U.S. patent application number 13/664662 was filed with the patent office on 2013-05-02 for component or coupon for being used under high thermal and stress load and method for manufacturing such component or coupon.
This patent application is currently assigned to ALSTOM Technology Ltd. The applicant listed for this patent is ALSTOM Technology Ltd. Invention is credited to Lukas Emanuel Rickenbacher, Jaroslaw Leszek Szwedowicz.
Application Number | 20130108460 13/664662 |
Document ID | / |
Family ID | 47040601 |
Filed Date | 2013-05-02 |
United States Patent
Application |
20130108460 |
Kind Code |
A1 |
Szwedowicz; Jaroslaw Leszek ;
et al. |
May 2, 2013 |
COMPONENT OR COUPON FOR BEING USED UNDER HIGH THERMAL AND STRESS
LOAD AND METHOD FOR MANUFACTURING SUCH COMPONENT OR COUPON
Abstract
A component or coupon for use in a thermal machine under extreme
thermal and mechanical conditions comprises an alloy material
having a controllable grain size (d). A grain size distribution
(d(X,Y,Z)) of the component or coupon corresponds to at least one
of an expected temperature distribution (T(X,Y,Z)), an expected
stress distribution (.sigma.(X,Y,Z)) and an expected strain
distribution (.epsilon.(X,Y,Z)), which vary with geometrical
coordinates (X,Y,Z) of the component or coupon, such that a
lifetime of the component or coupon is improved with respect to a
similar component or coupon having a substantially uniform grain
size.
Inventors: |
Szwedowicz; Jaroslaw Leszek;
(Bad Zurzach, CH) ; Rickenbacher; Lukas Emanuel;
(Basel, CH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ALSTOM Technology Ltd; |
Baden |
|
CH |
|
|
Assignee: |
ALSTOM Technology Ltd
Baden
CH
|
Family ID: |
47040601 |
Appl. No.: |
13/664662 |
Filed: |
October 31, 2012 |
Current U.S.
Class: |
416/241R ;
164/48 |
Current CPC
Class: |
B23K 26/342 20151001;
B33Y 80/00 20141201; B22F 3/1055 20130101; G05B 2219/45138
20130101; G05B 2219/35134 20130101; B22F 2003/1057 20130101; B33Y
50/02 20141201; G05B 19/4099 20130101; B22F 5/04 20130101; Y02P
10/25 20151101; B33Y 10/00 20141201; Y02P 10/295 20151101; C22F
1/10 20130101 |
Class at
Publication: |
416/241.R ;
164/48 |
International
Class: |
F01D 5/14 20060101
F01D005/14; B22D 25/06 20060101 B22D025/06 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 31, 2011 |
CH |
01755/11 |
Claims
1. A component or coupon for use in a thermal machine under extreme
thermal and mechanical conditions, the component or coupon
comprising: an alloy material having a controllable grain size (d)
and a grain size distribution (d(X,Y,Z)) that corresponds to at
least one of an expected temperature distribution (T(X,Y,Z)), an
expected stress distribution (.sigma.(X,Y,Z)) and an expected
strain distribution (.epsilon.(X,Y,Z)), which vary with geometrical
coordinates (X,Y,Z) of the component or coupon, such that a
lifetime of the component or coupon is improved with respect to a
similar component or coupon having a substantially uniform grain
size.
2. The component or coupon according to claim 1, wherein the
component or component is a part of a gas turbine.
3. The component or coupon according to claim 1, wherein the
component is a rotating turbine blade or the coupon is part of the
rotating turbine blade.
4. The component or coupon according to claim 1, wherein the alloy
material is a superalloy.
5. The component or coupon according to claim 1, wherein the
component or coupon is made by an additive manufacturing
process.
6. The component according to claim 5, wherein the additive
manufacturing process is selective laser melting (SLM).
7. A method for manufacturing a component or coupon, comprising:
generating 1D, 2D or 3D parameter distribution data of at least one
grain-size-relevant and lifetime-determining parameters (T,
.sigma., .epsilon. etc.) of the component or coupon under operating
conditions; and controlling, during manufacturing of the component
or coupon, a grain size distribution (d(X,Y,Z)) within the
component or coupon so as to maximize a lifetime of the component
or coupon.
