U.S. patent application number 12/461012 was filed with the patent office on 2010-02-25 for single crystal component and a method of heat treating a single crystal component.
This patent application is currently assigned to ROLLS-ROYCE PLC. Invention is credited to Robert A. Hobbs, Robert J. Mitchell, Catherine M.F. Rae, Sammy Tin.
Application Number | 20100043929 12/461012 |
Document ID | / |
Family ID | 41066906 |
Filed Date | 2010-02-25 |
United States Patent
Application |
20100043929 |
Kind Code |
A1 |
Hobbs; Robert A. ; et
al. |
February 25, 2010 |
Single crystal component and a method of heat treating a single
crystal component
Abstract
A single crystal component comprising a first region and a
second region. The component comprising a nickel base single
crystal superalloy having a gamma phase matrix and gamma prime
phase precipitates distributed in the gamma phase matrix. The first
region of the component comprises a bi-modal distribution of gamma
prime phase precipitates in the gamma phase matrix and the second
region of the component comprising a uni-modal distribution of
gamma prime phase precipitates in the gamma phase matrix. The
uni-modal distribution of gamma prime phase precipitates consisting
of primary cuboidal gamma prime phase precipitates and the bi-modal
distribution of gamma prime phase precipitates consisting of
primary cuboidal gamma prime phase precipitates and secondary
spherical gamma prime phase precipitates and/or cuboidal gamma
prime phase precipitates whereby the first region of the component
has enhanced resistance to low cycle fatigue and the second region
of the component has enhanced resistance to creep deformation.
Inventors: |
Hobbs; Robert A.; (London,
GB) ; Tin; Sammy; (Schaumberg, IL) ; Rae;
Catherine M.F.; (Cambridge, GB) ; Mitchell; Robert
J.; (Nottingham, GB) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 320850
ALEXANDRIA
VA
22320-4850
US
|
Assignee: |
ROLLS-ROYCE PLC
LONDON
GB
|
Family ID: |
41066906 |
Appl. No.: |
12/461012 |
Filed: |
July 29, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61136271 |
Aug 22, 2008 |
|
|
|
Current U.S.
Class: |
148/714 ;
148/405; 148/559 |
Current CPC
Class: |
F01D 5/28 20130101; C22F
1/10 20130101; F05D 2300/607 20130101; F01D 5/3007 20130101; F01D
5/225 20130101 |
Class at
Publication: |
148/714 ;
148/559; 148/405 |
International
Class: |
C22F 1/00 20060101
C22F001/00; C21D 9/00 20060101 C21D009/00 |
Claims
1. A single crystal component comprising a first region and a
second region, the component comprising a nickel base single
crystal superalloy having a gamma phase matrix and gamma prime
phase precipitates distributed in the gamma phase matrix, wherein
the first region of the component comprising a bi-modal
distribution of gamma prime phase precipitates in the gamma phase
matrix and the second region of the component comprising a
uni-modal distribution of gamma prime phase precipitates in the
gamma phase matrix, the uni-modal distribution of gamma prime phase
precipitates consisting of primary cuboidal gamma prime phase
precipitates and the bi-modal distribution of gamma prime phase
precipitates consisting of primary cuboidal gamma prime phase
precipitates and secondary spherical gamma prime phase precipitates
and/or cuboidal gamma prime phase precipitates whereby the first
region of the component has enhanced resistance to low cycle
fatigue and the second region of the component has enhanced
resistance to creep deformation.
2. A single crystal component as claimed in claim 1 wherein the
primary cuboidal gamma prime phase precipitates in the second
region of the component have edge lengths within the range 200 to
700 nm.
3. A single crystal component as claimed in claim 2 wherein the
primary cuboidal gamma prime phase precipitates in the second
region of the component have edge lengths within the range 250 to
500 nm.
4. A single crystal component as claimed in claim 1 wherein the
volume fraction of primary cuboidal gamma prime phase precipitates
in the second region of the component is at least 50 vol %.
5. A single crystal component as claimed in claim 4 wherein the
volume fraction of primary cuboidal gamma prime phase precipitates
in the second region of the component is at least 60 vol %.
6. A single crystal component as claimed in claim 5 wherein the
volume fraction of primary cuboidal gamma prime phase precipitates
in the second region of the component is 70 vol %.
