U.S. patent application number 16/084583 was filed with the patent office on 2019-03-14 for method for manufacturing an abradable plate and repairing a turbine shroud.
This patent application is currently assigned to SAFRAN AIRCRAFT ENGINES. The applicant listed for this patent is CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE, SAFRAN AIRCRAFT ENGINES, UNIVERSITE PAUL SABATIER-TOULOUSE III. Invention is credited to Yannick Marcel BEYNET, Geoffroy CHEVALLIER, Romain EPHERRE, Claude ESTOURNES, Jean-Baptiste MOTTIN.
Application Number | 20190076930 16/084583 |
Document ID | / |
Family ID | 56511659 |
Filed Date | 2019-03-14 |
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United States Patent
Application |
20190076930 |
Kind Code |
A1 |
MOTTIN; Jean-Baptiste ; et
al. |
March 14, 2019 |
METHOD FOR MANUFACTURING AN ABRADABLE PLATE AND REPAIRING A TURBINE
SHROUD
Abstract
The invention relates to a method for manufacturing an abradable
plate (32) for a turbomachine turbine shroud (24, 26), the method
comprising preparing a mixture comprising a cobalt- or nickel-based
metal powder and a powder based on a fluxing element, depositing a
layer of the powder mixture in a mold, and making the abradable
plate (32) by subjecting the powder mixture layer to a method of
SPS sintering. The invention also provides a method of preparing a
turbine shroud (24, 26) for a turbomachine.
Inventors: |
MOTTIN; Jean-Baptiste;
(Moissy-Cramayel, FR) ; BEYNET; Yannick Marcel;
(Toulouse, FR) ; CHEVALLIER; Geoffroy;
(Auzeville-Tolosane, FR) ; EPHERRE; Romain;
(Toulouse, FR) ; ESTOURNES; Claude; (Rieumes,
FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SAFRAN AIRCRAFT ENGINES
CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE
UNIVERSITE PAUL SABATIER-TOULOUSE III |
Paris
Paris
Toulouse |
|
FR
FR
FR |
|
|
Assignee: |
SAFRAN AIRCRAFT ENGINES
Paris
FR
CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE
Paris
FR
UNIVERSITE PAUL SABATIER-TOULOUSE III
Toulouse
FR
|
Family ID: |
56511659 |
Appl. No.: |
16/084583 |
Filed: |
March 10, 2017 |
PCT Filed: |
March 10, 2017 |
PCT NO: |
PCT/FR2017/050548 |
371 Date: |
September 13, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B22F 7/008 20130101;
B22F 7/02 20130101; B22F 3/105 20130101; F05D 2230/22 20130101;
F05D 2240/11 20130101; B22F 5/009 20130101; F05D 2230/237 20130101;
B22F 7/06 20130101; B22F 7/062 20130101; F01D 11/122 20130101; F05D
2230/61 20130101; B22F 5/106 20130101 |
International
Class: |
B22F 5/00 20060101
B22F005/00; B22F 5/10 20060101 B22F005/10 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 14, 2016 |
FR |
1652104 |
Claims
1. A method for manufacturing an abradable plate for a turbomachine
turbine shroud, the method comprising the following steps:
preparing a mixture comprising a cobalt- or nickel-based metal
powder and a powder based on a fluxing element; depositing a layer
of the powder mixture in a mold; and making the abradable plate by
subjecting the powder mixture layer to a method of SPS sintering;
and wherein at least two layers of the powder mixture are deposited
in the mold, the two layers being spaced apart from each other by a
chemically inert insert.
2. A method according to claim 1, wherein the chemically inert
insert comprises boron nitride or corundum.
3. A method according to claim 2, wherein boron nitride forms an
outer layer of the chemically inert insert.
4. A method according to claim 1, wherein the fluxing element is
silicon or boron.
5. A method according to claim 1, wherein the powder mixture
comprises a percentage by weight of the fluxing element that is
less than or equal to 5% by weight.