8. The method according to claim 7, wherein the generating includes
generating the 3D parameter distribution data including a computed
3D temperature distribution T(X,Y,Z) and von Mises stress
distribution .sigma.(X,Y,Z) using a calculation.
9. The method according to claim 8, wherein the calculation
includes a Finite Elements Method (FEM).
10. The method according to claim 7, wherein the manufacturing of
the component or coupon is performed using an additive
manufacturing method, the grain size distribution (d(X,Y,Z)) being
directly generated during the additive manufacturing process.
11. The method according to claim 10, wherein the additive
manufacturing method includes a selective laser melting (SLM)
process of a suitable powder with a first laser beam, a grain size
(d) being controlled by controlling a cooling rate of a melt pool
within the SLM process.
12. The method according to claim 11, wherein the cooling rate of
the melt pool within the SLM process is controlled by controlling
local thermal gradients at a melting zone.
13. The method according to claim 12, wherein the local thermal
gradients at the melting zone are controlled by at least one of a
second laser beam and a radiant heater.
14. The method according to claim 12, wherein the SLM process
includes heating or cooling a substrate plate by a heating or
cooling medium so as to lower or increase the local thermal
gradients.
15. The method according to claim 7, wherein the manufacturing
includes providing the component or coupon with a homogeneous
microstructure, the grain size distribution (d(X,Y,Z)) being
generated after the homogeneous microstructure has been
created.
16. The method according to claim 15, wherein the grain size
distribution (d(X,Y,Z)) is generated by at least one of locally
heating and locally cooling the component or coupon.
Description
CROSS-REFERENCE TO PRIOR APPLICATION
[0001] Priority is claimed to Swiss Patent Application No. CH
01755/11, filed on Oct. 31, 2011, the entire disclosure of which is
hereby incorporated by reference herein.
FIELD
[0002] The present invention relates to the configuration and
manufacturing of components or coupons (i.e. a part of a component,
preferably used for repairing the component), especially for gas
turbines, which are used under extreme thermal and mechanical
conditions and to a method for manufacturing such component or
coupon.
BACKGROUND
[0003] Components of gas turbines or other thermal machines, e.g.
rotating blades or the like, are subject to severe operating
conditions. In general, grain size has an impact on the lifetime of
a component made of metal and/or ceramic alloys. Depending on the
operating temperatures or stresses, the component can suffer from
various failure mechanisms that are described as Low-Cycle Fatigue
(LCF), Thermo-Mechanical Fatigue (TMF), Creep, Oxidation, as well
as High-Cycle Fatigue (HCF) damages. In terms of the operation
condition, the designed system can be loaded by one or more damage
mechanisms, as they are mentioned above. However, other damage
mechanisms may also be taken into account.
[0004] In accordance with common criteria for the best lifetime
arrangement, small or big grain sizes of the applied alloy are
convenient for minimizing damage rate of LCF or creep mechanism,
respectively. Since the temperature and stress distribution within
the mechanical component are non-uniform, like for instance in a
gas turbine blade, some more specific rules for grain size in terms
of a local component loading seems to be more adequate than these
common well-known criteria.
[0005] Frequently, different parts of the same component can suffer
either from LCF or from creep, and then more specific criteria of
the grain size dependence of minimum LCF or creep rate are
expected. Concerning only the creep mechanism, the creep rate can
perform with respect to grain size in different manners as it is
schematically illustrated in FIG. 4.
[0006] For higher temperatures above 0.5T.sub.m, (where T.sub.m
denotes the absolute melting temperature of the alloy) and
intermediate stress magnitudes .sigma., the creep rate decreases up
to the specific value, which then remains constant independent on
increasing grain size (see a solid curve A in FIG. 4). For this
behavior, a dislocation climb mechanism dominates the creep
deformation.
[0007] In the range of intermediate temperature varying between 0.4
and 0.5T.sub.m, and higher stresses, the creep rate shows a minimum
value at a particular grain size of the alloy (see the dotted curve
B in FIG. 4). For constant temperature and stress, the creep rate
increases for higher grain sizes of the alloy. This damage
mechanism can be explained by the Hall-Petch rule, which describes
plastic flow for various grain sizes.
