U.S. patent application number 12/226551 was filed with the patent office on 2010-07-01 for oscillating heat treatment method for a superalloy.
Invention is credited to Michael Ott, Rolf Wilkenhoner.
Application Number | 20100163142 12/226551 |
Document ID | / |
Family ID | 37003327 |
Filed Date | 2010-07-01 |
United States Patent
Application |
20100163142 |
Kind Code |
A1 |
Ott; Michael ; et
al. |
July 1, 2010 |
OSCILLATING HEAT TREATMENT METHOD FOR A SUPERALLOY
Abstract
Superalloy solidified in a directional manner often cannot be
subjected to heat treatment because the heat treatment leads to
recrystallization. As a result of the temperature profile during a
heat treatment according to the invention which oscillates in the
manner of a pendulum, a recrystallization during heat treatment can
be avoided because mechanical stresses are reduced thanks to the
recurring succession of dissolutions and precipitations of the
precipitate. The method can be applied to a Ni-based superalloy
with .gamma.-precipitates. After the cyclic heat treatment, the
temperature can be adjusted to and maintained at a temperature
which is the same as or higher than the complete dissolution
temperature. An oscillating movement can also take place above the
complete dissolution temperature.
Inventors: |
Ott; Michael; (Mulheim an
der Ruhr, DE) ; Wilkenhoner; Rolf; (Kleinmachnow,
DE) |
Correspondence
Address: |
SIEMENS CORPORATION;INTELLECTUAL PROPERTY DEPARTMENT
170 WOOD AVENUE SOUTH
ISELIN
NJ
08830
US
|
Family ID: |
37003327 |
Appl. No.: |
12/226551 |
Filed: |
March 15, 2007 |
PCT Filed: |
March 15, 2007 |
PCT NO: |
PCT/EP2007/052461 |
371 Date: |
March 19, 2010 |
Current U.S.
Class: |
148/675 |
Current CPC
Class: |
C21D 1/785 20130101;
C21D 11/00 20130101; C22F 1/10 20130101; F05B 2230/40 20130101;
C22F 1/043 20130101; C22C 21/02 20130101; C22C 19/05 20130101 |
Class at
Publication: |
148/675 |
International
Class: |
C22F 1/10 20060101
C22F001/10 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 26, 2006 |
EP |
06008688.1 |
Claims
1.-28. (canceled)
29. A method for heat treating a material having a precipitate that
is dissolvable at least partially in a matrix of the material above
a dissolution temperature, comprising: at least temporarily heat
treating the material above the dissolution temperature via a
temperature profile; and at least temporarily oscillating the
temperature profile for the heat treatment.
30. The method as claimed in claim 29, wherein the temperature
profile oscillates below the dissolution temperature and continues
to increase at least temporarily above the dissolution
temperature.
31. The method as claimed in claim 29, wherein the temperature
profile oscillates above the dissolution temperature.
32. The method as claimed in claim 29, wherein the temperature
profile initially rises to a temperature below the dissolution
temperature and further oscillately rises.
33. The method as claimed in claim 29, wherein the temperature
profile initially rises at least to the dissolution temperature and
further oscillately rises.
34. The method as claimed in claim 29, wherein the temperature
profile oscillates initially once or more than once from a
temperature above the dissolution temperature to a temperature
below the dissolution temperature.
35. The method as claimed in claim 29, wherein the temperature
profile oscillates from a temperature above the dissolution
temperature to a temperature not below the dissolution
temperature.
36. The method as claimed in claim 29, wherein the oscillation is
between two local maxima in the temperature profile and the
temperature profile comprises at least two oscillations.
37. The method as claimed in claim 29, wherein the temperature
profile oscillates for at least one hour.
38. The method as claimed in claim 29, wherein the temperature
profile oscillates sinusoidally or triangularly.
39. The method as claimed in claim 29, wherein the precipitate is
dissolved completely in the matrix at a full solution annealing
temperature.
40. The method as claimed in claim 39, wherein the temperature
profile oscillates between: the dissolution temperature and the
full solution annealing temperature, or a temperature above the
dissolution temperature and the full solution annealing
temperature, or the dissolution temperature and a temperature below
the full solution annealing temperature, or a temperature above the
dissolution temperature and a temperature below the full solution
annealing temperature, or a temperature below the dissolution
temperature and the full solution annealing temperature.
