CA1098425A - Heat treated superalloy single crystal article and process - Google Patents
Heat treated superalloy single crystal article and processInfo
- Publication number
- CA1098425A CA1098425A CA291,053A CA291053A CA1098425A CA 1098425 A CA1098425 A CA 1098425A CA 291053 A CA291053 A CA 291053A CA 1098425 A CA1098425 A CA 1098425A
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- CA
- Canada
- Prior art keywords
- gamma prime
- article
- single crystal
- carbon
- cobalt
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B21/00—Unidirectional solidification of eutectic materials
- C30B21/02—Unidirectional solidification of eutectic materials by normal casting or gradient freezing
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C19/00—Alloys based on nickel or cobalt
- C22C19/03—Alloys based on nickel or cobalt based on nickel
- C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
- C22C19/051—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W
- C22C19/056—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W with the maximum Cr content being at least 10% but less than 20%
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B11/00—Single-crystal growth by normal freezing or freezing under temperature gradient, e.g. Bridgman-Stockbarger method
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
- C30B29/10—Inorganic compounds or compositions
- C30B29/52—Alloys
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Crystallography & Structural Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Mechanical Engineering (AREA)
- Turbine Rotor Nozzle Sealing (AREA)
- Crystals, And After-Treatments Of Crystals (AREA)
- Heat Treatment Of Nonferrous Metals Or Alloys (AREA)
- Inorganic Compounds Of Heavy Metals (AREA)
- Compositions Of Oxide Ceramics (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
Nickel base superalloy single crystal articles formed from an alloy family and heat treated are described as is the process employed. The articles are substantially free from cobalt and the grain boundary strengtheners such as carbon, boron, and zirconium. The heat treatment process homogenizes the microstructure, and refines the gamma prime morphology.
The superalloy has particular utility in the fabrication of airfoils (blades and vanes) for use in gas turbine engines.
Nickel base superalloy single crystal articles formed from an alloy family and heat treated are described as is the process employed. The articles are substantially free from cobalt and the grain boundary strengtheners such as carbon, boron, and zirconium. The heat treatment process homogenizes the microstructure, and refines the gamma prime morphology.
The superalloy has particular utility in the fabrication of airfoils (blades and vanes) for use in gas turbine engines.
Description
1~84ZS
BACKGROUND OF THE INVENTION
-Field of the Invention - This invention relates to the field of homogeneous single crystal superalloy articles.
Description of the Prior Art - The nickel base superalloy art area has been extensively investigated for many years, and as a result there are very many issued patents in this area. Some of these disclose alloys in which no intentional additions of cobalt, carbon, boron, or zirconium are made, or alloys in which these elements are optional. These include for example U.S.
Patents Nos. 2,621,122; 2,781,264; 2,912,323; 2,994,605;
3,046,108; 3,166,412; 3,188,204; 3,287~110; 3,304,176;
and 3,322,534. These patents do not discuss single crystal applications.
U.S. Patent No. 3,494,709, assigned to the assignee of the present invention, discloses the use of single crystal articles in gas turbine engines. This patent discusses the desirability of li~iting certain elements such as boron and zirconium to low levels.
The limitation of carbon to low levels in single crystal superalloy articles is discussed in U.S. Patent No. 3,567,526 which is also assigned to the present assignee.
U.S. Patent No. 3,915,761, assigned to the present assignee discloses a nickel base superalloy article produced by a method which provides a hyperfine dendritic structure. As a result of the fineness of the structure, 1~8425 the article may be homogenized in relatively short times.
The conventional nickel base superalloys which are used to fabricate such parts have evolved over the last 30 years. Typically these alloys contain chromium in levels of about 10% primarily for oxidation resistance, aluminum and titanium in combined levels of about 5% for the formation of the strengthening gamma prime phase and refractory metals such as tungsten, molybdenum, tantalum and columbium in levels of about 5% as solid solution strengtheners. Virtually all nickel base superalloys also contain cobalt in levels of about 10%, and carbon in levels of about .1% which acts as a grain boundary strengthener and forms carbides which strengthen the alloy. Boron and zirconium are also often added in small amounts as grain boundary strengtheners.
Most commonly, gas turbine blades are formed by casting and the casting process most often utilized pro-duces parts having equiaxed nonoriented grains. It is well known that the high temperature properties of metals are usually quite dependent upon grain boundary properties, consequently efforts have been made to strengthen such boundaries (for example by the additions discussed previously), or to reduce or eliminate the grain boundaries transverse to the major stress axis of the part. One method of eliminating such transverse boundaries is termed directional solidification and is described in U.S. Patent No. 3,260,505. The effect of directional solidification is to produce an oriented microstructure of columnar grains whose major axis is parallel to the stress axis of the part and which has minimal or no grain boundaries perpendicular to the stress axis of the part.
A further extension of this concept is the utilization of single crystal parts in gas turbine blades. This concept is described in U.S. Patent No. 3,494,709. The obvious advantage of the single crystal blade is the complete absence of grain boundaries. In single crystals, there-fore, grain boundaries are eliminated as potential weaknesses, hence, the mechanical properties of the single crystal are completely dependent upon the inherent mechanical properties of the material.
In the prior art alloy development much effort was devoted to the solution of problems resulting from grain boundaries, through the addition of elements such as carbon, boron, and zirconium. Another problem which prior art alloy development sought to avoid was the develop-ment of deleterious phases after long term exposures at elevated temperatures (i.e. alloy instability~O These phases are of two general types. One, such as sigma, is undesirable because of its brittle nature while the other, such as mu, is undesirable because the phase ties up large amounts of the refractory solid solution strengtheners thus weakening the remaining alloy phases. These phases have been termed TCP phases for topologically close packed phases, and one of their common properties is that they all .-contain cobalt. There are of course TCP phases which can form in the absence of cobalt but these cobalt free ~8425 TCP phases contain other elements such as silicon which are not commonly found in nickel base superalloys. While an obvious remedy to control these deleterious phases is the removal of cobalt, this has not proved practical in prior art alloys for polycrystalline applications.
The problem is that if the cobalt is removed the carbon combines preferentially with the refractory metals to form M6C carbides which are dele~erious to the properties of the material as their formation depletes the alloy of the strengthening refractory elements.
U.S. Patent No. 3,567,526 teaches that carbon can be completely removed from single crystal superalloy articles and that such removal improves fatigue properties.
