Atom-probe investigations of TiAl alloys

Atom probe field ion microscopy (APFIM) and tomographic atom probe (TAP) have been used to study TiAl-based alloys. The element concentrations, the influence of additional elements such as Cr or Nb as well as the solubility of oxygen in α2 (Ti3Al) and γ (TiAl) phases in compounds with nominal concentration Ti54Al46 and Ti58Al42 have been determined. By using the detection of oxygen atoms as a very local probe, the present investigation revealed the existence of some intermediate phases during the phase transformation α→γ. The presence of the oxygen atoms during this transformation gives some peculiarities on the transformation path. The appearance of some metastable phases may be explained by the existence of the homologous series Ti2n−1Aln where n is an integer varying from 1 (stoichiometry TiAl) to ∞ (phase α3 Ti2Al).