Dual-phase TiAl/Ti3Al-alloys consisting of a lamellar structure, comprising gamma-phase plus a small amount of alpha2-phase, with addition of 1, 5 and 10at% Nb were prepared. The samples were investigated by means of field ion microscopy (FIM) and atom probe tomography (APT). The influence of doping elements on the variation of field evaporation and microstructural parameters in the gamma-phase as studied by FIM and APT will be reported in this contribution. The intermetallic gamma-Phase of TiAl exhibits a L1(0)-structure, which has alternating Ti- and Al-planes in the [001]-superstructure direction. Because of the significant difference in the evaporation field strengths of Ti and Al, it is usually not possible to directly distinguish Ti- and Al-planes in this direction in the APT data. Therefore, it is not possible to assign Nb to any plane, as well. To solve this problem an algorithm, using statistical methods, was developed, which allows to inherently distinguish the planes. A comparison of the results for [100]- and [001]-directions shows that Nb prefers Ti-sites. The sequence of field evaporation field strengths, which follows the trend E(Nb) > E(Al) > E(Ti), could also be deduced.