CA1133366A - Method of selective grain growth in nickel-base superalloys by controlled boron diffusion - Google Patents
Method of selective grain growth in nickel-base superalloys by controlled boron diffusionInfo
- Publication number
- CA1133366A CA1133366A CA341,220A CA341220A CA1133366A CA 1133366 A CA1133366 A CA 1133366A CA 341220 A CA341220 A CA 341220A CA 1133366 A CA1133366 A CA 1133366A
- Authority
- CA
- Canada
- Prior art keywords
- boron
- article
- carbon
- grain growth
- nickel
- 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
Links
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 title claims abstract description 22
- 229910052796 boron Inorganic materials 0.000 title claims abstract description 22
- 238000000034 method Methods 0.000 title claims abstract description 16
- 229910000601 superalloy Inorganic materials 0.000 title claims abstract description 12
- 238000009792 diffusion process Methods 0.000 title claims abstract description 9
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 20
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 20
- 229910045601 alloy Inorganic materials 0.000 claims abstract description 17
- 239000000956 alloy Substances 0.000 claims abstract description 17
- 239000012298 atmosphere Substances 0.000 claims abstract description 10
- 239000002131 composite material Substances 0.000 claims abstract description 7
- 239000000203 mixture Substances 0.000 claims description 7
- 238000006467 substitution reaction Methods 0.000 claims 1
- 238000010438 heat treatment Methods 0.000 abstract description 17
- 238000004519 manufacturing process Methods 0.000 abstract description 3
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 14
- 238000001816 cooling Methods 0.000 description 9
- 229910052759 nickel Inorganic materials 0.000 description 7
- 239000000843 powder Substances 0.000 description 5
- 238000005242 forging Methods 0.000 description 4
- 238000000576 coating method Methods 0.000 description 3
- 230000003247 decreasing effect Effects 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 238000003754 machining Methods 0.000 description 3
- 238000001953 recrystallisation Methods 0.000 description 3
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 2
- 239000011521 glass Substances 0.000 description 2
- 238000005482 strain hardening Methods 0.000 description 2
- 101100084503 Caenorhabditis elegans pas-3 gene Proteins 0.000 description 1
- 206010016352 Feeling of relaxation Diseases 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- 241000282346 Meles meles Species 0.000 description 1
- 206010037660 Pyrexia Diseases 0.000 description 1
- 208000003629 Rupture Diseases 0.000 description 1
- 229910000756 V alloy Inorganic materials 0.000 description 1
- ABEXMJLMICYACI-UHFFFAOYSA-N [V].[Co].[Fe] Chemical compound [V].[Co].[Fe] ABEXMJLMICYACI-UHFFFAOYSA-N 0.000 description 1
- 238000007792 addition Methods 0.000 description 1
- 229910052786 argon Inorganic materials 0.000 description 1
- 238000005266 casting Methods 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 230000001010 compromised effect Effects 0.000 description 1
- 235000019628 coolness Nutrition 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 238000005262 decarbonization Methods 0.000 description 1
- 238000005261 decarburization Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000009977 dual effect Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000000265 homogenisation Methods 0.000 description 1
- 238000007731 hot pressing Methods 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 230000000977 initiatory effect Effects 0.000 description 1
- 230000000873 masking effect Effects 0.000 description 1
- 238000010297 mechanical methods and process Methods 0.000 description 1
- 230000005226 mechanical processes and functions Effects 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 238000004663 powder metallurgy Methods 0.000 description 1
- 230000035939 shock Effects 0.000 description 1
- 238000007669 thermal treatment Methods 0.000 description 1
- 238000011282 treatment Methods 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
- C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
- C22F1/10—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of nickel or cobalt or alloys based thereon
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C8/04—Treatment of selected surface areas, e.g. using masks
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01D—NON-POSITIVE DISPLACEMENT MACHINES OR ENGINES, e.g. STEAM TURBINES
- F01D25/00—Component parts, details, or accessories, not provided for in, or of interest apart from, other groups
- F01D25/005—Selecting particular materials
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Materials Engineering (AREA)
- Organic Chemistry (AREA)
- Metallurgy (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Crystallography & Structural Chemistry (AREA)
- Thermal Sciences (AREA)
- Physics & Mathematics (AREA)
- General Engineering & Computer Science (AREA)
- Turbine Rotor Nozzle Sealing (AREA)
- Powder Metallurgy (AREA)
- Heat Treatment Of Nonferrous Metals Or Alloys (AREA)
Abstract
11 47,546 ABSTRACT OF THE DISCLOSURE
This is a method for producing a composite grain structure in nickel-base superalloy articles by causing a controlled amount of grain growth in selected regions.
