Abstract
A method is proposed for predicting the substitution behavior of ternary elements (X) in B2-type intermetallic compounds (AB) having substitutional (antistructure) defects at offstoichiometric compositions. Calculations are carried out using the pseudo-ground state analysis based on the nearest-neighbor, pair-approximation. The results revealed that the site preference of X can be determined by both heat of formation and alloy concentration: X occupies A sites only in case of ΔHBX<ΔHAB+ΔHAX(ΔHAB stands for the heat of formation between A and B), X occupies B sites only in case of ΔHAX<ΔHAB+ΔHBX, and in cases, X occupies both or either A and/or B sites unfilled by constituent elements depending on alloy concentration. It is shown that: in NiTi, CoTi and FeTi, most 3A- and 4A-group elements occupy Ti sites only, and most 8A-, 4B-and 5B-group elements occupy Ni, Co and Fe sites only; while in NiAl, Co, Rh etc. occupy Ni sites only, and Si occupy Al sites only. These results are in good agreement with available data in the literature.