7. A single crystal component as claimed in claim 1 wherein the
gamma channel widths between the gamma prime phase precipitates in
the second region of the component is within the range 10 to 100
nm.
8. A single crystal component as claimed in claim 7 wherein the
gamma channel widths between the gamma prime phase precipitates in
the second region of the component is within the range 30 to 60
nm.
9. A single crystal component as claimed in claim 1 wherein the
primary cuboidal gamma prime phase precipitates in the first region
of the component have edge lengths within the range of 200 to 700
nm.
10. A single crystal component as claimed in claim 9 wherein the
primary cuboidal gamma prime phase precipitates in the first region
of the component have edge lengths within the range of 250 to 500
nm.
11. A single crystal component as claimed in claim 1 wherein the
secondary spheroidal and/or cuboidal gamma prime phase precipitates
in the first region of the component have edge lengths within the
range of 1 to 50 nm.
12. A single crystal component as claimed in claim 11 wherein the
secondary spheroidal and/or cuboidal gamma prime phase precipitates
in the first region of the component have edge lengths within the
range of 5 to 20 nm.
13. A single crystal component as claimed in claim 1 wherein the
secondary spheroidal and/or cuboidal gamma prime phase precipitates
in the first region of the component are contained within the gamma
channels between the primary cuboidal gamma prime phase
precipitates.
14. A single crystal component as claimed in claim 1 wherein the
component is a turbine blade comprising a root, a shank, a platform
and an aerofoil.
15. A single crystal component as claimed in claim 14 wherein the
first region comprises the root and the shank and the second region
comprises the platform and the aerofoil.
16. A single crystal component as claimed in claim 15 wherein
turbine blade comprises a shroud and the second region comprises
the platform, the aerofoil and the shroud.
17. A single crystal component as claimed in claim 1 wherein the
nickel base single crystal superalloy comprises a 3.sup.rd,
4.sup.th or a 5.sup.th generation single crystal superalloy.
18. A method of heat treating a single crystal component comprising
a first region and a second region, the method comprising heat
treating the component to produce primary cuboidal gamma prime
precipitates in a gamma phase matrix in the first region and the
second region, heat treating the component to produce secondary
gamma prime phase precipitates in the first region.
19. A method as claimed in claim 18 wherein the method comprises
solution heat treating the component, primary ageing the component
and secondary ageing the component wherein the primary ageing of
the component comprises cooling the first region of the component
at a lower cooling rate than the cooling rate of the second region
of the component during the cooling from the primary ageing
temperature of the primary ageing heat treatment to room
temperature.
20. A method as claimed in claim 18 wherein the method comprises
solution heat treating the component, primary ageing the component
and secondary ageing the component wherein the secondary ageing of
the component comprises heating the second region of the component
to a temperature above the solvus temperature of the fine secondary
gamma prime precipitates while heating the first region of the
component to a temperature below the solvus temperature of the fine
secondary gamma prime precipitates during the secondary ageing heat
treatment.
21. A method as claimed in claim 19 comprising providing insulation
on the first region of the component during the primary ageing heat
treatment or providing insulation on the first region of the
component during the cooling part of the primary ageing heat
treatment to reduce the cooling rate of the first region of the
component after the primary ageing heat treatment.
22. A method as claimed in claim 19 comprising heating the first
region of the component to further reduce the cooling rate of the
first region of the component after the primary ageing heat
treatment.
23. A method as claimed in claim 19 comprising submerging the first
region of the component in a molten salt bath maintained at an
elevated temperature to reduce the cooling rate of the first region
of the component.
24. A method as claimed in claim 19 comprising directing a cooling
fluid onto the surface of the second region of the component to
reduce the cooling rate of the first region of the component
relative to the cooling rate of the second region of the
component.
25. A method as claimed in claim 20 comprising heating the second
region of the component to the temperature above the solvus
temperature of the fine secondary gamma prime precipitates to
dissolve them.
26. A method as claimed in claim 20 comprising providing insulation
on the second region of the component and locally heat treating the
first region of the component to precipitate secondary gamma prime
phase precipitates while the insulation maintains the second region
of the component at a temperature below the secondary gamma prime
solvus so that secondary gamma prime phase precipitates are not
formed in the second region of the component.