41. The method as claimed in claim 39, wherein the temperature
profile initially rises to a temperature below the dissolution
temperature and further oscillately rises to the full solution
annealing temperature.
42. The method as claimed in claim 39, wherein the temperature
profile reaches the full solution annealing temperature during the
oscillation at a specific time and is set constant at the full
solution annealing temperature for the specific time.
43. The method as claimed in claim 42, wherein the temperature
profile stays at the full solution annealing temperature for at
least one hour.
44. The method as claimed in claim 39, wherein the temperature
profile is set constant at a temperature above the full solution
annealing temperature at a specific time.
45. The method as claimed in claim 39, wherein the temperature
profile overshoots the full solution annealing temperature at a
specific time.
46. The method as claimed in claim 29, wherein the temperature
profile does not overshoot the full solution temperature.
47. The method as claimed in claim 29, wherein a metallic element
of the material is depleted before the heat treatment.
48. The method as claimed in claim 29, wherein the precipitate is a
.gamma.-phase of a nickel-based superalloy.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is the US National Stage of International
Application No. PCT/EP2007/052461, filed Mar. 15, 2007 and claims
the benefit thereof. The International Application claims the
benefits of European application No. 06008688.1, filed Apr. 26,
2006, both of the applications are incorporated by reference herein
in their entirety.
FIELD OF THE INVENTION
[0002] The invention relates to a heat treatment method for a
material which has a precipitate.
BACKGROUND OF THE INVENTION
[0003] Nickel-based superalloys which are used particularly for gas
turbine components, such as turbine blades or combustion chamber
inserts, have a .gamma.-phase which, within the framework of a
repair, that is to say during refurbishment, is subjected to what
is known as .gamma.-solution annealing in order to restore the
original material properties.
[0004] This is not possible without difficulty in components having
directionally solidified nickel-based superalloys. .gamma.-solution
annealing leads in the case of a mechanically deformed surface,
such as, for example, in the region of the moving blade feet, to a
recrystallization of the .gamma.-phase on the component surface.
Since, in contrast to conventional nickel-based superalloys,
directionally solidified nickel-based superalloys have no or only
few elements consolidating the grain boundaries, the grain
reformation, caused by recrystallization, on the component surface
is an unacceptable material weakening.
SUMMARY OF THE INVENTION
[0005] The object of the invention, therefore, is to overcome the
abovementioned problem.
[0006] The object is achieved by a heat treatment method according
to the independent claim, in which, by dissolving the precipitate,
precipitating the precipitate and, once again, dissolving and
precipitation, the mechanical stresses are reduced, so that no
recrystallization can occur.
[0007] The dependant claims list further advantageous measures
which may advantageously be combined with one another in any
desired way.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] In the drawing:
[0009] FIGS. 1-12 show exemplary embodiments of the temperature
profile of heat treatment methods according to the invention,
[0010] FIG. 13 shows a list of superalloys,
[0011] FIG. 14 shows a gas turbine,
[0012] FIG. 15 shows a turbine blade in perspective, and
[0013] FIG. 16 shows a combustion chamber in perspective.
DETAILED DESCRIPTION OF THE INVENTION
[0014] The heat treatment according to the invention is carried
out, in particular, for nickel-based superalloys. Such DX or SX
nickel-based superalloys (FIG. 13) are used, in particular, for
turbine blades 120, 130 (FIG. 14, 15) and combustion chamber
elements 155 (FIG. 16) for turbines, in particular for gas turbines
100 (FIG. 14).
[0015] The heat treatments may also be carried out with aircraft
turbine components (in particular, blades).
[0016] By way of example, the method of heat treatment of nickel
superalloys, which have the .gamma.-phase, is explained, that is to
say .gamma.-solution annealing.
[0017] Before heat treatment, fluoride ion cleaning (FIC) may also
be carried out, which may be utilized, on the one hand, in order to
clean oxides from cracks, but also in order, in particular, to
deplete the component surface of metallic elements of the material
of the substrate, in particular of aluminum and/or titanium, such
as superalloys, since these two elements are .gamma.-formers. A
depletion of the .gamma.-phase of superalloys in the region of the
component surface lowers the inherent stresses which have occurred
in the surface due to mechanical load. By this stress being
lowered, the motive force for grain reformation (recrystallization)
is reduced.
