Measurement of Thermo Physical Properties
of Nickel Based Superalloys
Lavakumar Avala1, Mamatha Bheema2, Prince Kr Singh3, Rabindra Kr Rai4 & Sanjay Srivastava5
1,3,4&5
Department of Materials Science and Metallurgical Engineering,
Maulana Azad National Institute of Technology: Bhopal - 462051, India
2
QA/QC Department, API Division, Bhushan Steel Limited, Khopoli-410203, India
cobalt, iron, chromium, molybdenum and tungsten gives
the possibility of strength of austenitic matrix. The
addition of aluminum and titanium causes precipitation
of an ordered compound based on formula Ni3(Al,Ti)
which is coherent with austenitic γ matrix. This phase is
required for high - temperature strength and creep
resistance.10-18 Disadvantageous property of superalloys
is low thermal conductivity which is due to the high
percentage of alloying elements. Thermal conductivity
is an important physical property of materials which
enable to evaluate the usefulness of a metallic material
to high temperature structural applications. Rapid heat
transfer afforded by high thermal conductivity enables
efficient cooling which moderates the appearance of life
limiting heat attacked spot. High thermal conductivity
assures also a uniform temperature distribution, which
reduces thermally induced stresses and thereby
improves fatigue properties.18-19
Abstract - Nickel based superalloys are used primarily in
turbine of aircraft engines, marine and power industry.
Thermal conductivity is an important physical property of
materials which enable to evaluate the usefulness of a
metallic material to high temperature structural
applications. In present study, thermal conductivity of
commercial nickel based superalloys Supercast 247A and
Superni 263A was measured. The thermal conductivity
was calculated as a function of density, specific heat and
thermal diffusivity. Analysis of these measurements
showed that the γ' phase (Ni3Al) affected the properties of
thermal diffusivity and thermal conductivity and
relationships have been identified between these properties
and the γ' phase content.
Keywords - Superalloy, Thermal conductivity, Density,
Specific heat.
I.
INTRODUCTION
Nickel base superalloys used for modern gas
turbines are continually being developed to increase
thrust, operating efficiency and durability. Ni base
superalloys such as Supercast 247A (equivalent to CM
247LC) and Superni 263A (equivalent to Nimonic
263LC) alloys have been used in gas turbines as blades
at high temperature because of its excellent high
temperature mechanical properties.1-5 Generally, the Nibase superalloys with complex and multi-phase
microstructures are stable at high temperatures and this
characteristic is the main reason for using them in
critical and severe service conditions.6-9 The hightemperature strength of superalloys is based on the
principle of a stable austenitic matrix (γ phase)
combined with solid solution hardening and/or
precipitation strengthening. Thermal stability of γ phase,
the possibility of solid solution hardening and
precipitation strengthening, high elastic modulus of the
matrix are main factors which define the application of
superalloys. High solubility of many elements such as
The aim of the present work was to evaluate the
thermal properties of selected nickel based superalloys
and the dependence of these properties on the
temperature.
II. EXPERIMENTAL PROCEDURE
The thermal diffusivities of the alloys were
measured using a NETZSCH 427 Laser flash apparatus
(Fig 1).20-21 Disc shaped specimen 1–3 mm thick (L)
were maintained in an atmosphere of purified argon. For
measurements on solids the front face of the specimen
was sprayed with graphite and a pulse of energy was
focused on the front face and the temperature of the
back face of the sample was monitored continuously
with an InSb infra red detectoralong with the time. The
thermal diffusivity of the sample at a specified
temperature was determined from the temperature
transient which yielded a value for the specimen to
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International Journal on Mechanical Engineering and Robotics (IJMER)
reach half of the maximum temperature rise (t). The
thermal diffusivity (a) was then determined from the
following relation 22
The thermal diffusivity measurements were
conducted under argon between room temperature to
1400K. Special sample holders with additional adapter
rings were used due to different dimensions of samples.
The samples were coated with graphite on the front and
back surfaces in order to increase absorption of the flash
light on the sample’s front surface and to increase the
emissivity on the sample’s back surface. The presented
thermal diffusivity results are the average values of five
individual tests. The amount of γ' formed in the alloy
was calculated using an image analyzer software.
Thermal conductivity (k) values were calculated
from the thermal diffusivity, specific heat (C p) and
density (ρ) values, and the relation is as follows.
𝐾 = 𝜌. 𝐶𝑝 . 𝑎
.
Table 1. Chemical composition of investigated alloys
Element content, % weight
Superalloy
Cr
Supercast
247A
Superni
263A
Co
Mo
Al
Ti
C
B
W
Zr
Hf
Mn
Fe
Ni
8.2
9.3
0.5
5.6
0.81
0.074
0.015
9.5
0.014
1.51
-
-
Bal.
Bal
20
19.4
5.9
0.44
2.1
-
-
-
-
-
0.38
0.10
.