6. A method according to claim 1, wherein the mold is made of
graphite, and wherein the SPS sintering is performed at a
temperature higher than or equal to 800.degree. C.
7. A method according to claim 1, wherein the mold is made of
tungsten carbide, and wherein the SPS sintering is performed at a
temperature higher than or equal to 500.degree. C.
8. A repairing method for repairing a turbine shroud for a
turbomachine, the method comprising the following steps: removing a
damaged abradable coating; and brazing onto the turbine shroud an
abradable plate obtained in accordance with claim 1.
9. A repairing method according to claim 8, wherein after the
abradable plate has been brazed onto the turbine shroud, a free
surface of the brazed abradable plate is machined.
Description
BACKGROUND OF THE INVENTION
[0001] The present disclosure relates to a method for manufacturing
a turbine shroud for a turbomachine.
[0002] In numerous rotary machines, it is now known to provide the
ring of the stator with abradable tracks facing the tips of the
blades of the rotor. Such tracks are made using so-called
"abradable" materials, which, when they come into contact with
rotating blades, become worn more easily than the blades
themselves. This serves to ensure minimum clearance between the
rotor and the stator, thereby improving the performance of the
rotary machine, without running the risk of damaging the blades in
the event of them rubbing against the stator. On the contrary, such
rubbing erodes the abradable track, thereby acting automatically to
match the diameter of the ring of the stator as closely as possible
to the rotor. Thus, such abradable tracks are often installed in
turbomachine compressors.
[0003] In contrast, use of such tracks is less common in the
turbines of such turbomachines, and in particular in the high
pressure turbines in which physico-chemical conditions are
extreme.
[0004] Specifically, the burnt gas coming from the combustion
chamber flows into the high-pressure turbine at very high levels of
temperature and pressure, thereby leading to premature wear of
conventional abradable tracks.
[0005] Under such circumstances, in order to protect the turbine
shroud, it is often preferred to provide it with a thermal barrier
type coating made of materials that serve to protect the shroud
against erosion and corrosion and that present density that is
high, too high for the coating to be effectively abradable.
[0006] Nevertheless, under such circumstances, it can naturally be
understood that the integrity of the blades is no longer ensured in
the event of coming into contact with the stator, which makes it
necessary to provide greater clearance between the rotor and the
stator, and therefore increases the rate of leakage past the tips
of the blades, thus reducing the performance of the turbine.
[0007] Furthermore, because of spots of rubbing against the blades
and because of the temperature of the burnt gas, the coating can
become damaged, thereby providing the stator with less
protection.
OBJECT AND SUMMARY OF THE INVENTION
[0008] The present disclosure seeks to remedy these drawbacks, at
least in part.
[0009] To this end, the present disclosure relates to a method for
manufacturing an abradable plate for a turbomachine turbine shroud,
the method comprising the following steps:
[0010] preparing a mixture comprising a cobalt- or nickel-based
metal powder and a powder based on a fluxing element;
[0011] depositing a layer of the powder mixture in a mold; and
[0012] making the abradable plate by subjecting the powder mixture
layer to a method of SPS sintering.
[0013] The term "cobalt-based" is used to mean a metal powder in
which cobalt presents the greatest percentage by weight. Likewise,
the term "nickel-based" is used to mean a metal powder in which
nickel presents the greatest percentage by weight. Thus, by way of
example, a metal powder comprising 38% by weight cobalt and 32% by
weight nickel is referred to as a cobalt based powder, since cobalt
is the chemical element having the greatest percentage by weight in
the metal powder.
[0014] Cobalt- or nickel-based metal powders are powders that
present good high-temperature strength after sintering. They can
thus perform the two functions of being abradable and of providing
a heat shield. For example, mention may be made of CoNiCrAlY
superalloys. These metal powders also have the advantage of
presenting a chemical composition that is similar to the chemical
composition of the material forming the turbine shroud, e.g. AM1 or
N5 superalloy.
