MX2014006344A - Nickel-base alloy heat treatments, nickel-base alloys, and articles including nickel-base alloys. - Google Patents

Abstract

A method for heat treating a 718-type nickel-base comprises heating a 718-type nickel-base alloy to a heat treating temperature, and holding the alloy at the heat treating temperature for a heat treating time sufficient to form an equilibrium or near- equilibrium concentration of δ-phase grain boundary precipitates within the nickel-base alloy and up to 25 percent by weight of total γ'-phase and y"-phase. The 718-type nickel-base alloy is air cooled. The present disclosure also includes a 718-type nickel-base alloy comprising a near-equilibrium concentration of δ-phase grain boundary precipitates and up to 25 percent by weight of total γ'-phase and y"-phase precipitates. Alloys according to the disclosure may be included in articles of manufacture such as, for example, face sheet, honeycomb core elements, and honeycomb panels for thermal protection systems for hypersonic flight vehicles and space vehicles.

Description

THERMAL TREATMENTS FOR NICKEL BASE ALLOYS, NICKEL BASE ALLOYS, AND ITEMS THAT INCLUDE NICKEL BASE ALLOYS BACKGROUND OF TECHNOLOGY FIELD OF TECHNOLOGY Embodiments of the present invention relate generally to methods of heat treatment of nickel-based alloys.

DESCRIPTION OF THE BACKGROUND OF THE TECHNOLOGY Alloy 718 (UNS 07718) is one of the most widely used nickel base alloys and is generally described in U.S. Patent No. 3,046,108, the disclosure of which is hereby incorporated by reference in its entirety. entirety to this document. Alloy 718 comprises elementary constituents comprised in the ranges shown in the following table, together with incidental impurities.

The extensive use of Alloy 718 is at least partially attributable to some advantageous properties of the alloy For example, Alloy 718 has high tensile strength and rupture properties, up to approximately 1200 ° F (648, 9 ° C). Additionally, Alloy 718 has good processing characteristics, such as favorable moldability and workability, as well as good weldability. These features make it possible to easily fabricate components made from Alloy 718 and, when necessary, repair said components. As discussed below, some of the favorable properties of Alloy 718 are the result of the precipitation hardened microstructure of the alloy, which is predominantly reinforced by phase precipitates? ' The nickel-base alloys hardened by precipitation include two main reinforcing phases; precipitated in phase? ' (or "gamma prima") and phase precipitates? ' 1 (or "double prime gamma"). So much the phase? ' as phase Y11 are stoichiometric, with intermetallic compounds rich in nickel. However, the phase? ' it usually comprises aluminum and titanium (ie, N 3 <Al, Ti)) as the main elements of the alloy, while the phase? ' 1 includes mainly niobium (ie, Ni3Nb). Although both the phase? ' how the phase? ' 'form coherent precipitates in the austenite matrix cubic centered on the faces, like the mismatch in the deformation energy associated with the precipitates in phase? ' 1 (which have a tetragonal crystal structure centered on the body) is greater than that of the precipitates in phase? ' (which have a cubic crystalline structure centered on the faces), the precipitates in phase? ' 'tend to be more effective reinforcers than those precipitated in the phase?' . That is, for the same fraction of precipitated volume and particle size, the nickel base alloys hardened primarily by phase precipitates? 1 are usually stronger than nickel-based alloys hardened primarily by phase precipitates? ' .

A disadvantage of nickel-based alloys that include a hardened microstructure by phase precipitation? 1 is that the phase? ' It is unstable at temperatures above about 1200 ° F (648, 9 ° C) and will become the more stable d (or "delta phase") phase. Although the precipitates in phase d have the same composition as those precipitated in the phase? '(ie, N 3 N b), the precipitates in phase d have an orthorhombic crystal structure and are incoherent with the austenite matrix. Accordingly, the hardening effect of the precipitates in phase d on the matrix is considered Generally that is insignificant. Therefore, a result of the transformation to phase d is that certain mechanical properties of the Alloy 718, such as life to break under stresses, deteriorates rapidly at temperatures above 1200 ° F (648, 9 ° C) . Therefore, the use of the 718 Alloy has typically been limited to applications in which the alloy is subjected to temperatures below 1200 ° F (648, 9 ° C).

To form the hardened microstructure by precipitation desired, the nickel-based alloys are subjected to heat treatment or precipitation hardening process. The precipitation hardening process of a nickel-based alloy generally involves a dissolution treatment of the alloy by heating the alloy to a temperature sufficient to dissolve virtually all of the precipitates in the phase? and the phase? ' 'in the alloy (ie, a temperature close to, or above the solvus temperature of the precipitates), cooling the alloy from the solution treatment temperature, and subsequent aging of the alloy in one or more stages of aging. Aging is carried out at temperatures below the temperature of solvus of the gamma precipitates to allow the desired precipitates to develop in a controlled manner.

The development of the desired microstructure in the nickel-based alloy depends on both the composition of the alloy and the precipitation hardening process (ie, the dissolution and aging treatment methods) employed. For example, a typical precipitation hardening process of Alloy 718 for high temperature service involves treatment by dissolving the alloy solution at a temperature of 1750 ° F (954 ° C) for 1 to 2 hours, cooling with air the alloy, followed by aging of the alloy in an aging process in two stages. The first aging step involves heating the alloy to a first aging temperature of 1325 ° F (718, 3 ° C) for 8 hours, cooling the alloy to approximately 50 to 100 ° F (28 to 55.6 ° C) per hour until a second aging temperature of 1150 ° F (621, 2 ° C), and aging the alloy at the second aging temperature for 8 hours. The alloy is then cooled with air to room temperature. The precipitation-hardened microstructure that results after heat treatment previously described is constituted by discrete precipitates in phase? ' and in phase? ' ', but is it predominantly hardened by the Y *' phase precipitates with smaller amounts of phase precipitates? ' that play a secondary hardening role.

In an effort to increase the allowable service temperatures of nickel-based alloys, several phase-reinforced nickel-based alloys have been developed? . An example of such an alloy is the Waspaloy nickel base alloy (UNS N07001), which is commercially available as an ATI Waspaloy alloy from ATI Allvac, Monroe, North Carolina, USA. As the Waspaloy nickel base alloy includes higher levels of alloy additions, including nickel, cobalt, and molybdenum, than the 718 alloy, the Waspaloy alloy is usually more expensive than the 718 alloy. Also, due to the more kinetic precipitation fast of the precipitates in the phase? ' With respect to the precipitates in phase? 11, the ease of hot work and weldability of the Waspaloy alloy is generally considered to be inferior to that of the Alloy 718.

Another nickel alloy hardened in phase? ' is the ATI 718Plus® alloy, which is commercially available from ATI Allvac, Monroe, NC. The ATI 718Plus® alloy discloses in U.S. Patent No. 6,730,264 ("the '264 patent" of the United States "), which is hereby incorporated by reference in its entirety herein.A characteristic of the ATI 718Plus alloy ® is that the aluminum, titanium and / or niobium levels and their relative ratio are adjusted in a manner that provides a thermally stable microstructure and advantageous mechanical properties at elevated temperature, including substantial resistance to breakage and creep. in aluminum and titanium of the ATI 718Plus® alloy together with the niobium content, results in the alloy being hardened in phase? ' and the phase? ", being the phase? ' the predominant hardening phase Unlike the high titanium content / low aluminum content composition typical of some other nickel-based superalloys, the composition of the ATI 718Plus® alloy has a relatively high ratio of the atomic percentage of aluminum with The thermal stability characteristics of the ATI 718Plus® alloy are important for maintaining good mechanical properties, such as the stress fracture properties, after long periods of time. exposure to temperatures elevated.

The ATI 718Plus® alloy can be subjected to processing including annealing, cooling, and aging of the solution. A typical heat treatment for the ATI 718Plus® alloy is depicted graphically in FIG. 1 as a schematic representation of a time-temperature thermal treatment profile. A typical heat treatment for the ATI 718Plus® alloy includes a dissolution treatment at temperatures between 1750 ° F (954, 4 ° C) and 1800 ° F (982, 2 ° C) to dissolve any phase? ' and phase? "and precipitate a small amount of phase d.The amount of precipitated phase d is usually less than about half the equilibrium content at low temperature.The dissolution treatment is followed by aging at 1450 ° F (787, 8 ° C) for 2 to 8 hours, and then at 1300 ° F (704, 4 ° C) for 8 more hours to precipitate coherent particles in phase? ' The alloy can be processed further to achieve an article of manufacture or in any other way descada.

[0001] Additional thermal treatments for hardening the ATI 718Plus® alloy are described in U.S. Patent Nos. 7,156,932; 7,491,275; and 7,527,702, each of which has been incorporated by the present by reference in its entirety to this document. U.S. Patent No. 7,531,054 ("U.S. Patent 54") discloses a heat treatment for the ATI 718Plus® alloy that includes direct aging. In the process of US Patent '054, after hot working of the ATI 718Plus® alloy, the alloy is rapidly and directly cooled to an aging temperature of about 1400 ° F (760 ° C) to prevent precipitation of the heavy precipitates in phase? ' . The cooled alloy is aged at the aging temperature or further cooled to room temperature.

In general, precipitation hardened alloys are not designed for use above their aging hardening temperatures. Precipitated hardened nickel alloys have not been used in applications where the alloy may experience thermal cycling, where the alloys may be repeatedly exposed to temperatures above their aging hardening temperatures and then cooled to temperatures below their temperatures. hardening temperatures due to aging. Conventional aging hardening practices for nickel-based alloys, which have been summarized above, would not result in mechanical properties consistent with the service period for nickel-based alloys with exposure to thermal cycling where the temperatures exceed the aging temperature of the alloy.