[0008] These considerations apply to the situation in a gas
turbine. FIG. 1 schematically illustrates the one-dimensional (1D)
radial distribution of temperature T and stress .sigma. acting on a
gas turbine blade rotating at the rotational speed .OMEGA. under
the nominal operation conditions. In the gas turbine 10 of FIG. 1,
11 denotes a rotor rotating around a machine axis 21 with
rotational speed .OMEGA.. A rotating blade 15 is mounted on the
rotor 11 with a root 12. The blade 15 further comprises a shank 13,
a platform 14 and an airfoil 22. Upstream of the blade 15 with
respect to the hot gas flow 20, a (stationary) vane 16 is shown.
The rotor 11 is surrounded by a stationary casing 17. 18 and 19 are
circumferential and axial sealing systems, respectively, preventing
from leakage of hot gas into the cooled lower part of the blade
15.
[0009] The gas turbine blade 15, which is schematically shown in
FIG. 1, is an example of a mechanical component whose lifetime
depends on the evaluated temperature, which generates non-uniform
thermal stress distribution within the component. The rotating
turbine blade 15 is additionally loaded by the centrifugal stresses
that depend on radius r and rotational speed .OMEGA. (see left part
of FIG. 1). The 1-dimensional centrifugal stresses a achieve their
maximum in root 12, which attaches blade 15 to the rotor 11.
[0010] The performance of a gas turbine engine increases with
higher firing temperature in the combustor, and therefore vane 16
and blade 15 operate in the range of high temperatures close to
T.sub.m. To protect the blades and vanes from oxidation damage,
they are covered by a thermal barrier coating (TBC) and in addition
cooled internally by a coolant, such as either air provided from
the compressor, or steam injected from other systems, like a steam
turbine (in a combined-cycle environment). The coolant is
redistributed under platform 14 of blade 15 to reduce the
temperature of the shank section 13 and root part 12, where the
stresses reach their maximum values due to the centrifugal loading
(see FIG. 1).
[0011] The complex geometries of blade 15 and vane 16 match with
requirements of the aerodynamic and mechanical integrity.
Therefore, many geometrical notches are present within the blade
and vane, thus inducing local stress concentrations.
[0012] The stresses .sigma. and temperatures T acting on the blade
15 under the nominal boundary condition can be computed with a
numerical approach, like e.g. the Finite Element Method (FEM),
Boundary Element Method (BEM), and others. In addition, the
temperatures and stresses are frequently measured in a prototyping
process of the engine, and those experimental results are used for
validation of the numerical values.
[0013] A metallurgical investigation of a component, which has been
in service, provides an empirical assessment of the real
temperatures in the system, which is also considered in the
validation of the numerical model and its thermal boundary
conditions. These three approaches or at least one of them can be
used for creating a detailed map of the temperature and stress
distribution within the whole component for the assessment of its
lifetime.
[0014] Based on the described variation of the temperature T and
mechanical stress .sigma. (or/and strain .epsilon.) magnitudes
within blade 15, which may lead either to LCF or creep damages, a
controlled variation of optimal grain sizes of the alloy is a
beneficial parameter for maximizing lifetime capability of the
component made of the same alloy or different alloys.
[0015] Document U.S. Pat. No. 5,649,280 A describes a method of
high retained strain forging for Ni-base superalloys, particularly
those which comprise a mixture of gamma and gamma prime phases, and
most particularly those which contain at least about 30 percent by
volume of gamma prime. The method utilizes an extended subsolvus
anneal to recrystallize essentially all of the superalloy and form
a uniform, free grain size. Such alloys may also be given a
supersolvus anneal to coarsen the grain size and redistribute the
gamma prime. The method permits the manufacture of forged articles
having a fine grain size in the range of about ASTM 5-12.