27. A method as claimed in claim 18 comprising heating the whole of
the component during part of the primary heat treatment, secondary
heat treatment and coating heat treatment step and controlling the
heating such that different temperature gradients are produced in
the first region and the second region of the component.
Description
[0001] The present invention relates to a single crystal component,
in particular a single crystal turbine blade and a method of heat
treating a single crystal turbine blade, in particular a method of
heat treating a single crystal turbine blade.
[0002] Nickel base single crystal superalloy components, e.g.
turbine blades and turbine vanes, are used in the hottest regions
of an engine, e.g. a gas turbine engine. In a gas turbine engine
hot combustion gases from the combustor impinge on turbine blades
within the turbine section and the turbine blades convert the
kinetic energy of the hot combustion gases into useful work energy
to drive the compressor section. The high-pressure turbine blades
are actively cooled and are often provided with thermal barrier
coatings to reduce metal temperatures and minimise creep
deformation of the turbine blades. However, nickel base single
crystal superalloy turbine blades are subject to a wide range of
stresses and temperatures that dictate the dominant mode of
deformation in these materials.
[0003] Resistance to creep deformation is traditionally considered
to be one of the most important design factors for a nickel base
single crystal superalloy turbine blade. Nickel base single crystal
superalloy turbine blades are carefully processed, heat treated, to
optimise the resulting grain and precipitate structure for creep
resistance. A nickel base single crystal superalloy is cast into an
investment casting mould, which has a single crystal selector or a
single crystal seed, and the nickel base single crystal superalloy
is directionally solidified and the orientation of the single
crystal is carefully controlled such that the <001> direction
of the single crystal is closely aligned with the primary stress
axis of the turbine blade.
[0004] Following directional solidification, multiple heat
treatments, as shown in FIG. 1, are performed on the nickel base
single crystal superalloy turbine blade to produce a uni-modal
distribution of gamma prime phase precipitates in a gamma phase
matrix to maximise the resistance to dislocations bowing between
the gamma prime phase precipitates under creep conditions.
[0005] An initial solution heat treatment S removes the residual
gamma/gamma prime eutectic within the as cast microstructure of the
nickel base single crystal superalloy turbine blade and assists
homogenisation of the dendritic microstructure. After the solution
heat treatment S the nickel base single crystal superalloy turbine
blades are cooled at a specific cooling rate and then primary aged
PA to nucleate a single distribution of gamma prime phase
precipitates. Upon subsequent cooling to room temperature
nano-sized secondary gamma prime phase precipitates often form
within the gamma channels to relieve super-saturation of elements
contained within the gamma phase matrix, as shown in FIG. 2. The
nickel base single crystal turbine blades are then secondary aged
SA to re-solution the nano-sized secondary gamma prime precipitates
and refine the morphology of the initial gamma prime phase
precipitates formed during cooling from the solution heat treatment
temperature and the subsequent primary age, see FIG. 3.
[0006] Nickel base single crystal superalloy turbine blades are
intentionally processed, heat treated, to produce a comparatively
homogeneous gamma prime precipitate size, shape and distribution
contained throughout the microstructure.
[0007] Due to the large variation in operating temperatures,
stresses and loading conditions experienced by a nickel base single
crystal turbine blade during operation, the turbine blade is
subjected to a wide range of deformation mechanisms. The aerofoil
of the turbine blade is subjected to elevated temperatures, greater
than 750.degree. C., and undergoes creep deformation during
service. The root of the turbine blade is subjected to lower
temperatures, less than 750.degree. C., and does not experience
significant amounts of creep. The root of the turbine blade is
subjected to large stresses during service that ultimately lead to
deformation and failure due to low cycle fatigue.
[0008] Currently the gamma prime phase precipitates within the
entire nickel base single crystal superalloy turbine blade are
arranged to provide high degree of creep resistance in the aerofoil
of the turbine blade without considering the effect on the low
cycle fatigue life of the root of the turbine blade.
[0009] It is known from U.S. Pat. No. 4,921,405 and U.S. Pat. No.