The method uses alloys containing 0.01-1.0 carbon and .02-.08 boron and a heat treatment in a non-reducing atmosphere after the alloy has been formed. The heat treatment causes diffusion of boron (but not carbon) in selected regions, lowering the amount of boron and causing controlled grain growth in these regions.
This is a method for producing a composite grain structure in nickel-base superalloy articles by causing a controlled amount of grain growth in selected regions.
The method uses alloys containing 0.01-1.0 carbon and .02-.08 boron and a heat treatment in a non-reducing atmosphere after the alloy has been formed. The heat treatment causes diffusion of boron (but not carbon) in selected regions, lowering the amount of boron and causing controlled grain growth in these regions.
Description
~33366 1 47,546 A METHOD OF SELECTIVE GRAIN GROWTH IN
NICKEL-BASE SUPERALLOYS BY
CONTROLLED BORON DIFFUSION
B GROUND O~ THE INVENTION
The present invention relates to nickel-based alloys having relatively great strength at high tempera-ture and generally referred to (e.g. U.S. Patent Re28,681 issued to Baldwin on January 13, 1976) as superalloys, and, in particular, to articles with different grain sizes in different portions of the article.
The literature shows that, for nickel-based superalloy systems, grain size has a definite effect on mechanical properties. In general, increasing grain size has the effect of increasing high temperature creep rup-ture properties. The effect of increasing grain size decreases the total grain boundary area and thereby re-duces the propensity of grain boundary failure mechanisms to occur.
Conversely, decreasing grain size enhances such properties as high cycle fatigue due to the increased fracture energy required to propagate cracks by enabling the increased grain boundary area to retard dislocation movement. In addition, such properties as impact strength 3 3 ~ 6~
NICKEL-BASE SUPERALLOYS BY
CONTROLLED BORON DIFFUSION
B GROUND O~ THE INVENTION
The present invention relates to nickel-based alloys having relatively great strength at high tempera-ture and generally referred to (e.g. U.S. Patent Re28,681 issued to Baldwin on January 13, 1976) as superalloys, and, in particular, to articles with different grain sizes in different portions of the article.
The literature shows that, for nickel-based superalloy systems, grain size has a definite effect on mechanical properties. In general, increasing grain size has the effect of increasing high temperature creep rup-ture properties. The effect of increasing grain size decreases the total grain boundary area and thereby re-duces the propensity of grain boundary failure mechanisms to occur.
Conversely, decreasing grain size enhances such properties as high cycle fatigue due to the increased fracture energy required to propagate cracks by enabling the increased grain boundary area to retard dislocation movement. In addition, such properties as impact strength 3 3 ~ 6~
2 47,546 are enhanced by decreasing grain size.
Grain size control in superalloys is generally considered critica~ in the manufacture of most turbine hardware. Difficulties, however, are routinely experi-enced by forging, casting and powder forming processes insofar as grain size and uniformity are concerned. The literature shows that increased carbon additions to nickel-based alloys generally aid grain size control in forged products.
