U.S. patent application number 13/951542 was filed with the patent office on 2015-01-29 for method for creating a textured bond coat surface.
The applicant listed for this patent is Gerald J. Bruck, Dhafer Jouini, Ahmed Kamel, Anand A. Kulkarni, Gary B. Merrill, Sachin R. Shinde, Jonathan E. Shipper, JR.. Invention is credited to Gerald J. Bruck, Dhafer Jouini, Ahmed Kamel, Anand A. Kulkarni, Gary B. Merrill, Sachin R. Shinde, Jonathan E. Shipper, JR..
Application Number | 20150030826 13/951542 |
Document ID | / |
Family ID | 51225054 |
Filed Date | 2015-01-29 |
United States Patent
Application |
20150030826 |
Kind Code |
A1 |
Kamel; Ahmed ; et
al. |
January 29, 2015 |
METHOD FOR CREATING A TEXTURED BOND COAT SURFACE
Abstract
A method for forming a textured bond coat surface (48) for a
thermal barrier coating system (44) of a gas turbine component
(34). The method includes selectively melting portions of a layer
of alloy particles (16) with a patterned energy beam (20) to form
successive layers of alloy material (16', 16'') until a desired
surface geometric feature (26) is achieved. The energy beam pattern
may be indexed between layers to form a protruding undercut (28) in
the geometric feature. The patterned energy beam may be formed by
directing laser energy from a diode laser (30) through a cartridge
filter (32). Particles of a flux material (18) may be melted along
with the alloy particles to form a protective layer of slag (22)
over the melted and cooling alloy material.
Inventors: |
Kamel; Ahmed; (Orlando,
FL) ; Merrill; Gary B.; (Orlando, FL) ;
Kulkarni; Anand A.; (Oviedo, FL) ; Bruck; Gerald
J.; (Oviedo, FL) ; Jouini; Dhafer; (Orlando,
FL) ; Shipper, JR.; Jonathan E.; (Orlando, FL)
; Shinde; Sachin R.; (Oviedo, FL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kamel; Ahmed
Merrill; Gary B.
Kulkarni; Anand A.
Bruck; Gerald J.
Jouini; Dhafer
Shipper, JR.; Jonathan E.
Shinde; Sachin R. |
Orlando
Orlando
Oviedo
Oviedo
Orlando
Orlando
Oviedo |
FL
FL
FL
FL
FL
FL
FL |
US
US
US
US
US
US
US |
|
|
Family ID: |
51225054 |
Appl. No.: |
13/951542 |
Filed: |
July 26, 2013 |
Current U.S.
Class: |
428/209 ;
427/555 |
Current CPC
Class: |
F01D 11/18 20130101;
C23C 24/106 20130101; Y10T 428/24917 20150115; F01D 5/288 20130101;
C23C 28/40 20130101 |
Class at
Publication: |
428/209 ;
427/555 |
International
Class: |
C23C 28/00 20060101
C23C028/00; F01D 11/18 20060101 F01D011/18 |
Claims
1. A method for forming a textured bond coat surface for a thermal
barrier coating system, the method comprising: depositing a layer
of powder comprising particles of a metal alloy and particles of a
flux material onto a surface; selectively melting portions of the
layer of powder with an energy beam to form a pattern of the metal
alloy covered by a layer of slag on the surface; removing the layer
of slag; and repeating the depositing and selectively melting steps
if required to achieve a desired textured surface.
2. The method of claim 1, where the depositing step comprises
depositing the layer of powder to comprise particles of a bond coat
material and particles of a flux material to form the desired
textured surface on a bond coat layer.
3. The method of claim 1, further comprising: depositing the layer
of powder to comprise particles of a superalloy material and
particles of a flux material onto the surface of a superalloy
substrate to create the desired textured surface on the superalloy
substrate; and depositing a layer of bond coat material over the
textured superalloy substrate surface.
4. The method of claim 1, wherein the step of selectively melting
comprises directing a laser energy beam toward the layer of powder
through beam shaping optics.
5. The method of claim 1, wherein the step of depositing comprises
pre-placing a layer of mixed metal alloy and flux material
particles onto the surface.
6. The method of claim 1, wherein the step of depositing comprises
simultaneously directing a spray of metal alloy particles and a
spray of flux material particles onto the surface.
7. The method of claim 1, wherein the step of depositing comprises
depositing a layer of particles of the metal alloy onto the surface
and then depositing a layer of particles of the flux material onto
the layer of particles of the metal alloy.
