Journal of Materials Science and Chemical Engineering, 2013, 1, 6-10
http://dx.doi.org/10.4236/msce.2013.11002 Published Online February 2013 (http://www.scirp.org/journal/msce)
Effects of Salt Quenching Temperatures on Microstructure
and Creep Properties of a PM Ni-based Superalloy
Jun Xie1, Sugui Tian1*, Jiao Liu1, Xiaoming Zhou2
1School of Materials Science and Engineering, Shenyang University of Technology, Shenyang 110870; China,
2Beijing Institute of Aeronautical Materials, Beijing 100095, China
Received 2013
Abstract
By means of the microstructure observation and creep properties measurement, an investigation has been made into the
influence of the salt quenching temperatures on the microstructure and creep property of FGH95 superalloy. The results
shown that, after full heat treatment, a high volume of  phase and some granular carbide dispersedly precipitate in the
matrix. Thereinto, as the molten salt temperature decreases from 650℃ to 520℃, the size of fine  phase in the alloy
decrease gradually and the amount of carbides increase in the alloy. And the alloy quenched in molten salt at 520℃
possesses better creep resistance due to the fact that there are more granular carbides precipitating in the alloy to en-
hance the grain strength. During creep, the deformation features of the alloy are that the configurations of stacking fault
and slipping dislocations are activated in the alloy.
Keywords: FGH95 Ni-Based Alloy; Salt Quenching Temperature; Microstructure; Creep Property; Deformation Feature
1. Introduction
With the development of aviation industry, the service
performance of aviation components is required to have
a better reliability. Especially in turbine disk of aero-
engine, it needs higher enduring temperature, carrying
capacity and better stress rupture properties under the
service condition [1-2]. With the alloying degree of tradi-
tional wrought superalloy increasing, the hot-workability
of the alloy goes from bad to worse due to the in- homo-
geneous microstructure and serious segregation of ele-
ments in the alloy. However, the Ni-based powder su-
peralloy is an excellent material used for preparing the
high temperature rotating parts of the advanced aero-
engine because of its advantages of fine grains, homo-
geneous microstructure, no macro-segregation in the
ingot and so on [3-5].
FGH95 alloy is a precipitation-hardened PM Ni- based
superalloy with a high fraction of  phase, and has high-
er tensile and yield strength at 650℃ [6,7]. FGH95 su-
peralloy has a compact structure after hot isosatic pressing
(HIP), here, there are coarse  phase precipitating along
previous particle boundaries (PPB), and the microstructures
of dendrite and recrystallization appear in the grain [8].
After the HIP alloy is heat treated by different technics,
the alloy can obtain different microstructures [9,10].
Some researches show that different quenching technics
(oil cooling and salt cooling) have an important effect on
the microstructure and creep properties, and the “salt
cooling” alloy possesses better stress rupture property [11].
But the influences of salt quenching temperatures on
microstructure and creep properties of FGH95 alloy are
still not clear.
In this paper, the FGH95 alloy is solution treated and
quenched in the molten salt at different temperatures, and
then aged. The creep properties of the alloy, cooled in
molten salt at different temperatures, are measured under
the condition of 650℃ and 1034MPa. Moreover, the
microstructures of the alloy are observed by scanning
electron microscopy (SEM) and transmission electron
microscopy (TEM), and the influences of salt cooling
temperature on microstructure and creep properties can
be investigated.
2. Experimental procedure
The powder particles of FGH95 nickel-base superalloy
with 150 meshes in size are put into a stainless steel can
to pretreat at 1050 for 4 h. The can containing FGH95 ℃
powder particles is hot isostatic pressing (HIP) treated
for 4 h under the conditions of 1150 and 120MPa to ℃
form the ingot of the alloy. The chemical composition of
FGH95 alloy is shown in Table 1. Moreover, the HIP
treated alloy is solution treated at 1150 for 1h, and℃

J. XIE ET AL. 2
then quenched in the molten salt at different tempera-
tures (520, 583 and 650) for 15 mins, respectively. ℃℃ ℃
Finally, the quenched alloys are treated for twice aging
(870 ℃ × 1h + 650 ℃ ×24h).
The ingot of FGH95 superalloy is cut into the speci-
mens with the cross-section of 4.5mm  2.5mm and the
gauge length of 20 mm. Uniaxial constant load tensile
testing is performed, in a GWT504 model creep testing
machine, for measuring the creep properties of the alloy
under the conditions of 1034 MPa and 650℃. The mi-
crostructures of the alloy after different heat treatment
are observed by SEM and TEM, so that the effects of salt
quenching temperatures on microstructure and creep
properties of the alloy can be investigated.