[0016] Document U.S. Pat. No. 5,759,305 A discloses a method of
making Ni-base superalloy articles having a controlled grain size
from a forging preform, comprising the steps of: providing a
Ni-base superalloy preform having a recrystallization temperature,
a gamma prime solvus temperature and a microstructure comprising a
mixture of gamma and gamma prime phases, wherein the gamma prime
phase occupies at least 30% by volume of the Ni-base superalloy;
hot die forging the superalloy preform at a temperature of at least
about 1600.degree. F., but below the gamma prime solvus temperature
and a strain rate from about 0.03 to about 10 per second to form a
hot die forged superalloy work piece; isothermally forging the hot
die forged superalloy work piece to form the finished article;
supersolvus heat treating the finished article to produce a
substantially uniform grain microstructure of about ASTM 6-8;
cooling the article from the supersolvus heat treatment
temperature.
[0017] Document U.S. Pat. No. 7,763,129 B2 teaches a method of
forming a component from a gamma-prime precipitation-strengthened
nickel-base superalloy so that, following a supersolvus heat
treatment the component is characterized by a uniformly-sized grain
microstructure. The method includes forming a billet having a
sufficiently fine grain size to achieve superplasticity of the
superalloy during a subsequent working step. The billet is then
worked at a temperature below the gamma-prime solvus temperature of
the superalloy so as to form a worked article, wherein the billet
is worked so as to maintain strain rates above a lower strain rate
limit to control average grain size and below an upper strain rate
limit to avoid critical grain growth. Thereafter, the worked
article is heat treated at a temperature above the gamma-prime
solvus temperature of the superalloy for a duration sufficient to
uniformly coarsen the grains of the worked article, after which the
worked article is cooled at a rate sufficient to reprecipitate
gamma-prime within the worked article.
[0018] Although these documents teach various methods for achieving
a certain optimized grain size within a gas turbine component, or
the like, there is no intent to establish, or knowledge about the
advantages of, a specified local variation of the grain size within
the component in accordance with the locally varying thermal and
mechanical loads on that component.
SUMMARY
[0019] In an embodiment, the present invention provides a component
or coupon for use in a thermal machine under extreme thermal and
mechanical conditions. The component or coupon comprises an alloy
material having a controllable grain size (d). A grain size
distribution (d(X,Y,Z)) of the component or coupon corresponds to
at least one of an expected temperature distribution (T(X,Y,Z)), an
expected stress distribution (.sigma.(X,Y,Z)) and an expected
strain distribution (.epsilon.(X,Y,Z)), which vary with geometrical
coordinates (X,Y,Z) of the component or coupon, such that a
lifetime of the component or coupon is improved with respect to a
similar component or coupon having a substantially uniform grain
size.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The present invention will be described in even greater
detail below based on the exemplary figures. The invention is not
limited to the exemplary embodiments. All features described and/or
illustrated herein can be used alone or combined in different
combinations in embodiments of the invention. The features and
advantages of various embodiments of the present invention will
become apparent by reading the following detailed description with
reference to the attached drawings which illustrate the
following:
[0021] FIG. 1 schematically illustrated the one-dimensional (1D)
radial distribution of temperature T and stress .sigma. acting on a
gas turbine blade rotating at the rotational speed .OMEGA. under
the nominal operation conditions;
[0022] FIG. 2 shows a computed 3D temperature (T) distribution in a
gas turbine blade in the Cartesian reference system (X,Y,Z), where
different grey scales correspond to different temperature
values;
[0023] FIG. 3 shows a computed 3D von-Mises stress (.sigma.)
distribution in a gas turbine blade in the Cartesian reference
system (X,Y,Z), where different grey scales correspond to different
stress values;
[0024] FIG. 4 shows two types of creep rate in terms of grain size,
where each of the curves A, B represents the creep behavior for a
constant temperature T and stress .sigma.;
[0025] FIG. 5 shows an illustration of the process according to the
invention based on the data from the 3D numerical results of
temperature T(X,Y,Z), strain .epsilon.(X,Y,Z), stress
.sigma.(X,Y,Z) or/and other parameter distributions for producing
of a component made of an alloy with controlled grain size d(X,Y,Z)
within the alloy for obtaining optimized material properties under
the operation condition of interest;
[0026] FIG. 6 shows a scheme of a suitable process apparatus for an
SLM manufacturing process for the component (turbine blade) to be
manufactured;
[0027] FIG. 7 shows a scheme of a suitable process apparatus with
additional heating and/or cooling means for processing the
component (turbine blade) to be manufactured; and
[0028] FIG. 8 shows a scheme of a suitable process apparatus, where
the grain size distribution is generated by a local heat treatment
of the manufactured component (turbine blade).
