U.S. patent application number 11/465288 was filed with the patent office on 2007-05-31 for mischmetal oxide tbc.
This patent application is currently assigned to GENERAL ELECTRIC CORPORATION. Invention is credited to Robert William BRUCE, Lyman A. JOHNSON, Mary Johnson.
Application Number | 20070122658 11/465288 |
Document ID | / |
Family ID | 34911785 |
Filed Date | 2007-05-31 |
United States Patent
Application |
20070122658 |
Kind Code |
A1 |
JOHNSON; Lyman A. ; et
al. |
May 31, 2007 |
MISCHMETAL OXIDE TBC
Abstract
The present invention is a turbine engine component comprising a
superalloy substrate, a bond coat overlying the substrate having a
thickness in the range of about 0.0005 inch to about 0.005 inch, a
thin alumina scale overlying the bond coat, and a thermal barrier
coating (TBC) overlying the thin alumina scale, the TBC having a
thickness in the range of about 0.0025 inch to about 0.010 inch,
and comprising at least mischmetal oxide.
Inventors: |
JOHNSON; Lyman A.;
(Cincinnati, OH) ; Johnson; Mary; (Cincinnati,
OH) ; BRUCE; Robert William; (Loveland, OH) |
Correspondence
Address: |
MCNEES WALLACE & NURICK LLC
100 PINE STREET
P.O. BOX 1166
HARRISBURG
PA
17108-1166
US
|
Assignee: |
GENERAL ELECTRIC
CORPORATION
Schenectady
NY
|
Family ID: |
34911785 |
Appl. No.: |
11/465288 |
Filed: |
August 17, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10792161 |
Mar 3, 2004 |
7175888 |
|
|
11465288 |
Aug 17, 2006 |
|
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|
Current U.S.
Class: |
428/699 ;
428/689; 428/701 |
Current CPC
Class: |
Y10T 428/12806 20150115;
C23C 14/08 20130101; Y10T 428/12549 20150115; C23C 28/3455
20130101; C23C 14/24 20130101; F05D 2300/134 20130101; F05D
2230/313 20130101; F05D 2300/15 20130101; F05D 2230/90 20130101;
C23C 28/321 20130101; F05D 2300/611 20130101; Y10T 428/12771
20150115; F01D 5/288 20130101; C23C 28/325 20130101 |
Class at
Publication: |
428/699 ;
428/689; 428/701 |
International
Class: |
B32B 19/00 20060101
B32B019/00; B32B 9/00 20060101 B32B009/00 |
Claims
1. A turbine engine component comprising: a superalloy substrate; a
bond coat on the superalloy substrate having a thickness in the
range of about 0.0005 inch to about 0.005 inch; an alumina scale
overlying the bond coat; and a thermal barrier coating overlying
the alumina scale having a thickness in the range of about 0.0025
inch to about 0.010 inch, comprising at least mischmetal oxide.
2. The turbine engine component of claim 1, wherein the thermal
barrier coating also comprises another oxide material selected from
the group consisting of yttria-stablized zirconia, zirconia,
yttria, hafnia, at least one other rare earth oxide, and
combinations thereof.
3. The turbine engine component of claim 2, wherein the oxide
material is yttria-stabilized zirconia and wherein the percentage
of yttria in the yttria-stabilized zirconia is in the range of 4%
to 8% yttria by weight.
4. The turbine engine component of claim 3, wherein the oxide
material is yttria-stabilized zirconia, wherein the percentage of
yttria is about 7% yttria by weight, and wherein the thermal
barrier coating comprises, based on 100% of weight, up to about 20%
ceria by weight, up to about 30% lanthanum oxide by weight, up to
about 7% praseodymium oxide by weight, up to about 20 percent
neodymium oxide by weight, and balance yttria-stabilized
zirconia.
5. The turbine engine component of claim 2, wherein the thermal
barrier coating does not contain any yttria-stabilized
zirconia.
6. The turbine engine component of claim 3, wherein the thermal
barrier coating comprises, based on 100% of weight, up to about 20%
ceria by weight, up to about 30% lanthanum oxide by weight, up to
about 7% praseodymium oxide by weight, up to about 20 percent
neodymium oxide by weight, and balance yttria-stabilized
zirconia.
7. The turbine engine component of claim 1, wherein the thermal
barrier coating comprises a bottom layer, a middle layer overlying
the bottom layer, and a top layer overlying the middle layer.
8. The turbine engine component of claim 7, wherein the bottom
layer is 7% YSZ, the middle layer is mischmetal oxide, and the top
layer is 7% YSZ.
