U.S. patent application number 13/937881 was filed with the patent office on 2014-01-16 for thermal barrier coating for industrial gas turbine blade, and industrial gas turbine using the same.
The applicant listed for this patent is Hitachi, Ltd., NATIONAL UNIVERSITY CORPORATION HOKKAIDO UNIVERSITY. Invention is credited to Hideyuki ARIKAWA, Takeshi IZUMI, Tadashi KASUYA, Yoshitaka KOJIMA, Akira MEBATA, Toshio NARITA.
Application Number | 20140017511 13/937881 |
Document ID | / |
Family ID | 48782982 |
Filed Date | 2014-01-16 |
United States Patent
Application |
20140017511 |
Kind Code |
A1 |
IZUMI; Takeshi ; et
al. |
January 16, 2014 |
THERMAL BARRIER COATING FOR INDUSTRIAL GAS TURBINE BLADE, AND
INDUSTRIAL GAS TURBINE USING THE SAME
Abstract
Disclosed is a turbine blade for an industrial gas turbine
including a blade substrate; a multilayer alloy coating containing
a diffusion barrier layer; a bond coat; and a top coat. The blade
substrate being formed of a single crystal alloy which consists
essentially of 0.06 to 0.08% of C, 0.016 to 0.035% of B, 0.2 to
0.3% of Hf, 6.9 to 7.3% of Cr, 0.7 to 1.0% of Mo, 7.0 to 9.0% of W,
1.2 to 1.6% of Re, 8.5 to 9.5% of Ta, 0.6 to 1.0% of Nb, 4.9 to
5.2% of Al, 0.8 to 1.2% of Co, and the balance being Ni and
incidental impurities by weight. The multilayer alloy coating, the
bond coat and the top coat being directly and sequentially
laminated on a surface of the blade substrate, in which the
diffusion barrier layer is a multilayer and a discontinuous
layer.
Inventors: |
IZUMI; Takeshi;
(Hitachi-shi, JP) ; ARIKAWA; Hideyuki; (Mito-shi,
JP) ; KOJIMA; Yoshitaka; (Hitachi-shi, JP) ;
MEBATA; Akira; (Kitaibaraki-shi, JP) ; KASUYA;
Tadashi; (Hitachinaka-shi, JP) ; NARITA; Toshio;
(Sapporo-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NATIONAL UNIVERSITY CORPORATION HOKKAIDO UNIVERSITY
Hitachi, Ltd. |
Sapporo-shi
Tokyo |
|
JP
JP |
|
|
Family ID: |
48782982 |
Appl. No.: |
13/937881 |
Filed: |
July 9, 2013 |
Current U.S.
Class: |
428/633 |
Current CPC
Class: |
F01D 5/288 20130101;
C23C 10/02 20130101; C23C 28/3455 20130101; Y10T 428/12618
20150115; C23C 28/42 20130101; F05D 2300/10 20130101; C23C 28/321
20130101; C23C 10/38 20130101; C23C 10/60 20130101; C23C 28/3215
20130101; C23C 28/325 20130101; Y02T 50/60 20130101; Y02T 50/672
20130101; C23C 28/00 20130101; C23C 10/00 20130101 |
Class at
Publication: |
428/633 |
International
Class: |
F01D 5/28 20060101
F01D005/28 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 10, 2012 |
JP |
2012-154401 |
Claims
1. A turbine blade for an industrial gas turbine comprising: a
blade substrate; a multilayer alloy coating containing a diffusion
barrier layer; a bond coat; and a top coat, the blade substrate
being formed of a single crystal alloy which consists essentially
of 0.06 to 0.08% of C, 0.016 to 0.035% of B, 0.2 to 0.3% of Hf, 6.9
to 7.3% of Cr, 0.7 to 1.0% of Mo, 7.0 to 9.0% of W, 1.2 to 1.6% of
Re, 8.5 to 9.5% of Ta, 0.6 to 1.0% of Nb, 4.9 to 5.2% of Al, 0.8 to
1.2% of Co, and the balance being Ni and incidental impurities by
weight, the multilayer alloy coating, the bond coat and the top
coat being directly and sequentially laminated on a surface of the
blade substrate, wherein the diffusion barrier layer is a
multilayer and a discontinuous layer.
