U.S. patent application number 14/873790 was filed with the patent office on 2016-01-28 for method for the manufacture of a coating having a columnar structure.
This patent application is currently assigned to OERLIKON METCO AG. The applicant listed for this patent is OERLIKON METCO AG. Invention is credited to Rajiv J. DAMANI, Arno REFKE.
Application Number | 20160024634 14/873790 |
Document ID | / |
Family ID | 39167173 |
Filed Date | 2016-01-28 |
United States Patent
Application |
20160024634 |
Kind Code |
A1 |
DAMANI; Rajiv J. ; et
al. |
January 28, 2016 |
METHOD FOR THE MANUFACTURE OF A COATING HAVING A COLUMNAR
STRUCTURE
Abstract
Method for the manufacture of a coating having a columnar
structure, preferably a dense structure, in which method a coating
material in the form of primary corpuscles is injected with a
carrier gas into a thermal process beam. The coating material is
transferred into a vapor phase in the process beam and is deposited
as a condensate in the form of a columnar coating on a substrate.
The primary corpuscles are formed by an agglomerate of particles
which are held together by cohesive forces of a connecting medium
or by adhesive forces.
Inventors: |
DAMANI; Rajiv J.;
(Winterthur, CH) ; REFKE; Arno; (Fahrwangen,
CH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
OERLIKON METCO AG |
Wohlen |
|
CH |
|
|
Assignee: |
OERLIKON METCO AG
Wohlen
CH
|
Family ID: |
39167173 |
Appl. No.: |
14/873790 |
Filed: |
October 2, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11905500 |
Oct 1, 2007 |
|
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|
14873790 |
|
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Current U.S.
Class: |
427/453 ;
427/446 |
Current CPC
Class: |
C23C 4/123 20160101;
C23C 4/12 20130101; Y02T 50/67 20130101; C23C 4/134 20160101; Y02T
50/60 20130101; C23C 4/11 20160101 |
International
Class: |
C23C 4/12 20060101
C23C004/12; C23C 4/10 20060101 C23C004/10 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 2, 2006 |
EP |
06121637.0 |
May 3, 2007 |
EP |
07107447.0 |
Claims
1. A method for the manufacture of a coating having a columnar
structure, preferably a dense structure, in which method a coating
material in the form of primary corpuscles is injected with a
carrier gas into a thermal process beam, the coating material is
transferred into a vapor phase in the process beam and is deposited
as a condensate in the form of a columnar coating on a substrate
and the primary corpuscles are formed by an agglomerate of
particles which are held together by cohesive forces of a
connecting medium or by adhesive forces, characterized in that the
primary corpuscles are disintegrated in the process beam by
mechanical and thermal interaction and the particles are dispersed
so that coating material is vaporized fully or partly by thermal
action on the individual particles.
2. A method in accordance with claim 1, characterized in that the
primary corpuscles are generated by spraying of a slurry, and in
that two cases can be distinguished: I) the spraying of the slurry
is carried out directly before the entry into the process beam,
with capillary forces of a liquid forming the cohesive forces and
this liquid, which as a rule contains a dispersing agent, having
been used for a slurrying of the particles and for the generation
of the slurry; or II) the slurry is manufactured from the particles
from a liquid, from a binder, and, optionally, from the dispersing
agent, the sprayed slurry is subsequently dried and the spray-dried
material is used as a spray powder, with the binder having been
dissolved in the liquid of the slurry at a high dilution so that
the cohesive forces generated by the binder after the drying only
effect a minimal holding together of the particles.
3. A method in accordance with claim 2, characterized in that the
binder portion after the drying amounts to 0.5 to 5% by weight,
preferably to 1-2% by weight, on the use of the spray powder; and
in that the following materials are used, for example, for the
slurry: as the liquid, demineralized water or an organic solvent,
in particular an alcohol; as the dispersing agent, polycarbonic
acid, a polycarboxylate compound or a polymetacarboxylate compound,
polyethyleneimines or an amino alcohol; and as the binder,
polyvinyl alcohol, polyvinylpyrrolidine, polysaccharide, acrylic
polymers and copolymers, starch, polyvinyl propylene, polyethylene
glycols or a cellulose compound, for example carboxy methyl
cellulose, methyl cellulose or hydroxyethylcellulose.
4. A method in accordance with claim 1, characterized in that the
thermal process beam is generated by a plume of a defocusing plasma
beam, with the properties of the process beam being determined by
adjustable process parameters, in particular by the parameters of
process pressure, enthalpy and composition of a process gas
mixture.
