Malleable gamma apos with high mechanical strength; phase-strengthened superalloy

Abstract

An age hardenable nickel-chromium-cobalt-based alloy composition suitable for forging of high temperature gas turbines, the composition having higher mechanical strength, toughness / inclusivity and thermal stability compared to current commercial alloys, and having acceptable inclusive factors, the composition comprises, in weight percent, 16 to 20 wt% chromium, 8 to 13 wt% cobalt, 4 to 8.5 wt% molybdenum, up to 8 wt% tungsten, 2.1 to 4.1 wt% aluminum, up to 1.9 wt% titanium, up to 3.7 wt% niobium, up to 5 wt% iron, up to 0.15 wt% carbon, up to 0.015 wt% boron, up to 7.1 wt% tantalum, up to 0.13 wt% silicon, up to 1.0 wt% manganese, and up to 0.06 wt% zirconium, and the balance of nickel and impurities. According to the three composition relations disclosed herein, the amount of certain alloying elements must be carefully controlled.

Description

Technical Field

[0001] This invention relates to malleable high-strength alloys for use at elevated temperatures. In particular, it relates to alloys with sufficient mechanical strength, toughness / containment, and thermal stability for use in gas turbine cases and other gas turbine components. Background Technology

[0002] To meet the demands for increased operating efficiency, gas turbine engine designers seek ever-increasing operating temperatures. However, the ability to raise operating temperatures is often limited by material properties. One application with this limitation is the gas turbine casing. The turbine casing surrounds and protects the turbine section of the engine. They are typically manufactured as forgings, thus requiring good forgeability. Gamma-reinforced alloys are often used in turbine casings due to their mechanical strength at elevated temperatures. In particular, they require high low-cycle fatigue (LCF) strength and high creep strength. High LCF strength is considered a good indicator of an alloy's resistance to thermal fatigue, caused by the cycling of engine temperatures throughout the engine's lifespan. However, currently commercially available forgeable γ-reinforced alloys do not possess sufficient LCF strength above approximately 1400°F. High creep strength is a measure of an alloy's ability to withstand loads for a sustained period at moderate to high temperatures.

[0003] Forged γ'-strengthened alloys are typically based on a nickel-chromium-cobalt system, although other base systems are also used. These alloys usually contain one or more of the elements aluminum, titanium, niobium, and tantalum, which are responsible for forming the γ' phase Ni3(X), where X = Ti, Al, Nb, Ta, etc. Age-hardening heat treatment is used to develop the γ' phase into the alloy's microstructure. This heat treatment is usually performed while the alloy is in the annealed state. The presence of the γ' phase results in considerable strengthening of the alloy over a wide temperature range. Other elemental additions may include molybdenum or tungsten for solid solution strengthening, carbon for carbide formation, and boron for improving high-temperature ductility. A certain amount of iron is permissible in these alloys and is usually present due to the manufacturing process.

[0004] Many gas turbine engine components, including the engine casing, require high mechanical strength at elevated temperatures. Depending on the component's operating temperature and the nature of the load, several types of strength may be required. At elevated temperatures, these include low-cycle fatigue strength, creep strength, and tensile strength. Another critical characteristic of the engine casing and certain other components is the material's toughness. Toughness is a measure of an alloy's ability to absorb energy before failure. Both strength and ductility contribute to alloy toughness. Alloys with high toughness are also considered to have high containment properties, as discussed further later in this specification.

[0005] Thermal stability is a measure of whether the microstructure of an alloy remains relatively unaffected during heat exposure. Many high-temperature alloys can form brittle intermetallic phases or carbide phases during heat exposure. The presence of these phases can significantly reduce the room-temperature ductility of the material. This loss of ductility can be effectively measured using standard room-temperature tensile tests.

[0006] In addition to the material properties required for gas turbine engine alloys during service, the alloys must also possess the necessary properties for manufacturing complex components. These may include qualities such as hot forgeability, cold formability, and weldability. For γ'-strengthened alloys, weldability typically limits their use or necessitates high manufacturing costs. The weldability of γ'-strengthened alloys is largely related to their resistance to strain-aging cracking, as described later in this specification.

[0007] Many malleable γ'-strengthened alloys are available on the market today. The Rene-41 or R-41 alloy (US Patent 2,945,758) was developed by General Electric in the 1950s for turbine engines. It exhibits excellent creep strength but is limited by poor thermal stability and resistance to strain aging cracking. A similar General Electric alloy, M-252 (US Patent 2,747,993), was also developed in 1950. M-252 has good creep strength and resistance to strain aging cracking, but like the R-41 alloy, it is limited by poor thermal stability. Pratt & Whitney developed an alloy commercially known as WASPALOY (apparently not covered by a US patent), another γ'-strengthened alloy designed for use in turbine engines, and it is available in sheet form. However, this alloy has insufficient LCF strength at 1500°F (816°C), a critical creep strength, and only moderate resistance to strain aging cracking. Commercially known as Alloy 263 (US Patent 3,222,165), this alloy was developed in the late 1950s and introduced by Rolls-Royce Limited in 1960. This alloy exhibits excellent thermal stability and resistance to strain-aging cracking, but displays very poor LCF and creep strength at 1500°F (816°C). HAYNES was introduced in 2005. ® 282 ® The alloy (US Patent 8,066,938B2) possesses a combination of resistance to strain-aging cracking, good thermal stability, and good creep strength. However, the LCF strength at 1500°F (816°C) is insufficient for some advanced engine casing applications. HAYNES was introduced in 2016. ® 233 ®Alloy (US Patent 10,577,680B2). This alloy possesses a combination of excellent oxidation resistance, good creep strength, good thermal stability, and good machinability. However, similar to Waspaloy and Alloy 282, the LCF strength of Alloy 233 at 1500°F (816°C) is insufficient for advanced engine casing applications.

[0008] As these embodiments demonstrate, established commercial alloys typically considered for engine room casing applications are in the 1500 range. It does not possess sufficiently high mechanical strength (LCF and / or creep) at 816℃, as well as high containment and good thermal stability to meet the growing demands of next-generation gas turbine engines.

[0009] British Patent Publication GB 1029609 discloses an alloy suitable for manufacturing gas turbine engines. However, the compositional scope claimed by the British patent includes compositions that are not expected to have at least one of the three key properties of the aforementioned turbine casing based on the teachings of this invention. The aluminum range of the compositions disclosed in that patent publication does not overlap with the aluminum range of the compositions of this invention. Furthermore, the disclosure does not teach how to control the composition to obtain these desired properties. Finally, no example alloys of this disclosure fall within the preferred scope of this invention.

