US20200080183A1

US20200080183A1 - Treatment processes for superalloy articles and related articles

Info

Publication number: US20200080183A1
Application number: US16/469,630
Authority: US
Inventors: Raghavendra Rao Adharapurapu; Sanjay Kumar Sondhi; Biju Dasan; Laurent Cretegny; Joseph John Martell; Warren Davis Grossklaus, Jr.
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 2016-12-15
Filing date: 2017-11-30
Publication date: 2020-03-12
Also published as: WO2018111566A1

Abstract

A treatment process for treating an article including a superalloy having a degraded microstructure is presented. The process includes subjecting the article to a first heat-treatment including successively heating and cooling the article between a low-end temperature and a high-end temperature and subjecting the article to a second heat-treatment at a solution annealing temperature in a range of from about 80 degrees Fahrenheit below a gamma-prime solvus temperature of the superalloy to about 80 degrees Fahrenheit above the gamma-prime solvus temperature of the superalloy after performing the first heat-treatment. The low-end temperature is in a range of from about 1000 degrees Fahrenheit to about 1800 degrees Fahrenheit and the high-end temperature is in a range of from about 1900 degrees Fahrenheit to about 2250 degrees Fahrenheit.

Description

BACKGROUND

Embodiments of the present disclosure generally relate to treatment processes for recovering desired properties of degraded superalloy articles. More particularly, embodiments of the present disclosure are directed to treatment processes applicable to single crystal and directionally solidified superalloy articles.
Directional solidification (DS) and single crystal (SX) superalloys have been widely used to produce turbine components, for example blades of aero-engines because of their excellent high-temperature mechanical properties. Although, the usage of DS and SX superalloys enables improved efficiency and increased creep life as compared to that of equiaxed polycrystalline superalloys, the DS and SX superalloy components may accumulate damage or deform under creep and thermo-mechanical fatigue in the high-temperature operating environments. The degradation of the microstructure occurs typically due to degraded gamma and gamma-prime phases, which causes significant reduction in desirable mechanical properties and necessitates replacement of the components. Instead of completely replacing the damaged component with a new component, it is often economically viable to repair or refurbish the damaged component for further use.
During refurbishment, the degraded superalloy components are typically subjected to a solution heat-treatment process. This solution heat-treatment may lead to undesirable recrystallization in regions (often, surfaces of the article) of the DS and SX superalloy components, which were subjected to high stresses and/or plastic strains during manufacturing. This recrystallization alters and damages the microstructure of the DS and SX superalloy components, and causes unacceptable material weakening.
Several attempts have been made to inhibit the generation of recrystallization such as adjusting manufacturing process by avoiding plastic deformation before solution heat-treatment processing, using modified heat-treatment processing, applying coatings on portions of the components for inhibiting recrystallization, generating a secondary-phase in the superalloy for pinning the recrystallization boundaries to hinder recrystallization, surface oxidation etc.
There continues a need for improved and alternative treatment processes for the DS/SX superalloy components for recovering desired mechanical properties and achieving controlled and/or reduced recrystallization.

BRIEF DESCRIPTION

Provided herein are processes for treating articles comprising superalloys. In one aspect, a treatment process includes heat-treating an article including a superalloy having a degraded microstructure. The heat-treatment includes subjecting the article to a first heat-treatment including successively heating and cooling the article between a low-end temperature and a high-end temperature, wherein the low-end temperature is in a range of from about 1000 degrees Fahrenheit to about 1800 degrees Fahrenheit and the high-end temperature is in a range of from about 1900 degrees Fahrenheit to about 2250 degrees Fahrenheit; and subjecting the article to a second heat-treatment at a solution annealing temperature in a range of from about 80 degrees Fahrenheit below a gamma-prime solvus temperature of the superalloy to about 80 degrees Fahrenheit above the gamma-prime solvus temperature of the superalloy after performing the first heat-treatment.
In another aspect, a treatment process includes heat-treating an article including a superalloy having a degraded microstructure, the heat-treatment includes subjecting the article to a first heat-treatment including successively heating and cooling the article at least two times between a low-end temperature and a high-end temperature, wherein the low-end temperature is in a range of from about 1300 degrees Fahrenheit to about 1600 degrees Fahrenheit and the high-end temperature is in a range of from about 1900 degrees Fahrenheit to about 2100 degrees Fahrenheit and subjecting the article to a second heat-treatment at a solution annealing temperature in a range of from about 80 degrees Fahrenheit below a gamma-prime solvus temperature of the superalloy to about 80 degrees Fahrenheit above the gamma-prime solvus temperature of the superalloy after performing the first heat-treatment. The process further includes cooling the heat-treated article from the solution annealing temperature with a cooling rate higher than 50 degrees Fahrenheit/minute.