0 Complex cooling schemes and insulated molds de-signed to control cooling rates of cast alloys have been employed for grain size control. Powder metallurgical component structures are generally restricted by the initial particle size. A dual grain structure for im-proved properties is described in U.S. Patent 3,741,821 issued June 26, 1973 to Athey et al., but requires complex equipment, extremely close temperature control, and two separate heat treatments. A mechanical process for pro-viding fine surface grains and coarse internal grains is described in U.S. Patent 3,S05,130, issued to Paul on April 7, 1970. It requires special surface cold working and a recrystallization heat treatment. Such cold working is impractical on some alloys because of the susceptibil-ity to cold work cracking and, further, the results of such mechanical working can be lost to relaxation at turbine operating temperatures. Thornburg's U.S. Patent
Grain size control in superalloys is generally considered critica~ in the manufacture of most turbine hardware. Difficulties, however, are routinely experi-enced by forging, casting and powder forming processes insofar as grain size and uniformity are concerned. The literature shows that increased carbon additions to nickel-based alloys generally aid grain size control in forged products.
0 Complex cooling schemes and insulated molds de-signed to control cooling rates of cast alloys have been employed for grain size control. Powder metallurgical component structures are generally restricted by the initial particle size. A dual grain structure for im-proved properties is described in U.S. Patent 3,741,821 issued June 26, 1973 to Athey et al., but requires complex equipment, extremely close temperature control, and two separate heat treatments. A mechanical process for pro-viding fine surface grains and coarse internal grains is described in U.S. Patent 3,S05,130, issued to Paul on April 7, 1970. It requires special surface cold working and a recrystallization heat treatment. Such cold working is impractical on some alloys because of the susceptibil-ity to cold work cracking and, further, the results of such mechanical working can be lost to relaxation at turbine operating temperatures. Thornburg's U.S. Patent
3,597,286 issued August 3, 1971 uses annealed cold rolled iron-cobalt-vanadium alloy and produces a partially re-crystallized grain structure with a balance of room temper-3 ~ 3 ~ ~
3 47,546 ature mechanical properties commensurate with magnetic characteristics. Such a recrystallization process is generally difficult with age hardenable nickel base comp-ositions and can also result in relaxa-tion at high operat-ing temperatures.
Boron is known to (up to certain amounts, where incipient melting occurs at operating temperature) improve stress rupture properties (see 4,093,476 issued to Boesch) It also acts as a grain boundary ductilizer (see the 0 aforementioned Re28,681).
U.S. Patent 2,763,584, issued to Badger on Sep-tember 18, 1956 employs decarbonization and deboronization of exterior surfaces of articles for the purpose improving thermal shock resistance. Heating in a hydrogen atmos-phere presents problems and is expensive, and the removal of carbon results in loss of control on grain size.
SUMMARY OF THE INVENTION
This is a method for producing a composite grain structure in nickel-based superalloy articles. The size of the grains is varied in a controlled manner (both the size of enlarged grains and location of the enlarged grains is controlled).
This method comprises preparing a nickel-based superalloy containing, by weight percent, 0.01-.10 carbon and 0.02-.08 boron, forming this alloy into a configura-tion approximating the final configuration, and heating the formed alloy in a non-reducing atmosphere to a temper-ature of 1800-2500C (but less than the homogenization temperature) for 1-10 hours. Diffusion of boron from
3 47,546 ature mechanical properties commensurate with magnetic characteristics. Such a recrystallization process is generally difficult with age hardenable nickel base comp-ositions and can also result in relaxa-tion at high operat-ing temperatures.
Boron is known to (up to certain amounts, where incipient melting occurs at operating temperature) improve stress rupture properties (see 4,093,476 issued to Boesch) It also acts as a grain boundary ductilizer (see the 0 aforementioned Re28,681).
U.S. Patent 2,763,584, issued to Badger on Sep-tember 18, 1956 employs decarbonization and deboronization of exterior surfaces of articles for the purpose improving thermal shock resistance. Heating in a hydrogen atmos-phere presents problems and is expensive, and the removal of carbon results in loss of control on grain size.
SUMMARY OF THE INVENTION
This is a method for producing a composite grain structure in nickel-based superalloy articles. The size of the grains is varied in a controlled manner (both the size of enlarged grains and location of the enlarged grains is controlled).