[0010] British Patent Publication GB 2712498 discloses alloys from which engineered components capable of withstanding high stresses at high temperatures are manufactured, including blades and other components within internal combustion gas turbines. However, the compositional scope claimed by the British Patent includes compositions that do not possess at least one of the three key properties of the aforementioned turbine casing, which are based on the teachings of this invention. For example, commercial alloys Waspaly and Haynes 282, as well as experimental alloys 3 and 7, fall within the compositions disclosed in that patent publication and do not possess all the key properties. Furthermore, the disclosure does not teach how to control the composition to obtain these desired properties. Finally, no example alloys from that disclosure fall within the preferred scope of this invention.

[0011] Japanese patent application JP 01129942 discloses a nickel-based alloy that is said to have excellent hot workability. This disclosure teaches that zirconium-modified alloys should be present in an amount of 0.02% to 0.1% by weight. However, such a zirconium content can cause hot cracking problems during alloy welding. The patent application also teaches that tungsten is necessary for high-temperature toughness, and I have found that very little tungsten can be used, but depending on certain relationships, tungsten can be present as a partial substitute for molybdenum. Furthermore, the compositional range claimed in JP 01129942 includes alloys that, based on the relationships taught in this invention, are not expected to possess one or more of the key properties for gas turbine casings. Finally, no example alloys from this disclosure fall within the preferred scope of this invention.

[0012] Japanese patent application JP 06172900 discloses a nickel-chromium-cobalt-molybdenum alloy containing 8-12 wt% molybdenum. However, this patent (granted in 1990) appears to claim protection for the compositions of earlier patented alloys such as alloys R-41 and M-252 (previously described in this disclosure). This document fails to recognize that a molybdenum content exceeding 8.5 wt% can be detrimental, leading to lower thermal stability, lower LCF strength, and / or lower containment in this type of alloy. The composition range claimed by this Japanese document includes compositions not expected to possess all of the aforementioned critical properties. The HAYNES 282 alloy and experimental alloys 2, 4, and 5 in Table 1 below contain small amounts of iron (the content of which is considered typical of iron impurities in commercially produced alloys of this type) and do not possess all the critical properties. Removing this iron would produce alloys within the composition range disclosed in JP 06172900. However, I would not expect removing iron to significantly alter the critical properties of these alloys. Furthermore, this disclosure does not teach how to control the composition to obtain these desired properties. Finally, no example alloys from this disclosure fall within the preferred scope of the present invention.

[0013] Therefore, an alloy is needed that possesses excellent mechanical strength, high compressibility, and performance at 1500 °C. The alloy exhibits good thermal stability at moderate temperatures (816℃). Furthermore, for certain applications, good weldability, particularly good resistance to strain-aging cracking, would be advantageous. Summary of the Invention

[0014] The main objective of this invention is to provide a new forgeable, age-hardening nickel-chromium-cobalt-based alloy suitable for high-temperature gas turbine casings and other gas turbine components, which exhibits high low-cycle fatigue strength, good thermal stability, and an acceptable containment factor.

[0015] It has been found that this objective can be achieved by an alloy containing a range of chromium and cobalt, a range of solid solution strengtheners (molybdenum and tungsten), and a range of γ' forming agents (aluminum, titanium, niobium, and tantalum), with the balance being nickel and various minor elements and impurities.

[0016] Specifically, the necessary range is 16 to 20 wt% chromium, 8 to 13 wt% cobalt, 4 to 8.5 wt% molybdenum, up to 8 wt% tungsten, 2.1 to 4.1 wt% aluminum, up to 1.9 wt% titanium, up to 3.7 wt% niobium, up to 5 wt% iron, up to 0.15 wt% carbon, up to 0.015 wt% boron, up to 7.1 wt% tantalum, up to 0.13 wt% silicon, up to 1.0 wt% manganese, and up to 0.06 wt% zirconium, with the balance being nickel and impurities. Furthermore, certain compositional relationships are necessary, imposing limitations on the total and relative amounts of γ'-forming agents and solid solution strengthening agents. As a result, some experimental alloys exist that satisfy all individual elemental requirements but are not considered part of this invention because they do not satisfy one of the stated compositional relationships. Such alloys do not meet one or more key performance objectives. Attached Figure Description

[0017] Figure 1 Under a total strain range of 0.6%, and in a fully inverse strain-controlled test, several forged age-hardening nickel-chromium-cobalt based alloys were tested at 1500 °C. 0 A graph showing the low-cycle fatigue life at F (816℃).

[0018] Figure 2 Several forged, age-hardening nickel-chromium-cobalt-based alloys at 1400 0 A graph of the containment factor at F (760℃).

[0019] Figure 3 It is at 1400 0 A graph showing the thermal stability of several forged, age-hardenable nickel-chromium-cobalt-based alloys, expressed as ductility, in a standard room temperature tensile test after 1000 hours of heat exposure at F (760°C).

[0020] Figure 4 This is a graph showing the creep strength of several forged, age-hardening nickel-chromium-cobalt-based alloys measured by 1% creep life in a creep test at 1500°F (816°C) under an applied stress of 30 ksi (207 MPa).

[0021] Figure 5 This is a graph of the weldability of several forged age-hardenable nickel-chromium-cobalt-based alloys measured by CHRT ductility in a controlled heating rate tensile test at 1450°F (788°C).

[0022] Figure 6 This is a graphical illustration of the R, G, and T factors, and the constraints on these factors described by the compositional relationship I I discovered. The figure also shows many experimental, commercial, and predictive alloy compositions described herein. Detailed Implementation

[0023] I offer Ni-Cr-Co-(Mo,W)-(Al,Ti,Nb,Ta)-based alloys containing 16-20 wt% chromium, 8-13 wt% cobalt, 4-8.5 wt% molybdenum, up to 8 wt% tungsten, 2.1-4.1 wt% aluminum, up to 1.9 wt% titanium, up to 3.7 wt% niobium, up to 7.1 wt% tantalum, certain minor elemental additives, and typical impurities and balance nickel. These alloys satisfy certain compositional relationships defined and disclosed herein and possess properties suitable for use in various gas turbine engine components such as engine casings. Based on an understanding of the requirements for engine casings in future gas turbine engines, alloys with the following properties are highly desirable: 1) high containment at moderate operating temperatures such as 1200-1500°F (649-816°C), 2) good thermal stability at moderate operating temperatures, and 3) excellent mechanical strength at moderate operating temperatures. In many applications, moderate or better weldability is also desired. Currently, there are no commercially available alloys possessing all these qualities. One of the more commonly used alloys for engine casings is Waspaloy. Waspaloy alloys have high containment and good thermal stability; however, their mechanical strength (LCF and creep) at 1500°F (816°C) is rather low, limiting the upper limit of the alloy's operating temperature. As will be shown, the alloy of the present invention provides significantly improved mechanical strength at 1500°F (816°C) compared to Waspaloy.

