U.S. patent application number 11/796989 was filed with the patent office on 2008-10-30 for method for removing carbide-based coatings.
This patent application is currently assigned to United Technologies Corporation. Invention is credited to Michael J. Minor, Paul M. Pellet.
Application Number | 20080264444 11/796989 |
Document ID | / |
Family ID | 39672642 |
Filed Date | 2008-10-30 |
United States Patent
Application |
20080264444 |
Kind Code |
A1 |
Minor; Michael J. ; et
al. |
October 30, 2008 |
Method for removing carbide-based coatings
Abstract
The present invention is a method for processing a metal
component comprising exposing a carbide-based coating to fluoride
ions, thereby extracting a carbide material from the carbide-based
coating to provide a residual coating on the metal component, and
removing the residual coating from the metal component.
Inventors: |
Minor; Michael J.;
(Arlington, TX) ; Pellet; Paul M.; (Arlington,
TX) |
Correspondence
Address: |
KINNEY & LANGE, P.A.
THE KINNEY & LANGE BUILDING, 312 SOUTH THIRD STREET
MINNEAPOLIS
MN
55415-1002
US
|
Assignee: |
United Technologies
Corporation
Hartford
CT
|
Family ID: |
39672642 |
Appl. No.: |
11/796989 |
Filed: |
April 30, 2007 |
Current U.S.
Class: |
134/3 ;
134/2 |
Current CPC
Class: |
F01D 5/005 20130101;
C23G 5/00 20130101 |
Class at
Publication: |
134/3 ;
134/2 |
International
Class: |
C23G 1/02 20060101
C23G001/02; C23G 1/00 20060101 C23G001/00 |
Claims
1. A method for processing a metal component having a carbide-based
coating, the method comprising: exposing the carbide-based coating
to fluoride ions, thereby extracting a carbide material from the
carbide-based coating to provide a residual coating on the metal
component; and removing the residual coating from the metal
component.
2. The method of claim 1, further comprising heating the metal
component to a temperature of at least about 820.degree. C.
3. The method of claim 2, wherein the metal component comprises a
material selected from the group consisting of a nickel-based
alloy, a nickel-based superalloy, a cobalt-based alloy, a
cobalt-based superalloy, and combinations thereof.
4. The method of claim 1, wherein at least about 50% by weight of
the carbide material is extracted from the chromium carbide-based
coating, based on a pre-extraction weight of the carbide-based
coating.
5. The method of claim 4, wherein at least about 75% by weight of
the carbide material is extracted from the carbide-based
coating.
6. The method of claim 5, wherein at least about 90% by weight of
the carbide material is extracted from the carbide-based
coating.
7. The method of claim 1, wherein the residual coating is removed
from the metal component with a first removal pressure that is less
than 25% of a second removal pressure required to remove the
carbide-based coating from the metal component in a same
duration.
8. The method of claim 7, wherein the first removal pressure is
less than 10% of the second removal pressure.
9. The method of claim 8, wherein the first removal pressure is
less than 5% of the second removal pressure.
10. The method of claim 1, wherein the carbide material is selected
from the group consisting of chromium carbide materials, tungsten
carbide materials, and combinations thereof.
11. A method for processing a metal component, the method
comprising: exposing the metal component to hydrogen fluoride, the
metal component having a surface and a carbide-based coating
disposed on at least a portion of the surface; heating the metal
component to react the hydrogen fluoride with the carbide-based
coating, thereby providing a residual coating on the surface of the
metal component; and removing the residual coating from the surface
of the metal component.
12. The method of claim 10, wherein the metal component is heated
to a temperature of at least about 820.degree. C.
13. The method of claim 1, wherein the hydrogen fluoride reacts
with the carbide-based coating until at least about 50% by weight
of a carbide material is extracted from the carbide-based coating,
based on a pre-extraction weight of the carbide-based coating.
14. The method of claim 13, wherein at least about 75% by weight of
the carbide material is extracted from the carbide-based
coating.
15. The method of claim 14, wherein at least about 90% by weight of
the carbide material is extracted from the carbide-based
coating.
