U.S. patent application number 13/808216 was filed with the patent office on 2013-05-09 for thermal barrier for turbine blades, having a columnar structure with spaced-apart columns.
This patent application is currently assigned to SNECMA. The applicant listed for this patent is Fabrice Crabos, Sarah Hamadi, Juliette Hugot, Andre Hubert Louis Malie, Justine Menuey. Invention is credited to Fabrice Crabos, Sarah Hamadi, Juliette Hugot, Andre Hubert Louis Malie, Justine Menuey.
Application Number | 20130115085 13/808216 |
Document ID | / |
Family ID | 43567933 |
Filed Date | 2013-05-09 |
United States Patent
Application |
20130115085 |
Kind Code |
A1 |
Menuey; Justine ; et
al. |
May 9, 2013 |
THERMAL BARRIER FOR TURBINE BLADES, HAVING A COLUMNAR STRUCTURE
WITH SPACED-APART COLUMNS
Abstract
A process for depositing a ceramic layer on a metal substrate
for producing a thermal barrier, the process including depositing
the ceramic in a columnar structure. The deposition is carried out
through a grid pierced with holes, which is positioned parallel to
a surface of the substrate so as to produce ceramic columns
separated from one another by a space. The process can further
include a subsequent depositing of an isotropic ceramic layer in
the spaces.
Inventors: |
Menuey; Justine; (Annecy,
FR) ; Hamadi; Sarah; (Paris, FR) ; Hugot;
Juliette; (Jaunay-Clan, FR) ; Malie; Andre Hubert
Louis; (Chatellerault, FR) ; Crabos; Fabrice;
(Assat, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Menuey; Justine
Hamadi; Sarah
Hugot; Juliette
Malie; Andre Hubert Louis
Crabos; Fabrice |
Annecy
Paris
Jaunay-Clan
Chatellerault
Assat |
|
FR
FR
FR
FR
FR |
|
|
Assignee: |
SNECMA
Paris
FR
|
Family ID: |
43567933 |
Appl. No.: |
13/808216 |
Filed: |
July 5, 2011 |
PCT Filed: |
July 5, 2011 |
PCT NO: |
PCT/FR2011/051596 |
371 Date: |
January 3, 2013 |
Current U.S.
Class: |
416/95 ; 427/265;
428/119 |
Current CPC
Class: |
F01D 5/288 20130101;
C23C 4/02 20130101; C23C 18/1225 20130101; C23C 14/58 20130101;
F05D 2230/90 20130101; C23C 18/1245 20130101; C23C 18/06 20130101;
F05D 2300/21 20130101; C23C 14/30 20130101; Y10T 428/24174
20150115; C23C 14/042 20130101; F01D 5/284 20130101; C23C 18/1208
20130101; Y02T 50/67 20130101; Y02T 50/6765 20180501; C23C 18/1254
20130101; Y02T 50/60 20130101 |
Class at
Publication: |
416/95 ; 428/119;
427/265 |
International
Class: |
F01D 5/28 20060101
F01D005/28 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 6, 2010 |
FR |
1055462 |
Claims
1-12. (canceled)
13. A process for depositing a ceramic layer onto a metallic
substrate for producing a thermal barrier, comprising: depositing
the ceramic in a columnar structure, the depositing taking place
through a grid pierced with holes, positioned parallel to a surface
of the substrate so as to produce at least two columns of ceramic
that are separated from one another by a spacing; and a subsequent
depositing an isotropic layer of ceramic in the spacings.
14. The process as claimed in claim 13, wherein a width of the
holes is between 10 and 300 microns.
15. The process as claimed in claim 13, wherein the spacing between
the holes is between 10 and 100 microns.
16. The process as claimed in claim 13, wherein the second
depositing is carried out by an operation for dip-coating the
substrate including its columns into a solution of sol-gel
type.
17. The process as claimed in claim 16, wherein the isotropic
depositing is carried out by a sequence of dip-coating and
withdrawal operations in the sol-gel solution and drying operations
carried out between two dip-coating and withdrawal operations,
until a thickness substantially equal to a height of the columns is
obtained.
18. The process as claimed in claim 13, further comprising a heat
treatment.
19. A thermal barrier deposited on a metallic substrate,
comprising: ceramic columns that extend perpendicular to a surface
of the substrate and that are separated from one another by
spacings, the spacings being filled with an isotropic ceramic
layer.
20. The thermal barrier as claimed in claim 19, wherein the columns
have a maximum width of between 10 and 300 microns.
21. The thermal barrier as claimed in claim 19, wherein the
spacings have a width of between 10 and 100 microns.
22. The thermal barrier as claimed in claim 19, wherein the
isotropic layer is made of porous ceramic.