[0024] I tested forty-one experimental alloys whose compositions are listed in Table 1. These experimental alloys are all nickel-based alloys, with chromium content ranging from 16.80 to 19.65 wt%, cobalt content ranging from 9.28 to 10.81 wt%, molybdenum content ranging from 3.73 to 8.59 wt%, aluminum content ranging from 1.35 to 3.90 wt%, and iron present at 0.87 to 9.93 wt%. Titanium was added to some alloys, ranging from less than 0.01 to 2.96 wt%. Niobium was added to some alloys, ranging from less than 0.02 to 5.33 wt%. Tantalum was added to some alloys, ranging from less than 0.01 to 2.01 wt%. Tungsten was added to some alloys, ranging from less than 0.01 to 8.43 wt%. Silicon was present as an impurity in some alloys and was intentionally added to some alloys, ranging from 0.01 to 0.17 wt%. Manganese was intentionally added to some alloys, ranging from less than 0.01% to 0.24% by weight. Minor amounts of carbon and boron were also added to the experimental alloys, present at most 0.081% and 0.006% by weight, respectively. No alloy contained intentionally added zirconium. Therefore, the measured zirconium levels in all experimental alloys were less than 0.02% by weight (these results are not included in Table 1 for brevity).

[0025] All tests of the alloy were performed on sheet materials ranging from 0.065″ to 0.125″ (1.6 to 3.2 mm) in thickness. The test alloy was vacuum induction melted at a melt size of 30–50 lbs (13.6 to 27.2 kg), followed by electroslag remelting. Hot forging of the ingot into slabs on an open die press was generally straightforward. The slab was then hot-rolled to an intermediate specification. The sheet was annealed, water-quenched, and cold-rolled to produce sheets of the desired specifications. Intermediate annealing of the cold-rolled sheet was necessary in the production of 0.065″ (1.6 mm) sheets. The cold-rolled sheet was annealed as needed to produce a fully recrystallized equiaxed grain structure, typically with ASTM grain sizes between 4 and 5. After annealing, the sheet samples were water-quenched and rapidly air-cooled. For some tests, the annealed samples underwent an age-hardening heat treatment suitable for the specific alloy prior to testing. Details of the age-hardening heat treatment are provided later in this specification.

[0026] Table 1

[0027] Composition of the experimental alloy (in weight %)

[0028]

[0029]

[0030] To evaluate key properties (encapsulation, thermal stability, mechanical strength) and auxiliary properties (weldability), up to five different types of tests were performed on the experimental alloys to determine their suitability for the intended applications. The results of these tests are described in the following sections. Additionally, key and auxiliary property tests were performed on three commercially available alloys (Alloy 282, Alloy Waspaly, and Alloy 233) to provide comparative information. Table 2 provides the measured composition of samples of the tested commercial alloys. Note that the sample chemistry of the commercial alloys was derived from actual samples of the commercial alloys and is considered representative, but may not correspond to the same melt tested in this procedure.

[0031] Table 2 Representative composition (wt%) of commercial alloys

[0032]

[0033] The first key property of the alloy of this invention is containment. High containment (or toughness) is desired in certain components of gas turbine engines, particularly in aero engines, at elevated operating temperatures. These components, which may include certain casings and rings, may require high containment in the event of engine failure. In addition to high strength, this containment property is also highly dependent on the alloy's ductility at operating temperatures. While containment property is best measured by expensive, specialized high-strain-rate tests, a reasonable measurement can be obtained by considering the ductility (elongation) values ​​derived from standard tensile tests at relevant temperatures. Yield strength (YS) and ultimate tensile strength (UTS) values ​​from tensile tests are also considered. The containment factor CF can be calculated from the results of tensile tests and is defined as CF = ½ (YS + UTS) (Elongation). (Note: In standard units, the containment factor is calculated in ksi using YS and UTS, and elongation is expressed as a percentage; therefore, the unit of the resulting containment factor is lbf-in / in.) 3 ×10 -1 For the sake of brevity, in the remainder of this specification, this unit descriptor will not be attached to the containment factor value and will be assumed to be lbf-in / in. 3 ×10 -1 Unless otherwise stated. To convert CF to metric units (MJ / m 3Multiply by 0.06895. For applications requiring containment properties, a high CF value is needed. When comparing the CF values ​​of various alloys, it is important to use similar product forms and sizes, as well as the same sample geometry, because tensile properties can be strongly dependent on product form and size, and the geometry of the test sample. Given that the tensile properties below are generally temperature-dependent, the containment factor depends on temperature. For applications where containment properties are valuable, the operating temperature can fall within a “moderate range” of approximately 1200°F–1500°F (649–816°C). For this purpose, a temperature of 1400°F (760°C) was chosen for testing.

[0034] Tensile tests were conducted at 1400°F on forty-one experimental alloys and three commercial alloys (HAYNES 282, HAYNES 233, and Waspaloy) to determine their strength and ductility. The results, along with the calculated containment factors, are provided in Table 3. Note that all samples were tested under the heat treatment conditions defined in Table 4.

[0035] Table 3 Tensile properties and containment factor at 1400°F (760℃) (age-hardening conditions)

[0036]

[0037] Table 4. Age-hardening heat treatment of various alloys

[0038]

[0039] The 1400°F (760°C) containment factors for the three commercial alloys were found to be 2305, 2924, and 3634 (159, 202, and 251 MJ / m²) for alloys 282, 233, and Waspaloy, respectively. 3 To account for the engine casing alloy, it is desirable to have an inclusion factor of 1400°F (760°C) as high as or higher than that of alloy 282, and therefore this is used as a target in this invention. Thirty-three of the forty-one experimental alloys were found to have an inclusion factor of 1400°F (760°C) higher than that of alloy 282, i.e., CF ≥ 2305 (159 MJ / m³). 3 It has a containment factor of less than 2305 (159 MJ / m²) at 1400°F (760°C). 3 The eight alloys are experimental alloys 3, 4, 7, 12, 13, 14, 18, and 19. Therefore, these eight alloys are considered to be outside the scope of this invention.

[0040] Figure 2This is a graph showing the containment factors of alloys 282, Waspaloy, and 233, as well as test alloys 8, 9, 17, 22, 23, and 30 in Table 1. The graph indicates that the containment factors of all these test alloys are higher than that of alloy 282. Experimental alloys 8, 9, 17, 22, 23, and 30 are some, but not all, of the experimental alloys of the present invention disclosed in this specification, and can be considered representative of the alloys of the present invention.