In single crystal articles which are free from carbon there are two important strengthening mechanisms. The most important strengthening mechanism is the inter-metallic gamma prime phase, Ni3(Al, Ti). In modern nickel base superalloys the gamma prime phase may occur in quantities as great as 60 volume percent. The second strengthening mechanism is the solid solution strengthen-ing which is produced by the presence of the refractory metals such as tungsten and molybdenum in the nickel solid solution matrix. For a constant volume fraction of gamma prime, considerable variations in the strength-ening effect of this volume fraction of gamma prime may be obtained by varying the size and morphology of the gamma prime precipitate particles. The gamma prime phase is characterized by having a solvus temperature above ~98425 which the phase dissolves into the matrix. In many cast alloys, however, the gamma prime solvus temperature is in fact above the incipient melting temperature so that it is not possible to effectively solutionize the gamma prime phase. Solutionizing of the gamma prime is the only practical way in which the morphology of the gamma prime can be modified, hence for many commercial nickel base superalloys the gamma prime morpholog~ is limited to the morphology which resulted from the original casting process. The other strengthening mechanism, solid solution strengthening, is most effective when the solid solution strengthening elements are uniformly distributed throughout the nickel solid solution matrix. Again this strengthening is reduced in effectiveness because of the nature of the casting process. Practical nickel base superalloys freeze over a wide temperature range. The freezing or solidification process involves the formation of high melting point dendrites followed by the subsequent .
freezing of the lower temperature melting interdendritic fluid. I'his solidification process leads to significant compositional inhomogenities throughout the microstructure.
Lt is theoretically possible to homogenize such a micro-structure by heating at elevated temperatures to permit diffusion to occur, however, in practical nickel base superalloys the maximum homogenization temperature, which is limited by the incipient melting temperature, is too low to permit significant homogenization in practical time intervals.
98~25 SUMMARY OF THE INVENTION
This invention includes three interrelated aspects.
The first aspect is the particular alloy employed. In its broadest form the alloy is a nickel base alloy containing from about 5 to about 18% chromium, at least 5% of an element chosen from the group consisting of from 2 to 8%
aluminum and from 1 to 5% titanium and mixtures thereof, at least 5% of an element chosen from the group consisting of up to 10% molybdenum, up to 15% tungsten, up to 12%
tantalum, up to 7% rhenium, up to 3.5% hafnium, and up to 3% columbium, and mixtures thereof, balance essentially nickel. The alloy employed in the present invention is free from intentional additions of cobalt, carbon, boron and zirconium, although obviously these elements may be present in impurity levels. The alloy is charac~erized by having an incipient melting temperature in excess of about 2300F and by having a gamma prime solvus tempera-ture which is significantly below this incipient melting temperature but at the same time is higher than the gamma prime solvus temperatures for typical commercial nickel base superalloys. Thus this alloy may be heat treated under conditions which permit complete solutionizing of the gamma prime phase without incipient melting. At the same time the high incipient melting temperature permits essentially complete homogenization of the alloy in commercially practicable times. The high incipient melt-ing temperature of the alloy is a result of the absence of carbon, boron and zirconium. The absence of cobalt ~0~8425 inhibits the formation of deleterious TCP phases.
The second important aspect of the invention is the formation of the previously described alloy into single crystal articles.
The third aspect of the invention is the heat treat-ment sequence by which the gamma prime morphology may be modified and refined at the same time that significant homogenization of the as cast microstructure is performed.
The resultant single crystal article will have a micro-structure whose typical gamma prime particle size is about 1/5 of the gamma prime particle size found in the as cast material. At the same time the heat treated single crystal microstructure will be essentially free from compositional inhomogenities and this uniform micro-structure combined with the increased gamma prime solvus temperature will permit the article of the present inven-tion to exhibit temperature capabilities, for equal mechanical properties, which are at least 30 F greater than the temperature capabilities of comparable prior art single crystal articles which are formed from conventional alloys containing cobalt, carbon, boron and zirconium.
The foregoing, and other objects, features and advantages of the present invention will become more apparent in the light of the following detailed descrip-tion of the preferred embodiment thereof as shown in the accompanying drawing.
:
lC~Q842S
In accordance with a broad aspect of the invention, there is provided a single crystal nicXel base superalloy arti-cle free from intentional additions of cobalt, carbon, boron and zirconium, containing in percentages by weight from about 5 to about 18% chromium, at least 5% of an element ch~serl from the group consisting of from 2 to 8% alu~inum and from 1 to 5%
titanium and mixtures thereof, at least 5% of an element chosen from the group consisting of up to 10% molybdenum, up to 15%
tungsten, up to 12% tantalum, up to 3% columbium, up to 3.5%
hafnium, up to 7% rhenium, and mixtures thereof balance essentially nickel, said single crystal article having a homogeneous microstructure which contains gam~a prime particles having a size of less than .5 microns, and said microstructures being free of MC type carbides, and TCP phases.
In accordance with another aspect of the invention, there is provided a method for producing nickel base superalloy single crystal articles which have a homogeneous microstructure and in which the gamma prime phase presents a refined morpholo-gy, including the steps of:
a. providing a mass of nickel base superalloy material which is free from intentional additions of cobalt, carbon boron, and zirconium, and contains in percentages by weight from about 5 to 18% chromium at least 5% of an element chosen from the group consisting of from 2 to 8% aluminum and from 1 to 5% titanium and mix-tures thereof, at least 5% of an element chosen from the group consisting of up to 10% molybdenum, up to 15% tungsten, up to 12% tantalum, up to 3%
columbium, up to 3.5% hafnium, up to 7% rhenium, and mixtures thereof balance essentially nickel, -8a-10~8425 b. melting the nickel base superalloy a~d solidify-ing the alloy under conditions of unidirectional heat flow so as to produce a single crystal arti-cle having a microstructure which consists essentially of gamma prime particles in a gamma prime matrix, with the gamma prime particles having a particle size of about 1.5 microns, said article having an incipient melting tempe-rature and a gamma prime solvus temperature, wherein the gamma prime solvus temperature is less than the incipient melting temperature, said microstructure being free of MC type carbides and TCP phase3, c. heating the article to a temperature greater than the gamma prime solvus temperature and less than the incipient melting temperature for a period of time sufficient to dissolve subs-tantially all of the gamma prime phase into solid solution while simultaneously homogenizing the microstructure, d. heating the article at a temperature below the gamma prime 301vu9 for a period of time sufficient to reprecipitate the gamma prime phase in refined form, whereby the heat treated single crystal article has a tempera-ture advantage of at least 30F over non-heat treated articles.
-8b-la~s4zs BRIEF DESCRIPTION OF THE DRAWING
Fig. 1 shows the as cast microstructure of the invention alloy;
Fig. 2 shows the microstructure of the invention alloy after a 4 hour exposure at 2200 F;
Fig. 3 shows the microstructure of the invention alloy after a 4 hour exposure at 2350 F;
Fig. 4 is an electron micrograph showing the as cast gamma prime morphology of the invention alloy;
Fig. 5 is an electron micrograph showing the gamma prime morphology of the invention alloy after heat treatment at 2350 F for 4 hours and 1975 F for 4 hours and 1600 F for 32 hours;
Fig. 6 shows a comparison of the creep strength of the article of the invention with the prior art;
Fig. 7 shows the microstructure of the invention alloy after 500 hours at 1800F; and Fig. 8 shows the microstructure of a prior art alloy after 500 hours at 1800 F.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In the description which follows, all percent figures are in weight percent unless otherwise specified.
