Heinrich J.G., Aldinger F. (Eds.) Ceramic Materials and Components for Engines
Подождите немного. Документ загружается.
RESULTS
The fabricated device which
has
been deposed
with a-Fezq
:
5
min and Sn@
:
8
min
shows
the
best
properties. The
gas
sensitivity for
H2
ranges from
62%
2:
76%,
for
(2%
from
16
2:
58
YO
and for
LPG
from
8%
2:
37%,
that is, the sensitivities
are
H2
>
CH,
>
LPG.
The sensitivity espectally showed the better
characteristics
at
low
concentration range
(500
ppm
a
1,000
ppm)
than
high concentration range
(3.000
ppm
s
10,000
ppm). The heat
treatment
daice
had
the
high
sensitikity
to
10%
rather
than
not
treated
it
in
LPG.
Although
21
sec
for no heat treatment device,
a
sensing
response
time
is
12
sec
for heat treatment
device.
The
multi-layer gas sensor device
has
a good
long-term
stability
to converge the sensitivity
30%
in
LPG
at
1,000
ppm.
Fig.
3
Sensor resistance on
air
as
doping
ratio
i
1
i
Tm~--aam
(F)
Fig.
4
Sensor resistance in air at
various
temperature
rC
/---
I-
'
--cn,;
/
Fig.
5
Sensitiklty of the
H2
Gas
92
Fig.
6
Sensitivity
of
the CH.,
Gas
Fig.
7
Sensitivity
of
the
LPG
Fig.
8
Comparison of the heat treated and the untreated
device
Fig.
9
Long-term stability
CONCLUSIONS
aFe~O3
/
Sn02 thin film devices
are
prepared
by
a
CVD process. The multi-layer device
has
the better
sensitivity and selectivity
than
single-layer delices.
1.
The device which deposed at
aFe203
:
5
min and
Sn02
:
8
min had the best properties.
2. The selectively showed H2
>
CH4
>
LPG.
3.
The sensitivity especially showed the better
characteristic at low concentration rang
(500
ppm
=
1,000 ppm) than high concentration range.
4. The heat treatment device
ha
the
hgh sensiti\ity
to
10% rather than not treated it in LPG.
5.
The multilayer gas sensor device
has
a good long-
term stability to converge the sensitivity
30% in
LPG at
1,000 ppm.
REFERENCES
R. Lalauze and C. Pijolat, A New Approach to
Selective Detection of Gas by an Sn02 Solid-
state
as
Sensor, Sensors and Actuators,
B.
5,55-
63 (1985).
A. A. Vasiliev and
M.
A. Polykarpom, Change
of Ferric Oxide (Fe203) Semiconductor
Conducti.r;ity Type in the Interaction
"lth
Reducing Gases, Sensors and Actuators,
B
7,
C. C. Chai,
J.
Peng and
B.
P. Yan,
Characterization of alpha-Fe203. Thin Films
Deposited by Atmospheric Pressure CVD onto
Alumina Substrates, Sensors and Actuators,
B,
31,412-116 (1995).
Sayago,
J.
Gutierrez,
L.
Ares,
J.
I.
Robla, M. C.
Honillo,
J.
Getino,
J.
Rino and J. A. Agapito,
The Effect of Additives in Tin Oxide on
Sensitivity and Selectivity to NO, and CO,
Sensors and Actuators,
B,
26-27, 19-23 (1995).
C. F. Schaus, W.
J.
Schaff and J. R. Shealy,
OMPVE Growth of GaXlnl-XP/GaAs(AlyGal-
yAs)
Hetero-structures for Optical und
Electronic Device Applications,
J.
Cvst.
Growth,
77, 360-366 (1986).
T.
Suzuki,
T. Yamazaki and M. Azumaya,
Hydrogen Gas Sensing properties in
Polycrystalline Tin Oxide Films
of
Submicron
Thickness,
J.
Cera. SOC. Jpn., 97, 1263-1273
(1989).
M. Kanamori.
Y.
Okamato. Y. Ohta and Y.
Takahashi, Thickness Dependence of Senshity
of
Gas
Sensor. J. J. Cera.
Soc.
Jpn..
103,
113-
116 (1995).
K.
D. Schierbaum, U. Weimar and W. G
pel,
Comparison
of
ceramic thick-film and thin-film
Chemical sensor based upon SnOz, Sensor and
Actuators
B.
7 (1992) 709-716.
J.
Watson, The tin oxide gas sensor and its
appplication, Sensor and
Actuators,
5
(1984) 29-
42.