This method comprises preparing a nickel-based superalloy containing, by weight percent, 0.01-.10 carbon and 0.02-.08 boron, forming this alloy into a configura-tion approximating the final configuration, and heating the formed alloy in a non-reducing atmosphere to a temper-ature of 1800-2500C (but less than the homogenization temperature) for 1-10 hours. Diffusion of boron from
4 ~17,546 portions of the article which are exposed (without mask-ing) to the atmosphere allows grain growth selectively in these exposed portions of the article. The non-reducing atmosphere generally maintains the carbon content constant Thus, the diffusion of boron of the exposed surfaces into the atmosphere allows grain growth in those regions of the alloy, but the carbon content is maintained to provide an effective upper limit to grain growth.
Preferably, unmasked passages are provided into 0 the interior of the article and the outside surfaces of the article are masked. This provides for grain growth only in the interior of the article adjacent to the pas-sages and thus a composite structure with larger grains in the interior and smaller grains on the exterior of the article.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
.... .. . _ If the carbon content of a nickel-based super-alloy is reduced, without replacing the carbon with boron, grain coarsening during solution heat treatment will ~0 result. If boron is substituted for the carbon, however, a fine grain structure can be maintained. Apparently, the grain boundary pinning by carbon provides grain size control during solution heat treatment but this control can also be provided by boron. The boron, however, can diffuse during solution heat treatment, resulting in deboronization of exposed metal surfaces. By maintaining the carbon level, and controlling which regions are ex-posed, controlled grain growth in selective regions can be achieved.
3 3 3 ~ 6 47,546 The usefulness of such a system is exemplified by rotating turbine blade hardware. Extensive efforts are being made to increase rupture strength capability of such hardware.
For rotating turbine blades, increased grain size would normally increase creep rupture strength, but, with all the grains increased in size, this would result in decreased fatigue resistance. Thus, with such effec-tively homogeneous grain sizes, properties are currently 0 compromised. The controlled deboronization of this inven-tion, however, can provide for turbine blades which util-ize large internal grains for creep strength and fine surface grain structure for maximum resistance to high cycle fatigue initiation.
A special alloy was prepared using a version of the Udimet-710 composition generally described in U.S.
Patent 3,667,938 issued to Boesch, modified to have low carbon (.024% versus the normal .08%) and higher boron (.05% versus the normal .01%). After forging, the grain structure was extremely fine and uniform. After solution heat treatment (2135~F for 4 hours in air) the grains exposed to the furnace atmosphere grew substantially in comparison to the unexposed grain structure, providing a composite structure having an extremely uniform band of enlarged grains, both of uniform band thickness and uni-form grain size.
As noted previously, the optimum turbine blade design should have large internal grains and fine external grains. This can be achieved by machining cooling pas-3 3 3 6 ~
6 47,546sages (cooling passages are commonly used in the turbine blades) prior to solution heat treatment and coating the external surfaces with oxide or glass coatings to gener-ally prevent diffusion of boron out of the external sur-faces. Thus, during so:Lution heat treatment, the cooling passages are exposed to the furnace environment and the external surfaces are masked. This process provides a structure having fine, fatigue-resistant grains on the exterior surfaces and other regions remote from the cool-ing passages together with enlarged, creep-resistant grains in regions adjacent to the cooling passages.
This same structure with large internal grains and fine external grains can alternately be achieved without the oxide or glass coatings by fabricating an oversized forging with cooling passages, heat treating, and then machining the surface. Thus, large grains are formed both in regions adjacent to the cooling passages and on the external surface during solution heat treatment, but the large grains on the external surfaces are removed during machining to provide a fine grain external surface.
This composite grain structure technology is not limited to forged structures, but can also be expanded to other structures such as cast or powder metallurgy and hot pressing structures. Cast or powder products may need additional hot working to increase stored strain energy for recrystallization and growth, and thus it may be convenient to use powder and cast structures as forging preforms. Heat treatment in a non-reducing atmosphere provides deboronization without decarburization and thus 3 33 ~ 6 7 47,546 provides control of the amount of grain growth and the location of grain growth in these types of structures as well.
