's indices of merit within the alloy composition domain. Examples of these indices of merit include entropy (related to the tendency of the elements in the alloy to form solid solution structures and thus related to strength and creep resistance), valence electron concentration (related to resistance to the formation of intermetallic phases and thus related to good ductility), Pilling-Bedworth index, melting point index, density and cost.

[0066] In the second stage, the calculated figures of merit over the entire region defined in Table 2 are compared to the required behavioral limits in configurational entropy and valence electron concentration, and these design constraints are considered as boundary conditions for the problem. All compositions that do not satisfy the boundary conditions are eliminated. In this stage, the size of the alloy region is reduced.

[0067] In the third stage, the remaining compositional data set was analyzed to provide sample compositions with favorable figures of merit compared to conventional alloys. Further restrictions on the range of alloys were made as a result of experimental observations.

[0068] Merit Index Explained Next, the sample merit figure will be described.

[0069] The first figure of merit is the entropy index. A sufficiently high entropy of mixing for a solid solution enhances the stability of the solid solution against the formation of intermetallic phases. This stability can often be extended to high temperatures, improving ease of processing. The entropy is given by:

number

[0070] The solid solution structure of RCCAs is stabilized by high entropy effects, which result in a greatly simplified microstructure compared to that expected from the constituent binary and ternary systems. The entropy of RCCAs is dominated by configurational entropy. There are many competing definitions for the threshold of configurational entropy at which an alloy can be considered a high entropy alloy and enjoy high entropy effects. The first definition is that the value of configurational entropy is equal to or greater than 1.5R(12.47), where R is the universal gas constant, which has a value of 8.3145 JK -1 Mol -1 (Murty et al., 2019) [4]. A further definition is based on an alloy composed of five or more major elements in equiatomic ratios, with a configurational entropy value of ln(5)R(13.38) or more [5]. Some HEA compositions studied are equiatomic and five-element, including but not limited to Gorr1, 2, 3, Miracle2, etc. in Table 1. These compositions have been reported to enjoy high entropy effects, and therefore their configurational entropy is a promising starting point for improvement [2], [3]. Therefore, in the present invention, a configurational entropy of 13.38 or more is required. More preferably, to further improve these properties, the present invention requires an entropy of 13.5 or more. This will further increase the stability of the solid solution, as well as increase lattice distortion and slow diffusion, which will enhance strength and creep resistance, respectively. As can be seen from Table 9 below, alloys with configurational entropy of 13.8 or more have been designed and are preferred.

[0071] The second figure of merit is the valence electron concentration index, which represents the number of outer electrons in an atom and is given by:

number

[0072] It has been reported that the valence electron concentration is a good predictor of the crystal structure in high-entropy alloys (Tsai et al., Criterion for sigma phase generation in Cr- and V-containing high-entropy alloys. Mater. Res. Lett. 2013,1, 207-212). Here, VEC<6.87 corresponds to a sigma-free alloy composed mainly of BCC phase. It has also been reported that further limiting the VEC may improve the intrinsic ductility of single-phase BCC high-entropy alloys [8]. No brittle behavior is observed at VEC<4.6, which is the design requirement of the present invention. The desired VEC is 4.4 or less, which ensures ductile behavior.

[0073] The third figure of merit is the Pilling-Bedworth index. It is a measure of the volume of oxide relative to the volume of the base alloy. The alloy of the present invention should have good oxidation resistance at temperatures above 1100°C. In this region, the passivated alumina oxide scale (Al2O3) is a good means of protecting the alloy from further oxidation damage. In the early stages of oxidation, several elements react simultaneously to form mixed oxides. At this stage, the mechanical stability of the oxide is determined by the relative volume of the oxide scale to the alloy substrate, as described by the Pilling-Bedworth ratio. A high Pilling-Bedworth ratio indicates that the volume of the oxide is much larger than the volume of the alloy, creating compressive stresses in the oxide and promoting spalling. Repeated spalling exposes the unprotected metal to the atmosphere and prevents the formation of a continuous protective alumina layer.

[0074] High values ​​of the PB index (>2) indicate that the oxide volume relative to the alloy is large, which may result in oxide spalling. Low values ​​(<1) indicate that the oxide is too thin and may not protect the base alloy. The Pilling-Bedworth index is given by the following formula:

number

[0075] The fourth figure of merit is the melting point index. A high melting point is required for high temperature applications, since melting of the alloy must be avoided. Also, a high melting point gives the highest high temperature strength and creep resistance. The melting point Tm is given by the following formula:

number

[0076] [Table 5]

[0077] The fifth figure of merit is density. Density ρ was calculated using a simple rule of mixture and a correction factor, where ρ i is the density of a given element, x i is the atomic fraction of the alloying element. Table 6 shows the densities of the relevant elements.

