ATOM-PROBE INVESTIGATIONS OF TIAL ALLOYS

Atom probe field ion microscopy (APFIM) and tomographic atom probe (TA P) have been used to study TiAi-based alloys. The element concentratio ns, the influence of additional elements such as Cr or Nb as well as t he solubility of oxygen in alpha(2) (Ti3Al) and gamma (TiAl) phases in compounds with nominal concentration Ti54Al46 and Ti58Al42 have been determined. By using the detection of oxygen atoms as a very local pro be, the present investigation revealed the existence of some intermedi ate phases during the phase transformation alpha --> gamma. The presen ce of the oxygen atoms during this transformation gives some peculiari ties on the transformation path. The appearance of some metastable pha ses may be explained by the existence of the homologous series Ti2n-1A ln where n is an integer varying from 1 (stoichiometry TiAl) to infini ty (phase alpha(2) Ti2Al). (C) 1998 Elsevier Science S.A. All rights r eserved.