U.S. patent application number 10/516085 was filed with the patent office on 2006-06-01 for method for removing at least one partial area of a component made of metal or a metallic compound.
Invention is credited to Ralph Reiche, Werner Stamm.
Application Number | 20060112976 10/516085 |
Document ID | / |
Family ID | 29414719 |
Filed Date | 2006-06-01 |
United States Patent
Application |
20060112976 |
Kind Code |
A1 |
Reiche; Ralph ; et
al. |
June 1, 2006 |
Method for removing at least one partial area of a component made
of metal or a metallic compound
Abstract
The invention relates to a method for removing at least one
layer area of a component made of metal or a metal compound. When
components are used in high temperature areas, they acquire
degraded areas which are removed by means of an acid attack.
Removal during said acid treatment is uneven since areas having
different acidic solubility behavior arise as a result of said
degradation. According to the inventive method, the chemical
composition and the phase composition of the component can be
altered in such a matter that an even removal can take place during
the acid treatment.
Inventors: |
Reiche; Ralph; (Berlin,
DE) ; Stamm; Werner; (Mulheim, DE) |
Correspondence
Address: |
Siemens Corporation;Intellectual Property Department
170 Wood Avenue South
Iselin
NJ
08830
US
|
Family ID: |
29414719 |
Appl. No.: |
10/516085 |
Filed: |
May 27, 2003 |
PCT Filed: |
May 27, 2003 |
PCT NO: |
PCT/EP03/05573 |
371 Date: |
November 29, 2004 |
Current U.S.
Class: |
134/41 |
Current CPC
Class: |
C23C 10/02 20130101;
C23C 10/60 20130101; C23F 4/00 20130101; C23G 5/00 20130101 |
Class at
Publication: |
134/041 |
International
Class: |
C23G 1/02 20060101
C23G001/02 |
Foreign Application Data
Date |
Code |
Application Number |
May 29, 2002 |
EP |
02011965.7 |
Claims
1-12. (canceled)
13. A method for removing a partial layer area of a component,
comprising: removing the partial area by an acid treatment or a
mechanical treatment; diffusing a diffusion agent comprised of a
first element and a second element into the partial area of the
component; and diffusing the first or second element of the
diffusion agent into the component directly from a gas phase.
14. The method as claimed in claim 13, wherein the component is
comprised of a metal and a metal compound.
15. The method as claimed in claim 13, wherein the component is
comprised of a metal or a metal compound.
16. The method as claimed in claim 13, wherein the second element
of the diffusion agent is metallic.
17. The method as claimed in claim 13, wherein the first or second
element of the diffusion agent is aluminum.
18. The method as claimed in claim 13, wherein the first or second
element of the diffusion agent is cobalt.
19. The method as claimed in claim 13, wherein the first element of
the diffusion agent is aluminum and the second element of the
diffusion agent is cobalt.
20. The method as claimed in claim 13, wherein the diffusion agent
is applied to a surface of the component.
21. The method as claimed in claim 20, wherein the diffusion agent
is applied by plasma spraying.
22. The method as claimed in claim 20, wherein the diffusion agent
is applied by evaporation coating.
23. The method as claimed in claim 20, wherein the diffusion agent
is applied by chemical vapor deposition.
24. The method as claimed in claim 20, wherein the diffusion agent
is applied by a pack method.
25. The method as claimed in claim 13, wherein the diffusion causes
a phase change in the component or partial area.
26. The method as claimed in claim 13, wherein the partial area is
an MCrAlY layer where M is an element iron, cobalt or nickel.
27. A method for removing a partial area of a component having a
metal compound layer, comprising: removing the partial area by an
acid treatment or a mechanical treatment, a diffusion agent
comprising two components diffusing into the partial area of the
metal compound layer, and two components of the diffusion agent are
metallic, and one component of the diffusion agent diffuses into
the component directly from a gas phase.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is the U.S. National Stage of International
Application No. PCT/EP03/05573, filed May 27, 2003 and claims the
benefit thereof. The International Application claims the benefits
of European application No. 02011965.7 EP filed May 29, 2002, both
of the applications are incorporated by reference herein in their
entirety.
FIELD OF THE INVENTION
[0002] The invention relates to a method for removing a partial
area, in particular a layer area, of a component consisting of
metal or a metal compound, so that the partial area can be removed
more easily after the method has been applied.