number

[0078] The sixth figure of merit is cost. To estimate the cost of each alloy, we multiply the atomic fraction of the alloying element by i , Current (2021) raw material costs of alloying elements c i A simple mixing rule was applied: multiply by (USD / mol).

number

[0079] This estimate assumes that processing costs are the same for all alloys, i.e., product yields are not affected by composition. Table 7 shows the costs of all relevant elements. [Table 7]

[0080] Based on initial modeling results, the inventors recognized that Table 2 contains alloys that have deleterious intermetallic volume fractions at levels that adversely affect ductility. Based on this, the ratio of zirconium content (atomic %) to aluminum was used to measure the formation of intermetallic phases. Thermodynamic calculations predict the formation of Al3Zr2, Al4Zr5, Al2Zr3, and Al3Zr5 in the alloy region shown in Table 2, which have Zr / Al ratios of approximately 0.7, 1.2, 1.5, and 1.7, respectively. A Zr / Al ratio of 0.7 or less avoids providing the optimum stoichiometric ratio of Zr and Al required for the formation of the predicted intermetallic phases. This is the seventh figure of merit. Further reduction in the Zr / Al ratio reduces the formation of Al. x Zr y The Zr / Al ratio is preferably equal to or less than 0.45, and even more preferably equal to or less than 0.3, since this further reduces the possibility of the formation of intermetallic compounds.

[0081] The ABD methodology described above was used to identify alloy compositions that met the entropy and VEC requirements described above and also exhibited other favorable properties as defined by the third through seventh figures of merit.

[0082] Of the elements in Table 2, cobalt, copper, iron, manganese, nickel, platinum, palladium, ruthenium, rhodium, and iridium have the highest VECs. Figure 1 is a series of plots showing alloys within the range of Table 2. The y-axis has the amount of a particular element and the x-axis has the VEC. Referring to Figure 1, to achieve a VEC of 4.6 or less, the concentrations of these elements in the alloy must be kept below the following values ​​to ensure ductility: A Co <5, A Cu <5, A Fe <10, A Mn <10, A Ni <5, A Pt <5, A Pd <5, A Ru <10, A Rh <5, A Ir <5

[0083] Here, A Co , A Cu , A Fe , A Mn , A Ni , A Pt , A Pd , A Ru , A Rh , A Irare the atomic percentages of cobalt, copper, iron, manganese, nickel, platinum, palladium, ruthenium, rhodium, and iridium, respectively, in the alloy. To reach even lower VEC levels, it is more preferable to further reduce the contents of these elements. Thus, copper is preferably maintained at a level of 3 atomic % or less, or 0 atomic %. Manganese is preferably maintained at a level of 7 atomic % or less, or even 5 atomic % or less, or even 0 atomic %. Cobalt is maintained at 3 atomic % or less in a preferred embodiment, and at 2 atomic % or less, or even 0 atomic % in a more preferred embodiment. Iron is preferably reduced to 7 atomic % or less, or even 5 atomic % or less, or even 0 atomic % in order to reduce the VEC. For the same reason, nickel is preferably kept low, for example, at 4 atomic % or less, or 3 atomic % or less, or even 1 atomic % or less, or 0 atomic %. Platinum is preferably maintained at 3 atomic % or less, or 0 atomic %. Palladium is preferably maintained at 3 atomic % or less, or 0 atomic %. Ruthenium is preferably maintained at 10 atomic % or less, or 8 atomic % or less, or 5 atomic % or less, or 3 atomic % or less. In one embodiment, ruthenium is preferably absent except in trace amounts. Rhodium is preferably maintained at 3 atomic % or less, or 0 atomic % or less. Iridium is preferably maintained at 3 atomic % or less, or 0 atomic % or less.

[0084] Modeling results indicate that a VEC≦4.6 is achievable throughout the ranges in Table 2 for Al, V, W, Cr, Ti, Ta, Mo, Zr, Nb, Hf, and Si and therefore were assumed to be acceptable.

[0085] The melting point of rhenium is higher than that of Ta and Nb, and also higher than that of W. This allows rhenium to give the alloy similar high temperature strength and therefore can be used in place of Ta, W, and Nb. Therefore, rhenium is permitted to contain no more than 35 atomic percent, with the atomic percentages of rhenium, tantalum, tungsten, and niobium being 35 atomic percent and 10 atomic percent, respectively. Re , A Ta , A W and A Nb Then, ARe ≦(35-A Ta )+(35-A W )+(20-A Nb ). Rhenium is very difficult to obtain, which results in high elemental costs. In addition, the density and elemental Pilling-Bedworth ratio are high, which increases the possibility of oxide peeling. For this reason, the rhenium content is preferably 20 atomic % or less, more preferably 15 atomic % or less, most preferably 10 atomic % or less, or even 5 atomic % or less. In order to achieve a particularly high melting point, it is preferable to sacrifice cost, density, and oxidation resistance as described above, and set the minimum rhenium content to 3 atomic %, or even 5 atomic % or more.

