U.S. patent application number 11/161114 was filed with the patent office on 2007-01-25 for powder metal rotating components for turbine engines and process therefor.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. Invention is credited to Joseph Jay Jackson, Jon Conrad Schaeffer.
Application Number | 20070020135 11/161114 |
Document ID | / |
Family ID | 37679231 |
Filed Date | 2007-01-25 |
United States Patent
Application |
20070020135 |
Kind Code |
A1 |
Jackson; Joseph Jay ; et
al. |
January 25, 2007 |
POWDER METAL ROTATING COMPONENTS FOR TURBINE ENGINES AND PROCESS
THEREFOR
Abstract
A process for producing turbine rotors and other large rotating
components of power-generating gas turbine engines using powder
metallurgy techniques. The process involves forming a powder of a
gamma prime or gamma double prime precipitation-strengthened
nickel-based superalloy whose particles are about 0.100 mm in
diameter or smaller. The powder is placed in a can and consolidated
to produce an essentially fully dense consolidation, which is then
hot worked to produce a billet of a size sufficient to form a
forging of at least 2300 kg. The billet is forged at a temperature
and strain rate to produce a forging with a uniform fine grain of
ASTM 10 or finer. Thereafter, the forging may undergo a heat
treatment to achieve a desired balance of mechanical properties
while retaining a uniform grain size of ASTM 10 or finer.
Inventors: |
Jackson; Joseph Jay;
(Topsfield, MA) ; Schaeffer; Jon Conrad;
(Greenville, SC) |
Correspondence
Address: |
HARTMAN & HARTMAN, P.C.
552 EAST 700 NORTH
VALPARAISO
IN
46383
US
|
Assignee: |
GENERAL ELECTRIC COMPANY
1 River Road
Schenectady
NY
|
Family ID: |
37679231 |
Appl. No.: |
11/161114 |
Filed: |
July 22, 2005 |
Current U.S.
Class: |
419/29 |
Current CPC
Class: |
B22F 2998/00 20130101;
B22F 1/0085 20130101; B23P 15/006 20130101; B22F 3/15 20130101;
B22F 3/20 20130101; B22F 1/0003 20130101; B22F 3/17 20130101; B22F
9/08 20130101; B22F 3/14 20130101; B22F 2998/00 20130101; B22F
2998/10 20130101; B22F 3/14 20130101; B22F 5/009 20130101; B22F
2998/10 20130101; C22C 19/055 20130101 |
Class at
Publication: |
419/029 |
International
Class: |
B22F 5/04 20070101
B22F005/04 |
Claims
1. A process of producing a component from a gamma prime or gamma
double prime precipitation-strengthened nickel-base superalloy, the
process comprising the steps of: forming a powder of the
superalloy; filling a can with the powder and evacuating and
sealing the can in a controlled environment; consolidating the can
and the powder therein at a temperature, time, and pressure to
produce a consolidation; hot working the consolidation to produce a
billet of a size sufficient to form a forging of at least 2300 kg;
and then forging the billet at a temperature and strain rate to
produce a forging with a uniform fine grain of ASTM 10 or finer
throughout.
2. A process according to claim 1, wherein the nickel-based
superalloy has a composition of, by weight, about 19 to about 23%
chromium, about 7 to about 8% molybdenum, about 3 to about 4%
niobium, about 4 to about 6% iron, about 0.3 to about 0.6%
aluminum, about 1 to about 1.8% titanium, about 0.002 to about
0.004% boron, about 0.35% maximum manganese, about 0.2% maximum
silicon, about 0.03% maximum carbon, the balance nickel and
incidental impurities.
3. A process according to claim 1, wherein the forming step
comprises producing a melt of the nickel-based superalloy in a
controlled environment and then rapidly cooling the melt to produce
the powder.
4. A process according to claim 3, wherein the forming step further
comprises sieving the powder in a controlled environment to remove
all particles larger than 0.100 mm in diameter.
5. A process according to claim 3, wherein the forming step further
comprises blending the powder with a second powder of the
nickel-based superalloy.
6. A process according to claim 1, wherein the consolidation formed
by the consolidation step has a density of at least 99.9% of
theoretical.
7. A process according to claim 1, wherein the forging produced by
the forging step weighs at least 2300 kg.
8. A process according to claim 1, wherein the billet formed by the
hot working step weighs about 1.2 to about 1.5 times the weight of
the forging.