Description
[0001] This application is a Divisional of U.S. patent application
Ser. No. 10/792,161, filed Mar. 3, 2004, the entire contents of
which are incorporated herein by reference in their entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to thermal barrier coatings
for components exposed to high temperatures, such as the hostile
thermal environment of a gas turbine engine. More particularly,
this invention is directed to thermal barrier coatings comprising
mischmetal oxide.
BACKGROUND OF THE INVENTION
[0003] 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.
While significant advances have been achieved with iron, nickel and
cobalt-base superalloys, the high-temperature capabilities of these
alloys alone are often inadequate for components located in certain
sections of a gas turbine engine, such as the turbine, combustor
and augmentor. A common solution is to thermally insulate such
components in order to minimize their service temperatures. For
this purpose, thermal barrier coatings (TBC) formed on the exposed
surfaces of high temperature components have found wide use.
[0004] To be effective, thermal barrier coatings must have low
thermal conductivity and adhere well to the component surface.
Various ceramic materials have been employed as the TBC,
particularly yttria (Y.sub.2O.sub.3) stabilized zirconia
(ZrO.sub.2), commonly known as YSZ. This material is widely
employed in the art because it can be readily deposited by plasma
spray and vapor deposition techniques. In addition, YSZ has good
erosion and impact resistance. An example of the latter is electron
beam physical vapor deposition (EB-PVD), which produces a thermal
barrier coating having a columnar grain structure that is able to
expand with its underlying substrate without causing damaging
stresses that lead to spallation, and therefore exhibits enhanced
strain tolerance. The component is supported in proximity to an
ingot(s) of the ceramic coating material (e.g., YSZ in a vacuum),
and an electron beam is projected onto the ingot(s) so as to melt
the surface of the ingot and produce a vapor of the coating
material that deposits onto the component. Such EB-PVD deposited
TBCs are generally deposited to a thickness in the range of about
0.005 inch to about 0.010 inch. Adhesion of the TBC to the
component is often further enhanced by the presence of a metallic
bond coat, such as a diffusion aluminide or an oxidation-resistant
alloy such as MCrAlX, where M is iron, cobalt and/or nickel, and
where X is yttria and/or another rare earth oxide
[0005] However, the application of a TBC by the EB-PVD process is
expensive and time consuming due to the thickness of the coating.
Also, maintenance of the EB-PVD apparatus is performed as a
function of operation of the apparatus, so fewer parts having a
thick coating can be processed in the period of time between
maintenance operations. In addition, the thickness of the coating
increases the load on the coated part in a high acceleration G-load
environment, particularly for TBC coated blades in a high pressure
turbine. One of the properties of the TBC that determines the
required thickness of the TBC is the thermal conductivity of the
TBC, since a coating with lower thermal conductivity does not have
to be as thick as a coating with higher thermal conductivity in
order to obtain the same thermal protection for the substrate.
Developments in the past have led to TBCs with lower thermal
conductivity simply by changing the manner in which the TBC is
applied using EB-PVD.
[0006] One such method is set forth in U.S. Pat. No. 6,620,465
('465) to Rigney et al. and assigned to the assignee of the present
invention. The '465 patent is directed to a method of improving the
thermal conductivity of the TBC resulting from an EB-PVD by moving
the article to be coated further from the ingot or source of
ceramic material.
[0007] In view of the above, there is considerable motivation to
further reduce the thickness of the TBC through the use of
materials that are lower in thermal conductivity. However,
limitations of the prior art are often the result of the relatively
narrow range of acceptable and readily available materials.
Accordingly, new materials for use in the EB-PVD process are
continuously being sought for depositing coatings, and particularly
ceramic coatings such as TBCs.
[0008] What is needed is a new type of material for use in the
EB-PVD process that has lower thermal conductivity, better erosion
resistance, and/or better impact resistance than presently
available TBC materials and is processible for use in TBC
materials. In particular, a material is needed that has a lower
thermal conductivity, and at least comparable erosion resistance,
and/or impact resistance as YSZ.
SUMMARY OF THE INVENTION
[0009] The present invention is a turbine engine component
comprising a superalloy substrate, a bond coat overlying the
substrate having a thickness in the range of about 0.0005 inch to
about 0.005 inch, a thin alumina scale overlying the bond coat, and
a thermal barrier coating (TBC) overlying the thin alumina scale,
the TBC having a thickness in the range of about 0.0025 inch to
about 0.010 inch, and comprising at least mischmetal oxide.
[0010] The present invention is a turbine engine component
comprising a superalloy substrate, a bond coat overlying the
substrate having a thickness in the range of about 0.0005 inch to
about 0.005 inch, a thin alumina scale overlying the bond coat, and
a TBC overlying the thin alumina scale, the TBC having a thickness
in the range of about 0.0025 inch to about 0.010 inch, and a
plurality of layers, wherein at least one of the layers comprises
at least mischmetal oxide.