[0086] Tables 8 and 9 show the compositions of conventional alloys and some exemplary alloys, as well as the calculated figures of merit.

[0087] Table 8 lists the nominal compositions (atomic %) of the newly designed refractory composite enriched alloys compared to the alloys listed in Table 1. [Table 8]

[0088] Table 9 shows the figures of merit calculated by the "Alloys-by-Design" software for the conventional RCCA listed in Table 1 and the newly designed RCCA compared to the alloys listed in Table 1. [Table 9]

[0089] The RHG2 alloy was produced and its properties were investigated. Based on the experimental results, the following further limitations are imposed on the alloy of the present invention:

[0090] The addition of vanadium is beneficial in increasing configurational entropy without adversely affecting other indices of merit due to its moderate valence electron concentration (see above), low density, and high melting point. In corrosive environments, VO x, especially the formation of the V2O5 oxide phase, has a detrimental effect on the alloy. The oxide species can form low-melting eutectic phases and promote corrosion

[10] . Therefore, a low vanadium content is preferred. In RHG2M, the VO x It was observed that a continuous layer of dense VO was formed in the two alloys with low vanadium content (RHG1F and RHG1R) at the early stage of oxidation. x No evidence of a layer is seen, only mixed oxides appear, which do not adversely affect the corrosion resistance. RHG1F and RHG1R contain 0.2 and 5.1 atomic % vanadium, respectively, as measured using ICP-OES. These alloys are outside the scope of the main claim of the present invention, due to their high VEC, which, as mentioned above, is related to the ductility of the alloys. Nevertheless, their oxidation behavior is representative of the present invention, due to their high aluminum and refractory contents. Furthermore, alloys with high vanadium content (Table 10) have been observed to form V2O5 as well, as shown in Figure 3. Alloys L1, L2, and L3 were oxidized at 1300 °C for 20 h, and alloy E1 was oxidized at 900 °C [9],

[10] . All alloys that formed V2O5 contained 7 atomic % or more vanadium. VO x To avoid the formation of the layer, the present invention encompasses alloys having a vanadium content of 7 atomic % or less, preferably 5.1 atomic % or less, and more preferably 3.0 atomic % or less.

[0091] Table 10 lists the atomic % (V limits) of the nominal compositions of the alloys referenced in FIG. [Table 10]

[0092] To ensure the formation of a mechanically stable oxide, the Pilling-Bedworth ratio is preferably less than 2.000. The elements W, V, Ta, and Nb form oxides with high Pilling-Bedworth ratios, which promotes peeling more than the other elements in Table 2.

[0093] Calculations have been made to derive the data in Figures 4-6, 9 and 11 and the following relevant relationships for the amount of hafnium, silicon, platinum, palladium, ruthenium, iridium and rhodium added from possible alloys: Thus, in a preferred embodiment, the alloy has no hafnium, silicon, platinum, palladium, ruthenium, iridium or rhodium added, and the relationships described below apply across the range of such alloys.

[0094] Figure 4 is a plot of the alloy region of Table 2, showing the Pilling-Bedworth ratio in greyscale for varying concentrations of W and V (top) and Ta and Nb (bottom). The top and bottom lines in Figure 4 indicate the location of alloys with a P-B ratio of 2.000. For values ​​below 2.000, the following relationship should be observed: A V +1.15A W ≦28.9. As a result, in the absence of vanadium, A W ≦25.1 atomic %, and ≦19.0 if vanadium is limited to 7 atomic %. A Nb +0.83A Ta <= 42.5

[0095] It is preferable to reduce the P-B ratio to a low value, below 2.000, since the difference in volume between the oxide and the alloy is smaller, which leads to less compressive stress in the oxide and less possibility of spalling. Therefore, the P-B ratio is preferably below 1.98, or even below 1.95.

[0096] The addition of chromium helps improve corrosion resistance in certain applications, such as industrial gas turbines. In these cases, the invention contains, for example, at least 1 atomic %, 2 atomic %, or 3 atomic % chromium, with the alloy preferably having a chromium level of 5 atomic % or more, or 10 atomic % or more. Further increasing the chromium level increases the supply of chromium atoms to the surface, further improving corrosion resistance. Excess chromium can promote the formation of Laves and Cr-rich phases, so reducing the chromium level reduces the likelihood of formation. An upper limit of 25 atomic %, 20 atomic %, or even 15 atomic % is preferred. Most preferably, chromium is limited to 10 atomic % or less.