This invention relates to an article made of a specific alloy by a critical series of process steps.
Although other articles may be produced according to this invention, this invention has particular utility in the fabrication of airfoils (blades and vanes) for use in gas turbine engines.
BACKGROUND OF THE INVENTION
-Field of the Invention - This invention relates to the field of homogeneous single crystal superalloy articles.
Description of the Prior Art - The nickel base superalloy art area has been extensively investigated for many years, and as a result there are very many issued patents in this area. Some of these disclose alloys in which no intentional additions of cobalt, carbon, boron, or zirconium are made, or alloys in which these elements are optional. These include for example U.S.
Patents Nos. 2,621,122; 2,781,264; 2,912,323; 2,994,605;
3,046,108; 3,166,412; 3,188,204; 3,287~110; 3,304,176;
and 3,322,534. These patents do not discuss single crystal applications.
U.S. Patent No. 3,494,709, assigned to the assignee of the present invention, discloses the use of single crystal articles in gas turbine engines. This patent discusses the desirability of li~iting certain elements such as boron and zirconium to low levels.
The limitation of carbon to low levels in single crystal superalloy articles is discussed in U.S. Patent No. 3,567,526 which is also assigned to the present assignee.
U.S. Patent No. 3,915,761, assigned to the present assignee discloses a nickel base superalloy article produced by a method which provides a hyperfine dendritic structure. As a result of the fineness of the structure, 1~8425 the article may be homogenized in relatively short times.
The conventional nickel base superalloys which are used to fabricate such parts have evolved over the last 30 years. Typically these alloys contain chromium in levels of about 10% primarily for oxidation resistance, aluminum and titanium in combined levels of about 5% for the formation of the strengthening gamma prime phase and refractory metals such as tungsten, molybdenum, tantalum and columbium in levels of about 5% as solid solution strengtheners. Virtually all nickel base superalloys also contain cobalt in levels of about 10%, and carbon in levels of about .1% which acts as a grain boundary strengthener and forms carbides which strengthen the alloy. Boron and zirconium are also often added in small amounts as grain boundary strengtheners.
Most commonly, gas turbine blades are formed by casting and the casting process most often utilized pro-duces parts having equiaxed nonoriented grains. It is well known that the high temperature properties of metals are usually quite dependent upon grain boundary properties, consequently efforts have been made to strengthen such boundaries (for example by the additions discussed previously), or to reduce or eliminate the grain boundaries transverse to the major stress axis of the part. One method of eliminating such transverse boundaries is termed directional solidification and is described in U.S. Patent No. 3,260,505. The effect of directional solidification is to produce an oriented microstructure of columnar grains whose major axis is parallel to the stress axis of the part and which has minimal or no grain boundaries perpendicular to the stress axis of the part.
A further extension of this concept is the utilization of single crystal parts in gas turbine blades. This concept is described in U.S. Patent No. 3,494,709. The obvious advantage of the single crystal blade is the complete absence of grain boundaries. In single crystals, there-fore, grain boundaries are eliminated as potential weaknesses, hence, the mechanical properties of the single crystal are completely dependent upon the inherent mechanical properties of the material.
In the prior art alloy development much effort was devoted to the solution of problems resulting from grain boundaries, through the addition of elements such as carbon, boron, and zirconium. Another problem which prior art alloy development sought to avoid was the develop-ment of deleterious phases after long term exposures at elevated temperatures (i.e. alloy instability~O These phases are of two general types. One, such as sigma, is undesirable because of its brittle nature while the other, such as mu, is undesirable because the phase ties up large amounts of the refractory solid solution strengtheners thus weakening the remaining alloy phases. These phases have been termed TCP phases for topologically close packed phases, and one of their common properties is that they all .-contain cobalt. There are of course TCP phases which can form in the absence of cobalt but these cobalt free ~8425 TCP phases contain other elements such as silicon which are not commonly found in nickel base superalloys. While an obvious remedy to control these deleterious phases is the removal of cobalt, this has not proved practical in prior art alloys for polycrystalline applications.
The problem is that if the cobalt is removed the carbon combines preferentially with the refractory metals to form M6C carbides which are dele~erious to the properties of the material as their formation depletes the alloy of the strengthening refractory elements.
U.S. Patent No. 3,567,526 teaches that carbon can be completely removed from single crystal superalloy articles and that such removal improves fatigue properties.
In single crystal articles which are free from carbon there are two important strengthening mechanisms. The most important strengthening mechanism is the inter-metallic gamma prime phase, Ni3(Al, Ti). In modern nickel base superalloys the gamma prime phase may occur in quantities as great as 60 volume percent. The second strengthening mechanism is the solid solution strengthen-ing which is produced by the presence of the refractory metals such as tungsten and molybdenum in the nickel solid solution matrix. For a constant volume fraction of gamma prime, considerable variations in the strength-ening effect of this volume fraction of gamma prime may be obtained by varying the size and morphology of the gamma prime precipitate particles. The gamma prime phase is characterized by having a solvus temperature above ~98425 which the phase dissolves into the matrix. In many cast alloys, however, the gamma prime solvus temperature is in fact above the incipient melting temperature so that it is not possible to effectively solutionize the gamma prime phase. Solutionizing of the gamma prime is the only practical way in which the morphology of the gamma prime can be modified, hence for many commercial nickel base superalloys the gamma prime morpholog~ is limited to the morphology which resulted from the original casting process. The other strengthening mechanism, solid solution strengthening, is most effective when the solid solution strengthening elements are uniformly distributed throughout the nickel solid solution matrix. Again this strengthening is reduced in effectiveness because of the nature of the casting process. Practical nickel base superalloys freeze over a wide temperature range. The freezing or solidification process involves the formation of high melting point dendrites followed by the subsequent .
freezing of the lower temperature melting interdendritic fluid. I'his solidification process leads to significant compositional inhomogenities throughout the microstructure.
Lt is theoretically possible to homogenize such a micro-structure by heating at elevated temperatures to permit diffusion to occur, however, in practical nickel base superalloys the maximum homogenization temperature, which is limited by the incipient melting temperature, is too low to permit significant homogenization in practical time intervals.
98~25 SUMMARY OF THE INVENTION
This invention includes three interrelated aspects.