[0041] The second key property of the alloys of this invention is thermal stability. Since applications such as engine casings require long-term operation at high temperatures, the thermal stability of the materials constituting them is crucial. The thermal stability of the experimental and commercial alloys was tested by subjecting them to 1000 hours of heat exposure at 1400°F (760°C). Note that for all alloys, the samples were subjected to age-hardening conditions for heat exposure. The room temperature (RT) tensile properties of the heat-exposed samples were then measured. The retained RT yield strength and retained RT tensile elongation (ductility) after heat exposure are measures of the alloy's thermal stability. These measurements are shown in Table 5. The exposure temperature of 1400°F (760°C) was chosen because many nickel-based alloys exhibit the lowest thermal stability near this temperature range, and it is the relevant temperature for engine casing applications. To achieve acceptable thermal stability for the applications of interest, the retained RT yield strength was determined to be as good as or better than that of Alloy 282, i.e., ≥104.1 ksi (718 MPa), and the retained RT ductility was to be at least 10%. The results for forty-one experimental alloys and three commercial alloys are shown in Table 5. Thirty-nine of the forty-one experimental alloys were found to have a retained yield strength greater than 104.1 ksi (718 MPa). Only experimental alloys 5 and 18 had insufficient residual yield strength and cannot be considered part of this invention. Alloys 233 and Waspaloy were found to have a retained yield strength greater than 104.1 ksi (718 MPa). Considering retained ductility, thirty-six of the forty-one experimental alloys were found to have values ​​greater than 10%. The five experimental alloys with retained ductility less than 10% are experimental alloys 11, 14, 15, 32, and 33, and these alloys are not considered part of this invention. The three commercial alloys all had retained ductility greater than 20%.

[0042] Figure 3 This is a graph showing the thermal stability (measured by retained room temperature ductility) of alloys 282, Waspaloy, and 233, as well as experimental alloys 8, 9, 17, 22, 23, and 30 in Table 1. All these alloys retain room temperature ductility greater than the target by 10%, in fact all greater than 15%, and some exceeding 20%.

[0043] Table 5. RT tensile properties after heat exposure at 1400°F (760°C) for 1000 hours.

[0044]

[0045] The third key property of the alloys of this invention is high mechanical strength, particularly high LCF and / or creep strength. A common test for evaluating LCF strength is the strain-controlled test, in which the sample is cyclically strained to a fixed strain level until failure, and the number of cycles to failure (also known as LCF life) is considered a measure of its LCF strength. In this specification, LCF test results at 1500°F (816°C) are provided for most of the tested alloys and all three commercial alloys. The test was strain-controlled, fully inverse (R = -1), with a triangular waveform and a frequency of 20 cycles / minute (0.33 Hz). Most tests were performed at 0.6% of the total strain range (TSR). The results are listed in Table 6. Note that due to the effort and cost of such testing, not all experimental alloys underwent LCF testing.

[0046] Table 6. LCF Test Results at 1500°F (816℃) (Age Hardening Conditions) TSR = 0.6%

[0047]

[0048] As shown in Table 6, under these test conditions, the LCF lives of the three commercial alloys—Alloy 282, Alloy Waspaly, and Alloy 233—were 6446, 6344, and 9507 cycles, respectively. Since newer gas turbine engine designs will require a significant improvement in LCF strength compared to currently available alloys, a minimum of 10,000 cycles was chosen as the ideal target for the alloys of this invention, representing an improvement of over 57% compared to Waspaly. Given this 10,000-cycle target, Table 6 shows that only 18 of the 28 tested alloys met the target, while 10 did not. The alloys that met the target are experimental alloys 3, 7, 8-10, 16, 17, 20, 22-25, 27, and 30-34. The alloys that did not meet the target are experimental alloys 2, 12-14, 18, 19, 21, 26, 28, and 29. The sixteen alloys that were not tested are experimental alloys 1, 4-6, 11, 15, 31-33, and 35-41.

[0049] Figure 1This is a graph showing the low-cycle fatigue life of alloys 282, Waspaloy, and 233, as well as experimental alloys 8, 9, 17, 22, 23, and 30 at 1500°F (816°C) and a TSR of 0.6%. Commercial alloys exhibit low-cycle fatigue lives of less than 10,000 cycles, while all experimental alloys have low-cycle fatigue lives of more than 10,000 cycles. Experimental alloys 9, 17, and 30 have low-cycle fatigue lives of more than 19,500 cycles.

[0050] In addition to the LCF tests described above, LCF tests were performed on eight experimental alloys at a lower TSR value of 0.5%. These tests took longer and were more expensive to run, but in some respects they were better predictors of the long-term fatigue strength of the alloys. Temperature and other test conditions were kept the same as those for the TSR = 0.6% test. The results are shown in Table 7 below.

[0051] Table 7. LCF Test Results at 1500°F (816℃) (Age Hardening Conditions) TSR = 0.5%

[0052]

[0053] As shown in Table 7, under these test conditions, the LCF lifetimes of the three commercial alloys were 13,130, 31,520, and 39,957 cycles for alloys 282, Waspaloy, and 233, respectively. For this TSR level, a target LCF lifetime of 40,000 cycles was chosen, representing a 27% improvement over Waspaloy. Of the eight experimental alloys tested under these conditions, three failed to meet the target (alloys 1, 5, and 6), while five met the target (7, 8, 23, 30, and 36). None of the three commercially tested alloys met the target LCF lifetime.

[0054] The creep strength of fifteen experimental alloys and the Waspaloy alloy was measured by creep testing at 1500°F (816°C) with an applied stress of 30 ksi (207 MPa). The 1% creep life (i.e., the time to reach 1% elongation) for each test was recorded, and the results are listed in Table 8. The 1% creep life of Waspaloy was 49.5 hours. For the alloys of this invention, a target of 70 hours for the 1% creep life was chosen, representing a 41% improvement over Waspaloy. All fifteen experimental alloys (3, 9, 17, 20, 22-23, 30-31, 35-41) subjected to creep testing at 1500°F (816°C) and 30 ksi (207 MPa) met this target.

[0055] Table 8. Creep test results at 1500°F (816℃) and 30 ksi (207 MPa)

[0056] Age hardening conditions) stress

[0057]

[0058] Figure 4 This is a graph showing the 1% creep life of the Waspaloy alloys and experimental alloys 9, 17, 22, 23, 30, 31, 37, and 41, measured during creep tests at 1500°F (816°C) under an applied stress of 30 ksi (207 MPa). The graph shows that all these experimental alloys have a higher 1% creep life than the Waspaloy alloys, while alloys 9, 17, 23, 30, 31, and 41 have significantly higher creep lives. Experimental alloys 9, 17, 22, 23, 30, 31, 37, and 41 are some, but not all, of the experimental alloys disclosed in this specification and can be considered representative of the alloys of this invention.

[0059] When considering all three key properties (containment, thermal stability, and mechanical strength) together, twenty-one experimental alloys were found to meet all three key property objectives and are considered alloys of this invention. These alloys are experimental alloys 8-10, 16, 17, 20, 22-25, 27, 30, 31, and 34-41 listed in Table 9. Note that since not all mechanical tests were performed on every alloy, alloys that meet the objectives in one or more of the three tests (i.e., two LCF test conditions and a creep test) are considered to have satisfactory mechanical strength. It can also be seen from Table 9 that twenty experimental alloys and all three commercial alloys were found not to meet one or more key performance objectives and are therefore not part of this invention.

