EXAFS STUDY OF THE LOCAL ATOMIC ORDER IN TI(2)ALX (X=NB, MO) B2 INTERMETALLIC COMPOUNDS

Extended X-ray absorption fine-structure (EXAFS) has been used to stud y the local atomic order in Ti2AlMo and Ti2AlNb in the B2 phase. It is found that the Mo and Nb atoms have different behaviors. Whereas the Ti2AlMo alloy is ordered as a pseudo-B2 structure in which the Mo and Al atoms are localized on one site and Ti atoms on the other, the Ti2A lNb alloy exhibits a more disordered behavior since the Nb and the Ti atoms are distributed on both sires. EXAFS experiments allowed us to q uantify the fraction of Nb on each site in Ti2AlNb as well as the bond lengths in both alloys.