5,451,142 to provide a layer/coating of polycrystalline superalloy
bonded to the root of a nickel base single crystal superalloy
turbine blade. The polycrystalline superalloy is plasma sprayed
onto the root of the turbine blade. The layer of polycrystalline
superalloy is intended to increase the low cycle fatigue life of
the turbine blade.
[0010] U.S. Pat. No. 5,106,266 discloses providing a core of
polycrystalline superalloy within and bonded in a cavity within the
root of a nickel base single crystal superalloy turbine blade. The
polycrystalline superalloy is plasma sprayed into the cavity in the
root of the turbine blade. The core of polycrystalline superalloy
is intended to increase the low cycle fatigue life of the turbine
blade.
[0011] A problem with the prior art is that it requires a layer of
polycrystalline superalloy on the root of the turbine blade or a
core of polycrystalline superalloy within the root of the turbine
blade to increase the fatigue life of a nickel base single crystal
superalloy turbine blade.
[0012] Accordingly the present invention seeks to provide a novel
single crystal turbine blade which reduces, preferably overcomes,
the above mentioned problem.
[0013] Accordingly the present invention provides a single crystal
component comprising a first region and a second region, the
component comprising a nickel base single crystal superalloy having
a gamma phase matrix and gamma prime phase precipitates distributed
in the gamma phase matrix, wherein the first region of the
component comprising a bi-modal distribution of gamma prime phase
precipitates in the gamma phase matrix and the second region of the
component comprising a uni-modal distribution of gamma prime phase
precipitates in the gamma phase matrix, the uni-modal distribution
of gamma prime phase precipitates consisting of primary cuboidal
gamma prime phase precipitates and the bi-modal distribution of
gamma prime phase precipitates consisting of primary cuboidal gamma
prime phase precipitates and secondary spherical gamma prime phase
precipitates and/or cuboidal gamma prime phase precipitates whereby
the first region of the component has enhanced resistance to low
cycle fatigue and the second region of the component has enhanced
resistance to creep deformation.
[0014] Preferably the primary cuboidal gamma prime phase
precipitates in the second region of the component have edge
lengths within the range 200 to 700 nm.
[0015] Preferably the primary cuboidal gamma prime phase
precipitates in the second region of the component have edge
lengths within the range 250 to 500 nm.
[0016] Preferably the volume fraction of primary cuboidal gamma
prime phase precipitates in the second region of the component is
at least 50 vol %.
[0017] Preferably the volume fraction of primary cuboidal gamma
prime phase precipitates in the second region of the component is
at least 60 vol %.
[0018] Preferably the volume fraction of primary cuboidal gamma
prime phase precipitates in the second region of the component is
70 vol %.
[0019] Preferably the gamma channel widths between the gamma prime
phase precipitates in the second region of the component is within
the range 10 to 100 nm.
[0020] Preferably the gamma channel widths between the gamma prime
phase precipitates in the second region of the component is within
the range 30 to 60 nm.
[0021] Preferably the primary cuboidal gamma prime phase
precipitates in the first region of the component have edge lengths
within the range of 200 to 700 nm.
[0022] Preferably the primary cuboidal gamma prime phase
precipitates in the first region of the component have edge lengths
within the range of 250 to 500 nm.
[0023] Preferably the secondary spheroidal and/or cuboidal gamma
prime phase precipitates in the first region of the component have
edge lengths within the range of 1 to 50 nm.
[0024] Preferably the secondary spheroidal and/or cuboidal gamma
prime phase precipitates in the first region of the component have
edge lengths within the range of 5 to 20 nm.
[0025] Preferably the secondary spheroidal and/or cuboidal gamma
prime phase precipitates in the first region of the component are
contained within the gamma channels between the primary cuboidal
gamma prime phase precipitates.
[0026] Preferably the component is a turbine blade comprising a
root, a shank, a platform and an aerofoil. Preferably the first
region comprises the root and the shank and the second region
comprises the platform and the aerofoil.
[0027] The single crystal turbine blade may comprise a shroud and
the second region comprises the platform, the aerofoil and the
shroud.
[0028] Preferably the nickel base single crystal superalloy
comprises a 3.sup.rd, 4.sup.th or a 5.sup.th generation single
crystal superalloy.