The first aspect is the particular alloy employed. In its broadest form the alloy is a nickel base alloy containing from about 5 to about 18% chromium, at least 5% of an element chosen from the group consisting of from 2 to 8%
aluminum and from 1 to 5% titanium and mixtures thereof, at least 5% of an element chosen from the group consisting of up to 10% molybdenum, up to 15% tungsten, up to 12%
tantalum, up to 7% rhenium, up to 3.5% hafnium, and up to 3% columbium, and mixtures thereof, balance essentially nickel. The alloy employed in the present invention is free from intentional additions of cobalt, carbon, boron and zirconium, although obviously these elements may be present in impurity levels. The alloy is charac~erized by having an incipient melting temperature in excess of about 2300F and by having a gamma prime solvus tempera-ture which is significantly below this incipient melting temperature but at the same time is higher than the gamma prime solvus temperatures for typical commercial nickel base superalloys. Thus this alloy may be heat treated under conditions which permit complete solutionizing of the gamma prime phase without incipient melting. At the same time the high incipient melting temperature permits essentially complete homogenization of the alloy in commercially practicable times. The high incipient melt-ing temperature of the alloy is a result of the absence of carbon, boron and zirconium. The absence of cobalt ~0~8425 inhibits the formation of deleterious TCP phases.
The second important aspect of the invention is the formation of the previously described alloy into single crystal articles.
The third aspect of the invention is the heat treat-ment sequence by which the gamma prime morphology may be modified and refined at the same time that significant homogenization of the as cast microstructure is performed.
The resultant single crystal article will have a micro-structure whose typical gamma prime particle size is about 1/5 of the gamma prime particle size found in the as cast material. At the same time the heat treated single crystal microstructure will be essentially free from compositional inhomogenities and this uniform micro-structure combined with the increased gamma prime solvus temperature will permit the article of the present inven-tion to exhibit temperature capabilities, for equal mechanical properties, which are at least 30 F greater than the temperature capabilities of comparable prior art single crystal articles which are formed from conventional alloys containing cobalt, carbon, boron and zirconium.
The foregoing, and other objects, features and advantages of the present invention will become more apparent in the light of the following detailed descrip-tion of the preferred embodiment thereof as shown in the accompanying drawing.
:
lC~Q842S
In accordance with a broad aspect of the invention, there is provided a single crystal nicXel base superalloy arti-cle free from intentional additions of cobalt, carbon, boron and zirconium, containing in percentages by weight from about 5 to about 18% chromium, at least 5% of an element ch~serl from the group consisting of from 2 to 8% alu~inum and from 1 to 5%
titanium and mixtures thereof, at least 5% of an element chosen from the group consisting of up to 10% molybdenum, up to 15%
tungsten, up to 12% tantalum, up to 3% columbium, up to 3.5%
hafnium, up to 7% rhenium, and mixtures thereof balance essentially nickel, said single crystal article having a homogeneous microstructure which contains gam~a prime particles having a size of less than .5 microns, and said microstructures being free of MC type carbides, and TCP phases.
In accordance with another aspect of the invention, there is provided a method for producing nickel base superalloy single crystal articles which have a homogeneous microstructure and in which the gamma prime phase presents a refined morpholo-gy, including the steps of:
a. providing a mass of nickel base superalloy material which is free from intentional additions of cobalt, carbon boron, and zirconium, and contains in percentages by weight from about 5 to 18% chromium at least 5% of an element chosen from the group consisting of from 2 to 8% aluminum and from 1 to 5% titanium and mix-tures thereof, at least 5% of an element chosen from the group consisting of up to 10% molybdenum, up to 15% tungsten, up to 12% tantalum, up to 3%
columbium, up to 3.5% hafnium, up to 7% rhenium, and mixtures thereof balance essentially nickel, -8a-10~8425 b. melting the nickel base superalloy a~d solidify-ing the alloy under conditions of unidirectional heat flow so as to produce a single crystal arti-cle having a microstructure which consists essentially of gamma prime particles in a gamma prime matrix, with the gamma prime particles having a particle size of about 1.5 microns, said article having an incipient melting tempe-rature and a gamma prime solvus temperature, wherein the gamma prime solvus temperature is less than the incipient melting temperature, said microstructure being free of MC type carbides and TCP phase3, c. heating the article to a temperature greater than the gamma prime solvus temperature and less than the incipient melting temperature for a period of time sufficient to dissolve subs-tantially all of the gamma prime phase into solid solution while simultaneously homogenizing the microstructure, d. heating the article at a temperature below the gamma prime 301vu9 for a period of time sufficient to reprecipitate the gamma prime phase in refined form, whereby the heat treated single crystal article has a tempera-ture advantage of at least 30F over non-heat treated articles.
-8b-la~s4zs BRIEF DESCRIPTION OF THE DRAWING
Fig. 1 shows the as cast microstructure of the invention alloy;
Fig. 2 shows the microstructure of the invention alloy after a 4 hour exposure at 2200 F;
Fig. 3 shows the microstructure of the invention alloy after a 4 hour exposure at 2350 F;
Fig. 4 is an electron micrograph showing the as cast gamma prime morphology of the invention alloy;
Fig. 5 is an electron micrograph showing the gamma prime morphology of the invention alloy after heat treatment at 2350 F for 4 hours and 1975 F for 4 hours and 1600 F for 32 hours;
Fig. 6 shows a comparison of the creep strength of the article of the invention with the prior art;
Fig. 7 shows the microstructure of the invention alloy after 500 hours at 1800F; and Fig. 8 shows the microstructure of a prior art alloy after 500 hours at 1800 F.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In the description which follows, all percent figures are in weight percent unless otherwise specified.
This invention relates to an article made of a specific alloy by a critical series of process steps.
Although other articles may be produced according to this invention, this invention has particular utility in the fabrication of airfoils (blades and vanes) for use in gas turbine engines.
2~
A primary feature in the alloys employed in the present invention is the substantial elimination of both cobalt and the grain boundary strengthening agents, carbon, boron and zirconium. The alloys of the invention are intended for use as gas turbine components in single crystal form. No i~tentional additions of these elements, cobalt, carbon, boron and zirconium are made, however, some will invariably be present as an impurity.
In order to ensure that TCP phases will not form in the alloy over a wide range of compositions and operating conditions, the level of cobalt, as an impurity, is restricted to less than about .5% and most preferably is restricted to less than about .2%.
Likewise, with regard to the grain boundary strengthening agents carbon, boron and zirconium, no intentional additions are made. If the maximum benefit is to be obtained from this invention, no single element of the group carbon, boron and zirconium should be present in an amount greater than 50 ppm and it is preferred that the total of such impurities be less than 100 ppm. Most preferably carbon is present in an amount less than 30 ppm and the remaining elements are each present in quantities less than 20 ppm. In any event, the carbon level must be restricted to be below that amount of carbon which will form MC type carbides. It must be emphasized that no intentional addition of these elements is contemplated and that their presence in the alloy or single crystal article of the invention is unintentional ~C! 98425 and undesirable.