9. A process according to claim 1, wherein the billet formed by the
hot working step weighs about 1.8 to about 4 times the weight of
the rotor component.
10. A process according to claim 1, wherein the component is a
rotor component of a gas turbine engine.
11. A process according to claim 1, wherein the rotor component is
chosen from the group consisting of turbine wheels and spacers.
12. A process of producing a gas turbine engine rotor component
from a gamma prime or gamma double prime precipitation-strengthened
nickel-base nickel-based superalloy, the process comprising the
steps of: melting the nickel-based superalloy in a controlled
environment to obtain a melt of the nickel-based superalloy;
convert the melt into a powder of generally spherical particles
that are predominantly about 0.100 mm in diameter or smaller;
sieving the powder in a controlled environment to remove all
particles larger than 0.100 mm in diameter; filling a mild steel
can with the sieved powder and evacuating and sealing the can in a
controlled environment; consolidating the can and the powder
therein at a temperature, time, and pressure to produce a
consolidation having a density of at least 99.9 percent of
theoretical; hot working the consolidation to produce a billet of a
size sufficient to form a forging of at least 2300 kg with a
uniform grain size of ASTM 10 or finer throughout the billet;
forging the billet into a forging at a temperature and strain rate
to achieve a uniform fine grain of ASTM 10 or finer throughout the
forging; performing a heat treatment on the forging to achieve a
desired balance of mechanical properties and maintain a uniform
grain size throughout of ASTM 10 or finer; and machining the
forging to produce the gas turbine engine rotor component.
13. A process according to claim 12, wherein the nickel-based
superalloy has a composition of, by weight, about 19 to about 23%
chromium, about 7 to about 8% molybdenum, about 3 to about 4%
niobium, about 4 to about 6% iron, about 0.3 to about 0.6%
aluminum, about 1 to about 1.8% titanium, about 0.002 to about
0.004% boron, about 0.35% maximum manganese, about 0.2% maximum
silicon, about 0.03% maximum carbon, the balance nickel and
incidental impurities.
14. A process according to claim 12, further comprising the step of
blending the powder with a second powder of the nickel-based
superalloy before the filling step.
15. A process according to claim 12, wherein the forging produced
by the forging step weighs at least 2300 kg.
16. A process according to claim 12, wherein the billet formed by
the hot working step weighs about 1.2 to about 1.5 times the weight
of the forging.
17. A process according to claim 12, wherein the billet formed by
the consolidation step weighs about 1.8 to about 4 times the weight
of the rotor component.
18. A process according to claim 12, wherein the rotor component is
chosen from the group consisting of turbine wheels and spacers.
19. A process according to claim 18, wherein the rotor component is
a component of a land-based gas turbine engine.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to processes for producing large
forgings using metal powders as the starting material. More
particularly, this invention is directed to a process for producing
turbine rotors and other large rotating components of turbine
engines using powder metallurgy techniques.
[0002] Rotor components for certain advanced land-based gas turbine
engines used in the power-generating industry, such as the H and FB
class gas turbines of the assignee of this invention, are currently
formed from gamma double-prime (.gamma.'')
precipitation-strengthened nickel-based superalloys, such as Alloy
718 and Alloy 706. For example, wheels and spacers have been formed
from triple-melted (vacuum induction melting (VIM)/electroslag
remelting (ESR)/vacuum arc remelting (VAR)) ingots with diameters
of about 27 to 36 inches (about 70 to about 90 cm), which are then
billetized and forged. Due to potential chemical or microstructural
segregation and anticipated hot working losses going from ingot to
final forging, starting ingot weights must be from about 1.5 to 3
times the weight of the finished forging, and about 2.5 to 7 times
the weight of the finish-machined part. In addition to these
substantial material losses, the best current processing practices
typically result in nonuniform and relatively coarse-grained
microstructures in the billet (e.g., ASTM 00 or larger) and the
finish forgings (e.g., ASTM 8.0 or larger) (reference throughout to
ASTM grain sizes is in accordance with the standard scale
established by the American Society for Testing and Materials). The
billet grain size is too large to permit any adequate ultrasonic
inspection to identify potential life limiting defects and is
consequently not performed on currently used billet. The finished
forgings must therefore be ultrasonically inspected for potential
life-limiting defects, and typically necessitate a minimum 0.25
inch (about 6 mm) thick sonic shape inspection envelope that
defines the finished forged shape envelope.
