Heterogeneous nucleation in an Al-Ni-Si alloy studied using a metallic glass technique

Heterogeneous nucleation of α-Al and other phases was investigated in an Al 70 Ni 13 Si 17 (in at. %) alloy, using a novel metallic glass technique. The glass was formed by melt spinning and its devitrification/crystallisation behaviour during isothermal and anisothermal anneals was investigated using differential scanning calorimetry and X-ray diffractometry. The results obtained indicated suitability of the above alloy system for the nucleation study. TiB 2 grain refiner particles were subsequently added to the melt and the melt-spun ribbons produced were examined using transmission electron microscopy. No α-Al nucleation was detected on the boride particles, while it was systematically observed on hexagonal dendrites present in the glassy matrix, which suggests that Si poisoning of the borides is occurring. The high Si content appears to suppress the formation of Al 3 Ti layers on the surface of TiB 2 particles, thus reducing their potency to nucleate α-Al.