23. A turbine blade for a turbomachine comprising a thermal barrier
as claimed in claim 19.
24. A turbomachine comprising at least one turbine blade as claimed
in claim 23.
Description
[0001] The field of the present invention is that of turbomachines
and, more particularly that of components for these turbomachines
which are subjected to high temperatures.
[0002] A turbomachine, as used for propulsion in the aeronautical
field, comprises an atmospheric air intake that communicates with
one or more compressors, generally including a fan, which are
rotated about one and the same axis. The main stream of this air,
after having been compressed, supplies a combustion chamber
positioned annularly around this axis and is mixed with a fuel in
order to provide hot gases, downstream, to one or more turbines
through which these hot gases are expanded, the turbine rotors
driving the rotors of the compressors. The engines operate at a
temperature of the engine gases at the turbine inlet which is
sought to be as high as possible because this temperature
conditions the performances of the turbomachine. For this purpose,
the materials of the hot sections are selected to withstand these
operating conditions and the walls of the components swept by the
hot gases, such as the turbine nozzles or the rotating turbine
blades, are provided with cooling means. Furthermore, due to the
metallic structure of these blades, made of a superalloy based on
nickel or on cobalt, it is also necessary to protect them against
the erosion and corrosion which are generated by the constituents
of the engine gases at these temperatures.
[0003] Among the protections devised for enabling these components
to withstand these extreme conditions is the deposition of a
coating, referred to as a thermal barrier, on their outer face. A
thermal barrier is generally composed of a ceramic layer of around
a hundred microns, which is deposited at the surface of the
metallic layer. An aluminum sublayer, of a few tens of microns,
placed between the ceramic and the metallic substrate, completes
the thermal barrier by providing the connection between these two
components and also the protection of the underlying metal against
oxidation. This aluminum sublayer, which is generally deposited by
a vapor phase aluminization process (referred to as APVS for the
version of the process used by the applicant), is fastened to the
substrate by metallic interdiffusion and forms a protective oxide
layer at the surface. An example of the implementation of this
technique is described in patent application FR 2928664 by the
applicant.
[0004] As regards the actual thermal barrier, made of ceramic, it
may be produced in several ways, depending on the use which will be
made thereof. Two types of structures are roughly distinguished for
thermal barriers: columnar barriers, the structure of which is that
of columns juxtaposed next to one another and which extend
perpendicular to the surface of the substrate, and laminar or
isotropic barriers that extend in uniform layers over the surface
of the substrate.
[0005] The first ones are generally produced by a process referred
to as EBPVD (electron beam physical vapor deposition) in which a
target anode is bombarded, under high vacuum, by an electron beam
emitted by a charged tungsten filament. The electron beam makes the
molecules from the target pass into the gaseous phase. These
molecules then precipitate in a solid form, covering the part to be
protected with a thin layer of the anode material. These thermal
barriers are characterized by a good resistance to thermal cycling
but also by a relatively high thermal conductivity.
[0006] The isotropic barriers are generally deposited by plasma,
using a thermal spraying process of the APS (atmospheric plasma
spraying) type or by a sol-gel process. The sol-gel process makes
it possible, via a simple polymerization of molecular precursors in
solution, to obtain, at a temperature close to ambient temperature,
glassy materials without passing through a melting step. These
precursors exist for a large number of metals and are, for the most
part, soluble in standard solvents. In this liquid phase that is
denoted under the name of sol, the chemical reactions contribute to
the formation of a three-dimensional inorganic network, known under
the name of gel, in which the solvent remains. The process of
obtaining the material, from the gel, passes through a drying step
which consists in evacuating the solvent out of the polymer
network. The advantage of such a barrier is the porosity that it
exhibits.
[0007] The isotropic barriers are therefore characterized by a low
thermal conductivity, which is the desired objective, but they have
an inadequate resistance to thermal cycling. The barriers obtained
by the sol-gel process have, themselves, a mediocre erosion
resistance.
[0008] Finally, multi-fissured thermal barriers are known, which
are obtained by plasma using a process described in several patents
by the applicant (EP 1 645 654 and EP 1 471 162), which exhibit an
acceptable compromise between the service life and the erosion
resistance.
[0009] All these barriers are not however sufficiently
high-performance and it is necessary to further improve their
performances in these two domains.
[0010] The objective of the present invention is to overcome these
drawbacks by proposing a process for producing a thermal barrier
which does not comprise some of the drawbacks of the prior art and,
in particular, which has a low conductivity combined with a good
service life.
[0011] For this purpose, one subject of the invention is a process
for depositing a ceramic layer onto a metallic substrate for
producing a thermal barrier, comprising a step of depositing said
ceramic in a columnar structure, characterized in that said
deposition is carried out through a grid pierced with holes,
positioned parallel to the surface of the substrate so as to
produce at least two columns of ceramic which are separated from
one another by a spacing.