[0060] Table 9 Summary of Key Properties of Alloys

[0061]

[0062] I have found that the major alloying elements of acceptable alloys fall within certain compositional ranges shown in Table 10, and that acceptable alloys satisfy three additional compositional relationships now disclosed. (Note: The range of minor alloying elements is discussed later in this specification). The first two compositional relationships involve γ'-forming elements (aluminum, titanium, niobium, and tantalum). As implied, these elements form strengthening γ' phases (Ni3X, where X = Al, Ti, Nb, and / or Ta) when subjected to the age-hardening heat treatment detailed in Table 4. I have found that γ'-forming elements should be controlled using the following formula (where elemental composition is expressed as wt%):

[0063] Equation (1) 0.7≤R≤1, where R = Al / T and T = Al + 0.56Ti + 0.29Nb + 0.15Ta

[0064] Equation (2) 1.8 < G < 2.4 where G = T – 1.67R

[0065] Note that, by definition, the upper limit of the R factor is 1. It is important to point out that the crucial role of the R and G factors in determining which alloy composition provides a unique combination of the three key properties of the alloys of this invention is an unexpected and surprising discovery.

[0066] The third compositional relationship involves the solid solution strengthening elements molybdenum and tungsten. Too much of these elements can lead to the presence of undesirable phases, which can affect many alloy properties, including but not limited to thermal stability and LCF. Conversely, too little of these solid solution strengthening elements is undesirable because high mechanical strength is important for the alloys of this invention. Based on the results of this invention and my understanding of similar alloy systems, in addition to the acceptable limits for each of these elements (listed in Table 10), I also require upper and lower limits for the sum of these two elements, as shown in the following formula (wherein the elemental composition is given in weight %):

[0067] Equation (3) 7.5 < Z < 9.5, where Z = Mo + 0.52W

[0068] For convenience, the calculated values ​​of T, R, G, and Z factors for experimental and commercial alloys in this specification are given in Table 11.

[0069] Table 10: Wide range of composition of major elements

[0070]

[0071] It satisfies the additional compositional relationships (Equations 1, 2, and 3).

[0072] In Table 10, the upper limits for titanium, niobium, and tantalum are 1.9 wt%, 3.7 wt%, and 7.1 wt%, respectively. These values ​​are calculated using Equations 1 and 2, with aluminum ranging from 2.1 to 4.1 wt%. While the range for aluminum is well supported by the example alloys, the calculated upper limits for titanium, niobium, and tantalum are significantly higher than those of the satisfactory example alloys, which are 0.50 wt%, 2.20 wt%, and 2.01 wt%, respectively. Given this fact and the typical tolerances of these elements in melt practice, more conservative upper limits for titanium, niobium, and tantalum would be 1 wt%, 2.7 wt%, and 2.5 wt%, respectively.

[0073] Table 11 Constituent Factors

[0074]

[0075]

[0076] When considering the compositional requirements of the alloys of this invention (Table 10 plus Formulas 1, 2, and 3), it was found that twenty-one experimental alloys (experimental alloys 8-10, 16-17, 20, 22-25, 27, 30-31, and 34-41) met all three key performance objectives and satisfied all compositional requirements. Conversely, twenty experimental alloys that did not meet one or more key performance objectives and all three commercial alloys (experimental alloys 1-7, 11-15, 18-19, 21, 26, 28-29, 32, and 33, and commercial alloys 282, Waspaloy, and 233) also did not meet one or more compositional requirements.

[0077] For certain gas turbine components, additional performance targets may be required. For example, if a component requires welding, sufficient weldability is desirable. For alloys strengthened by the γ' phase, weldability can be negatively affected by an effect known as strain-aging cracking. This phenomenon typically occurs after the welding operation, when the welded portion is first subjected to high temperatures. This is usually during the post-weld annealing process in the manufacture of most welded γ' alloys. Cracking occurs during heating to the annealing temperature due to the formation of the γ' phase. The formation of the strengthening γ' phase, along with the low ductility of many of these alloys at moderate temperatures and the mechanical constraints typically imposed by the welding operation, often leads to cracking. The problem of strain-aging cracking can limit the use of alloys to a certain thickness, as greater material thickness results in greater mechanical constraints.

[0078] Using Metzler Welding Journal The improved CHRT test, described in the supplement (October 2008, pp. 249s-256s), measures the strain-aging crack resistance of experimental and commercial alloys. This test was developed to determine the relative resistance of alloys to strain-aging cracking. It is based on U.S. Patent 8,066,938 and Rowe's... Welding Journal A variation of the test described in the Supplement (February 2006, pp. 27s-34s). The CHRT test was originally developed in the late 1960s as a method for determining the strain-aging crack susceptibility of various smelts of Rene 41 (R-41) alloy to strain-aging cracking (Fawley, RW, Prager, M., Carlton, B., and Sines, G. 1970). WRC BulletinNumber 150, Welding Research Council, NY. In the CHRT test, solution-annealed tensile test specimens are heated at a controlled rate to a test temperature within the γ' precipitation temperature range and then stretched to failure. CHRT elongation is an indicator of the alloy's resistance to strain-aging cracking / weldability. During the CHRT test, the sample undergoes γ' precipitation, which simulates the effects of welding and subsequent cooling. Therefore, the CHRT test reliably predicts the properties of materials in the welded state. The CHRT test is designed to be a relatively simple test, but the results are in very good agreement with reported strain-aging cracking studies (e.g., see Rowe in...). Welding Journal Supplement (February 2006, pp. 27-34). Key variables affecting performance, as identified in the CHRT test, included composition and grain size. In the improved CHRT test, the width of the gauge segment is variable, and the test is conducted on a dynamic thermomechanical simulation apparatus, rather than a screw-driven tensile apparatus. The results from the two different forms of testing are expected to be similar qualitatively, but the absolutely quantitative results will differ.

[0079] Improved CHRT tests were performed on forty-one experimental alloys using solution-annealed and surface-ground samples. Tests were conducted at 1450°F (788°C), and reported CHRT elongation values ​​were measured in terms of elongation exceeding 1.5 inches (38 mm). The results are shown in Table 12. Similar tests were performed on three commercial alloys (Alloy 282, Alloy Waspaloy, and Alloy 233) under in-plant annealing conditions, and the results are also shown in Table 12. The CHRT elongation values ​​for Alloy 282 and Alloy 233 were 13.0% and 12.5%, respectively. These relatively high values ​​indicate good resistance to strain-aging cracking in both alloys. This is consistent with reported field experience for these two alloys. However, the reputation of the Waspaloy alloy is quite different. While Waspaloy is moderately weldable, it can be susceptible to strain-aging cracking under certain conditions. CHRT tests were performed on Waspaloy under two conditions: in-plant annealing and in-plant annealing with surface grinding. The CHRT elongation values ​​under these two conditions are 6.8% and 6.0%, respectively. To ensure a certain degree of weldability in the alloy of the present invention, it is preferable that the CHRT elongation is greater than that of Waspaloy under surface grinding conditions, that is, greater than 6.0%. More preferably, the CHRT ductility is greater than that of Waspaloy under in-factory annealing conditions, i.e., greater than 6.8%.