It would be desirable to provide a heat treatment for the nickel-base alloys hardened by precipitation that would provide a solid microstructure and transmit properties that would not be significantly affected by thermal cycling. A nickel-based alloy treated in this way can be advantageous for use in, for example, the front sheet and the honeycomb core of the thermal protection systems for hypersonic flying vehicles, and also as material for other articles of manufacturing that undergo thermal cycling during service.

SUMMARY According to one aspect of the present disclosure, a method for heat treatment of a nickel-based alloy of type 718 comprises heating a nickel-based alloy of type 718 to a heat treatment temperature, and maintaining the nickel base alloy of type 718 at the heat treatment temperature for a sufficient heat treatment time to form a concentration in equilibrium or close to equilibrium of the phase d precipitates the intergranular boundary in the nickel base alloy. The heat treatment results in the formation of up to 25 weight percent of the total phase? and the phase "in the nickel-based alloy After maintaining the type 718 alloy at the heat treatment temperature during the heat treatment time, the nickel base alloy of type 718 is cooled and retained in phase in the intergranular limit in the alloy.

According to another aspect of the present disclosure, a method of heat treatment of a nickel base alloy comprises heating the nickel base alloy to a heat treatment temperature in a heat treatment temperature range which is 20 ° F (11, 11 ° C) greater than the nose of the Time-Temperature-Transformation diagram ("TTT diagram") for delta-phase precipitation of up to 100 ° F (55.6 ° C) below the nose of the TTT diagram, and maintain the nickel-based alloy in the heat treatment temperature range during a heat treatment time in a range of 30 minutes to 300 minutes.

After maintaining the nickel base alloy within the heat treatment temperature range during the heat treatment time, the alloy is cooled with air to room temperature. In a non-limiting embodiment, the nickel-based alloy is cooled at a cooling rate not greater than 1 ° F (0.56 ° C) per minute.

In a non-limiting embodiment, the nickel base alloy comprises, in weight percent, from 0.01 to 0.05 carbon, up to 0.35 manganese, up to 0.035 silicon, from 0.004 to 0.020 phosphorus, up to 0.025 of sulfur, from 17.00 to 21.00 of chromium, from 2.50 to 3.10 of molybdenum, from 5.20 to 5.80 of niobium, from 0.50 to 1.00 of titanium, of 1, 20 to 1.70 aluminum, from 8.00 to 10.00 cobalt, from 8.00 to 10.00 iron, from 0.008 to 1.40 tungsten, from 0.003 to 0.008 boron, nickel, and incidental impurities.

According to a further aspect of the present disclosure, there is provided a nickel base alloy of type 718 comprising nickel, chromium, and iron. The nickel base alloy is hardened by niobium and, optionally with one or more alloy additions of aluminum and titanium, and the alloy comprises an austenite matrix that includes intergranular austenite boundaries. There is a concentration in equilibrium or close to the balance of precipitates in phase d in the intergranular limits of austenite in the type 718 alloy, and the alloy includes up to 25 weight percent of phase precipitates? and Y ".

According to a further aspect of the present disclosure, a method for preparing an article of manufacture includes at least one of the methods described herein. In certain non-limiting embodiments, the method can be adapted to prepare an article of manufacture selected from a front sheet, a honeycomb core, and a honeycomb panel of a thermal protection system for a hypersonic flight vehicle .

According to another additional aspect of the present disclosure, an article of manufacture comprises an alloy described herein. Said article of manufacture may be selected from, but not limited to, a front sheet, a honeycomb core, and a honeycomb panel of a thermal protection system for a hypersonic flight vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS The characteristics and advantages of the alloys and methods described in this document may be better understood by reference to the accompanying drawings in which: Fig. 1 is a temperature-time thermal treatment diagram of a prior art conventional heat treatment for the hardening of nickel-based alloys; Fig. 2 is a schematic representation of an example of a thermal protection metal system; Fig. 3A is a schematic representation of an example of a honeycomb panel; Fig. 3B is a schematic representation of an exploded view of an example of a honeycomb panel; Fig. 4 is a flow chart of a non-limiting embodiment of a heat treatment for a nickel-based alloy according to the present disclosure; Fig. 5A is a Time-Temperature-Transform curve for the nickel-based superalloy Alloy 718; Fig. 5B is a Time-Temperature-Transformation curve for the ATI 718Plus® alloy;

[0002] Fig. 6 is a schematic temperature-time graph for a non-limiting embodiment of a method according to the present disclosure for the heat treatment of a nickel base alloy; Fig. 7 is a schematic representation of a thermal cyclization used to evaluate the non-limiting embodiments of the heat treatment methods of the nickel-based alloys according to the present disclosure; FIG. 8 provides graphical representations of the breaking stress as a function of the number of thermal cycles for the ATI 718Plus® alloy treated with the non-limiting heat treatment methods according to the present disclosure, and compared to the heat treatment methods? '/?' conventional before and after thermal cycling at 1650 ° F (898, 9 ° C) and 1550 ° F (843, 3 ° C); Fig. 9 provides graphical representations of the relative retained break stress as a function of the number of thermal cycles for the ATI 718Plus® alloy treated with the non-limiting heat treatment methods according to the present disclosure, and compared to the treatment methods thermal? '/? "conventional before and after thermal cycling at 1650 ° F (898, 9 ° C) and 1550 ° F (843, 3 ° C); Fig. 10 provides graphical representations of the elastic limit as a function of the number of thermal cycles for the ATI 718Plus® alloy treated with the methods of non-limiting heat treatments according to the present disclosure, and compared to conventional? /? "heat treatment methods before and after thermal cycling at 1650 ° F (898, 9 ° C) and 1550 ° F (843, 3 ° C); FIG. 11 includes graphical representations of the relative elastic limit as a function of the number of thermal cycles for the ATI 718Plus® alloy treated with the non-limiting heat treatment methods according to the present disclosure, and compared to the heat treatment methods? /? "conventional before and after thermal cycling at 1650 ° F (898, 9 ° C) and 1550 ° F (843, 3 ° C) FIG. 12 includes graphical representations of the percentage elongation as a function of the number of thermal cycles for the ATI 718Plus® alloy treated with the non-limiting heat treatment methods according to the present disclosure, and compared to the heat treatment methods? '/ • Conventional before and after thermal cycling at 1650 ° F (898, 9 ° C) and 1550 ° F (843, 3 ° C); Fig. 13 includes graphical representations of the relative percent elongation as a function of the number of thermal cycles for the ATI 718Plus® alloy treated with the non-limiting heat treatment methods according to the present disclosure, and compared to the heat treatment methods? /? "conventional before and after Thermal insulation at 1650 ° F (898, 9 ° C) and 1550 ° F (843.3 ° C); Fig. 14 includes graphical representations of the breaking stress as a function of the number of thermal cycles for the Alloy 718 treated with the non-limiting heat treatment methods according to the present disclosure, and compared to the heat treatment methods? '/ "Conventional before and after thermal cycling at 1650 ° F (898, 9 ° C); Fig. 15 includes graphical representations of the relative break stress retained as a function of the number of thermal cycles for the Alloy 718 treated with the non-limiting heat treatment methods according to the present disclosure, and compared to the heat treatment methods? '/?' conventional before and after thermal cycling at 1650 ° F (898, 9 ° C); Fig. 16 includes graphical representations of the elastic limit as a function of the number of thermal cycles for the Alloy 718 treated with the non-limiting heat treatment methods according to the present disclosure, and compared to the heat treatment methods? '/? " conventional before and after thermal cycling at 1650 ° F (898, 9 ° C); Fig. 17 includes graphic representations of the relative elastic limit retained as a function of the number of thermal cycles for the Alloy 718 treated with the non-limiting heat treatment methods according to the present disclosure, and compared with the conventional heat treatment methods? '/? "before and after the thermal delation at 1650 ° F (898, 9 ° C); Fig. 18 includes graphical representations of the percentage elongation as a function of the number of thermal cycles for the Alloy 718 treated with the non-limiting heat treatment methods according to the present disclosure, and compared to the heat treatment methods? '/? " conventional before and after thermal cycling at 1650 ° F (898, 9 ° C); Fig. 19 includes graphical representations of the relative percent elongation as a function of the number of thermal cycles for the Alloy 718 treated with the non-limiting heat treatment methods according to the present disclosure, and compared to the heat treatment methods? '/? "Conventional before and after thermal cycling at 1650 ° F (898, 9 ° C); Fig. 20A is a dark field optical micrograph of a surface region of a sheet of thermally treated ATI 718Plus® alloy according to a non-limiting embodiment of the present disclosure; Fig. 20B is a dark field optical micrograph of a surface region of a sheet of thermally treated ATI 718Plus® alloy according to a non-limiting embodiment of the present disclosure after 5 thermal cycles from room temperature to 1650 ° F (898, 9 ° C) and returning to room temperature; Fig. 20C is a dark field optical micrograph of a surface region of a sheet of an ATI 718Plus® alloy thermally treated in accordance with a conventional heat treatment? '/? "; Fig. 20D is a dark field optical micrograph of a surface region of a sheet of an ATI 718Plus® alloy thermally treated in accordance with a conventional? '/? "Heat treatment after 5 thermal cycles from room temperature to 1650 ° F ( 898, 9 ° C) and return to room temperature; Fig. 21A is a dark field optical micrograph of a surface region of a sheet of thermally treated ATI 718Plus® alloy according to a non-limiting embodiment of the present disclosure; Fig. 21B is a dark field optical micrograph of a surface region of a sheet of thermally treated ATI 718Plus® alloy according to a non-limiting embodiment of the present disclosure after 5 thermal cycles from room temperature to 1550 ° F (843, 3 ° C) and return to room temperature; Fig. 21C is a dark field optical micrograph of a surface region of a sheet of an ATI 718Plus® alloy thermally treated in accordance with a conventional heat treatment? '/? "; Fig. 21D is a dark field optical micrograph of a surface region of a sheet of an ATI 718Plus® alloy treated in accordance with a conventional? '/? "Heat treatment after 5 thermal cycles from room temperature to 1550 ° F (843.3 ° C) and return to room temperature; Fig. 22A is a dark-field optical micrograph of a surface region of a heat-treated Alloy 718 sheet according to a non-limiting embodiment of the present disclosure; Fig. 22B is a dark field optical micrograph of a surface region of a sheet of a heat-treated Alloy 718 according to a non-limiting embodiment of the present disclosure after 5 thermal cycles from room temperature to 1650 ° F (898.9). ° C) and return to room temperature; Fig. 22C is a dark field optical micrograph of a surface region of a sheet of an Alloy 718 thermally treated in accordance with a heat treatment ? '/? "conventional; Fig. 22D is a dark field optical micrograph of a surface region of a sheet of an Alloy 718 thermally treated in accordance with a conventional? '/? "Heat treatment after 5 thermal cycles from room temperature to 1650 ° F (898, 9 ° C) and return to room temperature; The reader will appreciate the above details, as well as others, after considering the following detailed description of certain non-limiting embodiments in accordance with the present disclosure.

