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EP 1 548 156 B1 |
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EUROPEAN PATENT SPECIFICATION |
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Mention of the grant of the patent: |
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23.03.2011 Bulletin 2011/12 |
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Date of filing: 09.12.2004 |
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International Patent Classification (IPC):
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Process for removing adherent oxide particles from an aluminized surface
Verfahren zur Entfernung von an einer aluminierten Oberfläche anhaftenden Oxidpartikeln
Procédé pour enlever des particules d'oxyde adhérantes d'une surface aluminée
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Designated Contracting States: |
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DE FR GB |
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Priority: |
16.12.2003 US 707465
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Date of publication of application: |
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29.06.2005 Bulletin 2005/26 |
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Proprietor: GENERAL ELECTRIC COMPANY |
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Schenectady, NY 12345 (US) |
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Inventors: |
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- Rosenzweig, Mark Alan
Liberty Township
Ohio 45011 (US)
- Pfaendtner, Jeffrey Allan
Blue Ash
Ohio 45242 (US)
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Representative: Bedford, Grant Richard et al |
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Global Patent Operation - Europe
GE International Inc.
15 John Adam Street London WC2N 6LU London WC2N 6LU (GB) |
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References cited: :
EP-A1- 1 010 776 US-A- 5 366 765
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EP-A1- 1 076 107 US-B1- 6 544 346
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Note: Within nine months from the publication of the mention of the grant of the European
patent, any person may give notice to the European Patent Office of opposition to
the European patent
granted. Notice of opposition shall be filed in a written reasoned statement. It shall
not be deemed to
have been filed until the opposition fee has been paid. (Art. 99(1) European Patent
Convention).
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[0001] The present invention generally relates to aluminizing processes. More particularly,
this invention relates to a process for removing oxide particles adhered to a surface
following aluminizing.
[0002] The operating environment within a gas turbine engine is both thermally and chemically
hostile, particularly within the turbine, combustor and augmentor sections. A common
practice is to protect the surfaces of gas turbine engine components with an environmental
coating that is resistant to oxidation and hot corrosion, and optionally a thermal
barrier coating (TBC) that provides thermal-insulating protection for the component
exterior. Environmental coatings that have found wide use include diffusion aluminide
coatings and overlay coatings such as MCrAlY. During high temperature exposure in
air, these coatings form a protective aluminum oxide (alumina) scale that inhibits
oxidation of the coating and the underlying substrate. Diffusion aluminide coatings
are particularly useful for providing environmental protection to components equipped
with internal cooling passages, such as high pressure turbine blades, because aluminide
coatings are able to provide environmental protection without significantly reducing
the cross-sections of the cooling passages.
[0003] An aluminizing process capable of selectively coating the internal cooling passages
of a turbine blade involves injecting a slurry into the passages. As with other types
of processes employed to form aluminide coatings, the slurry aluminizing process relies
on aluminiding vapors that react at exposed surfaces to form a diffusion aluminide
coating. More particularly, the slurry process makes us of a coating powder comprising
a metallic aluminum source (such as aluminum or an aluminum alloy, e.g., CrAl, CoAl,
FeAl, and TiAl), a carrier or activator (such as an alkali metal halide), and an inert
oxide dispersant (such as alumina (Al
2O
3) or zirconia (ZrO
2)). These solid particulate components are mixed with an organic or inorganic liquid,
whose role is a rheological additive to facilitate the injection of the coating powder
into the often complex system of internal cooling passages present in a turbine blade.
An example of a suitable inorganic binder is hectorite clay in water, while examples
of particularly suitable organic binders include acrylics such as polymethylmethacrylate
(PMMA), butyl methacrylate resin, ethyl methacrylate resin, methyl methacrylate resin
and methacrylate co-polymer resin. Other organic binders that may be used include
methyl cellulose, acrylic lacquer, alkyd resins such as phenolic-modified alkyd and
phenolic-modified soybean alkyd, shellac, rosin, rosin derivatives, ester gum, vinyls,
styrenics, polyesters, epoxides, polyurethanes, cellulose derivatives, and mixtures
thereof. Once the mixture is injected, the liquid is removed by drying, after which
the component containing the dried coating media is heated in an inert or reducing
atmosphere to a temperature of 1700°F (about 930°C) or more. At the elevated temperature,
the activator vaporizes and reacts with the aluminum source to form a volatile aluminum
halide, which then reacts at the surfaces of the passages to form the aluminide coating.
