Emerging Applications of Intermetallics
Emerging Applications of Intermetallics
Emerging Applications of Intermetallics
www.elsevier.com/locate/intermet
Abstract
Many intermetallic compounds display an attractive combination of physical and mechanical properties, including high melting
point, low density and good oxidation or corrosion resistance. This has led to their utilization in many non-structural applications,
but success in structural applications has, to date, been limited. This paper reviews the current status of intermetallic applications,
with emphasis on new uses that are in place or pending. Most of the paper deals with aluminides and silicides, but there are several
more complex intermetallics that are being employed in battery and magnetic applications. Research on improved processing and
studies of the role of environment in mechanical behavior are shown to be key to developing practical alloys. # 2000 Elsevier
Science Ltd. All rights reserved.
Keywords: A. iron aluminides (based on Fe3Al); A. Magnetic intermetallics; A. Nickel aluminides, based on Ni3Al; A. Molybdenum silicides;
B. Superplastic behavior
0966-9795/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0966-9795(00)00077-7
1314 N.S. Stolo et al. / Intermetallics 8 (2000) 1313±1320
3. Intermetallics for structural, heat-resistant and cor- applications. This is because oxidation and carburiza-
rosion-resistant applications tion resistance is high, as are resistance to wear and
cavitation-erosion. A summary of current and potential
The most widely studied intermetallics in this class applications appears in Table 3. These applications
include aluminides of titanium, nickel, iron and niobium, range from furnace rolls and radiant burner tubes for
silicides of nickel, molybdenum and niobium and Laves steel production to heat treating ®xtures, forging dies
phases such as Cr2Nb. The physical properties of these and corrosion-resistant ®xtures for chemical industries.
compounds are summarized in Table 2. Many of these A photograph of various sizes of heavy wall, cen-
compounds have excellent corrosion and oxidation trifugally cast tubes of Ni3Al alloy IC±221M (Ni±
properties because of the high content of elements that 8wt.%Al±7.7 Cr-1.43Mo±1.7Zr±0.008B) appears in Fig.
form protective oxides. Therefore, applications for these 1 [1]. Other applications for this alloy include radiant
compounds sometimes extend far beyond their strength burner tubes, center posts for pit-carburizing furnaces
and ductility. and guide rolls for continuous casters. A stronger, more
creep resistant Ni3Al alloy, IC-438, (Ni±8.1wt.%Al±
3.1. Ni3Al 5.23Cr±7.02Mo±0.13Zr±0.005B) has been identi®ed;
this alloy allows potential users to extend the maximum
This compound has been the object of much research use temperature of 1100 C for IC-221M to 1250±
to understand the factors controlling low temperature
ductility. It is now known that the brittleness of unal-
Table 3
loyed Ni3Al stems from an environmental eect, and Applications of Ni3Al
boron serves to suppress the embrittlement. Numerous
alloys based upon Ni3Al have been developed with the Steel
As furnace rolls
aim of improving high temperature creep resistance.
Casting rolls
Although the mechanical properties are attractive, most Radiant burner tubes
current usage is mainly in corrosion-related structural
Heat treating
Fixtures for carburizing, furnaces, and air
Table 1 Link belts for heating treating furnaces
Applications of intermetallics Furnace mues
Radiant burner tubes
Structural
automotive Chemical
aerospace Reaction vessels for higher temperatures
Magnetic Tube hangers
Energy storage Pallet tips for phosphate ore calcination
batteries Pump impellers for slurries
hydrogen storage Forging
Heating elements Forging dies
Tools and dies Die repair as weld overlay
Furnace hardware
Corrosion-resistant Chemical
piping for chemical industries For ethylene crackers
cladding Air de¯ectors for burning of high sulfur fuel
coatings
Electronic devices
Table 2
Properties of high temperature intermetallics
1300 C for IC-438. Creep rupture strengths of the two of alloying elements such as Cr for Fe3Al and B for
alloys, based upon the Larson±Miller parameter, are FeAl, and the application of oxide or copper coatings
compared in Fig. 2 [1,2]. [4]. These developments, combined with improved creep
and impact resistance provided by alloying, have
3.2. NiAl improved the likelihood that monolithic iron aluminides
may be utilized for structural applications. Alter-
Much eort has been invested in attempts to utilize natively, the excellent corrosion and oxidation resis-
NiAl alloys for gas turbine hardware. Unfortunately, tance of iron aluminides suggests their possible
while NiAl single crystals were developed with creep usefulness as coatings. For example, steels have been
strengths comparable to those of Ni-base superalloy successfully coated by (Fe,Cr)3Al by a two-step pack
single crystals, other mechanical properties of NiAl cementation process, as shown in Fig. 3 [5].