[0015] The powder based on a fluxing element makes it possible to
reduce the sintering temperature of the powder mixture.
[0016] The SPS sintering method (SPS standing for "spark plasma
sintering") is also known as field assisted sintering technology
(FAST), or as flash sintering, and it is a method of sintering
during which a powder is subjected simultaneously to high-current
pulses and to uniaxial pressure in order to form a sintered
material. SPS sintering is generally performed under a controlled
atmosphere, and it may be assisted by heat treatment.
[0017] The duration of SPS sintering is relatively short, and SPS
sintering makes it possible to select starting powders with
relatively few limitations. Specifically, SPS sintering makes it
possible in particular to sinter, i.e. to densify, materials that
are relatively complicated to weld, or indeed impossible to weld,
because they are materials that crack easily when heated. As a
result of selecting SPS sintering and of the short duration of such
sintering, it becomes possible to make an abradable layer out of a
very wide variety of materials.
[0018] Furthermore, since SPS sintering is performed under uniaxial
pressure exerted by the mold on the powder layer, the shrinkage of
the powder layer that results from the sintering for producing the
abradable plate is restricted to the direction in which pressure is
applied. No shrinkage of the powder layer is thus to be observed in
directions perpendicular to the direction in which pressure is
applied. Thus, it is relatively simple to control the dimensions of
the abradable plate.
[0019] It is possible to deposit at least two layers of the powder
mixture in the mold, the two layers being spaced apart from each
other by a chemically inert insert.
[0020] Is thus possible to make a plurality of abradable plates in
a single SPS sintering step. By way of example, it is thus possible
to deposit ten layers of powder mixture, each layer being separated
from an adjacent layer by a chemically inert insert. It is thus
possible to form ten abradable plates, each having thickness that
may lie in the range 1 millimeter (mm) to 5 mm, each of the
abradable plates being separated from an adjacent abradable plate
by a chemically inert insert.
[0021] During SPS sintering, the chemically inert insert makes it
possible to reduce chemical reactions between the layers of powder
mixtures or indeed to eliminate them.
[0022] Since each layer of powder mixture is separated from the
adjacent layer by a chemically inert insert, the layers of powder
mixture do not sinter to one another and it is therefore easier to
make a plurality of abradable plates that do not stick
together.
[0023] The chemically inert insert may also be arranged between the
powder mixture and the mold.
[0024] During SPS sintering, the chemically inert insert makes it
possible to reduce chemical reactions between the layer of powder
mixture and the mold, or even to eliminate them, and thus to reduce
any sticking of the abradable plate to portions of the mold, or
even to eliminate any such sticking.
[0025] The chemically inert insert also makes it possible to reduce
the formation of a layer of carbide at the surface of the abradable
plate that is in contact with the mold, or even to eliminate any
such formation. It is desirable to avoid forming such a carbide
layer since any carbide layer that is formed needs to be removed
from the abradable plate before it is used.
[0026] The chemically inert insert may comprise boron nitride or
corundum.
[0027] When the chemically inert insert is said to "comprise" boron
nitride, that is used to mean that the insert comprises at least
95% by weight boron nitride. Likewise, when the chemically inert
insert is said to "comprise" corundum, that is used to mean that
the insert comprises at least 95% by weight corundum.
[0028] The chemically inert insert may be in the form of a layer of
boron nitride deposited on the mold by using a spray. The
chemically inert insert may also be in the form of a plate
reproducing the shape of the abradable plate. Thus, during the step
of SPS sintering, the chemically inert insert makes it possible to
impart its shape to the abradable plate.
[0029] Boron nitride may form an outer layer of the chemically
inert insert.
[0030] The chemically inert insert may be a plate of dense material
covered by a layer of boron nitride deposited onto the plate by
means of a spray.
[0031] The fluxing element may be silicon or boron.
[0032] The powder mixture may comprise a percentage by weight of
the fluxing element that is less than or equal to 5% by weight,
preferably less than or equal to 3% by weight.