DRAWINGS

These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

FIG. 1 is a scanning electron micrograph of an originally prepared SX superalloy component.

FIG. 2 is a scanning electron micrograph of the SX superalloy component after it has been used in high-temperature service environment for several hours.

FIG. 3 is flow chart of a treatment process in accordance with one embodiment of the treatment processes described herein.

FIG. 4 is a temperature-time profile of a treatment process in accordance with one embodiment of the treatment processes described herein.

FIG. 5 is a temperature-time profile of a treatment process in accordance with another embodiment of the treatment processes described herein.

FIG. 6 is a scanning electron micrograph of a portion of a treated article that has been undergone a conventional treatment process.

FIG. 7 is a scanning electron micrograph of a portion of a treated article that has been undergone a treatment process in accordance with one embodiment of the treatment processes described herein.

FIG. 8 is a scanning electron micrograph of a portion of a treated article that has been undergone a treatment process in accordance with another embodiment of the treatment processes described herein.

DETAILED DESCRIPTION

The disclosure generally encompasses treatment processes that can be performed on superalloy articles, and particularly DS and SX superalloy articles for recovering their mechanical properties. As used herein, the term “DS superalloy article” refers to an article that is originally prepared by a method including directional solidification of a superalloy. The term “SX superalloy article” refers to an article originally prepared by a method that involves casting from a superalloy in single crystal form. An originally prepared article is usually cast from a superalloy in single crystal form or directionally solidified form followed by the solution heat treatment. Commonly known superalloys include gamma-prime strengthened nickel-based, cobalt-based and iron-based superalloys. Typically, in nickel-based superalloys, one or more of chromium, tungsten, molybdenum, iron and cobalt are principal alloying elements that combine with nickel to form a base matrix, and one or more aluminum, titanium, tantalum, niobium, and vanadium are principal alloying elements that combine with nickel to form desirable strengthening precipitates such as gamma-prime phase i.e., Ni₃(Al, X) and/or gamma-double-prime phase i.e., Ni₃(Nb, X), where X can be one or more of titanium, tantalum, niobium and vanadium.
The present processes are generally applicable to articles that operate within environments characterized by relatively high temperatures, for example higher than 1000 degrees Fahrenheit and subject to severe thermal stresses and thermal cycling. Such operating environments may also be referred to as high-temperature service environments. Examples of such articles include turbine components, for example blades, shrouds, combustor liner, vanes, and augmenter hardware of turbine engines. It is understood that articles other than turbine components that are cast from a superalloy in single crystal form or directionally solidified form, are considered to be within the scope of the present disclosure.
As discussed previously, use of a superalloy article under the high-temperature service environments leads to creep deformation and hence degraded or rafted microstructure. This degraded or rafted microstructure typically results in reduction of the superalloy strength and ductility. As used herein, the term “degraded microstructure” refers to a microstructure of an article including a superalloy, which has been used under the high-temperature service environment. In some embodiments, the degraded microstructure exhibits degraded gamma-prime phase in the microstructure of the article including the superalloy. FIG. 1 shows scanning electron micrograph (SEM) of a portion of an originally prepared SX superalloy component. The microstructure of the originally prepared SX superalloy component exhibits uniformly precipitated gamma-prime (Ni₃Al) phase in the nickel matrix. FIG. 2 shows SEM of a portion of the degraded component after the SX superalloy component has been used under the high-temperature service environment of a turbine. Deformation due to creep during use led to distortion of the gamma-prime phase in the form of ‘rafts’ (as shown in FIG. 2).
Moreover, the superalloy articles include mechanically deformed portions, for example the dovetail portion of a turbine blade. Often, the superalloy articles are subjected to post-solidification processing steps, such as grinding, polishing, shot peening, and grit blasting, to achieve near-net shape during manufacturing. Such processing steps can produce localized elastic residual stresses and/or increased dislocation density in the microstructure of the superalloy article. As used herein, the term “mechanically deformed portions” refers to portions of the superalloy articles that have undergone plastic deformation and exhibit elastic residual stresses and/or high dislocation density due to plastic strains.
As noted, a typical recovery process involves a solution heat-treatment above the gamma-prime solvus temperature to dissolve the degraded gamma-prime phase and then precipitate a refined gamma-prime phase in order to recover the microstructure and the desired mechanical properties of the superalloy article. Though the conventional recovery processes are effective in restoring or recovering gamma-prime phases and desirable mechanical properties, the mechanically deformed portions may undergo excessive recrystallization in a surface area (typically in a depth of less than 0.05 inches, and more particularly less than 0.01 inch from the surface of the article) upon exposure to elevated temperatures, particularly when the temperature exceeds the gamma-prime solvus temperature of the superalloy during the recovery processes.
