U.S. patent application number 10/969160 was filed with the patent office on 2006-04-20 for low porosity powder metallurgy produced components.
Invention is credited to Gopal Das.
Application Number | 20060083653 10/969160 |
Document ID | / |
Family ID | 35445832 |
Filed Date | 2006-04-20 |
United States Patent
Application |
20060083653 |
Kind Code |
A1 |
Das; Gopal |
April 20, 2006 |
Low porosity powder metallurgy produced components
Abstract
Components produced by powder metallurgy techniques are
described herein. Embodiments of these components have little or no
porosity therein after processing. Embodiments of these components
are created by creating a preform from a powder; creating a
component from the preform; heat treating the component to create a
predetermined microstructure therein; and then hot isostatic
pressing the heat treated component to reduce any porosity therein.
The components can then be machined to their final dimensions, if
necessary.
Inventors: |
Das; Gopal; (Simsbury,
CT) |
Correspondence
Address: |
PRATT & WHITNEY
400 MAIN STREET
MAIL STOP: 132-13
EAST HARTFORD
CT
06108
US
|
Family ID: |
35445832 |
Appl. No.: |
10/969160 |
Filed: |
October 20, 2004 |
Current U.S.
Class: |
419/36 ;
75/249 |
Current CPC
Class: |
B22F 3/15 20130101 |
Class at
Publication: |
419/036 ;
075/249 |
International
Class: |
B22F 3/15 20060101
B22F003/15 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0001] The U.S. Government may have certain rights in this
invention pursuant to Contract Number F33615-01-C-2181 with the
United States Air Force.
Claims
1. A method for forming a component comprising: providing a powder;
creating a preform from the powder; creating a component from the
preform; heat treating the component to create a predetermined
microstructure therein; and hot isostatic pressing the heat treated
component to reduce any porosity therein.
2. The method of claim 1, wherein the powder comprises at least one
of: a gamma-TiAl powder, a nickel aluminide powder, an iron
aluminide powder, a titanium alloy powder, and a superalloy
powder.
3. The method of claim 1, wherein the powder comprises about 44-48
atomic percent aluminum, about 1-2 atomic percent niobium, about
1-2 atomic percent chromium, about 1-2 atomic percent molybdenum,
about 0.1-0.2 atomic percent boron, and about 0.1-0.2 atomic
percent carbon, the balance substantially titanium.
4. The method of claim 1, wherein the powder has an average
particle size of about 70 .mu.m.
5. The method of claim 1, wherein creating the preform from the
powder comprises hot isostatic pressing the powder at a temperature
sufficient to densify the preform and consolidate the powder
through bonding thereof.
6. The method of claim 5, wherein hot isostatic pressing the powder
occurs at about 925-1320.degree. C. and about 15-45 ksi for about
2-10 hours.
7. The method of claim 5, wherein hot isostatic pressing the powder
occurs in an argon atmosphere.
8. The method of claim 1, wherein the component is created from the
preform via at least one of: extrusion and isothermal forging.
9. The method of claim 8, wherein the component is created from the
preform at a temperature below the alpha transus temperature of the
powder.
10. The method of claim 1, wherein after the component is created,
and prior to heat treating the component, the component comprises a
near gamma microstructure.
11. The method of claim 1, wherein heat treating the component
occurs at a temperature above the alpha transus temperature of the
powder.
12. The method of claim 1, wherein heat treating the component
occurs at about 925-1370.degree. C. for about 2-10 hours.
13. The method of claim 1, wherein the predetermined microstructure
is a lamellar microstructure.
14. The method of claim 1, wherein hot isostatic pressing the heat
treated component occurs at a temperature low enough to prevent
significant grain growth from occurring in the component.
15. The method of claim 1, wherein hot isostatic pressing the heat
treated component occurs at a temperature sufficient to preserve a
lamellar microstructure in the component.
16. The method of claim 1, wherein hot isostatic pressing the heat
treated component occurs at about 925-1320.degree. C. and about
15-45 ksi for about 2-10 hours.
17. The method of claim 1, wherein any porosity in the heat treated
and hot isostatic pressed component is less than about 0.005 inches
in size.
