U.S. patent application number 09/190066 was filed with the patent office on 2001-05-31 for method of forming hollow channels within a component.
Invention is credited to DOBBS, JAMES R., DUPREE, PAUL L., JACKSON, MELVIN R., ZHAO, JI CHENG.
Application Number | 20010001897 09/190066 |
Document ID | / |
Family ID | 22699893 |
Filed Date | 2001-05-31 |
United States Patent
Application |
20010001897 |
Kind Code |
A1 |
ZHAO, JI CHENG ; et
al. |
May 31, 2001 |
METHOD OF FORMING HOLLOW CHANNELS WITHIN A COMPONENT
Abstract
A method of forming an internal channel within an article, such
as a cooling channel in an air-cooled blade, vane, shroud,
combustor or duct of a gas turbine engine. The method generally
entails forming a substrate to have a groove recessed in its
surface. A sacrificial material is then deposited in the groove to
form a filler that can be preferentially removed from the groove. A
permanent layer is then deposited on the surface of the substrate
and over the filler, after which the filler is removed from the
groove to yield the desired channel in the substrate beneath the
permanent layer. Certain sacrificial materials are described by
which the filler can be deposited and
Inventors: |
ZHAO, JI CHENG; (NISKAYUNA,
NY) ; JACKSON, MELVIN R.; (NISKAYUNA, NY) ;
DUPREE, PAUL L.; (SCOTIA, NY) ; DOBBS, JAMES R.;
(TALLAHASSEE, FL) |
Correspondence
Address: |
GENERAL ELECTRIC COMPANY
CRD PATENT DOCKET ROOM 4A59
P O BOX 8
BUILDING K 1 SALAMONE
SCHENECTADY
NY
12301
US
|
Family ID: |
22699893 |
Appl. No.: |
09/190066 |
Filed: |
November 12, 1998 |
Current U.S.
Class: |
29/889 |
Current CPC
Class: |
Y10T 29/49316 20150115;
C23C 28/023 20130101; B23P 15/04 20130101; F01D 25/12 20130101;
Y10T 29/49346 20150115; Y10T 29/49348 20150115; F01D 5/187
20130101; C23C 26/00 20130101; B23P 2700/13 20130101; F02K 9/64
20130101; F01D 5/18 20130101; C23C 4/02 20130101; C23C 14/0005
20130101; C23C 28/028 20130101 |
Class at
Publication: |
29/889 |
International
Class: |
B23P 015/00 |
Claims
What is claimed is:
1. A method of forming an internal channel in an article, the
method comprising the steps of: forming a substrate having a
surface and a groove recessed in the surface; depositing a paste in
the groove so as to fill the groove, the paste comprising a
sacrificial material in a binder, the sacrificial material being
chosen from the group consisting of NaCl, KBO.sub.2, NiCl.sub.2,
MgSO.sub.4, NiF.sub.2, NaAlO.sub.2, and mixtures of NaAlO.sub.2 and
NaAlSiO.sub.4; removing the binder so as to leave the sacrificial
material in the groove, the sacrificial material defining a fill
surface that is substantially coplanar with the surface of the
substrate; depositing a permanent layer on the surface of the
substrate and over the sacrificial material in the groove; and then
removing the sacrificial material from the groove so as to form an
internal channel in the substrate and beneath the permanent
layer.
2. A method as recited in claim 1, wherein the permanent layer is
deposited by electron beam physical vapor deposition.
3. A method as recited in claim 1, wherein the sacrificial material
is removed by dissolving in water, an alcohol, acetone, sodium
hydroxide or potassium hydroxide.
4. A method as recited in claim 1, wherein the article is a
component of a gas turbine engine.
5. The article formed by the method of claim 1.
6. A method of forming an internal channel in an article, the
method comprising the steps of: forming a substrate having a
surface and a groove recessed in the surface; consolidating a
sacrificial material into the groove so as to fill the groove at a
temperature of less than 200.degree. C., the sacrificial material
being chosen from the group consisting of KBr, NaCl, NiBr.sub.2,
BN, and mixtures of talc and pyrophyllite, the sacrificial material
defining a fill surface that is substantially coplanar with the
surface of the substrate; depositing a permanent layer on the
surface of the substrate and over the sacrificial material in the
groove; and then removing the sacrificial material from the groove
so as to form an internal channel in the substrate and beneath the
permanent layer.
7. A method as recited in claim 6, wherein the permanent layer is
deposited by electron beam physical vapor deposition.
8. A method as recited in claim 6, wherein the sacrificial material
is removed by dissolving in water, an alcohol, acetone, sodium
hydroxide or potassium hydroxide.