As discussed in detail below, provided herein are improved processes for treating articles including DS or SX superalloys having degraded microstructure. The described embodiments provide treatment processes for achieving the optimal gamma-prime phase while inhibiting or controlling the generation of recrystallization in the mechanically deformed portions of the treated articles. More particularly, embodiments of the disclosed processes provide controlled and/or reduced grain size (average grain size<100 microns) of the recrystallized grains in the mechanically deformed portions of the treated articles. The treated articles may also be referred to as rejuvenated articles.
In the following specification and the claims, the singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise. As used herein, the term “or” is not meant to be exclusive and refers to at least one of the referenced components being present and includes instances in which a combination of the referenced components may be present, unless the context clearly dictates otherwise.
Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about,” is not limited to the precise value specified. In some instances, the approximating language may correspond to the precision of an instrument for measuring the value.
Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of skill in the art to which this disclosure belongs. The terms “comprising,” “including,” and “having” are intended to be inclusive, and mean that there may be additional elements other than the listed elements.
As used herein, the term “gamma-prime solvus temperature” refers to a temperature above which, in equilibrium, the gamma-prime phase is unstable and dissolves. The gamma-prime solvus temperature is a characteristic of a superalloy composition, and is generally measured by Differential Scanning calorimetry (DSC). The gamma-prime solvus temperature of a superalloy as described herein is in a range of from about 2000 degrees Fahrenheit to about 2500 degrees Fahrenheit. In some embodiments, a nickel-based superalloy has the gamma-prime solvus temperature in a range of from about 2100 degrees Fahrenheit to about 2400 degrees Fahrenheit, and in some embodiments, from about 2150 degrees Fahrenheit to about 2350 degrees Fahrenheit.
Some embodiments of the disclosure are directed to a treatment process including heat-treating an article including a superalloy having a degraded microstructure. In some embodiments, the article includes the superalloy in single crystal form or directionally solidified form. In some embodiments, the article including the superalloy has been used under the high-temperature service environment. These used articles include degraded microstructure as discussed previously. Such used articles may also be referred to as field-returned articles or degraded articles.
In certain embodiments, the article is cast from a nickel-based superalloy in single crystal form or directionally solidified form. In some embodiments, a nickel-based superalloy includes from about 7 weight percent to about 25 weight percent cobalt, from about 4 weight percent to about 25 weight percent chromium, from about 2 weight percent to about 8 weight percent aluminum, from about 0.5 weight percent to about 10 weight percent tantalum, from about 0.1 weight percent to 5 weight percent niobium, from about 2 weight percent to about 10 weight percent tungsten, from about 1 weight percent to about 8 weight percent molybdenum, from about 0.0 weight percent to about 6 weight percent titanium, from about 0.0 weight percent to about 8 weight percent rhenium, from about 0.0 weight percent to about 1.5 weight percent hafnium, from about 0.0 weight percent to about 1 weight percent silicon, from about 0.0 weight percent to about 0.2 weight percent boron, from about 0 weight percent to about 0.2 weight percent carbon, from about 0 weight percent to about 0.1 weight percent zirconium, from about 0 weight percent to about 0.1 weight percent yttrium, and balance nickel. The term, “weight percent”, as used herein, refers to a weight percent of each referenced element in the nickel-based superalloy based on a total weight of the nickel-based superalloy, and is applicable to all incidences of the term “weight percent” as used herein throughout the specification.
Examples of suitable superalloys include, but not limited to, precipitation hardenable superalloys such as Rene 41® (registered trademark of General Electric), the metallic alloy sold under the trademark GTD-111 (GTD-111 is a registered trademark of General Electric Company), the metallic alloy sold under the trademark GTD-222 (GTD-222 is a registered trademark of General Electric Company), the metallic alloy sold under the trademark GTD-444 (GTD-444 is a registered trademark of General Electric Company) and Rene N5, Rene 80. Rene 104, Rene 108 (Trademark of General Electric Company).
The degraded articles usually include protective coatings such as aluminide coating and thermal barrier coatings. Prior to subjecting such degraded articles to the treatment process, a cleaning process may be carried out for removing these protective coatings from the surfaces of the degraded articles. Several cleaning procedures known in the art such as mechanical removal (for example, grit blasting, grinding), water jet machining, chemical etching etc. can be used for the purpose.
