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

The paper reports studies on the nature of metastable microstructure evolve d during pulsed-laser-ablated thin films of Al-Fe alloys with Al72Fe28 and Al40Fe60 average compositions. The microstructure of these films consists o f vapour-plasma-quenched matrix and solidified liquid droplets of various s izes embedded in the matrix. For both alloy compositions, vapour quenching yields an amorphous phase. The microstructure of the embedded droplets exhi bits size dependence. In Al72Fe28 films, a hierarchy of structures from amo rphous to metastable nanosized bcc to bcc with ordered omega precipitate wa s observed as a function of increasing size. The formation of ordered omega phase is a new observation. The sequence of structure evolution of droplet s in Al40Fe60 films with increasing size was found to be amorphous to metas table bcc to ordered B2. We argue that disorder trapping occurs during soli dification of these droplets.