DETAILED DESCRIPTION OF CERTAIN UNLIMITED REALIZATIONS In the present description of the non-limiting embodiments, except in the operative examples or when otherwise indicated, it is understood that all numbers expressing quantities or characteristics are intended to be modified in all cases by the term "approximately". At a minimum, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should be considered at least taking into account the number of significant figures reported and applying the usual rounding techniques.

Any patent, publication, or other disclosure material that is said to be incorporated, in whole or in part, by reference herein is incorporated herein only insofar as the incorporated material does not conflict with the present document. with the definitions, statements, or other existing disclosure material shown in this disclosure. In this way, and to the extent necessary, the disclosure as defined in this document replaces any conflicting material incorporated herein by reference. Any material, or part thereof, that is said to be incorporated by reference in this document), but which conflicts with the definitions, statements, or other existing disclosure material shown in this document is incorporated only to the extent that there is no conflict between the incorporated material and the existing disclosure material.

Certain nickel-based alloys are being considered for use as front face and core elements for panels of honeycombs to be used in thermal protection systems for hypersonic flying vehicles. The surface temperature of a vehicle Hypersonic flight when in service will cycle between the ground temperature and approximately 2200 ° F (1204 ° C) at least once per flight mission. Exposure of nickel-based alloys hardened by aging to such a thermal cycle can result in a change in the volume fraction and the size of the precipitated phases, particularly the phase precipitates? and? ", compared to the welding and hardening condition by aging of the nickel base alloy prior to the flight of the first flight mission.In addition, it should be expected that different flight missions have different thermal exposure profiles, resulting in some properties of the microstructure and mechanics of the nickel-based alloy hardened by aging that will vary based on the mission or missions flown.

A thermal protection system (TPS) protects the key components of hypersonic flight vehicles and spacecraft from melting or other damage due to heat generated at high speeds and / or during reentry into the atmosphere. A TPS must be lightweight, reusable, and easy to maintain. A schematic representation of an example of a metallic TPS (10) employing honeycomb-type panels is presented in the FIG. 2. The metallic TPS (10) can be fitted to an external reinforcing member (12) of a component such as, for example, a cryogenic fuel tank (not shown) of a hypersonic flight vehicle or spacecraft. The metallic TPS (10) may comprise, for example, metal panels of honeycomb type (14) and a folded encapsulated insulation (16).

An example of a honeycomb panel (20) is shown schematically in FIG. 3A, and an exploded schematic view of a honeycomb panel (20) has been graphically depicted in FIG. 3B. The honeycomb panel (20) comprises a compartmentalized honeycomb core (22) interposed between and attached to opposite front faces (24), thus providing several closed cameras inside the panel. As used herein, the term "honeycomb panel" refers to a metal honeycomb core interposed or arranged in a sandwich between metal end faces. As used herein, the terms "honeycomb" and "honeycomb core" refer to a manufactured product that comprises a cell arrangement with a generally polygonal shape (eg, hexagonal shaped) formed to from an alloy sheet and which can be applied as core material interposed or arranged in sandwich form between two front faces of a metallic material or other suitable material to provide a honeycomb panel. As used herein, the term "front sheet" refers to a sheet, sheet, or metal plate that is bonded to a core of a metal bee panel as generally depicted in FIG. 2 to provide a honeycomb panel. The honeycomb cores are used to form honeycomb panels by joining, brassizing, welding, or otherwise joining the front sheets to the open cells of the honeycomb core. A honeycomb-type panel has high compression and shear properties, while minimizing the weight required to achieve these properties compared to a monolithic material. Honeycomb panels are used in aerospace, marine, and terrestrial applications to reduce vehicle weight and reduce fuel consumption. The methods for forming honeycomb cores, front sheets, and honeycomb panels are well known to those skilled in the art and, thus, are not further described herein.

It is believed that the aerospace industry has seriously considered only the use of metal TPS in the past 15 years, and little attention has been paid to the alloys used for the front sheet and the honeycomb core of the aerospace panels. In general, alloys hardened by precipitation have been avoided, and alloys hardened by dissolution or hardened by oxide dispersion have been used in TPS applications due to the inherent instability of the phase in the microstructure of a precipitation hardened alloy.

Certain non-limiting embodiments of the present invention are directed to heat treatment methods for nickel-based alloys that provide a microstructure that is generally stable when subjected to thermal cycling. Since the microstructure achieved by the present methods remains practically the same during the one or more thermal cycles to which the nickel-based alloy is subjected, the mechanical properties of the nickel-based alloy will remain practically the same at a particular temperature. when the alloy subjected to thermal cycling returns to said particular temperature. For example, non-limiting embodiments of the treatment methods thermal in accordance with the present disclosure provide a nickel-based alloy with certain properties at 1550 ° F (843, 3 ° C) in a second thermal cycle that are practically the same as the properties of the same nickel-based alloy at 1550 ° F (843, 3 ° C) in a thermal cycle of ten times, but which are not the same as the mechanical properties of the nickel-based alloy, for example, 1650 ° F (898, 9 ° C) or 1700 ° F (926, 7 ° C).

It has been determined that the phase? ' contributes little to the mechanical strength of the alloys with a low volumetric fraction of the phase? such as, for example, alloy 718, at temperatures above about 1500 ° F (815.6 ° C). Therefore, it has been determined that heat treatments designed to optimize the phase and 'are not beneficial for applications such as the TPS of hypersonic flying vehicles, which may experience repeated thermal cycling between room temperature and temperatures up to 2200 ° F. (1204 ° C). Thermal treatments that provide a stable microstructure during such thermal cycling would be beneficial for use in thermal protection systems.

For example, a non-limiting embodiment according to the present disclosure is directed to a method of heat treatment for a nickel-based alloy to produce a thermally stable microstructure in a nickel-based alloy of type 718 that is capable of withstanding thermal cycling between ambient temperatures at ground level and a maximum temperature of about 1450 ° F (787 , 8 ° C) to approximately 75 ° F (42 ° C) below the d-solvus temperature. The thermally stable microstructure is a microstructure that provides the alloy with mechanical properties that do not change practically when exposed to thermal cycling in a temperature range between room temperature and a maximum temperature in a range of approximately 1450 ° F (787, 8 ° C) at approximately 75 ° F (42 ° C) below the d-solvus temperature of the alloy. If a thermal cycling in service results in exposure of the nickel-based alloy to temperatures above the heat treatment temperature range according to the present disclosure, detrimental changes in the microstructure and mechanical properties of the alloy.

The d-solvus temperature for Alloy 718 is approximately 1881 ° F (1027 ° C). The d-solvus temperature for the ATI 718Plus® alloy is approximately 1840 ° F (1004 ° C). Temperatures d-solvus of other alloys of nickel base are known or can easily be determined without undue experimentation by a person ordinarily skilled in the metallurgical art.

In a non-limiting embodiment according to this disclosure, the method results in a concentration in equilibrium or close to the equilibrium of the intergranular boundary phase d in the intergranular boundaries of the austenite matrix, with a precipitation of up to 25 percent in total weight of the precipitates in phase? ' and phase? "Given the precipitation of a concentration in equilibrium or close to the equilibrium of the intergranular limit phase d in the embodiments according to this disclosure, the embodiments of the heat treatment methods according to this disclosure are referred to in the present document "thermal treatments in phase d".

The embodiments of the d-phase thermal treatments according to the present disclosure provide a volumetric fraction of the d-phase which does not decrease practically until the temperatures in service exceed approximately 75 ° F (42 ° C) below the temperature d- solvus Therefore, the embodiments of the thermal treatments in phase d described herein promote a stable microstructure for applications where temperatures can cycle to a maximum temperature of approximately 75 ° F (42 ° C) below the d-solvus temperature. The phase d precipitated in the intergranular limits according to the methods of the present disclosure also serves for the purpose of preventing grain growth, further stabilizing the microstructure. The embodiments of the d-phase thermal treatments described herein result in lower mechanical strengths in the alloys below about 1500 ° F (815.6 ° C). However, in comparison, while in service, a piece of nickel-based alloy of type 718 heat treated in a conventional manner subjected to temperatures in excess of 1500 ° F (815.6 ° C) would present only relatively greater mechanical strength at temperatures per below 1500 ° F (815, 6 ° C) for the first thermal cycle to which the piece is subjected.