As noted, the treatment process includes heat-treating the article. The heat-treatment includes subjecting the article to a first heat-treatment including successively heating and cooling the article between a low-end temperature and a high-end temperature, wherein the low-end temperature is in a range of from about 1000 degrees Fahrenheit to about 1800 degrees Fahrenheit and the high-end temperature is in a range of from about 1900 degrees Fahrenheit to about 2250 degrees Fahrenheit, and subjecting the article to a second heat-treatment at a solution annealing temperature in a range of from about 80 degrees Fahrenheit below a gamma-prime solvus temperature of the superalloy to about 80 degrees Fahrenheit above the gamma-prime solvus temperature of the superalloy after performing the first heat-treatment. In some embodiments, the treatment process further includes cooling the heat-treated article from the solution annealing temperature.
Any numerical values recited herein include all values from the lower value to the upper value in increments of one unit provided that there is a separation of at least 2 units between any lower value and any higher value. As an example, if it is stated that a value of a process variable such as, for example, temperature, pressure, time and the like is, for example, from 1000 to 1500, preferably from 1100 to 1400, more preferably from 1200 to 1300, it is intended that values such as 1020 to 1485, 1054 to 1430, 1135 to 1370, etc. are expressly enumerated in this specification. For values which are less than one, one unit is considered to be 0.0001, 0.001, 0.01 or 0.1 as appropriate. These are only examples of what is specifically intended and all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application in a similar manner.
In some embodiments, a treatment process 100 for treating an article including a superalloy (as described herein) is described with reference to FIGS. 3, 4, and 5. As illustrated in FIGS. 3, 4, and 5, the treatment process 100 includes the step 110 of heat-treating the article and the step 120 of cooling the heat-treated article. The heat-treatment step 110 includes the step 102 of subjecting the article to a first heat-treatment (first heat-treatment step) and the step 104 of subjecting the article to a second heat-treatment (second heat-treatment step) after performing the first heat-treatment step 102.
The first heat-treatment step 102 may be performed to remove or reduce the residual stresses and dislocation density that had been produced due to annihilation of the dislocations in the degraded article. As noted, the first heat-treatment step 102 includes successively heating and cooling the article between a low-end temperature and a high-end temperature. The low-end temperature may vary in a range of from about 1000 degrees Fahrenheit to about 1800 degrees Fahrenheit. In some embodiments, the low-end temperature is in a range of from about 1200 degrees Fahrenheit to about 1600 degrees Fahrenheit. The high-end temperature depends on the superalloy composition, and should be lower than the recrystallization temperature of the superalloy. In some embodiments, the high-end temperature is in a range of from about 1900 degrees Fahrenheit to about 2250 degrees Fahrenheit. In some embodiments, the high-end temperature is in a range of from about 1900 degrees Fahrenheit to about 2200 degrees Fahrenheit. In some specific embodiments, the high-end temperature is in a range of from about 1900 degrees Fahrenheit to about 2150 degrees Fahrenheit. In some more specific embodiments, the low-end temperature is in a range of from about 1300 degrees Fahrenheit to about 1600 degrees Fahrenheit, and the high-end temperature is in a range of from about 1900 degrees Fahrenheit to about 2100 degrees Fahrenheit.
As used herein, the term “recrystallization temperature” refers to a temperature at which the deformed metal grains are replaced by new metal grains through nucleation and growth.
This successive heating and cooling of the article may be performed one or more times depending on the extent of mechanical damage and/or dislocation density in the degraded article, and the desirable control of recrystallization and reduction of the grain size in a rejuvenated article. FIG. 4 illustrates an embodiment where the first heat-treatment step 102 includes successively heating and cooling the article one time prior to subjecting the article to the second heat-treatment step 104. FIG. 5 illustrates another embodiment where the first heat-treatment step 102 includes successively heating and cooling the article multiple times, for example five times prior to subjecting the article to the second heat-treatment step 104. The successive heating and cooling the article may be performed up to 100 times. In some embodiments, the first heat-treatment step 102 includes successively heating and cooling the article up to 50 times. In certain embodiments, the first heat-treatment step 102 includes successively heating and cooling the article from 2 times to about 20 times. In some embodiments, the successive heating and cooling the article may be performed 3 times to 15 times for attaining desirable properties, and in some specific embodiments, from about 5 times to about 10 times.
The first heat-treatment step 102 may further include holding the article at one or both the low-end temperature and the high-end temperature for a hold time during the successive heating and cooling steps. The hold times at the low-end temperature and the high-end temperature may be up to 5 hours, for example. In some embodiments, the hold times at the low-end temperature and at the high-end temperature may range from about 1 minute to about 2 hours. Furthermore, the successive heating and cooling of the article may be performed with the corresponding heating and cooling rates. In some embodiments, the first heat-treatment step 102 includes successively heating and cooling the article with the corresponding heating rate or cooling rate in a range of from about 5 degrees Fahrenheit/minute to about 80 degrees Fahrenheit/minute. In some embodiments, the heating rate, the cooling rate or both are in a range of from about 5 degrees Fahrenheit/minute to about 30 degrees Fahrenheit/minute, and in some embodiments, the rates range from about 10 degrees Fahrenheit/minute to about 20 degrees Fahrenheit/minute.