[0029] The present invention also provides a method of heat
treating a single crystal component comprising a first region and a
second region, the method comprising heat treating the component to
produce primary cuboidal gamma prime precipitates in a gamma phase
matrix in the first region and the second region, heat treating the
component to produce secondary gamma prime phase precipitates in
the first region.
[0030] Preferably the method comprises solution heat treating the
component, primary ageing the component and secondary ageing the
component wherein the primary ageing of the component comprises
cooling the first region of the component at a lower cooling rate
than the cooling rate of the second region of the component during
the cooling from the primary ageing temperature of the primary
ageing heat treatment to room temperature.
[0031] The method may comprise providing insulation on the first
region of the component during the primary ageing heat treatment or
providing insulation on the first region of the component during
the cooling part of the primary ageing heat treatment to reduce the
cooling rate of the first region of the component after the primary
ageing heat treatment.
[0032] The method may comprise heating the first region of the
component to further reduce the cooling rate of the first region of
the component after the primary ageing heat treatment.
[0033] The method may comprise submerging the first region of the
component in a molten salt bath maintained at an elevated
temperature to reduce the cooling rate of the first region of the
component.
[0034] The method may comprise directing a cooling fluid onto the
surface of the second region of the component to reduce the cooling
rate of the first region of the component relative to the cooling
rate of the second region of the component.
[0035] Alternatively the method comprises solution heat treating
the component, primary ageing the component and secondary ageing
the component wherein the secondary ageing of the component
comprises heating the second region of the component to a
temperature above the solvus temperature of the fine secondary
gamma prime precipitates while heating the first region of the
component to a temperature below the solvus temperature of the fine
secondary gamma prime precipitates during the secondary ageing heat
treatment.
[0036] The method may comprise heating the second region of the
component to the temperature above the solvus temperature of the
fine secondary gamma prime precipitates to dissolve them.
[0037] The method may comprise providing insulation on the first
region of the component and locally heat treating the first region
of the component to precipitate secondary gamma prime phase
precipitates while the insulation maintains the second region of
the component at a temperature below the secondary gamma prime
solvus so that secondary gamma prime phase precipitates are not
formed in the second region of the component.
[0038] The method may comprise heating the whole of the component
during part of the primary heat treatment, secondary heat treatment
and coating heat treatment step and controlling the heating such
that different temperature gradients are produced in the first
region and the second region of the component.
[0039] The present invention will be more fully described by way of
example with reference to the accompanying drawings in which:--
[0040] FIG. 1 is graph of temperature against time for a prior art
heat treatment cycle for a nickel base single crystal
superalloy.
[0041] FIG. 2 is a photograph of a bi-modal gamma prime phase
distribution after primary ageing in FIG. 1.
[0042] FIG. 3 is a photograph of a uni-modal gamma prime phase
distribution after secondary ageing in FIG. 1.
[0043] FIG. 4 is a nickel base single crystal superalloy turbine
blade according to the present invention.
[0044] FIG. 5 is a further nickel base single crystal superalloy
turbine blade according to the present invention.
[0045] FIG. 6 is a graph of temperature against time for a heat
treatment cycle to produce a nickel base single crystal superalloy
turbine blade according to the present invention.
[0046] FIG. 7 is a graph of temperature against time for an
alternative heat treatment cycle to produce a nickel base single
crystal superalloy turbine blade according to the present
invention.
[0047] A single crystal turbine blade 10, as shown in FIG. 4,
comprises a root 12, a shank 14, a platform 16 and an aerofoil 18.
The root 12, shank 14, platform 16 and aerofoil 18 are integral and
the root 12 is connected to the platform 16 by the shank 14 and the
aerofoil 18 is connected to the platform 16. The root 12 is
fir-tree shaped or dovetail shaped in cross-section. The turbine
blade 10 comprises a nickel base single crystal superalloy having a
gamma phase matrix and gamma prime phase precipitates distributed
in the gamma phase matrix. The root 12 and the shank 14 of the
turbine blade 10 comprise a bi-modal distribution of gamma prime
phase precipitates in the gamma phase matrix. The platform 16 and
the aerofoil 18 comprise a uni-modal distribution of gamma prime
phase precipitates in the gamma phase matrix.
[0048] The uni-modal distribution of primary gamma prime phase
precipitates consists of cuboidal gamma prime phase precipitates.