18. The method of claim 1, further comprising: machining the heat
treated and hot isostatic pressed component to its final
dimensions.
19. The method of claim 1, wherein the component comprises a gas
turbine engine component.
20. The method of claim 19, wherein the gas turbine engine
component comprises at least one of: a compressor disk, a
compressor blade, a low pressure turbine blade, and a tangential on
board injector.
21. A method for forming a component comprising: providing a
gamma-TiAl powder; consolidating the gamma-TiAl powder into a
preform; creating a component from the preform; heat treating the
component to create a predetermined microstructure therein; and hot
isostatic pressing the heat treated component to reduce any
porosity therein.
22. The method of claim 21, wherein the gamma-TiAl powder comprises
about 44-48 atomic percent aluminum, about 1-2 atomic percent
niobium, about 1-2 atomic percent chromium, about 1-2 atomic
percent molybdenum, about 0.1-0.2 atomic percent boron, and about
0.1-0.2 atomic percent carbon, the balance substantially
titanium.
23. The method of claim 22, wherein the gamma-TiAl powder has an
average particle size of about 70 .mu.m.
24. The method of claim 21, wherein consolidating the gamma-TiAl
powder into a preform comprises hot isostatic pressing the
gamma-TiAl powder at about 1260.degree. C. and about 25 ksi for
about 4 hours in an argon atmosphere.
25. The method of claim 21, wherein the component is created from
the preform via at least one of: extrusion and isothermal
forging.
26. The method of claim 21, wherein after the component is created,
and prior to heat treating the component, the component comprises a
near gamma microstructure.
27. The method of claim 21, wherein heat treating the component to
create a predetermined microstructure therein comprises heat
treating the component at about 1354.degree. C. for about 4
hours.
28. The method of claim 27, wherein the predetermined
microstructure is a lamellar microstructure.
29. The method of claim 21, wherein hot isostatic pressing the heat
treated component occurs at about 1232.degree. C. and about 25 ksi
for about 10 hours.
30. The method of claim 21, wherein the microstructure of the heat
treated and hot isostatic pressed component comprises a lamellar
microstructure substantially similar to the lamellar microstructure
that existed in the heat treated component prior to being hot
isostatic pressed.
31. The method of claim 21, wherein the heat treated and hot
isostatic pressed component has less porosity than the heat treated
component prior to being hot isostatic pressed.
32. The method of claim 21, wherein any porosity in the heat
treated and hot isostatic pressed component is less than about
0.005 inches.
33. The method of claim 21, further comprising: machining the heat
treated and hot isostatic pressed component to its final
dimensions.
34. The method of claim 21, wherein the component comprises a gas
turbine engine component.
35. The method of claim 34, wherein the gas turbine engine
component comprises at least one of: a compressor disk, a
compressor blade, a low pressure turbine blade, and a tangential on
board injector.
36. A component formed by the method of claim 1.
Description
FIELD OF THE INVENTION
[0002] The present invention relates generally to components
prepared by powder metallurgy techniques. More specifically, the
present invention relates to hot isostatic pressing such components
after heat treating to eliminate, or at least minimize or shrink,
any porosity therein.
BACKGROUND OF THE INVENTION
[0003] The efficiency of high performance gas turbine engines
increases with increasing operating temperatures. Therefore, there
is a large incentive to raise the combustion and exhaust gas
temperatures of such engines. However, while increased operating
temperatures are desired, there is also a large incentive to
decrease the weight of the rotating components as much as possible,
to increase the thrust-to-weight ratio of the engines, particularly
for aerospace applications. Thus, there is a desire to have
components that are lighter than existing components.
[0004] Two-phase gamma-TiAl based intermetallic alloys have
received considerable attention as potential materials for
high-temperature aerospace and automotive applications,
particularly as possible replacements for conventional nickel and
titanium alloys in gas turbine engines. Such alloys exhibit
improved high temperature mechanical properties and improved
oxidation resistance as compared to conventional high temperature
titanium alloys. Furthermore, such alloys have good creep
resistance and strength at elevated temperatures, and have a lower
density than conventional nickel and titanium alloys. Such alloys
could be used to make lightweight gas turbine engine components,
such as blades, vanes, disks, etc., where higher operating
temperatures would allow increased efficiency to be achieved.
