Crystallization in Al₈₈Re₈Ni₄ glass-forming alloys

The results from transmission electron microscopy (TEM) microstructural studies of devitrified amorphous alloys with a composition A1₈₈RE₈Ni₄are presented as a function of average rare-earth atomic radii (between 1.76 and 1.87 A). Rare-earth elements RE s Gd, Er and La were co-substituted to vary the average atomic radius r_REwhile maintaining an 8at.% rare-earth concentration. As reported previously for Al₈₈La₂Gd₆Ni4 glasses, compositional phase separation prior to crystallization was observed in all alloys of this series. TEM examination of amorphous samples following low- temperature annealing treatments showed the development of strong image contrast prior to crystallization, corresponding to a segregation of the glassy matrix into aluminium-rich and solute-rich regions over a length scale of a few tens of nanometres. The subsequent crystallization behaviour depended on the average rare-earth radii, with metastable intermetallic phases forming first in glasses made with larger r_REand with fee α-Al nanocrystallization in smaller r_REglasses, showing preferential nucleation and growth of ot-Al near the boundaries of the phase-separated regions.