[0004] Following aluminiding, remnants of the solid components of the slurry must be removed
so as not to inhibit the flow of cooling air through the passages. In practice, there
is a tendency for particles of the aluminum source to oxidize and sinter to the aluminized
surfaces as a result of the high temperatures sustained during the aluminiding process.
In that these adherent particles are sintered to the aluminized surfaces, they have
proven to be very difficult to remove. Mechanical cleaning techniques such as high-pressure
water jets and flushing have been used with limited success. Other approaches that
employ caustic compounds at high temperatures and pressures (e.g., performed in an
autoclave) to strip TBC from exterior surfaces or remove dirt and contamination from
internal passages of gas turbine engine components are undesirable in view of the
cost of autoclaving operations. Therefore, in order to maximize air flow through aluminized
cooling passages of an air-cooled component, a need exists for a reliable method of
removing adherent sintered oxide particles.
[0005] The present invention provides a process for removing particles that become adherently
sintered to an aluminized surface during an aluminiding process. An important example
is the internal cooling passages of gas turbine engine components, such as components
within the turbine, combustor or augmentor sections of a gas turbine engine. The method
is particularly suited for the removal of oxidized particles that form as a result
of oxidation of the aluminum source powder used in slurry aluminiding processes, wherein
the oxidized powder particles become attached by sintering to the aluminized surface.
The method also serves to remove other particles that may be sintered to the aluminized
surface following the aluminiding process, such as oxide particles that were mixed
with the aluminum source powder as an inert dispersant. The processing steps of this
invention include contacting the aluminized surface with an aqueous caustic hydroxide
solution until these adherent particles are removed therefrom.
[0006] According to the invention, an aqueous potassium hydroxide solution at moderate elevated
temperatures and atmospheric pressures (i.e., without autoclaving) has been shown
to facilitate removal of adherent residual coating materials, particularly if accompanied
by agitation with ultrasonic energy. In this manner, adherent oxidized and oxide particles
can be completely removed from the aluminized surfaces of an internal cavity, such
as the internal cooling passages of a gas turbine engine component so that cooling
air flow through the passages is not reduced. Finally, aqueous caustic hydroxide solutions
of this invention are compatible with aluminide coatings, so as not to attack such
coatings during removal of the adherent oxide particles.
[0007] Other objects and advantages of this invention will be better appreciated from the
following detailed description.
[0008] The present invention is directed to the removal of particles that form by oxidation
of metal particles contacting a surface undergoing aluminizing, such that the particles
adhere to the aluminized surface through a sintering mechanism. As such, the particles
of concern to this invention are distinguishable from dirt and contaminants that collect
within internal cooling passages of air-cooled gas turbine engine components during
engine operation. Furthermore, the particles are distinguishable from ceramic coatings
formed of metal oxides that are deposited as thermal barrier coatings (TBC) on gas
turbine engine components. While the advantages of this invention will be described
with reference to turbine blades, the teachings of this invention are generally applicable
to any component having internal surfaces that benefit from protection by aluminide
coating.
[0009] Notable examples of gas turbine engine components that benefit from the present invention
include air-cooled high and low pressure turbine nozzles and blades, shrouds, combustor
liners and augmentor. Of particular interest are air-cooled components whose interior
surfaces are protected by a diffusion aluminide coating deposited by a non-line-of-sight
technique, such as a slurry aluminiding process in which metallic particles of an
aluminum source can directly contact the surface being aluminized. At the elevated
temperatures necessary to transfer aluminum from the aluminum source to the internal
surface being aluminized, particles of the aluminum source may oxidize and subsequently
become adhered by sintering to the internal aluminized surface. For example, a slurry
aluminiding process that uses particles of a Cr-44Al (wt.%) alloy as the aluminum
source can result in the oxidation of at least the outer surfaces of these particles,
resulting in the formation of oxidized particles that adhere to the aluminized surface.
An additional source of particles that may sinter to an aluminized surface as a result
of an aluminiding process is the oxide particles that are conventionally mixed with
aluminum source particles to act as an inert dispersant during the aluminiding process.