[0005] Powder metallurgy techniques can produce components having
greater homogeneity than cast components, and higher strengthener
content than conventionally wrought components. Therefore, it may
be desirable to use powder metallurgy techniques to form such
components.
[0006] However, the powder metallurgy techniques currently used to
produce such components often create components having porosity
therein that is too large or too numerous for many applications.
Therefore, it would be desirable to have improved powder metallurgy
techniques for producing such components. It would also be
desirable to have methods for minimizing the porosity in such
components, or at least reducing the porosity therein to an
acceptable level. It would be further desirable to have powder
metallurgy processing techniques that are useful for a variety of
materials.
SUMMARY OF THE INVENTION
[0007] The above-identified shortcomings are overcome by
embodiments of the present invention, which relates to improved
powder metallurgy processing techniques that can be used to produce
components having an acceptable level of porosity therein. These
techniques may be utilized with a variety of materials to create
various components, such as, but not limited to, gas turbine engine
components.
[0008] Embodiments of this invention comprise components and
methods for forming such components, comprising: providing a
powder; creating a preform from the powder; creating a component
from the preform; heat treating the component to create a
predetermined microstructure therein; and hot isostatic pressing
the heat treated component to reduce any porosity therein.
Embodiments may further comprise machining the heat treated and hot
isostatic pressed component to its final dimensions. Any porosity
remaining in the heat treated and hot isostatic pressed component
is generally less than about 0.005 inches in size. This invention
may be utilized to create gas turbine engine components such as,
but not limited to, compressor disks, compressor blades, low
pressure turbine blades, and tangential on board injectors.
[0009] Creating the preform from the powder may comprise hot
isostatic pressing the powder at a temperature sufficient to
densify the preform and consolidate the powder through bonding
thereof. In embodiments, this hot isostatic pressing may occur at
about 925-1320.degree. C. and about 15-45 ksi for about 2-10 hours
in an argon atmosphere. More specifically, in embodiments, this hot
isostatic pressing may occur at about 1260.degree. C. and about 25
ksi for about 4 hours in an argon atmosphere.
[0010] The component may be created from the preform in numerous
ways, such as via extrusion and/or isothermal forging, etc. In
embodiments, the component may be created from the preform at a
temperature below the alpha transus temperature of the powder so
that a near gamma microstructure exists in the preform.
[0011] Heat treating the component occurs at a time and temperature
sufficient to create the desired microstructure in the component.
In embodiments, this heat treating may occur at a temperature above
the alpha transus temperature of the powder, for example, at about
925-1370.degree. C. for about 2-10 hours, to create a lamellar
microstructure in the component. More specifically, in embodiments,
this heat treating may occur at about 1354.degree. C. for about 4
hours.
[0012] After heat treating, the component is hot isostatic pressed
at a temperature low enough to prevent significant grain growth
from occurring in the component. In embodiments, this temperature
may preserve a lamellar microstructure in the component, and be
carried out at about 925-1320.degree. C. and about 15-45 ksi for
about 2-10 hours. More specifically, in embodiments, this hot
isostatic pressing may be carried out at about 1232.degree. C. and
about 25 ksi for about 10 hours. After this hot isostatic pressing
step, the component will have less or smaller porosity than existed
in the component prior to this step.
[0013] The powder utilized in this invention may comprise any
suitable material, including, but not limited to, gamma-TiAl,
nickel aluminides, iron aluminides, titanium alloys, and
superalloys. In embodiments, the powder may comprise about 44-48
atomic percent aluminum, about 1-2 atomic percent niobium, about
1-2 atomic percent chromium, about 1-2 atomic percent molybdenum,
about 0.1-0.2 atomic percent boron, and about 0.1-0.2 atomic
percent carbon, the balance substantially titanium. The powder may
have an average particle size of about 70 .mu.m.
[0014] Further details of this invention will be apparent to those
skilled in the art during the course of the following
description.