The bi-modal distribution of gamma prime phase precipitates
consists of primary cuboidal gamma prime phase precipitates and
secondary spherical gamma prime phase precipitates and/or cuboidal
gamma prime phase precipitates.
[0049] The root 12 and the shank 14 of the turbine blade 10 have
enhanced resistance to low cycle fatigue and the platform 16 and
the aerofoil of the turbine blade 10 have enhanced resistance to
creep deformation.
[0050] The primary cuboidal gamma prime phase precipitates in the
platform and the aerofoil of the turbine blade have edge lengths
within the range 200 to 700 nm, more preferably within the range
250 to 500 nm. The volume fraction of primary cuboidal gamma prime
phase precipitates in the platform and the aerofoil of the turbine
blade is at least 50 vol %, more preferably at least 60 vol %, for
example 70 vol %. The gamma channel widths between the gamma prime
phase precipitates in the platform 16 and aerofoil 18 of the
turbine blade 10 is within the range 10 to 100 nm, more preferably
within the range 30 to 60 nm. Due to the high anti-phase boundary
(APB) energy associated with dislocation shearing of the gamma
prime phase precipitates, dislocations are forced to bow in-between
the gamma prime phase precipitates within the gamma phase channels
during deformation. The combination of a large volume fraction of
gamma prime phase precipitates and narrow gamma phase channels
maximises the Orowan resistance to dislocation bowing thereby
minimising creep deformation at elevated temperature, above
750.degree. C.
[0051] The primary cuboidal gamma prime phase precipitates in the
root 12 and shank 14 of the turbine blade 10 have edge lengths
within the range of 200 to 700 nm, more preferably within the range
of 250 to 500 nm. The secondary spheroidal and/or cuboidal gamma
prime phase precipitates in the root 12 and shank 14 of the turbine
blade 10 have edge lengths within the range of 1 to 50 nm, more
preferably within the range of 5 to 20 nm. The secondary spheroidal
and/or cuboidal gamma prime phase precipitates in the root 12 and
the shank 14 of the turbine blade 10 are contained within the gamma
channels between the primary cuboidal gamma prime phase
precipitates. Low cycle fatigue is the dominant failure mechanism
at lower temperatures and occurs at temperatures lower than those
for creep deformation and the fine dispersion of secondary gamma
prime phase precipitates effectively serve as obstacles to restrict
dislocation mobility. The root 12 and shank 14 of the turbine blade
10 are not subjected to elevated temperatures, above 750.degree.
C., and do not suffer dislocation climb mechanisms or dissolution
of the small secondary gamma prime precipitates and hence the low
cycle fatigue response and low cycle fatigue life of the root 10 of
the turbine blade 10 is improved.
[0052] The uni-modal distribution of gamma prime phase precipitates
in the aerofoil 18 and the platform 16 and the narrow gamma
channels associated with the microstructure offer maximum
resistance against tensile and creep deformation at temperatures
above 800.degree. C. in the aerofoil 18 of the turbine blade 10.
The b-modal distribution of gamma prime phase precipitates in the
root 12 and shank 14 improves the low cycle fatigue properties of
the turbine blade 10. The turbine blade 10 is able to sustain a
greater number of engine operating cycles before inspection or
overhaul of the turbine blades 10 is required or the root 12 of the
turbine blade 10 is able to withstand higher stresses.
[0053] The present invention is applicable to any nickel base
single crystal superalloy strengthened by gamma prime phase
precipitates. The present invention is particularly applicable to
nickel base single crystal superalloys with relatively high content
of refractory elements, e.g. tantalum, tungsten, molybdenum,
niobium and/or rhenium, and in particular to 3.sup.rd, 4.sup.th or
5.sup.th generation nickel base single crystal superalloys. This is
due to the high concentration of refractory elements
supersaturating the gamma phase, modifying the kinetics of the
superalloy system and stabilising the secondary gamma prime phase
precipitates to temperatures above 750.degree. C.
[0054] The 3.sup.rd generation nickel base single crystal
superalloys have greater than 3 wt % rhenium, the 4.sup.th
generation nickel base single crystal superalloys have less than 4
wt % ruthenium and the 5.sup.th generation of nickel base single
crystal superalloys have more than 4 wt % ruthenium. An example of
a 3.sup.rd generation nickel base single crystal superalloy is
CMSX10, an example of a 4.sup.th generation nickel base single
crystal superalloy is TMS138A and an example of a 5.sup.th
generation nickel base single crystal superalloy is TMS196.
