World Journal Of Engineering
OXIDATION OF Ni3Al-(Cr, Zr, Mo, B) ALLOY BETWEEN 900 AND
1100C IN AIR
Seul-Ki Kim, Min-Jung Kim, Sang-Hwan Bak, Dong-Bok Lee
School of Advanced Materials Science & Engineering, Sungkyunkwan University, Suwon 440-746, Korea
* Corresponding author. Tel.: +82-31-2907355; fax: +82-31-2907371.
E-mail address: dlee@skku.ac.kr (D. B. Lee)
alcohol for oxidation tests at 900, 1000 and 1100C
in atmospheric air.
Isothermal oxidation tests were performed using a
TGA. Cyclic oxidation tests were performed using
a horizontal tube furnace. The test cycles involved
exposing the specimen for 1 h, cooling quickly to
room temperature for 30 min, and returning them to
the furnace. The oxidized specimens were inspected
by XRD, SEM, EPMA, and TEM operated at
300kV.
Introduction
The formulation and processing of commercial
alloys generally represents a compromise aimed at
striking a balance among various engineering
requirements and constraints. The desire to
maximize the strength of an alloy, for instance, may
be relaxed in order to develop acceptable toughness,
corrosion resistance, formability or other properties,
and to control the costs of raw materials or
processing. The response of alloy development
efforts to simultaneously satisfy multiple
constraints was responsible for the IC221M (ASTM
A1002-99) alloy [1]. IC221M is based on the Ni3Al
intermetallic compound. Chromium was added to
the Ni3Al-based alloy to suppress oxygen-induced
embrittlement [1,2], and, because Cr is
accommodated in the L12 structure [3,4] the Al
concentration was reduced. Molybdenum was
added to improve ambient and high-temperature
strength. Zirconium was added to improve hightemperature strength.
The properties of IC221M make it an attractive
candidate for many applications that require cast
heat-resistant alloys. The present study was
undertaken to investigate the high-temperature
oxidation behavior of IC221M exposed to air.
Results and Discussion
Experimental procedures
Fig. 1 XRD patterns of the scales after oxidation in
air: (a)~(b) isothermal oxidation; (c)~(e)
cyclic oxidation.
The chemical composition of the IC221M was
74.028%Ni-16.004%Al-7.844%Cr-1.263%Zr0.836%Mo-0.025%B, at%. The alloy was cut into
coupons of 4 x 6 x 15 mm3, polished on 1000 grit
paper, and ultrasonically cleaned in acetone and
Typical XRD patterns taken from the external
surface of oxidized specimens are shown in Fig. 1.
Here, Ni3Al matrix peaks were seen owing to either
573
World Journal Of Engineering
thin scale formation or scale spalling. The NiO
always formed initially. As the extent of oxidation
increased, -Al2O3, NiAl2O4, and ZrO2 gradually
appeared. Generally, the intensities of diffraction
pattern were in the decreasing order of NiO, Al2O3, NiAl2O4 and ZrO2. The NiO always
displayed the strongest patterns among the oxides
formed, because NiO existed as an outer oxide layer.
Faint patterns of both monoclinic- and tetragonalZrO2 were detected only at the later stage of
oxidation. The oxides of Cr, Mo and B were
undetectable from XRD due to their small amount
or dissolution in the other oxide phases.
is a cation-deficient, p-type semiconductor. As the
Fig. 3 SEM/EDS results of the oxide scale formed
on IC221M after isothermal oxidation at
1000 C for 190 h: (a) top view; and (b)
mappings of Ni, Al, and Cr.
oxidation progressed, those surface oxide grains
grew to coarse NiO grains, becoming the outer
oxide layer. The oxides that formed underneath the
alloy surface were rich in Al and Cr, indicating that
they were formed mainly by the inward diffusion of
oxygen.
Conclusion
Fig. 2 Wight gain vs. time curves of IC221M at 900,
1000 and 1100C in air: (a) isothermal
oxidation; and (b) cyclic oxidation.
The isothermal oxidation kinetics for IC221M are
plotted in Fig. 2a. As the oxidation temperature
increased, weight gains also increased. Though the
alloy exhibited a parabolic growth rate, relatively
large weight gains were obtained at 1100C. Fig. 2b
shows the results of cyclic oxidation tests. The
cyclic oxidation curves resembled the isothermal
ones at 900 and 1000C with little spallation, even
though the scale adherence could be affected by
thermal stresses generated during thermal cycling.
At 1100C, the alloy suffered from considerable
weight losses owing to massive scale spallation
after about 220 h. Hence, it is proposed that, for
oxidation in air, protective scales form on the
IC221M alloy at 900 and 1000°C, but not at
1100°C.
Fig. 3 shows the SEM/EDS results of the oxide
scale formed after isothermal oxidation at 1000C
for 190 h. In Fig. 3a, retained polishing grooves
surrounded by surface oxides indicated the original
alloy surface. The surface heterogeneity seemed to
be related to the original cast specimen. The EDS
mappings shown in Fig. 3b depict that numerous,
round surface oxide grains were mostly NiO, which
formed by the outward diffusion of Ni because NiO
The oxidation behavior of Ni3Al-based IC221M
was studied by air exposures between 900 and
1100C. Isothermal and cyclic weight gain
measurements indicated that protective scales
formed on the alloy at 900 and 1000°C. At 1100°C,
massive scale spallation after 220 h of exposure
was observed for cyclic oxidation conditions. The
oxide scales consisted mainly of an outer NiO oxide
layer, and inner, mixed oxides of α-Al2O3, NiAl2O4,
and (monoclinic, tetragonal)-ZrO2. Some alumina
and zirconia existed as internal oxide stringers.
Acknowledgement
This work was supported by the Human Resources
Development of the Korea Institute of Energy
Technology Evaluation and Planning (KETEP)
grant funded by the Korea government Ministry of
Knowledge Economy (No. 20101020300460).
References
1.
2.
3.
4.
574
Liu, C.T., In: R. Darolia et al. (Eds.),
Structural Intermetallics, TMS, Warrendale,
USA, (1993), 365.
Liu, C.T., Sikka, V.K., J. Met. 38(5) (1986), 19.
Hammond, C.M., Flinn, R.A., Thomassen, L.,
Trans. AIME, 221 (1961), 400.
Ochiai, S., Oya, Y., Suzuki, T., Acta Metall.
32 (1984), 289.