5. A method in accordance with claim 4, characterized in that a) a
value is selected for the process pressure between 50 and 2,000 Pa,
preferably between 100 and 500 Pa and the specific enthalpy of the
plasma beam is generated by delivering an effective power which is
to be determined empirically and which lies, according to
experience, in a range from 20 to 100 kW, preferably 40 to 80 kW;
b) the process gas includes a mixture of insert gases, in
particular a mixture of argon Ar and helium He, and furthermore,
optionally, hydrogen, nitrogen and/or a reactive gas, with the
volume ratio of Ar to He advantageously lying in the range from 2:1
to 1:4 and the total gas flow lying in the range from 30 to 150
SLPM; c) the primary corpuscles are injected at a conveying rate
between 5 and 60 g/min, preferably between 10 and 40 g/min; and d)
the substrate is preferably moved relative to a cloud of the
vaporized material during the material application, in particular
by rotary or pivot movements and/or by movements in
translation.
6. A method in accordance with claim 1, characterized in that a
coating material is used whose portion which can be vaporized
amounts to at least 70%; and in that a plasma beam with
sufficiently high specific enthalpy is generated or that at least
5% of the coating material, preferably at least 50%, is transferred
into the vapor phase during vaporization.
7. A method in accordance with claim 1, characterized in that
regions of the substrate are coated which are located in the
geometrical shadow of the process beam.
8. A method in accordance with claim 1, wherein the substrate is a
turbine vane or a segment having at least two turbine vanes.
9. A method in accordance with claim 1, wherein the powder is an
aggregate of corpuscles which are formed in each case by an
agglomerate of particles; and in that the particles are connected
by cohesive forces of a binder, or by adhesive forces, with the
binder portion amounting to 0.5-5% by weight, preferably 1-2% by
weight; wherein the diameters lie in the range between 0.1 and 5
.mu.m for the particles of the primary corpuscles; and wherein the
diameters of the primary corpuscles are smaller than 35 .mu.m and
larger than 5 .mu.m.
10. A method in accordance with claim 9, characterized in that
oxide ceramic materials are used as the coating materials; in that
the materials are oxides of Zr, Al, Ti, Cr, Ca, Mg, Si, Ti, Y, La,
Ce, Sc, Pr, Dy, Gd, Sm, Mn, Sr or combination of these chemical
elements.
11. A method in accordance with claim 9, characterized in that a
material suitable for a thermal barrier coating TBC is used as the
coating material, in particular one of the following oxides or a
combination of these oxides: zirconium oxide ZrO.sub.2, yttrium
oxide Y.sub.2O.sub.3, ytterbium oxide Yb.sub.2O.sub.5, dysprosium
oxide Dy.sub.2O.sub.3, gadolinium oxide Gd.sub.2O.sub.3, cerium
oxide CeO.sub.2, magnesium oxide MgO, calcium oxide CaO, europium
oxide Eu.sub.2O.sub.3, erbium oxide Er.sub.2O.sub.3 scandium oxide
Sc.sub.2O.sub.3, lanthanide oxides and actinide oxides, with these
materials being able to be present in a fully stabilized or partly
stabilized form and with the following stabilizers and
concentration ranges being provided with a TBC of ZrO.sub.2: a)
Y.sub.2O.sub.3--4-20% by weight, preferably 6-9% by weight; b)
Yb.sub.2O.sub.5--4-20% by weight, preferably 10-16% by weight; c)
Y.sub.2O.sub.3 and Yb.sub.2O.sub.5--4-20% by weight, preferably
4-16% by weight; d) Y.sub.2O.sub.3 and Yb.sub.2O.sub.5 and
Sc.sub.2O.sub.3 or lanthanide oxides--4-20% by weight, preferably
4-16% by weight.
12. A method in accordance with claim 9, characterized in that the
particles in the corpuscles form a homogeneous or heterogeneous
mixture with materials which are the same or different.
13. A method in accordance with claim 9, characterized in that the
particles in the corpuscles form a mixture of materials which react
chemically in the process beam after the vaporization at least
partly with one another or with a reactive gas of the process gas
mixture and are condensed out as reaction products during the
coating.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation of U.S.
application Ser. No. 11/905,500 filed Oct. 1, 2007, which claims
priority under 35 U.S.C. .sctn.119(a) of European Patent
Application No. 06 121 637.0 filed Feb. 10, 2006 and of European
Patent Application No. 07 107 447.0 filed Mar. 5, 2007. The
disclosure of U.S. application Ser. No. 11/905,500, and all
documents expressly incorporated by the same, is expressly
incorporated by reference herein in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to a method for the manufacture of a
coating having a columnar structure as well as to a spray powder
with which the method can be carried out.