[0012] The columns thus produced are sufficient to ensure the
mechanical strength of the barrier and its erosion resistance and
leave, furthermore, space between them in order to fill the latter
with the most appropriate material. The invention thus creates a
great flexibility for the composition of the thermal barrier.
[0013] Advantageously, the width of the holes is between 10 and 300
microns.
[0014] Preferably, the spacing between the holes is between 10 and
100 microns.
[0015] In one particular embodiment, the process also comprises a
subsequent step of depositing an isotropic layer of ceramic in said
spacings.
[0016] The isotropic structure of the deposit in the spacings
guarantees a good impermeability of the barrier against the
invasion of oxidizing gases from the stream in the direction of the
substrate.
[0017] Advantageously, the second deposition is carried out by an
operation for dip-coating the substrate equipped with its columns
into a solution of sol-gel type.
[0018] A ceramic with an isotropic structure is thus obtained,
which has a high porosity and therefore a low thermal
conductivity.
[0019] Preferably, the isotropic deposition is carried out by a
sequence of dip-coating and withdrawal operations in said sol-gel
solution and drying operations carried out between two dip-coating
and withdrawal operations, until a thickness substantially equal to
the height of the columns is obtained.
[0020] In this configuration, the columns ensure both a good
mechanical strength and a protection of the isotropic layer.
[0021] Advantageously, the process also comprises a final step of
heat treatment.
[0022] The invention also relates to a thermal barrier deposited on
a metallic substrate, characterized in that it comprises ceramic
columns that extend perpendicular to the surface of said substrate
and that are separated from one another by spacings, said spacings
being filled with an isotropic ceramic layer.
[0023] Advantageously, the columns have a maximum width of between
10 and 300 microns.
[0024] Preferably, the spacings have a width of between 10 and 100
microns.
[0025] In one particular embodiment, the isotropic layer is made of
porous ceramic.
[0026] The invention finally relates to a turbine blade for a
turbomachine comprising a thermal barrier as described above and to
a turbomachine comprising at least one such blade.
[0027] The invention will be better understood, and other
objectives, details, features and advantages thereof will become
more clearly apparent in the course of the detailed explanatory
description which follows of an embodiment of the invention given
by way of purely illustrative and non-limiting example, with
reference to the appended schematic drawings.
[0028] In these drawings:
[0029] FIG. 1 is a schematic view of the physical composition of a
thermal barrier for a turbine blade;
[0030] FIG. 2 is a schematic cross-sectional view of a thermal
barrier after carrying out a first step of a process according to
one embodiment of the invention;
[0031] FIG. 3 represents the four phases for carrying out the
second step of the process according to one embodiment of the
invention;
[0032] FIG. 4 is a schematic cross-sectional view of a thermal
barrier at the end of the process according to the invention.
[0033] With reference to FIG. 1, seen in cross section is the
composition of a thermal barrier deposited on the surface of a
turbine blade, the latter being based by a stream of hot gas
represented by an arrow pointed toward the left of the figure. The
metal constituting the blade, typically a superalloy based on
nickel or cobalt, forms a substrate 1, deposited on which is a
sublayer made of aluminum 2, sandwiched between the substrate 1 and
a ceramic layer 3. The role of the aluminum sublayer is to retain
the ceramic layer and to offer a certain elasticity to the assembly
in order to enable it to absorb the difference in expansion,
represented by two arrows in opposite directions, that exists
between the high-expansion substrate 1 and the low-expansion
ceramic 3.
[0034] The ceramic 3 represented here is of columnar structure,
which allows lateral displacements, owing to the appearance of
cracks between the columns, and which gives it a good service life.
The aluminum is then brought into contact with the oxygen conveyed
by the gases that circulate in the stream of the turbomachine,
which results in an average thermal conductivity of the barrier and
a gradual damaging thereof.
[0035] Referring now to FIG. 2, the progress of the production of a
thermal barrier after the implementation of the first step of the
process according to the invention is seen. Placed on top of the
substrate 1 to be covered is a grid 10 formed of evenly-spaced
holes 11 so as to let through the vapor-phase deposition carried
out by the EBPVD process or by any other process enabling the
production of a columnar deposition (such as for example the APS
process under very low pressure, carried out by the company Sulzer
and known under the name LPPS-TF). The grid forms a mask which
enables the deposition of the ceramic in the form of columns or of
a group of columns 5 spaced apart from one another. The spacing
thereof is, on the one hand, large enough so that a subsequent
inter-columnar deposition can be carried out and, on the other
hand, close enough to guarantee the mechanical strength of the
whole of the thermal barrier. Typically, the columns or the groups
of columns 5 have a thickness between 10 and 300 microns and the
spacing 6 between them varies between one and a few tens of
microns.
