TEM investigation of heterogeneous nucleation mechanisms in Al–Si alloys

Abstract

Heterogeneous nucleation was studied in an Al 80Ni 10Cu 8Si 2 glass containing hexagonal TiB 2 particles within the glassy matrix. Distinct orientation relationships were found for different phases on the TiB 2 faces. On basal faces copious nucleation of α-Al occurred with the close-packed planes and directions of Al and TiB 2 parallel, while on prism faces copious nucleation of tetragonal Al 2Cu was observed. Holding for 30 min at 1173 K prior to melt-spinning resulted in the formation of TiSi 2 on the basal faces instead of Al. The implications of the observed nucleation mechanism are discussed with respect to industrial casting practice, in particular to Si poisoning.