[0004] 2. Discussion of Background Information
[0005] Large areas can be provided uniformly with thin films using
a special LPPS process ("low pressure plasma spraying process"),
that is an LPPS TF process ("LPPS thin film process"). This
process, known for example from U.S. Pat. No. 5,853,815, is a
plasma spraying process. The manufacture of a uniform coating is
achieved by a spray gun having a geometrically suitable design. A
substrate to be coated is put into a process chamber in which a
pressure lower than 10 kPa is established, whereas a pressure of,
for example, around 100 kPa (approximately ambient pressure) is
present in the spray gun. The pressure drop between the interior of
the spray gun and the process chamber has the effect that the
thermal process beam expands to a broad beam in which the material
to be sprayed is uniformly distributed: it is a thermal process
beam which is generated by the plume of a defocusing plasma beam. A
dense layer can be deposited over a relatively large area in a
single passage by means of a process beam widened in this manner.
Coatings having special properties can be generated by multiple
deposition of such layers. Coating thicknesses in the micrometer
range can be in particular be generated.
[0006] In a special LPPS TF process, a hybrid coating is carried
out using the thermal process beam. This process, which is known
from EP-A 1 034 843 (=P.7192) or from EP-A-1 479 788 (=P.7328),
permits thermal spraying to be combined with a vapor phase
deposition and so to unify the possibilities of both methods. The
properties of the process beam are determined by controllable
process parameters, in particular by the parameters of pressure,
enthalpy, composition of a process gas mixture and composition and
form of application of the material to be sprayed. A thermal
barrier coating (TBC) with a columnar microstructure can be
manufactured using the hybrid coating method. This coating or layer
is approximately composed of cylindrical or spindle-like particles
whose central axes are aligned perpendicular to the substrate
surface. This columnar layer with an anisotropic microstructure is
stretch tolerant with respect to a thermal strain variation, i.e.
to changing strains, which result from repeatedly occurring
temperature changes. The coating reacts to the changing strains in
a largely reversible manner, i.e. without any formation of cracks,
so that its service life is considerably extended in comparison
with the service life of a coating which does not have a columnar
microstructure.
[0007] The described plasma spraying method is a preferred coating
method. Instead of a plasma beam, another thermal process beam
could also be used to manufacture a coating having a columnar
structure as well as a dense structure, if the coating material can
be vaporized using such a thermal process beam. The invention
described in the following includes this generalisation. Examples
for further thermal process beams include but are not limited to:
electron beams, flames of reactive gas mixtures, electrical arcs,
laser beams.
SUMMARY OF THE EMBODIMENTS
[0008] The invention provides a method for the manufacture of a
coating having a columnar structure in which a necessary
vaporization of coating material and deposition can be carried out
more efficiently than in the known methods.
[0009] In the method for the manufacture of a coating (10) having a
columnar structure, preferably a dense structure, a coating
material in the form of primary corpuscles (1) is injected with a
carrier gas into a thermal process beam. The coating material is
transformed in the process beam into a vapor phase and is deposited
as condensate in the form of a columnar coating on a substrate
(100). The primary corpuscles are liquid droplets or they are in
each case formed by an agglomerate of particles which are held
together by cohesive forces of a connecting medium or by adhesive
forces. The liquid droplets include a chemical precursor of the
coating material in the form of a salt solution and are transformed
by thermal action in the process beam into secondary corpuscles
containing particles (2). The primary or secondary corpuscles are
disintegrated in the process beam by mechanical and thermal
interaction. In this connection, the particles are dispersed so
that coating material is vaporised fully or partly by thermal
action on the individual particles.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The invention will be explained in the following with
reference to the drawings. There are shown:
[0011] FIG. 1 shows a section of a coating which was manufactured
using the method in accordance with the invention;
[0012] FIG. 2 shows a schematic representation of an agglomerate
which is a corpuscle composed of particles;
[0013] FIG. 3 shows an illustration for the disintegration of the
agglomerate;
[0014] FIG. 4 shows a measured size distribution of the corpuscles
of a spray powder in accordance with the invention;
[0015] FIG. 5 shows a segment of a turbine having two turbine
vanes; and
[0016] FIG. 6 shows a section through the segment in FIG. 4
parallel to the base plate.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0017] In the example of a coating 10 which is manufactured in
accordance with the invention using a plasma spraying method and
which is shown as a narrow section in FIG. 1, the coating 10
applied to a substrate 100 has a thickness of approximately one
third of a millimeter. The section shown is drawn in the manner of
a micrograph. Slit-like gaps 13, which are characteristic for a
columnar structure, are disposed in the direction of the axes
between elongate zones 12 whose axes are substantially
perpendicular to the substrate 100. The coating material is in a
state between the gaps 13 which is dense thanks to a low porosity.
