Comparative analysis of crystallization of Al₈₅RE₈Ni₅Co₂ (RE = Rare-Earth Metals) metallic glasses with and without supercooled liquid region

The present study is devoted to an effect of a supercooled liquid region on crystallization behaviour of the Al₈₅RE₈Ni₅Co₂ metallic glasses produced by rapid solidification of the melt. The Al₈₅RE₈Ni₅Co₂ amorphous alloys can be divided into two groups depending on whether they show glass-transition on heating or not. Under annealing at the temperature above the glass-transition or under continuous heating at high enough heating rate, most of the Al-RE-Ni-Co glasses exhibiting formation of the supercooled liquid region primarily crystallize by precipitation of the nanoscale α-Al particles, Al-RE-Ni-Co alloys having no glass transition form intermetallic compounds primarily or corporately with α-Al. Amorphous alloys exhibiting no glass-transition crystallize equally at different modes studied. However, crystallization of the Al-RE-Ni-Co metallic glasses below glass-transition temperature follows different transformation mechanism. During isothermal annealing below glass-transition temperature an unknown metastable phase is formed conjointly with α-Al. Although transformation mechanism looks similar to an eutectic one some differences are found.