8. The method of claim 1, further comprising selecting the
particles of metal alloy and the particles of flux material to have
overlapping mesh size ranges.
9. The method of claim 1, further comprising forming the desired
textured surface to include a geometric feature comprising a
protruding undercut by: selectively melting portions of a first
layer of powder with the energy beam having a first pattern to form
a first layer of the geometric feature; and selectively melting
portions of a second layer of powder with the energy beam having a
second pattern indexed from the first pattern to form a second
layer of the geometric feature cantilevered beyond the first layer
to at least partially define the protruding undercut.
10. A gas turbine engine component comprising a thermal barrier
coating system comprising the geometric feature formed by the
method of claim 9.
11. A method for forming a textured surface for a thermal barrier
coating system, the method comprising: depositing particles of a
bond coat material onto a surface; selectively melting portions of
the bond coat material particles with an energy beam pattern to
form a first layer of a desired textured surface of the bond coat
material on the surface; and repeating the depositing and
selectively melting steps to form subsequent layers of the textured
surface until the desired textured surface of the bond coat
material is achieved.
12. The method of claim 11, further comprising indexing the energy
beam pattern between layers such that not all layers have the same
geometry.
13. The method of claim 11, further comprising indexing the energy
beam pattern between layers to form a geometric feature comprising
a protruding undercut.
14. A gas turbine engine component comprising a thermal barrier
coating system comprising the geometric feature formed by the
method of claim 13.
15. The method of claim 11, further comprising: depositing
particles of the bond coat material and particles of a flux
material onto the surface; selectively melting portions of the bond
coat and flux material particles to form a first layer of the bond
coat material covered by a layer of slag on the surface; and
removing the slag prior to any subsequent depositing and
selectively melting step.
16. The method of claim 11, further comprising selectively melting
the portions of the bond coat material particles with a laser beam
patterned by beam shaping optics comprising a filter cartridge.
17. The method of claim 16, wherein a first filter cartridge is
used to form a first laser beam pattern for a first layer, and a
second filter cartridge is used to form a second laser beam pattern
different than the first laser beam pattern for a subsequent layer.
Description
FIELD OF THE INVENTION
[0001] This invention relates generally to the field of materials
technology, and more particularly to a method for creating a
textured surface in a bond coat of a thermal barrier coating
system.
BACKGROUND OF THE INVENTION
[0002] Ceramic thermal barrier coating systems are used on gas
turbine engine hot gas path components to protect the underlying
metal alloy substrate from combustion gas temperatures that exceed
the safe operating temperature of the alloy. A typical thermal
barrier coating system may include a bond coat, such as an MCrAlY
material, deposited onto the substrate alloy and a ceramic topcoat,
such as yttria stabilized zirconia, deposited onto the bond coat.
It is known that strong adhesion between the layers of such systems
is critical for proper functioning and long life of the coating
system, and that a degree of surface roughness in the interface
between the layers provides a beneficial mechanical interlock in
that regard.
[0003] Bond coat material is often deposited by a spray process,
such as High Velocity Oxy-Fuel (HVOF) or Air Plasma Spray (APS). It
is known to control spray parameters when depositing a bond coat
layer in order to achieve a degree of surface roughness in the
deposited coating. However, the degree of roughness and the shape
of the surface features in the deposited coating that are created
by controlling the spray parameters are limited.
[0004] It is also known to texture the surface of a bond coat layer
prior to the deposition of a ceramic insulating layer by using a
material removal process, such as laser ablation, micromachining or
photolithography, such as described in U.S. Pat. No. 5,723,078. As
the firing temperatures of advance gas turbine engines continue to
increase, further improvements in thermal barrier coating systems
and methods of applying such coatings are desired.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] The invention is explained in the following description in
view of the drawings that show:
[0006] FIGS. 1-5 illustrate sequential steps for depositing a
coating onto a substrate with a surface texture including geometric
features having protruding undercuts.
[0007] FIG. 6 illustrates a layer of thermal barrier coating
material deposited over a textured surface of a bond coat
material.
[0008] FIG. 7 illustrates a layer of bond coat material deposited
over a textured surface of a superalloy component with an overlying
layer of ceramic thermal barrier coating material.
DETAILED DESCRIPTION OF THE INVENTION
[0009] The present inventors have recognized that known bond coat
texturing processes that rely upon material removal are inherently
inefficient because unwanted material is first deposited and is
then removed. The methods of the present invention cause material
to be initially deposited in a way that creates the desired texture
pattern. Furthermore, because the methods of the present invention
create a textured surface by depositing a plurality of layers of
material, a wide range of surface feature geometries, including
undercuts, are made possible.