Alloys which can be produced using the concept of the present invention will contain:
1) from 5 to 18% chromium, 2) at least 5% of an element chosen from the group consisting of from 2 to 8% aluminum and from 1 to 5% titanium and mixtures thereof,
A primary feature in the alloys employed in the present invention is the substantial elimination of both cobalt and the grain boundary strengthening agents, carbon, boron and zirconium. The alloys of the invention are intended for use as gas turbine components in single crystal form. No i~tentional additions of these elements, cobalt, carbon, boron and zirconium are made, however, some will invariably be present as an impurity.
In order to ensure that TCP phases will not form in the alloy over a wide range of compositions and operating conditions, the level of cobalt, as an impurity, is restricted to less than about .5% and most preferably is restricted to less than about .2%.
Likewise, with regard to the grain boundary strengthening agents carbon, boron and zirconium, no intentional additions are made. If the maximum benefit is to be obtained from this invention, no single element of the group carbon, boron and zirconium should be present in an amount greater than 50 ppm and it is preferred that the total of such impurities be less than 100 ppm. Most preferably carbon is present in an amount less than 30 ppm and the remaining elements are each present in quantities less than 20 ppm. In any event, the carbon level must be restricted to be below that amount of carbon which will form MC type carbides. It must be emphasized that no intentional addition of these elements is contemplated and that their presence in the alloy or single crystal article of the invention is unintentional ~C! 98425 and undesirable.
Alloys which can be produced using the concept of the present invention will contain:
1) from 5 to 18% chromium, 2) at least 5% of an element chosen from the group consisting of from 2 to 8% aluminum and from 1 to 5% titanium and mixtures thereof,
3) at least 5% of an element chosen from the group consisting of up to 10% molybdenum, up to 15%
tungsten, up to 12a/o tantalum, up to 3% columbium, up to 3.5% hafnium, up to 7% rhenium, and mixtures thereof, and
tungsten, up to 12a/o tantalum, up to 3% columbium, up to 3.5% hafnium, up to 7% rhenium, and mixtures thereof, and
4) balance essentially nickel.
Hafnium has been used in prior art alloys as a grain boundary strengthener. In the absence of grain boundaries (i.e. single crystals), hafnium can perform other func-tions, for example it has been observed to substitute for Al in gamma prime. In addition, it does not have the extreme effects on incipient melting points that the ; 20 other grain boundary strengthening agents, such as carbon, and boron have. For these reasons, hafnium need not be excluded from the alloy.
Alloys selected within the above ranges will have incipient melting temperatures which exceed 2300 F and gamma prime solvus temperatures which are at least 35F
below the incipient melting temperature.
Alloys made according to the preceding limitation will comprise a nickel chromium solid solution containing ~8~2S
a~ least 30% by volume of an ordered phase of the composi-tion Ni3M where M is aluminim, titanium, columbium, tantalum, tungsten, hafnium or mixtures thereof.
The alloys within the ranges set forth above are thermally stable since microstructural instab~lities such as the cobalt containing TCP phases will not form, even after extended exposure at elevated temperature as for example 500 hours at 1800F. Further the alloys have good fatigue properties since the formation of deleterious carbide particles is prevented. The refractory metals which would normally combine with car-bon or precipitate in TCP phase formation remain in solid solution and result in an alloy having exceptional mechanical properties.
An important benefit which arises from the elimination of boron, carbon and zirconium is an increase in the incipient melting temperature. Typically the incipient melting tempera-ture of the present alloys, that temperature at which the alloy first begins localized melting, will be increased by at least 50F over the incipient melting temperature of a similar (prior art) alloy which contains normal amounts of carbon, boron and zirconium. The incipient melting tempera-ture of the alloy of this invention will typically exceed 2300F while conventional high strength, high volume fraction ~' alloys have incipient melting temperatures below about 2300F. This increased temperature permits solution-izing heat treatments to be performed at temperatures ~g84~5 where complete solutionizing of the gamma prime is possible while simultaneously permitting a significant amount of homo-genization within reasonable times.
The alloys of the present invention will not form the carbides which have been found necessary for grain boundary strenthening in polycrystalline nickel base superalloys. For this reason the alloys of the present invention must be used as single crystal articles. The formation of the alloy into single crystal form is a critical aspect of the present inven-10 tion, but the method of single crystal formation is uniimpor-tant. Typical articles and solidification techniques are described in U.S. Patent ~o. 3,494,709 to Piearcey, which is assigned to the assignee of the present application.
The final aspect of the invention involves the specific heat treatment applied to the single crystal article.
The as cast single crystal article will contain the gamma prime phase in dispersed form with a typical particle size of 1.5 microns. The gamma prime solvus of the alloy will typically fall in the range of 2250-2450F and the incipient melting 20 temperature will be in excess of about 2300F. Thus heat treatment in the range of 2285-2500F will place the gamma prime phase into solution without deleterious localized melt-ing. Times on the order of 1/2 to 8 hours will normally be satisfactory ~3{at3425 although longer times may be employed. Such heat treatment temperatures are about 100 F higher than those which can be employed with polycrystalline articles of conventional superalloys. This elevated temperature permits a substan-tial amount of homogenization to occur during the solutionizing steps.
Fig. 1 shows the microstructure of the alloy of the invention in the as cast condition. Fig. 2 shows the microstructure after a 4 hour heat treatment at 2200F
(typical of treatments used with conventional superalloys) showing that little homogenization has occurred. Fig. 3 shows the microstructure of another sample of the same alloy after a 4 hour treatment at 2350 F. A high degree of homogenization is readily apparent.
Following the solutionizing treatment, an aging treatment at 1600-2000 F may be utilized to reprecipitate the gamma prime in refined form. Typical gamma prime particle sizes after reprecipitation will be less than about .5 microns.
Fig. 4 shows an electron micrograph showing the gamma prime particle morphology in the as cast single crystal alloy of the present invention. Fig. 5 shows the gamma prime morphology after the heat treatment discussed above (4 hours at 2350F followed by 4 hours at 1975 F
and 32 hours at 1600 F). The refinement of the gamma prime is obvious.