[0011] As is known in the art, most rare earth oxides are found in
one type of ore, commonly known as mischmetal ore, which, once
mined, is cleaned and then smelted to a mixture of rare-earth
metals, such as cerium (Ce), lanthanum (La), praseodymium (Pr), and
neodymium (Nd), and impurities. This mixture of metals is commonly
known as "mischmetal." As used herein the term "mischmetal" refers
to clean mischmetal ore as known in the art. As used herein the
term "mischmetal oxide" means oxidized clean mischmetal ore as
known in the art that is obtained by oxidizing clean mischmetal.
The specific combination of rare earth metals in the mischmetal ore
varies depending on the mine and vein from which the ore was
extracted. Mischmetal generally has a composition, based on 100% of
weight, of about 30% to about 70% Ce by weight, about 19% to about
56% La by weight, about 2% to about 7% Pr by weight and from about
0% to about 20% Nd by weight, and impurities. Mischmetal is often
refined to its individual rare-earth metals constituents. The
present invention uses mischmetal, which has not been separated and
refined into its individual metal constituents, as a source of
oxides for the deposition of TBC by EB-PVD, such that the TBC
comprises the rare earth oxides present in mischmetal.
[0012] The present invention is also a method for the application
of a mischmetal oxide TBC to a superalloy turbine engine component
including the steps of providing an electron beam physical vapor
deposition apparatus, providing a turbine engine component
comprising a surface to be coated, providing a first mischmetal
ingot, and providing a second ingot comprising another oxide
material selected from the group consisting of yttria-stablized
zirconia, zirconia, yttria, hafnia, at least one other rare earth
oxide, and combinations thereof. The component and the ingots are
placed in to the apparatus as known in the art. Melt pools are
formed on the ingots by the electron beam as known in the art. The
mischmetal is then oxidized by bleeding a small controlled amount
of oxygen into the EB-PVD apparatus. Mischmetal oxide vapors and
other oxide vapors are then dispersed as known in the art. The
mischmetal oxide vapors and the yttria-stabilized vapors are then
deposited onto the surface to be coated. The deposition process
forms a TBC having a thickness in the range of about 0.0025 inch to
about 0.010 inch. Thicker TBCs provide enhanced thermal
protection.
[0013] As is known in the art, thermal conductivity is calculated
by the following equation: k=.alpha..rho.C.sub.p
[0014] where k is thermal conductivity (W/m/K), .alpha. is thermal
diffusivity (cm.sup.2/s), .rho. is density (g/cm.sup.3), and
C.sub.p is specific heat (Ws/g/K). The higher the thermal
conductivity of a TBC material, the thicker the TBC has to be, as
the purpose of the TBC is to resist heat transfer of heat from the
hot gases of combusting into the underlying superalloy substrate.
Preferably, the thermal conductivity of the TBC should be lower so
that a thinner TBC layer may be used. The TBC formed that includes
the mischmetal oxide has a lower thermal conductivity than does
YSZ.
[0015] The present invention is also a method for the application
of oxide TBC that includes a mischmetal oxide to a superalloy
turbine engine component including the steps of providing an
electron beam physical vapor deposition apparatus, providing a
turbine engine component comprising a surface to be coated,
providing a first ingot that includes mischmetal oxide, and
providing an second ingot comprising another oxide material
selected from the group consisting of yttria-stablized zirconia,
zirconia, yttria, hafnia, at least one other rare earth oxide, and
combinations thereof. The component and the ingots are placed in
the EB-PVD apparatus as known in the art. Melt pools are formed on
the ingots as known in the art. Mischmetal oxide vapors and other
oxide vapors are then dispersed as known in the art. The mischmetal
oxide vapors and other oxide vapors are then deposited onto the
surface to be coated. The deposition process forms a TBC having a
thickness in the range of about 0.0025 inch to about 0.010
inch.
[0016] The present invention is also a method for the application
of an oxide TBC that includes a mischmetal oxide to a superalloy
turbine engine component including the steps of providing an
electron beam physical vapor deposition apparatus, providing a
turbine engine component comprising a surface to be coated, and
providing an ingot that includes a mischmetal oxide. The component
and the ingot are placed in the apparatus as known in the art. Melt
pools are formed on the ingot as known in the art. Mischmetal oxide
vapors are then dispersed as known in the art. The mischmetal oxide
vapors are then deposited onto the surface to be coated. The
deposition process forms a TBC having a thickness in the range of
about 0.0025 inch to about 0.010 inch.