Table 2. Specific heat, density and thermal diffusivity of
superalloy Supercast 247A as a function of temperature
Nickel base superalloy : Supercast 247A
Specific
Thermal
Thermal
Temperat
heat,
Density
conducti
diffusivity
ure (K)
J/(g.K)
g/cm3
vity
mm2/s
W/(m.K)
298
0.428
8.643
2.781
10.283
400
0.434
8.611
3.126
11.682
600
0.462
8.599
3.349
13.304
800
0.491
8.556
3.861
16.220
1000
0.542
8.434
4.344
19.857
1200
0.590
8.396
4.762
23.589
1400
0.620
8.209
5.159
26.257
0.65
8.7
Specific heat
Density
8.6
8.5
0.55
8.4
0.50
Density, g/cm
3
Specific heat, J/(g.K)
0.60
8.3
0.45
8.2
0.40
200
Fig. 1: General view of LFA 427 device: a) laser system
connected via fiber optics, b) measuring unit with
furnace, a sample carrier and In-Sb detector, c)
controller for measuring unit
400
600
800
1000
1200
1400
Temperature, K
Fig. 2(a) : Specific heat and Density of nickel base
superalloy Supercast 247A as a function of temperature
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International Journal on Mechanical Engineering and Robotics (IJMER)
6.0
600
0.482
8.161
4.216
16.580
800
0.516
8.099
4.892
20.421
1000
0.576
7.862
5.122
23.189
1200
0.635
7.751
5.637
27.741
1400
0.652
7.700
5.826
29.248
27
Thermal diffusivity
Thermal conductivity
5.5
/s
2
Thermal diffusivity, mm
21
4.5
4.0
18
3.5
15
3.0
Thermal conductivity, W/(m.K)
24
5.0
12
2.5
8.4
Specific heat
Density
0.65
8.3
0.60
8.2
9
400
600
800
1000
1200
1400
Temperature, K
8.0
0.50
7.9
3
Fig. 2(b) : Thermal diffusivity and Thermal conductivity
of nickel base superalloy Supercast 247A as a function
of temperature
8.1
0.55
Density, g/cm
200
Specific heat, J/(g.K)
2.0
0.45
7.8
7.7
0.40
III. RESULTS AND DISCUSSION
7.6
The thermal properties of nickel based superalloys
Supercast 247A and Superni 263A were investigated.
The change in thermal diffusivity, thermal conductivity,
specific heat and density of Supercast 247A was showed
in Fig. 2(a) & (b) and corresponding values are shown in
Table 2. The thermal properties are dependent upon
electron transport. Consequently, for the solid phase
measured values are affected by the microstructure since
electrons can be scattered by particles, grain boundaries,
etc. Thus, there tends to be some variation in thermal
diffusivity values for the solid phase since they are
dependent upon the microstructure which is, in turn,
dependent on the thermal history of the specimen.
Measured thermal diffusivity values derived in the
temperature ranges where the γ' phase particles coarsen
and then dissolve also tend to vary because these
transformations are dependent upon both temperature
and time.
200
Density
g/cm3
298
0.417
8.361
3.349
11.678
400
0.442
8.310
3.926
14.420
800
1000
1200
1400
Fig.3(a) : Specific heat and Density of nickel base
superalloy Superni 263A as a function of temperature
Similar dependencies of thermal properties were
detected for sample Superni 263A as functions of
temperature were measured. The change in thermal
diffusivity, thermal conductivity, specific heat and
density of Supercast 247A was showed in Fig. 3(a) &
(b) and corresponding values are shown in Table 3.
Lower values of thermal conductivity are the results of
higher alloying elements contamination in this
superalloy (see Table 1). Slight steps were detected in
thermal diffusivity, heat capacity and thermal
conductivity for all samples above 800K (Figs. 2 & 3).
Much the same results was obtained by Przeliorz23 and
other authors who investigated the heat capacity of
superalloys by the DSC method. They observed the
increase of heat capacity above the temperature of 800K
and then the drop up to the temperature of 1000K, on
the DSC curve. This phenomena is probably due to the
distribution of γ' phase. Between temperature of 1100K
and 1200K the thermal conductivities remains constant
and then slightly increase (Figs. 2&3). Lower values of
thermal diffusivity and conductivity were detected for
samples of Supercast 247A which has the highest
alloying elements content (Fig. 2, Table 2).
Nickel base superalloy : Superni 263A
Specific
heat,
J/(g.K)
600
Temperature, K
Table 3. Specific heat, density and thermal diffusivity of
superalloy Superni 263A as a function of temperature
Temper
ature
(K)
400
Thermal
Thermal
conductivi
diffusivity
ty
mm2/s
W/(m.K)
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International Journal on Mechanical Engineering and Robotics (IJMER)
IV. CONCLUSIONS
7.0
Thermal conductivity of superalloys depends on the
chemical composition of alloy and the temperature. It
was confirmed that alloying elements decrease the
thermal conductivity of superalloys. Thermal
conductivity increases with the increase of the
temperature from 10.2 Wm-1K-1 at room temperature to
26.2 Wm-1K-1 at 1400K for alloy Supercast 247A
(equivalent to CM 247LC), and 11.6 Wm-1K-1 at room
temperature to 29.24 Wm-1K-1 at 1400K for Superni
263A (equivalent to Nimonic 263C).
30
Thermal diffusivity
Thermal conductivity
28
26
2
6.0
Thermal diffusivity, mm
24
5.5
22
5.0
20
18
4.5
16
4.0
14
3.5
Thermal conductivity, W/(m.K)
/s
6.5
The γ' phase content of the alloy has a significant
effect on the thermal properties. Slight steps were
detected in thermal diffusivity and conductivity for
samples above 500°C which is probably due to the
distributing of γ' phase.
12
3.0
10
200
400
600
800
1000
1200
1400
Temperature, K
V. REFERENCES
Fig. 3(b) : Thermal diffusivity and Thermal conductivity
of nickel base superalloy Superni 263A as a function of
temperature
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