The formation of γ-TiAl from Ti/Al multilayers with different periods

In this paper multilayer thin films with periods (Λ) ranging from 4 to 1000 nm are studied in order to determine the maximum period leading to the γ-TiAl phase. The production of high period multilayers (Λ > 20 nm) requires the use of Ti and Al targets one by one. The influence of silver on the thin films transformation Ti/Al multilayer → γ-TiAl is also analysed. The introduction of a few percent of silver was performed by superimposing small Ag foils on the targets. The kinetics of the phase transformation was studied by differential scanning calorimetry and X-ray diffraction. Up to Λ = 200 nm, heat treating at 600 °C during 1 h leads to γ-TiAl, with or without small amounts of α2-Ti3Al, while for Λ = 500 and 1000 nm the presence of extra Al-rich phases is detected. For high periods (200, 500 and 1000 nm) an Al3Ti intermediate phase is formed. In the presence of silver the peak temperatures are shifted to lower values and the activation energy values slightly decrease.