Estimation of Defect Structure and Site Preference of Additional Elements in B2-Type Nial, Coal and Feal at Offstoichiometry

Abstract

AbstractDefect structures induced by deviation of composition from stoichiometry and site preference of additional elements are predicted for B2-type aluminides (NiAl, CoAl and FeAI) consisting of 8A-group elements by comparing formation energies of particular atomic configurations under the pseudo-ground state. Interaction energies between atoms and vacancies are estimated using a modification of Doyama’s relationship. The results show that vacancy-type defects are formed in NiAl and CoAl only when the total composition of Al and additional elements occupying the Al-site is more than the stoichiometry, whilst with less than the stoichiometry, substitutional defects are formed. In FeAI, only substitutional defects are formed in either case of deviation. Similar to Al, Si occupies only the Al-site, although elements in 1A- and 8A-groups of the periodic table mostly occupy only the Ni-, Co- and Fe-site. The other elements occupy either Al-site or the site of 8A-group elements, or both, depending on the composition.