DETAILED DESCRIPTION
[0029] In an embodiment, the present invention provides a component
or coupon which is optimized in its internal structure with respect
to the locally different thermal and mechanical loads.
[0030] Another embodiment of the invention provides a method for
manufacturing such a component or coupon.
[0031] The component/coupon according to an embodiment of the
invention is made of an alloy material with a controllable grain
size, and is in service subjected to an expected temperature and/or
stress and/or strain distribution, which varies with the
geometrical coordinates of the component/coupon. It is
characterized in that it has a grain size distribution, which
depends on said expected temperature and/or stress and/or strain
distribution such that the lifetime of the component is improved
with respect to a similar component with a substantially uniform
grain size.
[0032] According to another embodiment of the invention said
component is a part of a gas turbine.
[0033] According to another embodiment of the invention said
component is a rotating turbine blade.
[0034] According to a further embodiment of the invention said
component or coupon is made of a superalloy.
[0035] According to another embodiment of the invention said
component or coupon is made by an additive manufacturing process,
especially selective laser melting (SLM).
[0036] The inventive method for manufacturing a component or coupon
according to an embodiment of the invention comprises the steps
of.
[0037] generating 1D or 2D or 3D parameter distribution data of one
or more grain-size-relevant and lifetime-determining parameters for
said component/coupon being under operating conditions; and
[0038] controlling during manufacturing of said component or coupon
the grain size distribution within said component or coupon in
order to maximize the lifetime of said component.
[0039] Grain-size-relevant means that the effect of these
parameters on the component can be controlled by grain size.
[0040] According to an embodiment of the inventive method 3D
parameter distribution data comprising a computed 3D temperature
distribution and von Mises stress distribution are generated by a
calculation, especially with a Finite Element Method (FEM).
[0041] According to another embodiment said component or coupon is
manufactured by means of an additive manufacturing method, and the
desired lifetime-maximizing grain size distribution is directly
generated during said additive manufacturing process.
[0042] Preferably, said additive manufacturing method includes
selective laser melting (SLM) of a suitable powder with a first
laser beam, whereby the grain size is controlled by controlling the
cooling rate of the melt pool within the SLM process.
[0043] Especially, the cooling rate of the melt pool within the SLM
process is controlled by controlling the local thermal gradients at
the melting zone.
[0044] Especially, the local thermal gradients at the melting zone
are controlled by a second laser beam and/or a radiant heater.
[0045] According to another embodiment a substrate plate for the
SLM process is used, which is heated or cooled by a heating or
cooling medium to lower or increase said thermal gradients.
[0046] According to a further embodiment said component is
manufactured with a homogeneous microstructure, and the desired
lifetime-maximizing grain size distribution is generated after said
manufacturing process.
[0047] Preferably, said lifetime-maximizing grain size distribution
is generated by locally heating and/or cooling said component.
[0048] The present invention recognizes that the grain size has an
impact on the lifetime of the component operating at elevated
temperatures. An additive manufacturing process (selective laser
sintering or melting (SLS or SLM), electron beam melting (EBM), 3D
printing or other additive manufacturing processes) of the entire
component or only its repair coupon is controlled in terms of the
three-dimensional temperature T, strain .epsilon. or/and stress
.sigma. distribution obtained from numerical, experimental, or/and
empirical approaches. In the numerical or/and lifetime model of the
component, the stress field is described with a vector of 6 stress
components such as:
[0049] .sigma..sub.xx the normal stress in the X-direction of the
Cartesian reference system,
[0050] .sigma..sub.yy the normal stress in the Y-direction of the
Cartesian reference system,
[0051] .sigma..sub.zz the normal stress in the Z-direction of the
Cartesian reference system,
[0052] .sigma..sub.xy the shear stress on the XY-plane of the
Cartesian reference system,
[0053] .sigma..sub.yz the shear stress on the YZ-plane of the
Cartesian reference system, and
[0054] .sigma..sub.zx the shear stress on the ZX-plane of the
Cartesian reference system.