[0017] The present invention is also a method for the application
of a TBC that includes a mischmetal oxide to a superalloy turbine
engine component including the steps of providing an electron beam
physical vapor deposition apparatus, providing a turbine engine
component comprising a surface to be coated, and providing an ingot
that includes mischmetal oxide and another oxide material selected
from the group consisting of yttria-stablized zirconia, zirconia,
yttria, hafnia, at least one other rare earth oxide, and
combinations thereof. The component and the ingot are placed in the
EB-PVD apparatus as known in the art. Melt pools are formed on the
ingot by the electron beam as known in the art. Mischmetal oxide
vapors and other oxide vapors are then dispersed as known in the
art. The mischmetal oxide vapors and other oxide vapors are then
deposited onto the surface to be coated. The deposition process
forms a TBC having a thickness in the range of about 0.0025 inch to
about 0.010 inch.
[0018] An advantage of the present invention is that the use of the
rare earth oxides in the mischmetal oxide, which have lower thermal
conductivity than yttria-stabilized zirconia, reduces the
conductivity of the TBC, allowing a thinner TBC layer to be applied
to the turbine engine component.
[0019] Another advantage of the present invention is erosion
resistance of the TBC layer is improved through the use of the rare
earth oxides in the mischmetal, which are believed to have at least
comparable erosion resistance compared to yttria-stabilized
zirconia.
[0020] Another advantage of the present invention is that the
impact resistance of the TBC layer is improved through the use of
the rare earth oxides in the mischmetal, which are believed to have
at least comparable impact resistance compared to yttria-stabilized
zirconia.
[0021] Another advantage of the present invention is that using a
mischmetal or a mischmetal oxide ingot separate along with another
oxide ingot permits intermittent co-evaporation, which allows the
deposition of a TBC comprising a plurality of layers with different
properties.
[0022] Other features and advantages of the present invention will
be apparent from the following more detailed description of the
preferred embodiment, taken in conjunction with the accompanying
drawings which illustrate, by way of example, the principles of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a flow chart illustrating a method of applying a
mischmetal oxide TBC to a superalloy turbine engine component of
the present invention.
[0024] FIG. 2 a flow chart illustrating an alternative method of
applying a mischmetal oxide TBC to a superalloy turbine engine
component of the present invention.
[0025] FIG. 3 is a flow chart illustrating another alternative
method of applying a mischmetal oxide TBC to a superalloy turbine
engine component of the present invention.
[0026] FIG. 4 is a flow chart illustrating another alternative
method of applying a mischmetal oxide TBC to a superalloy turbine
engine component of the present invention.
[0027] FIG. 5 is a flow chart illustrating another alternative
method of applying a TBC comprising mischmetal oxide to a
superalloy turbine engine component.
[0028] FIG. 6 is a perspective view of a typical turbine blade.
[0029] FIG. 7 is a cross-sectional view of a the turbine blade of
FIG. 6 through a cooling channel with the TBC layer comprising
mischmetal oxide of the present invention applied to the outer
surface.
[0030] FIG. 8 is a cross-sectional view of a the turbine blade of
FIG. 6 through a cooling channel with the TBC layer comprising a
plurality of layers, at least one layer of which comprises
mischmetal oxide of the present invention, applied to the outer
surface.
DETAILED DESCRIPTION OF THE INVENTION
[0031] Referring now to FIG. 1 there is shown the method of the
present invention for applying a mischmetal oxide TBC to a
superalloy turbine engine component of the present invention. The
initial step 100 of the process comprises providing an EB-PVD
apparatus, a superalloy turbine engine component comprising a
surface to be coated, a first mischmetal ingot, and a second oxide
ingot comprising another oxide material selected from the group
consisting of yttria-stablized zirconia, zirconia, yttria, hafnia,
at least one other rare earth oxide, and combinations thereof. The
mischmetal ingot preferably comprises, based on 100% of weight,
about 30% to about 70% Ce by weight, about 19% to about 56% La by
weight, about 2% to about 7% Pr by weight and from about 0% to
about 20% Nd by weight. The preferred mischmetal ingot may also
contain impurities, such as iron and/or silicon. In a more
preferred embodiment, the mischmetal ingot comprises, based on 100%
of weight, about 30% to about 70% Ce by weight, about 19% to about
40% La by weight, about 2% to about 7% Pr by weight, about 0% to
about 20% Nd by weight, and balance impurities. Ingots for EB-PVD
processes are well known in the art. Such superalloy components may
comprise nickel-based, iron-based, or cobalt-based superalloys as
known in the art. The EB-PVD apparatus may be any such apparatus as
known in the art. For example, the EB-PVD apparatus disclosed in
U.S. Pat. No. 6,589,351 B1 can be used for the present invention.