9. A method as recited in claim 6, wherein the article is a
component of a gas turbine engine.
10. The article formed by the method of claim 6.
11. A method of forming an internal channel in an article, the
method comprising the steps of: forming a substrate having a
surface and a groove recessed in the surface; depositing and
sintering a sacrificial material in the groove so as to fill the
groove, the sacrificial material being chosen from the group
consisting of MgF.sub.2, NiF.sub.2, and mixtures of talc and
pyrophyllite, the sacrificial material defining a fill surface that
is substantially coplanar with the surface of the substrate;
depositing a permanent layer on the surface of the substrate and
over the sacrificial material in the groove; and then removing the
sacrificial material from the groove so as to form an internal
channel in the substrate and beneath the permanent layer.
12. A method as recited in claim 11, wherein the permanent layer is
deposited by electron beam physical vapor deposition.
13. A method as recited in claim 11, wherein the sacrificial
material is removed by dissolving in water or nitric acid.
14. A method as recited in claim 11, wherein the article is a
component of a gas turbine engine.
15. The article formed by the method of claim 11.
16. A method of forming an internal channel in an article, the
method comprising the steps of: forming a substrate having a
surface and a groove recessed in the surface; depositing a
sacrificial material in the groove so as to fill the groove, the
sacrificial material being chosen from the group consisting of
MoO.sub.3 and substances with sublimation temperatures between
about 500.degree. C. and 1100.degree. C., the sacrificial material
defining a fill surface that is substantially coplanar with the
surface of the substrate; depositing a first permanent layer on the
surface of the substrate and over the sacrificial material in the
groove; heating the sacrificial material to remove the sacrificial
material from the groove by sublimation so as to form an internal
channel in the substrate and beneath the first permanent layer; and
then depositing a second permanent layer on the first permanent
layer, the first permanent layer being more compliant than the
second permanent layer.
17. A method as recited in claim 16, wherein the first and second
permanent layers are deposited by electron beam physical vapor
deposition.
18. A method as recited in claim 16, wherein only a portion of the
sacrificial material decomposes by sublimation during the heating
step, with a remaining portion of the sacrificial material being
removed by dissolving in water, an alcohol, acetone or an acid.
19. A method as recited in claim 16, wherein the article is a
component of a gas turbine engine.
20. The article formed by the method of claim 16.
Description
[0001] The present invention relates to methods of forming internal
channels in components. More particularly, this invention is
directed to materials and methods for forming a cooling channel
beneath the surface of an air-cooled component, such as a blade,
vane, shroud, combustor or duct of a gas turbine engine.
BACKGROUND OF THE INVENTION
[0002] Higher operating temperatures for gas turbine engines are
continuously sought in order to increase their efficiency. However,
as operating temperatures increase, the high temperature durability
of the components of the engine must correspondingly increase.
Significant advances in high temperature capabilities have been
achieved through formulation of iron, nickel and cobalt-based
superalloys, though components formed from such alloys often cannot
withstand long service exposures if located in certain sections of
a gas turbine engine, such as the turbine, combustor or
augmentor.
[0003] A common solution is to provide internal cooling of turbine,
combustor and augmentor components, at times in combination with a
thermal barrier coating. Airfoils of gas turbine engine blades and
vanes often require a complex cooling scheme in which cooling air
flows through cooling channels within the airfoil and is then
discharged through carefully configured cooling holes at the
airfoil surface. Convection cooling occurs within the airfoil from
heat transfer to the cooling air as it flows through the cooling
channels. In addition, fine internal orifices can be provided to
direct cooling air flow directly against inner surfaces of the
airfoil to achieve what is referred to as impingement cooling,
while film cooling is often accomplished at the airfoil surface by
configuring the cooling holes to discharge the cooling air flow
across the airfoil surface so that the surface is protected from
direct contact with the surrounding hot gases within the
engine.
[0004] In the past, cooling channels have typically been integrally
formed with the airfoil casting using relatively complicated cores
and casting techniques. More recently, U.S. Pat. Nos. 5,626,462 and
5,640,767, both to Jackson et al. and commonly assigned with the
present invention, teach a method of forming a double-walled
airfoil by depositing an airfoil skin over a separately-formed
inner support wall (e.g., a spar) having surface grooves filled
with a sacrificial material. After the airfoil skin is formed,
preferably by deposition methods such as plasma spraying and
electron-beam physical vapor deposition (EBPVD), the sacrificial
material is removed to yield a double-walled airfoil with cooling
channels that circulate cooling air against the interior surface of
the airfoil skin.