In the first heat-treatment step 102, the low-end temperature, the high-end temperature, the heating rate, the cooling rate, and the hold times at the low-end temperature and the high-end temperature may be identical or different during the successive heating and cooling step(s). In some embodiments, the first heat-treatment step 102 includes successively heating and cooling between the low-end temperature and the high-end temperature. In certain embodiments, the successive heating and cooling occurs between about 1300 degrees Fahrenheit to about 2100 degrees Fahrenheit. In some more specific embodiments, the successive heating and cooling occurs between about 1350 degrees Fahrenheit to about 2050 degrees Fahrenheit, and in some embodiments to about 2000 degrees Fahrenheit. In some embodiments, the first heat-treatment step 102 includes cyclically heat-treating the article using at least one heating and cooling cycle between the low-end temperature and the high-end temperature. In some other embodiments, a subsequent heating and cooling step may have a low-end temperature and a high-end temperature lower than or higher than that of the previous heating and cooling step. It may be understood (one performing the invention with regard to a particular alloy may well find) that the heating rates and the cooling rates during the successive heating and cooling steps are not necessarily identical; and that the low-end and the high-end temperatures and the hold times are not likewise necessarily identical in order to achieve a desired result in a desired period.
Following the first heat-treatment step 102, the treatment process 100 includes the second heat-treatment step 104. In the second heat-treatment step 104, the treatment process 100 includes subjecting the article to the second heat-treatment at a solution-annealing temperature in a range of from about 80 degrees Fahrenheit below the gamma-prime solvus temperature of the superalloy to about 80 degrees Fahrenheit above the gamma-prime solvus temperature of the superalloy. The second heat-treatment step 104 may be performed to partially or fully dissolve the degraded gamma-prime phase in the superalloy. In certain embodiments, the second heat-treatment step 104 is performed to fully dissolve the degraded gamma-prime phase in the superalloy. In some embodiments, the solution-annealing temperature is in a range of from about 60 degrees Fahrenheit below a gamma-prime solvus temperature to about 60 degrees Fahrenheit above the gamma-prime solvus temperature of the superalloy. In some embodiments, the solution-annealing temperature is in a range of from about 45 degrees Fahrenheit below a gamma-prime solvus temperature to about 45 degrees Fahrenheit above the gamma-prime solvus temperature of the superalloy. The second heat-treatment step 104 may be carried out up to 20 hours. In some embodiments, the second heat-treatment step 104 is carried out for a period of from about 1 minute to about 10 hours. In certain embodiments, the period for the second heat-treatment 104 is in a range of from about 5 minutes to about 4 hours.
After completing the heat-treatment step 110, the treatment process 100 further includes the step 120 of cooling the heat-treated article from the solution-annealing temperature. In some embodiments, the cooling step 120 includes cooling the heat-treated article from the solution annealing temperature to a temperature lower than 2000 degrees Fahrenheit. The cooling step 120 may promote the nucleation and growth of the gamma-prime phase and/or the gamma-double-prime phase within the microstructure of the superalloy. The cooling step 120 may allow for obtaining a cooled article that includes desirable gamma-prime and/or gamma-double-prime phases with desired particle size.
The step 120 of cooling the heat-treated article can be performed with a controlled manner, for example with a cooling rate greater than 50 degrees Fahrenheit/minute. A cooling rate greater than 80 degrees Fahrenheit/minute may be desirable because a low cooling rate (e.g., lower than 80 degrees Fahrenheit/minute) may grow coarse gamma-prime phase that may be detrimental for desired mechanical properties. According to some embodiments, the cooling step 120 is performed by cooling the heat-treated article with a cooling rate in a range of from about 85 degrees Fahrenheit/minute to about 300 degrees Fahrenheit/minute. In yet some embodiments, the cooling rate is in a range of from about 100 degrees Fahrenheit/minute to about 250 degrees Fahrenheit/minute. In yet some embodiments, the cooling rate is in a range of from about 120 degrees Fahrenheit/minute to about 220 degrees Fahrenheit/minute.
In one embodiment, the cooling step 120 is carried out for cooling the heat-treated article from the solution annealing temperature to about 2000 degrees Fahrenheit. In some embodiments, the heat-treated article is cooled to a temperature between 2000 degrees Fahrenheit and 1000 degrees Fahrenheit. In some embodiments, the cooling step 120 is performed upon cooling the heat-treated article to an aging temperature (e.g., between 1500 degrees Fahrenheit and 2100 degrees Fahrenheit). In some embodiments, the heat-treated article is cooled to a temperature lower than 1000 degrees Fahrenheit, and in some embodiments, to room temperature. In some embodiments, the cooling step 120 further includes furnace cooling the heat-treated article to a temperature lower than 1000 degrees Fahrenheit after cooling the heat-treated article in a controlled manner up to a desirable temperature, for example about 2000 degrees Fahrenheit. In some embodiments, the heat-treated article is cooled to room temperature.