[0080] Figure 5This is a graph showing the CHRT ductility of alloys 282, Waspaloy, and 233, as well as experimental alloys 8, 9, 17, 22, 23, and 30, as listed in Table 1. Three of the tested alloys (22, 23, and 30) have a higher CHRT ductility (6.8%) than the factory-annealed Waspaloy alloy. Experimental alloy 17 has a CHRT ductility close to 6.7%. Experimental alloys 8 and 9 have definite CHRT ductility values ​​less than 6.8%. Of these two alloys, experimental alloy 9 has a CHRT ductility of 6.0%, equal to that of Waspaloy under surface-polished conditions, while experimental alloy 8 has a CHRT ductility less than 6.0%.

[0081] Table 12 CHRT Test Results at 1450°F (788℃) (Annealing Conditions)

[0082]

[0083] It was found that a CHRT elongation greater than 6.0% could be achieved by further limiting the amount of γ'-forming elements. Specifically, it was found that Al should be limited to 3.1–4.1 wt%, Ti to at most 0.4 wt%, Nb to at most 1.3 wt%, and Ta to at most 2.5 wt%. Furthermore, the R factor should be further limited as follows (where elemental composition is given in wt%):

[0084] Equation (4) 0.9≤R≤1, where R = Al / T and T = Al + 0.56Ti + 0.29Nb + 0.15Ta

[0085] Therefore, the preferred composition requirements for the major elements when a CHRT elongation > 6.0% is desired are summarized in Table 13. Note that preferred requirements for minor alloying elements are discussed later in this specification. The eighteen experimental alloys that meet the preferred composition requirements are experimental alloys 9, 17, 20, 22-25, 27, 30-31, and 34-41. All eighteen alloys exhibit a CHRT elongation > 6.0%.

[0086] Table 13. Preferred Composition Range of Main Elements

[0087]

[0088] The additional compositional relationships (Equations 2, 3, and 4) are satisfied.

[0089] Further compositional constraints can lead to even further improvements in weldability and other properties. Specifically, I have found alloy compositions that exhibit greater CHRT elongation than Waspaloy alloys (surface-ground) and significant simultaneous improvements in all three key properties (encapsulation, thermal stability, and mechanical strength). These improved compositions are referred to here as “preferred” compositions, and the major alloying elements are summarized in Table 14. The preferred compositions involve tightening the elemental ranges for several elements, including increasing the minimum required values ​​for tungsten and iron, both of which have been found to contribute to maximizing alloy performance. Furthermore, the R and G factors should be further constrained as follows (where elemental composition is given in weight %):

[0090] Equation (5) 0.95≤R≤1, where R = Al / T and T = Al + 0.56Ti + 0.29Nb + 0.15Ta

[0091] Equation (6) 1.9 < G < 2.4 where G = T – 1.67R

[0092] Note that more preferred requirements for minor alloying elements are discussed later in this specification. I have found that alloys with more preferred compositions have a CHRT elongation value greater than 6.8% and a containment factor (172 MJ / m²) greater than 2500 at 1400°F (760°C). 3 The alloys exhibited yield strength and elongation values ​​greater than 115 ksi (793 MPa) and 15% RT after 1400°F (760°C) / 1000h, and one or more of the following three mechanical strength measures: 1) 1500°F (816°C), TSR = 0.6%, LCF life greater than 19,500 cycles; 2) 1500°F (816°C), TSR = 0.5%, LCF life greater than 80,000 cycles; 3) 1500°F (816°C), 30 ksi (207 MPa), 1% creep life greater than 125 hours. This combination of properties represents a significant improvement over Waspaloy alloys (the most commonly used turbine casing alloy), making these alloys strong candidates for next-generation gas turbine engines. The eight experimental alloys that meet the preferred composition requirements in Table 14 are experimental alloys 23, 30-31, 36, and 38-41. All eight alloys exhibit CHRT ductility greater than 6.8% and meet the modified containment, thermal stability, and mechanical strength targets defined in this paragraph.

[0093] Table 14. More preferred composition range of main elements

[0094]

[0095] The additional compositional relationships (Equations 3, 5, and 6) are satisfied.

[0096] The alloys of this invention are nickel-based alloys, most of which are so-called superalloys, a class of alloys known for providing high strength, environmental resistance, etc., under the harsh conditions common in gas turbine engines. The benefits of the main alloying elements in the alloys of this invention are briefly described below, but this should not be considered exhaustive. Chromium provides useful oxidation resistance and resistance to hot corrosion, as well as some strengthening. It is present in relatively high amounts in many forged superalloys, and a range of 16-20 wt% chromium in the alloys of this invention is quite typical. The specification range of chromium in nickel-based superalloys can be quite large. For example, one specification of chromium in Waspaloy is in the range of 3 wt% (or ±1.5 wt%), while one specification of Alloy 282 is in the range of 2 wt% (or ±1 wt%). Cobalt provides some strengthening and modulates the γ' solution temperature. However, due to its chemical similarity, cobalt can be used interchangeably with nickel in relatively large amounts without significantly affecting performance. In the alloys of this invention, the range of cobalt can be 8-13 wt% (or ±2.5 wt%), more preferably 9-11 wt% (or 10 ±1 wt%). These ranges are advantageous compared to industry specifications. Similar to chromium, the specification range for cobalt in nickel-based superalloys can be quite large. For example, one specification for cobalt in Waspaloy is 3 wt% (or ±1.5 wt%), while one specification for Alloy 282 is 2 wt% (or ±1 wt%). Iron can be intentionally added or present as a typical impurity in nickel-based alloys. I have found that the intentional addition of at least 1.5 wt% iron provides a beneficial effect on manufacturability. However, to meet all key performance targets, iron should be kept to no more than 5 wt%. More preferably, iron should be kept to 4 wt% or less. Aluminum, titanium, niobium, and tantalum provide significant strengthening by forming the γ' phase during heat treatment. Regarding the relative amounts of these four γ'-forming elements, I have found that a higher aluminum content is beneficial, and titanium should preferably be kept to 0.4 wt% or less. Even lower titanium contents below 0.1 wt% will provide further benefits. Aluminum must be present at a minimum of 2.1 wt%, but should preferably be at least 3.1 wt%. Molybdenum and tungsten are effective solid solution strengthening elements. A minimum of 4% by weight of molybdenum is required. Although tungsten is not required in this invention, a more preferred composition will have at least 1% by weight, as tungsten has been found to provide beneficial effects. A tungsten content of at least 2% by weight is preferred. However, tungsten should be kept below 8% by weight to avoid thermal stability issues. More preferably, tungsten should be limited to no more than 6% by weight.