[0055] Also, the strain state is defined in the same manner like
the stress by using 3 normal .epsilon..sub.xx, .epsilon..sub.yy,
.epsilon..sub.zz, and 3 shear .epsilon..sub.xy, .epsilon..sub.yz,
.epsilon..sub.zx strain components referred in the Cartesian
reference system. By using the matrix notation, the relation
between the stress and strain at every point of the component is
determined for the three-dimensional stress field based on Hooke's
law by
{.sigma.}=[C]{.epsilon.}, (1)
[0056] where {.sigma.} and {.epsilon.} are vectors of the six
stress and strain components, whereby [C] denotes a (6.times.6)
matrix, called the elastic stiffness, which in the general case of
anisotropic materials, contains 36 elastic constants C.sub.i,j,
where i=1, 2, . . . , 6, and j=1, 2, . . . , 6. In case of an
isotropic material, the matrix [C] is determined with Poisson's
ratio v and Young modulus E(T), which depends on the metal
temperature T.
[0057] In general, the stress and strain components depend on
displacements (deformations) of an arbitrary point of the deformed
part. These deformations are driven by the thermal expansion and/or
mechanical loadings that can act as a static or dynamic pressure
and/or forces on the component. The deformations of an arbitrary
point are defined with the displacement vector {q}=col{q.sub.x,
q.sub.y, q.sub.z}, determining displacements of this point in the
Cartesian reference system along the X, Y, and Z axis,
respectively. The relation of the strain to the deformation at an
arbitrary point (X,Y,Z) of the part is defined by:
.epsilon..sub.xx=.differential.q.sub.x/.differential.X, (2)
.epsilon..sub.yy=.differential.q.sub.y/.differential.Y, (3)
.epsilon..sub.zz=.differential.q.sub.z/.differential.Z, (4)
.epsilon..sub.xy=(.differential.q.sub.x/.differential.Y+.differential.q.-
sub.y/.differential.X)/2, (5)
.epsilon..sub.yz=(.differential.q.sub.y/.differential.Z+.differential.q.-
sub.z/.differential.y)/2, (6)
.epsilon..sub.zx=(.differential.q.sub.z/.differential.X+.differential.q.-
sub.x/.differential.Z)/2. (7)
[0058] In the design process, the stress {.sigma.}, strain
{.epsilon.}, displacement {q} and temperature T of an arbitrary
point are computed with an engineering software based on the Finite
Element Methods, Boundary Element Methods, and others. A typical
example of these analyses is shown in FIGS. 2 and 3 for the
three-dimensional temperature (FIG. 2) and stress (FIG. 3)
distribution of a gas turbine blade defined in the Cartesian
reference system.
[0059] With respect to the temperature and stress distribution,
these tools exactly predict the lifetime of the part using the
failure mechanisms of creep, Low Cycle Fatigue, High Cycle Fatigue,
Fracture Mechanic, Relaxation, and others. In order to include the
grain size d of the polycrystalline materials, the general creep
equation can be expressed by
d.epsilon..sub.C/dt=(C .sigma..sup.m exp(-Q/kT))/d.sup.b (8)
[0060] where .epsilon..sub.C denotes the creep strain, C means is a
material constant of the specific creep mechanism, m and b are
exponents dependent on the creep mechanism, Q corresponds to the
activation energy of the creep mechanism, T is the absolute
temperature at point (X,Y,Z), .sigma. is the stress acting on the
point (X,Y,Z) of interest, d is the size of the grain of the
material, and k is Boltzmann's constant. In the literature,
different models of the creep being dependent on the grain size are
given are well-known.
[0061] Regarding the grain size d, the yield stress .sigma..sub.p
can be defined for instance by
.sigma..sub.p=G b(.rho.).sup.1/2+K/(d).sup.1/2, (9)
[0062] where G is the shear modulus G(T)=E(T)/[2(1+v)] dependent on
temperature T, b denotes Burger's vector, K means Hall-fetch
coefficient, and .rho. is the dislocation density.