The porosity in relation to the total coating 10 is lower than 10
to 15%.
[0018] This coating 10 is generated with a spray powder which has
the size distribution of corpuscles 1 documented in FIG. 4. The
corpuscles 1 are composed of particles 2 to form an agglomerate
such as is shown schematically in FIG. 2. The illustration shows a
two-dimensional model of a corpuscle 1. The particles 2 drawn as
polygons represent grains which have been generated, for example,
from homogeneous solids by breaking and milling. The corpuscles 1
are each formed by an agglomerate of particles 2 which are held
together by cohesive forces 4 of a connection medium 3 (binder).
The medium 3 is present on the surfaces of the particles 2 as a
thin film and as bridges communicating cohesive forces 4 between
the particles 2.
[0019] In the plasma spraying process for the manufacture of the
coating 10 having a columnar structure as well as a dense
structure, the thermal process beam is generated by the plume of a
defocusing plasma beam (cf. EP-A-1 034 843). A coating material in
the form of the corpuscles 1 is injected with a carrier gas into
the plasma beam. The properties of the plasma beam are determined
by adjustable process parameters, in particular by the parameters
of process pressure, enthalpy and composition of a process gas
mixture. The method in accordance with the invention can also be
carried out using other thermal process beams than the plasma beam.
A further generalisation relates to the shape of the corpuscles 1.
Primary corpuscles are distinguished from secondary ones:
[0020] The primary corpuscles 1 are formed by liquid droplets or in
each case by an agglomerate of particles 2 which are held together
by cohesive forces 4 of a connecting medium 3 (binder) or by
adhesive forces. The adhesive forces are exerted directly between
the particles without any binder, with a mechanical
inter-engagement of surface structures (for example dendrites)
being able to effect these forces. Binder-free connections between
the particles 2 can also be generated by calcination at a low
calcinating temperature and/or with a short treatment period. At
this temperature or with this period, weak sintered connections are
formed at contact points between the particles 2 which can also be
understood as adhesive forces.
[0021] The droplet-like corpuscles 1 contain a chemical precursor
of the coating material in the form of a salt solution and are
transformed by thermal action in the process beam into the
secondary corpuscles containing particles. Such a salt is, for
example, zirconium nitrate which is transformed into zirconium
oxide while splitting off nitric oxides.
[0022] The primary or secondary corpuscles are disintegrated in the
process beam by mechanical and thermal interaction and the
particles are dispersed so that coating material is melted and
vaporized fully or partly by thermal action on the individual
particles. A thermal decomposition or vaporization of the
connecting medium 3 results from the thermal interaction. The
disintegration of the corpuscles 1 is illustrated by FIG. 3. The
medium 3 is thermally eliminated at the surfaces 20 of the
peripheral particles 2 so that the particles 2 are separated by
mechanical interaction and can be efficiently vaporized as
dispersed particles 2* by the plume. The mechanical interaction
results due to the viscosity of the plasma by shear forces between
the plasma and the corpuscles 1.
[0023] The spray powder of the plasma spraying method is an
aggregate of the primary corpuscles 1 which are formed in each case
by an agglomerate of the particles 2. These primary corpuscles 1
can be generated by spraying of a slurry or slip. The slurry is
made from the particles 2, from a liquid, a binder and, where
necessary, a dispersing agent. The sprayed slurry is dried and the
spray-dried material is used as a spray powder (with a
post-treatment as a rule being necessary by further communition and
sifting). The binder has been dissolved in the liquid of the slurry
at a high dilution so that the cohesive forces 4 generated by the
binder after the drying only effect a minimal holding together of
the particles. The disintegration capability of the corpuscles 1 in
the process beam can thereby be implemented.
[0024] Spray-dried spray powder can be manufactured as follows, for
example. Powder-form coating material is slurried with a suitable
liquid, preferably deionized water, and an organic binder to form a
slurry. CMC (carboxy methyl cellulose) is a preferred binder.