[0055] CMSX10 consists of 5.7 wt % Al, 2.0 wt % Cr, 3.0 wt % Co,
0.4 wt % Mo, 0.2 wt % Ti, 8.0 wt % Ta, 5.0 wt % W, 6.0 wt % Re,
0.03 wt % Hf and the balance Ni plus incidental impurities.
[0056] TMS138A consists of 5.7 wt % Al, 3.2 wt % Cr, 5.8 wt % Co,
2.9 wt % Mo, 5.6 wt % Ta, 5.6 wt % W, 5.8 wt % Re, 3.6 wt % Ru,
0.01 wt % Hf and the balance Ni plus incidental impurities.
[0057] TMS196 consists of 5.6 wt % Al, 4.6 wt % Cr, 5.6 wt % Co,
2.4 wt % Mo, 5.6 wt % Ta, 5.0 wt % W, 6.4 wt % Re, 5.0 wt % Ru, 0.1
wt % Hf and the balance Ni plus incidental impurities.
[0058] A further single crystal turbine blade 110, as shown in FIG.
5, comprises a root 112, a shank 114, a platform 116, an aerofoil
118 and a shroud 120. The root 112, shank 114, platform 116,
aerofoil 118 and shroud 120 are integral and the root 112 is
connected to the platform 116 by the shank 114 and the shroud 120
is connected to the platform 116 by the aerofoil 118. The root 112
is fir-tree shaped or dovetail shaped in cross-section. The turbine
blade 110 comprises a nickel base single crystal superalloy having
a gamma phase matrix and gamma prime phase precipitates distributed
in the gamma phase matrix. The root 112 and the shank 114 of the
turbine blade 110 comprise a bi-modal distribution of gamma prime
phase precipitates in the gamma phase matrix. The platform 116, the
aerofoil 118 and the shroud 120 comprise a uni-modal distribution
of gamma prime phase precipitates in the gamma phase matrix.
[0059] A nickel base single crystal superalloy turbine blade
according to the present invention has a non-uniform gamma prime
phase precipitate microstructure which possesses mechanical
properties that match more closely the actual operating conditions
of the turbine blade and provides performance advantages over a
turbine blade with a uniform gamma prime phase precipitate
microstructure. This extends turbine blade life, particularly
turbine blades prone to low cycle fatigue failure below the
platform of the turbine blade in the root and/or shank of the
turbine blade. Alternatively the turbine rotor/turbine disc and
turbine blades may be operated at higher rotational speeds to
increase the efficiency of the gas turbine engine with the same
turbine blade life.
[0060] The nickel base single crystal turbine blade is produced by
pouring the molten nickel base superalloy in an investment mould
and then directionally solidifying the nickel base superalloy
within the investment mould to produce a nickel base superalloy
turbine blade 10. The investment mould either contains a single
crystal seed at the base of the investment mould and contacting a
chill plate or the investment mould comprises a single crystal
selector, e.g. a spiral, to ensure that a single crystal is formed
in the investment mould during directional solidification.
[0061] The dual microstructure is produced in the nickel base
single crystal superalloy turbine blade 10 by heat treating the
turbine blade 10 to produce primary cuboidal gamma prime
precipitates in a gamma phase matrix in the root 12, the shank 14,
the platform 16 and the aerofoil 18 and by heat treating the
turbine blade 10 to produce secondary gamma prime phase
precipitates in the root 12 and the shank 14.
[0062] In particular the dual microstructure is produced by cooling
the root 12 and the shank 14 of the turbine blade 10 at a lower
cooling rate B than the cooling rate A of the platform 16 and the
aerofoil 18 of the turbine blade 10 during the cooling from the
primary ageing temperature of the primary ageing heat treatment PA
to room temperature as shown in FIG. 6.
