Abstract
We study single-site and two-site defect structures in B2-type Fe-Al alloys by means of density functional theory supercell calculations. The defect formation energies are calculated as functions of the chemical potential, which are used to obtain the dependence of the defect concentrations on Al content at different temperatures. We also examine the converging behavior of the formation energies with respect to the supercell size to study the corresponding limit of dilute defects. The effect of magnetism is investigated by considering nonmagnetic, ferromagnetic, and paramagnetic states, calculations for the latter showing that the magnitude of the local magnetic moments strongly impacts the defect formation energies. The methodological studies are used to provide explanations for the wide spread of defect formation energies reported by experiments and other theoretical investigations. Based on these insights, the stability of the B2-FeAl structure as a function of Al concentration is obtained and discussed.
Highlights
Fe-Al alloys have been a field of interest in materials science since the 1930s
By performing density functional theory (DFT) calculations, here we show from first principles that the main reasons explaining such a wide range of defect formation energies reported in the literature
We have carried out ab initio calculations based on density functional theory to investigate the defect structures and solubility of B2-FeAl alloys at finite temperature
Summary
Fe-Al alloys have been a field of interest in materials science since the 1930s. They have been promising candidates for industrial applications since it was discovered that Fe-Al alloys have high corrosion and sulfidation resistance properties [1] with composition of more than 20 at. % Al, compared with steels and Fe-based commercial alloys. It has been realized that alloys with this composition have lower density than stainless steels [2] and have comparable tensile strength to that of ferritic and austenitic steels [3] These properties make Fe-Al alloys attractive for the industry, where inexpensive and high-temperature structural materials are used. The group of Fähnle used a grand canonical approach and reported several extended studies [17,18,20,24] One of their main results is that there are no Al vacancies in B2-FeAl, which has been confirmed by other authors. Case of Al vacancy) are as follows: (i) unconverged supercells, i.e., the use of too-small supercells that are tied to large defect concentrations; (ii) lack of consideration of the formation of local magnetic moments at Fe sites, i.e., a nonmagnetic simulation; and (iii) calculations that do not take into account self-consistently the role of the chemical potential of Fe and Al. We investigate the effect of a paramagnetic state and discuss the stabilization range of the B2-FeAl structure.
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