However, other known binders can also be used, for example PVA
(polyvinyl alcohol) or MC (methyl cellulose). In a preferred
embodiment of the slurry, the binder portion therein amounts to
between approximately 0.5 and 5% by weight with respect to the dry
weight of the coating material. The viscosity of the slurry
influences the size of the spray-dried corpuscles so that this size
can be varied simply by changing the liquid portion. The slurry is
a suspension, which can be stabilized using a dispersing agent, for
example using "Nopcosperse" (around 2% by weight).
[0025] The powder-form coating material can be gained by breaking
of a material present in block form which is manufactured, for
example, from a powder generated chemically and by precipitation
and subsequently sintered. The powder gained in this manner
consists of edged grains which are substantially more compact than
the particles of the original powder. The compaction can be carried
out in an induction oven or in an electrical arc.
[0026] The size distribution of the primary corpuscles 1 in the
diagram of FIG. 4 can be represented by a bell curve. (X=cumulated
volume portions; .DELTA.X=differential volume portions). This curve
can be characterized by three parameters, namely the maximum
diameters D.sub.i (i=10, 50, 90) for the volume portions X10%, X50%
and X90% which each include 10, 50 or 90% by volume of the primary
corpuscles 1.
[0027] The following ranges apply to the diameters of a spray
powder in accordance with the invention and to the corresponding
volume portions: for X10%: D.sub.10<10 .mu.m; for X50%:
D.sub.50<20 .mu.m; for X90%: D.sub.90<40 .mu.m.
In FIG. 4, D.sub.10=1. .mu.m, D.sub.50=4.94 .mu.m and
D.sub.90=12.60 .mu.m.
[0028] It is important for the invention that the primary
corpuscles 1 are not too large. The corpuscles 1 may also not be
too small so that the injecting into the process beam can take
place without complications. The diameters should be less than 35
.mu.m--corresponds to around--400 mesh. It might be advantageous if
said diameter is larger than around 5 .mu.m. The diameters for the
particles 2 of the primary corpuscles 1 can in the range between
0.1 and 5 .mu.m. In the extreme case, a primary corpuscle 1 can
comprise only one particle 2.
[0029] Three options are distinguished on how the coating material
can be injected into the process beam: I) in the form of slurry
droplets; II) in the form of droplets of the salt solution
explained above; and III) as spray powder in the form of solid
agglomerates. It in particular applies:
[0030] I) In the case of slurry droplets, capillary forces of a
liquid form the cohesive forces. In this connection, this liquid,
which as a rule contains a dispersing agent (but not a binder), has
been used for the slurrying of the particles and for the generation
of the slurry. The spraying of the slurry is carried out directly
before the entry into the plasma beam.
[0031] II) The spraying of the salt solution is carried out
directly before the entry into the process beam so that the
particles of the secondary corpuscles are generated in the process
beam.
[0032] III) If the coating material is used as a spray powder, the
binder portion after the drying of the slurry droplets should
amount to a maximum of 5% by weight and a minimum of 0.5% by
weight. The binder portion preferably lies in the range between 1
and 2% by weight.
[0033] The following materials can be used, for example, for the
slurry: as the liquid, demineralized water or an organic solvent,
in particular an alcohol;
[0034] as the dispersing agent, polycarbonic acid, a
polycarboxylate compound or a polymetacarboxylate compound,
polyethyleneimines or an amino alcohol;
[0035] and as the binder, polyvinyl alcohol, polyvinyl pyrolidine,
polysaccharide, acrylic polymers and copolymers, starch, polyvinyl
propylene, polyethylene glycols or a cellulose compound, for
example carboxy methyl cellulose, methyl cellulose or
hydroxyethylcellulose.
[0036] If the method in accordance with the invention is carried
out as a plasma spraying process, this is done in accordance with
the following specifications: a) a value is selected for the
chamber process pressure between 50 and 5,000 Pa, preferably
between 100 and 500 Pa. The specific enthalpy of the plasma beam is
generated by delivering an effective power which is to be
determined empirically and which lies, according to experience, in
the range from 20 to 100 kW, preferably 40 to 80 kW.
[0037] b) The process gas includes a mixture of inert gases, in
particular a mixture of argon Ar and helium He, and furthermore,
optionally, hydrogen, nitrogen and/or a reactive gas, with the
volume ratio of Ar to He advantageously lying in the range from 2:1
to 1:4 and the total gas flow lying in the range from 30 to 150
SLPM.