DESCRIPTION OF THE DRAWINGS
[0015] Embodiments of this invention are described herein below
with reference to various figures, wherein like characters of
reference designate like parts throughout the drawings, in
which:
[0016] FIG. 1 is a flowchart showing an exemplary powder metallurgy
processing technique that may be utilized in embodiments of this
invention to create a component having minimal or no porosity;
[0017] FIG. 2 is a SEM photomicrograph showing the near gamma
microstructure of a disk utilized in embodiments of this
invention;
[0018] FIG. 3 is a SEM photomicrograph showing the lamellar
microstructure of the disk of FIG. 2 after it was heat treated;
[0019] FIG. 4 is an ultrasonic C-scan showing a portion of the heat
treated disk of FIG. 3, showing two visible flaws;
[0020] FIGS. 5(a) and (b) are ultrasonic A-scans confirming the
presence of the flaws depicted in FIG. 4;
[0021] FIG. 6 is an ultrasonic C-scan showing the same portion of
the disk of FIG. 3 after the heat treated disk was hot isostatic
pressed, showing no visible indication of the flaws identified in
FIGS. 4 and 5;
[0022] FIGS. 7(a) and (b) are ultrasonic A-scans confirming the
elimination of the flaws identified in FIGS. 4 and 5; and
[0023] FIG. 8 is a SEM photomicrograph showing that the lamellar
microstructure of the disk of FIG. 3 was maintained after the heat
treated disk was hot isostatic pressed.
DETAILED DESCRIPTION OF THE INVENTION
[0024] For the purposes of promoting an understanding of the
invention, reference will now be made to some embodiments of this
invention as illustrated in FIGS. 1-8 and specific language used to
describe the same. The terminology used herein is for the purpose
of description, not limitation. Specific structural and functional
details disclosed herein are not to be interpreted as limiting, but
merely as a basis for teaching one skilled in the art to variously
employ the present invention. Any modifications or variations in
the depicted structures and methods, and such further applications
of the principles of the invention as illustrated herein, as would
normally occur to one skilled in the art, are considered to be
within the spirit and scope of this invention as described and
claimed.
[0025] This invention relates to improved powder metallurgy
processed components that have little or no porosity therein.
Powder metallurgy techniques are used to make the components of
this invention because such techniques provide microstructural and
chemical homogeneities in the consolidated powder, and therefore,
also in the final extruded and/or forged components produced
therefrom. This invention may be utilized with any material formed
from a rapidly solidified powder produced by powder metallurgy in
insoluble gas (i.e., argon or helium), and having thermally induced
porosity therein in its consolidated and heat treated form.
Materials created from powders produced via powder metallurgy in
argon or helium gas generally contain thermally induced porosity
after heat treatment because argon and helium are both insoluble in
metals, and when heat treated at elevated temperatures, these gases
become mobile and precipitate as pores (i.e., as thermally induced
porosity) in the material.
[0026] Embodiments of this invention comprise the general powder
metallurgy technique 10 shown in FIG. 1. First, a powder may be
provided 11. Next, a preform may be created 13 from the powder.
Thereafter, a component may be created 15 from the preform. Next,
the component may be heat treated 17 to create a desired
microstructure therein. Thereafter, the component may be hot
isostatic pressed 19 to minimize any porosity therein that is
created during heat treatment. Thereafter, if the component is not
already in its final desired shape or form, the component can then
be machined or otherwise formed into its final desired shape, form
or dimensions.
[0027] The powders 11 utilized in this invention may comprise any
rapidly solidified, insoluble gas produced powder, such as, but not
limited to, gamma-TiAl powders, nickel aluminide powders, iron
aluminide powders, titanium alloy powders, any other superalloy
powders utilized to make gas turbine engine components, etc. In
embodiments, argon gas atomized gamma-TiAl powder may be desirable
because it comprises a fine grain microstructure with virtually no
chemical segregation. Furthermore, such gamma-TiAl components may
be used instead of the superalloy components currently used in many
gas turbine engine components. As used herein and throughout,
"gamma titanium aluminides" and derivations thereof (i.e.,
gamma-TiAl, .gamma.-TiAl, etc.) are those compositions that are
capable of forming the two-phase (.gamma.+.alpha..sub.2)
microstructure found generally centered around about 44-48 atomic
percent aluminum in the binary titanium-aluminum phase diagram.