U.S. Pat. No. 6,589,351 B1, which is assigned to the assignee of
the present invention, is incorporated by reference herein. The
turbine engine component may be partially masked with an
appropriate maskant to protect preselected surfaces from being
coated as known in the art.
[0032] The next step 110 of the process is placing the component
and the ingots into the apparatus as known in the art and drawing
in oxygen as required to oxidize the mischmetal. The next step 120
of the process is forming melt pools on the ingots, oxidizing the
mischmetal, and dispersing mischmetal oxide vapors and other oxide
vapors. In a preferred embodiment, the molar percentage of the
mischmetal oxide vapor includes up to about 14 percent of the total
vapor. As oxygen is required to oxidize the mischmetal in the
EB-PVD apparatus, if excess oxygen is provided to the process, that
is more oxygen than is required to produce about 14 molar percent
of mischmetal oxide, the EB-PVD process becomes difficult to
control. The next step 130 of the process is co-depositing the
mischmetal oxide vapors and other oxide vapors, preferably
yttria-stabilized zirconia vapors, onto the surface to be coated,
said deposition forming a thermal barrier coating having a
thickness in the range of about 0.0025 inch to about 0.010 inch. In
an optional embodiment, the co-deposition may be intermittent,
where the electron beam is only directed at one ingot at a time.
With intermittent co-deposition, the TBC may comprise a plurality
of layers, wherein at least one layer comprises mischmetal oxide
and at least one layer comprises the other oxide. In an alternate
embodiment, the yttria-stabilized zirconia is in the range of about
4% yttria by weight to about 8% yttria by weight (4%-8% YSZ). In a
more preferred alternate embodiment, the yttria-stabilized zirconia
is about 7% yttria by weight (7% YSZ). 7% YSZ is well known in the
art and is commonly used for TBC layers. The final step 140 of the
process is removing the coated component from the apparatus.
[0033] Referring now to FIG. 2 there is shown an alternate method
of the present invention for applying a mischmetal oxide TBC to a
superalloy turbine engine component. The initial step 200 of the
process comprises providing an EB-PVD apparatus, a superalloy
turbine engine component comprising a surface to be coated, a first
mischmetal oxide ingot, and an second ingot comprising another
oxide material selected from the group consisting of
yttria-stablized zirconia, zirconia, yttria, Hafnia, at least one
other rare earth oxide, and combinations thereof. The turbine
engine component may be partially masked with an appropriate
maskant as known in the art. The mischmetal which is oxidized to
form the mischmetal oxide ingot preferably comprises, based on 100%
of weight, about 30% to about 70% Ce by weight, about 19% to about
56% La by weight, about 2% to about 7% Pr by weight and from about
0% to about 20% Nd by weight. The preferred mischmetal, which is
oxidized to produce the mischmetal oxide ingot, may also contain
impurities. In a more preferred embodiment, the mischmetal, which
is oxidized to produce the mischmetal oxide ingot, comprises, based
on 100% of weight, about 30% to about 70% Ce by weight, about 19%
to about 40% La by weight, about 2% to about 7% Pr by weight, about
0% to about 20% Nd by weight, and balance impurities.
[0034] The next step 210 of the process is placing the component
and the ingots into the apparatus as known in the art and drawing a
vacuum within the apparatus. The next step 220 of the process is
forming melt pools on the ingots and dispersing mischmetal oxide
vapors and other oxide vapors. The next step 230 of the process is
co-depositing the mischmetal oxide vapors and the other oxide
vapors onto the surface to be coated, the co-deposition forming a
thermal barrier coating having a thickness in the range of about
0.0025 inch to about 0.010 inch. In an optional embodiment, the
co-deposition may be intermittent, where the electron beam is only
directed at one ingot at a time. With intermittent co-deposition,
the TBC may comprise a plurality of layers, wherein at least one
layer comprises mischmetal oxide and at least one layer comprises
the other oxide. In a preferred embodiment, the other oxide is
4%-8% YSZ. In a more preferred embodiment, the other oxide is 7%
YSZ, with the TBC comprising, based on 100% of weight, up to about
20% ceria by weight, up to about 30% lanthanum oxide by weight, up
to about 7% praseodymium oxide by weight, up to about 20 percent
neodymium oxide by weight, and balance YSZ. The TBC may also
contain impurities. A weight percentage of ceria in the TBC above
about 20 percent reduces the erosion resistance of the TBC. The
final step 240 of the process is removing the coated component from
the apparatus.