[0036] At the end of this first step, the thermal barrier is in the
situation represented, with a substrate 1 and a sublayer 2 which
are surmounted by an assembly of columns 5 made of ceramic. These
columns conventionally have a shape which gets wider towards the
top and which results from the gradual aggregation of the particles
deposited. Between these columns are empty spaces which will be
filled during the second step of the process according to the
invention.
[0037] FIG. 3 shows, in four diagrams referenced 3a to 3d, the
carrying out of this second step. Each diagram corresponds to a
phase during which:
[0038] 1-phase 3a: the substrate equipped with its ceramic columns
5 is dip-coated in a solution 20 of sol-gel type based in
particular on precursors of yttriated zirconia, which is used in
the processes for producing an isotropic thermal barrier. The
viscosity of the solution is such that it is sufficiently fluid in
order to be able to be inserted into the spacing 6 between the
columns 5 and fill them completely, and it is sufficiently viscous
so that it remains stuck to the component during the withdrawal
thereof;
[0039] 2-phase 3b: the component to be covered remains submerged in
the solution 20 long enough for the spacing 6 between the columns 5
to be correctly filled;
[0040] 3-phase 3c: the component is then withdrawn from the
solution 20 at a controlled speed so that a film of a desired
thickness can be formed at the surface of the thermal barrier,
homogeneously and with good adhesion;
[0041] 4-phase 3d: it is dried so that the solution 20 which has
remained trapped between the columns 5 solidifies. After drying and
removal of the solvent, a thin layer of ceramic is obtained which
remains lodged between the columns. Since the thickness of ceramic
deposited during the fourth phase is very small, it is necessary to
carry out the operation, known as dip-coating, several times, that
is to say to repeat the four operations after the drying of each of
the layers formed in 3d.
[0042] FIG. 4 gives the result obtained after repetition of the
four operations from FIG. 3. The substrate 1 and its sublayer 2 are
covered with a thermal barrier 3 composed of evenly-spaced columns
5, between which ceramic is deposited in isotropic form 7. This
isotropic layer has many air bubbles that are trapped, which gives
it a high porosity, and also gives the thermal barrier a good
resistance to heat conduction.
[0043] The procedure of the process for producing a thermal barrier
according to the invention will now be described.
[0044] The substrate constituting the material of the blade to be
protected is first covered with a sublayer made of aluminum or of
any other metal capable of constituting a thermal barrier sublayer.
It is placed in equipment for the deposition of a ceramic layer,
for example by electron beam physical vapor deposition, by
positioning a grid 10, pierced with holes 11, on top of the
component to be protected, at a distance that enables the formation
of ceramic columns or a group of ceramic columns. The deposition
takes place through holes 11 and the ceramic is deposited on the
substrate 1 by growing perpendicularly to said substrate. Due to
the mask generated by the solid parts of the grid 10, the
deposition takes place along columns 5 distributed discretely over
the surface of the substrate 1; between these columns 5 empty
spacings 6 remain, which will be filled during the next step of the
process. The component to be protected is then withdrawn from the
columnar deposition equipment and transferred to a second piece of
equipment for the deposition of the porous portion.
[0045] The second step of the process consists of a succession of
dip-coating operations in a sol-gel type solution, comprising the
four phases described previously. During each of these operations,
the spacings 6 are filled with a thin layer of porous ceramic which
accumulates, dip coating after dip coating, until a layer 7 is
formed that completely fills the spacings 6.
[0046] The production of the thermal barrier is completed by a
conventional heat treatment, during which the ceramic is stabilized
and acquires the desired crystalline structure.
[0047] Finally, a mixed thermal barrier is obtained that comprises,
on the one hand, a series of columns 5 which ensure a good
mechanical strength and a good resistance to erosion by the gases
which sweep over the component, and, on the other hand, a highly
porous isotropic layer which ensures a good resistance to thermal
conduction in the direction of the substrate. This protects the
substrate 1 and the sublayer 2 against oxidation by the gases from
the stream that circulates in the engine. Furthermore, the presence
of columns enables the thermal barrier to spread out longitudinally
over the surface of the substrate, during the expansion thereof,
without risking the appearance of cracks which would enable oxygen
from the gases to reach the metal of the substrate and damage
it.
[0048] The objective of having a thermal barrier which combines a
low thermal conductivity, a good erosion resistance and a good
adaptation to thermo mechanical stresses, is thus achieved.
[0049] The first step of the production of the thermal barrier was
described using the EBPVD process, but it can just as well be
carried out with the other known deposition processes, such as
thermal spraying, the presence of the mask formed by the grid being
sufficient to generate the desired columnar structure during this
step.
* * * * *