U.S. patent application number 12/794453 was filed with the patent office on 2010-09-30 for method of manufacturing or repairing a coating on a metallic substrate.
This patent application is currently assigned to SNECMA MOTEURS. Invention is credited to Catherine RICHIN, Alain Siccat.
Application Number | 20100247755 12/794453 |
Document ID | / |
Family ID | 34942356 |
Filed Date | 2010-09-30 |
United States Patent
Application |
20100247755 |
Kind Code |
A1 |
RICHIN; Catherine ; et
al. |
September 30, 2010 |
METHOD OF MANUFACTURING OR REPAIRING A COATING ON A METALLIC
SUBSTRATE
Abstract
The invention provides a method of manufacturing or repairing a
coating on a metallic substrate. Production of said coating
comprises forming a pre-layer on the substrate or on a sub-layer of
the coating placed on the substrate by applying one or more layers
of a paint containing at least one metal selected from the group
constituted by platinum class metals (platinoids) and chromium.
Application to the formation or localized repair of a thermal
barrier on a superalloy turbo engine part.
Inventors: |
RICHIN; Catherine;
(Roinville Sous Dourdan, FR) ; Siccat; Alain;
(Bondoufle, FR) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND MAIER & NEUSTADT, L.L.P.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
SNECMA MOTEURS
Paris
FR
|
Family ID: |
34942356 |
Appl. No.: |
12/794453 |
Filed: |
June 4, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11138300 |
May 27, 2005 |
7758914 |
|
|
12794453 |
|
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Current U.S.
Class: |
427/142 |
Current CPC
Class: |
Y02T 50/67 20130101;
Y02T 50/60 20130101; Y10T 428/12736 20150115; C23C 10/58 20130101;
B05D 5/005 20130101; Y10T 428/12875 20150115; C23C 28/021 20130101;
Y10T 428/12847 20150115; C23C 28/023 20130101; C23C 10/02 20130101;
C23C 28/022 20130101; C23C 28/00 20130101 |
Class at
Publication: |
427/142 |
International
Class: |
B05D 3/02 20060101
B05D003/02 |
Foreign Application Data
Date |
Code |
Application Number |
May 28, 2004 |
FR |
04 05778 |
Claims
1. A method of manufacturing or repairing a coating forming a
thermal barrier on a superalloy substrate, wherein said coating
comprises a binding sub-layer formed by an MCrAlY alloy, M being a
metal selected from the group consisting of nickel, cobalt, iron
and a mixture of said metals, said binding sub-layer being modified
by forming a pre-layer on a surface of said binding sub-layer by:
first applying one or more layers of a paint including platinum
class metals (platinoids) to the binding sub-layer, and second,
performing diffusion heat treatment of the one or more layers of
paint.
2. A method according to claim 1, wherein said metal is
platinum.
3. A method according to claim 1, wherein said pre-layer is formed
with a thickness within a range of 1 .mu.m to 30 .mu.m.
4. A method according to claim 1, wherein said pre-layer is formed
by applying said paint using a brush, a spray gun, a pad, and/or by
immersion (dip-coating).
5. A method according to claim 1, wherein said thickness is within
a range of 2 .mu.m to 10 .mu.m.
6. A method according to claim 1, wherein said sub-layer comprises
NiAl.
7. A method according to claim 1, wherein said sub-layer is based
on an aluminide.
8. A method according to claim 1, wherein said paint is a
suspension of solid material in a liquid, said solid material being
a metal powder of said at least one metal.
9. A method according to claim 8, wherein said liquid is
water-based.
10. A method according to claim 8, wherein said liquid is oil
based.
11. A method according to claim 8, wherein said liquid is based on
an hydrocarbon mixture.
Description
[0001] This application is a divisional of U.S. application Ser.
No. 11/138,300 filed May 27, 2005, the entire contents of which is
incorporated herein by reference, and is based upon and claims the
benefit of priority from prior French Patent Application No. 04
05778 filed May 28, 2004.