[0005] A challenge with the process disclosed by Jackson et al. is
the compositional, physical, mechanical and environmental
requirements of the sacrificial material. These requirements
include: (a) compositional compatibility with the airfoil spar and
skin materials, particularly at skin deposition temperatures, e.g.,
at least 700.degree. C. and preferably at least 1200.degree. C. for
EBPVD; (b) compositional stability at deposition temperatures; (c)
ease of removal after skin deposition; (d) adhesion to the spar;
(e) minimal densification shrinkage relative to the spar as the
spar is heated during skin deposition; (f) comparable coefficient
of thermal expansion (CTE) to that of the spar; (g) ease of
cleaning from the spar surface so that the skin is deposited and
bonded directly to the spar; and (h) formable to completely fill
the groove and achieve a smooth, reasonably dense fill surface on
which the skin is deposited. If any of items (d) through (h) are
not met, a gap may be present within the groove during skin
deposition, which, if sufficiently large, will lead to an
unacceptable surface defect in the airfoil skin. Airfoil skins
deposited by EBPVD are particularly sensitive to surface
discontinuities due to the atom-by-atom manner in which the coating
is built up. Shrinkage and adhesion of the sacrificial material to
the spar have been identified as particularly key issues to the
reliable production of airfoils using the technique taught by
Jackson et al.
[0006] In Jackson et al., the sacrificial material is a braze alloy
deposited in excess amounts in a spar groove, with the excess being
removed by machining or another suitable technique so that the
surface of the braze alloy is flush with the surrounding surface of
the spar. The sacrificial material is then removed after deposition
of the airfoil skin by melting/extraction, chemical etching,
pyrolysis or another suitable method. Though braze alloys have been
successful in the process disclosed by Jackson et al., efforts have
continued to develop other materials that better meet the
requirements described previously. Notably, sacrificial materials
proposed for other applications have been tried without success.
For example, a combination of K.sub.2SO.sub.4 and Na.sub.2AlO.sub.3
was experimented with as a sacrificial backfill material, but found
to be corrosive and severely attacked a spar formed of Ren N5, a
General Electric nickel-based superalloy having a nominal
composition, in weight percent, of
Ni-7.5Co-7.0Cr-6.5Ta-6.2Al-5.0W-3.0Re--
1.5Mo-0.15Hf-0.05C-0.004B-0.01Y. Other known sacrificial materials,
including those disclosed in U.S. Pat. No. 4,956,037 to Vivaldi and
U.S. Pat. No. 5,249,357 to Holmes et al., are unable to withstand
high-temperature deposition processes such as EBPVD.
[0007] In view of the above, it would be desirable if improved
sacrificial materials and processes were available that could
ensure that all of the aforementioned requirements of the
sacrificial material were adequately met to produce an air-cooled
component with a deposited skin that is substantially free of
surface defects.
BRIEF SUMMARY OF THE INVENTION
[0008] According to the present invention, there are provided
sacrificial materials and methods for forming an internal channel
in an article, and particularly a cooling channel in an air-cooled
component, such as a blade, vane, shroud, combustor or duct of a
gas turbine engine. Each of the methods generally entails forming a
substrate to have a groove recessed in its surface. The sacrificial
material is deposited and consolidated in the groove so that the
groove is completely filled. A permanent layer is then deposited on
the surface of the substrate and over the sacrificial material in
the groove, after which the sacrificial material is removed from
the groove to form a channel in the substrate beneath the permanent
layer.
[0009] Four embodiments of this invention are disclosed, each of
which generally entails the use of different candidates for the
sacrificial material. The preferred process for depositing the
permanent layer on the spar and sacrificial material is electron
beam physical vapor deposition (EBPVD). In a first embodiment of
the invention, the sacrificial material is either NaCl, KBO.sub.2,
NiCl.sub.2, MgSO.sub.4, NiF.sub.2, NaAlO.sub.2, or mixtures of
NaAlO.sub.2 and NaAlSiO.sub.4, and is deposited in the form of a
paste. In a second embodiment, the sacrificial material is
formulated to enable depositing and consolidating the material in
the groove at low temperatures (i.e., cold pressing), preferably
less than 200.degree. C. Suitable sacrificial materials for this
process are KBr, NaCl, NiBr.sub.2, BN, and mixtures of talc
(Mg.sub.6[Si.sub.8O.sub.20](OH).sub.4) and pyrophyllite
(Al.sub.4[Si.sub.8O.sub.20](OH).sub.4). In a third embodiment, the
sacrificial material is deposited and then sintered in the groove
at an elevated temperature (i.e., hot pressing). Sacrificial
materials suitable for this process are MgF.sub.2, NiF.sub.2, and
mixtures of talc and pyrophyllite. Finally, the fourth embodiment
of this invention employs as the sacrificial material MoO.sub.3 or
another material capable of being sublimed above a certain
temperature. This method entails depositing a relatively compliant
layer over the sacrificial material, heating the sacrificial
material to remove the sacrificial material by sublimation, and
then depositing a second, less compliant layer on the first layer
to produce a multilayer skin on the substrate.