[0018] The FIC cleaning required for this purpose is preferably
carried out at temperatures of around 1000.degree. C. by means of
HF/H.sub.2 mixtures.
[0019] The .gamma.-solution annealing for the complete dissolving
of the precipitate (here .gamma.) according to the prior art has
for superalloys a .gamma.-full solution annealing temperature
T.sub.LG which is calculated according to the following
formula:
T.sub.LG=1229.315+3.987 W-3.624 Ta+2.424 Ru+0.958 Re-6.362 Cr-4.943
Ti-2.602 Al-2.415 Co-2.224 Mo.
[0020] The solution annealing temperature profile in time T(t) is
dealt with below.
[0021] In the figures, the temperature profile T(t) is plotted
against the time t, the temperature T.sub.LG representing the full
solution annealing temperature described above, and the dissolution
temperature T.sub.SOLV representing a material-specific temperature
beyond which the precipitate can first be dissolved, but a complete
dissolution of the precipitates lasts too long.
[0022] The time duration t1, preferably at least 1 h, is the time
from when the temperature T.sub.SOLV is first overshot to the time
point t3 from which the temperature T dwells, preferably constant,
at the full solution annealing temperature T.sub.LG. The dwell
duration at the full solution annealing temperature preferably
amounts to at least 1 hour (1 h).
[0023] In FIG. 1, the oscillating movement of the temperature T
commences even below the temperature T.sub.SOLV and then rises
continuously (see the dashed ascending line) and in an oscillating
manner to the temperature T.sub.LG.
[0024] After overshooting the temperature T.sub.SOLV, the
temperature T.sub.SOLV can be undershot due to the oscillating
movement (not the case in FIG. 1).
[0025] Preferably from a specific time t3, the temperature T
dwells, constant, at the full solution annealing temperature
T.sub.LG at which it dwells preferably for at least 1 h.
[0026] In FIG. 1, four local maxima of the temperature profile can
be seen, that is to say four oscillating movements are present.
However, even five or more oscillating movements may be
generated.
[0027] In FIG. 2, the temperature profile is similar to that in
FIG. 1, but the oscillating movement commences only above the
temperature T.sub.SOLV. The temperature T.sub.SOLV is preferably
not undershot due to the oscillating movement.
[0028] Preferably from a specific time t3, the temperature T
dwells, constant, at the full solution annealing temperature
T.sub.SOLV at which it dwells preferably for at least 1 h.
[0029] In FIG. 2, three local maxima can be seen, so that, here,
three oscillating movements are present.
[0030] In FIG. 3, the temperature T rises (not in an oscillating
manner) above the temperature T.sub.SOLV and here falls again, for
example once, below the temperature T.sub.SOLV and then rises in an
oscillating manner up to the temperature T.sub.LG.
[0031] Preferably from a specific time t3, the temperature T
dwells, constant, at the full solution annealing temperature
T.sub.LG at which it dwells preferably for at least 1 h.
[0032] Three local maxima can be seen in FIG. 3, so that, here,
three oscillating movements are present.
[0033] In the continuously rising oscillating movement (see the
dashed lines) of the temperature T according to FIGS. 1, 2 and 3,
the temperature may oscillate once or more than once from a
temperature above T.sub.SOLV to below the temperature
T.sub.SOLV.
[0034] In FIG. 4, the temperature T rises (not in an oscillating
manner) above the temperature T.sub.SOLV to the solution annealing
temperature T.sub.LG and oscillates to and fro between these two
temperatures T.sub.LG, T.sub.SOLV.
[0035] The oscillating temperature profile T(t) then preferably
runs uniformly, as can be seen from the dashed line running
horizontally.
[0036] Preferably from a specific time t3, the temperature T
dwells, constant, at the full solution annealing temperature
T.sub.LG at which it preferably dwells for at least 1 h.
[0037] FIG. 4 illustrates two oscillating movements. However, three
or more oscillating movements may be carried out.
[0038] In FIG. 5, the temperature T also rises (not in an
oscillating manner) to the full solution annealing temperature
T.sub.LG and then falls, although the temperature T.sub.SOLV is not
reached (difference .DELTA.T>0).
[0039] The oscillating temperature profile T(t) then preferably
runs uniformly, as can be seen from the dashed line running
horizontally.