[0063] In a first method this is achieved by applying insulation on
the root 12 and shank 14 of the turbine blade 10 during the primary
ageing heat treatment or alternatively only during the cooling part
of the primary ageing heat treatment. The insulation may be a
metallic, refractory or other suitable insulation material located
on the root 12 and shank 14 of the turbine blade 10. The increased
thermal mass around the root 12 and the shank 14 reduces the
cooling rate for the root 12 and the shank 14 relative to the
un-insulated platform 16 and aerofoil 18 and therefore promotes the
precipitation of the fine secondary gamma prime precipitates. The
insulating material is selected to give the desired cooling rate in
conjunction with a process model of the cooling of the turbine
blade after the primary ageing heat treatment PA.
[0064] In a second method this is achieved by applying insulation
on the root 12 and shank 14 of the turbine blade 10 and providing a
heater in the insulation to heat the root 12 and the shank 14 of
the turbine blade 14 to further reduce the cooling rate of the root
12 and the shank 14 of the turbine blade 10 after the primary
ageing heat treatment PA. It may be possible to simply provide a
heater to heat the root 12 and the shank 14 without the insulation
to reduce the cooling rate of the root 12 and the shank 14 of the
turbine blade 10 after the primary ageing heat treatment PA. The
heater may be a localised induction heater, direct or indirect.
[0065] In a third method the root 12 and shank 14 of the turbine
blade 10 are submerged in a molten salt bath maintained at an
elevated temperature to reduce the cooling rate of the root 12 and
shank 14 of the turbine blade 10.
[0066] In a fourth method the dimensions of the cast turbine blade
10 in the region of the root 12 and shank 14 are oversized so that
the mass in the region of the root 12 and shank 14 is increased and
hence reduces the cooling rate of the root 12 and shank 14 of the
turbine blade 10. However, the additional mass in the region of the
root 12 and shank 14 of the turbine blade 10 results in the removal
of more material by machining to the required finished
dimensions.
[0067] In a fifth method a cooling fluid, liquid or gas, is
directed onto the internal surface or external surface of the
platform 16 and the aerofoil 18 of the turbine blade 10 to reduce
the cooling rate of the root 12 and the shank 14 of the turbine
blade 10 relative to the cooling rate of the platform 16 and the
aerofoil 18 of the turbine blade 10. This method may be used in
conjunction with the first, second, third and fourth methods
discussed above.
[0068] Alternatively the dual microstructure is produced by heating
the platform 16 and the aerofoil 18 of the turbine blade 10 to a
temperature C above the solvus temperature of the fine secondary
gamma prime precipitates while heating the root 12 and the shank 14
of the turbine blade 10 to a temperature D below the solvus
temperature of the fine secondary gamma prime precipitates during
the secondary ageing heat treatment SA, as shown in FIG. 7.
[0069] In a sixth method this is achieved by providing a heater to
heat the platform 16 and the aerofoil 18 to the temperature C above
the solvus temperature of the fine secondary gamma prime
precipitates to dissolve them. The heater may be a localised
induction heater, direct or indirect.
[0070] In a seventh method insulation is provided on the platform
16 and aerofoil 18 of the turbine blade 10 and the root 12 and the
shank 14 of the turbine blade 10 are given a local heat treatment
to precipitate secondary gamma prime phase precipitates while the
insulation maintains the platform 16 and the aerofoil 18 at a
temperature below the secondary gamma prime solvus so that
secondary gamma prime phase precipitates are not formed in the
platform 16 and the aerofoil 18. The insulation may be cooled by a
cooling fluid, liquid or gas.
[0071] In an eighth method induction heaters are provided to heat
to the whole of the turbine blade 10 as part of the primary heat
treatment, secondary heat treatment and coating heat treatment
step. The current supplied to the induction heaters/induction coils
is controlled such that different temperature gradients are
produced in different sections of the root 12, shank 14, platform
16 and aerofoil 18.
[0072] In general the cooling rate B is lower, or slower, than
cooling rate A. The rate chosen affects the solvus temperature
T.sub.solv of the fine gamma prime precipitates and therefore
temperatures C and D depend on the previous cooling rate A or B.
Each nickel base superalloy will have its own cooling rates A and B
and temperatures C and D.
[0073] Although the present invention has been described with
reference to a nickel base superalloy turbine blade it is equally
applicable to other nickel base superalloy components where it is
desired to have different mechanical properties in different
regions of the nickel base single crystal component.
* * * * *