626-629 (1992).
Sensor, Seoul National University, 193-199
(1998).
(11)
Zheng, Jiao, Zhang, Jinhuai, Liu, Stability of
Sn02/Fe203 Multilayer thin film gas sensor,
Proceedings of the
3rd
East Asian Conference
Seoul National Univ.
(
1998)
22
1-226.
(12)
D.
Kohl,
Surface processes in the detection
of
reducing gases
with
SnOz based devices, Sensor
(13)
M.
H. Madhusudhana Reddy and A.
N.
Chandorka, Response study of electron
evaporated thin-film hn Oxide gas sensor,
Sensor and Actuators
B,
9 (1992)l-8
(14)
R
C. Evans, An introduction to
crystal
chemistry, Cambridge University Press. (1 966)
(15)
P.
A.
Mulheran and
J.
H. Harding, The stability
of
SnO:
surfaces, Modelling Simul. Mater.
Sci.
Eng.
1
(1993) 39-44
(16)
W. G. pel,
K.
D. Schierbaum and M.D.
Wiemhofer, Solid State Ionics.
and Actuators,
18 (1989) 71-114.
148-149.
(10)
K. H. Song,
S.
H.
Shin,
J.
I.
Park,
K.
J.
Park and
S.
J. park, Effect
of
film oxygen content on gas
SensiFity
of
tin dioxide thin film, Proceedings
of
The
31d
East Asian Conference on Chemical
93
This Page Intentionally Left Blank
11.
Performance
/
Reliability
This Page Intentionally Left Blank
EVALUATION OF MECHANICAL RELIABILITY OF SijNq NOZZLES
AFTER EXPOSURE IN
AN
INDUSTRIAL GAS TURBINE
H.
T. Lin*", M.
K.
Ferber', M. van Roodeb
(")
Metals and Ceramics Division, Oak Ridge National Laboratory
Oak Ridge, TN 37831-6068,
USA
(b)
Solar Turbines Incorporated
San Diego,
CA
92101,
USA
ABSTRACT
This paper provides a review of a recent study
undertaken to evaluate the mechanical reliability of
SN88 Si3N4 ceramic nozzles exposed in an industrial
gas turbine.
Two field tests with exposures time of
10
and 68 h were carried out. The first
10
h field test
revealed minor changes
in
both microstructure and
strength of airfoil region. However, nozzles with crack
generation, which initiated in low temperature airfoil
region
(<
1000°C), were observed after 68
h
test,
resulting in the termination of second engine test.
Analyses of the cracked nozzles by scanning electron
microscopy and x-ray diffraction revealed changes
in
microstructure and secondary phase due to
environmental exposure. Dynamic fatigue tests on as
received SN88 Si3N4 at intermediate temperatures in air
suggested that changes in secondary phase could result
in the formation of an extensive damage zone, due to
the generation of a large residual tensile stress, which
substantially reduced the mechanical reliability and
probably led to the failure of turbine nozzles.
INTRODUCTION
Silicon nitride ceramics with reinforcing elongated
grain microstructure are leading candidates
for
use as
high-temperature, structural components
in
advanced
gas turbines due to their superior thermomechanical
properties
[
1-51.
Recent ceramic gas turbine programs
at both Solar Turbines and Rolls Royce Allison [6-81
have executed many field tests to increase the
experience base concerning the behavior of ceramic
components in industrial gas turbine environments.
A
key lesson learned
in
both programs is that
environmental effects may severely limit the long-term
reliability of Si3N4 materials. In particular, the high
velocities and presence
of
water vapor in the
environment can lead to the volatilization
of the
normally protective silica layer. Researchers have
shown that the presence of water vapor leads to the
formation of a gaseous Si(OH)4 species via a reaction
with the silica layer
[9-111.
The rate of Si(OH).,
formation of this species and thus the rate at which the
Si3N4 is consumed by its continued oxidation are a
function of gas velocity, pressure of the water vapor,
and total pressure of the environment. In addition to the
volatility issues, which may lead to
loss
of function due
to excessive changes in component dimensions, the
effect of the environment upon the long-term
mechanical reliability must be understood as well. One
approach addressing this issue is to evaluate the
component properties directly using small test
specimens. For example, the availability of the small
dog-bone tensile specimen
[
121
has provided for the
measurement of the tensile stress rupture properties of
silicon nitride samples from first stage turbine blades.
Results showed that there were significant differences
in
the creep response characteristics obtained for
various parts of the ceramic blade due to variations in
grain size and secondary phase content and chemistry.