BACKGROUND OF THE INVENTION
[0003] In modern energy generation plants, such as for example gas
turbine installations, efficiency plays an important role, since it
is a parameter which can be used to reduce the costs of operation
of the gas turbine installation. One possible way of increasing the
efficiency and thereby reducing the operating costs is to increase
inlet temperatures of a combustion gas within a gas turbine.
[0004] For this reason, ceramic thermal barrier coatings have been
developed and are applied to components that are subject to thermal
loading, for example made from superalloys, which are no longer
able to withstand even the high inlet temperatures over the course
of time.
[0005] The ceramic thermal barrier coating offers the advantage of
a high thermal stability on account of its ceramic properties, and
the metallic substrate offers the advantage of good mechanical
properties in this assembly or layer system.
[0006] A bonding layer of composition MCrAlY (main constituents),
in which M means that a metal comprising nickel, chromium or iron
is used, is typically applied between the substrate and the ceramic
thermal barrier coating.
[0007] The composition of these MCrAlY layers may vary, but despite
the ceramic layer on top of them, all MCrAlY layers are subject to
corrosion or degradation as a result of oxidation, sulfiding,
nitriding, diffusion or other chemical and/or mechanical
attacks.
[0008] It is often the case that the MCrAlY layer is degraded to a
greater extent than the metallic substrate, i.e. the service life
of the composite system comprising substrate and layer is
determined by the service life of the MCrAlY layer.
[0009] After prolonged use, the MCrAlY interlayer only has a
limited ability to function, whereas the substrate may still be
fully functional.
[0010] Therefore, there is a need for the components which have
been degraded in use, for example turbine blades, guide vanes or
combustion chamber parts, to be reworked, during which process the
corroded layers of the zones of the MCrAlY layer have to be removed
in order if appropriate for new MCrAlY layers and/or then a thermal
barrier coating to be applied. The use of existing, used substrates
reduces the costs of operation of gas turbine installations.
[0011] In this context, it must be ensured that the design of the
turbine blades is not altered, i.e. that there is a uniform removal
of material from the surface.
[0012] Furthermore, there should be no residues of corrosion
products, which represent a defect source during new coating with
an MCrAlY layer and/or a ceramic thermal barrier coating and lead
to poor bonding of the thermal barrier coating.
[0013] A method for removing corrosion products is known from U.S.
Pat. No. 6,217,668. In this method, the corroded component is
accommodated in a large crucible, where the component is arranged
in a powder bed with an aluminum source. The crucible must be
partially closed and then heated in a furnace. The heating process
supplies aluminum to the corroded component, with the result that
the regions which had hitherto been more difficult to remove, i.e.
which had a higher resistance to removal, can be removed by means
of subsequent acid treatment. Large amounts of material are
required for the powder bed, and the crucible takes up a large
amount of space in the furnace during the heat treatment. The
heating process also lasts longer, on account of the high heat
capacity.
[0014] A further method for removing surface layers of metallic
coatings is known from U.S. Pat. No. 6,036,995. In this method, an
aluminum source is applied to a corroded component in the form of a
paste. However, the component together with the paste has to be
heated until the aluminum melts, and consequently it is only then
that aluminum can diffuse into the component. The molten aluminum
layer is difficult to remove, since it bonds very well to the
component.
SUMMARY OF THE INVENTION
[0015] The invention overcomes the described drawbacks by means of
a method as described in the claims.
[0016] Further advantageous configurations of the method are listed
in the subclaims.
[0017] The diffusion agent can be applied by simple, known coating
methods; such as plasma spraying, evaporation coating, CVD, pack
methods (component in a powder bed) or other methods (paste
application).
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The figures illustrate exemplary embodiments of the method
according to the invention.
[0019] In the drawings:
[0020] FIG. 1 shows a corroded metallic component,
[0021] FIG. 2 shows a component to which the diffusion agent has
been applied,
[0022] FIG. 3 shows the component illustrated in FIG. 2 following a
heat treatment,
[0023] FIG. 4 shows components which are being subjected to an acid
treatment,
[0024] FIGS. 5, 6 show components after an acid treatment for a
method according to the invention and a method according to the
prior art.
DETAILED DESCRIPTION OF THE INVENTION
[0025] FIG. 1 shows a component 1 made of metal, a metal alloy
and/or a metal compound, which in at least one partial area at a
surface 13 and/or in the interior of the component 1 has corrosion
products 4 which are present, for example, in regions formed
separated from one another. The corrosion products 4 may also be
linked together or may be present on/underneath the entire surface
13, i.e. may also form a corrosion layer 4.