[0097] As previously stated, the amounts of γ'-forming elements and solid solution strengthening elements must be carefully controlled (using compositional relationships I, which I have discovered and described) to provide the necessary balance of alloy properties. Due to the requirements of these compositional relationships, some alloys may satisfy all individual elemental requirements but still fall outside the scope of this invention. For example, alloys 7, 28, 29, and 32 are within the broad elemental range of this invention, but these alloys have excessively high G-factors (>2.40) and, as described in Table 9, do not meet one of the key performance objectives. Similarly, alloys may satisfy the compositional relationship requirements but fall outside the range of one or more individual elements. For example, alloys 3, 4, and 21 satisfy all compositional relationship requirements, but alloys 3 and 4 have excessively high levels of molybdenum, while alloy 21 has excessively high levels of iron. Similar results can be obtained with respect to preferred or more preferred claims, in addition to the cases of the broad claims described above.

[0098] To graphically illustrate the R, G, and T factors, and the constraints on these factors described by the compositional relationships given in Equations 1, 2, 4, 5, and 6, I constructed... Figure 6 The figure shows many of the aforementioned experimental, commercial, and prospective alloy compositions. The alloys of the present invention (wide claims) are all contained within a larger parallelogram inscribed by four lines: G = 1.8, G = 2.4, R = 0.7, and R = 1. The preferred alloys of the present invention are located within a medium-sized parallelogram to the right of the R = 0.9 line. More preferred alloys are located within a smallest parallelogram, situated to the right of the R = 0.95 line and between the G = 2.4 and G = 1.9 lines. Figure 6 Experimental and commercial alloys located outside the maximal parallelogram are not alloys of this invention and do not meet one or more key performance objectives. Note that, for clarity, in Figure 6 Experimental and commercial alloys that are located within a given parallelogram but contain one or more individual elements not included in the relevant claims are omitted. For Figure 6 The selected pre-selected alloys shown are expected to meet the key performance objectives of the invention for those within the largest parallelogram, while those on the outer sides (particularly pre-selected alloys XX and YY) are not expected to meet all key performance objectives. Table 18 shows the composition of the pre-selected alloys.

[0099] In addition to the carbon required in these alloys, other minor element additions may include boron, manganese, silicon, zirconium, magnesium, calcium, hafnium, and one or more rare earth elements (including but not limited to yttrium, lanthanum, and cerium). The acceptable ranges for minor elements are described below and summarized in Table 15. These acceptable ranges are considered to be the same regardless of whether the minor element is intentionally added or exists only as an impurity.

[0100] Carbon is intentionally added to the alloys of the present invention to provide interstitial strengthening, carbide strengthening, and improved grain size control. In the alloys of the present invention, carbon is limited to a maximum of 0.15% by weight, a maximum of 0.1% by weight for preferred compositions, and a maximum of 0.08% by weight for more preferred compositions. Boron may be added in low but effective trace amounts, up to a maximum of 0.015% by weight, to obtain certain benefits known in the art. For preferred and more preferred compositions, boron is limited to a maximum of 0.008% by weight to ensure good solderability. Although boron is present in all experimental alloys and is considered to have the most beneficial effects, it is an optional additive. To enable the removal of oxygen and sulfur during melting, these alloys may contain small amounts of manganese, up to about 1% by weight, and may contain trace amounts of magnesium, calcium, and rare earth elements (e.g., yttrium, cerium, and lanthanum), each up to about 0.05% by weight. While silicon is sometimes similarly added to alloys for oxygen and sulfur control, I have found silicon to be detrimental to the LCF strength of these alloys. Therefore, silicon should be limited to 0.13% by weight, preferably 0.12% by weight, and even more preferably less than 0.1% by weight. Zirconium may be present in these alloys as an impurity or intentional addition (e.g., to improve creep life), but should be maintained at 0.06% by weight or less to maintain reasonable manufacturability. To ensure resistance to heat cracking during welding, zirconium is preferably limited to 0.03% by weight or less, more preferably less than 0.02% by weight. Hafnium may be present in these alloys as an impurity or intentional addition, but should be maintained at 0.5% by weight or less.

[0101] Table 15. Addition of minor elements (by weight %)

[0102]

[0103] One or more rare earth elements

[0104] The permissible amounts of certain impurities are summarized in Table 16. Other unlisted impurities may also be present and tolerated if they do not reduce critical performance below specified standards.

[0105] Table 16 Impurity Tolerances (by weight %)

[0106]

[0107] For convenience, experimental and commercial alloys are listed in Table 17, and those alloys are indicated to satisfy a wide range of compositions, preferred ranges, and more preferred ranges.

[0108] Table 17 Alloys that meet the defined composition range (major and minor elements).

[0109]

[0110] Based on the information provided in this specification, I anticipate that all the indicated alloy compositions listed in Table 18 also possess the desired properties of this invention (with the exception that alloys XX, YY, and ZZ are outside the broad claims of this invention).

[0111] Table 18 shows the alloy composition (in weight %).

[0112]

[0113] Further consideration of these three commercial alloys is useful: Alloy 282, Alloy Waspaly, and Alloy 233. All three alloys were found to have acceptable containment and thermal stability in relation to the key properties of the engine casing identified herein. All three alloys also exhibited sufficient weldability / strain-aging crack resistance (although Waspaly is critical). However, the mechanical strength at 1500°F (816°C) of all three alloys was unacceptable. Observing the composition of these three alloys provides an understanding of why this is the case. All three commercial alloys have compositions outside the scope of this invention. The composition of Alloy 282 does not meet the compositional requirements of this invention, primarily due to the γ'-forming elements. This alloy does not satisfy formula (1), and both aluminum and titanium are outside the stated wide range. Additionally, the levels of molybdenum, tungsten, and iron are outside the preferred range. Similarly, the composition of Alloy Waspaly does not satisfy formula (1), and aluminum and titanium are also outside the stated wide range. Additionally, the levels of cobalt, tungsten, and iron are outside the preferred range. Alloy 233 is closer to the alloys of this invention; however, the cobalt content is significantly higher than the wide range of alloys of this invention. In addition, the titanium content is outside the preferred range, while the tungsten, iron, carbon, silicon and zirconium content is outside the more preferred range.

[0114] In addition to the three key properties mentioned above and the auxiliary properties of good weldability / resistance to strain aging cracking, other desired properties of the alloy of the present invention may include: high room temperature tensile strength and ductility under age hardening conditions, good resistance to thermal cracking during welding, good resistance to oxidation / hot corrosion, good hot forging properties, and good cold formability.