[0040] Preferably from a specific time t3, the temperature T
dwells, constant, at the full solution annealing temperature
T.sub.LG at which it dwells preferably for at least 1 h.
[0041] Three local maxima can be seen in FIG. 5, and therefore,
here, three oscillating movements are present.
[0042] In FIG. 6, the temperature T rises (not in an oscillating
manner) beyond the temperature T.sub.SOLV to a temperature below
the temperature T.sub.LG and then oscillates to and fro between
these two values. The oscillating temperature profile T(t) then
preferably runs uniformly, as can be seen from the dashed line
running horizontally.
[0043] Preferably from a specific time t3, the temperature T
dwells, constant, at the full solution annealing temperature
T.sub.LG at which it dwells preferably for at least 1 h.
[0044] FIG. 6 illustrates two oscillating movements. However, even
three or more oscillating movements may be carried out.
[0045] In FIG. 7, the temperature T rises (not in an oscillating
manner) beyond the temperature T.sub.SOLV to a temperature below
the temperature T.sub.LG and oscillates to and fro between this
temperature below T.sub.LG and a temperature above T.sub.SOLV. The
oscillating temperature profile T(t) then preferably runs
uniformly, as can be seen from the dashed line running
horizontally.
[0046] Preferably from a specific time t3, the temperature T
dwells, constant, at the full solution annealing temperature
T.sub.LG at which it dwells preferably for at least 1 h.
[0047] Three local maxima can be seen in FIG. 7, and therefore,
here, three oscillating movements are present.
[0048] In contrast to FIGS. 4 and 6, the temperature T in FIGS. 8
and 9 also oscillates below the temperature T.sub.SOLV.
[0049] In FIG. 8 the temperature always reaches a maximum value of
the full solution annealing temperature T.sub.LG, whereas, in FIG.
9, the maximum value of the temperature profile reaches a
temperature above T.sub.SOLV, but below the full solution annealing
temperature T.sub.LG.
[0050] Preferably from a specific time t3, the temperature T in
FIGS. 8 and 9 dwells, constant, at the full solution annealing
temperature T.sub.LG at which it dwells preferably for at least 1
h.
[0051] FIG. 8 illustrates two oscillating movements. However, even
three or more oscillating movements may be carried out.
[0052] FIG. 9 illustrates two oscillating movements. However, even
three or more oscillating movements may be carried out.
[0053] In FIG. 10, the temperature T rises (not in an oscillating
manner) above the temperature T.sub.SOLV and oscillates to and fro
between this value and a lower value (.gtoreq.T.sub.SOLV). The
oscillating temperature profile T(t) then preferably runs
uniformly, as can be seen from the dashed line running
horizontally.
[0054] Thereafter, after a specific time t2, the temperature rises,
in particular in an oscillating manner, to the full solution
annealing temperature T.sub.LG.
[0055] Preferably from a specific time t3, the temperature T
dwells, constant, at the full solution annealing temperature
T.sub.LG at which it dwells preferably for at least 1 h.
[0056] In FIG. 10, four local maxima are present, and therefore
four oscillating movements occur. However, even five or more
oscillating movements may be carried out.
[0057] FIG. 12 illustrates a further exemplary embodiment of the
oscillating temperature profile T(t) according to the
invention.
[0058] The average value of the temperature T about which the
temperature fluctuates is increased in steps here until, from a
time t3, the temperature is set, constant, at a temperature
T.sub.LG.
[0059] Initially, the temperature T oscillates about the
temperature T.sub.SOLV, then rises to a higher temperature, so that
the temperature T.sub.SOLV is preferably no longer undershot,
oscillates and rises further again in a third or in further steps,
the maximum temperature T.sub.LG being reached here or a clearance
with respect to the temperature T.sub.LG being present.
[0060] Preferably from a specific time t3, the temperature T
dwells, constant, at the full solution annealing temperature
T.sub.LG at which it dwells preferably for at least 1 h.
[0061] FIGS. 1 to 12 illustrate the oscillating movements only
preferably in wavy or sinusoidal form, but they may also be formed
triangularly (FIG. 11), rectangularly (not illustrated) or
otherwise.
[0062] Likewise, in the oscillating movements, the temperature
T.sub.LG may also be reached or overshot once or more than once by
means of the oscillating movement.