More importantly the data obtained from testing
specimens prepared from the production billets greatly
over-estimated the lifetime of components with
complex shapes.
This paper describes' the results
of
a recent
component verification study involving SN88 Si3N4
nozzles exposed in an industrial gas turbine.
Silicon
nitride nozzles after exposure to
10 h and 68
h
field
tests were examined in this study.
Scanning electron
microscopy was used to elucidate the changes
in
the
microstructure arising from the oxidation process.
In
addition, the stability of secondary phase(s) was
evaluated using x-ray analysis.
The exposed surface
strength was measured as a function of field test time
using a miniature biaxial specimen.
EXPERIMENTAL PROCEDURES
The nozzles examined in this study werefabricated from
NGK SN88 Si3N4 material (NGK Insulators Ltd.,
Nagoya, Japan). They were gas-pressure-sintered using
rare-earth sintering additives and then post-heat-treated
by NGK to form a protective silica surface layer. The
predominant secondary phase present after densification
is Yb4Si207N2, designated
as
the J-phase.
The first stage ceramic nozzles (Figure
1)
were
designed for retrofit into a Centaur
50s
turbine engine
(Solar Turbines Incorporated, San Diego, CA)
[
131.
The first engine test was carried out with one hour full
load and
10
h total run time.
The second engine test
was planed for
100
h endurance test. However, the test
was terminated after 68 h total run time including 15
97
Figure
1
Solar
SN88 first stage Si3N, nozzles after
engine test time
of
10 h (a) and 68 h (b).
start/stop cycles due to crack generation in the nozzles
(Fig. lb).
X-ray diffraction was used to identify the
predominant secondary phases in the airfoil as a
function of engine test time. Scanning electron
microscopy (SEM) was first used to examine the
surfaces of the airfoils and platforms after removal of
the nozzles from the engine. Nozzles were
subsequently sectioned by making a longitudinal cut
parallel and adjacent to the trailing edge.
These pieces
were subsequently polished and examined with SEM.
The biaxial flexure strength
[
14-16] was measured
for samples from selected vanes using the ball-on-ring
arrangement. Specimens were machined from both the
airfoil and platform surfaces by first diamond core
drilling small cylinders having nominal diameters of
5.5
mm. Each cylinder was then machined on one face
only until the thickness was
0.4
to
0.5
mm. In this way
the tensile face of each specimen always consisted of
the exposed surface of either the airfoil
or
platform.
The details of testing fixture and procedures can be
found
in
Ref. 17
RESULTS AND DISCUSSION
Macroscopically, the SN88 Si3N4 nozzles after 10
h
engine test revealed little change on airfoil surface
features except some reddish deposits (Fig.la). On the
other hand, the nozzles after 68 h engine test showed a
white-colored, powder-like scale with crack generation
(Fig. lb). X-ray analysis indicated that the white-
colored scale present on airfoil surfaces of 68
h
nozzles
was mainly the Yb2Si207 plus Yb2Si05, which formed
due to the oxidation of initial secondary phase (J-Phase)
present in the as-received nozzles. Note that the
dominant crack always initiated
in
the low temperature
(<
1
OOO°C)
airfoil region
[
181.
SEM examinations of airfoil surfaces of both 10
and 68
h
engine tested nozzles showed the presence of
corrosion pits associated with Fe-Si-0 deposits (Fig. 2).
The Fe element detected in the deposits was attributed
the erosion of superalloy components
in
the engine.
Figure
2.
SEM of airfoil surface features of SN88
silicon nitride nozzles after (a) 8 h and (b) 68 h engine
test.
Also,
the 68
h
tested nozzles revealed more surface
porosity due to oxidation and volatilization of Si3N4
as
compared with 10 h tested nozzles. In addition, SEM
analysis confirmed that the white-colored, powder-like
scale observed in 68 h nozzles was indeed a secondary
phase, which consisted of Yb, Si,
0
and trace amount of
Y. The accumulation
of
the Yb2Si207 plus YbzSiOs on
the surface was most likely due to the selective
recession of Si3N4 grains,
as
seen in Fig. 2b. The Si3N4
grains were removed by a combination of oxidation and
volatilization processes, resulting in the accumulation of
secondary phases on the airfoil surface.