[0033] The mold may be made of graphite, and the SPS sintering may
be performed at a temperature higher than or equal to 800.degree.
C., preferably higher than or equal to 900.degree. C.
[0034] The SPS sintering is performed at a pressure higher than or
equal to 10 megapascals (MPa), preferably higher than or equal to
20 MPa, still more preferably higher than or equal to 30 MPa.
[0035] The mold may be made of tungsten carbide, and the SPS
sintering may be performed at a temperature higher than or equal to
500.degree. C., preferably higher than or equal to 600.degree.
C.
[0036] The SPS sintering may be performed at a pressure higher than
or equal to 100 MPa, preferably higher than or equal to 200 MPa,
still more preferably higher than or equal to 300 MPa.
[0037] The present disclosure also relates to a repair method for
repairing a turbomachine turbine shroud, the method comprising the
following steps:
[0038] removing a damaged abradable coating; and
[0039] brazing onto the turbine shroud an abradable plate obtained
by the above-defined method.
[0040] The fluxing element included in the powder mixture used for
forming the abradable plate also serves to facilitate the method of
brazing the abradable plate onto the turbine shroud.
[0041] Brazing the abradable plate onto the turbine shroud makes it
possible to avoid depositing a new abradable coating directly onto
the shroud or onto the shroud sector.
[0042] Specifically, after the abradable plate has been brazed onto
the turbine shroud, a free surface of the brazed abradable plate
may be machined.
[0043] An abradable plate that has just been brazed onto the
turbine shroud may present a free surface that need not necessarily
extend the free surface of the adjacent undamaged abradable
coating. Thus, the free surfaces of the abradable plate and of the
abradable coating are machined so as to present a surface for
facing the turbine wheel that presents as little discontinuity as
possible. Specifically, if any such discontinuity is present, then
the turbine wheel could strike against such a discontinuity,
thereby leading to impacts within the turbine, which is not
desirable.
BRIEF DESCRIPTION OF THE DRAWINGS
[0044] Other characteristics and advantages of the invention appear
from the following description of implementations of the invention,
given as nonlimiting examples, and with reference to the
accompanying figures, in which:
[0045] FIG. 1 is a diagrammatic longitudinal section view of a
turbomachine;
[0046] FIG. 2 is a diagrammatic perspective view of a turbine
shroud sector including an abradable plate;
[0047] FIG. 3 is a diagrammatic perspective view of a stack of
abradable plates and of chemically inert inserts;
[0048] FIG. 4 is a diagrammatic section view of a stack in the mold
for SPS sintering, on a section plane similar to the section plane
IV-IV of FIG. 3;
[0049] FIGS. 5A-5D are scanning electron microscope images showing
the microstructure of the various abradable plates;
[0050] FIG. 6 is a diagrammatic view of a shroud sector including a
damaged abradable coating; and
[0051] FIGS. 7A and 7B are diagrammatic side views of a turbine
shroud in which a portion of the abradable coating has been
replaced by an abradable plate, shown respectively before and after
machining a free surface of the abradable plate.
DETAILED DESCRIPTION OF THE INVENTION
[0052] FIG. 1 shows a bypass jet engine 10 seen in section on a
vertical plane containing its main axis A. From upstream to
downstream in the flow direction of the air stream, the bypass jet
engine 10 comprises a fan 12, a low-pressure compressor 14, a
high-pressure compressor 16, a combustion chamber 18, a
high-pressure turbine 20, and a low-pressure turbine 22.
[0053] The high-pressure turbine 20 has a plurality of blades 20A
that rotate with the rotor, and vanes 20B that are mounted on the
stator. The stator of the turbine 20 has a plurality of stator
shrouds 24 arranged facing the blades 20A of the turbine 20.
[0054] As can be seen in FIG. 2, each stator shroud 24 is made up
of a plurality of shroud sectors 26. Each shroud sector 26 has an
inner surface 28, an outer surface 30, and an abradable plate 32
against which the blades 20A of the rotor come into rubbing
contact.