[0063] By using the equations (8)-(9), or similar equations given
in the literature or obtained from an internal investigation, a
trend of the strain behaviors in terms of grain size d can be
calculated with respect to the arbitrary position (X,Y,Z) of the
part. For the component of interest, whose stress and temperature
fields are computed with respect to the service conditions for
maximizing the lifetime, the required grain size d is transferred
to the manufacturing machine or processing apparatus, which
produces the component with the locally controlled grain sizes
d(X,Y,Z) dependent on the temperature T(X,Y,Z), stress
.sigma.(X,Y,Z) or/and strain .epsilon.(X,Y,Z) or other parameter
based on the lifetime model.
[0064] This process is illustrated in FIG. 5, where different
technologies of additive manufacturing can be used. The process
according to FIG. 5 is an additive manufacturing process or
customized local heat treatment process based on 3D parameter
distribution data 24 from the 3D finite element temperature T and
stress .sigma. results of the shrouded gas turbine blade under the
nominal service condition.
[0065] The numerical model of temperature T(X,Y,Z), strain
.epsilon.(X,Y,Z), stress .sigma.(X,Y,Z) and other parameters is
used for determining the demanded grain size d(X,Y,Z) resulting in
the maximum lifetime of the part with respect to the desired
operation conditions. The 3D parameter distribution data 24 are
transferred to a processing apparatus 25, which processes the
desired component 26.
[0066] In a preferred embodiment of this invention and
representative for any potential additive manufacturing process,
selective laser melting (SLM) is used to produce the mechanical
component. Selective laser melting (SLM) is an additive
manufacturing technology used to directly produce metallic parts
from powder materials. As described for example in document U.S.
Pat. No. 6,215,093 B1, thin powder layers with a thickness of
typically between 20 .mu.m to 60 .mu.m are generated on a metallic
base plate or the already produced fraction of an object,
respectively. The cross-sections of a sliced CAD model stored in
the SLM machine are scanned subsequently using a high power laser
beam to compact the powder material. In general the STL-format is
used to transfer the model geometry to the SLM machine.
[0067] FIG. 6 shows a schematic diagram of a respective processing
apparatus using SLM. The processing apparatus 27 of FIG. 6
comprises a displaceable substrate plate 28 for the processed and
non-processed powder layers 29, which successively build up the
component 26. A scanning focused laser beam 32 is generated by a
laser source 31. Movement and power of the laser source 31 or laser
beam 32 and movement of the substrate plate 28 are controlled by a
control unit 30.
[0068] In an embodiment of the present invention the STL file
mentioned above will be replaced accordingly by a CAD file
including not only the geometrical information but also the
temperature T(X,Y,Z), stress .sigma.(X,Y,Z) or/and strain
.epsilon.(X,Y,Z) or other parameter distribution based on the
lifetime model. The optimal grain size distribution can then be
derived from the above-mentioned information and equations. The
optimal grain size d(X,Y,Z) can either be already included in the
mentioned CAD file or can be calculated on the SLM machine (27)
during processing.
[0069] To achieve the desired grain size d(X,Y,Z), the process
parameters of the manufacturing process have to be adapted
accordingly. This can be done for the whole layer or selectively.
In general, the grain size correlates to the cooling rate of the
melt pool within the SLM process: the higher the thermal gradient
the smaller the resulting grain size, and vice versa. Therefore,
the precise local adaption of the process parameters, such as but
not limited to, laser power, laser mode (continuous wave or
pulsed), laser focus diameter, scan speed and scan strategy is
crucial to achieve the desired thermal gradient and grain sizes,
respectively.
[0070] Further process equipment or processing apparatus can be
used to better adjust local thermal gradients. In a preferred
embodiment of this invention, a second laser beam 32' (FIG. 6) is
used to heat up surrounding material and therefore selectively
lowering the local thermal gradients to achieve the desired grain
sizes.
[0071] In another embodiment of this invention (FIG. 7) a radiant
heater 33 can be used in the processing apparatus 27' instead or in
combination with the second laser beam 32' to adjust the
temperature distribution within the powder layer 29 or even within
the whole process chamber. An example of such a radiant heater 33
is described in document EP 1 762 122 B2. Additionally, a substrate
plate 28' heated or cooled by a heating or cooling medium 34 (FIG.