The SEM micrographs of the polished cross-
sections are shown in Figure 3. The SN88 Si3N4
nozzles showed minor changes in microstructure, e.g.,
pores in secondary phase and very limited intergranular
cracks, in the region adjacent to the airfoil surface after
10
h engine exposure (Fig. 3a). However, extensive
98
generation of intergranular cracks plus pores in the
secondary phase was observed
in
nozzles after
68
h
engine exposure (Fig. 3b). The changes in
microstructure, i.e., formation of environment-induced
damage zone, were attributed to the oxidation of Si3N4
materials in the presence of high-pressure water vapor.
A previous study had showed that the presence of high-
temperature, high- pressure water steam would lead to
formation of an extensive subsurface damage zone in
Si3N4 materials [19]. Also, results of Vickers
indentation in oxidation zone in the vicinity of crack
initiation site showed a preferential crack growth along
the oxidation zonehlk material boundary, which was
in sharp contrast to the symmetrical indentation feature
observed in the bulk material region (Fig.
4).
The
feature of preferential crack growth in the oxidation
zone suggested the presence of a large residual stress.
SEM examinations also showed that the airfoiVplatform
transition region, where the dominant crack normally
Figure
4.
SEM
micrographs show indentations in (a)
oxidation zone and (b) inner bulk region. The inserted
photo shows the presence of an oxidation zone (light
region).
initiated and led to failure of nozzles, exhibited a more
extensive damage zone formation
(-30-40
pm) than the
middle airfoil surface region
(-10
pm). Note that the
temperature and air velocity in the transition region
were lower than the middle airfoil surface region.
The
finite-element-analysis of temperature distribution at
steady state during engine operation indicated that the
temperature in the airfoiVplatform transition region
ranges from
800
to 95OOC [18]. The SEM observations
just described are in contrast to the experimental results
and oxidation models [9-111. It was possible that
in
the
middle airfoil region the high gas velocity aggravated
the removal of silica due to volatilization of the silica
layer, resulting in less extensive damage zone evidence.
On the other hand, in the transition region little, if any,
protective silica would form after the initial silica layer
present in the as-received nozzle receded and could lead
to an extensively accumulated damage zone (Figure 3b).
Strength test results at room temperature of samples
extracted from nozzle airfoils after engine test are
summarized in Figure
5.
Note that the disk samples
were tested with exposed, pressured sides as tensile
surfaces. Results showed that the 10
h
tested samples
exhibited -10% decrease in strength, while the
68
h
tested samples exhibited -30% strength degradation.
The extensive strength degradation observed
in
nozzles
after
68
h engine exposure is due to the extensive
formation of subsurface damage zone (Fig. 3b).
The crack initiation
in
low temperature
airfoil/platform transition region has led
to
a hypothesis
that SN88 Si3N4 might exhibit a mechanical instability
Figure
3.
SEM micrographs of polished cross-section at intermediate temperatures
in
air. Note that previous
of nozzle airfoil surface region after (a)
10
h
and (b)
68
creep studies indicated that SN88 Si3N4 exhibited
h engine test.
excellent creep performance at temperature
L
1038°C
in
air
[20].
Recently, studies of dynamic fatigue by
99
1000
800
2
600
400
200
0
n
8
b
cn
0
0.5
1
1.5 2 2.5 3 3.5
(mm)
Figure
5.
Stress versus displacement curves of biaxial
samples extracted from airfoils of SN88 nozzles after
10
and 68 h engine test.
Wereszczak et al. have shown that some commercial
Si3N4 materials exhibited substantial strength
degradation at temperature
5
850°C in air [21].
Therefore, a dynamic fatigue test in four-point bending
was conducted to evaluate the mechanical reliability of
SN88 Si3N4 at 850°C in air [22].
Figure 6 summarizes the earlier dynamic fatigue
response of SN88 Si3N4 tested at 85OOC in air at
stressing rates of 30
MPds
and 0.003
MPa/s.
Note the
NT154 Si3N4, which contained YzSi207 as secondary
phase, is used as a benchmark in this study. Results
showed that the fracture strength of NT154 Si3N4 was
similar those obtained at room-temperature and was
independent of stressing rates accompanied by a high
fatigue exponent of 87. On the other hand, strength
of
SN88 Si3N4 was very sensitive to stressing rates. For
instance, samples tested at 30
MPds
exhibited similar
strength as those obtained at
room
temperature, while
samples tested at 0.003
MPds
exhibited - 43% strength
decrease. In addition, SN88 Si3N4 exhibited a low
fatigue exponent of 16, indicative of a high
susceptibility to slow crack growth (SCG) process at
high temperatures
in
air.