2. The turbine blade according to claim 1, wherein the diffusion
barrier layer is an alloy which contains Re, Cr, and Ni.
3. An industrial gas turbine including the turbine blade of claim
1.
Description
CLAIM OF PRIORITY
[0001] The present application claims priority from Japanese Patent
application serial No. 2012-154401, filed on Jul. 10, 2012, the
content of which is hereby incorporated by reference into this
application.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a thermal barrier coating
structure preferable for, for example, turbine blades for an
industrial gas turbine.
[0004] 2. Description of Related Art
[0005] In gas turbines, there has been an increasing trend for
higher combustion gas temperatures for improved efficiency. For
materials of turbine blades and nozzles, directional solidification
alloys, and single crystal alloys having high heat-resistant
temperature have been developed as replacements for common
polycrystalline alloys. However, the combustion gas temperature
already exceeds the melting points of such blade materials, and it
is now common to form a thermal barrier coating (TBC) on substrate
surfaces of turbine blades and nozzles, in addition to using
various cooling techniques.
[0006] The TBC is configured from a top coat as a thermal barrier,
and a bond coat for providing oxidation resistance and corrosion
resistance. Oxides of low coefficient of thermal conductivity are
used for the top coat, and yttria stabilized zirconia (YSZ), in
which the crystalline structure is made stable by addition of
yttria is widely used. For the bond coat, MCrAlY alloys (M is at
least one of Ni, Co, and Fe), and aluminides such as Ni--Al, and
Ni--Al--Pt are used.
[0007] The bond coat forms a thermal grown oxide (TGO) on the
surface, and protects the substrate from oxidative and corrosive
environment. Because alumina is preferably used for the TGO, the
bond coat typically has a higher Al concentration than the
substrate. On the other hand, diffusion of Al from the bond coat to
the substrate is promoted, and formation of an altered layer which
is called a secondary reaction zone (SRZ) in the substrate surface
has become apparent along with the increasing trend for higher
combustion temperatures. In the SRZ, a precipitated phase is
generated in abundance, and the structure greatly differs from the
original alloy structure. These are detrimental to mechanical
property important for gas turbine blades such as creep strength
and fatigue strength.
[0008] As a countermeasure, International Publication WO2008/059971
(Patent Document 1) discloses a method for suppressing element
diffusion into a substrate during high-temperature use with the use
of a multilayer alloy coating configured from a stabilizing layer,
and a diffusion barrier layer formed of a Re-containing alloy.
[0009] In the process for producing a heat-resistant alloy member
that includes the multilayer alloy coating described in Patent
Document 1, the diffusion barrier layer is deposited by plating and
heat treatment, and this is followed by a solution heat treatment
and an aging treatment to control structure of the substrate, and
to stabilize structure of the multilayer alloy coating.
[0010] From the standpoint of preventing element diffusion into the
substrate, the diffusion barrier layer is described as being
desirably formed as a continuous layer in the producing process of
Patent Document 1.
[0011] Japanese Patent No. 3559670 (Patent Document 2) describes a
Ni-based single crystal alloy consisting essentially of 0.06 to
0.08% of C, 0.016 to 0.035% of B, 0.2 to 0.3% of Hf, 6.9 to 7.3% of
Cr, 0.7 to 1.0% of Mo, 7.0 to 9.0% of W, 1.2 to 1.6% of Re, 8.5 to
9.5% of Ta, 0.6 to 1.0% of Nb, 4.9 to 5.2% of Al, 0.8 to 1.2% of
Co, and the balance being Ni and incidental impurities by
weight.
SUMMARY OF THE INVENTION
[0012] A turbine blade for an industrial gas turbine of the present
invention includes an Ni-based single crystal alloy which is
prepared by adding grain boundary enhancing elements such as C, B,
and Hf, and having a large acceptable crystal orientation
difference for heterocrystals of different orientations from single
crystals.
[0013] The present invention can prevent element diffusion into the
substrate with the use of the diffusion barrier layer, and improve
durability against thermal fatigue due to thermal cycles and
durability against mechanical fatigue. Thus the present invention
makes it possible to improve the strength reliability of the
turbine blade for industrial gas turbine, and increase the lifetime
of the turbine blade for industrial gas turbine.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a flowchart showing procedures of a multilayer
alloy coating deposition method of Example.