[0055] The abradable plate 32 is brazed onto the shroud sector 26.
The abradable plate 32 has a free surface 34 and a surface 36 that
is to be brazed onto the shroud sector 26.
[0056] By way of example, the shroud sector 26 is made of a cobalt-
or nickel-based superalloy, such as the AM1 superalloy or the N5
superalloy, and the abradable plate 32 is obtained from a metal
powder based on cobalt or on nickel.
[0057] In the described implementation, the shroud 24 is made up of
a plurality of shroud sectors 26 that are assembled to one another
in order to form a shroud 24. The shroud 24 could equally well be
made as a single piece.
[0058] In order to fabricate an abradable plate 32, a mixture is
prepared comprising a cobalt- or nickel-based metal powder and a
powder based on a fluxing element. By way of example, the cobalt-
or nickel-based powder may be a powder of the CoNiCrAlY family, and
the fluxing element may be boron or silicon. By way of example, the
powder mixture may comprise 2% by weight of boron.
[0059] As shown in FIGS. 3 and 4, the powder mixture is deposited
in the form of layers in an SPS sintering mold 42. By way of
example, the mold 42 is made of graphite. The mold 42 comprises an
outer mold 44 forming a chamber in which the powder mixture is
deposited. The mold 42 also has a top piston 46 and a bottom piston
48 that serve to apply axial pressure on the layers of powder
mixture during the SPS sintering step.
[0060] FIG. 3 shows a stack 38 comprising two abradable plates 32
with a first chemically inert insert 40 inserted between them. In
this example, a second chemically inert insert 40 and a third
chemically inert insert 41 are also arranged on either side of the
stack 38 such that each layer of powder mixture is sandwiched
between two chemically inert inserts 40. By way of example, the
chemically inert inserts 40 may be made from plates of sintered
boron nitride.
[0061] In the implementation of FIGS. 3 and 4, each abradable plate
32 is obtained by depositing a layer of powder mixture between two
chemically inert inserts 40 and by performing an SPS sintering
step.
[0062] FIGS. 3 and 4 show two stacks 38 after SPS sintering, the
stacks respectively comprising two and four abradable plates
32.
[0063] Before depositing the powder mixture layer, it is also
possible to deposit a layer of boron nitride on the mold 42 by
using a spray, in particular onto the surfaces of the mold 42 that
are to come into contact with the powder mixture layer during SPS
sintering. This layer of boron nitride likewise forms a chemically
inert insert between the powder mixture and the mold 42.
[0064] The chemically inert inserts 40 may also be made out of a
material other than boron nitride. The chemically inert inserts 40
may optionally be covered in a layer of boron nitride.
[0065] The chemically inert inserts 40, whether in the form of
plates or in the form of layers, serve to reduce chemical reactions
between the powder mixture layer and the mold 42 during SPS
sintering. The chemically inert inserts 40 make it possible in
particular to reduce, or even to avoid, any sticking of the powder
mixture layer to portions of the mold before SPS sintering, and
also any sticking of the abradable plate 32 to portions of the mold
42 after SPS sintering.
[0066] The chemically inert inserts 40 also make it possible to
reduce, or even to avoid, any formation of a layer of carbide on
the surface of the abradable plate 32.
[0067] It can be understood that the thickness of the abradable
plate 32 obtained after SPS sintering depends in particular on the
thickness of each layer of powder mixture deposited in the mold 42,
and also on the parameters of SPS sintering. The thickness of the
abradable plate 32 obtained after SPS sintering may also depend on
the grain size and on the morphology of the powder used. In
particular, the morphology of the powder may depend on the method
for manufacturing the powder. Thus, a powder fabricated by gaseous
atomization or by a rotating electrode has grains of substantially
spherical shape, while a powder fabricated by liquid atomization
has grains of shape that is less regular.