[0002] The invention relates to a method of manufacturing or
repairing a coating on a metallic substrate.
BACKGROUND OF THE INVENTION
[0003] The search for increasing the efficiency of turbomachines,
in particular in the field of aviation, and for reducing the fuel
consumption and polluting emissions of gas and non-burned residues
has resulted in using fuel in near-stoichiometric proportions. That
situation is accompanied by an increase in the temperature of the
gas leaving the combustion chamber and going towards the
turbine.
[0004] As a consequence, the materials used in the turbine must be
adapted to such an increase in temperature by developing techniques
for cooling the turbine blades (hollow blades) and/or by improving
the abilities of such materials to withstand high temperatures.
That second route, in combination with the use of superalloys based
on nickel and/or cobalt, has produced several solutions including
depositing a thermally insulating coating termed a thermal
barrier.
[0005] That type of ceramic coating forming a thermal barrier can
create a thermal gradient across the coating on a cooled part
running under steady operating conditions, with a total amplitude
which may exceed 200.degree. C. for a coating that is about 150
.mu.m (micrometers) thick. The operating temperature of the
underlying metal forming the substrate for the coating is reduced
by the same amplitude, which induces large increases in the volume
of cooling air required, reduces the service life of the part, and
increases the specific consumption of the turbine engine.
[0006] Of the coatings that are in use, mention can be made of a
ceramic based on zirconia stabilized with yttrium oxide.
[0007] Clearly, in order to improve the thermal barrier properties,
in particular those of binding with the substrate and/or of
providing protection against oxidation of the metal of the
substrate, a sub-layer can be provided between the substrate and
the outer layer of the coating.
[0008] In particular, it is known to use a sub-layer made of a
MCrAlY type alloy, M being a metal selected from nickel, cobalt,
iron, and a mixture of said metals, which alloy consists of a gamma
matrix of nickel-cobalt with, in solution, chromium containing
.beta. NiAl precipitates.
[0009] It is also known to use a sub-layer formed by one or more
aluminides, in particular comprising a nickel aluminide optionally
containing a metal selected from platinum, chromium, palladium,
ruthenium, iridium, osmium, rhodium, or a mixture of said metals,
and/or a reactive element selected from zirconium (Zr), hafnium
(Hf), and yttrium (Y). As an example, a Ni.sub.(1-x)Pt.sub.xAl type
coating is used in which the platinum is inserted into a nickel
matrix. The platinum is deposited electrolytically prior to the
thermochemical aluminizing treatment.
[0010] Normally, ceramic coatings are deposited onto the part to be
coated either using a projection technique (in particular plasma
projection) or a physical vapor deposition technique, i.e. by
evaporation (in particular EB-PVD or "Electron Beam Physical Vapor
Deposition", forming a coating deposited in a vacuum evaporation
chamber under electron bombardment).
[0011] With a projected coating, a deposit of oxide based on
zirconia is made using plasma projection type techniques, which
results in the formation of a coating constituted by a stack of
fused droplets which are then shock quenched, flattened, and
stacked to form an imperfect densified deposit which is generally
in the range 50 micrometers (.mu.m) to 1 millimeter (mm) thick.
[0012] A coating which is deposited physically, in particular by
evaporation under electron bombardment, produces a coating
constituted by an assembly of small columns directed substantially
perpendicularly to the surface to be coated, over a thickness in
the range 20 .mu.m to 600 .mu.m. Advantageously, the space between
the columns allows the coating to compensate effectively for
thermomechanical stresses due, at operating temperatures, both to
the expansion differential with the superalloy substrate and to
centrifugal mechanical stresses due to rotation of the blades.
[0013] Further, to obtain a coating and/or a sub-layer of the
coating, a step consisting in modifying the surface of the
superalloy part is sometimes carried out by depositing a layer of
platinum that is more than 10 .mu.m thick, and then carrying out a
thermal diffusion treatment.