[0015] FIG. 2A is a cross sectional view schematically illustrating
a TBC including diffusion barrier layers of Example.
[0016] FIG. 2B is a cross sectional view schematically illustrating
a TBC including diffusion barrier layers of Example.
[0017] FIG. 3 is a SEM image showing a cross section of a barrier
layer of a TBC including diffusion barrier layers of an
Example.
[0018] FIG. 4 is a SEM image showing a cross section of the TBC
including diffusion barrier layers of the Example after a heat
testing.
[0019] FIG. 5 is a SEM image showing a cross section of the TBC
including diffusion barrier layers of the Example after a thermal
cycle testing.
[0020] FIG. 6 is a SEM image showing a cross section of a TBC
including a multilayer alloy coating of a Comparative Example after
the thermal cycle testing.
[0021] FIG. 7A is a partial cross sectional view illustrating a
turbine blade for industrial gas turbine.
[0022] FIG. 7B is a partially enlarged cross sectional view
illustrating details of portion A of FIG. 7A.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0023] Turbine blades for industrial gas turbine experience thermal
fatigue caused by fluctuations of thermal stress due to thermal
cycles during operation and upon shutdown. The present inventors
conducted an element test for a test piece, and confirmed that a
multilayer alloy coating deposited by using the method described in
Patent Document 1 undergoes horizontal cracking in its brittle
diffusion barrier layer and at the interface of the diffusion
barrier layer under thermal cycle conditions. A problem of the
continuous diffusion barrier layer, then, is the rapid propagation
of cracking.
[0024] One characteristic of turbine blades for industrial gas
turbine is that they require more long-term durability than turbine
blades for aircraft, and it is important to maintain the alloy
structure over a long lifetime, and to prevent generation of
heterocrystals, particularly in single-crystal gas turbine
blades.
[0025] In the present invention, the Ni-based single crystal alloy
described in Patent Document 2 is materially suited as the material
of a large single-crystal blade, the alloy being prepared by adding
grain boundary enhancing elements such as C, B, and Hf, and having
a large acceptable crystal orientation difference for
heterocrystals of different orientations from single crystals. In
the following, such an alloy will be referred to as a single
crystal alloy for use in the present invention.
[0026] Applying the diffusion barrier layer-containing multilayer
alloy coating of Patent Document 1 to a turbine blade for
industrial gas turbine formed of the single crystal alloy for use
in the present invention is effective in suppressing the growth of
the secondary reaction zone due to element diffusion into the
substrate at high temperature. The downside, however, is that the
diffusion barrier layer is damaged under the thermal fatigue caused
by thermal cycles during operation and upon shutdown considered
important in gas turbine blades, and under the fatigue caused by
changes in mechanical stress. This is detrimental to effectiveness,
and has the risk of promoting cracking in the diffusion barrier
layer.
[0027] The present invention has been completed over the foregoing
problems, and it is an object of the present invention to provide a
thermal barrier coating structure that includes a diffusion barrier
layer and for use in single-crystal turbine blades for industrial
gas turbine formed of a single crystal alloy for use in the present
invention, and that can suppress the growth of the secondary
reaction zone due to element diffusion into the substrate, and can
provide durability against thermal fatigue due to thermal cycles,
and durability against mechanical fatigue.
[0028] The present inventors conducted intensive studies to solve
the foregoing problems, and found that the problems can be solved
by forming a discontinuous multilayer diffusion barrier layer. The
present invention was completed on the basis of this finding.
[0029] An embodiment of the present invention (hereinafter, also
referred to as "the present embodiment" as appropriate) is
described below in detail. It should be noted that the present
embodiment is not limited to the contents of the following
descriptions, and may be modified in any ways, provided that such
changes do not depart from the gist of the present invention.