[0003] In contrast, rotor components for aircraft gas turbine
engines have often been formed by powder metallurgy (PM) processes,
which are known to provide a good balance of creep, tensile and
fatigue crack growth properties to meet the performance
requirements of aircraft gas turbine engines. Typically, a powder
metal component is produced by consolidating metal powders in some
form, such as extrusion consolidation, then isothermally or hot die
forging the consolidated material to the desired outline, and
finally heat treating the forging before finish machining to
complete the manufacturing process. The processing steps of
consolidation and forging are designed to retain a very fine grain
size within the material to enable high resolution ultrasonic
inspection of billets, minimize die loading, and improve shape
definition of the finished forging. Unlike advanced turbine systems
for land-based gas turbine engines, PM rotor components for
aircraft gas turbine engines have been typically formed from gamma
prime (.gamma.') precipitation-strengthened nickel-based
superalloys with very high temperature and stress capabilities
demanded by those parts. In order to improve the fatigue crack
growth resistance and mechanical properties at elevated
temperatures, some of these alloys are heat treated above their
gamma prime solvus temperature (generally referred to as
supersolvus heat treatment) to cause significant, uniform
coarsening of the grains. The nickel-based superalloy rotors used
in large electrical power generating turbines currently do not
require the higher temperature gamma prime alloys nor this grain
coarsening process to meet their mission and component mechanical
property requirements, though it is foreseeable that such higher
temperature alloys could be required at some future date to
increase turbine efficiencies or increase component life.
[0004] While powder metal nickel-based superalloys have been
processed for use in aircraft engine turbine rotor forgings, whose
forgings are typically less than 2000 pounds (about 900 kg), powder
metal techniques have not been used to produce the significantly
larger forgings required by gas turbines used in the
power-generating industry, which can weigh in excess of 5000 pounds
(about 2300 kg). However, the ability to use a powder metallurgy
process to produce large nickel-based superalloy forgings suitable
for rotor components of power-generating gas turbine engines would
provide the capability of producing more near-net-shape forgings,
thereby reducing material losses. Until recently, these power
generation turbine alloys were iron or nickel-based with low alloy
content, i.e., three or four primary elements, which permit their
melting and processing with relative ease and minimal chemical or
microstructural segregation. Powder metal versions of these alloys
would offer no significant benefit, either in ease of processing or
property gains, to compensate for the higher base cost of PM
compared to the cast ingots which can be readily converted into
rotor forgings. However, as more complex alloys such as Alloy 718
and beyond become preferred and the size of forgings continues to
increase, the concerns of chemical and microstructure segregation,
high material losses associated with converting large grained
ingots to finish forgings, and limited industry capacity to process
large, high strength forgings make the higher base cost PM alloys
potentially more cost effective. Reduced processing losses,
expanded industry capacity, improved inspectibility of fine grain
PM billets and parts, and the ability to produce more
near-net-shape forgings are all contributing factors to achieving
lower cost large rotor forgings from PM than from the current cast
plus wrought practice.
BRIEF SUMMARY OF THE INVENTION
[0005] The present invention provides a process for producing
turbine rotors and other large rotating components of
power-generating gas turbine engines using powder metallurgy
techniques. The method significantly reduces the ratio of input
weight to final forging weight by eliminating yield losses during
conversion from large grained ingot to a fine grained forging. The
method also virtually eliminates chemical and microstructural
segregation, and results in a fine, uniform grain size (ASTM 10 or
finer) that advantageously reduces the required sonic shape
envelope and therefore further reduces the finish forging weight.
Additionally, the use of fine grain PM billet has the capability of
reducing the press forces required to produce finish forgings,
thereby reducing capital equipment cost and expanding the potential
supplier base.
[0006] The process of this invention involves forming a powder of a
precipitation-strengthened (gamma prime or gamma double prime)
nickel-base superalloy whose particles are about 0.004 inch (about
0.100 mm) in diameter or smaller. The powder is placed in a can,
which is evacuated and sealed in a controlled environment and then
consolidated at a temperature, time, and pressure to produce an
essentially fully-dense consolidation. The consolidation is then
hot worked at a temperature to produce a billet with a uniform
grain size of ASTM 10 or finer and of a size sufficient to form a
forging of at least 5000 pounds (about 2300 kg). The billet is then
forged at a temperature and strain rate selected to produce a
forging with a uniform fine grain of ASTM 10 or finer throughout.