As used herein, the term “cooled article” refers to an article including a superalloy received after cooling the heat-treated article as described herein by a cooling rate greater than 50 degrees Fahrenheit/minute to a temperature below 2000 degrees Fahrenheit.
Without being limited by any theory, it is believed that the first heat-treatment that includes successively heating and cooling the article, as described herein, annihilates dislocations and significantly reduces the dislocation density in the mechanically deformed portions of the article. This lowering of the dislocation density affects the recrystallization in the mechanically deformed portions of the article (for example, on the surfaces of the article). The reduced dislocation density leads to lower recrystallized grain size or no formation of recrystallized grains in the mechanically deformed portions during the second heat-treatment at the solution-annealing temperature.
In some embodiments, the process further includes aging the cooled article. Aging may help in precipitating gamma-prime phase and/or double gamma-prime phase in desirable particle size. The aging step may be performed by heating the cooled article at an aging temperature that may be in a range of from about 1500 degrees Fahrenheit to about 2100 degrees Fahrenheit. This aging step may be performed at a combination of time and temperature to achieve the desired properties. The aging step may include heat-treating the cooled article at one or more temperatures for a duration of time (for example, >2 hours). Some embodiments include aging the cooled article by heat-treating the cooled article at a first aging temperature for a duration of time followed by heat-treating the cooled article at a second aging temperature for a duration of time. The second aging temperature may be lower than the first aging temperature. In some embodiments, the aging further includes heat treating the cooled article at a third aging temperature for a duration of time, where the third aging temperature is lower than the second aging temperature.
The heating rates and the cooling rates, as described herein, during one or more of the first heat-treatment step 102, the second heat-treatment step 104, the cooling step 120 and the aging step, refer correspondingly to the heating rates and the cooling rates in a direction through a maximum dimension of an article. The maximum dimension may experience the slowest heating or cooling rates. In some embodiments, a length, a width, a radius or a thickness of the article may be the maximum dimension of the article. It will be understood that cooling and/or heating at any rate described herein across the maximum dimension of an article provides the most efficient cooling rate and/or heating rate for any article described herein, although there may be instances where cooling and/or heating across a dimension other than the maximum dimension may be desirable.
In some embodiments, a treated article is received after treating a degraded article by a treatment process as described herein. The treated article may also be referred to as a rejuvenated article. The rejuvenated article may include a microstructure similar to the microstructure of the originally formed article. That is, the treatment process as described herein enables the recovery of the mechanical properties of the originally prepared article while avoiding or reducing the recrystallization in the mechanically deformed portion of the treated article. In some embodiments, the treated article exhibits at least 40 percent of the mechanical properties of the originally formed article.
In some embodiments, the mechanically deformed portion includes a population of grains (i.e., recrystallized grains) in the surface of the article. The population of grains may have an average grain size less than 100 microns. In some embodiments, the mechanically deformed portion includes the population of grains (i.e., recrystallized grains) having an average grain size in a range from about 1 micron to about 90 microns. In some embodiments, the average grain size is in a range of from about 5 microns to about 80 microns. In some embodiments, the population of grains has a maximum grain size less than 150 microns. In certain embodiments, the population of grains has a maximum grain size less than 125 microns.
Some embodiments of the present disclosure advantageously provide reduction in grain size (average grain size<100) of the recrystallized grains in the mechanically deformed portions of a rejuvenated article including a SX or DS superalloy, and enables reduced recrystallization during the recovery process. Such embodiments thus allow the rejuvenation of SX and DS superalloy articles such as turbine blades with improved mechanical properties by controlling recrystallization in the mechanically deformed portions (for example, the machined serrations of a turbine blade dovetail) of the article during the recovery process and thus reducing or preventing damages in the rejuvenated article for further use.
In some embodiments, the treated article may undergo one or more repairing processes after performing the aging step. The repairing processes may include welding and/or brazing for repairing cracks, disposing aluminide coating, and disposing thermal barrier coating (TBC) on the treated article.