[0097] Although the addition of titanium is effective in lowering the valence electron concentration, adding too much titanium promotes rapid growth of an outer TiO2 layer, reduces the ability to form a protective alumina layer, and removes titanium from the matrix, destabilizing the microstructure. Therefore, the titanium content is preferably 33 atomic % or less, and more preferably 30 atomic % or less. Further reduction of titanium beyond these levels is even more beneficial as it reduces the supply of titanium atoms available to form TiO2 at the surface. Thus, titanium is present in one embodiment at 25 atomic % or less, and in another embodiment at 20 atomic % or less.

[0098] Although the addition of molybdenum is effective in increasing the melting point of the alloy, adding large amounts increases the possibility of the formation of volatile oxide species such as MoO3, which are detrimental to oxidation. Mass loss behavior due to volatilization of MoO3 has been recorded for alloys Ma1, Ma2, Ma3, Ma4 and Z1 with compositions defined in Table 11

[11] ,

[12] . Furthermore, oxide destruction due to MoO3 volatilization has been demonstrated for alloys Mu1, Mu2 and Mu3. All of these oxides reported to form MoO3 have a molybdenum content of 20 atomic % or more

[13] . Therefore, it is preferred that the molybdenum content is 20 atomic % or less, or even 15 atomic % or less. More preferably, molybdenum is present in an amount of 12 atomic % or less, or even 7 atomic % or less.

[0099] Table 11 shows the nominal composition (atomic %) of the Mo-containing alloys. [Table 11]

[0100] It is desirable to minimize density. This is done by controlling the addition of elements with large atomic mass, specifically tungsten and tantalum. The relationship between the levels of these two elements and the predicted alloy density is shown in Figures 5a-c. The maximum target alloy density (10 g / cm3) to be below FS85 is 3 (below) is achieved when: A W +0.8A Ta ≦37.8 atomic%

[0101] Here, A W and A Ta are the atomic percentages of tungsten and tantalum, respectively, in the alloy. More preferably, the alloy density is 9 g / cm 3 or less, i.e. C103 or less, which results in a lighter weight part that does not require as much creep strength when used in rotating applications. This is achieved when: A W +0.72A Ta ≦26.8 atomic%

[0102] This includes A W The most preferred maximum alloy density is 8 g / cm 3 In the following, CMSX-4 and below correspond to the following formula: A W +0.6A Ta ≦20 atomic% This includes A Ta and A W However, they need to be below 33.3 and 20 respectively.

[0103] Of the elements within the design space of this invention, aluminum, zirconium, and titanium, with the exception of hafnium and silicon, are the only components with elemental VECs lower than the alloy's target (4.6). As shown in Figure 6, minimum amounts of these elements are required to meet the VEC target (below 4.6), entropy target, Pilling-Bedworth target, and density target. With the design space thus restricted, the requirements for these low VEC elements are as follows: A Al +A Zr +A Ti ≧41 atomic% When Al<35%, it is preferable that Zr+Ti≧6 atomic %.

[0104] It is preferred to increase the levels of aluminum, zirconium and titanium to even higher levels than those mentioned above to lower the VEC even further and increase ductility even further. For example, to achieve a VEC of 4.05 or less, the following conditions are required: A Al +A Zr +A Ti ≧60 atomic%

[0105] Figure 7 shows three regions of zirconium content. The plotted points are labeled T1, T2, T3…, which correspond to the alloys in Table 11 as defined in the Metals2019 article

[14] . Additional plotted points are labeled 2D, 2E, which correspond to alloys RHG2D and RHG2E, respectively, as defined in Table 8. As shown in Figure 8, both RHG2D and RHG2E were found to be free of Al-Zr based intermetallic compounds. All alloys reported to form Zr-Al intermetallic compounds contain 16.7 atomic % or more zirconium. The present invention encompasses alloys with zirconium content of 16.7 atomic % or less to avoid the formation of Zr-Al intermetallic compounds. T7, RHG2D, and RHG2E all contain both Al and Zr, but no Zr-Al intermetallic compounds were observed. Therefore, it is preferred that alloys encompassed by the present invention contain 11.1 atomic % or less zirconium, or even 10 atomic % or less zirconium. Preferably, zirconium is present at 9 atomic % or less, such as in Examples 2E and 2D where no Al-Zr intermetallic compounds are present. [Table 12]

[0106] The alloys of the present invention are designed to have good mechanical strength and creep resistance at high temperatures as well as good ductility. Since strength is a function of both entropy (as discussed above) and melting point, the latter must be maximized. Furthermore, creep rates are most severe above a homologous temperature of 0.6.