[0030] A turbine blade for industrial gas turbine of an embodiment
of the present invention has a structure that includes a diffusion
barrier layer-containing multilayer alloy coating, a bond coat, and
a top coat directly and sequentially laminated on a surface of a
blade substrate formed of a single crystal alloy which consists
essentially of 0.06 to 0.08% of C, 0.016 to 0.035% of B, 0.2 to
0.3% of Hf, 6.9 to 7.3% of Cr, 0.7 to 1.0% of Mo, 7.0 to 9.0% of W,
1.2 to 1.6% of Re, 8.5 to 9.5% of Ta, 0.6 to 1.0% of Nb, 4.9 to
5.2% of Al, 0.8 to 1.2% of Co, and the balance being Ni and
incidental impurities by weight, in which the diffusion barrier
layer is a multilayer and a discontinuous layer.
[0031] In the turbine blade for industrial gas turbine, the
diffusion barrier layer is preferably an alloy that contains Re,
Cr, and Ni.
[0032] As used herein, for example, "0.06% or more to 0.08% or
less" has the same meaning as "0.06% or more and 0.08% or less",
and can also be recited as "0.06 to 0.08%". The same applies to all
the other numerical ranges recited herein.
[0033] The step of forming the diffusion barrier layer-containing
multilayer alloy coating and the TBC on the single crystal alloy
for use in the present invention in a diffusion barrier deposition
method of an embodiment of the present invention is performed
according to the following procedures, as shown in FIG. 1.
[0034] (1) The substrate is subjected to a solution heat treatment
(solution heat treatment step).
[0035] (2) The substrate is processed into a blade shape (shaping
step).
[0036] (3) The diffusion barrier layer-containing multilayer alloy
coating is deposited on the substrate (multilayer alloy coating
deposition step).
[0037] The multilayer alloy coating deposition step includes a
plating step and a Cr cementation step. The multilayer alloy
coating deposition step is also referred to as a "barrier
deposition step".
[0038] (4) The bond coat is deposited on the diffusion barrier
layer-containing alloy coating (bond coat deposition step).
[0039] (5) The substrate is aged with the diffusion barrier
layer-containing multilayer alloy coating and the bond coat
deposited thereon (aging step).
[0040] (6) The top coat is deposited on the bond coat (top coat
deposition step).
[0041] The steps (4) to (6) are also collectively referred to as a
"TBC deposition step".
[0042] Each step is described below.
(Barrier Deposition Step)
[0043] The diffusion barrier-containing multilayer alloy coating of
the embodiment of the present invention includes a diffusion
barrier layer and an interlayer, the diffusion barrier layer being
directly in contact with the substrate surface of the single
crystal alloy for use in the present invention. When depositing the
TBC by using thermal spray, a protective layer may be inserted to
protect the diffusion barrier layer from the impact of thermal
spray.
[0044] Various techniques can be used for the deposition method.
First, a metal coating of Ni, Re--Ni, and Ni--W is formed on the
blade substrate surface, using electrolytic plating and
nonelectrolytic plating. In the embodiment of the present
invention, the diffusion barrier layer is a Re-containing alloy,
and contains Cr as another metallic element. As such, a Cr
cementation process is performed to cause the Cr to react with the
metal coating deposited on the blade substrate surface, depositing
the multilayer alloy coating that contains the diffusion barrier
layer of a Re-containing alloy.
[0045] The multilayer alloy coating deposition method described in
Patent Document 1 teaches a Cr cementation process performed at
about 1,300.degree. C. to make the diffusion barrier layer
continuous, and to smooth the interface. The publication also
describes a solution heat treatment and an aging treatment
preferably performed after the deposition of the multilayer alloy
coating to control the substrate structure, reduce defects in the
multilayer alloy coating, and smooth the layer interface.
[0046] On the other hand, in the embodiment of the present
invention, the Cr cementation process temperature is set at or
below the substrate aging temperature to discontinuously form the
diffusion barrier layer in a form reflecting the discontinuous
portion (discontinuous area) that occurs in the Re--Ni metal
coating deposited by plating.
[0047] As used herein, "discontinuous area" refers to portions
where the interlayer component has entered the diffusion barrier
layer.
[0048] The aging temperature for the single crystal alloy for use
in the present invention ranges from 800.degree. C. to
1,150.degree. C., and can suppress deterioration of the substrate
structure.