The fracture surface of SN88 samples tested at
85O0C/0.O03
MPds
in air revealed a light-colored ring
surrounding the bend bar (as shown
in
Fig. 7),
indicating the presence of an environment-affected zone
(EAZ). SEM
examinations showed that a - 30
pm
damage zone, containing multiple cracks plus pores in
secondary phase, developed
in
the light-colored
EAZ.
Note that the
EAZ
developed in all four-side surfaces,
suggesting the development of
EAZ
was not a stress-
promoted phenomenon. Results of x-ray analysis for
0.003
MPds
tested samples also indicated a change in
secondary phase from J-phase to Yb2Si207 plus
YbzSiOs.
The phase transformation phase from J-phase to
Yb2Si207 could introduce an extreme high residual
tensile stress in the
EAZ
due to a -64% decrease in
material volume [23], consistent with the indentation
100
results in the oxidation zone of cracked nozzles (Fig. 4).
Note that there
is
a minor material volume increase
(-5%)
for J-phase changing to Yb2SiOs. The
development of a high tensile stress would then lead to
fracture of Si3N4 grains and, also, generation of multiple
intergranular cracks. Similar mechanical instability due
to phase changes was previously reported for Si3N4
materials sintered with
Yz03
additive [23].
The results of dynamic fatigue tests at 85OOC in air
suggested that an
EAZ
developed in the airfoil/platform
transition region, where the temperature was low and no
protective silica layer would form during the exposure,
after the initial silica layer present in the as-received
nozzles recessed. The generation of extensive multiple
cracking in
EAZ
would significantly reduce the
mechanical reliability and, thus, greatly increase the
susceptibility of nozzles to SCG processes.
Consequently, a critical crack would readily initiate at
the transition region and lead to the failure of nozzles.
On the other hand, the reason why the
EAZ
was not
observed in the higher temperature regions; i.e., middle
airfoil region, appeared to be due the elimination of the
EAZ
by
oxidationlvolatilization
processes and thus
continuous material recession.
1000
.
=.-
.
900
=
800 850°C in air
.
.
.
0
0
SN88
'
C
NT154
300
200
~~
0.001 0.01 0.1 1
10
100
Stressing
Rate
(MPds)
Figure 6. Fracture strength versus stressing rate results
of SN88 silicon nitride tested at 85OOC in air.
SUMMARY
Silicon nitride nozzles were designed and field-
tested in an industrial gas turbine. Dominant crack
developed in the airfoil/platform transition region after
68 h test, resulting in the termination of engine test.
Both
SEM
and x-ray analyses indicated changes in
microstructure and secondary phase due to the exposure
in engine environment. An extensive damage zone,
containing multiple cracks and pores in secondary
phase, developed in the subsurface region after 68 h
engine test.
A
supporting dynamic fatigue test at
85OOC
in
air suggested that changes
in
secondary phase could
result in the formation of an extensive damage zone,
due to the generation of a large residual tensile stress,
which substantially reduced the mechanical reliability
and led to the failure of turbine nozzles.
ACKNOWLEDGEMENTS
The authors thank Drs. M. Lance, T. N. Tiegs, and
P. F. Becher for reviewing the manuscript. Research is
sponsored by the U.S. Department of Energy, Office of
Power Technologies, Microturbine Technologies
Program, under Contract DE-AC05-000R22725 with
UT-Battelle, LLC.
Figure 7.
Fracture surface of SN88 bend bar tested at
85O0C/0.O03 MPa in air exhibited an environment-
affected zone
as
indicated by arrows.
REFERENCES
D. Anson,
K.
S.
Ramesh, and M. DeCorso,
“Application of Ceramics To Industrial Gas
Turbines”; DOE/CE/40878-
1
&2; Battelle
Columbus, March 1991.
H. E. Helms, R. A. Johnson, and L. E. Groseclose,
“AGT 1 00-Advanced Gas Turbine Technology
Development Project,” Proc. 23rd Automotive
Technology Development Contractors’
Coordination Meeting P- 165, Warrendale, PA,
M. van Roode, “Ceramic Retrofit Program,” Proc.
Joint Contractors Meeting: FEIEE Advanced
Turbine Systems Conference FE Fuel Cells and
Coal-Fired Heat Engines Conference, DOE/METC-
D.
Carruthers and
L.
Lindberg, “Critical Issues for
Ceramics for Gas Turbines,” Proc. 3rd Int. Symp.
on Ceramic Components and Materials for
Engines, Westerville, Ohio (1988) 1258-1272.