number

[0107] where T is the ambient temperature, T m is the melting point. To lower the homologous temperature and reduce the creep rate, T mcan be maximized. This can be achieved by maximizing the melting point index (discussed above). As can be seen from Table 9, the invention encompasses alloys with melting point indices above 1800K, even above 2000K, even above 2100K and even above 2200K, which are the preferred limits. Alloys with melting point indices of 2400K and above, and even above 2450K (or 2500K) are also possible and are preferred in one embodiment. These correspond to the minimum amount of refractory elements in the alloy, which is defined in terms of W equivalents with reference to FIG. 9, where A W , A Ta , A Mo and A Nb are the atomic percentage concentrations of tungsten, tantalum, molybdenum, and niobium in the alloy. W eq = A W +A Ta +A Mo +A Nb

[0108] For melting point indexes exceeding 1800K, 2000K, 2200K, 2400K, and 2500K, W eq should be greater than approximately 10, 13, 26, 39, and 50, respectively, and should comply with the following formula (derived from Figure 9). More precisely, the melting point index is greater than the following values: 1800K, W eq ≧ 10 2000K, W eq ≧0.75A Al -4.75 2200K, W eq ≧0.75A Al +8.75 2400K, W eq ≧0.8A Al +23 2500K, W eq ≧1.25A Al +21.25

[0109] As shown in Figure 10, there is also a trade-off between melting point and density. As the lower melting point limit increases, so does the minimum density achievable. Similarly, as the upper density limit decreases, so does the maximum melting point achievable. Balancing these properties is part of the invention, because higher densities cause higher stresses during rotation, but lowering density reduces the melting point, lowers strength and creep strength, and reduces the alloy's ability to withstand loads.

[0110] The present invention is desirably cost-competitive with existing refractory and nickel-base superalloys. The maximum elemental alloy cost is desirably 8.00 USD / mol or less, which corresponds to a lower elemental cost than FS85, C103 and CMSX-4, preferably 6.50 USD / mol or less, and more preferably 5.00 USD / mol or less. Vanadium and Tantalum have the highest elemental costs. The relationship between the levels of these two elements and the alloy cost is shown in Figure 11, which leads to the model described below. f(cost) = A V +3A Ta Here, A V and A Ta are the atomic percentages of vanadium and tantalum in the alloy, respectively. f(cost) is a number that must be less than 75 to keep the cost index below 14.00, and A Ta must be 25 or less. Preferably, f(cost) is 64 or less to keep the cost index at 12.00 or less, and A Ta f(cost) should be 21.3 or less. More preferably, f(cost) should be 53 or less to keep the cost index at 10.00 or less. Ta It is necessary that f(cost) is 17.7 or less. More preferably, in order to make the cost index 8.00 or less, f(cost) is 42 or less, and A Ta It is necessary that f(cost) is 14 or less. More preferably, in order to make the cost index 6.50 or less, f(cost) is 34 or less, and A Tashould be 11.3 or less. Most preferably, f(cost) should be 26 or less to keep the cost index at 5.00 or less. Ta must be less than or equal to 8.7.

[0111] As mentioned above, the addition of aluminum is beneficial for oxidation resistance, but too much aluminum lowers the alloy's melting point and reduces its strength at high temperatures, so the upper limit is 33 atomic percent, and preferably 31 atomic percent.

[0112] Although increased zirconium content can lead to the formation of zirconium-based intermetallic compounds, the addition of zirconium also has the benefit of lowering the valence electron concentration and increasing ductility. Other benefits include a reduction in the Pilling-Bedworth ratio and a reduction in density. For these reasons, it is preferred to increase the zirconium content to 2 at.% or even 4 at.% or more. Further improvements are obtained at higher levels, so that levels of 6 at.% or more, and even 8 or 10 at.% or more, are most preferred when high ductility and low density are required.

[0113] As mentioned above, high vanadium contents can adversely affect corrosion resistance. However, at low levels, its unique combination of high melting point and low density improves high temperature strength capabilities and reduces rolling loads, respectively. For these reasons, increased vanadium content is preferred. Thus, vanadium levels of 2 at.% or greater, and preferably 5.0 at.% or greater, are preferred.

[0114] Tungsten has a high density and a high Pilling-Bedworth ratio, so it is reasonable to reduce its content. On the other hand, tungsten has the highest melting point of the elements of the present invention, so increasing its content may improve temperature and strength capabilities. Therefore, the preferred lower limit of the amount of tungsten is 2 atomic %, or even 5 atomic %, or even 8 atomic %. If the tungsten content is 11 atomic % or more, it is preferable when the high temperature strength is excellent and this characteristic is required.

[0115] Iron has a moderate effect on properties such as the Pilling-Bedworth ratio and melting point, but does not significantly improve or decrease performance. Increasing iron reduces density, and adding more elements in small increments can increase the entropy of the alloy and stabilize the microstructure. This also improves printability by laser powder bed fusion additive manufacturing, especially when combined with chromium. For these reasons, increasing the iron level to above 0.5 atomic %, or even above 2 atomic % or even 4 atomic % is preferred.