EXAMPLES

The following example illustrates methods, materials and results, in accordance with a specific embodiment, and as such should not be construed as imposing limitations upon the claims.
Two components were produced from single crystal Rene N5 that had been provided with a standard, proprietary heat treatment. The components were exposed to high-temperature service environment for several hours. Component 1 was treated using a control treatment process and component 2 was treated using a conventional treatment process. Before undergoing the treatment processes, components 1 and 2 were processed to strip away the aluminide and the thermal barrier coatings.

Example 1: Control Treatment Process

Component 1 was first heated up to a about 2000 degrees Fahrenheit (° F.) with a heating rate of about 10 degrees Fahrenheit/minute (° F./min). After holding the component 1 at about 2000° F. for about 30 minutes, the component 1 was cooled to about 1350° F. with a cooling rate about 20° F./min After holding at about 1350° F. for 30 minutes, the component 1 was again heated up to about 2000° F. with heating rate of about 10° F./min followed by holding for about 30 minutes and then again cooling to about 1350° F. with the cooling rate of about 20° F./m. These heating and cooling cycles were carried out five times. After completing five heating and cooling cycles, the temperature was raised up to a solution annealing temperature that was close to the gamma-solvus temperature (that was measured using DSC) of the Rene N5 superalloy with a heating rate of about 10° F./min for the solution heat-treatment. The component 1 was held at the solution annealing temperature for about 40 minutes followed by cooling the component 1 to about 1800° F. with a cooling rate of about 180° F./min followed by a standard proprietary cooling process and aging treatment.

Comparative Example: Conventional Treatment Process

Component 2 was first heated up to about 2000° F. with a heating rate of about 10° F./min followed by holding the component 2 at about 2000° F. for about 5 hours. The component 2 was further heated to raise the temperature up to the solution annealing temperature (as in example 1) with a heating rate of about 10° F./min for solution heat-treatment. The component 2 was held at the solution annealing temperature for about 40 minutes followed by cooling the component 2 to about 1800° F. with a cooling rate of about 180° F./min followed by the same standard proprietary cooling process and aging treatment as performed in example 1 for component 1.

Testing of Two Components

After the components 1 and 2 had been undergone the treatment processes as described in example 1 and comparative example 2, the microstructures of components 1 and 2 were then examined in a scanning electron microscope (SEM). FIG. 6 shows SEM image of a portion of the component 2 that was treated using the conventional treatment process of comparative example 2 and FIGS. 7 and 8 show SEM images of two portions of the component 1 that was treated using the control treatment process of example 1. It was observed that component 2 after the conventional treatment process of comparative example 2 developed a continuous band of recrystallized grains 10 (FIG. 6) with an average grain size of more than 100 microns and a maximum grain size of greater than 150 microns. Component 1 that was subjected to the control treatment process of example 1 exhibited recrystallized grains of an average grain size of 50 microns or less and a maximum grain size of less than 125 microns. As shown in FIG. 7, certain areas 20 in component 1 were completely devoid of large recrystallized grains as compared to that of the component 2 that was subjected to conventional treatment process of comparative example 2 (FIG. 6). Furthermore, other areas 30 in component 1 such as those shown in FIG. 8, exhibited an occasional grain; or a discontinuous or semi-continuous grain growth with an average grain size of less than 50 microns.
While only certain features of the disclosure have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the disclosure.