Although not limiting herein, embodiments of the phase d thermal treatments described herein may be used in conjunction with nickel-based alloy compositions containing niobium (Nb), including nickel-based alloys of type 718. and derivatives thereof. As used herein, the term "nickel base alloy" is refers to an alloy that includes predominantly nickel, together with one or more different alloying elements and incidental impurities. As used herein, the term "nickel base alloy of type 718" means a nickel base alloy, as defined herein, which comprises or consists of nickel, chromium, iron, hardening additions of niobium, and optionally one or both of aluminum and titanium, together with incidental impurities. Non-limiting examples of nickel-based alloys of type 718 include Alloy 718 and other alloys which are described hereinafter.

A non-limiting example of a nickel-based alloy of type 718 for which it is believed that non-limiting embodiments of heat treatments according to the present disclosure are particularly well suited is a nickel-based alloy including nickel, chromium, up to 14 percent iron, niobium hardener additions, optionally one or both additions of the aluminum and titanium alloys, and incidental impurities. Another non-limiting example of a nickel-based alloy of type 718 for which it is believed that the non-limiting embodiments of thermal treatments according to the present disclosure are particularly very suitable is a nickel-based alloy, as defined herein, including chromium, from 6 to 14 percent iron, niobium hardener additions, optionally with one or more additions of aluminum and titanium alloys, and impurities incidental A further non-limiting example of a nickel-based alloys of type 718 for which the embodiments of the heat treatment methods according to the present disclosure can be carried out is the nickel-based alloy described in the United States patent. No. 6,730,264 ("the '264 patent"), which comprises or consists, in percent by weight: up to 0.1 carbon; from 12 to 20 of chromium; up to 4 molybdenum; up to 6 tungsten; from 5 to 12 cobalt; from 6 to 14 of iron; from 4 to 8 of niobium; from 0.6 to 2.6 of aluminum; from 0.4 to 1.4 titanium; from 0.003 to 0.03 phosphorus; from 0.003 to 0.015 boron; nickel; and incidental impurities; where the sum of the weight percentage of molybdenum and the weight percentage of tungsten is at least 2 and not more than 8; where the sum of the atomic percentage of aluminum and the atomic percentage of titanium is from 2 to 6; where the ratio between the atomic percentage of aluminum and the atomic percentage of titanium is at least 1.5; and where the sum of the atomic percentage of aluminum and the percentage atomic titanium divided by the atomic percentage of niobium is 0.8 to 1.3. The full disclosure of U.S. Patent No. 6,730,264 is hereby incorporated by reference.

Another non-limiting additional example of a nickel base alloy type 718 for which embodiments of the heat treatment methods according to the present disclosure can be carried out is the nickel base alloy described in the 'U.S. Pat. 264 and comprising or consisting of, in percent by weight: from 50 to 55 nickel; from 17 to 21 of chromium; from 2.8 to 3.3 molybdenum; from 4.7 to 5.5 niobium; up to 1 cobalt; from 0.003 to 0.015 boron; up to 0.3 copper; up to 0.08 carbon; up to 0.35 of manganese; from 0.003 to 0.03 phosphorus; up to 0.015 sulfur; up to 0.35 silicon; iron; aluminum; titanium; and incidental impurities; where the sum of an atomic percentage of aluminum and an atomic percentage of titanium is from about 2 to about 6 atomic percentage; where the ratio between the atomic percentage of aluminum and the atomic percentage of titanium is about 1.5; and where the sum of an atomic percentage of aluminum plus an atomic percentage of titanium divided by the atomic percentage of niobium is from 0.8 to 1.3. In certain embodiments of the alloy, the weight percentage of iron is from 12 to 20.

Another additional non-limiting example of a nickel-based alloy of type 718 for which the embodiments of the heat treatment methods according to the present disclosure can be carried out is the ATI 718Plus® alloy (UNS N07818), which is a nickel base alloy which is available from ATI Allvac, Monroe, North Carolina, USA, and which comprises or consists, in weight percent: from 17.00 to 21.00 chromium; from 2.50 to 3.10 molybdenum; from 5.20 to 5.80 niobium; from 0.50 to 1.00 titanium; from 1.20 to 1.70 aluminum; from 8.00 to 10.00 cobalt; from 8.00 to 10.00 iron; from 0.008 to 1.40 tungsten; from 0.003 to 0.008 of boron; from 0.01 to 0.05 carbon; up to 0.35 of manganese; up to 0.035 silicon; from 0.004 to 0.020 phosphorus; up to 0.025 sulfur; nickel; and incidental impurities. AMS 5441 and AMS 5442, which refer to bars, slabs, and rings resistant to corrosion and heat, are two AMS specifications that describe thermal treatments conventionally used with the ATI 718Plus® alloy. Each of AMS 5441 and AMS 5442 is hereby incorporated by reference herein in its entirety.

Another non-limiting example of an alloy of nickel base type 718 for which the embodiments of the heat treatment methods according to the present disclosure can be carried out is the alloy 718 (UNS N07718), whose composition is well known in the industry. In certain non-limiting embodiments, Alloy 718 comprises or consists, in percent by weight: from 50.0 to 55.0 nickel; from 17 to 21.0 of chromium; up to 0.08 carbon; up to 0.35 of manganese; up to 0.35 percent silicon; from 2.8 to 3.3 molybdenum; more than zero to 5.5 niobium and tantalum, where the sum of niobium and tantalum is 4.75 to 5.5; from 0.65 to 1.15 titanium; from 0.20 to 0.8 of aluminum; up to 0,006 boron; iron; and incidental impurities.

As used herein, the term "mechanical properties" refers to the properties of an alloy that refer to an elastic or inelastic reaction when the force is applied to the alloy, or which involves the relationship between stress and the deformation that is the result of the application of force to the alloy. The mechanical properties included in the meaning of the present disclosure relate specifically to tensile strength, yield strength, elongation, and stress fracture life. As used herein, the expression "mechanical properties "thermally stable" refers to a condition where the mechanical properties of an alloy do not change by more than 20% when the alloy undergoes repeated thermal cycling enters the room temperature at ground level and 75 ° F (41.7 °) C) below the d-solvus temperature As used herein, the term "ambient temperature at ground level" is defined as any ambient temperature from a natural terrestrial climate at ground level.

The present inventors have pointed out an impact of the peak temperature of the thermal cycle on the degree of deterioration of the mechanical properties for the nickel-based alloys for a given phase d heat treatment in accordance with the non-limiting embodiments of the present disclosure. The choice of the heat treatment temperature in phase d should be selected to match or correspond closely to the expected peak temperature in service of the nickel base alloy.

Referring now to FIG. 4, in a non-limiting embodiment according to the present disclosure, a method for heat treatment of a nickel-based alloy (30) of type 718 comprises: heating (32) a nickel-based alloy of type 718 to a temperature of heat treatment in a temperature range of heat treatment; maintaining (34) the nickel base alloy of type 718 within the range of heat treatment temperature during a sufficient heat treatment time to form a concentration in equilibrium or close to equilibrium of the precipitates in phase d the intergranular boundary in the alloy of nickel base, and also up to the formation of up to 25 percent by weight of total phase? ' and phase? "in the nickel-based alloy; and air-cooling (36) of the nickel-based alloy of type 718.

As used herein, the term "heat treatment temperature" is defined as a temperature that results in the precipitation of a concentration in equilibrium or close to equilibrium of a nickel base alloy of type 718 and up to 25%. percent in total phase weight? ' and phase? "As used herein, the term" thermal treatment time "means a time sufficient to precipitate a concentration in equilibrium or close to equilibrium of the phase d precipitates at the intergranular limits of an aluminum alloy. base nickel type 718 and up to 25 percent by total phase weight? ' and phase? " . As used herein, the term "equilibrium concentration" is defined as the maximum concentration of the precipitates in phase d which can be formed at the heat treatment temperature according to the composition of the nickel base alloy or the nickel base alloy of type 718. As used herein, the term "concentration close to the "equilibrium" means the condition where a nickel-based alloy includes about 5 percent to about 35 percent by weight of phase d within the intergranular boundaries. In a non-limiting embodiment, after a d-phase heat treatment, the nickel-based alloy can include from about 6 percent to about 12 percent by weight of phase d precipitate within the intergranular boundaries. It was observed that said result was normal for Alloy 718. In another non-limiting embodiment, after a d-phase heat treatment, the nickel-based alloy can include from about 10 percent to about 25 percent by weight of precipitate in phase d in the intergranular limits, it was observed that said result was normal for the ATI 718Plus® alloy. It should be understood that the quantity in phase d, phase? ' , and phase? "formed during a d-phase heat treatment according to the present disclosure depends to some degree on the specific composition of the nickel-based alloy, and that the amount formed of said phases can be readily determined without undue experimentation by persons ordinarily skilled in the art.