were found to be inadequate. Ductility and fracture Another development that favors the near-term utili-
surfaces remain low. In addition, Walston and Darolia zation of iron aluminides is the development of the Exo-
[3] showed in 1997 that impact resistance of high MeltTM process, see Fig. 4 [6]. This low cost, easily
strength single crystals is inadequate for turbine blades, controllable process is useful also for nickel aluminides,
but might be sucient for stationary parts such as vanes as it exploits the exothermic heat of reaction between
and combustor liners. A directionally solidi®ed NiAl aluminum and other elements to reduce the need for
alloy was more resistant to impact. Physical vapor external power during melting.
deposited thermal barrier coatings did not improve
impact resistance. It appears unlikely that these short-
comings can be overcome in the near future.
Fig. 2. Comparison of creep-rupture strength of IC-438 with the data Fig. 4. Furnace-loading scheme of the EXO-MeltTM process for
for IC-221M [1]. melting of iron and nickel aluminides [6].
1316 N.S. Stolo et al. / Intermetallics 8 (2000) 1313±1320
Yet another promising processing technique for iron appears in Table 5. The most important use to date is as
aluminides is the use of superplastic forming. Li et al. [7] heating elements (Kanthal). Recent work by Akinc et al.
and Lin et al. [8] have demonstrated superplasticity for [14] has shown that improvements in electrical resisivity
FeAl and Fe3Al alloys, respectively. However, no of MoSi2 can be achieved by alloying with B-containing
applications utilizing this technique have been reported. phases, see Fig. 6. An important advantage of this
compound is the ability to utilize a wide range of pro-
3.4. TiAl cessing techniques to synthesize. One of the most pro-
mising of these techniques is powder processing to
One of the most promising intermetallics for turbine produce an alloy or a functionally gradient material
applications is TiAl. This compound has a higher melting (FGM) between MoSi2 and ceramics such as Si3N4 [15].
point, better oxidation resistance and resistance to ®res, The latter is particularly bene®cial as a solute in MoSi2
as well as lower density than conventional titanium because increased strength is accompanied by resistance
alloys, but has suered from low room temperature to catastrophic oxidation (pesting). A schematic draw-
ductility and fracture toughness. Nevertheless, numerous ing of a diesel energy combustion chamber, see Fig. 7
potential aircraft applications have been identi®ed, see [16] illustrates the use of MoSi2±Si3N4 glow plugs pro-
Table 4 [9]. However, the aircraft industry is extremely duced from a FGM process. Another recent application
demanding in qualifying new alloys, and the diculty in for FGM MoSi2 is in a hybrid direct energy conversion
fabricating these compounds, coupled with the lack of an system under development in Japan, as shown in Fig. 8
adequate data base of mechanical properties, have been [17] This device aims to convert solar energy into elec-
serious impediments to implementation. An advantage tricity by combining thermionic and thermoelectric con-
of TiAl is that this compound has a higher melting point version stages in a single device. The objective is increased
than competing alloys that combine the requisite ducti- energy conversion eciency. Other MoSi2-ceramic alloys
lity and creep resistance for turbine applications. One
such alloy, developed by M.Nazmy and co-workers, is
Ti±47at.%Al±2.1W±0.5Si. [10,11]. This alloy has
improved oxidation and creep resistance, such that it is
being proposed as a marine turbine alloy for a high speed
ferry. In this application, the maximum turbine inlet
temperature is 610 C. It has been successfully run in tests
to 1856 h, when it underwent its ®rst inspection (Sep-
tember, 1999). Additional uses of TiAl alloys may arise
from the ability to superplastically deform this com-
pound at relatively low temperatures [12] or to spray
form deposits on a substrate, see Fig. 5 [13]. These pro-
cessing techniques, as well as the ability to cast large
shapes, avoid the problems arising from lack of form-
ability by conventional working processes.