[0010] FIG. 1 is a partial cross-sectional view of a gas turbine
component 10 having a relatively smooth surface 12 to which it is
desired to add a textured surface geometry. The surface 12 may be a
surface of an existing bond coat material layer that is to be
textured, or it may be the surface of a superalloy substrate over
which a layer of bond coat material is to be applied. A layer of
powder 14 is deposited onto the surface 12. The layer of powder 14
includes particles of a metal alloy 16 and particles of a flux
material 18. The metal alloy 16 may be superalloy material for the
embodiment where the surface of the superalloy substrate is to be
textured, or it may be a bond coat material for the embodiment
where the surface of a bond coat is to be textured. The flux
material 18 is applied to provide cleansing and atmospheric
protection functions during a subsequent melting step. Accordingly,
the particles of metal alloy 16 and particles of flux material 18
may be mixed together and applied as a single layer in one
embodiment, or mixed and applied simultaneously by directing a
spray of metal alloy particles and a spray of flux material
particles simultaneously toward the surface. Alternatively, the
particles of metal alloy 16 may be applied to the surface 12 first
and then covered by the particles of flux material 18 in another
embodiment.
[0011] FIG. 2 illustrates the layer of powder 14 being exposed to a
pattern of energy 20 to melt selected regions of the layer of
powder 14 to form a pattern of the metal alloy 16' covered by slag
22 on the surface 12. Upon cooling, the slag 22 and excess powder
14 are removed to reveal the component 10 with a textured surface
12', as illustrated in FIG. 3.
[0012] The steps of FIGS. 1 and 2 may then be repeated, as
illustrated in FIG. 4 to add a further layer of metal alloy 16''.
Note that the pattern of energy 20' in FIG. 4 is somewhat different
than the pattern of energy 20 in FIG. 2, and as a result, the
second layer of deposited metal alloy 16'' has a region 24 that is
indexed from and somewhat cantilevered beyond the first layer of
deposited metal alloy 16'. The heat input of the energy 20 is
selected such that the region of melting does not extend to a full
depth of the layer of powder 14 in the cantilevered region 24. Such
indexing of the pattern of energy 20 between layers can be repeated
for additional layers as desired to create a desired final textured
surface 12'' having geometric features 26 including protruding
undercuts 28, as illustrated in FIG. 5. One skilled in the art will
appreciate that any surface geometric feature will provide a degree
of mechanical interlocking with a subsequently applied overcoat
layer (i.e. bond coat or thermal barrier coating), and that a
feature 26 with a protruding undercut 28 may be especially
beneficial in that regard.
[0013] FIG. 6 illustrates the component 10 after the further
deposit of a layer of material 31 over the surface 12'' having the
layer of geometric features 26. In this illustration, the surface
12'' is bond coat material and the layer of material 31 is a
ceramic thermal barrier coating material wherein the protruding
undercuts 28 function to mechanically anchor the ceramic material
31. One will appreciate that the bond coat material may be
deposited onto a superalloy substrate that is not illustrated in
this view.
[0014] FIG. 7 is a partial cross-sectional illustration of a gas
turbine component 34 wherein a layer of bond coat material 36 is
deposited over a textured surface 38 of a superalloy substrate 40
with an overlying layer of ceramic thermal barrier coating material
42 to form a thermal barrier coating system 44. The surface 38 is
textured by the addition of geometric features 46 that were
deposited by the process described above. Note that the texturing
of surface 38 is reflected in a more subtle but still effective
texturing of the surface 48 of the bond coat material 36.
Advantageously, when the superalloy substrate 40 is a cast product
and the superalloy material is one of the many difficult to weld
materials that are commonly used for gas turbine engine components,
the process described herein facilitates the joining of additional
superalloy material to form the geometric features 46 with a
greatly reduced risk of cracking and higher degree of geometric
precision that could otherwise be achieved by using a welding
additive process, as more fully described below.
[0015] The layer of powder 14 may be one to several millimeters in
thickness in some embodiments rather than the fraction of a
millimeter typical with known selective laser melting and sintering
processes. Typical powdered prior art flux materials have particle
sizes ranging from 0.5-2 mm, for example. However, the powdered
alloy material 16 may have a particle size range (mesh size range)
of from 0.02-0.04 mm or 0.02-0.08 mm or other sub-range therein.