[0026] By way of example, the region enclosed by a dot-dashed line
represents a partial area 28.
[0027] The component 1 may be a bulk component or a layer or a
region of a composite or layer system 14. In the case of a layer
system 14, there is a substrate 7 made from metal or ceramic, to
which the metallic layer 10, for example an MCrAlY layer, has been
applied; M indicates that a metal composed of nickel, chromium or
iron is used.
[0028] The partial area 28 may also be a partial area of the layer
10 or may represent the entire layer 10 of the layer system 14
and/or part of the metallic substrate 7.
[0029] The corrosion products 4 have formed while the component 1
was in use and are undesirable for further use of the component and
need to be removed. This is often done by a treatment in an acid
bath.
[0030] However, it is also the case that the material of the
component 1 beneath or above the layer 10 of degraded regions
and/or the corrosion products 4 have a different reactivity in an
acid bath, i.e. are more resistant to removal. The different
solubility in the acid bath is caused by the different solubility
of the corrosion products 4 or because an original composition of
the material of the component 1 or the layer 10 has changed, e.g.
because the corrosion product 4 removes a component from a region
of the component 1 in the region around the corrosion product 4,
where it produces a depletion region. This leads to nonuniform
removal or even no removal of the corrosion products 4 or the
material in the depletion region.
[0031] The method according to the invention makes it possible to
remove the corrosion products or the altered layer or base material
regions completely and uniformly with the material of the component
1 or the layer 10.
[0032] By way of example, in a first method step coarse removal of
the corrosion products 4 or other regions can be effected by
mechanical methods, such as for example sand blasting and/or
chemical means, such as for example an acid bath.
[0033] In a further method step (FIG. 2), a multi-component
diffusion agent 16 is, for example, applied to the corroded
component 1 on the surface 13, in particular in the region having
the corrosion products 4, or to the corrosion layer 4, or at least
one component of the diffusion agent 16 diffuses into the component
1 directly from the gas phase, the corrosion products 4 in this
example representing the regions which are more resistant to
removal.
[0034] The diffusion agent 16 contains, for example, two
components, both of which diffuse into the layer 10 or the
component 1 as a result of a heat treatment, where they alter the
chemical composition and materials. The diffusion and heat
treatment can also give rise to the formation of new phases which
can be removed more easily by an acid bath 19 (FIG. 4).
[0035] FIG. 3 shows a component as shown in FIG. 2, in which the
diffusion agent 16 has completely diffused into the layer 10 as a
result of a heat treatment at a temperature T. The layer 10
represents the partial area 28 that is to be removed, comprising
not just regions that are more resistant to removal. The diffusion
agent 16 is made up of at least two components. At least one
component of the diffusion agent 16 is, for example, metallic, such
as for example aluminum. By way of example, cobalt represents a
further metallic component. Other components may include silicon or
carbon.
[0036] The method functions particularly well if cobalt and
aluminum diffuse into the partial area 28 as components of the
diffusion agent 16.
[0037] In the example of an MCrAlY protective layer (M.dbd.Fe, Ni,
Co), the .gamma.' phase is prevented from re-forming.
[0038] On the other hand, enriching the MCrAlY layer with aluminum
and/or cobalt causes .gamma. and .gamma.' phase to be converted
into an aluminum-rich .beta. phase.
[0039] The enrichment with the elements or the phase transformation
described allows improved acid attack.
[0040] FIG. 4 shows two components which are arranged in an acid
bath 19 or are exposed to an acid attack.
[0041] The component 1 or the layer system 14 and a component 22
according to the prior art, on which the method according to the
invention has not been carried out, have corrosion products 4 and
are exposed to the acid attack for the same time.
[0042] FIG. 5 shows the component 22 following the acid treatment.
The component 22 still has acid-resistant regions 25 which have not
been removed or have been removed to a lesser extent during the
acid attack, resulting in nonuniform removal of a layer area of the
component 22.
[0043] By contrast, FIG. 6 shows a component 1 or layer system 14
in which a layer area of the component I or the layer 10 has been
removed uniformly.
[0044] The diffusion of the diffusion agent 16 has also enabled the
partial area 28 to become so brittle that the partial area 28 can
be removed by a mechanical treatment (sand blasting, ultrasound,
dry ice blasting).
* * * * *