[0014] Further still, the Applicant uses a thermochemical coating
termed C1A formed by an aluminide coating modified with chromium
and resulting from repeatedly carrying out two vapor deposition
steps in succession: a first step of depositing a 2 .mu.m to 6
.mu.m thick layer of chromium followed by an aluminizing step.
[0015] Said coating is used as a coating to protect parts from
oxidation or heat corrosion or, possibly, as a sub-layer for the
thermal barrier.
[0016] Thus, parts are obtained with long service lives as regards
high temperature thermal fatigue.
[0017] Conventionally, coatings forming thermal barriers thus
create a thermal conductivity discontinuity between the outer layer
of the mechanical part, including said thermal barrier, and the
substrate of said coating forming the constituent material of the
part.
[0018] However, such coatings, whether of the thermal barrier type
or which protect against heat corrosion or oxidation, are obtained
by methods (projection and/or physical vapor deposition and/or
electrolytically) which are complex and expensive.
[0019] Further, in the event of localized damage to such coatings,
whether during manufacture or during operation, the coating is
completely reconditioned since a local repair is not possible,
thereby engendering other problems. Stripping operations are
difficult as they result in a reduction in the thickness of the
substrate and an increase in the size of openings, with a
corresponding reduction in the service life of the coated parts.
After stripping, the coating manufacturing steps are recommenced
over the entire surface of the part, and as a result the healthy
zones are unnecessarily subjected to risky removal and
reconditioning operations. Furthermore, a quantity of precious
metal or metals (platinum, chromium, etc) is then lost.
[0020] It should also be noted that certain parts exhibit wear in
particular zones, in particular at the leading edges and trailing
edges of blades in the field of aviation, whether they be fan
blades, compressor blades and/or turbine blades of a turbo
engine.
[0021] In that case, cracks may be produced where the outer layer
or even the sub-layer disappears locally, causing oxidation of the
part. Such deterioration may require total repair of the part,
which consists in removing the old coating, cleaning the part,
reconstituting it, and rebuilding a new coating. Although they are
very expensive, those operations are nevertheless carried out
because the overall cost of the part is very high.
[0022] In some cases, said coating (sub-layer and outer layer in
the case of a thermal barrier) is mechanically removed as well as
reconditioned over a portion only of the part, but over an area
which is generally quite large.
OBJECTS AND SUMMARY OF THE INVENTION
[0023] The aim of the present invention is to provide a method
which can overcome the disadvantages of the prior art and, in
particular, can offer the possibility of repairing a coating
without having to remove it entirely or to remove a large area
thereof.
[0024] To this end, the present invention provides a method wherein
said coating is produced by forming a pre-layer on the substrate,
or on a sub-layer of the coating placed on the substrate, by
applying one or more layers of a paint containing at least one
metal selected from the group constituted by platinum class metals
(platinoids) and chromium.
[0025] The term "platinum class metal" or "platinoid" means
platinum, palladium, iridium, osmium, rhodium, or ruthenium.
[0026] In this manner, it will be understood that merely by
applying one or more layers of paint, with an intermediate drying
stage, all of the problems linked with complex methods (projection
and/or physical vapor deposition and/or electrolytic deposition)
used until now to deposit said selected precious metal which forms
part of the coating, are overcome.
[0027] This solution has the additional advantage, apart from
manufacturing the coating, of also allowing it to be repaired
locally in a zone which is strictly limited to the zone that is
damaged, without modifying either the surface characteristics or
the continuity of the properties of the coating.
[0028] Overall, by means of the solution of the present invention,
it is possible to overcome many of the limitations and
disadvantages due to the complex deposition techniques used until
now for depositing the selected metal, either directly onto the
substrate as the first step, or onto a sub-layer of the coating
which is itself placed directly on the substrate, during the method
of manufacturing or repairing the coating.