This difference in mesh size range may work well in the embodiment
where the materials constitute separate layers; however, in the
embodiment where the particles are mixed together before being
applied to the surface 12, it may be advantageous for the powdered
alloy material 38 and the powdered flux material 40 to have
overlapping mesh size ranges, or to have the same mesh size range
in order to facilitate mixing and feeding of the powders and to
provide improved flux coverage during the melting process.
[0016] The flux material 18 and resultant layer of slag 22 provide
a number of functions that are beneficial during the melting
process. First, they function to shield both the region of molten
material and the solidified (but still hot) alloy material 16' from
the atmosphere as the material cools. The slag floats to the
surface to separate the molten or hot metal from the atmosphere,
and the flux may be formulated to produce a shielding gas in some
embodiments, thereby avoiding or minimizing the use of expensive
inert gas. Second, the slag 22 acts as a blanket that allows the
solidified alloy material 16' to cool slowly and evenly, thereby
reducing residual stresses that can contribute to cracking. Third,
the slag 22 helps to shape the pool of molten alloy 16'. Fourth,
the flux material 18 provides a cleansing effect for removing trace
impurities such as sulfur and phosphorous that contribute to
cracking. Such cleansing includes de-oxidation of the metal alloy
powder 16. Because the flux powder 18 is in intimate contact with
the alloy powder 16, it is especially effective in accomplishing
this function. Furthermore, the flux material 18 may provide energy
absorption and trapping functions to more effectively convert the
beam energy 20 into heat energy, thus facilitating a precise
control of heat input, such as within 1-2%, and a resultant tight
control of material temperature during the process. Finally, the
flux may be formulated to compensate for loss of volatized elements
during processing or to actively contribute elements to the deposit
that are not otherwise provided by the alloy powder itself.
[0017] The patterned energy beam 20 may be produced by a diode
laser 30 having a generally rectangular cross-sectional shape,
although other known types of energy beams may be used, such as
electron beam, plasma beam, one or more circular laser beams, a
scanned laser beam (scanned one, two or three dimensionally), an
integrated laser beam, etc. The rectangular shape may be
particularly advantageous for embodiments having a relatively large
area to be textured. The broad area beam produced by a diode laser
helps to reduce weld heat input, heat affected zone, dilution from
the substrate and residual stresses, all of which reduce the
tendency for the cracking effects normally associated with
superalloy repair. The laser energy may be patterned by any known
beam shaping optics, such as a cartridge filter 32 having
pre-determine openings. The cartridge 32 used to deposit the first
layer of material in FIG. 2 is conveniently changed to a cartridge
32' having a somewhat different pattern of openings for depositing
the second layer in FIG. 4. Optical conditions and hardware optics
used to generate a broad area laser exposure may include but are
not limited to: defocusing of the laser beam; use of diode lasers
that generate rectangular energy sources at focus; use of
integrating optics such as segmented mirrors to generate
rectangular energy sources at focus; scanning (rastering) of the
laser beam in one or more dimensions; and the use of focusing
optics of variable beam diameter (e.g. 0.5 mm at focus for fine
detailed work varied to 2.0 mm at focus for less detailed work).
The motion of the optics and/or substrate may be programmed as in a
selective laser melting or sintering process to build a custom
shape layer deposit. Advantages of this process over known laser
melting or sintering processes include: high deposition rates and
thick deposit in each processing layer; improved shielding that
extends over the hot deposited metal without the need for inert
gas; flux will enhance cleansing of the deposit of constituents
that otherwise may lead to cracking; flux will enhance laser beam
absorption and minimize reflection back to processing equipment;
slag formation will shape and support the deposit, preserve heat
and slow the cooling rate, thereby reducing residual stresses; flux
may compensate for elemental losses or add alloying elements, and
powder and flux pre-placement or feeding can efficiently be
conducted selectively because the thickness of the deposit greatly
reduces the time involved in total part building.
[0018] Flux materials which could be used include commercially
available fluxes such as those sold under the names Lincolnweld
P2007, Bohler Soudokay NiCrW-412, ESAB OK 10.16 or 10.90, Special
Metals NT100, Oerlikon OP76, Sandvik 50SW or SAS1. The flux
particles may be ground to a desired smaller mesh size range before
use. Any available structural alloy, superalloy or bond coat
material that is appropriate for thermal barrier coating systems
may be used.
[0019] While various embodiments of the present invention have been
shown and described herein, it will be obvious that such
embodiments are provided by way of example only. Numerous
variations, changes and substitutions may be made without departing
from the invention herein. Accordingly, it is intended that the
invention be limited only by the spirit and scope of the appended
claims.
* * * * *