[0063] After the end of the oscillating movement, the temperature
can be set at a temperature equal to or higher than the full
solution annealing temperature T.sub.LG and be held there, in
particular for at least one hour.
[0064] If a temperature higher than the full solution annealing
temperature T.sub.LG is set at the end in a specific time t3, an
oscillating movement above the full solution annealing temperature
T.sub.LG may preferably take place.
[0065] It is also advantageous if the full solution annealing
temperature is not overshot, apart from an unwanted overshooting
when the temperature is being set to the full solution annealing
temperature.
[0066] It is also advantageous that the temperature rises in an
oscillating manner. The oscillating rise of the temperature T in
FIGS. 1, 2, 3 and 10 takes place at least intermittently, in
particular at least during the overshooting of the temperature
T.sub.SOLV.
[0067] In particular, the oscillating rise in the temperature T is
followed by a holding time at a temperature .gtoreq. of the full
solution annealing temperature T.sub.LG.
[0068] The oscillating rise in the temperature can be seen from the
dashed line which rises, the temperature of a maximum of the
oscillating movement being increased in relation to the maximum of
the preceding maximum. Correspondingly, the minima, that is to say
the valleys of the oscillating movement, are not identical, but
rise with the time t.
[0069] FIG. 13 shows a list of nickel-based DS or SX superalloys
which can be treated by means of the method according to the
invention.
[0070] For the material IN 6203 DS, the temperature T.sub.SOLV
amounts to 1100.degree. C. and the temperature T.sub.LG to
1150.degree. C.
[0071] For the material IN 792 DS, the temperature T.sub.SOLV
amounts to 1140.degree. C. and the temperature T.sub.LG to
1230.degree. C.
[0072] The material PWA 1483 SX has a temperature T.sub.SOLV of
1150.degree. C. and a temperature T.sub.LG of 1250.degree. C.
[0073] FIG. 14 shows a gas turbine 100 by way of example in a
longitudinal part section.
[0074] The gas turbine 100 has inside it a rotor 103 rotary-mounted
about an axis of rotation 102 and having a shaft 101, said rotor
also being designated as a turbine rotor.
[0075] An intake casing 104, a compressor 105, a, for example,
toroidal combustion chamber 110, in particular annular combustion
chamber, with a plurality of coaxially arranged burners 107, a
turbine 108 and the exhaust gas casing 109 succeeding one another
along the rotor 103.
[0076] The annular combustion chamber 110 communicates with a, for
example, annular hot-gas duct 111. There, for example, four turbine
stages 112 connected one behind the other form the turbine 108.
[0077] Each turbine stage 112 is formed, for example, from two
blade rings. As seen in the direction of flow of a working medium
113, a guide blade row 115 is followed in the hot-gas duct 111 by a
row 125 formed from moving blades 120.
[0078] The guide blades 130 are in this case fastened to an inner
casing 138 of a stator 143, whereas the moving blades 120 of a row
125 are mounted on the rotor 103, for example, by means of a
turbine disk 133. A generator or a working machine (not
illustrated) is coupled to the rotor 103.
[0079] While the gas turbine 100 is in operation, air 135 is sucked
in by a compressor 105 through the intake casing 104 and is
compressed. The compressed air provided at the turbine-side end of
the compressor 105 is routed to the burners 107 and is mixed there
with a fuel. The mixture is then burnt in the combustion chamber
110 so as to form the working medium 113.
[0080] The working medium 113 flows from there along the hot-gas
duct 111 past the guide blades 130 and the moving blades 120. At
the moving blades 120, the working medium 113 expands so as to
transmit a pulse, so that the moving blades 120 drive the rotor 103
and the latter drives the working machine coupled to it.
[0081] The components exposed to the hot working medium 113 are
subject to thermal loads while the gas turbine 100 is in operation.
The guide blades 130 and moving blades 120 of the first turbine
stage 112, as seen in the direction of flow of the working medium
113, are subjected to the highest thermal load, in addition to the
heatshield elements lining the annular combustion chamber 110.
[0082] In order to withstand the temperatures prevailing there,
these blades may be cooled by means of a coolant.
[0083] Likewise, substrates of the components may have a
directional structure, that is to say they are monocrystalline (SX
structure) or have only longitudinally directed grains (DS
structure).