Alloying additions of X, where X may include, but is not limited
to, chromium, niobium, molybdenum, boron, and/or carbon, etc., may
be provided in embodiments of this invention to modify and/or
improve the properties of the alloy for a given application.
[0028] The preform may be formed 13 from the powder in any suitable
manner, such as, for example, by hot isostatic pressing, hot die
compaction, etc. In embodiments, the powder may be canned and hot
isostatic pressed at a temperature sufficient to densify the
preform and consolidate the powder through bonding thereof. Hot
isostatic pressing the powder in this manner allows the powder
grains to connect metallically and/or to sinter together. In
gamma-TiAl embodiments, the preform should have a near gamma
microstructure if the hot isostatic pressing is performed below the
alpha transus temperature (T.sub..alpha.) of the powder.
[0029] Once the preform is created, the component can be created 15
therefrom in any suitable manner, such as, for example, by forging,
extrusion, and/or by a combination of extrusion and then forging,
etc. In some embodiments, the preform may be isothermally forged to
create a desired component, such as a disk. In gamma-TiAl
embodiments, the extrusion and/or isothermal forging are typically
carried out at a temperature in the (.alpha.+.gamma.) phase field
of the Ti--Al phase diagram, which is well below T.sub..alpha. for
this material. Therefore, gamma-TiAl components should have a near
gamma microstructure after they are formed. In other embodiments
(i.e., nickel aluminides, iron aluminides, other titanium alloys
and other superalloys), the extrusion and/or isothermal forging may
be carried out at temperatures as high as about 1023.degree. C. or
higher.
[0030] Once the component is created, the component can be heat
treated 17 to create the desired microstructure therein. Since
fully lamellar microstructures are strong and crack resistant, they
are desirable in many applications. A crack resistant lamellar
microstructure can be achieved in gamma-TiAl components by heat
treating the component at a temperature above the T.sub..alpha. of
the component alloy. In other embodiments (i.e., nickel aluminides,
iron aluminides, other titanium alloys and other superalloys), heat
treating at temperatures of about 1000-1200.degree. C. for about
2-4 hours may be used to create a desirable microstructure in the
components.
[0031] Such elevated temperature heat treatment often leaves behind
cavities in the component, which can be confirmed in various
manners, such as, for example, by ultrasonic scanning, x-ray
radiography, serial sectioning, etc. In embodiments, it is believed
that such porosity may be thermally induced porosity that is
created by the argon or other insoluble gas that is entrapped in
the powder, which agglomerates in the form of cavities/pores during
heat treatment. This is an undesirable condition known as thermally
induced porosity. Regardless of the mechanism of formation, this
porosity may be much larger than acceptable for many components.
Furthermore, depending upon how this porosity was formed, the
porosity may be associated with grain boundaries, which may reduce
the low cycle fatigue properties of the final component by serving
as preferential sites for crack initiation. Therefore, this
porosity must be eliminated, or at least be reduced to an
acceptable level, in order for powder metallurgy techniques to be
acceptably utilized for forming many components.
[0032] It has been discovered that hot isostatic pressing 19 the
component after heat treating 17 may eliminate the porosity
therein, or at least reduce the porosity therein to an acceptable
level. Hot isostatic pressing can eliminate internal voids and
microporosity in a component through a combination of plastic
deformation, creep and diffusion, thereby producing a denser
component. This hot isostatic pressing step should have minimal
effect on the microstructure, other than decreasing the amount or
size of porosity therein. A simple calculation may be done to show
whether or not the compressive creep strain that is developed
during this hot isostatic pressing step is enough to heal the
porosity therein sufficiently to make the component acceptable for
use for a given application. Alternatively, ultrasonic inspection
may be utilized to verify that any porosity remaining in the
component is acceptable.
