Phase evolution during crystallization of sputter-deposited amorphous titanium-aluminium alloy thin films: dimensional and solute effects

Abstract

Abstract Ti-Al thin films have been deposited by magnetron sputtering on oxidized Si substrates. The targets consisted of a binary Ti-48 at.% Al alloy and a quaternary Ti–48 at.% Al–2at.% Nb–2at.% Mn alloy. In the as-deposited condition, the thin film grown from the quaternary alloy was completely amorphous whereas the film grown from the binary alloy consisted of crystalline α-Ti(Al) precipitates embedded in an amorphous matrix. In order to study the microstructural evolution during crystallization of these thin films two types of annealing experiment have been performed: ex situ in a furnace under a protective Ar atmosphere and in situ on a hot stage in the transmission electron microscope. Both the binary and the quaternary films crystallized into a two-phase mixture of γ-Tial and α2-Ti3Al as a result of ex situ crystallization. A thickness dependence in the evolution of microstructure has been observed during the in situ annealing. Thus, thick regions on the binary film evolved into the two phase microstructure during in situ annealing, which was similar to that observed in the ex situ annealed samples. In contrast, the thin regions of the binary thin film specimen exhibited growth of the pre-existing α-Ti(Al) crystallites into large grains and the formation of a new ordered tetragonal phase. The details of these investigations are presented in this paper.