The preceding discussion of the preferred embodiment will be clarified through reference to the following 8~25 illustrative examples-Example 1 Two alloys were prepared for comparative tests. The alloys had compositions as follows:
TABLE I
Alloy 444 PWA 1409 (nominal~
Carbon 50 ppm max 0.15 Tungsten 11.5-12,5 12.5 Titanium 1.75-2.25 2.0 Columbium .75-1.25 1.0 Zirconium 20 ppm max ,05 Cobalt .1 max 10.0 Chromium 8.0-10.0 9.0 Aluminum 4.75-5~25 5.0 Boron 20 ppm max 0.015 Nickel balance balance The alloy identified as Alloy 444 had a composition falling within the ranges disclosed in the present appli-cation while the alloy denoted as PWA 1409 had a similar composition except for the presence of cobalt, boron, carbon and zirconium. These alloys were fashioned into single crystals having similar crystallographic orientationsO
Example 2 The alloys prepared as Example 1 were tested at ele-vated temperatures. The test conditions and test results are listed below in Table II.
~(~984ZS
TABLE II
Time to Temp.Stress 1% Creep Life Alloy (F) (ksi) (hrs.) (hrs.) Alloy 444 1400 110 144 567 These results clearly demonstrate the superior mechanical properties as compared to a similar prior art nickel base superalloy containing cobalt, carbon, boron and zirconium. Both the time to 1% creep and the time to rupture are increased, except at 1600F where the time to 1% creep is unaffectedD The alloy of the present invention is particularly superior at 1800F which is significant in view of the increased operating tempera-tures used in current gas turbine engines.
Example 3 Alloys having nominal compositions as set forth in Table III were prepared in single crystal form (except for alloys A and B which were prepared in directionally solidified columnar grain form according to current commercial practice). These alloys differed only in the amounts of cobalt, boron, zirconium, hafnium and carbon which were present. Thus alloy D (the invention) may be completely solutionized since the incipient melting -1~3Q8~2S
temperature is safely above the gamma prime solvus temperature. The permitted homogenization temperature for alloy D is 175 greater than that usable with the commercial alloy.
The incipient melting temperature was determined to be: alloy A, 2200F; alloy B, 2265F; alloy C, 2325F; and alloy D, 2375F. Thus alloy D (the invention) may be completely solutionized since the incipient melting temperature is safely above the gamma prime solvus temperature. The permitted homogenization temperature for alloy D is 175 F greater than that usable with the commercial alloy.
Fig. 6 shows a plot of the stress rupture properties of allo~ A and D. Calculation from this figure shows that the alloy of the invention displays a temperature advantage of about 50 F for equivalent conditions or stress and time at 1800 F over alloy A.
TABLE III
A B C D
Carbon .15 .15~ 20 ppm~10 ppm Boron .015 .015.015~ 5 ppm Zirconium .1 .1 .1 ~ 5 ppm Hafnium 2.0 < 50 ppm< 50 ppm~ 50 ppm Cobalt 10.0 lO.Q10.0 ~ .1 Chromium 9.0 9.09.0 9.0 Tungsten 12.0 12.012.0 12.0 Columbium 1.0 1.01.0 1.0 Titanium 2.0 2.02.0 2.0 Aluminum 5.0 5.05.0 5.0 Nickel Bal BalBal Bal ~ sol~us2250 22502250 2335 Incipient2200 22652325 2375 melting point Example 4 Samples of the alloys of Example 3 were exposed at 1800F for 500 hours and examined.
Fig. 7 shows the microstructure of Alloy 444 (alloy D, the invention) at a magnification of 250X, and Fig. 8 shows the microstructure of alloy C at a ma~nification of 500X~ Figs. 7 and 8 show the metallographic structures after this long term, high temperature exposure. An acicular TCP~ phase is clearly visible in the cobalt containing alloy in Fig. 8.
10~8425 Although the invention has been shown and described with respect to a preferred embodiment thereof, it should be understood by those skilled in the art that various changes and omissions in the form and detail thereof may be made therein without departing from the spirit and scope of the invention.
Hafnium has been used in prior art alloys as a grain boundary strengthener. In the absence of grain boundaries (i.e. single crystals), hafnium can perform other func-tions, for example it has been observed to substitute for Al in gamma prime. In addition, it does not have the extreme effects on incipient melting points that the ; 20 other grain boundary strengthening agents, such as carbon, and boron have. For these reasons, hafnium need not be excluded from the alloy.
Alloys selected within the above ranges will have incipient melting temperatures which exceed 2300 F and gamma prime solvus temperatures which are at least 35F
below the incipient melting temperature.
Alloys made according to the preceding limitation will comprise a nickel chromium solid solution containing ~8~2S
a~ least 30% by volume of an ordered phase of the composi-tion Ni3M where M is aluminim, titanium, columbium, tantalum, tungsten, hafnium or mixtures thereof.
The alloys within the ranges set forth above are thermally stable since microstructural instab~lities such as the cobalt containing TCP phases will not form, even after extended exposure at elevated temperature as for example 500 hours at 1800F. Further the alloys have good fatigue properties since the formation of deleterious carbide particles is prevented. The refractory metals which would normally combine with car-bon or precipitate in TCP phase formation remain in solid solution and result in an alloy having exceptional mechanical properties.
An important benefit which arises from the elimination of boron, carbon and zirconium is an increase in the incipient melting temperature. Typically the incipient melting tempera-ture of the present alloys, that temperature at which the alloy first begins localized melting, will be increased by at least 50F over the incipient melting temperature of a similar (prior art) alloy which contains normal amounts of carbon, boron and zirconium. The incipient melting tempera-ture of the alloy of this invention will typically exceed 2300F while conventional high strength, high volume fraction ~' alloys have incipient melting temperatures below about 2300F. This increased temperature permits solution-izing heat treatments to be performed at temperatures ~g84~5 where complete solutionizing of the gamma prime is possible while simultaneously permitting a significant amount of homo-genization within reasonable times.
The alloys of the present invention will not form the carbides which have been found necessary for grain boundary strenthening in polycrystalline nickel base superalloys. For this reason the alloys of the present invention must be used as single crystal articles. The formation of the alloy into single crystal form is a critical aspect of the present inven-10 tion, but the method of single crystal formation is uniimpor-tant. Typical articles and solidification techniques are described in U.S. Patent ~o. 3,494,709 to Piearcey, which is assigned to the assignee of the present application.
The final aspect of the invention involves the specific heat treatment applied to the single crystal article.
The as cast single crystal article will contain the gamma prime phase in dispersed form with a typical particle size of 1.5 microns. The gamma prime solvus of the alloy will typically fall in the range of 2250-2450F and the incipient melting 20 temperature will be in excess of about 2300F. Thus heat treatment in the range of 2285-2500F will place the gamma prime phase into solution without deleterious localized melt-ing. Times on the order of 1/2 to 8 hours will normally be satisfactory ~3{at3425 although longer times may be employed. Such heat treatment temperatures are about 100 F higher than those which can be employed with polycrystalline articles of conventional superalloys. This elevated temperature permits a substan-tial amount of homogenization to occur during the solutionizing steps.