[0049] The thickness of the diffusion barrier layer is not
particularly limited, and is desirably 1 to 5 microns (.mu.m) to
enable the diffusion barrier layer of a Re-containing alloy of a
high melting point to be easily formed at a temperature not greater
than the substrate aging temperature, and to make the diffusion
barrier layer more discontinuous. With a thickness of 5 microns or
more, the diffusion barrier layer tends to become continuous,
whereas the effect of suppressing diffusion becomes insufficient
with a thickness of 1 micron or less.
[0050] It is desirable that the discontinuous portion of the
diffusion barrier layer occurs at 5 to 100 micron intervals,
particularly 10 to 60 micron intervals. It was found in an element
test conducted for a test piece by the present inventors that
intervals of 5 microns or less increase the occurrence of the
discontinuous portion, and are insufficient for suppressing
diffusion. It was also found in a thermal cycle test that intervals
of 100 microns or more cause rapid propagation of the cracking
generated in the diffusion barrier layer.
[0051] The horizontal width of the discontinuous portion is
desirably 0.5 to 5 microns, particularly desirably 1 to 3 microns.
With a discontinuous portion width of 0.5 microns or less, the
cracking generated in the diffusion barrier layer easily propagates
into the adjacent diffusion barrier in a thermal cycle test. On the
other hand, a discontinuous portion width of 5 microns or more is
insufficient in terms of the effect of suppressing diffusion.
[0052] The number of diffusion barrier layers is not particularly
limited, as long as more than one layer is provided to obtain the
diffusion suppressing effect. However, 2 to 10 layers, particularly
3 to 5 layers are desirable for maintaining the effect over
extended time periods even with the discontinuous diffusion barrier
layers.
(TBC Deposition Step)
[0053] The bond coat is deposited on the diffusion barrier
layer-containing multilayer alloy coating after the deposition of
the multilayer alloy coating.
[0054] For example, MCrAlY that exhibits excellent corrosion
resistance and oxidation resistance is used as the bond coat. The
thickness of the bond coat is not particularly limited, and is
typically about 100 to 200 microns. Specific examples of the
deposition method include low pressure plasma spray (LPPS), and
high velocity oxy-fuel frame-spraying (HVOF).
[0055] The top coat is deposited on the bond coat deposited as
above.
[0056] For example, yttria stabilized zirconia (YSZ ZrO2-6 to
8Y2O3) of low coefficient of thermal conductivity is typically used
for the top coat, and the thickness of the top coat is typically
about 300 to 500 microns. The top coat is normally deposited by
using, for example, air plasma spray (APS) under atmospheric
pressure.
[0057] This completes the deposition of the TBC that contains the
diffusion barrier layer of the embodiment of the present invention.
FIGS. 2A and 2B are schematic views representing the TBC that
contains the diffusion barrier layer of the embodiment of the
present invention. FIG. 2A represents a configuration in which the
multilayer alloy coating includes a diffusion barrier layer and an
interlayer. FIG. 2B represents a configuration in which the
multilayer alloy coating includes the diffusion barrier layer, the
interlayer, and a protective layer.
[0058] Referring to FIG. 2A, an alloy coating 5 containing
diffusion barrier layers 2 (multilayer alloy coating), a bond
coating 6, and a top coating 7 are formed in order on a surface of
a substrate 1. The alloy coating 5 is a laminate in which the
diffusion barrier layers 2 and interlayers 3 are alternately
disposed. The diffusion barrier layers 2 include a discontinuous
area 8. The discontinuous area 8 is configured from the component
of the interlayer 3.
[0059] Referring to FIG. 2B, a protective layer 4 is provided in a
portion of the alloy coating 5 in contact with the bond coat 6.
[0060] Examples of the present invention are described below.
Example 1
[0061] A single crystal alloy for use in the present invention
preferred for a gas turbine member was cast into a rod shape, and
was subjected to a solution heat treatment in a vacuum atmosphere
under the following multi-stage heating conditions.
1,250.degree. C.4h.fwdarw.1,260.degree. C.4h.fwdarw.1,270.degree.