[0116] Increasing the nickel content reduces the Pilling-Bedworth ratio, reduces spalling of the oxide scale, and improves the protection the alloy can offer under high temperature oxidation. When these properties are desired, nickel contents above 1 atomic % and even above 2 atomic % are desirable.

[0117] Titanium has a low Pilling-Bedworth ratio, so adding titanium to the alloy is beneficial in preventing oxide spalling during the early stages of oxidation. The addition of titanium also has a significant effect on reducing density. For these reasons, it is preferred to increase the titanium level to 5 atomic % or more. Higher amounts of titanium may be beneficial in certain applications. In some embodiments, the alloy contains 8 atomic % or more titanium, or even 13 atomic % or more or 20 atomic % or more titanium.

[0118] Tantalum is expensive because the metal is difficult to source from conflict-free regions. This, plus its high density and the promotion of oxide exfoliation due to its high Pilling-Bedworth ratio, means that reduced levels of tantalum are preferred in the present invention. Tantalum's high melting point significantly improves high temperature strength. Higher levels, for example 2 atomic % or more, preferably 5 atomic % or more, or even 10 atomic % or more, are therefore preferred. Where high strength is required, levels of 15 atomic % or more, or even 20 atomic % or more, are preferred.

[0119] The addition of niobium increases the melting point and improves high temperature strength. This effect is not as strong as other elements such as tungsten, but it is an advantage for some alloy processing methods such as arc melting, where elements with very high melting points are difficult to incorporate into the alloy melt. Thus, in some embodiments, niobium is present in an amount of 5 atomic % or more, or 8 atomic % or more, and most preferably 10 atomic % or more.

[0120] The addition of molybdenum helps increase the melting point and enhance the high temperature strength of the alloy, provided the molybdenum concentration is kept low enough to avoid the formation of volatile MoO3. Unlike elements that have a similar effect on the melting point, it does not significantly increase the Pilling-Bedworth ratio, so delamination is not as much of a concern. For these reasons, it can be beneficial to increase the molybdenum level, for example, to 2 atomic % or more. In some embodiments, molybdenum is present in amounts of 4 atomic % or more, or even 6 atomic % or more.

[0121] The addition of cobalt reduces the Pilling-Bedworth ratio to a critical level of 2, preferably below 2, reducing the likelihood of oxide spalling. Cobalt has a moderate effect on density, cost and melting point. Small additions increase entropy and stabilize the microstructure. For these reasons, it may be beneficial to increase the cobalt content, for example to 0.5 atomic % or more. In some embodiments, to take advantage of these effects, cobalt is present in an amount of 1 atomic % or more. More preferably, cobalt is present in an amount of 2 atomic % or more, or even 3 atomic % or more. Most preferably, cobalt is present in an amount of 4 atomic % or more.

[0122] Copper has the effect of lowering the Pilling-Bedworth ratio, promoting the formation of oxides that are less likely to peel. It is preferable to increase the copper level to 0.5 atomic % or higher, and even to 1 atomic % or higher or 2 atomic % or higher.

[0123] The addition of manganese can adversely affect oxidation behavior due to its tendency to form rapidly growing Mn-based oxides. Lowering the manganese concentration reduces the supply of manganese atoms and thus avoids this problem. Reducing the manganese density is effective in reducing self-loading, so increasing the level to 0.5 atomic % or higher is beneficial. In some embodiments, manganese is present at higher levels, for example 2 atomic % or higher, or 5 atomic % or higher. [Table 13]