Thereafter, the forging preferably undergoes a heat treatment
designed to achieve a desired balance of mechanical properties
while retaining a grain size of ASTM 10 or finer.
[0007] As a result of the above process, very large rotor
components that were previously limited to processing by
conventional cast and wrought techniques may now be formed by
powder metallurgy techniques with reduced material losses, as well
as microstructural, compositional, and mechanical property
advantages that can be achieved with powder metallurgy
processes.
[0008] Other objects and advantages of this invention will be
better appreciated from the following detailed description.
DETAILED DESCRIPTION OF THE INVENTION
[0009] The present invention provides a process for manufacturing
very large nickel-base alloy rotor forgings, generally in excess of
5000 pounds (about 2300 kg), using powder metallurgy techniques.
Powder metal alloys are used to produce nickel-base consolidations,
which are then hot worked into billets and subsequently forged into
large turbine wheels, spacers, or other rotating components of a
size suitable for large gas turbine engines used in the power
generating industry.
[0010] A particularly suitable alloy for illustrating the
advantages of this invention is a gamma-prime
precipitation-strengthened nickel-base superalloy based on the
commercially-available Alloy 725. The superalloy, identified herein
as ARA725, has a composition of, by weight, about 19 to about 23%
chromium, about 7 to about 8% molybdenum, about 3 to about 4%
niobium, about 4 to about 6% iron, about 0.3 to about 0.6%
aluminum, about 1 to about 1.8% titanium, about 0.002 to about
0.004% boron, about 0.35% maximum manganese, about 0.2% maximum
silicon, about 0.03% maximum carbon, the balance nickel and
incidental impurities. Properties of conventionally cast plus
wrought ARA725 cited in U.S. Pat. No. 6,315,846 to Hibner et al.
and U.S. Pat. No. 6,531,002 to Henry et al. that are believed to
render the alloy particularly well suited for producing very large
forgings from powder metal include room and elevated temperature
tensile strength and ductility similar to Alloy 718 with
significantly improved time dependent crack growth resistance
compared to Alloy 718. Though no mechanical property data is yet
available for a powder metallurgy version of ARA725, it is
anticipated that a properly processed powder metal forging will
have similar or possibly better properties than the cast plus
wrought forgings. While the invention will be described in
reference to the ARA725 alloy, the teachings of this invention are
applicable to other gamma prime and gamma double prime
precipitation-strengthened nickel-based superalloys, such as Alloy
625, LC Astroloy (U700), Udimet 720, ARA054, ARA017, and any other
nickel-based superalloy with tensile properties equal to or better
than Alloy 718 combined with superior time dependent crack growth
resistance compared to Alloy 718.
[0011] For the applications of interest to the invention, optimum
processibility and mechanical properties are achieved by uniform
grain sizes of not larger than ASTM 10. Grain sizes larger than
ASTM 10 are undesirable in that the presence of such grains can
significantly reduce the low cycle fatigue resistance of the
component, can have a negative impact on other mechanical
properties of the component such as tensile and high cycle fatigue
(HCF) strength, increase hot working load requirements, and inhibit
the thorough ultrasonic inspection of billets and thick section
forgings. Therefore, a preferred aspect of this invention is to
achieve a uniform grain size within a nickel-base superalloy, in
which random grain growth is prevented so as to yield a maximum
grain size of ASTM 10 or finer.
[0012] The process of this invention involves forming a melt whose
chemistry is that of the desired alloy (e.g., ARA725). This is
typically accomplished by VIM processing but could also be
performed by adaptation of ESR or VAR processes to provide melt for
subsequent atomization or other powder making method. In view of
the reactivity of elements (e.g., aluminum and titanium) contained
in preferred gamma prime and gamma double prime
precipitation-strengthened alloys, the melt is formed under vacuum
or in an inert environment (hereinafter, a controlled environment).
While in the molten condition and within chemistry specifications,
the alloy is converted into powder by atomization or another
suitable process to produce generally spherical powder particles.