[0084] The material used for the components, particularly for the
turbine blade 120, 130 and components of the combustion chamber
110, is, for example, iron-, nickel- or cobalt-based
superalloys.
[0085] Such superalloys are known, for example, from EP 1 204 776
B1, EP 1 306 454, EP 1 319 729 A1, WO 99/67435 or WO 00/44949;
these publications are part of the disclosure with regard to the
chemical composition of the alloys.
[0086] The guide blade 130 has a guide blade foot (not illustrated
here) facing the inner casing 138 of the turbine 108 and a guide
blade head lying opposite the guide blade foot. The guide blade
head faces the rotor 103 and is secured to a fastening ring 140 of
the stator 143.
[0087] FIG. 15 shows a perspective view of a moving blade 120 or
guide blade 130 of a turbomachine which extends along a
longitudinal axis 121.
[0088] The turbomachine may be a gas turbine of an aircraft or of a
power station for electricity generation, a steam turbine or a
compressor.
[0089] The blade 120, 130 has successively along the longitudinal
axis 121 a fastening region 400, a blade platform 403 contiguous to
the latter and also a blade leaf 406 and a blade tip 415.
[0090] As a guide blade 130, the blade 130 may have (not
illustrated) a further platform at its blade tip 415.
[0091] In the fastening region 400, a blade foot 183 is formed
which serves (not illustrated) for fastening the moving blades 120,
130 to a shaft or a disk. The blade foot 183 is configured, for
example, as a hammer head. Other configurations as a pinetree or
dovetail foot are possible. The blade 120, 130 has a leading edge
409 and a trailing edge 412 for a medium which flows past the blade
leaf 406.
[0092] In conventional blades 120, 130, for example, solid metallic
materials, in particular superalloys, are used in all regions 400,
403, 406 of the blade 120, 130. Such superalloys are known, for
example, from EP 1 204 776 B1, EP 1 306 454, EP 1 319 729 A1, WO
99/67435 or WO 00/44949; these publications are part of the
disclosure with regard to the chemical composition of the
alloy.
[0093] The blade 120, 130 may in this case be manufactured by means
of a casting method, also by means of a directional solidification,
by a forging method, by a milling method or combinations of
these.
[0094] Workpieces with a monocrystalline structure or structures
are used as components for machines which are exposed to high
mechanical, thermal and/or chemical loads during operation.
[0095] The manufacture of monocrystalline workpieces of this type
takes place, for example, by directional solidification from the
melt. These are casting methods in which the liquid metallic alloy
solidifies into the monocrystalline structure, that is to say into
the monocrystalline workpiece, or directionally solidifies.
[0096] In this case, dendritic crystals are oriented along the heat
flow and form either a columnar-crystalline grain structure
(columnar, that is to say grains which run over the entire length
of the workpiece and here, according to general linguistic
practice, are designated as being directionally solidified) or a
monocrystalline structure, that is to say the entire workpiece
consists of a single crystal. These methods must avoid the
transition to globulitic (polycrystalline) solidification, since,
due to undirected growth, transverse and longitudinal grain
boundaries are necessarily formed which nullify the good properties
of the directionally solidified or monocrystalline component.
[0097] When directionally solidified structures are referred to in
general terms, this means both monocrystals which have no grain
boundaries or at most small-angle grain boundaries and
columnar-crystal structures which have grain boundaries running in
the longitudinal direction, but no transverse grain boundaries. In
the case of these second-mentioned crystalline structures,
directionally solidified structures are also referred to.
[0098] Such methods are known from U.S. Pat. No. 6,024,792 and EP 0
892 090 A1; these publications are part of the disclosure with
regard to the solidification method.
[0099] The blades 120, 130 may likewise have coatings against
corrosion or oxidation, for example (MCrAlX; M is at least one
element of the group iron (Fe), cobalt (Co), nickel (Ni), X is an
active element and stands for yttrium (Y) and/or silicon and/or at
least one rare earth element, or hafnium (HO). Such alloys are
known from EP 0 486 489 B1, EP 0 786 017 B1, EP 0 412 397 B1 or EP
1 306 454 A1 which are to be part of the disclosure with regard to
the chemical composition of the alloy.
[0100] The density is preferably around 95% of the theoretical
density.
