Solidification microstructure formation in the Al-rich Al–La–Ni system

Alloys within the composition range Al– 5 to 17 wt.% La and Al– 5 to 8 wt.% Ni have been solidified by the Bridgman technique at a temperature gradient of ≈12 K mm−1 and growth velocity V in the range 0.01–5 mm s−1. Resulting microstructures were governed primarily by proximity of the alloy composition to that of the near-eutectic alloy (Al–11.3La–5.4Ni) included in the study. The primary Al11La3 and Al3Ni formed at the higher alloy contents became increasingly nonfaceted and dendritic with increasing V, with an increasing amount of α-Al halo formation around the primary phase. The residual eutectic in both lower (where α-Al was the primary phase), and higher alloy contents comprised distinct Al/Al11La3 and Al/Al3Ni areas rather than the single fully coupled Al/Al11La3/Al3Ni ternary eutectic formed as the only constituent in the near-eutectic alloy at V up to 2 mm s−1.