It should be noted that no significant further deboronization (after solution heat treatment) will occur during service (e.g. during the operation of the turbine) as maximum service temperatures are not sufficiently high for significant diffusion of boron. While a variety of compositions can be used, this invention can be conven-o iently practiced by modifying a known alloy by substitut-ing (approximately an equal atom percentage) boron for a portion of the carbon in the commercially available com-position. Preferably between 25 and 75 atom percent of the carbon in the known composition is replaced with boron.
Generally the solution heat treatment is per-formed at a temperatwre between 2100F and 2500F and the alloy is held at that temperature for 2-4 hours. The atmosphere during the treatment can be either inert (e.g.
argon) or oxidizing (e.g. air).
Thus, it can be seen that grain size control by a deboronization process of carbon, nickel-base super-alloys can be utilized to produce a composite grain struc-ture with enlarged grain structures of controlled maximum size in specific regions to attain significantly improved hardware creep rupture life and simultaneously fine grain, high cycle fatigue-resistant regions. This is attained by a single heat treatment procedure and this procedure may be employed with forged, cast, or powder metallurgical ~133366 8 ~7,546 thermal treatment cycles.
As variations additional to the above can be made without varying the inventive concept described herein, the invention should not be construed as limited to the particular forms described, as these described forms are to be regarded as illustrative rather than restrictive. The invention is intended to cover all forms which should not depart from the spirit and scope of the invention.
Preferably, unmasked passages are provided into 0 the interior of the article and the outside surfaces of the article are masked. This provides for grain growth only in the interior of the article adjacent to the pas-sages and thus a composite structure with larger grains in the interior and smaller grains on the exterior of the article.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
.... .. . _ If the carbon content of a nickel-based super-alloy is reduced, without replacing the carbon with boron, grain coarsening during solution heat treatment will ~0 result. If boron is substituted for the carbon, however, a fine grain structure can be maintained. Apparently, the grain boundary pinning by carbon provides grain size control during solution heat treatment but this control can also be provided by boron. The boron, however, can diffuse during solution heat treatment, resulting in deboronization of exposed metal surfaces. By maintaining the carbon level, and controlling which regions are ex-posed, controlled grain growth in selective regions can be achieved.
3 3 3 ~ 6 47,546 The usefulness of such a system is exemplified by rotating turbine blade hardware. Extensive efforts are being made to increase rupture strength capability of such hardware.
For rotating turbine blades, increased grain size would normally increase creep rupture strength, but, with all the grains increased in size, this would result in decreased fatigue resistance. Thus, with such effec-tively homogeneous grain sizes, properties are currently 0 compromised. The controlled deboronization of this inven-tion, however, can provide for turbine blades which util-ize large internal grains for creep strength and fine surface grain structure for maximum resistance to high cycle fatigue initiation.
A special alloy was prepared using a version of the Udimet-710 composition generally described in U.S.
Patent 3,667,938 issued to Boesch, modified to have low carbon (.024% versus the normal .08%) and higher boron (.05% versus the normal .01%). After forging, the grain structure was extremely fine and uniform. After solution heat treatment (2135~F for 4 hours in air) the grains exposed to the furnace atmosphere grew substantially in comparison to the unexposed grain structure, providing a composite structure having an extremely uniform band of enlarged grains, both of uniform band thickness and uni-form grain size.
As noted previously, the optimum turbine blade design should have large internal grains and fine external grains. This can be achieved by machining cooling pas-3 3 3 6 ~
6 47,546sages (cooling passages are commonly used in the turbine blades) prior to solution heat treatment and coating the external surfaces with oxide or glass coatings to gener-ally prevent diffusion of boron out of the external sur-faces. Thus, during so:Lution heat treatment, the cooling passages are exposed to the furnace environment and the external surfaces are masked. This process provides a structure having fine, fatigue-resistant grains on the exterior surfaces and other regions remote from the cool-ing passages together with enlarged, creep-resistant grains in regions adjacent to the cooling passages.
