Abstract: Numerical analysis confirms that in some cases the prepeak in the structure factor causes obvious change in the coordination number, but change in the interatomic distance can be neglected for the study of the medium range order(MRO). In order to model the MRO, it is not possible to get enough information based on the pair correlation function; however the quasi-Bragg equation can be employed to characterize the quasi-period of MRO corresponding to the prepeak position. By assuming that the interatomic distance between Fe and Al atoms hardly varies with composition, structural models were constructed based on the B2-type structure units of ordered FeAl alloy. The quasi-periods for different alloys obtained from the model structures are in reasonable agreement with the experimental ones.

Key words:  Al-Fe alloy; molten structure; medium range order