Modeling of site occupancies in B2FeAl and NiAl alloys with ternary additions

The addition of ternary alloying elements to FeAl and NiAl based intermetallic compounds could potentially influence their mechanical properties in a significant manner. Knowledge of the site occupancies of different species in these ternary compounds is of importance since it influences the bonding characteristics and consequently the mechanical properties. In this paper a simple approach involving chemical rate theory has been used to calculate the site occupancies in the ternary B2 compounds. These calculations predict that with increasing atomic number of 3d transition metal additions to B2 FeAl, the site occupancy of the ternary addition increases on the Fe site with the exception of Cu. The predicted exception for Cu has been experimentally verified using ALCHEMI. In addition, the site occupancies in B2 Ni-Al-Fe compounds of different compositions have been predicted and experimentally verified. The role of the relative ordering or clustering tendencies of the three different binary pairs in the ternary compound on the site preferences has also been discussed. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.