In a non-limiting embodiment, the heat treatment temperature is in a heat treatment temperature range having a lower limit of 20 ° F (11 ° C) greater than the nose of the Time-Temperature-Transformation diagram ("TTT diagram"). ") for a phase d precipitation for the specific nickel base alloy, up to an upper limit that is 100 ° F (55.6 ° C) below the nose for a phase d precipitation in the specific TTT diagram. A TTT diagram for a concrete nickel base alloy is a graphical representation of the temperature as a function of the time logarithm for the alloy. TTT diagrams are used to determine when the transformations of the second phase begin and end, such as the transformations in phase d, phase? ' , and phase? ", during an isothermal heat treatment for a nickel base alloy previously treated by dissolution A person skilled in the art understands that a concrete TTT diagram is specific to a particular alloy composition. TTT diagram for an embodiment of the 718 Alloy, and a typical TTT diagram for the ATI 718Plus® alloy in FIG. 5B. The precipitation curve in phase d in these TTT diagrams is marked "d (GB)" in FIG. 5A and "d (grain)" in FIG. 5B. As understood by a person skilled in the art, a normally skilled person knows the "nose" of the phase curve d as the portion of the curve in phase d that is plotted in the direction of the time point earlier in the time axis . For example, the nose of the curve in phase d in FIG. 5A occurs at about 0.045 hours and about 900 ° C. The nose of the curve in phase d in FIG. 5B occurs at about 0.035 hours and about 900 ° C. The curves shown in FIG. 5A and FIG. 5B are reproduced from Xie, et al., "TTT Diagram of a Newly Developed Nickel-Base Superalloy -Allvac 718Plus®, Proceedings: Superalloys 718, 625, 706 and Derivatives 2005, TMS (2005) pp. 193-202, which is The present document is hereby incorporated by reference.A person who is ordinarily skilled in the art is capable of interpreting and using TTT diagrams and, therefore, no additional description is needed concerning the use of TTT diagrams in this document. TTT diagrams for nickel-based specific alloys are publicly available or can be generated by a person ordinarily skilled in the art without excessive experimentation Referring to the schematic temperature-time profile of the heat treatment (40) shown in FIG. 6, and with reference to the method steps shown generally in FIG. 4, a non-limiting embodiment of a method for heat treatment of a nickel-based alloy of type 718 according to the present disclosure comprises heating (32) a nickel-based alloy of type 718 to a heat treatment temperature in a range of heat treatment temperatures of 1700 ° F (926, 7 ° C) to 1725 ° F (940, 6 ° C). In a non-limiting embodiment of the method, the heated nickel-type base 718 alloy is maintained (34) in the range of the heat treatment temperature during a heat treatment time of 30 minutes to 300 minutes. After holding it (34) at the heat treatment temperature during the heat treatment time, the nickel base alloy of type 718 is cooled with air and retains the phase d precipitates at the intergranular boundaries. According to the embodiments of the d-phase heat treatment method described herein, the precipitates at the intergranular boundary in phase d are formed mainly during the heating (32) and maintenance (34) steps. By this reason, the heating (32) and maintenance (34) stages can be referred to collectively as "aging in phase d" In a non-limiting embodiment, after keeping the nickel base alloy in the heat treatment temperature range during the heat treatment time, the nickel base alloy is cooled with air from the heat treatment temperature to room temperature. In a specific non-limiting embodiment, the nickel-based alloy is cooled at a cooling rate not greater than 1 ° F (0.56 ° C) per minute. Slow cooling is advantageous in certain non-limiting embodiments according to the present disclosure because some phase precipitation is possible? in a nickel base alloy. The small amount of phase? ' which can precipitate during cooling will be within the structure in the form of coarse particles and, therefore, will have greater stability with respect to thermal cycling and less impact on the mechanical properties of the alloy. It is preferred to have small amounts of precipitate in phase? ' relatively stable during slow cooling than having an uncontrolled precipitation of the phase? ' during thermal cycling in the service.

The alloys processed according to any of the methods described herein can be formed into ground products or other articles of manufacture. In certain non-limiting embodiments according to the present disclosure, the nickel base alloy of type 718 is processed in a manufacturing article selected from a sheet, a honeycomb core, a front sheet, and a honeycomb panel of bee by a method that includes an embodiment of a method described herein. As used herein, the term "sheet" refers to a sheet having a thickness less than 0.006 inches (0.15 mm) and any width and length. Practically, the width of a sheet is limited by the capacity of the cold rolling equipment used to laminate the alloy. In certain non-limiting embodiments of the methods according to the present disclosure, the alloys processed according to the embodiments of the methods described herein can be processed into sheets having a width of up to 18 inches (0.46 m) , up to 24 inches (0.61 m), or up to 36 inches (0.91 m).

For applications in which the maximum temperature in service to which the alloy will be subjected is known and is approximately 1700 ° F (926, 7 ° C) or less, non-limiting embodiments of a method according to the present disclosure may further include a stabilizing heat treatment subsequent to the cooling step of the nickel base alloy from the temperature of heat treatment. In a non-limiting embodiment according to the present disclosure, the stabilizing heat treatment comprises heating the nickel-based alloy to a stabilizing heat treatment temperature and maintaining the alloy at the temperature for at least 2 hours, or for at least 2 hours to 4 hours. In non-limiting embodiments, the temperature of the stabilizing heat treatment is the maximum temperature in service at which the alloy is to be subjected and is in a range of 1700 ° F (926, 7 ° C) or less, or in a range of 1700 ° F (926, 7 ° C) at 1450 ° F (787, 8 ° C). As used herein, the term "maximum temperature in service" refers to the maximum temperature expected to be experienced by the particular nickel-based alloy when the alloy or an article including the alloy is used for its intended purpose . Subsequent to the stabilizing heat treatment according to the present disclosure, the nickel-based alloy is cooled with air from the heat treatment temperature stabilizing to the room temperature. In another non-limiting embodiment, the nickel-based alloy is cooled at a cooling rate not greater than 1 ° F (0.56 ° C) per minute from the temperature of the stabilizing heat treatment to room temperature.

It is recognized that the non-limiting embodiments of the d phase heat treatment and d phase aging according to this disclosure could be used in any form or shape of the nickel base alloy or the nickel base alloy of type 718. Various forms include commercial milled products such as, but not limited to, bar, rod, plate, sheet, web, and extrusion. It is further recognized that non-limiting embodiments of the d-phase heat treatment and d-phase aging according to this disclosure could also be used as fabricated products such as, but not limited to, shaped products, bonded products, and the like comprising alloys of base nickel or nickel-based alloys of type 718.

In a non-limiting embodiment of a method of heat treatment of a nickel-based alloy according to the present disclosure, the nickel-based alloy comprises or consists, in percent by weight: 17.00 to 21.00 chromium; from 2.50 to 3.10 molybdenum; from 5.20 to 5.80 niobium; from 0.50 to 1.00 titanium; from 1.20 to 1.70 aluminum; from 8.00 to 10.00 cobalt; from 8.00 to 10.00 iron; from 0.008 to 1.40 tungsten; from 0.003 to 0.008 of boron; from 0.01 to 0.05 carbon; up to 0.35 of manganese; up to 0.035 silicon; from 0.004 to 0.020 phosphorus; up to 0.025 sulfur; nickel; and incidental impurities. Said non-limiting embodiment further comprises: heat treating the nickel-based alloy at a heat treatment temperature in a range of 1700 ° F (926, 7 ° C) to 1725 ° F (940, 6 ° C); maintaining the nickel base alloy at the heat treatment temperature during a heat treatment time in a range of 30 minutes to 300 minutes, which is sufficient to form a concentration in equilibrium or close to the equilibrium of the phase d precipitates of the intergranular boundary inside the nickel-based alloy and up to 25 percent by weight of phase? ' and overall phase "inside the alloy, and air cooling of the nickel-based alloy In non-limiting embodiments, the nickel-based alloy comprises one of a sheet, a honeycomb core, a front sheet, and a honeycomb panel.

A non-limiting aspect according to the present The disclosure is directed to a nickel base alloy of type 718, as this term is defined herein, and which comprises an austenite matrix that includes intergranular boundaries. A concentration in equilibrium or close to the equilibrium of precipitates in phase d is present in the intergranular limits, and up to 25 percent in total weight of the phase? and the total phase? "is present in the alloy.

A specific non-limiting example of a nickel base alloy of type 718 according to the present disclosure comprises an austenite matrix including intergranular boundaries, a concentration in equilibrium or close to the equilibrium of phase d precipitates at the intergranular boundaries, with an precipitation of up to 25 percent by total weight of precipitates in phase? ' and phase? "and up to 14 weight percent iron Another non-limiting specific example of a nickel base alloy of type 718 according to the present disclosure comprises an austenite matrix including intergranular boundaries, an equilibrium concentration or close to the equilibrium of precipitates in phase d in the intergranular limits, with a precipitation of up to 25 percent by total weight of the precipitates in the phase? and phase? " . and from 6 percent to 14 percent in weight of iron.

Another specific non-limiting example of a nickel-based alloy of type 718 according to the present disclosure comprises an austenite matrix which includes the intergranular boundaries, a concentration close to the equilibrium of precipitates in phase d at the intergranular boundaries, and up to 25 percent by total weight of the precipitates in phase? ' and phase? "The alloy also comprises or consists of, in percentage by weight: up to 0.1 carbon; from 12 to 20 of chromium; up to 4 molybdenum; up to 6 tungsten; from 5 to 12 cobalt; from 6 to 14 of iron; from 4 to 8 of niobium; from 0.6 to 2.6 of aluminum; from 0.4 to 1.4 titanium; from 0.003 to 0.03 phosphorus; from 0.003 to 0.015 boron; nickel; and incidental impurities; where the sum of the weight percentage of molybdenum and the weight percentage of tungsten is at least 2 and not more than 8; the sum of the atomic percentage of aluminum and the atomic percentage of titanium is from 2 to 6; the ratio between the atomic percentage of aluminum and the atomic percentage of titanium is at least 1.5; and the sum of the atomic percentage of aluminum and the atomic percentage of titanium divided by the atomic percentage of niobium is 0.8 to 1.3.

