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To be published in Proceedings of the 2nd International Conference on Heat-Resistant Materials, to be
hplJd 11-14 September, 1995, Gatlinburg, TN, sponsored by ASM-International and NACE-International.
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OVERVIEW OF THE DEVELOPMENT OF FeAI
Philip J. Maziasz, C.T. Liu and Gene M. Goodwin
Oak Ridge National Laboratory
P.O. Box 2008
Oak Ridge, TN 37831, USA
B2-phase FeAI ordered intermetallic alloys based on an Fe-36
at.% Al composition are being developed to optimize a
combination of properties that includes high-temperature
strength, room-temperature ductility, and weldability. Micro-
alloying with boron and proper processing are very important
for FeAI properties optimization. These alloys also have the
good to outstanding resistance to oxidation, sulfidation, and
corrosion in molten salts or chlorides at elevated temperatures,
characteristic of FeAI with 30-40 at.% Al. Ingot- and powder-
metallurgy (IM and PM, respectively) processing both produce
good properties, including strength above 400 MPa up to about
750 C. Technology development to produce FeAI components
for industry testing is in progress. In parallel, weld-overlay
cladding and powder coating technologies are also being
developed to take immediate advantage ofthe high-temperature
corrosion:oxidation and erosion/wear resistance of FeAI.
IRON- AND NICKEL-ALUMINIDE INTERMETALLICS
generally have outstanding oxidation/corrosion resistance
(>1000-1100*C) because they form a thin, stable, adherent
A1,0, film [1-3]. However, the thermodynamic forces driving
this reaction can also cause environmental/hydrogen
embrittlement at room temperature due to moisture in the air
[4-6]. There are metallurgical solutions to this problem, and
with proper allowing (particularly boron addition) and
processing to control m icrostructure, ductilities in the range of
5-40% or more can seen in FeAI, Ni,AI or FeAI alloys. The
considerable effort at the Oak Ridge National Laboratory
(ORNL) on the development and commercialization of Fe,AI-
type iron-aluminide alloys has been well documented and
reviewed [3,7-11]. Related work on FeAI alloys began later
at ORNL and was not published until patents were filed [12-
14]. The purpose of this paper is to overview ORNL work on
developing FeAI alloys, with emphasis on the current status
and on potential industrial applications. Key results will be
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highlighted, with experimental details to be found elsewhere.
INITIAL FeAI ALLOY DEVELOPMENT
FeAI is attractive because it maintains its excellent
oxidation and corrosion resistance to higher temperatures than
Fe3Al, and has a much higher ordered-B2 to disordered-a
phase transition temperature (>1100*C compared to 800-900*C
for Fe3AI alloys). However, FeAI alloys tended to be more
brittle and more difficult to fabricate than lower aluminum
alloys, and to be weak above 600*C. FeAI development at
ORNL was initiated in 1989-1990 to provide a new structural
material resistant to highly-oxidizing molten nitrate salts at
650*C . Base binary FeAI alloy compositions ranging
from 28-43 at.% Al showed that alloys with 35-40 at.% had
good high-temperature ductility (Fig. la), but that alloys with
>35 at.% Al had the best resistance to molten salt corrosion at
650*C (Fig. Ib). Examination of the fracture mode indicated
that FeAI alloys with <40 at.% Al showed transgranular
failure, while alloys with >40 at.% Al exhibited mainly grain
boundary failure. Therefore, Fe-36 at.% Al was chosen as the
base FeAI alloy for alloy development to improve the room-
temperature ductility and high-temperature strength (13].
These FeAI alloys also showed oxidation resistanceto> 1100*C
and sulfidation resistance, at least at 800*C, that was far
superior to FeCrNi and FeCrAI alloys, and similar to Fe-28
at.% Al (Fig. lc).
The first phase of FeAI alloy development explored
additions of Cr, Ni, Co, Mn, Ti, Zr, V, Mo, B and C to a base
alloy of Fe-36 at.% Al. The most effective elements for
increasing high-temperature strength and room-temperature
ductility of these FeAI alloys were small additions of Mo, Zr
and B in combination, with the synergistic effects being much
more potent than the single element effects [12,17]. While Zr
and B additions were very important for improved room-
temperature ductility, Mo+Zr+B additions produced the best
tensile and creep-rupture strength at 600*C (Fig. 2a) in an
alloy designated FA-362 (Table 1). The FA-362 alloy also
showed the highest room-temperature ductility in air (11.8%)
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Maziasz, P.J.; Liu, C.T. & Goodwin, G.M. Overview of the development of FeAl intermetallic alloys, article, September 1, 1995; Tennessee. (https://digital.library.unt.edu/ark:/67531/metadc623434/m1/1/?rotate=270: accessed May 22, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.