16. A method for processing a metal component having a first
coating, the method comprising: extracting a carbide material from
the first coating with hydrogen fluoride to provide a second
coating having a first removal pressure from the metal component
that is less than 25% of a second removal pressure required to
remove the first coating from the metal component in a same
duration; and removing the residual coating from the metal
component.
17. The method of claim 16, wherein extracting the carbide material
from the first coating with hydrogen fluoride comprises generating
fluoride ions from the hydrogen fluoride.
18. The method of claim 16, wherein the carbide material comprises
at least one of: a chromium carbide material and a tungsten carbide
material.
19. The method of claim 16, wherein the first removal pressure is
less than 10% of the second removal pressure.
20. The method of claim 19, wherein the first removal pressure is
less than 5% of the second removal pressure.
Description
BACKGROUND
[0001] The present invention relates the repair of metal
components, such as gas turbine engine components. In particular,
the present invention relates to the removal of protective coatings
during the repair of metal components.
[0002] Turbine engine components are exposed to extreme
temperatures and pressures during the course of operation. As such,
these engine components typically employ high-strength alloys
(e.g., superalloys) to preserve the integrity of the components.
However, over time, exposed portions of the components are subject
to wear, cracking, and other degradations, which can lead to
decreases in operational efficiencies and damage to the
components.
[0003] Due to economic factors, it is common practice in the
aerospace industry to restore turbine engine components rather than
replace them. However, many of the engine components include
protective coatings that need to be removed before the restoration
can begin. For example, carbide-based coatings, such as chromium
carbide-based coatings, are typically coated onto engine components
to increase wear resistance and sliding mechanics between moving
parts.
[0004] Current techniques for removing carbide-based coatings
typically involve machining, grinding, or grit blasting the
coatings. However, these techniques may remove portions of the
underlying metal components along with the coatings. Thus, if the
coating removal processes are not sufficiently monitored, they may
reduce the wall thicknesses of the metal components to levels that
are too thin for repair. In these situations, the metal component
is no longer repairable, and is discarded or recycled. Accordingly,
there is a need for a process for removing carbide-based coatings
from metal components that also substantially preserves the
underlying metal components.
SUMMARY
[0005] The present invention relates to a method for processing a
metal component having a carbide-based coating. The method includes
exposing the carbide-based coating to fluoride ions, thereby
extracting a carbide material from the carbide-based coating. This
provides a residual coating on the metal component, which is then
removed from the metal component.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 is a sectional view of a metal component containing a
carbide-based coating.
[0007] FIG. 2 is a sectional view of the metal component containing
a residual coating after the carbide-based coating is exposed to
fluoride ions.
[0008] FIG. 3 is a sectional view of the metal component after the
residual coating is removed.
DETAILED DESCRIPTION
[0009] FIG. 1 is a sectional view of metal component 10, which
includes substrate 12 and coating 14. Metal component, 10 may be
any type of component capable of containing coating 14, such as
turbine engine components. Substrate 12 is a metal substrate (e.g.,
nickel-based alloys and superalloys, cobalt-based alloys and
superalloys, and combinations thereof) of metal component 10, and
includes surface 16. Coating 14 is a carbide-based coating formed
on surface 16 of substrate 12 (e.g., via plasma spray deposition)
to provide wear resistance and sliding properties during use. As
used herein, the term "carbide-based coating" refers to a coating
that includes at least one carbide material. Examples of suitable
carbide materials for use in the carbide-based coating include
chromium carbide materials (e.g., Cr.sub.3C.sub.2, Cr.sub.7C.sub.3,
and Cr.sub.23C.sub.6), tungsten carbide materials (e.g., WC), and
combinations thereof. Coating 14 may also include other materials,
such as nickel chromium (NiCr) alloys, cobalt (Co) alloys, and
combinations thereof. An example of a suitable chromium
carbide-based coating for coating 14 includes about 75% by weight
of a chromium carbide material and about 25% by weight of a nickel
chromium alloy. Suitable coating thicknesses for coating 14 range
from about 25 micrometers (about 1 mil) to about 500 micrometers
(about 20 mils).
[0010] Pursuant to the present invention, coating 14 may be removed
by initially exposing metal component 10 to fluoride ions, which
react with coating 14 to extract at least a portion of the carbide
material (e.g., the chromium-carbide material) from coating 14.
