Evolution of metastable phases during crystallization of pulsed laser deposited amorphous Al-Fe films

Abstract

Amorphous thin films of different Al-Fe compositions were produced by plasma/vapor quenching during pulsed laser deposition. The chosen compositions Al₇₂Fe₂₈, Al₄₀Fe₆₀, and Al₁₈Fe₈₂ correspond to Al₅Fe₂ and B₂-ordered AlFe intermetallic compounds and a-Fe solid solution, respectively. The films contained fine clusters that increased with iron content. The sequences of phase evolution observed in the heating stage transmission electron microscopy studies of the pulsed laser ablation deposited films of Al₇₂Fe₂₈, Al₄₀Fe₆₀, and Al₁₈Fe₈₂ compositions showed evidence of composition partitioning during crystallization for films of all three compositions. This composition partitioning, in turn, resulted in the evolution of phases of compositions richer in Fe, as well as richer in Al, compared to the overall film composition in each case. The evidence of Fe-rich phases was the B2 phase in Al₇₂Fe₂₈ film, the L1₂- and DO₃-ordered phases in Al₄₀Fe₆₀ film, and the hexagonal å-Fe in the case of the Al₁₈Fe₈₂ film. On the other hand, the Al-rich phases were Al₁₃Fe₄ for both Al₇₂Fe₂₈ and Al₄₀Fe₆₀ films and DO₃ and Al₅Fe₂ phases in the case of Al₁₈Fe₈₂ film. We believe that this tendency of composition partitioning during crystallization from amorphous phase is a consequence of the tendency of clustering of the Fe atoms in the amorphous phase during nucleation. The body-centered cubic phase has a nucleation advantage over other metastable phases for all three compositions. The amorphization of Al₁₈Fe₈₂ composition and the evolution of L1₂ and å-Fe phases in the Al-Fe system were new observations of this work.