Claims

1. A treatment process comprising: heat-treating an article comprising a superalloy having a degraded microstructure, the heat-treatment comprising:

subjecting the article to a first heat-treatment comprising successively heating and cooling the article between a low-end temperature and a high-end temperature, wherein the low-end temperature is in a range of from about 1000 degrees Fahrenheit to about 1800 degrees Fahrenheit and the high-end temperature is in a range of from about 1900 degrees Fahrenheit to about 2250 degrees Fahrenheit; and

subjecting the article to a second heat-treatment at a solution annealing temperature in a range of from about 80 degrees Fahrenheit below a gamma-prime solvus temperature of the superalloy to about 80 degrees Fahrenheit above the gamma-prime solvus temperature of the superalloy after performing the first heat-treatment.

2. The treatment process of claim 1, wherein the article comprises the superalloy in a single crystal form or directionally solidified form.

3. The treatment process of claim 1, wherein the low-end temperature is in a range of from about 1300 degrees Fahrenheit to about 1600 degrees Fahrenheit and the high-end temperature is in a range of from about 1900 degrees Fahrenheit to about 2100 degrees Fahrenheit.

4. The treatment process of claim 1, wherein the first heat-treatment comprises successively heating and cooling the article up to 50 times.

5. The treatment process of claim 1, wherein the first heat-treatment comprises successively heating and cooling the article from 2 times to about 20 times.

6. The treatment process of claim 1, wherein the successive heating and cooling is carried out with a corresponding heating rate or cooling rate in a range of from about 5 degrees Fahrenheit/minute to about 80 degrees Fahrenheit/minute.

7. The treatment process of claim 1, wherein the successive heating and cooling is carried out with a corresponding heating rate or cooling rate in a range of from about 10 degrees Fahrenheit/minute to about 50 degrees Fahrenheit/minute.

8. The treatment process of claim 1, wherein the second heat-treatment is carried out up to 20 hours.

9. The treatment process of claim 1, wherein the second heat-treatment is carried out for a duration of time in a range of from about 5 minutes to about 5 hours.

10. The treatment process of claim 1, wherein the second heat-treatment is carried out at a temperature in a range of from about 45 degrees Fahrenheit below the gamma-prime solvus temperature of the superalloy to about 45 degrees Fahrenheit above the gamma-prime solvus temperature of the superalloy.

11. The treatment process of claim 1, further comprising cooling the heat-treated article from the solution annealing temperature.

12. The treatment process of claim 11, wherein the cooling of the heat-treated article is carried out with a cooling rate higher than 50 degrees Fahrenheit/minute.

13. The treatment process of claim 12, wherein the cooling rate is in a range of from about 80 degrees Fahrenheit/minute to about 300 degrees Fahrenheit/minute.

14. The treatment process of claim 12, wherein the cooling rate is in a range of from about 100 degrees Fahrenheit/minute to about 250 degrees Fahrenheit/minute.

15. An article received after performing the treatment process in accordance with claim 1.

16. The article of claim 15, wherein a mechanically deformed portion of the article comprises a population of grains having an average grain size less than 100 microns.

17. The article of claim 16, wherein the population of grains has an average grain size in a range of from about 1 micron to about 90 microns.

18. The article of claim 16, wherein the population of grains has a maximum grain size less than 150 microns.

19. The article of claim 18, wherein the population of grains has a maximum grain size less than 125 microns.

20. A treatment process comprising: heat-treating a single crystal or directionally solidified article of a nickel-based superalloy comprising a degraded microstructure, the heat-treatment comprising:

subjecting the article to a first heat-treatment comprising successively heating and cooling the article at least 2 times between a low-end temperature and a high-end temperature, wherein the low-end temperature is in a range of from about 1300 degrees Fahrenheit to about 1600 degrees Fahrenheit and the high-end temperature is in a range of from about 1900 degrees Fahrenheit to about 2100 degrees Fahrenheit;

subjecting the article to a second heat-treatment at a solution annealing temperature in a range of from about 80 degrees Fahrenheit below a gamma-prime solvus temperature of the superalloy to about 80 degrees Fahrenheit above the gamma-prime solvus temperature of the superalloy after performing the first heat-treatment; and

cooling the heat-treated article from the solution annealing temperature with a cooling rate higher than 50 degrees Fahrenheit/minute.