[0124] [1] Y. Cao, Y. Liu, B. Liu, W. Zhang, J. Wang, and M. Du, “Effects of Al and Mo on high temperature oxidation behavior of refractory high entropy alloys,” Trans. Nonferrous Met. Soc. China, vol. 29, no. 7, pp. 1476-1483, 2019, doi: 10.1016 / S1003-6326(19)65054-5. [2] B. Gorr et al., “High-Temperature Oxidation Behavior of Refractory High-Entropy Alloys: Effect of Alloy Composition,” Oxid. Met., vol. 88, no. 3-4, pp. 339-349, 2017, doi: 10.1007 / s11085-016-9696-y. [3] DB Miracle, ON Senkov, JM Scott, GB Wilks, and F. Approved, “Mechanical properties of Nb 25 Mo 25 Ta 25 W 25 AND V 20 Nb 20 Mo 20 Ta 20 W 20 refractory high-entropy alloys,” 2011. [4] B. S. Murty, J. W. Yeh, S. Ranganathan, and P. P. Bhattacharjee, “Chapter 2: High-entropy alloys: basic concepts,” High-Entropy Alloy., pp. 13-30, 2019, doi: 10.1016 / b978-0-12-816067-1.00002-3. [5] J. W. Yeh, “Alloy design strategies and future trends in high-entropy alloys,” Jom, vol. 65, no. 12, pp. 1759-1771, 2013, doi: 10.1007 / s11837-013-0761-6. [6] D. B. Miracle and O. N. Senkov, “A critical review of high entropy alloys and related concepts,” Acta Mater., vol. 122, pp. 448-511, 2017, doi: 10.1016 / j.actamat.2016.08.081. [7] M. H. Tsai, K. Y. Tsai, C. W. Tsai, C. Lee, C. C. Juan, and J. W. Yeh, “Criterion for sigma phase formation in Cr- and V-Containing high-entropy alloys,” Mater. Res. Lett., vol. 1, no. 4, pp. 207-212, 2013, doi: 10.1080 / 21663831.2013.831382. [8] S. Sheikh et al., “Alloy design for intrinsically ductile refractory high-entropy alloys,” J. Appl. Phys., vol. 120, no. 16, pp. 1-5, 2016, doi: 10.1063 / 1.4966659. [9] C. M. Liu, H. M. Wang, S. Q. Zhang, H. B. Tang, and A. L. Zhang, “Microstructure and oxidation behavior of new refractory high entropy alloys,” J. Alloys Compd., vol. 583, pp. 162-169, 2014, doi: 10.1016 / j.jallcom.2013.08.102.

[10] M. Esmaily, Y. Qiu, S. Bigdeli, M. B. Venkataraman, A. Allanore, and N. Birbilis, “High-temperature oxidation behaviour of AlxFeCrCoNi and AlTiVCr compositionally complex alloys,” npj Mater. Degrad., vol. 4, no. 1, pp. 1-10, 2020, doi: 10.1038 / s41529-020-00129-2.

[11] T. Maruyama, B. X. Fang, and K. Nagata, “Aluminized molybdenum by pack cementation and its resistance to high-temperature oxidation.” 1991.

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Claims

1. In atomic percent, Aluminum: 20% or more and 35% or less, Zirconium: 16.7% or less, Vanadium: 7% or less, Tungsten: 35% or less, Chromium: 35% or less, Iron: 10% or less, Nickel: 5% or less, Titanium: 40% or less, Tantalum: 35% or less, Niobium: 20% or less, Molybdenum: 35% or less, Cobalt: 5% or less, Manganese: 10% or less, Copper: 5% or less, Hafnium: 10% or less, Silicon: 5% or less, Platinum: 5% or less, Palladium: 5% or less, Ruthenium: 10% or less, Rhodium: 5% or less, Iridium: 5% or less, Rhenium: 35% or less Including, The atomic percentages of rhenium, tantalum, tungsten, and niobium are A Re , A Ta , A W and A Nb When A Re ≦(35-A Ta )+(35-A W )+(20-A Nb ) is satisfied, The total amount of unavoidable impurities is 1 atomic % or less, [Equation 1] where x i is the atomic fraction of element i in the alloy, and VEC i is the number of valence electrons associated with an atom of element i, and R is the universal gas constant of the alloy.

2. Satisfy the following formula: [Equation 2] where A Al and A Zr 10. The alloy of claim 1, wherein .gtoreq..times ...

3. Satisfy the following formula: [Equation 3] where x i is the atomic fraction of element i in the alloy, and R PB i 3. The alloy of claim 1 or 2, wherein i is the Pilling-Bedworth ratio of pure element i.

4. Satisfy the following formula: [Equation 4] where x i is the atomic fraction of element i in the alloy, and ρ i 10. The alloy of claim 1, wherein i is the density of pure element i.

5. Satisfy the following formula: [Equation 5] where x i is the atomic fraction of element i in the alloy bulk composition, and T mi 10. The alloy of claim 1, wherein i is the melting point of pure element i.

6. Satisfy the following formula: [Equation 6] where x i 10. The alloy of claim 1, wherein x is the atomic fraction of element i in the alloy bulk composition.

7. Satisfy the following formula: [Equation 7] where x x 10. The alloy of claim 1, wherein x is the atomic fraction of element x in the alloy.

8. Satisfy the following formula: 75≧A V +3A Ta Here, A V and A Ta 10. The alloy of claim 1, wherein .gtoreq..times ...

9. 10. The alloy of claim 1 comprising at least 21 atomic percent and at most 35 atomic percent aluminum.

10. 10. The alloy of claim 1 comprising up to 33 atomic percent aluminum.

11. 10. The alloy of claim 1 comprising up to 11.1 atomic percent zirconium.

12. 10. The alloy of claim 1 comprising at least 2 atomic percent zirconium.

13. 10. The alloy of claim 1 comprising up to 5.1 atomic percent vanadium.