Another additional non-limiting specific example of a nickel base alloy of type 718 according to the present disclosure comprises an austenite matrix which includes the intergranular boundaries, a concentration close to the equilibrium of precipitates in phase d at the intergranular limits, and up to 25 percent by total weight of the precipitated in the phase? ' and phase and "The alloy comprises or further comprises, in weight percent: from 0 to about 0.08 carbon, from 0 to about 0.35 carbon, from about 0.003 to about 0.03 phosphorus; 0 to about 0.015 of sulfur, of about 0 to about 0.35 of silicon, of about 17 to about 21 of chromium, of about 50 to about 55 of nickel, of about 2.8 to about 3.3 of molybdenum, of about 4.7 to about 5.5 niobium, from 0 to about 1 cobalt, from 0.003 to about 0.015 boron, from 0 to about 0.3 copper, and iron moiety (typically from about 12 to about 20 per cent) cent), aluminum, titanium, and incidental impurities, where the sum of an atomic percentage of aluminum and an atomic percentage of titanium is from about 2 to about 6 percent, the ratio between the atomic percentage of aluminum and the atomic percentage of t titanium is approximately 1.5; Y the sum of an atomic percentage of aluminum plus an atomic percentage of titanium divided by the atomic percentage of niobium is equal to about 0.8 to about 1.3.

A further specific non-limiting example of a nickel base alloy of type 718 according to the present disclosure comprises an austenite matrix including intergranular boundary, a concentration close to equilibrium of phase d precipitates at intergranular boundaries, and up to 25 percent in total weight of the precipitates in phase? ' and phase? "The alloy also comprises or consists, in percent by weight: from 0.01 to 0.05 carbon, up to 0.35 manganese, up to 0.035 silicon, from 0.004 to 0.020 phosphorus, up to 0.025 of sulfur, from 17.00 to 21.00 of chromium, from 2.50 to 3.10 of molybdenum, 5.20 to 5.80 of niobium, 0.50 to 1.00 of titanium, of 1.20 a 1.70 of aluminum, from 8.00 to 10.00 of cobalt, of 8.00 to 10.00 of iron, of 0.008 to 1.40 of tungsten, of 0.003 to 0.008 of boron, nickel, and impurities incidental A further more specific non-limiting example of a nickel base alloy of type 718 according to the present disclosure comprises an austenite matrix including intergranular boundary, a close concentration to the balance of precipitates in phase d in the intergranular limits, and up to 25 percent in total weight of the precipitates in the phase? and phase? "The alloy comprises or further comprises, in percent by weight: from 50.0 to 55.0 nickel, from 17 to 21.0 chromium, up to 0.08 carbon, up to 0.35 manganese, up to 0.35 silicon, 2.8 to 3.3 molybdenum, more than 0 to 5.5 niobium and tantalum, where the sum of niobium and tantalum is 4.75 to 5.5; 0.65 to 1.15 titanium, 0.20 to 0.8 aluminum, up to 0.006 boron, iron, and incidental impurities.

One aspect of this disclosure includes an article of manufacture manufactured in accordance with a method of this disclosure and / or including an alloy in accordance with this disclosure. Non-limiting examples of articles of manufacture in accordance with this disclosure include a front sheet, a honeycomb core, and a honeycomb panel of a TPS for a hypersonic flight vehicle or spacecraft.

It is intended that the following examples further describe certain non-limiting embodiments, without restricting the scope of the present invention. Persons who are ordinarily skilled in the art will appreciate that variations of the following examples within the scope of the invention are possible. defined solely by the claims.

EXAMPLE 1 A 0.080 inch (2.03 mm) thick sheet of the ATI 718Plus® alloy and a 0.4 inch (10.2 mm) diameter rod of the Alloy 718 were heat treated in accordance with a non-limiting embodiment of the present disclosure by heating the two alloys to 1725 ° F (940, 6 ° C) and maintaining at temperature for 3 hours. The samples were then cooled with air.

For comparison purposes, samples of the same alloys were thermally treated in accordance with the following normalized 'normal' aging treatments.

A 0.080 inch (2.03 mm) thick sheet of ATI 718Plus® alloy was heated to 1750 ° F (954.4 ° C), maintained at the temperature for 45 minutes, and air-cooled. After cooling, the sample was aged at 1450 ° F (787, 8 ° C) for 8 hours. The sample was cooled to 100 ° F / h (55.6 ° C / h) at 1300 ° F (704, 4 ° C), and maintained at 1300 ° F (704, 4 ° C) for 8 hours. After aging, the sample of the ATI 718Plus® alloy was cooled with air.

In addition, a rod with a diameter of 0.4 inches (10.2 mm) of Alloy 718 was heated to 1750 ° F (954, 4 ° C), kept at the temperature for 45 minutes, and cooled with air. After cooling, the sample of Alloy 718 was aged at 1325 ° F (718, 3 ° C) for 8 hours. The sample was cooled to 100 ° F / h (55.6 ° C / h) to 1150 ° F (621, 1 ° C), and maintained at 1150 ° F (621, 1 ° C) for 8 hours. After aging, the sample was cooled with air.

EXAMPLE 2 The heat treated samples from Example 1 were subjected to thermal cycling. Samples of the ATI 718Plus® alloy were cycled from room temperature to either 1650 ° F (898.9 °) or 1550 ° F (843, 3 ° C). Samples of Alloy 718 were cycled from room temperature to 1650 ° F (898.9 °). Fig. 7 is a schematic representation of the thermal cycles used, where the indicated temperatures are of the alloy samples, and not the furnace temperature. The upper graphic representation included in FIG. 7 reflects a slower cooling rate of the alloy (approximately 10 ° F / min (5.6 ° C / min)) and represents the general behavior of the thickest samples. The lower graphic representation reflects a faster cooling rate (approximately 1500 ° F / min (833 ° C / min)) and represents the general behavior of the finest samples. The cooling rates depicted graphically in FIG. 7 are estimated, but peak temperatures and holding times in FIG. 7 accurately represent what the alloys experienced.

EXAMPLE 3 After exposure to thermal cycling, the samples were subjected to a tensile test at room temperature according to the standardized test procedures described in ASTM E8-09 / E8M-09. Burst strain graphs of thermally treated samples and after 1 and 5 thermal cycles are given in FIG. 8. The graphs on the left side of FIG. 8 show the breaking stresses as a function of the number of heat treatment cycles for samples of the ATI 718Plus® alloy that were cooled at the slower cooling rate discussed in Example 2. The graphs on the right side of FIG. 8 shows the breaking stresses as a function of the number of heat treatment cycles for the ATI 718Plus® alloy which was cooled to the fastest cooling rate discussed in Example 2. The upper row of graphs in FIG. 8 correspond to the ATI 718Plus® alloy which was thermally treated according to the embodiments of the present disclosure as described in Example 1, thermally cycled at a peak sample temperature of 1650 ° F (898, 9 ° C) . The lower row of graphs in FIG. 8 correspond to the ATI 718Plus® alloy which was thermally treated according to the embodiments of the present disclosure as described in Example 1, thermally cycled at a peak sample temperature of 1550 ° F (843, 3 ° C) .

The examination of FIG. 8 shows that the aging treatments of the inventive step d can provide initial mechanical strengths lower than those of conventional? /? "Aging treatments, but there is significantly less variability in the tensile stress during thermal cycling. evident in Fig. 9, which shows the data of Fig. 8 but where the y-axis represents the relationship between the breaking stress after the sample was subjected to thermal cycling and the breaking stress in the thermally-treated condition. Fig. 9 clearly shows that the performance of the d-phase heat treatment according to the present disclosure produced an alloy that had a significantly higher breaking stress. stable after thermal cycling for at least 5 thermal cycles.

Fig. 10 includes graphs of the elastic limits of the samples included in FIG. 8. The graphs of FIG. 10 are in the same orientations as in FIG. 8 with respect to the cooling rates and the peak temperatures of the samples. Considering what is shown in FIG. 10, it will be noted that the aging treatments of the inventive step d can provide lower initial elastic limits than those of conventional aging '/?' Treatments, but with significantly less variability of the elastic limits for the alloys heat treated in the phase d during thermal cycling This is more evident in FIG 11, which shows the data of FIG 10 but where the y-axis represents the relationship between the elastic limit after the sample was subjected to thermal cycling and the Fig. 11 shows clearly that the performance of the d-phase heat treatment according to the present disclosure produced an alloy having a significantly more stable elastic limit after thermal cycling for at least 5 thermal cycles .

Fig. 12 includes graphs of the percentage of elongation of the samples included in FIG. 8. The graphs of FIG. 12 are in the same orientations as in FIG. 8 with respect to the cooling rates and the peak temperatures of the samples. Considering what is shown in FIG. 12, it will be noted that the aging treatments of the inventive step d can provide higher elongation rates than those of the conventional '/? "Aging treatments, but with significantly less variability of the elongation percentage for the d phase during the cyclization This is most evident in FIG.13, which shows the data of FIG.12 but where the y-axis represents the relationship between the percentage of elongation after the sample was subjected to thermal cycling and the percentage of elongation in The thermally treated condition Fig. 13 clearly shows that carrying out the d-phase heat treatment according to the present disclosure produced an alloy having a significantly more stable elongation percentage after thermal cycling for at least 5 thermal cycles.

Samples of Alloy 718 that were thermally treated in Example 1 and thermally cycled at 1650 ° F (898.9 °) in Example 2 were tested in a tensile test at room temperature according to the standardized test procedures described in ASTM E8-09 / E8M-09. Graphs of resistance to breakage of thermally treated samples and after 1 and 5 thermal cycles are shown in FIG. 14. The graphs on the left side of FIG. 14 show the breaking strengths as a function of the number of heat treatment cycles for Alloy 718 which was thermally cycled using the slower cooling rate described in Example 2, and the graphs on the right were thermally cycled using the velocity of faster cooling described in Example 2.