[0035] Referring now to FIG. 3 there is shown another alternate
method of the present invention for applying of applying a
mischmetal oxide TBC to a superalloy turbine engine component. The
initial step 300 of the process comprises providing an EB-PVD
apparatus, a superalloy turbine engine component comprising a
surface to be coated, and a mischmetal oxide ingot. The turbine
engine component may be partially masked with an appropriate
maskant to protect preselected surfaces from being coated as known
in the art. The mischmetal which is oxidized to form the mischmetal
oxide ingot preferably comprises, based on 100% of weight, about
30% to about 70% Ce by weight, about 19% to about 56% La by weight,
about 2% to about 7% Pr by weight and from about 0% to about 20% Nd
by weight. The preferred mischmetal, which is oxidized to produce
the mischmetal oxide ingot, may also contain impurities. In a more
preferred embodiment, the mischmetal, which is oxidized to produce
the mischmetal oxide ingot, comprises, based on 100% of weight,
about 30% to about 70% Ce by weight, about 19% to about 40% La by
weight, about 2% to about 7% Pr by weight, about 0% to about 20% Nd
by weight, and balance impurities.
[0036] The next step 310 of the process is placing the component
and the ingot into the apparatus and drawing a vacuum within the
apparatus as known in the art. The next step 320 of the process is
forming a melt pool on the ingot and dispersing mischmetal oxide
vapors. The next step 330 of the process is depositing the
mischmetal oxide vapors onto the surface to be coated, said
deposition forming a thermal barrier coating having a thickness in
the range of about 0.0025 inch to about 0.010 inch. The mischmetal
which is oxidized to form the mischmetal oxide ingot preferably
comprises, based on 100% of weight, about 30% to about 70% Ce by
weight, about 19% to about 56% La by weight, about 2% to about 7%
Pr by weight and from about 0% to about 20% Nd by weight. The
preferred mischmetal, which is oxidized to produce the mischmetal
oxide ingot, may also contain impurities. In a more preferred
embodiment, the mischmetal, which is oxidized to produce the
mischmetal oxide ingot, comprises, based on 100% of weight, about
30% to about 70% Ce by weight, about 19% to about 40% La by weight,
about 2% to about 7% Pr by weight, about 0% to about 20% Nd by
weight, and balance impurities. The final step 340 of the process
is removing the coated component from the apparatus.
[0037] Referring now to FIG. 4 there is shown yet another alternate
method of the present invention for applying of applying a
mischmetal oxide TBC to a superalloy turbine engine component. The
optional initial step 400 of the process is the provision of an
EB-PVD apparatus, a superalloy turbine engine component comprising
a surface to be coated, and an oxide ingot comprising a mischmetal
oxide insert and another oxide material selected from the group
consisting of yttria-stablized zirconia, zirconia, yttria, hafnia,
at least one other rare earth oxide, and combinations thereof. The
other optional initial step 410 of the process comprises providing
an EB-PVD apparatus, a superalloy turbine engine component
comprising a surface to be coated, and a mischmetal oxide ingot
comprising another oxide insert comprising another oxide material
selected from the group consisting of yttria-stablized zirconia,
zirconia, yttria, Hafnia, at least one other rare earth oxide, and
combinations thereof. The turbine engine component may be partially
masked with an appropriate maskant to protect preselected surfaces
from being coated as known in the art. The oxide ingot preferably
comprises, based on 100% of weight, up to about 20% ceria by
weight, up to about 30% lanthanum oxide by weight, up to about 7%
praseodymium oxide by weight, up to about 20 percent neodymium
oxide by weight, and balance other oxides. The oxide ingot may
contain impurities.
[0038] The next step 420 of the process is placing the component
and the ingot into the apparatus as known in the art. The next step
430 of the process is forming a melt pool on the ingot including
both the mischmetal oxide and other oxide, and dispersing
mischmetal oxide vapors and other oxide vapors. The next step 440
of the process is co-depositing the mischmetal oxide vapors and the
other oxide vapors onto the surface to be coated, said
co-deposition forming a thermal barrier coating having a thickness
in the range of about 0.0025 inch to about 0.010 inch. In a
preferred embodiment, the other oxide is 4%-8% YSZ. In a more
preferred embodiment, the yttria-stabilized zirconia is 7% YSZ,
with the TBC comprising, based on 100% of weight, up to about 20%
ceria by weight, up to about 30% lanthanum oxide by weight, up to
about 7% praseodymium oxide by weight, up to about 20 percent
neodymium oxide by weight, and balance YSZ. The TBC may also
contain impurities. The final step 450 of the process is removing
the coated component from the apparatus.
