APFIM investigations on ordered γ-TiAl using single-layer detection method

The defect structure in the γ-phase of an α2γ-Ti51Al46Cr3 alloy and the site occupation of chromium has been studied using atom-probe field-ion microscopy (APFIM). Because of the difficult separation of adjacent atomic layers during conventional APFIM measurements a video-controlled field-evaporation technique was carried out. The γ-phase is hyperstoichiometric in aluminium. Many Al antistructure atoms were detected in Ti layers but no Ti antistructure atoms were found in Al layers. Chromium has a strong preference for occupying Ti sites in the ordered γ-phase (L10 type of superlattice). This seems to be in contrast with the results obtained by ALCHEMI (atom location by channelling-enhanced microanalysis). However, this discrepancy can be explained with the dependence of the site preference of chromium on the local Al concentration.