[0010] The process of this invention entails treating the aluminized surface with an aqueous
caustic hydroxide solution, a suitable example of which contains at least 100 grams/liter
of potassium hydroxide (KOH). A more preferred solution contains about 175 to about
225 grams/liter of KOH, with the balance de-ionized water. It is believed that other
caustic hydroxides such as sodium hydroxide (NaOH) can be used in combination with
or in place of potassium hydroxide in the solution. The internal aluminized surfaces
are contacted with the solution at a moderate elevated temperature, such as about
150 to about 190°F (about 66 to about 88°C) and preferably about 160 to about 170°F
(about 71 to about 77°C). This operation is carried out to ensure that all internal
aluminized surfaces are contacted by the solution, such as by immersing the entire
component in a bath of the solution, and preferably flushing the internal cavities
with the solution while the component is immersed to ensure complete filling with
the solution. Contact with the solution is preferable maintained for a duration of
at least two hours, such as about two to about eight hours and more preferably about
four hours. During this step, the solution is preferably agitated with ultrasonic
energy. For example, the solution may be held in a commercially-available ultrasonic
cleaning tank employing magnetostrictive or piezoelectric transducers. Suitable frequencies
are about 20 kHz to about 40 kHz and suitable power levels are about 20 to about 120
watts per gallon (about 80 to about 450 watts per liter) of solution, preferably about
50 to about 100 watts per gallon (about 190 to about 380 watts per liter) of solution.
Following treatment with the solution, the component is rinsed and its internal cavities
flushed with water for a minimum of about five minutes to remove the solution, after
which the component is dried.
[0011] During an investigation leading to this invention, high pressure turbine blades were
obtained whose internal cooling passages had been selectively aluminized by a slurry
aluminiding technique in which metallic particles of Cr-44AI were used as the aluminum
source material. Visual inspection of the cooling passages showed that particles were
adhered to the aluminized internal surfaces. These particles, generally about 10 to
about 100 micrometers in diameter, were concluded to have been formed by some of the
Cr-44Al particles that had oxidized and become attached to the aluminide coating as
a result of sintering at the high temperature (about 970°C) sustained during the aluminizing
process. One of the blades was cleaned by submersion, blade tips down, in an aqueous
solution containing about 40 to about 50 weight percent KOH for about four hours.
The solution was maintained at a temperature of about 170°F (about 77°C), and agitated
by ultrasonic energy at a frequency of about 25 kHz and a power level of about 100
watts per gallon (about 380 watts per liter) of solution. On removal from the solution,
the internal cavities of the blade were flushed with tap water and dried. Visual inspection
of the cavities evidenced that the adherent oxidized particles had been completely
removed from the internal cavities of the blade. The cleaning procedure was then repeated
on an additional four blades with the same results.
1. A process comprising the steps of:
forming an aluminized surface within an internal cavity of a component by placing
within the internal cavity a material comprising metallic particles of an aluminum
source, wherein some of the metallic particles oxidize to form adherent particles
that are sintered to the aluminized surface; and then
contacting the aluminized surface with an aqueous caustic hydroxide solution until
the adherent particles are removed from the surface.
2. The process according to claim 1, characterized in that the solution contains at least 100 grams/liter of potassium hydroxide and the balance
essentially de-ionized water.
3. The process according to claim 1, characterized in that the solution contains about 175 to about 225 grams/liter of potassium hydroxide and
the balance essentially de-ionized water.
4. The process according to claim 1, characterized in that the solution consists of about 175 to about 225 grams/liter of potassium hydroxide
and the balance de-ionized water.
5. The process according to any one of claims 1 through 4, characterized in that the aluminizing step comprises a slurry aluminizing process in which the material
comprises the metallic particles suspended in a liquid vehicle.
6. The process according to any one of claims 1 through 5, characterized in that the adherent particles comprise metallic particles whose outer surfaces are oxidized.
7. The process according to any one of claims 1 through 6 characterized in that the forming step results in oxide particles being sintered to the aluminized surface,
and the oxide particles are removed from the aluminized surface by the contacting
step.
8. The process according to any one of claims 1 through 7 characterized in that the contacting step is performed at a temperature of about 66□C to about 88□C and
at atmospheric pressure.
9. The process according to any one of claims 1 through 8, further comprising the step
of agitating the solution while the solution contacts the surface.
10. The process according to any one of claims 1 through 9, characterized in that the component is a gas turbine engine component and the internal cavity is a cooling
passage.
1. Verfahren umfassend die Stufen:
Bilden einer aluminierten Oberfläche innerhalb eines inneren Hohlraumes einer Komponente
durch Anordnen eines metallische Teilchen einer Aluminiumquelle umfassenden Materials
in dem inneren Hohlraum, wobei einige der metallischen Teilchen unter Bildung anhaftender
Teilchen oxidieren, die an die aluminierte Oberfläche gesintert werden und dann
Kontaktieren der aluminierten Oberfläche mit einer wässrigen kaustischen Hydroxidlösung,
bis die anhaftenden Teilchen von der Oberfläche entfernt worden sind.