3.5. MoSi2
3.6. Nb3Si
3.7. Ni3Si
are used as superconductors, ohmic contacts for inte- Nd2Fe14B, which has the highest energy product of
grated circuits, for growth of epitaxial ®lms and as commercial permanent magnets [31]. Improvements in
infrared detectors and sensors. Other intermetallics are the fracture stress and toughness of these magnets
now being studied for electronic applications. For would allow greater machinability, easier handling and
example, NiAl and Ni3Al substrates are being used to use as a structural element. However, very little work
form an insulating alumina layer by oxidation in air at has been done in recent years on the mechanical prop-
temperatures between about 900 and 1200 C, prior to erties of hard magnets. Improved mechanical properties
applying conductive elements to the alumina layer [29]. are needed to fabricate electric vehicle wheel motors.
These circuit components have improved mechanical The use of improved permanent magnets in heat pump
properties and higher thermal conductivity compared to compressors and fan motors could provide substantial
alumina substrates sold in Japan and the United States. energy savings. Researchers at Oak Ridge National
The shape-memory alloys typi®ed by TiNi have been Laboratory have initiated an investigation of mechan-
examined extensively for possible use in small devices such ical properties of Nd2Fe14B [32].
as microvalves. These devices have the potential to be
used in microelectromechanical systems (MEMS) [30]. 4.3. Batteries
Table 6
Families of hydride-forming intermetallic compounds for Ni-metal hydride batteries from [33]
hydride batteries, see Table 6 [33]. A schematic of a intermetallics with abundant, low-cost elements such as
reversible battery with LaNi5 metal hydride and aluminum and silicon.
NiOOH electrodes in a KOH electrolyte is shown in
Fig. 10 [34]. NiMH batteries comprise more than 30%
of a $6 billion market for rechargeable batteries used in Acknowledgements
many portable electronic devices such as cell phones
and laptop computers [34±36]. Advantages of NiMH This research was sponsored by the Division of
batteries include higher storage capacity than Pb-acid Materials Science and Engineering, U.S. Department of
and Ni-Cd batteries, less toxicity than lead and cad- Energy under contract DE-AC05-00OR22725 with UT-
mium and lower cost than Li-ion batteries. However, Battelle, LLC.
NiMH batteries have lower energy density than Li-ion
and high initial costs than Pb-acid and Ni-Cd batteries.
New intermetallic alloys: (Zr,Ti)(Ni,Cr,V,Mn)2 have References
been developed as hydrogen storage materials for poss- [1] Sikka VK, Santella ML, Seindeman RW, Aramayo G. Inter-
ible use in electric cars. The capacity of batteries based metallic alloy development and technology transfer, pp. 89±107
upon the new compounds is 50% higher than for Advanced Industrial Materials (AIM) Program Annual Progress
LaNi5. Report for FY 1998, May 1999, ORNL/TM-1999/83, Oak Ridge
National Laboratory, Oak Ridge, TN 37831, 1999. p. 89±107.
[2] Deevi SC, Sikka VK. Intermetallics 1996;4:357±75.
[3] Walston WS, Darolia R. In: Nathal MV et al. editors. Structural
5. Summary intermetallics 1997. Warrendale, USA: TMS, 1997. p. 613.
[4] Stolo NS, Liu C.T. In: Stolo NS, Sikka VK, editors. Physical
This paper has described a wide range of industrial metallurgy and processing of intermetallic compounds. New
York: Chapman and Hall, 1996. p.159.
applications of intermetallic compounds. Although
[5] Zheng M, He Y, Rapp RA. Proceedings of the 11th Annual
many alloys with attractive high temperature strength Conference on Fossil Energy Materials, ORNL/FMP-97/1, May
and ductility have been developed, applications in 1997, Oak Ridge National Laboratory, Oak Ridge, TN 37831,
aerospace have been sparse. This arises in part from the 1997.
inherent conservatism of this industry when new mate- [6] Sikka VK. In Intl. Symp. on Nickel and Iron Aluminides; Mate-
rials Park, USA, ASM, 1997. p. 361.
rials are considered, especially in view of the lack of a [7] Li D., Shan A., Liu Y., Lin D. Scripta Metall Mater.1995;33:681.
large database for most intermetallics. Recent develop- [8] Lin D, Shan A, Li D. Scripta Metall Mater 1995;31:1455.
ments in processing (e. g. the use of powders to produce [9] Austin CM, Kelly TJ, Mcallister KJ, Chesnutt JC. Structural
functionally gradient materials) suggests that inter- intermetallics. TMS Warrendale, USA.
