Mechanical properties of FeAl

Abstract

Only in the last few years has considerable progress been made in obtaining reproducible mechanical properties data for FeAl. Two sets of observations are the foundation of this progress. The frrst is that the large vacancy concentrations that exist in FeAl at high temperature are easily retained at low temperature and that these strongly affect the iowtemperature mechanical properties. The second is that room temperature ductiiity is adversely affected by the presence of water vapor. The purpose of this paper is not to present a comprehensive overview of the mechanical properties of FeAl but rather to highlight our understanding of key phenomena and to show how an understanding of the factors which control the yield strength and fracture behavior has followed from the discovery of the above two effects.In trod uc tion FeAl is a B2 or ordered body-centered-cubic compound that exists over a large compositional range, from 36.5 to 49.5 at. % A1 at room temperature, and up to a maximum temperature of Th Figure 1. The B2 structure adopted by FeAl, showing the slip vectors at low temperature, <111>, and high temperature, <loo>.1583 K (at 46 at. % Al) (1). Iron-rich-deviations from the stoichiometric composition are accommodated by Fe anti-site atoms. In addition, triple defects -two vacancies on the Fe sublattice site with an antisite (Fe) atom on the other (Al) sublattice -are present, especially in near-stoichiometric compositions (2). Irrespective of Fe:AI ratio, slip in FeAl occurs by the movement of anti-phase boundary (APB) coupled a/2<111> dislocations at low temperature but by the glide of perfect <100> dislocations at high temperature, see Figure 1. The temperature of this transition appears to decrease with increasing aluminum concentration (3-6). Slip occurs on { 112) or { 110) at low temperature but at room temperature and above slip is on { 110) (3,7-21).The summed manuscript has been authored by a WWaCtOr 960~464. Accordingly the U S. Government retains a nonexctusm royalty-free kmse to publish or reproduce the pubilshed foA of this ccntritpan. or allow others to do so, for U S. Government purposes of the U S Government under contract NO DE-ACOS-.t mechanical properties of FeAl were first reported as long ago as 1956 (22), but it is only in the last few years that progress has been made in obtaining reproducible mechanical data. Two sets of observations are the foundation of this recent progress. The first is that the large vacancy concentrations that exist in FeAl at high temperature are easily retained at low temperature (23) and that these strongly affect the lowtemperature mechanical properties (23-25), see Figure 2. The second is that room temperature ductility is reduced by water vapor (26).

Formation of an Aluminide Coating on Hot Stamped Steel

“…The ductile to brittle transition showed a clear dependence on the Al content and the deformation temperature. 12) In the present study the FeAl phase was found to be brittle when tested at strain rate of 0.5/s in the temperature range of 600-800°C. In this case the FeAl phase contained 5 at% Si.…”

The Effect of in-situ Formation of Al2O3 or Fe3AlC on the Structural and Mechanical Properties of FeAl Intermetallic Alloys

“…The proof stress of all of the FeAl alloy depicted in Fig. 4, more precisely B2 type FeAl alloy (1) , begins to decrease rapidly when the temperature exceeds around 700 -800 K, regardless of the existence of high strength reinforcements. Some models have been suggested to explain the relationship between the proof stress and the testing temperature of FeAl, for example cross-slip/pinning, anti-phase boundary mechanism, dislocation decomposition, vacancy hardening mechanism, and so on (1) .…”

“…According to the XRD analyses of milled powders and compacts as shown in Fig. 2, matrix FeAl phase can be synthesized mostly by MA process, and the reinforcement, Al 2 O 3 or Fe 3 AlC, are synthesized during consolidation process up to 1 273 K. After 1 800 ks milling, the volume fractions of FeAl phase of both MA powders were about 70%, which were obtained by the rough estimation using the height ratio of the major peak (1) . Additionally, it is strongly affected by the presence of thermal vacancy whose concentration increases by increasing cooling rate after heat treatment.…”

“…Therefore, it is often said that the FeAl intermatallic compound is particularly attractive for high temperature structural applications at intermediate temperature (up to 800 K) and a potential candidate to substitute stainless steels (1) . However, its application has been limited because of the poor ductility and toughness at room temperature and the poor creep strength at high temperature.…”

Overview of Lightweight Ferrous Materials: Strategies and Promises

“…1, Al forms disordered solid solution in Fe up to about 11 wt.% of alloying; beyond this amount of Al, various intermetallic phases such as D0 3 -based Fe 3 Al and B2-based FeAl appear. These intermetallics are usually brittle in nature and have been the subject of thorough research [15][16][17] in the last decades of the 20th century, especially for high-temperature applications, with a view to replace stainless steels and Ni-based superalloys. Therefore, these materials will not be considered in this overview.…”