The examination of FIG. 14 shows that the aging treatments of the inventive step d can provide an alloy having initial mechanical strengths lower than those of conventional aging '/?' Treatments, but also having significantly less variability of the breaking stress when it undergoes thermal cycling This is more evident in FIG.15, which shows the data of FIG.14 but where the y-axis represents the relationship between the breaking stress after the sample was subjected to thermal cycling and stress of breakage in the condition heat treated. Fig. 15 clearly shows that the conduct of the d-phase heat treatment according to the present disclosure produced an alloy having a significantly more stable breaking stress after thermal cycling for at least 5 thermal cycles.

Fig. 16 includes graphs of the elastic limits of the samples included in FIG. 14. The graphs of FIG. 16 are in the same orientations as in FIG. 14 with respect to the cooling rates and peak temperatures of the samples. Considering what is shown in FIG. 16, it will be noted that the aging treatments of the inventive step d can provide lower initial elastic limits than those of conventional? /? "Aging treatments, but with significantly less variability of the elastic limits for the alloys heat treated in the phase d during thermal cycling This is most evident in FIG.17, which shows the data of FIG.16 but where the y-axis represents the relationship between the elastic limit after the sample was subjected to thermal cycling and the elastic limit in the thermally treated condition Fig. 17 clearly shows that the realization of the thermal treatment in phase d according to with the present disclosure it produced an alloy which had a significantly more stable elastic limit after thermal cycling for at least 5 thermal cycles.

Fig. 18 includes graphs of the percentage of elongation of the samples included in FIG. 14. The graphs of FIG. 18 are in the same orientations as in FIG. 14 with respect to the cooling rates and peak temperatures of the samples. Considering what is shown in FIG. 18, it will be observed that the aging treatments of the inventive phase d can provide higher percentages of elongation than those of the aging treatments? ' /? "conventional, but with significantly less variability of the elongation percentage for phase d during thermal cycling This is more evident in FIG.19, which shows the data of FIG.18 but where the y-axis represents the ratio between the percentage of elongation after the sample was subjected to thermal cycling and the percentage of elongation in the thermally treated condition Fig. 19 clearly shows that performing the d-phase heat treatment according to the present disclosure produced an alloy which had a percentage of elongation significantly more stable after thermal delation during at least 5 thermal cycles.

EXAMPLE 4 The surface regions of the samples that were tested for a tensile test in Example 3 were examined using a dark field optical microscope. Fig. 20A is a photomicrograph of a surface region of an ATI 718Plus® alloy sample that was thermally treated as described in Example 1. The thicker white platelets that were arranged primarily at the intergranular boundaries in FIG. 20A are platelets in phase d which are the result of the heat treatment in phase d according to the non-limiting embodiments of the present disclosure. Fig. 20B is a photomicrograph of a surface region of the same sample of ATI 718Plus® alloy after undergoing 5 thermal cycles at a peak sample temperature of 1650 ° F (898.9 °). It can be observed that there is little, if any, difference in the amount of platelets in phase d in the samples after 5 thermal cycles at a peak temperature of the sample of 1650 ° F (898, 9 °). This correlates well with the tensile test tests of Example 3 which show that the ATI alloy samples 718Plus® in phase d heat treated as described in Example 1 exhibited lower variability in tensile properties during thermal cycling.

FIG. 20C is a photomicrograph of a surface region of an ATI 718Plus® alloy sample that was thermally treated in accordance with the conventional? '/? "Heat treatment described in Example 1. It has been observed that the microstructure includes a small amount of precipitates in the intergranular boundary in phase d and that the amount is less than in the samples subjected to the heat treatment in phase d, as observed in FIG 20A, however, it has been observed in FIG. 20D that, after the 5 thermal cycles at 1650 ° F (898.9 °), the microstructure has clearly changed to include a significant amount of phase d at the intergranular boundaries.This change in the microstructure resulting from the thermal cycling was reflected in the deterioration in tensile properties of nickel-based superalloy samples? '/? " heat treated and thermally cycled presented in Example 3.

Fig. 21A is a photomicrograph of a surface region of an ATI 718Plus® alloy sample that was thermally treated as described in Example 1.

The thicker white plates mainly at the intergranular boundaries are platelets in phase d which are the result of the heat treatment in phase d according to the non-limiting embodiments of the present disclosure. Fig. 2 IB is a photomicrograph of a surface region of the same sample after 5 thermal cycles at a peak temperature of the sample of 1550 ° F (843, 3 ° C). It can be observed that there is little, if any, difference in the amount of platelets in phase d after 5 thermal cycles at a peak temperature of the sample of 1550 ° F (843, 3 ° C). This correlates well with the tensile tests of Example 3, which show that thermally treated ATI 718Plus® alloy samples in d as described in Example 1 exhibited lower variability of tensile properties in the cyclisation. thermal Fig. 21C is a photomicrograph of a surface region of an ATI 718Plus® alloy sample that was thermally treated according to the heat treatment? /? "conventional described in Example 1. It is observed that the microstructure can include a small amount of precipitates in the intergranular boundary in phase d, and that the amount is smaller than in the samples subjected to the thermal treatment in phase d, as has observed in the FIG. twenty-one?. However, it has been observed in FIG. 21D that, after the 5 thermal cycles at 1550 ° F (843, 3 ° C), the microstructure has clearly changed to include a significant amount of phase d at the intergranular boundaries. This change in the microstructure resulting from the thermal cycling was reflected in the deterioration in the tensile properties of the thermally treated and thermally cycled nickel-based superalloy superalloy samples presented in Example 3.

Fig. 22A is a photomicrograph of a surface region of an Alloy 718 sample that was thermally treated in phase d as described in Example 1. The thicker white plates that are mainly in the intergranular boundaries are platelets in phase d which are the result of the heat treatment in phase d according to the non-limiting embodiments of the present disclosure. Fig. 22B is a photomicrograph of a surface region of the same sample after 5 thermal cycles at a peak sample temperature of 1650 ° F (898, 9 ° C). It is observed that there is little, if any, difference in the amount of platelets in phase d after 5 thermal cycles at a peak temperature of the sample of 1650 ° F (898, 9 ° C). This correlates well with the tensile tests of Example 3, which show that the samples of ATI 718 alloy in thermally treated phase d as described in Example 1 exhibited lower variability of tensile properties in thermal cycling.

Fig. 22C is a photomicrograph of a surface region of an ATI 718 alloy sample that was thermally treated in accordance with the conventional? '/? "Heat treatment described in Example 1. It is noted that the microstructure may include a small amount of precipitates in the intergranular boundary in phase d, and that the amount is less than in the samples subjected to the heat treatment in phase d, as observed in FIG.22A, however, it has been observed in FIG. after the 5 thermal cycles at 1650 ° F (898.9 °), the microstructure has clearly changed to include a significant amount of phase d at the intergranular boundaries.This change in the microstructure resulting from the thermal cycling was reflected in the deterioration in tensile properties of nickel-based superalloys? '/? " heat treated and thermally cycled presented in Example 3.

The present disclosure has been written with reference to various exemplary, illustrative, and non-limiting embodiments. People who are normally experts in It will be recognized that various substitutions, modifications, or combinations of the described embodiments (or parts thereof) may be made without departing from the scope of the invention, which is defined solely by the claims. In this way, it is contemplated and understood that the present disclosure encompasses additional embodiments that are not expressly shown herein. This disclosure is not limited by the description of the various exemplary, illustrative, and non-limiting embodiments, but rather solely by the claims. Thus, it will be understood that the claims can be amended during the process of the present patent application to add features to the claimed invention as variously described herein.

Claims (26)