This same structure with large internal grains and fine external grains can alternately be achieved without the oxide or glass coatings by fabricating an oversized forging with cooling passages, heat treating, and then machining the surface. Thus, large grains are formed both in regions adjacent to the cooling passages and on the external surface during solution heat treatment, but the large grains on the external surfaces are removed during machining to provide a fine grain external surface.
This composite grain structure technology is not limited to forged structures, but can also be expanded to other structures such as cast or powder metallurgy and hot pressing structures. Cast or powder products may need additional hot working to increase stored strain energy for recrystallization and growth, and thus it may be convenient to use powder and cast structures as forging preforms. Heat treatment in a non-reducing atmosphere provides deboronization without decarburization and thus 3 33 ~ 6 7 47,546 provides control of the amount of grain growth and the location of grain growth in these types of structures as well.
It should be noted that no significant further deboronization (after solution heat treatment) will occur during service (e.g. during the operation of the turbine) as maximum service temperatures are not sufficiently high for significant diffusion of boron. While a variety of compositions can be used, this invention can be conven-o iently practiced by modifying a known alloy by substitut-ing (approximately an equal atom percentage) boron for a portion of the carbon in the commercially available com-position. Preferably between 25 and 75 atom percent of the carbon in the known composition is replaced with boron.
Generally the solution heat treatment is per-formed at a temperatwre between 2100F and 2500F and the alloy is held at that temperature for 2-4 hours. The atmosphere during the treatment can be either inert (e.g.
argon) or oxidizing (e.g. air).
Thus, it can be seen that grain size control by a deboronization process of carbon, nickel-base super-alloys can be utilized to produce a composite grain struc-ture with enlarged grain structures of controlled maximum size in specific regions to attain significantly improved hardware creep rupture life and simultaneously fine grain, high cycle fatigue-resistant regions. This is attained by a single heat treatment procedure and this procedure may be employed with forged, cast, or powder metallurgical ~133366 8 ~7,546 thermal treatment cycles.
As variations additional to the above can be made without varying the inventive concept described herein, the invention should not be construed as limited to the particular forms described, as these described forms are to be regarded as illustrative rather than restrictive. The invention is intended to cover all forms which should not depart from the spirit and scope of the invention.
Claims (5)
1. A method of producing a composite grain structure in nickel-base superalloy articles, said method comprising:
(a) preparing an alloy containing, by weight percent, .01-.10 carbon and .02-.08 boron;
(b) forming said alloy into a configuration approximating the final configuration; and (c) exposing at least portions of said formed alloy to a non-reducing atmosphere at a temperature of 1800-2500°F for 1-10 hours, whereby diffusion of boron from portions of said article will allow grain growth in said portions of said article and carbon content is main-tained to provide an effective upper limit to grain growth
(a) preparing an alloy containing, by weight percent, .01-.10 carbon and .02-.08 boron;
(b) forming said alloy into a configuration approximating the final configuration; and (c) exposing at least portions of said formed alloy to a non-reducing atmosphere at a temperature of 1800-2500°F for 1-10 hours, whereby diffusion of boron from portions of said article will allow grain growth in said portions of said article and carbon content is main-tained to provide an effective upper limit to grain growth
2. The method of claim 1, wherein selected areas of said article are masked to minimize the diffusion of boron in said masked areas.
3. The method of claim 1, wherein said alloy is prepared by modifying a known nickel-base superalloy composition by substituting a substantially equal atom percentage of boron for a portion of the carbon, said substitution being for between 25 and 75 atom percent of 47,546 the carbon in the known composition.
4. The method of claim 1, wherein said formed alloy is held at a temperature of between 2100 and 2500°F
for 2-5 hours.
for 2-5 hours.