P.
J.
Haley, R. L. Holtman, L. E. Groseclose,
S.
J.
Hilpisch, and A. H. Bell
111,
“Advanced Turbine
Technology Applications Project (ATTAP)”, Proc.
29th Automotive Technology Development
Contractors’ Coordination Meeting, Warrendale,
Penn. (1992) 19-29.
M. van Roode, W. D. Brentnall, K.
0.
Smith, B. D.
Edwards, L.
J.
Faulder, and P. F. Norton, “Ceramic
Stationary Gas Turbine Development
-
Third
Annual Summary”, ASME Paper 96-GT-460, to be
published
in
the Proc. of ASME Turbo Expo ‘96
Conference, Birmingham, UK, June 10-13, 1996.
March (1986) 137-55.
93/6 132
(
1993) 77-93.
(7)
V. Parthasarathy,
M.
van Roode, J. Price,
S.
Gates,
S.
Waslo, and P. Hoffman,
“Review of Solar’s
Ceramic Stationary Gas Turbine Development
Program,
Pro. 6th Int. Symp. Ceramic Materials
and Components for Engines, Arita, Japan, (1 997)
(8) R. Wenglarz,
S.
Ali, and A. Layne, “Ceramics for
ATS Industrial Turbines,” to be published in the
Proc. of ASME Turbo Expo ‘96 Conference,
Birmingham, UK, June 10-13, 1996.
(9) E.
J.
Opila and R. E. Hann, Jr., “Paralinear
Oxidation of Sic in Water Vapor,
“J. Am. Ceram.
(10) E.
J.
Opila, “Variation of the Oxidation Rate of
Silicon Carbide with Vapor Pressure,”
J. Am.
Ceram.
SOC.,
Vol. 82, No. 3, pp. 625-36, (1999).
(11) J. L. Smialek, R. C. Robinson, E. J. Opila, D.
S.
Fox, and
N.
Jacobson, “Sic and Si3N4 Recession
due to SiOl Scale Volatility Under Combustor
Conditions,
I‘
Advanced Composite Materials,
Vol.
8, No. 1 (1999) 33-45.
(12) H. T. Lin, P. F. Becher, M. K. Ferber, and V.
Partasarathy, “Verification of Creep Performance
of a Ceramic Turbine Blade,” Proc. 2nd Int. Symp.
Science of Engineering Ceramics, Osaka, Japan
(1
998).
(13) A. F. Kirstein and R. M. Woolley, “Symmetrical
Bending of Thin Circular Elastic Plates on Equally
Spaced Point Supports,”
Journal
of
Research
of
the
National Bureau
of
Standards
-
C. Engineering and
Instrumentation,
Vo17 1 C, No 1, Jan-Mar 1967.
(14) R. Thiruvengadaswamy and R.
0.
Scattergood,
“Biaxial Flexure Testing of Brittle Materials,”
Scripta Metall. et Mater.,
Vol 25 (1991) 2529-
2532.
(16) D. K. Shetty, A. R. Rosenfield, P. McGuire, B. K.
Bansal, and W. H. Duckworth, “Biaxial Flexure
Tests for Ceramics,”
Ceram.
Bull.,
Vol 59 [12]
(17) M. K. Ferber, H. T. Lin, V. Parthasarathy, and R.
A. Wenglarz, “Degradation of Silicon Nitrides
in
High Pressure, Moisture Rich Environments,” to be
published in the Transactions of ASME,
2000
(IGTI, ASME TURBO EXPO 2000, May 8-11,
2000, Munich, Germany).
(1 8)
0.
Jimenez, Solar Turbines, private
communication.
(19) M.
K.
Ferber,
H.
T. Lin, and J. Keiser, “Oxidation
Behavior
of
Non-Oxide Ceramics in a High-
Pressure, High-Temperature Steam Environment,”
Mechanical, Thermal and Environmental Testing
and Performance
of
Ceramic Composites and
Components, ASTM STP
1392,
American Society
for Testing and Materials, West Conshohocken,
PA, 2000.
(20) A. A. Weresczak and T. P. Kirkland “Creep
Performance of Candidate SIC and Si3N4 materials
for Land-based, Gas Turbine Engine Components,
ASME Paper 96-GT-385,
to be published
in
the
Proc. of ASME Turbo Expo ‘96 Conference,
Birmingham,
UK,
June 10-13.1996.
259-264.
SOC.,
Vol. 80 [l] (1997) 197-205.
(1980) 1193-97.
101