[0029] Said deposition of the metal of the pre-layer of the coating
using a paint may be carried out by applying said paint using a
brush, a spray, a pad, and/or by immersion (dip-coating).
DETAILED DESCRIPTION OF THE INVENTION
[0030] Other advantages and characteristics of the invention become
apparent from the following description of non limiting examples of
applications of the method of the present invention.
[0031] Particularly preferred coatings used without a sub-layer
include, firstly, the thermochemical aluminide coating termed C1A
formed by repeatedly carrying out two vapor deposition steps in
succession: a first step of depositing a 2 .mu.m to 6 .mu.m layer
of chromium, followed by an aluminizing step.
[0032] The order of carrying out these two depositions is strict
since it is impossible to deposit chromium onto aluminum by vapor
deposition.
[0033] After operation, when a local repair is required, it is
impossible to redo the deposit in an identical manner limited to
said zone, since the aluminum of the part is evaporated during the
chromizing stage. As a result, repairing a C1A coating is currently
not possible, except by depositing a simple coating of aluminum,
with reduced performance in particular as regards heat
corrosion.
[0034] In the present invention, a pre-layer of platinum is locally
applied to the bare substrate, replacing the first deposit of
chromium by applying one or more layers of a paint containing
platinum. Subsequent aluminizing followed by diffusion heat
treatment result in the formation of a coating of platinum
aluminide with performance that is far superior to a simple
aluminum coating.
[0035] More generally, in this first application of the method of
the present invention, a repair method is carried out, wherein said
coating to be repaired is of the C1A type obtained by prior
deposition of chromium onto the substrate followed by a step of
vapor aluminizing onto the chromium, and wherein the following
steps are carried out in the zone or zones of the coating to be
repaired:
[0036] a) completely removing the spoilt coating down to the bare
substrate;
[0037] b) forming said pre-layer on the substrate by applying one
or more layers of a paint containing at least one metal selected
from the group constituted by platinum class metals (platinoids)
and chromium; and
[0038] c) vapor aluminizing onto the pre-layer, to obtain said
aluminide of the selected metal.
[0039] It should be understood that only the zone or zones to be
repaired have been treated, which is both cheaper and avoids
damaging or changing zones which were in good condition prior to
the repair step.
[0040] Further, in said first application of the method of the
present invention, the whole coating may be manufactured ab initio
using the solution of the present invention. In this case, in the
manufacturing method, said coating comprises an aluminide of the
selected metal resulting from the following steps:
[0041] a) forming a pre-layer on the substrate by applying one or
more layers of a paint containing at least one metal selected from
the group constituted by platinum class metals (platinoids) and
chromium; and
[0042] b) vapor aluminizing onto the pre-layer, to obtain said
aluminide of the selected metal.
[0043] Optionally, and in complementary manner, an additional step
c) of diffusion by heat treatment may be carried out.
[0044] Secondly, the coatings may act as a thermal barrier with a
sub-layer.
[0045] Said coating then comprises a binding sub-layer which is
produced by forming said pre-layer by applying one or more layers
of a paint containing at least one metal selected from the group
constituted by platinum class metals (platinoids) and chromium.
[0046] Occasionally, for coatings with a binding sub-layer, said
binding sub-layer results entirely from forming a pre-layer on the
substrate by applying one or more layers of a paint containing at
least one metal selected from the group constituted by platinum
class metals (platinoids) and chromium, then by diffusion heat
treatment.
[0047] The above disposition is carried out in particular when the
sub-layer consists solely of modifying the surface of a superalloy
forming the metallic substrate by depositing a relatively thick
layer of platinum 10 .mu.m or more in thickness using the principle
of the invention by applying multiple layers of paint, then
carrying out diffusion heat treatment.