[0101] A protective aluminum oxide layer (TGO=thermal grown oxide
layer) is formed on the MCrAlX layer (as an intermediate layer or
as the outermost layer).
[0102] On the MCrAlX, a heat insulation layer may also be present,
which is preferably the outermost layer and consists, for example,
of ZrO.sub.2, Y.sub.2O.sub.3--ZrO.sub.2, that is to say it is not
or is partially or is completely stabilized by yttrium oxide and/or
calcium oxide and/or magnesium oxide. The heat insulation layer
covers the entire MCrAlX layer.
[0103] By means of suitable coating methods, such as, for example,
electron beam evaporation (EB-PVD), columnar grains are generated
in the heat insulation layer.
[0104] Other coating methods may be envisaged, for example
atmospheric plasma spraying (APS), LPPS, VPS or CVD. The heat
insulation layer may have porous microcrack- or
macrocrack-compatible grains for better thermal shock resistance.
The heat insulation layer is therefore preferably more porous than
the MCrAlX layer.
[0105] The blade 120, 130 may be hollow or solid. If the blade 120,
130 is to be cooled, it is hollow and, if appropriate, also has
film-cooling holes 418 (indicated by dashes).
[0106] FIG. 16 shows a combustion chamber 110 of the gas turbine
100. The combustion chamber 110 is configured, for example, as what
is known as an annular combustion chamber, in which a multiplicity
of burners 107 arranged around an axis of rotation 102 in the
circumferential direction issue into a common combustion chamber
space 154 and generate the flames 156. For this purpose, the
combustion chamber 110 is configured in its entirety as an annular
structure which is positioned around the axis of rotation 102.
[0107] To achieve comparatively high efficiency, the combustion
chamber 110 is designed for a comparatively high temperature of the
working medium M of about 1000.degree. C. to 1600.degree. C. In
order to make it possible to have a comparatively long operating
time even in the case of these operating parameters which are
unfavorable for the materials, the combustion chamber wall 153 is
provided on its side facing the working medium M with an inner
lining formed from heatshield elements 155.
[0108] On account of the high temperatures inside the combustion
chamber 110, moreover, a cooling system may be provided for the
heatshield elements 155 or for their holding elements. The
heatshield elements 155 are then, for example, hollow and, if
appropriate, also have cooling holes (not illustrated) issuing into
the combustion chamber space 154.
[0109] Each heatshield element 155 consisting of an alloy is
equipped on the working medium side with a particularly
heat-resistant protective layer (MCrAlX layer and/or ceramic
coating) or is manufactured from material resistant to high
temperature (solid ceramic bricks).
[0110] This protective layer may be similar to those of the turbine
blades, that is to say, for example, MCrAlX means: M is at least
one element of the group iron (Fe), cobalt (Co), nickel (Ni), X is
an active element and stands for yttrium (Y) and/or silicon and/or
at least one rare earth element or hafnium (Hf). Such alloys are
known from EP 0 486 489 B1, EP 0 786 017 B1, EP 0 412 397 B1 or EP
1 306 454 A1 which are to be part of the disclosure with regard to
the chemical composition of the alloy.
[0111] On the MCrAlX, a, for example, ceramic heat insulation layer
may also be present and consist, for example, of ZrO.sub.2,
Y.sub.2O.sub.3--ZrO.sub.2, that is to say it is not or is partially
or is completely stabilized by yttrium oxide and/or calcium oxide
and/or magnesium oxide.
[0112] By means of suitable coating methods, such as, for example,
electron beam evaporation (EB-PVD), columnar grains are generated
in the heat insulation layer.
[0113] Other coating methods may be envisaged, for example
atmospheric plasma spraying (APS), LPPS, VPS or CVD. The heat
insulation layer may have porous microcrack- or
macrocrack-compatible grains for better thermal shock
resistance.
[0114] Refurbishment means that turbine blades 120, 130 and
heatshield elements 155, after their use, must, where appropriate,
be freed of protective layers (for example, by sandblasting). A
removal of the corrosion and/or oxidation layers or products is
then carried out. In solution annealing, the method according to
the invention is used. If appropriate, cracks in the turbine blade
120, 130 or in the heatshield element 155 are also repaired. A
recoating of the turbine blades 120, 130 and heatshield elements
155 and a renewed use of the turbine blades 120, 130 or of the
heatshield elements 155 then take place.
* * * * *