An atomistic study of segregation to lamellar interfaces in non-stoichiometric TiAl alloys

Segregation to γ/γ interfaces in non-stoichiometric L10 TiAl is analyzed on the atomic level using a Monte Carlo method and central force many-body potentials of the Finnis–Sinclair type to describe atomic interactions. While these alloys are Ti-rich and thus segregation of Ti is of principal interest, the calculations have also been made for Al-rich bulk in order to investigate the generality of structural features revealed in this study. No segregation takes place to ordered twins but both Ti and Al, depending on which of them is in surplus in the bulk, segregate to the 120° rotational faults, pseudotwins and ordered twins with the APB. The segregation of Ti to 120° rotational faults and pseudotwins leads to an apparent formation of a thin layer of the DO19 Ti3Al at these interfaces. However, an analogous DO19 type structure, but with stoichiometry Al3Ti, is also obtained when Al segregates to these interfaces. Hence, the segregation propensity cannot be associated with a thermodynamically favored formation of the DO19 phase at γ/γ interfaces. Rather, the distribution of Al sites that are favored for segregation is such that their filling by Ti leads to the formation of the structure which is the same as that of the basal plane in Ti3Al. Consequently, the conspicuous formation of the DO19 Ti3Al at 120° rotational faults and pseudotwins results from the topology of the nearest neighbors of the atoms at these interfaces. Segregation is also favored to the ordered twin with the APB but it invokes dissociation of this interface into the 120° rotational fault and the pseudotwin which then possess the same structure as the corresponding isolated interfaces.