[0115] Even if the tested samples are limited to forged sheets, alloys having compositions within the ranges in Tables 10, 13, and / or 14 should exhibit considerably improved properties in other forged forms (e.g., plates, bars, tubes, forgings, and wires) and in casting, spray forming, additive manufacturing (including powders used to produce them), or powder metallurgy forms (i.e., powders, compacted powders, and sintered compacted powders). Therefore, this invention encompasses all forms of alloy compositions. It should be noted that the key property objectives defined in this specification are specifically for developing supporting data on product form, processing parameters, and microstructure (e.g., grain size). These variables are kept as constant as possible among the experimental alloys to better facilitate fair comparisons. If these variables change (e.g., if the product form is a hot-rolled ring instead of a sheet, or if the material is annealed to produce a different grain size), the absolute values ​​of the key property values ​​may change. However, the relative improvements provided by the alloys of this invention are expected to remain effective.

[0116] The alloys of this invention possess a unique combination of three key properties: high containment, good thermal stability, and excellent mechanical strength, which can be further controlled to provide good resistance to strain-aging cracking. These properties make the alloys of this invention suitable for gas turbine engine components, particularly for turbine casings in these engines. Such components and engines incorporating them can operate at higher temperatures without failure and should have a longer service life than currently available components and engines. It should be recognized that this unique combination of properties is also attractive for other high-temperature applications not described herein.

[0117] Although certain preferred embodiments of the alloy have been disclosed, it should be clearly understood that the invention is not limited thereto, but can be implemented in various ways within the scope of the following claims.

Claims

1. A nickel-chromium-cobalt based alloy, comprising, by weight percentage, the following composition: 16-20 Chromium 8-13 Cobalt 4-8.5 molybdenum Up to 8 tungsten Up to 5 iron 2.1-4.1 Aluminum Up to 1.9 titanium At most 7.1 tantalum Up to 3.7 niobium There are at most 0.15 carbon atoms. At most 0.015 boron At most 0.13 silicon At most 1 manganese At most 0.06 zirconium Maximum 0.05 magnesium At most 0.05 calcium Maximum 0.05 yttrium At most 0.05 lanthanum At most 0.05 cerium At most 0.5 hafnium The balance is nickel and impurities. By weight percentage, the alloy also satisfies the following compositional relationships defined by elemental amounts: T = Al +0.56Ti +0.29Nb +0.15 Ta R = Al / T; 0.7≤R≤1 G = T –1.67R; 1.8<G<2.4 Z = Mo + 0.52W; 7.5<Z<9.

5.

2. The nickel-chromium-cobalt based alloy of claim 1, wherein the alloy contains, by weight percentage: Up to 1.0 titanium Up to 2.5 tantalum At most 2.7 niobium.

3. The nickel-chromium-cobalt based alloy of claim 1, wherein the alloy contains, by weight percentage: 3.1-4.1 Aluminum At most 0.4 titanium Up to 2.5 tantalum At most 1.3 niobium On a weight percentage basis, the alloy also satisfies the following compositional relationships defined by elemental amounts: T = Al +0.56Ti +0.29Nb +0.15 Ta R = Al / T; 0.9≤R≤1 G = T –1.67R; 1.8<G<2.4 Z = Mo + 0.52W; 7.5<Z<9.

5.

4. The nickel-chromium-cobalt based alloy of claim 1, wherein the alloy contains, by weight percentage: There is at most 0.1 carbon. At most 0.008 boron At most 0.12 silicon At most 0.03 zirconium.

5. The nickel-chromium-cobalt based alloy according to claim 1, wherein the alloy contains 8.5 to 11.5% by weight of cobalt.

6. The nickel-chromium-cobalt based alloy according to claim 1, wherein iron is at least 1.5% by weight.

7. The nickel-chromium-cobalt based alloy according to claim 1, wherein titanium is less than 0.1% by weight.

8. The nickel-chromium-cobalt based alloy of claim 1, wherein the alloy contains, by weight percentage: 16-20 Chromium 9-11 Cobalt 4.5-8 molybdenum 1-6 Tungsten 1.5-4 iron 3.1-4.1 Aluminum At most 0.4 titanium At most 1 tantalum At most 1 niobium There are at most 0.08 carbon atoms. At most 0.008 boron By weight percentage, the alloy also satisfies the following compositional relationships defined by elemental amounts: T = Al +0.56Ti +0.29Nb +0.15 Ta R = Al / T, 0.95≤R≤1 G = T –1.67R, 1.9 < G < 2.4 Z = Mo + 0.52W, 7.5<Z<9.

5.

9. The nickel-chromium-cobalt based alloy according to claim 8, further comprising, by weight percentage: Less than 0.1 silicon Less than 0.02 zirconium.

10. The nickel-chromium-cobalt based alloy of claim 8, wherein tungsten is greater than 2% by weight.

11. The nickel-chromium-cobalt based alloy of claim 8, wherein titanium is less than 0.1 wt%.

12. The nickel-chromium-cobalt based alloy according to claim 1, wherein the impurity comprises: At most 0.5 copper At most 0.5 vanadium At most 0.015 sulfur At most 0.03 phosphorus.

13. The nickel-chromium-cobalt based alloy of claim 1, wherein the alloy contains, by weight percentage: 16.80-19.46 Chromium 9.28-10.31 Cobalt 5.50-8.41 molybdenum Up to 5.18 tungsten 0.89-4.49 iron 3.0-3.90 aluminum At most 0.5 titanium At most 2.01 tantalum Up to 2.2 niobium 0.048-0.081 carbon 0.003-0.006 boron.

14. The nickel-chromium-cobalt based alloy of claim 1, wherein the alloy further contains at least one element selected from magnesium, calcium, yttrium, cerium and lanthanum, wherein each of the elements present accounts for at most 0.05% by weight of the alloy.

15. The nickel-chromium-cobalt based alloy of claim 1, wherein the alloy contains, by weight percentage 16-20 Chromium 8.5-11.5 Cobalt 4-8.5 molybdenum Up to 8 tungsten Up to 5 iron 3.1-4.1 Aluminum At most 0.4 titanium Up to 2.5 tantalum At most 1.3 niobium There are at most 0.15 carbon atoms. The balance is nickel and impurities. By weight percentage, the alloy also satisfies the following compositional relationships defined by elemental amounts: T = Al +0.56Ti +0.29Nb +0.15 Ta R = Al / T; 0.9≤R≤1 G = T –1.67R; 1.8<G<2.4 Z = Mo + 0.52W; 7.5<Z<9.

5.

16. The nickel-chromium-cobalt based alloy according to claim 1, wherein the alloy is selected from the forms of forging, casting, spray forming and powder metallurgy.

17. The nickel-chromium-cobalt based alloy according to claim 1, wherein the alloy is a forging form selected from sheets, plates, bars, wires, tubes and forgings.

18. The nickel-chromium-cobalt based alloy of claim 1, wherein the alloy is formed as an assembly for a gas turbine engine casing.

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