2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass die Lösung mindestens 100 g/l Kaliumhydroxid enthält und der Rest im wesentlichen
entionisiertes Wasser ist.
3. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass die Lösung etwa 175 bis etwa 225 g/l Kaliumhydroxid enthält und der Rest im wesentlichen
entionisiertes Wasser ist.
4. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass die Lösung etwa 175 bis etwa 225 g/l Kaliumhydroxid enthält und der Rest im wesentlichen
entionisiertes Wasser ist.
5. Verfahren nach irgendeinem der Ansprüche 1 bis 4, dadurch gekennzeichnet, dass die Aluminierungsstufe ein Aufschlämmungs-Aluminierungsverfahren umfasst, bei dem
das Material die metallischen Teilchen in einem flüssigen Träger suspendiert umfasst.
6. Verfahren nach irgendeinem der Ansprüche 1 bis 5, dadurch gekennzeichnet, dass die anhaftenden Teilchen metallische Teilchen umfassen, deren äussere Oberflächen
oxidiert sind.
7. Verfahren nach irgendeinem der Ansprüche 1 bis 6, dadurch gekennzeichnet, dass die Formstufe in Oxidteilchen resultiert, die an die aluminierte Oberfläche gesintert
werden und die Oxidteilchen durch die Kontaktierungsstufe von der aluminierten Oberfläche
entfernt werden.
8. Verfahren nach irgendeinem der Ansprüche 1 bis 7, dadurch gekennzeichnet, dass die Kontaktierungsstufe bei einer Temperatur von etwa 66°C bis etwa 88°C und bei
Atmosphärendruck ausgeführt wird.
9. Verfahren nach irgendeinem der Ansprüche 1 bis 8, das wieter die Stufe des Rührens
umfasst, während die Lösung die Oberfläche kontaktiert.
10. Verfahren nach irgendeinem der Ansprüche 1 bis 9, dadurch gekennzeichnet, dass die Komponente eine Komponente eines Gasturbinen-Triebwerkes ist und der innere Hohlraum
ein Kühldurchgang ist.
1. Procédé comportant les étapes suivantes :
- former une surface aluminisée dans une cavité interne d'un composant, en plaçant
dans cette cavité interne un matériau comprenant des particules métalliques d'une
source d'aluminium, dont un certain nombre s'oxydent et donnent des particules adhérentes
qui s'agglutinent par frittage à la surface aluminisée ;
- et mettre en suite la surface aluminisée en contact avec une solution aqueuse d'hydroxyde
caustique jusqu'à ce que les particules adhérentes soient enlevées de la surface.
2. Procédé conforme à la revendication 1, caractérisé en ce que la solution contient au moins 100 grammes d'hydroxyde de potassium par litre, le
reste étant essentiellement de l'eau désionisée.
3. Procédé conforme à la revendication 1, caractérisé en ce que la solution contient d'environ 175 à environ 225 grammes d'hydroxyde de potassium
par litre, le reste étant essentiellement de l'eau désionisée.
4. Procédé conforme à la revendication 1, caractérisé en ce que la solution est constituée d'environ 175 à environ 225 grammes d'hydroxyde de potassium
par litre, le reste étant de l'eau désionisée.
5. Procédé conforme à l'une des revendications 1 à 4, caractérisé en ce que l'étape d'aluminisation comprend une opération d'aluminisation à l'aide d'une suspension,
pour laquelle ledit matériau comprend lesdites particules métalliques à l'état de
suspension dans un véhicule liquide.
6. Procédé conforme à l'une des revendications 1 à 5, caractérisé en ce que les particules adhérentes comprennent des particules métalliques dont les surfaces
externes sont oxydées.
7. Procédé conforme à l'une des revendications 1 à 6, caractérisé en ce que l'étape de formation d'une surface aluminisée a pour résultat que des particules
d'oxyde s'agglutinent par frittage à la surface aluminisée, et en ce que ces particules d'oxyde sont enlevées de la surface aluminisée lors de l'étape de
mise en contact.
8. Procédé conforme à l'une des revendications 1 à 7, caractérisé en ce que l'étape de mise en contact est effectuée à une température d'environ 66 °C à environ
88 °C et sous la pression atmosphérique.
9. Procédé conforme à l'une des revendications 1 à 8, qui comporte en outre une étape
consistant à agiter la solution pendant que celle-ci est en contact avec la surface.
10. Procédé conforme à l'une des revendications 1 à 9, caractérisé en ce que le composant est une pièce d'un moteur à turbine à gaz et la cavité interne est un
conduit de refroidissement.