C.4h.fwdarw.1,280.degree. C.4h
[0062] The rod-shaped casting material after the solution heat
treatment was processed into a test piece (diameter 1 inch;
thickness 3 mm) to obtain a substrate. In this example, the barrier
deposition was performed by using plating, and thus the surface was
pretreated by being wet polished with a #600 wet abrasive paper,
and degreased with acetone.
[0063] The multilayer plating film was deposited on the washed
substrate surface in the following order.
[0064] (1) Ni plating: thickness, 2 microns
[0065] (2) Re--Ni plating: thickness, 2 microns
[0066] (3) Ni--W plating: thickness, 2 microns
[0067] (4) Re--Ni plating: thickness, 2 microns
[0068] (5) Ni--W plating: thickness, 2 microns
[0069] (6) Re--Ni plating: thickness, 2 microns
[0070] (7) Ni plating: thickness, 10 microns
[0071] In this example, the plating deposition of the multilayer
plating film on the substrate surface was followed by a Cr
cementation process. Specifically, the test piece was buried in a
processing powder (Al.sub.2O.sub.3-15Cr-5NH.sub.4Cl mass %) in an
Ar atmosphere, and held for 4 hours at a heating temperature, for
which the aging temperature 1,120.degree. C. of the single crystal
alloy for use in the present invention was selected.
[0072] The Ni plating film (1) was inserted to improve the adhesion
between the single crystal substrate and the Re--Ni plating film
(2), and reacts with the Re--Ni plating film (2) in the Cr
cementation process, upon which the Ni plating film (1) becomes
apart of the diffusion barrier layer and disappears. The Ni plating
film (7) reacts with the Re--Ni plating film (6), and becomes a
part of the diffusion barrier layer. When the TBC is deposited by
using thermal spray, the Ni plating film (7) becomes the protective
layer for protecting the diffusion barrier layer from the impact.
The Cr cementation process forms a multilayer alloy coating
structure in which two interlayers are interposed between three
diffusion barrier layers.
[0073] After the deposition of the diffusion barrier
layer-containing multilayer alloy coating as above, the bond coat
was thermal sprayed on the test piece of the single crystal alloy
for use in the present invention. As a pretreatment for thermal
spray, blasting for improving adhesion was performed with alumina
particles of grain size 24 under pressure of 5 kgf/cm.sup.2.
[0074] A commercially available CoNiCrAlY (Co-32Ni-21Cr-8Al-0.5Y
mass %) powder was used for the bond coat. As expected, various
techniques can be used for the deposition method. However, in this
example, the bond coat was deposited on the multilayer alloy
coating in about 150 microns by using high velocity oxy-fuel
frame-spraying (HVOF) and low pressure plasma spray (LPPS).
[0075] The thermal spray of the bond coat was followed by a heat
treatment, which was performed in a vacuum atmosphere under the
following heating conditions to improve the adhesion of the bond
coat.
1,120.degree. C.4h.fwdarw.871.degree. C.20h
After the aging treatment, the top coating was formed in about 300
microns by the atmospheric plasma spraying (APS) of commercially
available yttria stabilized zirconia (YSZ).
[0076] FIG. 3 is a magnified view in the vicinity of the barrier
layer of the TBC that includes the diffusion barrier
layer-containing multilayer alloy coating of the embodiment of the
present invention prepared as above.
[0077] Referring to FIG. 3, an alloy coating 5 is present that
includes two interlayers 3 and three diffusion barrier layers 2.
The diffusion barrier layers 2 have the discontinuous area 8.
[0078] The effect of the diffusion barrier layer obtained according
to the embodiment of the present invention was investigated by
conducting a heat test at 1,050.degree. C. for 500 hours.
[0079] FIG. 4 is a SEM image of a cross sectional structure after
the heat testing of the TBC that includes the diffusion barrier
layer-containing multilayer alloy coating of the embodiment of the
present invention.
[0080] After the heat test, a common TBC with no diffusion barrier
layer had a deteriorative layer (or SRZ) in which the precipitated
phase was formed in abundance by diffusion into the substrate. On
the other hand, in the TBC with the multilayer alloy coating 5
containing the diffusion barrier layers 2 according to the
embodiment of the present invention (FIG. 4), the barrier effect
was sufficiently maintained, and the SRZ was not observed, because
the diffusion barrier layers 2 were provided as multiple layers to
reduce the diffusion cross sectional area although the diffusion
barrier layers 2 being discontinuous.