7) can be used to lower or increase thermal gradients. An
embodiment of such a heated substrate plate is described in
document DE 101 04 732 C1. However, one skilled in the art may find
other beneficial equipment helping to locally adjust thermal
gradients, which are included herein as well.
[0072] By using the described method and means a component or its
part can be produced with locally optimized grain sizes in respect
to the local 6 normal and shear stresses {.sigma.(X,Y,Z)} or
strains {.epsilon.(X,Y,Z)} obtained from the 1D, 2D, or 3D
numerical simulations. Therefore, these components have superior
lifetime compared to conventionally manufactured components.
[0073] The description of the stress and/or strain field of the
component/part can be simplified by other approaches. For instance,
the stress and strain distribution can be represented by the
average normal and shear stress or/and strain instead of
digitalized stress .sigma.(X,Y,Z) state of the component/part. In
this case, the stress, temperature, strain and other parameters
vary with respect to the one direction of the reference system like
it is shown in FIG. 1, where stress .sigma. and temperature T vary
in terms of the radial coordinate r. Also, different modeling
methods of the stress/strain at the arbitrary point (X,Y,Z) can be
used, for instance the principle stress/strain definition or
others.
[0074] If the component or its repair coupon is produced with a
homogenous microstructure of the alloy for a constant grain size, a
customized and locally varying heat treatment can be applied
according to FIG. 8. The component/part 26 is heat-treated in a
processing apparatus 27'' with respect to a customized variation of
grain sizes using the numerical, experimental or empirical results
of temperature T and stress .sigma. (or strain .epsilon.). A focal
pointing heat generator 35 or/and a cooling system 36 could be
considered as example of a device for generation of variable grain
sizes within the produced component/part depending on the known
temperature T and mechanical stress .sigma. (or strain
.epsilon.).
[0075] A suitable and exemplary alloy for a component or coupon
(repair part of the component) according to the invention may be
IN738LC. Other Ni base superalloys or superalloys on a different
basis are also suitable.
[0076] The process of the additive manufacturing produces the
object for the controlled local optimal grain sizes with respect to
the expected loading. Arbitrary approaches, such as: different
sizes of the metal powder applied to the process, adjusting laser
power, and others may be taken in consideration, but are not
presented here in detail for each process.
[0077] While the invention has been illustrated and described in
detail in the drawings and foregoing description, such illustration
and description are to be considered illustrative or exemplary and
not restrictive. It will be understood that changes and
modifications may be made by those of ordinary skill within the
scope of the following claims. In particular, the present invention
covers further embodiments with any combination of features from
different embodiments described above and below.
[0078] The terms used in the attached claims should be construed to
have the broadest reasonable interpretation consistent with the
foregoing description. For example, the use of the article "a" or
"the" in introducing an element should not be interpreted as being
exclusive of a plurality of elements. Likewise, the recitation of
"or" should be interpreted as being inclusive, such that the
recitation of "A or B" is not exclusive of "A and B." Further, the
recitation of "at least one of A, B and C" should be interpreted as
one or more of a group of elements consisting of A, B and C, and
should not be interpreted as requiring at least one of each of the
listed elements A, B and C, regardless of whether A, B and C are
related as categories or otherwise.
LIST OF REFERENCE NUMERALS
[0079] 10 gas turbine [0080] 11 rotor [0081] 12 root [0082] 13
shank [0083] 14 platform [0084] 15 blade [0085] 16 vane [0086] 17
casing [0087] 18,19 sealing system [0088] 20 hot gas flow [0089] 21
machine axis [0090] 22 airfoil [0091] 23 blade [0092] 23a airfoil
[0093] 23b platform [0094] 23c root [0095] 24 3D parameter
distribution data [0096] 25,27,27',27'' processing apparatus [0097]
26 component (part, coupon) [0098] 28 substrate plate
(displaceable) [0099] 29 powder layer [0100] 30 control unit [0101]
31 laser source [0102] 32,32' laser beam (focused) [0103] 33
radiant heater [0104] 34 cooling/heating medium [0105] 35 focal
pointing heat generator [0106] 36 cooling system [0107] A,B curve
[0108] r,r.sub.0 radius [0109] T temperature [0110] .sigma. stress
[0111] .OMEGA. rotational speed
* * * * *