[0038] c) The primary corpuscles 1 are injected at a conveying rate
between 5 and 60 g/min, preferably between 10 and 40 g/min.
[0039] d) The substrate is preferably moved relative to a cloud of
the vaporised coating material during the material application, in
particular by rotary or pivot movements and/or by translatory
movements.
[0040] A coating material is used whose portion which can be
vaporized amounts to at least 70%. The plasma beam is generated
with a sufficiently high specific enthalpy so that at least 5% of
the coating material, preferably at least 50%, is transformed into
the vapor phase during vaporisation.
[0041] The particles 2 form a homogeneous or heterogeneous mixture
with materials which are the same or different in the primary
corpuscles 1.
[0042] The particles 2 can form a mixture of materials which react
chemically in the process beam after the vaporisation at least
partly with one another or with a reactive gas of the process gas
mixture. The reaction products are condensed out during
coating.
[0043] In the manufacture of a TBC coating having a columnar
structure, an advantageous connection of the coating to the
substrate arises onto which the columnar coating is applied.
Whereas a large-area peeling of the coatings caused by thermal
strain variation is observed with non-columnar coatings, the same
thermal strain variation results in milder damage with the columnar
coating: A dandruff like precipitation of relatively small-area
coating islands is created.
[0044] In a preferred process management, regions of the substrate
100 are coated which are located in the geometrical shadow of the
process beam. Thermal spray processes are usually so-called
"line-of-sight processes", that is the substrate 100 is only coated
where the thermal process beam impacts directly. Regions which are
located in the geometrical shadow, that is are not directly exposed
to the process beam, are not coated in such processes.
[0045] It is, however, also possible with the method in accordance
with the invention to coat regions of the substrate 100 which are
not directly exposed--in the geometrical sense--to the process
beam. That is, "non-line-of-sight" coating can also be carried out
with the method in accordance with the invention. Coating can take
place so-to-say around the corner. This should be explained in the
following with respect to FIG. 5 and to FIG. 6.
[0046] FIG. 5 shows, in a very simplified representation, a segment
of a turbine which is designated in total by the reference numeral
50. FIG. 6 shows this segment 50 in a sectional presentation, with
the cut taking place parallel to a base plate designated by 51 in
FIG. 5.
[0047] The turbine, for example, a gas turbine, usually includes a
plurality of rotating impellers and stationary guide elements. Both
the impellers and the guide elements each include a plurality of
turbine vanes 52. The turbine vanes 52 can each be mounted
individually at their foot to a common axle of the turbine or they
can be provided in the faun of segments which each include a
plurality of turbine vanes 52. This configuration is frequently
called a cluster-vane segment or, depending on the number of
turbine vanes, a double-vane segment, a triple-vane segment,
etc.
[0048] In FIG. 5 and in FIG. 6, there is shown in a very simplified
representation such a segment 50 of a gas turbine which includes
two turbine vanes 52 which each extend from the base plate 51 up to
a cover plate 53. The segment 50 can be in one piece or consist of
a plurality of individual parts. The presentation of details known
per se such as cooling air bores or cooling air passages has been
omitted in FIGS. 5 and 6 for reasons of better clarity.
[0049] In such substrates 100 such as the segment 50, geometrical
shadow regions, hidden regions, or otherwise covered regions exist
which cannot be acted on directly--in the geometrical sense--by the
process beam. Such regions are designated by the reference symbol B
in FIG. 6. It is frequently the case that such regions B can also
not be reached due to a rotation of the substrate 100 in the
process beam or due to another relative movement between the
process beam and the substrate.
[0050] A coating can also be manufactured using the method in
accordance with the invention in such regions B which are located
in the geometrical shadow of the process beam, that is not in the
line-of-sight of the process beam. It is consequently possible with
the method in accordance with the invention to coat around corners,
edges and rounded portions.
[0051] This is in particular advantageous for the coating of
turbine vanes of gas turbines and specifically for segments of such
turbines which include two or more turbine vanes.
[0052] In addition, the method in accordance with the invention
also allows to coat regions of the substrate 100 that are at a low
incidence angle of less than 45 degrees relative to the process
beam. Most thermal spray processes operate at a perpendicular
incidence angle in order for the particles to deposit. Reducing
this angle usually reduces effectiveness in achieving a desirable
coating (both in thickness and structure). The benefit of the
method according to the invention is it can deposit at low
incidence angles and/or non-line-of-sight.
* * * * *