[0010] In accordance with the above, the present invention
identifies certain compositions suitable for use as sacrificial
materials when appropriately processed by one of the four
above-noted methods. The sacrificial materials of this invention
and their associated process requirements address the
aforementioned requirements for the sacrificial material,
particularly with respect to exhibiting adequate adhesion to the
spar and minimal shrinkage prior to and during the deposition step.
As a result, the disclosed materials and processes are able to
produce air-cooled components with deposited skins that are
substantially free of surface defects.
[0011] Other objects and advantages of this invention will be
better appreciated from the following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 shows a processing stage when forming a cooling
channel below the skin of a double-walled airfoil in accordance
with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0013] The present invention is generally applicable to any
component in which an internal channel is desired. The advantages
of this invention are particularly applicable to gas turbine engine
components that employ internal cooling to maintain their service
temperatures at an acceptable level. Notable examples of such
components include shrouds, combustors, ducts and airfoils of high
and low pressure turbine vanes and blades.
[0014] The invention is generally an improvement of the method
disclosed in U.S. Pat. Nos. 5,626,462 and 5,640,767, both to
Jackson et al., which are incorporated herein by reference.
Referring to FIG. 1, four embodiments of the invention will be
described in terms of a component, such as a turbine vane or blade
airfoil, having a double-walled construction formed by the
deposition of an airfoil skin 12 over a substrate 10, such as a
cast spar, having a groove 14 formed in its outer surface 16. The
groove 14 will typically have a rectilinear cross-section and
extend in the longitudinal direction of the airfoil, though it is
foreseeable that the groove 14 could have any configuration
suitable for a particular component. In each embodiment, a
sacrificial material is deposited and, if necessary, consolidated
in the groove 14 to form a sacrificial filler 18 that completely
fills the groove 14. The permanent skin 12 is then deposited on the
surface 16 of the substrate 10 and over the sacrificial filler 18
in the groove 14, after which the filler 18 is removed from the
groove 14 to form a hollow cooling channel in the substrate 10
beneath the skin 12.
[0015] In each embodiment, certain compositions have been shown to
be able to form suitable sacrificial fillers 18 when appropriately
processed by one of four processes. Particularly, these
compositions form fillers 18 that exhibit: (a) compositional
compatibility with nickel-base superalloys at temperatures required
to deposit the airfoil skin 12, e.g., at least 700.degree. C. and
preferably at least 1200.degree. C. for EBPVD; (b) compositional
stability at skin deposition temperatures; (c) ease of removal
after skin deposition; (d) adhesion to a nickel-based substrate 10
at low and high temperatures prior to and during skin deposition,
respectively; (e) minimal densification shrinkage relative to a
nickel-based substrate 10 as the filler 18 is heated during skin
deposition; (f) a comparable coefficient of thermal expansion (CTE)
to nickel-based superalloys; (g) ease of cleaning from the
substrate 10 prior to skin deposition so that the skin 12 is
deposited and bonded directly to the substrate 10; and (h) formable
to completely fill the groove 14 and achieve a smooth, reasonably
dense fill surface on which the skin 12 is deposited. When
appropriately processed, each of the sacrificial materials
addresses the aforementioned requirements, particularly with
respect to exhibiting adequate adhesion to the nickel-based
superalloys and minimal shrinkage prior to and during skin
deposition.
[0016] In the first embodiment of the invention, the sacrificial
filler 18 is formed by depositing in the groove 14 a paste that
contains a solvent or binder and a sacrificial material of either
NaCl (sodium chloride), KBO.sub.2 (potassium borate), NiCl.sub.2
(nickel chloride), MgSO.sub.4 (magnesium sulfate), NiF.sub.2
(nickel fluoride), NaAlO.sub.2 (sodium aluminate), or mixtures of
NaAlO.sub.2 and NaAlSiO.sub.4 (sodium aluminosilicate). Suitable
binders include a water-based composition known as Vitta Gel and
commercially available from Vitta Corporation. Suitable solvents
will depend on the specific sacrificial material used, and include
water, alcohols, acetone, sodium hydroxide (NaOH) and potassium
hydroxide (KOH). The paste is deposited to completely fill the
groove 14, and then ground and polished after curing (drying) to
yield a smooth surface that is substantially coplanar with the
surface 16 of the substrate 10, such that the skin 12 will not
develop a depression over the groove 14. The skin 12 is then
preferably deposited by EBPVD to cover the substrate 10 and the
sacrificial filler 18, after which the filler 18 is completely
removed by etching or dissolution to yield a cooling channel. A
preferred EBPVD technique for depositing the skin 12 is disclosed
in U.S. Pat. No. 5,474,809, incorporated herein by reference.
