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

Abstract

Abstract 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 Al 11 La 3 and Al 3 Ni 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/Al 11 La 3 and Al/Al 3 Ni areas rather than the single fully coupled Al/Al 11 La 3 /Al 3 Ni ternary eutectic formed as the only constituent in the near-eutectic alloy at V up to 2 mm s −1 .