According to a preferred aspect of the invention, the particles are
produced by atomization to have diameters of predominantly 0.004
inch (about 0.100 mm) or smaller. The powder is then sieved in a
controlled environment to remove essentially all particles larger
than 0.004 inch (about 0.100 mm) for the purpose of reducing the
potential for defects in the subsequent billet/forgings. Larger
powder sizes may be acceptable if defect particles (e.g., ceramics,
etc.) larger than 0.004 inch (about 0.100 mm) can be removed other
than by a screening process. Because of the large quantity of
powder required to produce billets of the size required by this
invention, e.g., 5000 to 20,000 pounds (about 2300 to about 10,000
kg), it may be necessary to blend powders produced from multiple
atomization steps to accumulate sufficient powder for use in the
process of this invention. Any required storage of such powders is
preferably in a controlled environment container.
[0013] Once a sufficient amount of powder has been produced, the
powder is placed in a suitable can, preferably a mild steel can,
whose size will meet the billet size requirement after
consolidation. Loading of the can is performed in a controlled
environment (inert gas or vacuum), after which the can is evacuated
while subjected to moderate heating (e.g., above about 200.degree.
F. (about 93.degree. C.)) to drive off moisture and any volatiles,
and then sealed. Thereafter, the can and its contents are
consolidated at a temperature, time, and pressure sufficient to
produce a consolidation having a density of at least about 99.9% of
theoretical. Consolidation can be accomplished by hot isostatic
pressing (HIP), extrusion, or another suitable consolidation
method.
[0014] The powder consolidation is then hot worked by any of
several techniques, such as extrusion, upset plus drawing, etc., to
produce an appropriate input billet size for forging. Conditions
used to produce the input billet should result in uniform ASTM 10
or finer grain size throughout in order to facilitate ultrasonic
inspection thereof prior to forging into the final part shape.
[0015] The billet is then forged using known techniques, such as
those currently utilized to produce Alloy 706 and Alloy 718 rotor
forgings for large industrial turbines but modified to take
advantage of fine grain billet techniques. Forging is performed at
temperatures and loading conditions that allow complete filling of
the finish forging die cavity, avoid fracture, and produce or
retain a fine uniform grain size within the material of not larger
than ASTM 10. Notably, because chemical and microstructural
segregation are virtually eliminated and a very fine grain size can
be achieved through use of the powder metal starting material, the
ratio of input (billet) weight to final forging weight can be
significantly reduced. For example, it is believed the starting
billet weight can be as little as about 1.2 to about 1.5 times the
weight of the finished forging, and about 1.8 to about 4 times the
weight of the finish-machined rotor component. This weight
reduction is enabled by the improved processibility of fine grained
billet as well as the enhanced sonic inspectibility thereof.
[0016] The resulting rotor forging preferably undergoes ultrasonic
inspecting for potential life-limiting defects. However, due to the
enhanced ultrasonic inspectibility of the input billet, this step
of component processing could potentially be eliminated which would
enable more near-net-shaped forgings to be produced and further
reduce input weights.
[0017] Inspection (if performed) is followed by finish machining by
any suitable known method to produce the finish-machined rotor
component. In order to achieve required mechanical properties of
the rotor component, prior to machining the forging is solution
heat treated and aged at temperatures and times which achieve the
preferred balance of properties for long time industrial gas
turbine service. An illustrative example of an appropriate heat
treatment process for the ARA725 alloy entails a solution heat
treatment at a temperature of about 1650.degree. F. (about
900.degree. C.) for approximately our hours, followed by two step
aging at a temperature of about 1400.degree. F. (about 760.degree.
C.) for approximately eight hours, then cooling at a rate of
100.degree. F. (about 56.degree. C.) per minute to about
1150.degree. F. (about 620.degree. C.) and holding for
approximately eight hours, followed by air cooling.
[0018] In addition to the preferred ARA725 alloy, the process
described above can be applied to a broad range of metal alloys
whose compositions and temperature capabilities meet a variety of
specific product needs. For example, alloys containing conventional
strengthening and/or grain boundary pinning dispersoids or
nano-dispersoids such as inert oxides, nitrides, and/or carbides
may be desired to impart long-term stability. Alloys containing
higher levels of high temperature strengthening elements such as
cobalt, tungsten, molybdenum, tantalum, niobium, etc., may be
desired for applications requiring service up to 1800.degree. F.
(about 1000.degree. C.) or higher. In addition to direct melting
and atomization of specific alloy compositions, mechanically
alloying two or more separately processed powders can also be
employed to obtain desired properties for a rotor component.
[0019] While the invention has been described in terms of a
preferred embodiment, it is apparent that other forms could be
adopted by one skilled in the art. Accordingly, the scope of the
invention is to be limited only by the following claims.
* * * * *