[0017] The sacrificial materials indicated above for the filler 18
are each compatible with substrates 10 formed of nickel-based
superalloys in terms of CTE, adhesion and composition.
Specifically, each of these sacrificial materials has a CTE
sufficiently close to nickel-based superalloys to prevent the
formation of an excessive gap from shrinkage during deposition of
the skin 12. These materials have also been shown to adhere well to
nickel-base superalloys, and to be compatible with nickel-based
superalloys to the sense that minimal interdiffusion occurs during
the consolidation and deposition steps. Finally, fillers 18 formed
of these sacrificial materials can be preferentially etched from
nickel-based substrates 10. Preferred etchants or solvents for this
purpose include water, alcohols, acetone, sodium hydroxide and
potassium hydroxide.
[0018] In a second embodiment of this invention, the sacrificial
material is formulated to enable filling the groove 14 by a cold
pressing operation, i.e., depositing and consolidating the material
in the groove 14 at a low temperature, preferably less than
200.degree. C. Consolidation of the sacrificial material within the
groove 14 can be achieved using various techniques known in the
art, such as cold pressing with a die. Suitable sacrificial
materials for cold pressing must have very low hardness, e.g., less
than about 4 on the Moh scale of hardness, so that they can be
pressed at ambient or low temperatures to yield a filler 18 whose
surface is roughly coplanar with the surface 16 of the substrate
10. Preferred sacrificial materials having this characteristic are
KBr (potassium bromide), NaCl, NiBr.sub.2 (nickel bromide), BN
(boron nitride), and mixtures of talc and pyrophyllite. Fillers 18
formed of these sacrificial materials can be removed from
nickel-based substrates 10 using water, alcohols or acetone. For
example, BN filler can be removed with, sodium hydroxide and
potassium hydroxide.
[0019] In the third embodiment, the sacrificial material is
formulated to fill the groove 14 by hot pressing, i.e., deposited
and then sintered in the groove 14 at an elevated temperature to
form the filler 18, in accordance with hot pressing techniques
known in the art. Thermal expansion matching, compatibility with
nickel-based superalloys, and high melting points are of most
concern for sacrificial materials used in the hot pressing process.
According to this invention, materials that address these
considerations are MgF.sub.2 (magnesium fluoride), NiF.sub.2, and
mixtures of talc and pyrophyllite. Sintering temperatures for these
materials are generally less than 1000.degree. C., allowing their
use with nickel-based superalloys. Fillers 18 formed of these
sacrificial materials can be preferentially removed from
nickel-based substrates 10 using water, nitric acid (HNO.sub.3),
sodium hydroxide and potassium hydroxide.
[0020] Finally, in the fourth embodiment of this invention, the
filler 18 is formed with a sacrificial material containing
MoO.sub.3 (molybdenum trioxide) or other substances capable of
sublimation or of being sufficiently decomposed to release a
portion of their volume as a gaseous phase at temperatures between
about 500.degree. C. and 1100.degree. C. Any remaining portion of
the filler 18 is then removed by dissolving in water, an alcohol,
acetone or an acid. As with the previous sacrificial materials, the
filler 18 is formed by depositing the sacrificial material in the
groove 14 so that the surface of the filler 18 is substantially
coplanar with the surrounding surface 16 of the substrate 10. A
relatively compliant metallic layer 12A is then deposited by EBPVD
on the sacrificial filler 18, after which the filler 18 is heated
to above its sublimation temperature, which is about 800.degree. C.
for MoO.sub.3. The remaining layer 12B of the skin 12 is then
deposited on the first layer 12A. According to the invention, the
first layer 12A is preferably formed to be more compliant that the
second layer 12B in order to mitigate the effect of any filler
shrinkage. For example, a compliant layer 12A of pure nickel may be
deposited followed by the deposition of a less compliant layer 12B
of a nickel-based superalloy. Where shrinkage is a problem with any
embodiment of this invention, the skin 12 may be deposited as
multiple discreet permanent layers with at least the first being
relatively more compliant, in accordance with this last embodiment
of the invention.
[0021] 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. Therefore, the scope of the
invention is to be limited only by the following claims.
* * * * *