[0039] Referring now to FIG. 5 there is shown yet another alternate
method of the present invention for applying of applying a TBC
comprising mischmetal oxide to a superalloy turbine engine
component. The initial step 500 of the process comprises providing
an EB-PVD apparatus, a superalloy turbine engine component
comprising a surface to be coated, and an oxide ingot comprising a
mixture of mischmetal oxide powder and another oxide powder
selected from the group consisting of yttria-stablized zirconia,
zirconia, yttria, Hafnia, at least one other rare earth oxide, and
combinations thereof. The oxide ingot comprising mischmetal oxide
powder and another oxide powder may have been manufactured by
processing mischmetal ore to form mischmetal oxide powder as known
in the art followed by forming the mischmetal oxide powder and the
other oxide, in the form of a powder, into an oxide ingot. The
oxide ingot preferably comprises, based on 100% of weight, up to
about 20% ceria by weight, up to about 30% lanthanum oxide by
weight, up to about 7% praseodymium oxide by weight, up to about 20
percent neodymium oxide by weight, and balance other oxides. The
oxide ingot may contain impurities. The turbine engine component
may be partially masked with an appropriate maskant to protect
preselected surfaces from being coated as known in the art.
[0040] The next step 510 of the process is placing the component
and the ingot into the apparatus and drawing a vacuum within the
apparatus as known in the art. The next step 520 of the process is
forming a melt pool on the ingot and dispersing oxide vapors. The
next step 530 of the process is co-depositing the mischmetal oxide
vapors and the other oxide vapors onto the surface to be coated,
said co-deposition forming a thermal barrier coating having a
thickness in the range of about 0.0025 inch to about 0.010 inch. In
a preferred embodiment, the other oxide is 4%-8% YSZ. In a more
preferred embodiment, the other oxide is 7% YSZ, with the TBC
comprising, based on 100% of weight, up to about 20% ceria by
weight, up to about 30% lanthanum oxide by weight, up to about 7%
praseodymium oxide by weight, up to about 20 percent neodymium
oxide by weight, and balance YSZ. The TBC may also contain
impurities. The final step 540 of the process is removing the
coated component from the apparatus.
[0041] FIG. 6 depicts a component article of a turbine engine such
as a turbine blade or turbine vane, and in this illustration a
turbine blade 20 coated with a bond coat layer, an alumina scale
layer and a mischmetal oxide TBC layer of the present invention.
The turbine blade 20 is formed of any operable substrate material,
and is preferably an iron, nickel or cobalt-base superalloy (or
combinations thereof). The turbine blade 20 includes an airfoil 22
against which the flow of hot exhaust gas is directed. The turbine
blade 20 is mounted to a turbine disk (not shown) by a dovetail 24
that extends downwardly from the airfoil 22 and engages a slot on
the turbine disk. A platform 26 extends longitudinally outward from
the area where the airfoil 22 is joined to the dovetail. A number
of internal cooling passages extend through the interior of the
airfoil 22, ending in openings 28 in the surface of the airfoil 22.
A flow of cooling air is directed through the internal cooling
passages, to reduce the temperature of the airfoil 22. The airfoil
may be described as having a root end 30 adjacent to the dovetail
24, and an oppositely disposed tip end 32 remote from the dovetail
24.
[0042] FIG. 7 is a longitudinal section through the airfoil 22,
showing one of the internal cooling passages 34 extending through
an interior of the airfoil 22. The internal cooling passage 34 has
an internal surface 36, and there is also an external airfoil
surface 38 of the metallic portion of the airfoil 22.
[0043] An optional diffusion aluminide protective layer 40 is
formed on the airfoil surfaces 36, 38. The diffusion aluminide is
formed by depositing and diffusing aluminum onto and into the
passageways and external to the airfoil where it deposits onto and
into the substrate material 42 of the airfoil 22. The aluminum is
interdiffused with the material of the substrate 42 to form the
aluminum-enriched protective layer 40 lying above and below the
airfoil surfaces 36, 38, forming an internal diffusion aluminide
layer 44 and a topical diffusion aluminide layer 46. The diffusion
aluminide protective layer 40 has a composition with the aluminum
concentration highest near and above the airfoil surfaces 36, 38,
and decreasing aluminum concentration with increasing distance into
the substrate 42 from the airfoil surfaces 36, 38. The diffusion
aluminide protective layer 40 is typically from about 0.0005 inch
to about 0.005 inch thick and also functions as a bond coat. When
exposed to a high-temperature oxidizing environment, the topical
diffusion aluminide layer 46 at the external airfoil surface 38
oxidizes to form a highly adherent alumina protective scale 48,
inhibiting and slowing further oxidation damage. The
aluminum-enriched layer serves as a reservoir to heal any loss of
aluminum during normal operation.