[0033] Once the component is heat treated and hot isostatic
pressed, it may be machined or otherwise formed to its desired
final dimensions, if necessary. The fully lamellar microstructure
of the gamma-TiAl components should be maintained if this
additional processing step is carried out at a temperature below
the T.sub..alpha. of the component alloy.
[0034] The powder metallurgy processing techniques of this
invention may be utilized to make a variety of components, such as,
for example, gas turbine engine components (i.e., compressor disks,
compressor blades, low pressure turbine blades, tangential on board
injectors, etc.) or any other components that may be exposed to
high mechanical loads at high temperatures.
EXAMPLE
[0035] An exemplary non-limiting sample gamma-TiAl disk was made
and evaluated to verify this invention. This sample was prepared
utilizing argon gas atomized gamma-TiAl powder 11 having a nominal
composition, in atomic percent, of Ti-46Al-3.7(Nb,Cr,Mo)-0.4(B,C)
and having an average particle size of about 70 .mu.m. A preform
was created 13 by canning and hot isostatic pressing this powder at
about 1260.degree. C. and about 25 ksi for about 4 hours in an
argon atmosphere. Once the preform was consolidated, the preform
was isothermally forged 15 into a disk in a two-step operation in
the (.alpha.+.gamma.) phase field at about 1177.degree. C. using
about an 85% reduction. At this point, the disk had a near gamma
microstructure, as shown in FIG. 2. The disk was then heat treated
17 at about 1354.degree. C. for about 4 hours under vacuum to
create a fully lamellar microstructure comprising alternating
platelets of .gamma.-TiAl phase and .alpha..sub.2-Ti.sub.3Al with
an average lamellar grain size of about 250 .mu.m, as shown in FIG.
3. In general, gamma-TiAl having a duplex microstructure provides
better elongation and strength properties, whereas gamma-TiAl
having a lamellar microstructure provides better creep resistance,
toughness, and crack resistance. Ultrasonic scans and serial
sectioning indicated that a small amount of cavities/pores 50, 55
existed in this heat treated disk, as shown in FIG. 4. As shown in
FIGS. 5(a) and (b), ultrasonic scans confirmed the presence of this
porosity 50, 55. This porosity 50, 55, which had diameters of about
0.013'' and 0.019'' respectively, was much larger than acceptable
for many components, such as for rotating compressor disks used in
gas turbine engines. Therefore, further processing was undertaken
in an attempt to eliminate this porosity 50, 55. In that regard,
the heat treated disk was hot isostatic pressed 19 at about
1232.degree. C. and about 25 ksi for about 10 hours in an argon
atmosphere in an attempt to minimize the porosity 50, 55 therein.
As shown in FIGS. 6 and 7(a) and (b), ultrasonic scanning confirmed
that, after hot isostatic pressing, the porosity 50, 55 that had
previously existed in the heat treated disk was eliminated.
Furthermore, as can be seen in FIGS. 3 and 8, no significant
changes were detected in the microstructure of the heat treated
disk after hot isostatic pressing (FIG. 8) as compared to before
hot isostatic pressing (FIG. 3).
[0036] As described above, this invention provides improved powder
metallurgy processing techniques for producing components having
little or no porosity therein. Advantageously, these techniques can
be used with a variety of materials to produce components that have
good mechanical properties at elevated temperatures. These
techniques may be utilized to make gas turbine engine components
and other components that are subjected to high mechanical loads at
high temperatures. Many other embodiments and advantages will be
apparent to those skilled in the relevant art.
[0037] Various embodiments of this invention have been described in
fulfillment of the various needs that the invention meets. It
should be recognized that these embodiments are merely illustrative
of the principles of various embodiments of the present invention.
Numerous modifications and adaptations thereof will be apparent to
those skilled in the art without departing from the spirit and
scope of the present invention. For example, while gamma-TiAl
powders were described herein in one non-limiting exemplary
embodiment, this invention is not limited to use with such powders.
This invention may be used with any rapidly solidified, insoluble
gas produced powder that creates thermally induced porosity in a
component during heat treatment thereof. Thus, it is intended that
the present invention cover all suitable modifications and
variations as come within the scope of the appended claims and
their equivalents.
* * * * *