3. Experimental Results and Analysis
3.1. Influence of Salt Quenching Temperatures
on Microstructure of the Alloy
The SEM microstructures of solution treated alloy after
quenching in the molten salt at different temperatures
(520℃, 583℃ and 650℃) and aging are shown in Fig-
ure 1, respectively. Here, after quenching in molten salt
at 520℃, the grain size is about 10 μm ~ 25 μm, and
there is some coarse  phase discontinuously distributing
along the grain boundaries as marked with short arrow in
Figure 1(a). Moreover, many white carbide particles [12]
dispersedly precipitate in the alloy as marked with long
arrow in Figure 1(a).
As the salt quenching temperature increases to 583℃,
there are still some coarse  phase exsiting in the
boundary regions, and the amoount of carbide particles
decreases gradually as marked with the short arrow in
Figure 1(b), and the twinning appears in the grain as
marked with the long arrow in Figure 1(b). As the
molten salt temperature further enhacnes to 650℃, the
coarse  phase with 1~2.5μm in size appears in the grain
boundary, and the amount of carbide particles further
decrease as shown Figure 1(c).
The TEM microstructures of fine  phase precipi-
tated in the alloy quenched in the molten salt at different
temperatures and aged are shown in Figure 2. After
Table 1. Chemical composition of FGH95 alloy (mass fraction, %).
C B Cr Co Al Ti W Mo Nb Ni
0.060 0.012 12.98 8.003.48 2.55 3.40 3.40 3.50 Bal
(c)
10m
(a)
10m 10m
(b)
Figure 1. SEM microstructures of the solution treated alloy after quenching in molten salt at different temperatures and aged.
(a) 520℃, (b) 583℃, (c) 650℃.
0.2m
(a) (b)
0.2m
(c)
0.2m
Figure 2. Morphology of the fine  phase precipitated in the alloy after quenched in melting salt at different temperatures
and aged. (a) 520℃, (b) 583℃, (c) 650℃
C opyright © 2013 SciRes. MSCE

J. XIE ET AL.3
quenching in the molten salt at 520℃, the fine  phase
with 0.1 ~ 0.16 μm size dispersedly precipitates in the
alloy as shown in Figure 2(a). As the temperature of the
molten salt increases to 583℃, the fine  phase grows up
slightly, and its size is about 0.12 ~ 0.18 μm as shown in
Figure 2(b). As the molten salt temperature further in-
creases to 650℃, the fine  phase with the size of 0.15 ~
0.2 μm appears in the grain, as shown in Figure 2(c).
This indicates that the size of  phase precipitated in the
alloys after different quenching treatments increases
slightly as the salt quenching temperature increases,
therefore, the size of  phase in the alloy can be adjusted
by quenching in molten salt at different temperatures.
3.2. Influence of Salt Quenching Temperatures
on Creep Properties of the Alloy
After the alloy quenched at molten salt at different
temperatures and aged, the creep curves of the alloys are
measured under the condition of 650℃/1034MPa, as
shown in Figure 3.
Here, when the alloy is quenched in molten salt at
520℃, the alloy possesses the lowest steady strain rate
about 0.00654%/h as illustrated by the curve 1 in Figure
3, and its creep lifetime of the alloy is about 70h. As the
molten salt temperature increases to 583℃, the creep
curve of the alloy is marked with number 2 in Figure 3,
which indicates that the strain rate of the alloy is
measured to 0.00789%/h during steady creep stage, and
its creep lifetime decreases to 67h. The curve of the alloy
quenched in molten salt at 650℃ is marked with number
3 in Figure 3, illustrating that the steady strain rate of the
alloy further increases to 0.0151%/h, and the creep
lifetime of the alloy further decreases to 37.2h. This
indicated that the alloy cooled in the molten salt at lower
temperature possesses longer creep lifetime.
3.3. The Deformed Features of FGH95 Alloy
After the solution treated alloy is quenched in the molten
salt at 520℃ and aged, the TEM microstructures of the
alloy crept to fracture are shown in Figure 4.
In the local region of the fracture alloy, the configuration
of dislocation network appears in the alloy as marked
with letter A in Figure 4(a). In addition, there are fine
carbide particles precipitating in the grain as marked
with the white arrow in Figure 4(a), and the deformed
dislocations slip in the matrix and pile up near the
carbide particles as marked with the black arrow. This
indicates that the carbide particles can hinder the dislocation
movement effectively to enhance the creep resistance of
the alloy.