14. 10. The alloy of claim 1 comprising at least 2 atomic percent vanadium.

15. 10. The alloy of claim 1 comprising up to 26.8 atomic percent tungsten.

16. 10. The alloy of claim 1 comprising at least 2 atomic percent tungsten.

17. 10. The alloy of claim 1 containing up to 25 atomic percent chromium.

18. 10. The alloy of claim 1 containing up to 7 atomic percent iron.

19. 10. The alloy of claim 1 comprising at least 0.5 atomic percent iron.

20. 10. The alloy of claim 1 comprising up to 4 atomic percent nickel.

21. 10. The alloy of claim 1 comprising at least 0.5 atomic percent nickel.

22. 10. The alloy of claim 1 comprising up to 35 atomic percent titanium.

23. 10. The alloy of claim 1 comprising at least 5 atomic percent titanium.

24. 10. The alloy of claim 1 comprising up to 33.3 atomic percent tantalum.

25. 10. The alloy of claim 1 comprising at least 2 atomic percent tantalum.

26. 10. The alloy of claim 1 comprising up to 16 atomic percent niobium.

27. 10. The alloy of claim 1 comprising at least 5 atomic percent niobium.

28. 10. The alloy of claim 1 comprising up to 20 atomic percent molybdenum.

29. 10. The alloy of claim 1 comprising at least 2 atomic percent molybdenum.

30. 10. The alloy of claim 1 comprising up to 3 atomic percent cobalt.

31. 10. The alloy of claim 1 comprising at least 0.5 atomic percent cobalt.

32. 10. The alloy of claim 1 comprising up to 4 atomic percent copper.

33. 10. The alloy of claim 1 comprising at least 0.5 atomic percent copper.

34. 10. The alloy of claim 1 containing up to 7 atomic percent manganese.

35. 10. The alloy of claim 1 comprising at least 0.5 atomic percent manganese.

36. 10. The alloy of claim 1 comprising up to 20 atomic percent rhenium.

37. 10. The alloy of claim 1 comprising at least 3 atomic percent rhenium.

38. 2. The alloy of claim 1, wherein the alloy satisfies the following formula: [Equation 8]

39. Satisfy the following formula: A W +0.8A Ta ≦37.8 where A Ta and A W 10. The alloy of claim 1, wherein .gtoreq..times ...

40. Satisfy the following formula: A Al +A Zr +A Ti ≧41 where A Al , A Zr and A Ti 10. The alloy of claim 1, wherein x, y, zirconium, and titanium are the atomic percentages of aluminum, zirconium, and titanium, respectively, in the alloy.

41. Satisfy the following formula: A Zr +A Ti ≧6 where A Zr and A Ti 10. The alloy of claim 1, wherein .mu.A and .mu.B are the atomic percent amounts of zirconium and titanium, respectively.

42. Satisfy the following formula: A V +1.15A W ≦28.9 where A V and A W 10. The alloy of claim 1, wherein .mu.m is the atomic percent amount of vanadium and tungsten, respectively.

43. Satisfy the following formula: <h2 style=";text-align:left;direction:ltr">A<h2 style=";text-align:left;direction:ltr"> Nb <h2 style=";text-align:left;direction:ltr"> +0.83A<h2 style=";text-align:left;direction:ltr"> Ta <h2 style=";text-align:left;direction:ltr"> ≦42.5 where A Nb and A Ta 10. The alloy of claim 1, wherein Λ is the atomic percent amount of niobium and tantalum, respectively.

44. 10. The alloy of claim 1 comprising at least 1 atomic percent chromium.

45. Satisfy the following formula, 10≦A W +A Ta +A Mo +A Nb where A W , A Ta , A Mo and A Nb 2. The alloy of claim 1, wherein tungsten, tantalum, molybdenum, and niobium are present in atomic percent amounts, respectively.

46. Satisfy the following formula, A W +A Ta +A Mo +A Nb ≧10 where A Al , A W , A Ta , A Mo and A Nb 10. The alloy of claim 1, wherein t, tantalum, molybdenum, and niobium are the atomic percent amounts of aluminum, tungsten, tantalum, molybdenum, and niobium, respectively.

47. 10. The alloy of claim 1 comprising up to 5.5 atomic percent hafnium.

48. 10. The alloy of claim 1 comprising up to 3.0 atomic percent silicon.

49. 10. The alloy of claim 1 comprising up to 5 atomic percent platinum.

50. 10. The alloy of claim 1 comprising up to 5 atomic percent palladium.

51. 10. The alloy of claim 1 comprising up to 8 atomic percent ruthenium.

52. 10. The alloy of claim 1 comprising up to 3 atomic percent rhodium.

53. 10. The alloy of claim 1 comprising up to 3 atomic percent iridium.

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