[0068] FIGS. 5A-5D show various microstructures of abradable plates
32 presenting respective apparent porosities of about 10%, about
7%, about 3%, and practically zero.
[0069] It can thus be seen that by modifying the SPS sintering
parameters, such as temperature, pressure, and sintering time, it
is possible to obtain abradable plates 32 presenting structures
that are different. For example, FIG. 7A shows an abradable plate
32 obtained during an SPS sintering step at 925.degree. C. for 10
minutes while applying a pressure of 20 MPa. FIG. 7D shows an
abradable plate 32 obtained during an SPS sintering step at
950.degree. C. for 30 minutes while applying a pressure of 40
MPa.
[0070] FIG. 6 is a plan view of a shroud sector 26 including a
damaged abradable coating 50. The abradable coating 50 may have
been obtained by the method described above. The abradable coating
50 could also have been deposited directly on the shroud sector 26
by using a known method.
[0071] In the example of FIG. 6, the abradable coating 50 includes
a zone 52 of damage due to rubbing, e.g. between a blade and the
abradable coating 50, and a zone 54 of damage due to thermal
degradation of the abradable coating 50 under the effect of hot
gas. In the damaged zones 52, 54, the abradable coating 50 is
damaged, i.e. its thickness has been reduced compared with the
original thickness of the abradable coating 50. Nevertheless, in
certain circumstances, in the damaged zones, the abradable coating
50 may have been removed completely, so that the shroud 24 is then
exposed.
[0072] In order to repair the shroud sector 26 having the damaged
abradable coating 50, the abradable coating 50 is removed, e.g. by
machining, and then an abradable plate 32 is brazed, e.g. at
1205.degree. C. in a vacuum, onto the inner surface 28 of the
shroud sector 26.
[0073] As shown in FIG. 7A, the shroud sector 26 including a brazed
abradable plate 32 is then assembled so as to form the shroud 24.
FIG. 7A shows a shroud sector 26 having a brazed abradable plate 32
that is arranged between two shroud sectors 26, each having an
abradable coating 50. Once the turbine shroud sectors 26 have been
assembled together, the abradable plate 32 presents a free surface
34 that need not necessarily extend the free surfaces 56 of the
abradable coatings 50 of the adjacent shroud sectors 26. Thus, the
free surfaces 34, 56 of the various shroud sectors 26 are machined
so as to present a machined surface 58 that is to face the turbine
wheel. As shown in FIG. 7B, the machined surface 58 presents as
little discontinuity as possible. Specifically, if any such
discontinuity is present, then the turbine wheel could strike
against such a discontinuity, thereby leading to impacts within the
turbine, which is not desirable.
[0074] FIGS. 7A and 7B show a single shroud sector 26 having an
abradable plate 32 brazed thereon. Naturally, a plurality of shroud
sectors 26 could be repaired, or indeed all of the shroud sectors
26. The repaired shroud sectors 26 may be adjacent or
otherwise.
[0075] When the shroud 24 is not divided or divisible into sectors,
it is possible to remove a portion of the abradable coating 50 of
the shroud that corresponds to an abradable plate 32 and then to
braze the abradable plate 32 onto the inner surface 28 of the
shroud 24. It is also possible to remove the damaged portion of the
abradable coating 50 and to cut down an abradable plate 32 or to
assemble together a plurality of abradable plates 32 in order to
cover the inner surface 28 of the shroud that has been laid bare in
this way.
[0076] The inner surface 28 of the shroud and the blades are once
more protected effectively by means of an abradable coating 50 and
an abradable plate 32 brazed onto the shroud. The shroud 24 is thus
repaired.
[0077] Although the present disclosure is described with reference
to a specific implementation, it is clear that various
modifications and changes may be undertaken on those
implementations without going beyond the general ambit of the
invention as defined by the claims. Also, individual
characteristics of the various implementations mentioned above may
be combined in additional implementations. Consequently, the
description and the drawings should be considered in a sense that
is illustrative rather than restrictive.
* * * * *