[0044] Such diffusion aluminide protective layers 40, which
function as bond coats, and alumina scales 48 are generally known
in the art, although specific compositions may not be known. A TBC
50 comprising mischmetal oxide is deposited on top of and bonded to
the alumina scale 48 to provide additional thermal protection for
the airfoil 22. The TBC 50, which comprises mischmetal oxide, is
about 0.0025 to about 0.010 inch thick. The TBC may also comprise
another oxide material selected from the group consisting of
yttria-stablized zirconia, zirconia, yttria, Hafnia, at least one
other rare earth oxide, and combinations thereof. In a preferred
embodiment, the TBC 50 comprises, based on 100% of weight, up to
about 20% ceria by weight, up to about 30% lanthanum oxide by
weight, up to about 7% praseodymium oxide by weight, up to about 20
percent neodymium oxide by weight, and balance other oxides. The
TBC 50 may also contain impurities. In an alternative preferred
embodiment, the oxide material is 4%-8% YSZ. In a more preferred
embodiment, the oxide material is 7% YSZ and the TBC 50 comprises,
based on 100% of weight, up to about 20% ceria by weight, up to
about 30% lanthanum oxide by weight, up to about 7% praseodymium
oxide by weight, up to about 20 percent neodymium oxide by weight,
and balance other oxides. The TBC 50 may also contain
impurities.
[0045] FIG. 8 is an alternative embodiment showing a longitudinal
section through the airfoil 22, showing one of the internal cooling
passages 34 extending through an interior of the airfoil 22. The
internal cooling passage 34 has an internal surface 36, and there
is also an external airfoil surface 38 of the metallic portion of
the airfoil 22.
[0046] An optional diffusion aluminide protective layer 40 is
formed on the airfoil surfaces 36, 38. The diffusion aluminide is
formed by depositing and diffusing aluminum onto and into the
passageways and external to the airfoil where it deposits onto and
into the substrate material 42 of the airfoil 22. The aluminum is
interdiffused with the material of the substrate 42 to form the
aluminum-enriched protective layer 40 lying above and below the
airfoil surfaces 36, 38, forming an internal diffusion aluminide
layer 44 and a topical diffusion aluminide layer 46. The diffusion
aluminide protective layer 40 has a composition with the aluminum
concentration highest near and above the airfoil surfaces 36, 38,
and decreasing aluminum concentration with increasing distance into
the substrate 42 from the airfoil surfaces 36, 38. The diffusion
aluminide protective layer 40 is typically from about 0.0005 inch
to about 0.005 inch thick and also functions as a bond coat. When
exposed to a high-temperature oxidizing environment, the topical
diffusion aluminide layer 46 at the external airfoil surface 38
oxidizes to form a highly adherent alumina protective scale 48,
inhibiting and slowing further oxidation damage. The
aluminum-enriched layer serves as a reservoir to heal any loss of
aluminum during normal operation.
[0047] Such diffusion aluminide protective layers 40 and alumina
scales 48 are generally known in the art, although specific
compositions may not be known. A TBC 50 comprises a plurality of
TBC layers 52, 54, 56 overlying one another. A bottom layer 52,
which serves to bond the TBC 50 to the alumina scale 48, comprises
an oxide material selected from the group consisting of
yttria-stablized zirconia, zirconia, yttria, Hafnia, at least one
other rare earth oxide, and combinations thereof. The bottom layer
is preferably 4%-8% YSZ, and more preferably 7% YSZ. A middle layer
54, which simply functions as a portion of the TBC 50, overlies the
bottom layer 52 and comprises mischmetal oxide. A top layer 56,
which serves as an erosion layer, overlies the middle layer 54 and
comprises an oxide material selected from the group consisting of
yttria-stablized zirconia, zirconia, yttria, hafnia, at least one
other rare earth oxide, and combinations thereof. The bottom layer
is preferably 4%-8% YSZ, and more preferably 7% YSZ. Although three
TBC layers 52, 54, 56 are shown in FIG. 8, the there may be two TBC
layers or more than three TBC layers. The TBC 50 is deposited on
top of and bonded to the alumina scale 48 to provide additional
thermal protection for the airfoil 22. The TBC 50 is about 0.0025
to about 0.010 inch thick. In a preferred embodiment, the TBC 50
comprises, based on 100% of weight, up to about 20% ceria by
weight, up to about 30% lanthanum oxide by weight, up to about 7%
praseodymium oxide by weight, up to about 20 percent neodymium
oxide by weight, and balance other oxides. The TBC 50 may also
contain impurities
[0048] While the invention has been described with reference to a
preferred embodiment, it will be understood by those skilled in the
art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the invention. In addition, many modifications may be made to
adapt a particular situation or material to the teachings of the
invention without departing from the essential scope thereof.
Therefore, it is intended that the invention not be limited to the
particular embodiment disclosed as the best mode contemplated for
carrying out this invention, but that the invention will include
all embodiments falling within the scope of the appended
claims.
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