Metastable microstructures in laser-ablation-deposited Al–Fe thin films

Abstract

The paper reports studies on the nature of metastable microstructure evolved during pulsed-laser-ablated thin films of Al–Fe alloys with Al₇₂Fe₂₈ and Al₄₀Fe₆₀ average compositions. The microstructure of these films consists of vapourplasma-quenched matrix and solidified liquid droplets of various sizes embedded in the matrix. For both alloy compositions, vapour quenching yields an amorphous phase. The microstructure of the embedded droplets exhibits size dependence. In Al₇₂Fe₂₈ films, a hierarchy of structures from amorphous to metastable nanosized bcc to bcc with ordered ω precipitate was observed as a function of increasing size. The formation of ordered ω phase is a new observation. The sequence of structure evolution of droplets in Al₄₀Fe₆₀ films with increasing size was found to be amorphous to metastable bcc to ordered B2. We argue that disorder trapping occurs during solidification of these droplets.