1. CLAIMS 1. A method for heat treating a nickel-based alloy, comprising: heating a nickel base alloy of type 718 to a heat treatment temperature in a range of heat treatment temperatures; maintaining the alloy within the range of heat treatment temperatures for a sufficient heat treatment time to form a concentration in equilibrium or close to equilibrium of the intergranular boundary precipitates in phase d of the alloy and up to 25 percent by total weight of phase? ' and phase? "inside the alloy; Cool the nickel base alloy. 2. The method of claim 1, wherein the temperature range of heat treatment is in the range of a temperature that is 20 ° F (11 ° C) greater than the nose of the TTT diagram for delta-phase precipitation at a temperature that is 100 ° F (55.6 ° C) below the nose of the TTT diagram. 3. The method of claim 1, wherein the thermal treatment time is in a range of 30 minutes to 300 minutes. 4. The method of claim 1, wherein the cooling of the nickel base alloy comprises cooling with air. 5. The method of claim 1, wherein the cooling of the nickel base alloy comprises cooling the alloy at a cooling rate not greater than 1 ° F (0.56 ° C) per minute. 6. The method of claim 1, wherein the nickel base alloy of type 718 comprising nickel, chromium, and iron. it is hardened by niobium, and optionally comprises one or more alloy additions of aluminum and titanium. 7. The method of claim 1, wherein the nickel base alloy of type 718 comprises, in percent by weight: up to 0.1 carbon; from 12 to 20 of chromium; up to 4 molybdenum; up to 6 tungsten; from 5 to 12 cobalt; from 6 to 14 of iron; from 4 to 8 of niobium; from 0.6 to 2.6 of aluminum; from 0.4 to 1.4 titanium; from 0.003 to 0.03 phosphorus; from 0.003 to 0.015 boron; nickel; and incidental impurities; where the sum of the weight percentage of molybdenum and the weight percentage of tungsten is at least 2 and not more than 8; the sum of the atomic percentage of aluminum and the atomic percentage of titanium is from 2 to 6; the ratio between the atomic percentage of aluminum and the atomic percentage of titanium is at least 1.5; and the sum of the atomic percentage of aluminum and the atomic percentage of titanium divided by the atomic percentage of niobium is 0.8 to 1.3. 8. The method of claim 1, wherein the nickel base alloy of type 718 comprises, in weight percent: from 0 to about 0.08 carbon; from 0 to about 0.35 carbon; from about 0.003 to about 0.03 phosphorus; from 0 to about 0.015 sulfur; from 0 to about 0.35 of silicon; from about 17 to about 21 chromium; from about 50 to about 55 nickel; from about 2.8 to about 3.3 molybdenum; from about 4.7 percent to about 5.5 niobium; from 0 to about 1 cobalt; from about 0.003 to about 0.015 of boron; from 0 to about 0.3 copper; from 12 to 20 of steel-aluminum; titanium; and incidental impurities; where the sum of an atomic percentage of aluminum and an atomic percentage of titanium is from about 2 to about 6 percent; the ratio between the atomic percentage of aluminum and the atomic percentage of titanium is about 1.5; and the sum of an atomic percentage of aluminum plus titanium divided by the atomic percentage of niobium is equal to about 0.8 to about 1.3. 9. The method of claim 1, wherein the nickel base alloy of type 718 comprises, in percent by weight: from 0.01 to 0.05 carbon; up to 0.35 of manganese; up to 0.035 silicon; from 0.004 to 0.020 phosphorus; up to 0.025 sulfur; from 17.00 to 21.00 chromium; from 2.50 to 3.10 molybdenum; from 5.20 to 5.80 niobium; from 0.50 to 1.00 titanium; from 1.20 to 1.70 aluminum; from 8.00 to 10.00 cobalt; from 8.00 to 10.00 iron; from 0.008 to 1.40 tungsten; from 0.003 to 0.008 of boron; nickel; and incidental impurities. 10. The method of claim 1, wherein the nickel base alloy of type 718 comprises, in weight percent: from 50.0 to 55.0 nickel; from 17 to 21.0 of chromium; up to 0.08 carbon; up to 0.35 of manganese; up to 0.35 silicon; from 2.8 to 3.3 molybdenum; more than 0 to 5.5 niobium and tantalum, where the sum of niobium and tantalum is 4.75 to 5.5; from 0.65 to 1.15 titanium; from 0.20 to 0.8 of aluminum; up to 0.006 of boron; iron; and incidental impurities. The method of claim 1, wherein the nickel base alloy of type 718 comprises at least one of a sheet, a honeycomb core, and a honeycomb panel. 12. The method of claim 1, further comprising, after the cooling of the alloy, a thermal treatment of stabilization of the alloy, where the thermal stabilization treatment comprises: heating the nickel-based alloy of type 718 to a stabilization heat treatment temperature of 1700 ° F (926, 7 ° C) or less, where the heat treatment temperature is equivalent to a maximum expected service temperature of an article that it comprises the alloy; Y Cool the alloy from the stabilization heat treatment temperature. 13. The method of claim 12, wherein the cooling of the alloy from the stabilization heat treatment temperature comprises cooling with air. 14. The method of claim 12, wherein the cooling of the alloy from the temperature of the stabilization heat treatment comprises cooling at a cooling rate not greater than about 1 ° F per minute (0.56 ° C per minute). 15. A method for heat treating a nickel-based alloy, comprising: heating a nickel-based alloy to a heat treatment temperature in a range of 1700 ° F (926, 7 ° C) to 1725 ° F (940, 6 ° C); maintaining the alloy at the heat treatment temperature during a heat treatment time in a range of 30 minutes to 300 minutes; Y air-cooling the nickel-based alloy; where the alloy comprises, in percentage by weight, 17.00 to 21.00 for chromium, 2.50 to 3.10 for molybdenum, 5.20 to 5.80 for niobium, from 0.50 to 1.00 for titanium, from 1.20 to 1, 70 from aluminum, from 8.00 to 10.00 for cobalt, from 8.00 to 10.00 for iron, from 0.008 to 1.40 for tungsten, from 0.003 to 0.008 for boron, from 0.01 to 0 , 05 of carbon, up to 0.35 of manganese, up to 0.035 of silicon, from 0.004 to 0.020 of phosphorus, up to 0.025 of sulfur, nickel, and incidental impurities. 16. The method of claim 15, further comprising, after cooling the nickel-based alloy, a thermal treatment of stabilization of the nickel-based alloy, wherein the thermal stabilization treatment comprises: heating the nickel base alloy to a temperature of the stabilization heat treatment which is a maximum expected service temperature of an article comprising the nickel base alloy and is approximately 1700 ° F (926, 7 ° C) or less; Y air-cooling the nickel-based alloy. 17. The method of claim 15, wherein the nickel base alloy comprises at least one of a sheet, a honeycomb core, and a honeycomb panel. 18. A nickel-based alloy of type 718 comprising: an austenite matrix including intergranular boundary; a concentration in equilibrium or close to the equilibrium of precipitates in phase d in the intergranular limits; Y up to 25 percent by total weight of the precipitates in phase? ' and phase y ", and wherein the nickel base alloy of type 718 comprising nickel, chromium, and iron, and hardened by niobium, and optionally one or more alloy additions of aluminum and titanium. 19. The nickel base alloy of type 718 of claim 18, which comprises in weight percentage, up to 0.1 carbon, 12 to 20 chromium, up to 4 molybdenum, up to 6 tungsten, 5 to 12 cobalt , from 6 to 14 of iron, from 4 to 8 of niobium, from 0.6 to 2.6 of aluminum, from 0.4 to 1.4 of titanium, from 0.003 to 0.03 of phosphorus, of 0.003 to 0.015 boron, nickel, and incidental impurities; where the sum of the weight percentage of molybdenum and the weight percentage of tungsten is at least 2 and not more than 8; where the sum of the atomic percentage of aluminum and the atomic percentage of titanium is from 2 to 6; where the ratio between the atomic percentage of aluminum and the atomic percentage of titanium is at least 1.5; Y where the sum of the atomic percentage of aluminum and the atomic percentage of titanium divided by the atomic percentage of niobium is from 0.8 to 1.3. 20. The nickel base alloy of type 718 of claim 18, comprising, in weight percent: 0 to about 0.08 carbon; from 0 to about 0.35 carbon; from about 0.003 to about 0.03 phosphorus; from 0 to about 0.015 sulfur; from 0 to about 0.35 of silicon; from about 17 to about 21 chromium; from about 50 to about 55 nickel; about 2.8 to about 3.3 molybdenum; from about 4.7 to about 5.5 niobium; from 0 to about 1 cobalt; from about 0.003 to about 0.015 of boron; from 0 to about 0.3 copper; from 12 to 20 iron; aluminum; titanium; and incidental impurities; where the sum of an atomic percentage of aluminum and an atomic percentage of titanium is from about 2 to about 6 percent; the ratio between the atomic percentage of aluminum and the atomic percentage of titanium is about 1.5; and the sum of an atomic percentage of aluminum plus titanium divided by the atomic percentage of niobium is equal to about 0.8 to about 1.3. 21. The nickel base alloy of type 718 of claim 18, comprising, in percent by weight: 0.01 to 0.05 carbon; up to 0.35 of manganese; up to 0.035 silicon; from 0.004 to 0.020 phosphorus; up to 0.025 sulfur; from 17.00 to 21.00 chromium; from 2.50 to 3.10 molybdenum; from 5.20 to 5.80 niobium; from 0.50 to 1.00 titanium; from 1.20 to 1.70 aluminum; from 8.00 to 10.00 cobalt; from 8.00 to 10.00 iron; from 0.008 to 1.40 tungsten; from 0.003 to 0.008 of boron; nickel; and incidental impurities. 22. The nickel base alloy of type 718 of claim 18, comprising, in percent by weight: 50.0 to 55.0 nickel; from 17 to 21.0 of chromium; up to 0.08 carbon; up to 0.35 of manganese; up to 0.35 silicon; from 2.8 to 3.3 molybdenum; more than 0 to 5.5 niobium and tantalum, where the sum of niobium and tantalum is 4.75 to 5.5; from 0.65 at 1.15 titanium; from 0.20 to 0.8 of aluminum; up to 0.006 of boron; iron; and incidental impurities. 23. An article of manufacture made by a method comprising the method of claim 1. 24. The article of manufacture of claim 23, wherein the article of manufacture comprises at least one of a front sheet, a honeycomb core, and a honeycomb panel of a thermal protection system for a hypersonic flight vehicle or a space vehicle. 25. An article of manufacture comprising an alloy according to claim 12. 26. The article of manufacture of claim 25 comprising one of a front sheet, a honeycomb core, and a honeycomb panel of a thermal protection system for a hypersonic flight vehicle. SUMMARY A method for heat treatment of a nickel-based alloy of type 718 comprising heating a nickel-based alloy of type 718 to a heat treatment temperature, and maintaining the alloy at the heat treatment temperature for a sufficient heat treatment time to form a concentration in equilibrium or close to the equilibrium of the precipitates in phase d of the intergranular boundary within the nickel-based alloy and up to 25 percent by weight of phase? and total phase "" in the interior of the alloy: The nickel-based alloy of type 718 is air-cooled The present disclosure also includes a nickel-based alloy of type 718 comprising a concentration close to the equilibrium of the phased precipitates d in the intergranular limit and up to 25 percent in total weight of the precipitates in phase? ' and phase? " . Alloys according to the disclosure can be included in articles of manufacture such as, for example, front sheets, core elements of the bee panel type, and honeycomb panels for the thermal protection systems for hypersonic flight vehicles and space vehicles.