Fig. 1 shows the microstructure of the alloy of the invention in the as cast condition. Fig. 2 shows the microstructure after a 4 hour heat treatment at 2200F
(typical of treatments used with conventional superalloys) showing that little homogenization has occurred. Fig. 3 shows the microstructure of another sample of the same alloy after a 4 hour treatment at 2350 F. A high degree of homogenization is readily apparent.
Following the solutionizing treatment, an aging treatment at 1600-2000 F may be utilized to reprecipitate the gamma prime in refined form. Typical gamma prime particle sizes after reprecipitation will be less than about .5 microns.
Fig. 4 shows an electron micrograph showing the gamma prime particle morphology in the as cast single crystal alloy of the present invention. Fig. 5 shows the gamma prime morphology after the heat treatment discussed above (4 hours at 2350F followed by 4 hours at 1975 F
and 32 hours at 1600 F). The refinement of the gamma prime is obvious.
The preceding discussion of the preferred embodiment will be clarified through reference to the following 8~25 illustrative examples-Example 1 Two alloys were prepared for comparative tests. The alloys had compositions as follows:
TABLE I
Alloy 444 PWA 1409 (nominal~
Carbon 50 ppm max 0.15 Tungsten 11.5-12,5 12.5 Titanium 1.75-2.25 2.0 Columbium .75-1.25 1.0 Zirconium 20 ppm max ,05 Cobalt .1 max 10.0 Chromium 8.0-10.0 9.0 Aluminum 4.75-5~25 5.0 Boron 20 ppm max 0.015 Nickel balance balance The alloy identified as Alloy 444 had a composition falling within the ranges disclosed in the present appli-cation while the alloy denoted as PWA 1409 had a similar composition except for the presence of cobalt, boron, carbon and zirconium. These alloys were fashioned into single crystals having similar crystallographic orientationsO
Example 2 The alloys prepared as Example 1 were tested at ele-vated temperatures. The test conditions and test results are listed below in Table II.
~(~984ZS
TABLE II
Time to Temp.Stress 1% Creep Life Alloy (F) (ksi) (hrs.) (hrs.) Alloy 444 1400 110 144 567 These results clearly demonstrate the superior mechanical properties as compared to a similar prior art nickel base superalloy containing cobalt, carbon, boron and zirconium. Both the time to 1% creep and the time to rupture are increased, except at 1600F where the time to 1% creep is unaffectedD The alloy of the present invention is particularly superior at 1800F which is significant in view of the increased operating tempera-tures used in current gas turbine engines.
Example 3 Alloys having nominal compositions as set forth in Table III were prepared in single crystal form (except for alloys A and B which were prepared in directionally solidified columnar grain form according to current commercial practice). These alloys differed only in the amounts of cobalt, boron, zirconium, hafnium and carbon which were present. Thus alloy D (the invention) may be completely solutionized since the incipient melting -1~3Q8~2S
temperature is safely above the gamma prime solvus temperature. The permitted homogenization temperature for alloy D is 175 greater than that usable with the commercial alloy.
The incipient melting temperature was determined to be: alloy A, 2200F; alloy B, 2265F; alloy C, 2325F; and alloy D, 2375F. Thus alloy D (the invention) may be completely solutionized since the incipient melting temperature is safely above the gamma prime solvus temperature. The permitted homogenization temperature for alloy D is 175 F greater than that usable with the commercial alloy.
Fig. 6 shows a plot of the stress rupture properties of allo~ A and D. Calculation from this figure shows that the alloy of the invention displays a temperature advantage of about 50 F for equivalent conditions or stress and time at 1800 F over alloy A.
TABLE III
A B C D
Carbon .15 .15~ 20 ppm~10 ppm Boron .015 .015.015~ 5 ppm Zirconium .1 .1 .1 ~ 5 ppm Hafnium 2.0 < 50 ppm< 50 ppm~ 50 ppm Cobalt 10.0 lO.Q10.0 ~ .1 Chromium 9.0 9.09.0 9.0 Tungsten 12.0 12.012.0 12.0 Columbium 1.0 1.01.0 1.0 Titanium 2.0 2.02.0 2.0 Aluminum 5.0 5.05.0 5.0 Nickel Bal BalBal Bal ~ sol~us2250 22502250 2335 Incipient2200 22652325 2375 melting point Example 4 Samples of the alloys of Example 3 were exposed at 1800F for 500 hours and examined.
Fig. 7 shows the microstructure of Alloy 444 (alloy D, the invention) at a magnification of 250X, and Fig. 8 shows the microstructure of alloy C at a ma~nification of 500X~ Figs. 7 and 8 show the metallographic structures after this long term, high temperature exposure. An acicular TCP~ phase is clearly visible in the cobalt containing alloy in Fig. 8.
10~8425 Although the invention has been shown and described with respect to a preferred embodiment thereof, it should be understood by those skilled in the art that various changes and omissions in the form and detail thereof may be made therein without departing from the spirit and scope of the invention.
Claims (8)
1. A single crystal nickel base superalloy article free from intentional additions of cobalt, carbon, boron and zirconium, containing in percentages by weight from about 5 to about 18% chromium, at least 5% of an element chosen from the group consisting of from 2 to 8% aluminum and from 1 to 5%
titanium and mixtures thereof, at least 5% of an element chosen from the group consisting of up to 10% molybdenum, up to 15%
tungsten, up to 12% tantalum, up to 3% columbium, up to 3.5%
hafnium, up to 7% rhenium, and mixtures thereof, balance essentially nickel, said single crystal article having a homogeneous microstructure which contains gamma prime particles having a size of less than .5 microns, and said microstructures being free of MC type carbides, and TCP phases.
titanium and mixtures thereof, at least 5% of an element chosen from the group consisting of up to 10% molybdenum, up to 15%
tungsten, up to 12% tantalum, up to 3% columbium, up to 3.5%
hafnium, up to 7% rhenium, and mixtures thereof, balance essentially nickel, said single crystal article having a homogeneous microstructure which contains gamma prime particles having a size of less than .5 microns, and said microstructures being free of MC type carbides, and TCP phases.
2. An article as in claim 1 in which the impurity levels of carbon, boron and zirconium do not individually exceed 50 ppm.
3. An article as in claim 1 in which the impurity levels of carbon, boron and zirconium do not collectively exceed 100 ppm.
4. An article as in claim 1 in which the impurity level of cobalt does not exceed .5%.
5. An article as in claim 1 in which the impurity level of cobalt does not exceed .2%.
6. An article as in claim 1 which contains from 8 to 10% chromium, from 11.5 to 12.5% tungsten, from 1.75 to 2.25% titanium, from 4.75 to 5.25% aluminum, from .75 to 1.25% columbium, and as impurities, not more than .1% cobalt, not more than 50 ppm carbon, not more than 20 ppm boron, not more than 20 ppm zirconium, and not more than 20 ppm hafnium.
