Phase separation mediated devitrification of Al₈₈Y ₇Fe₅ glasses

The mechanisms responsible for the nanoscale devitrification of Al-based metallic glasses are unclear. A particularly well-studied case is Al ₈₈Y₇Fe₅, where non-isothermal differential scanning calorimetry (DSC) measurements show an exothermic peak that is consistent with glass devitrification to α-Al, but with no glass transition. Additionally, isothermal DSC studies show a monotonic decrease in enthalpy release with annealing, a feature generally taken to indicate grain coarsening. The results of coordinated DSC bright field transmission electron microscopy, in situ electrical resistivity and atom probe tomography (APT) studies of Al₈₈Y₇Fe₅ support a nucleation/ growth-based crystallization process. The APT data indicate the presence of sub-nanometer pure Al zones and coarser scale (separation distance ∼ 74-126 nm) Al-rich regions in the glass. The pure Al zones dispersed in the Al-rich regions appear to catalyze α-Al nucleation, explaining the high nucleation rates. The solute-rich regions between the Al-rich regions inhibit long-range diffusion, explaining the low growth rates.