Metal component 10 may be exposed to fluoride ions by placing metal
component 10 in a chamber containing hydrogen fluoride (HF) gas.
The chamber may also include additional gases (e.g., H.sub.2) to
accommodate desired pressures and reaction rates. While within the
chamber, the hydrogen fluoride gas and metal component 10 are then
heated to a temperature sufficient to generate the fluoride ions
from the hydrogen fluoride gas. Examples of suitable temperatures
for generating the fluoride ions include temperatures of at least
about 820.degree. C. (about 1500.degree. F.), with particularly
suitable temperatures ranging from about 870.degree. C. (about
1600.degree. F.) to about 1100.degree. C. (about 2000.degree. F.).
This causes the fluoride ions of the hydrogen fluoride gas to react
with coating 14, thereby extracting at least a portion of the
carbide material from coating 14.
[0011] The amount of carbide material removed from coating 14 is
generally dependent on the concentration of the fluoride ions, the
temperature used, the surface area of coating 14, and the duration
of the extraction. In one embodiment, the extraction is continued
until at least about 50% by weight of the carbide material is
removed from coating 14. In a more preferred embodiment, the
extraction is continued until at least about 75% by weight of the
carbide material is removed from coating 14. In an even more
preferred embodiment, the extraction is continued until at least
about 90% by weight of the carbide material is removed from coating
14. The weight percents of the removed carbide material are based
on the pre-extraction weight of coating 14. Examples of suitable
durations for the extraction process range from about 10 minutes to
about 3 hours, with particularly suitable durations ranging from
about 30 minutes to about 1 hour. When the extraction process is
complete, metal component 10 may be removed from the chamber and
cooled.
[0012] FIG. 2 is a sectional view of metal component 10 after the
extraction process, which includes residual coating 18 disposed on
surface 16 of substrate 12. Residual coating 18 is the remaining
coating of coating 14 (shown in FIG. 1) after the extraction
process. Because of the carbide material removal, residual coating
18 primarily includes the non-carbide portion of coating 14 (e.g.,
the nickel chromium alloy) and any residual amount of the carbide
material that was not extracted. However, because a substantial
portion of the carbide material was removed, residual coating 18 is
structurally weaker than coating 14. Thus, residual coating 18 can
be removed from surface 16 of substrate 12 without requiring the
high-intensity machining, grinding, or grit blasting that are
typically used to remove carbide-based coatings.
[0013] Residual coating 18 may be removed from surface 16 with
low-pressure abrasive techniques (e.g., low-pressure grit
blasting). The duration of the removal process may vary depending
on the pressure used. However, the pressure required to remove
residual coating 18 is substantially less than what is otherwise
required to remove a carbide-based coating not subjected to the
fluoride-ion extraction process (i.e., coating 14). Suitable
pressures for removing residual coating 18 from surface 16 include
removal pressures that are less than 25% of removal pressures
required to remove coating 14 from surface 16 in the same duration,
with particularly suitable removal pressures including less than
10% of the removal pressures required to remove coating 14 from
surface 16 in the same duration, and with even more particularly
suitable removal pressures including less than 5% of the removal
pressures required to remove coating 14 from surface 16 in the same
duration. As used herein, the term "removal pressure" refer to a
pressure that is actually applied to the coating (e.g., coating 14
or residual coating 18). For removal techniques that are distance
dependant (e.g., grit blasting), the discharge pressure is
typically greater than the pressure actually applied to the
coating.
[0014] FIG. 3 is a sectional view of metal component 10 after the
residual coating 18 is removed. After residual coating 18 is
removed, the resulting metal component 10 may undergo the necessary
repair processes to restore metal component 10 to operable
condition. Because residual coating 18 (shown in FIG. 2) can be
removed with a low-pressure technique, the risk of damaging surface
16 during the removal process is reduced. Accordingly, pursuant to
the present invention, coating 14 (shown in FIG. 1) may be removed
from substrate 12 while substantially preserving the dimensions of
surface 16.
[0015] Although the present invention has been described with
reference to preferred embodiments, workers skilled in the art will
recognize that changes may be made in form and detail without
departing from the spirit and scope of the invention.
* * * * *