7. A method for producing nickel base superalloy single crystal articles which have a homogeneous microstructure and in which the gamma prime phase presents a refined morphology, including the steps of:
a. providing a mass of nickel base superalloy material which is free from intentional additions of cobalt, carbon boron, and zirconium, and contains in percentages by weight from about 5 to 18% chromium; at least 5% of an element chosen from the group consisting of from 2 to
a. providing a mass of nickel base superalloy material which is free from intentional additions of cobalt, carbon boron, and zirconium, and contains in percentages by weight from about 5 to 18% chromium; at least 5% of an element chosen from the group consisting of from 2 to
8% aluminum and from 1 to 5% titanium and mix-tures thereof, at least 5% of an element chosen from the group consisting of up to 10% molybdenum, up to 15% tungsten, up to 12% tantalum, up to 3%
columbium, up to 3.5% hafnium, up to 7% rhenium, and mixtures thereof, balance essentially nickel, b. melting the nickel base superalloy and solidify-ing the alloy under conditions of unidirectional heat flow so as to produce a single crystal arti-cle having a microstructure which consists essentially of gamma prime particles in a gamma prime matrix, with the gamma prime particles having a particle size of about 1.5 microns, said article having an incipient melting tempe-rature and a gamma prime solvus temperature, wherein the gamma prime solvus temperature is less than the incipient melting temperature, said microstructure being free of MC type carbides and TCP phases, c. heating the article to a temperature greater than the gamma prime solvus temperature and less than the incipient melting temperature for a period of time sufficient to dissolve subs-tantially all of the gamma prime phase into solid solution while simultaneously homogenizing the microstructure, d. heating the article at a temperature below the gamma prime solvus for a period of time sufficient to reprecipitate the gamma prime phase in refined form, whereby the heat treated single crystal article has a tempera-ture advantage of at least 30°F over non-heat treated articles.
columbium, up to 3.5% hafnium, up to 7% rhenium, and mixtures thereof, balance essentially nickel, b. melting the nickel base superalloy and solidify-ing the alloy under conditions of unidirectional heat flow so as to produce a single crystal arti-cle having a microstructure which consists essentially of gamma prime particles in a gamma prime matrix, with the gamma prime particles having a particle size of about 1.5 microns, said article having an incipient melting tempe-rature and a gamma prime solvus temperature, wherein the gamma prime solvus temperature is less than the incipient melting temperature, said microstructure being free of MC type carbides and TCP phases, c. heating the article to a temperature greater than the gamma prime solvus temperature and less than the incipient melting temperature for a period of time sufficient to dissolve subs-tantially all of the gamma prime phase into solid solution while simultaneously homogenizing the microstructure, d. heating the article at a temperature below the gamma prime solvus for a period of time sufficient to reprecipitate the gamma prime phase in refined form, whereby the heat treated single crystal article has a tempera-ture advantage of at least 30°F over non-heat treated articles.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US742,967 | 1976-11-17 | ||
| US05/742,967 US4116723A (en) | 1976-11-17 | 1976-11-17 | Heat treated superalloy single crystal article and process |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1098425A true CA1098425A (en) | 1981-03-31 |
Family
ID=24986969
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA291,053A Expired CA1098425A (en) | 1976-11-17 | 1977-11-16 | Heat treated superalloy single crystal article and process |
Country Status (13)
| Country | Link |
|---|---|
| US (1) | US4116723A (en) |
| JP (1) | JPS5934776B2 (en) |
| BE (1) | BE860414A (en) |
| BR (1) | BR7707601A (en) |
| CA (1) | CA1098425A (en) |
| CH (1) | CH637165A5 (en) |
| DE (1) | DE2749080A1 (en) |
| FR (1) | FR2371516A1 (en) |
| GB (1) | GB1559711A (en) |
| IL (1) | IL53314A (en) |
| IT (1) | IT1089426B (en) |
| NO (1) | NO148930C (en) |
| SE (1) | SE443998B (en) |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3494709A (en) * | 1965-05-27 | 1970-02-10 | United Aircraft Corp | Single crystal metallic part |
| DE1936007A1 (en) * | 1968-07-19 | 1970-01-22 | United Aircraft Corp | Process to make the nickel superalloys processable |
| BE743403A (en) * | 1969-03-26 | 1970-05-28 | ||
| BE756653A (en) * | 1969-09-26 | 1971-03-01 | United Aircraft Corp | THERMO-MECHANICAL INCREASE IN THE STRENGTH OF SUPERALLOYS ( |
-
1976
- 1976-11-17 US US05/742,967 patent/US4116723A/en not_active Expired - Lifetime
-
1977
- 1977-11-01 GB GB45422/77A patent/GB1559711A/en not_active Expired
- 1977-11-02 SE SE7712365A patent/SE443998B/en not_active IP Right Cessation
- 1977-11-02 CH CH1334177A patent/CH637165A5/en not_active IP Right Cessation
- 1977-11-02 DE DE19772749080 patent/DE2749080A1/en not_active Withdrawn
- 1977-11-03 BE BE182291A patent/BE860414A/en not_active IP Right Cessation
- 1977-11-04 FR FR7733164A patent/FR2371516A1/en active Granted
- 1977-11-07 IL IL53314A patent/IL53314A/en unknown
- 1977-11-08 JP JP52134022A patent/JPS5934776B2/en not_active Expired
- 1977-11-09 NO NO773829A patent/NO148930C/en unknown
- 1977-11-14 BR BR7707601A patent/BR7707601A/en unknown
- 1977-11-15 IT IT29685/77A patent/IT1089426B/en active
- 1977-11-16 CA CA291,053A patent/CA1098425A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| GB1559711A (en) | 1980-01-23 |
| SE443998B (en) | 1986-03-17 |
| BR7707601A (en) | 1978-08-22 |
| CH637165A5 (en) | 1983-07-15 |
| SE7712365L (en) | 1978-05-18 |
| FR2371516A1 (en) | 1978-06-16 |
| JPS5363212A (en) | 1978-06-06 |
| NO148930C (en) | 1984-01-11 |
| IL53314A (en) | 1981-02-27 |
| BE860414A (en) | 1978-03-01 |
| NO148930B (en) | 1983-10-03 |
| FR2371516B1 (en) | 1981-01-02 |
| NO773829L (en) | 1978-05-19 |
| IL53314A0 (en) | 1978-01-31 |
| US4116723A (en) | 1978-09-26 |
| IT1089426B (en) | 1985-06-18 |
| JPS5934776B2 (en) | 1984-08-24 |
| DE2749080A1 (en) | 1978-05-24 |
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