In another region of the fracture alloy, it is clearly seen
that the stacking fault appears in the alloy as marked
with the arrow in Figure 4(b), and there are some
deformed dislocations tangling up near the stacking fault
as mark with letter B in Figure 4(b), which indicates that
the stacking fault can hinder the dislocation slipping in
the matrix. Figure 4(c) is another local region of the alloy
crept for 70h to fracture, thereinto, the microstructure of
trigeminal grain boundaries is marked by the white arrow
in Figure 4(c), and some granular carbides discontinuously
0 1020304050607080
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5 T=650oC
=1034Mpa
Strain ε (%)
Time (h)
1
2
3
Figure 3. Creep curves of the alloy measured under the
condition of 650℃ and 1034MPa.
(a)
A
0.3m0.2m
B
(b)
C
0.5m
(c)
Figure 4. After solution treatment and quenching in molten salt at 520℃, TEM microstructure of the alloy crept to fracture
under the applied stress of 1034 MPa at 650℃. (a) Dislocation network in the alloy; (b) the stacking fault appeared in the
alloy, (c) slipping dislocations ending at grain boundary.

J. XIE ET AL. 4
istribute along the boundaries as marked with the black d
arrow in Figure 4(c), and the slipping dislocations are
end at the grain boundary as marked by letter C, which
indicates that the grain boundaries can hinder the
dislocation movement during creep.
4. Discussion
d-solution temperature (1150) was ℃
ated alloy is quenched in molten
sa
5. Conclusions
eatment, some coarse  phase dis-
co
2) The alloy quenched in molten salt at lower tem-
ze and distri-
bu
[1] Hu Ben-fu, T-chang, et al. De-
velopment in e disk of P/M su-
for turbine blades[J]. Materials and De-
-metallurgical nickel-based
atment of PREP FGH95 superalloy podwers[J].
ical behavior study of non-metallic inclusions
of a powder metallurgical turbine
 phase in FGH95 superalloy[J]. Rare Metal
peralloy
H95 Powder Ni-Base Superalloy [J]. Chinese Journal
nd properties of
n-wei, YU Li-li, WANG Wu-xiang.
95
Because the soli
lower than the melting point of  phase (T=1160℃[13]),
the coarse  phase can’t be dissolved completely in the
alloy, so that some coarse  phase discontinuously dis-
tributes along the boundary regions of the alloy after full
heat treatment, as shown in Figure 1. When the solution
treated alloy is quenched in the molten salt at 520℃, the
matrix of the alloy can obtain higher saturation due to the
higher cooling rate for the alloy, which causes the in-
ner-stress existing in the matrix of the alloy [14]. More-
over, because the elements (Nb, Ti et al) with bigger
atom radius can’t be diffused enough during quenching
in the molten salt, the rich regions of solute are formed in
the matrix [15]. The facts mentioned above provide the
advantage conditions for the carbide particles precipitat-
ing in the alloy during quenching and aging. Therefore,
there are more granular carbides precipitating in the alloy
quenched in molten salt at lower temperatures, as shown
in Figure 1. Besides due to the fact that the cooling rate
of the alloy decreases as the molten salt temperature in-
creases, the diffusion degree of the alloy elements is suf-
ficient comparatively during quenching in the molten salt
at 650℃. Therefore, the alloy quenched in the molten
salt at 650℃ can obtain the bigger  phase in size as
shown in Figure 2(c).
After the solution tre
lt at 520℃ and aged, there is a high volume fraction of
 phase with smaller size precipitating in the grain, and
more carbide particles discontinuously distribute in the
grain and along the boundaries (as shown in Figure 1(a)),
which can improve the grain strength and hinder the dis-
location movement during creep. Besides the stacking
fault formed in the alloy can restrain the dislocation slip-
ping as shown in Figure 4(b). The facts mentioned
above are the important factors for the alloy possessing
the higher creep resistance.
1) After full heat tr
ntinuously distribute in the boundary regions, and a
high volume fraction of  phase and some carbide parti-
cles precipitate in the alloy. Here, as the salt quenching
temperature increases from 650℃ to 520℃, the size of
fine  phase increases slightly, but the amount of granu-
lar carbide decrease in the alloy gradually.
perature possesses a better match on the si
tion of  phase and carbides, which can enhance the
grain strength for the alloy possessing a better creep re-
sistance. The deformed features of the alloy are that the
deformed dislocations slip in the matrix and stacking
fault forms in the alloy during creep.
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