[0048] Coatings with a binding sub-layer include sub-layers based
on aluminide. These are known as alumino-former systems, i.e.
forming an adherent protective alumina film by oxidation, which
isolates the metal from the oxidizing environment. The film of
alumina formed by the sub-layers is intended to form a layer
similar to a layer of adhesive for the ceramic coating and has a
substrate protection function. Adding a precious metal such as
platinum to the protective coatings and/or to the coating/thermal
barrier sub-layers has the effect of improving the quality of the
sub-layer formed and promoting adhesion to the metal.
[0049] In this case, in a first variation, said binding sub-layer
results from the formation of a pre-layer on the substrate by
applying one or more layers of a paint containing at least one
metal selected from the group constituted by platinum class metals
(platinoids) and chromium, then vapor aluminizing onto the
pre-layer and optional diffusion heat treatment.
[0050] Here, as in the majority of cases, the metallic substrate is
a superalloy so that reaction with the nickel of the substrate
produces a binding NiAl type sub-layer with an intermetallic
structure, forming compounds defined as 50 atomic % of nickel and
aluminum. Because the pre-layer contains at least one metal
selected from the group constituted by platinum class metals
(platinoids) and chromium, a coating of aluminide is obtained which
is modified by a precious metal and is of the
Ni.sub.(1-x)Pt.sub.xAl type. In particular, if the selected metal
is platinum, a structure is obtained in which the platinum is
inserted into the nickel lattice.
[0051] Coatings with a binding sub-layer based on aluminide include
a second variation in which said binding sub-layer is an alloy of
the MCrAlY type, M being a metal selected from nickel, cobalt,
iron, or a mixture of said metals, said sub-layer being modified by
forming said pre-layer on its surface, by applying one or more
layers of a paint containing at least one metal selected from the
group constituted by platinum class metals (platinoids) and
chromium, then by a diffusion heat treatment.
[0052] In general, said pre-layer is formed with thickness in the
range 1 .mu.m to 30 .mu.m, preferably in the range 2 .mu.m to 10
.mu.m.
[0053] By definition, the paint used is a suspension of solid
materials in a liquid, the solid materials being formed by
particles (metal powder) of metal selected from the group
constituted by platinum class metals (platinoids) and chromium.
[0054] The liquid may be water-based, leaving no deposit after
drying, or oil- or resin-based, or based on any other hydrocarbon
(mixture), or an oil-water emulsion; heating to a high temperature
in the firing step during manufacture or during the initial
operation of the part degrades all the compounds apart from the
metal.
[0055] Various trials have carried out which have satisfactorily
implemented the method of the present invention; these included the
following example.
[0056] This test was carried out to repair a Ni.sub.(1-x)Pt.sub.xAl
type coating. Instead of depositing the platinum electrochemically,
the deposit was produced by applying the paint described below,
before the thermochemical aluminizing step.
[0057] A paint from HERAUS was used, containing 8% by weight of
platinum in powder form (mean diameter of the order of 2 .mu.m).
Said paint is very fluid and is produced in a terpene binder in
solution in other solvents.
[0058] Paint of that type is routinely used to decorate
crockery.
[0059] Twenty layers of paint were applied using a brush with an
intermediate drying period of 10 to 15 minutes in air, then on a
hotplate at 200.degree. C. for 5 minutes and finally in an oven for
15 minutes at 600.degree. C.
[0060] A firing step was carried out at 700.degree. C. for 15
minutes in a furnace.
[0061] The aluminizing step was carried out at 1050.degree. C. for
5 hours using the following procedure: the sample was placed in an
aluminizing chamber containing the aluminum donor cement, and a
sufficient quantity of NH.sub.4F was added.
[0062] The diffusion step then consisted in placing the sample at
1050.degree. C. for one hour.
[0063] After analysis, aluminizing was confirmed by the presence of
an outer layer of aluminide 10 .mu.m to 15 .mu.m or even 20 .mu.m
thick on an inner layer of intermetallic compounds which was of the
order of 10 .mu.m thick.
[0064] Thus, it is possible to produce a coating of aluminide
modified with platinum from a paint producing the platinum
deposit.
* * * * *