[0081] As demonstrated above, the TBC having the diffusion barrier
layer-containing multilayer alloy coating of the embodiment of the
present invention had a confirmed effect as the barrier layer. The
TBC was further evaluated for durability by conducting a thermal
cycle test that involved heating and cooling.
[0082] The thermal cycle test involved repeated heating and cooling
between room temperature and 1,093.degree. C., and was performed in
100 cycles, each cycle consisting of holding at room temperature
for 15 min, and at 1,093.degree. C. for 10 hours.
[0083] FIG. 5 is a SEM image of a cross sectional structure after
the thermal cycle testing of the TBC having the diffusion barrier
layer-containing multilayer alloy coating of the embodiment of the
present invention.
[0084] The TBC with the multilayer alloy coating 5 containing the
diffusion barrier layers 2 according to the embodiment of the
present invention had partial decomposition in the diffusion
barrier layers 2 after the prolonged heating. However, the
diffusion barrier layers 2 did not show any damage such as cracking
and exfoliation caused by stress that occurred during the
temperature changes.
[0085] This is because of the effect of the discontinuity in the
diffusion barrier layers 2, and the discontinuous area 8 relaxing
the stress-induced strain and thereby suppressing the generation of
cracking in the diffusion barrier layers 2. Further, any cracking
can be suppressed from further propagation at the discontinuous
portion although the cracking quickly propagates in the diffusion
barrier layers 2.
[0086] The substrate 1 did not show any SRZ, and the diffusion
barrier function was maintained by the formation of the multiple
layers, even though the barrier was discontinuous.
[0087] FIG. 6 is a photographic image showing a cross section after
the thermal cycle testing of a TBC containing a multilayer alloy
coating deposited by using the method described in Patent Document
1 (Comparative Example).
[0088] As can be seen in FIG. 6, no SRZ was formed in the substrate
1, and the barrier function was maintained even after the thermal
cycle test. However, horizontal cracking 9 was observed in the
diffusion barrier layers 2, running in a straight line in the
continuously formed diffusion barrier layers 2. That is, the
cracking 9 rapidly propagates in the diffusion barrier layers 2
when the diffusion barrier layers 2 are continuous and do not have
the discontinuous area that becomes an obstacle to the propagation
of the cracking 9.
[0089] The relationship between the horizontal length of cracking
and the number of thermal cycles, specifically the cracking
propagation speed can be reduced to about 1/3 with the diffusion
barrier layer-containing multilayer alloy coating of the embodiment
of the present invention, as compared to the multilayer alloy
coating deposited by using the method of Patent Document 1.
Example 2
[0090] A turbine blade for industrial gas turbine formed of the
single crystal alloy for use in the present invention used in
Example 1 was coated with the coating of Example 1 to obtain a
turbine blade for industrial gas turbine. The coating was formed on
the blade surface exposed to combustion gas.
[0091] FIG. 7A schematically shows the industrial gas turbine that
uses the turbine blade for industrial gas turbine of the
example.
[0092] As shown in the figure, the gas turbine is configured from
an air intake portion 17, a compressor 18, a combustor 19, a
turbine section 20 (including blades and nozzles), and an exhaust
unit 21.
[0093] FIG. 7B is a magnified cross sectional view of portion A of
FIG. 7A, illustrating details of the turbine section 20 that
includes blades and nozzles.
[0094] As shown in the figure, the turbine section is configured
from a turbine rotor 11, a shroud 12, a combustor 13, a gas path
14, nozzles 15, and blades 16.
[0095] The turbine blade for industrial gas turbine coated with the
coating of the embodiment of the present invention had improvements
in durability against thermal cycles and fatigue during operation
and upon shutdown, and was able to maintain the strength
reliability of the gas turbine blade, making it possible to extend
the lifetime of the gas turbine.
[0096] The foregoing described the present invention using specific
examples. It should be noted, however, that the present invention
is not limited to the embodiment above, and may be applied in many
variations, provided such variations do not exceed the scope of the
present invention described above.
* * * * *