5. The method of claim 2, wherein unmasked passages are provided into the interior of said article and the outside surfaces of said article are masked, whereby grain growth will selectively occur in the inter-ior of said article.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US97004778A | 1978-12-15 | 1978-12-15 | |
| US970,047 | 1978-12-15 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1133366A true CA1133366A (en) | 1982-10-12 |
Family
ID=25516358
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA341,220A Expired CA1133366A (en) | 1978-12-15 | 1979-12-04 | Method of selective grain growth in nickel-base superalloys by controlled boron diffusion |
Country Status (9)
| Country | Link |
|---|---|
| JP (1) | JPS5582757A (en) |
| BE (1) | BE880645A (en) |
| CA (1) | CA1133366A (en) |
| CH (1) | CH648866A5 (en) |
| DE (1) | DE2949673A1 (en) |
| FR (1) | FR2444086A1 (en) |
| GB (1) | GB2043116A (en) |
| IT (1) | IT1126062B (en) |
| NL (1) | NL7908902A (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3664930D1 (en) * | 1985-03-15 | 1989-09-14 | Bbc Brown Boveri & Cie | Process for enhancing the oxidation and corrosion resistance of a component made from a dispersion-hardened superalloy by means of a surface treatment |
| EP0214080A3 (en) * | 1985-08-16 | 1987-11-25 | United Technologies Corporation | Reduction of twinning in directional recrystallization of nickel base superalloys |
| JP6685800B2 (en) | 2016-03-31 | 2020-04-22 | 三菱重工業株式会社 | Turbine blade design method, turbine blade manufacturing method, and turbine blade |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1127157A (en) * | 1966-06-13 | 1968-09-11 | Orenda Ltd | Method for improving the fatigue resistance of turbine blades |
| FR1528328A (en) * | 1966-06-21 | 1968-06-07 | Int Nickel Ltd | Refining of metal grain |
| US3597286A (en) * | 1968-02-23 | 1971-08-03 | Westinghouse Electric Corp | Method of treating a high strength high ductility iron-cobalt alloy |
| US3741821A (en) * | 1971-05-10 | 1973-06-26 | United Aircraft Corp | Processing for integral gas turbine disc/blade component |
| US4078951A (en) * | 1976-03-31 | 1978-03-14 | University Patents, Inc. | Method of improving fatigue life of cast nickel based superalloys and composition |
| US4093476A (en) * | 1976-12-22 | 1978-06-06 | Special Metals Corporation | Nickel base alloy |
-
1979
- 1979-12-04 CA CA341,220A patent/CA1133366A/en not_active Expired
- 1979-12-04 GB GB7941819A patent/GB2043116A/en not_active Withdrawn
- 1979-12-11 DE DE19792949673 patent/DE2949673A1/en active Granted
- 1979-12-11 NL NL7908902A patent/NL7908902A/en not_active Application Discontinuation
- 1979-12-14 CH CH11125/79A patent/CH648866A5/en not_active IP Right Cessation
- 1979-12-14 BE BE0/198587A patent/BE880645A/en not_active IP Right Cessation
- 1979-12-14 FR FR7930742A patent/FR2444086A1/en not_active Withdrawn
- 1979-12-14 JP JP16170579A patent/JPS5582757A/en active Granted
- 1979-12-14 IT IT41681/79A patent/IT1126062B/en active
Also Published As
| Publication number | Publication date |
|---|---|
| BE880645A (en) | 1980-06-16 |
| JPS5582757A (en) | 1980-06-21 |
| DE2949673C2 (en) | 1989-06-22 |
| GB2043116A (en) | 1980-10-01 |
| DE2949673A1 (en) | 1980-06-26 |
| IT7941681A0 (en) | 1979-12-14 |
| FR2444086A1 (en) | 1980-07-11 |
| IT1126062B (en) | 1986-05-14 |
| NL7908902A (en) | 1980-06-17 |
| JPS6344816B2 (en) | 1988-09-07 |
| CH648866A5 (en) | 1985-04-15 |
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