metallics may be useful in structural applications where [10] Nazmy M., Noseda C., Staubli M., Phillipsen B., Processing and
design issues in high temperature materials. Warrendale, USA:
ceramics are now contemplated for use. Fortunately, TMS 1997, p. 159.
numerous non-structural applications that exploit the [11] Tomasi A., Noseda C., Nazmy M., Gialanella S. MRS Symp.
electrical, thermal, magnetic and corrosion properties of Proc. 460, Pittsburgh USA, 1997, p. 225.
intermetallics have been identi®ed. Even in these appli- [12] Nieh TG, Wadsworth J. Intl Mater Reviews 1999;44(2):59.
cations, continuing research to improve strength, ducti- [13] Schimansky FP, Meyer MK, Gerling R. Intermetallics
1999;7:1275.
lity and toughness will add to the usefulness of [14] Akinc M, Meyer MK, Kramer MJ, Thom AJ, Hoebsch JJ, Cook
intermetallics. A summary of new alloys described in this B. Mater Sci and Engng 1999;A261:16.
paper, together with their major attributes, appears in [15] Sadananda K, Feng CR, Mitra R, Deevi SC. Mater Sci Engng
Table 6. While alloy design principles are well under- 1999;A261:223.
stood, better computational techniques to aid in alloy [16] Yamada K, Kamiya N. Mater Sci Eng 1999;A261:270.
[17] FGM-II, Research Activity Reports. FGM News 1996;30:16±25
development are needed. The major impact of proces- (in Japanese).
sing techniques on mechanical properties demonstrates [18] Washburn ME, Patent No. 5,045,237, 3 September 1991.
a need to optimize processing parameters to provide the [19] Crandall WB, Shipley LE, US Patent No. 3,875,476, 1 April
best balance of strength and toughness or ductility. 1975.
Further work on suppressing environmental embrittle- [20] Bartlett AH, Castro RG, Bu DP, Kung H, Petrovic JJ, Zurceki
Z. Industrial Heating, January 1996.
ment at low temperatures is desirable, as is the [21] Nowotny H, Kimakopoulou E, Kudielka H. Mh Chem
improvement of high temperature oxidation resistance 1957;88:180±92.
for alloys slated for structural applications. The estab- [22] Meyer MM, Kramer MJ, Akinc M. Intermetallics 1996;4:273.
lishment of property databases and the ability to demon- [23] Perepezko J, Nunez CA, Yi SH, Thoma DJ. High temperature
strate scale-up of laboratory research to production are ordered intermetallic compounds. MRS Symp Proc 1997;460:3.
[24] Bewlay BP, Lewandowski JJ, Jackson MR. Journal of Metals
prerequisites for widespread application of intermetallic 1997;49(8):44.
compounds. Finally, while not addressed in this paper, [25] Oliver WC, Liu CT. Improved mechanical properties of alloys
there is continuing necessity to hold down costs of ®n- based on Ni3Si. ORNL/TM-12154, November 1992.
ished products, notwithstanding the advantages of using [26] Liu CT, George EP, Oliver WC. Intermetallics 1996;4:77.
1320 N.S. Stolo et al. / Intermetallics 8 (2000) 1313±1320
[27] Zhu J., Liu C.T. Oak Ridge National Laboratory, 1999, unpub- [32] Horton JA, Wright JL, Herchenroeder JW. IEEE Trans On
lished. Magnetics 1996;32:4374±6.
[28] Kumar KS. In: Westbrook JH, Fleischer RL, editors. Intermetallic [33] Schlapbach L, Meli F, Zuttel A. In: Westbrook JH, Fleischer RL,
compoundsÐprinciples and practice, Vol. 2. 1995. p. 211. editors. Intermetallic compoundsÐprinciples and practice, Vol.
[29] Deevi S.C., Sikka V.K., US Patent No. 5,965,274, 12 October 2, John Wiley, 1995. p.475.
1999. [34] GM OvonicÐThe NiMH Choice. Troy, MI: G.M. Ovonic
[30] Wolf RH, Heuer AH. J Microelectromech Syst 1995;4:206±12. L. L.C., 1996.
[31] Stadelmaier, HH, Reinsch B, In: Westbrook JH, Fleischer RL, [35] Ovshinsky SR, Fetcenko MA, Ross J. Science 1993;260:76.
editors. Intermetallic compoundsÐprinciples and practice, Vol. [36] George EP, Unpublished results, Oak Ridge National Labora-
2, John Wiley, 1995. p. 303. tory, Oak Ridge, TN, 1999.