A novel microstructure in the Al-La-Ni ternary eutectic alloy

Abstract

The morphology of growth of phases involved in eutectic solidification continues to attract interest because of its impact on properties and performance of materials containing eutectic constituents. Al-11.3La-5.4Ni (wt%) forms a ternary eutectic at growth velocities V in the range 0.01 to 2mm/s comprising fragmented pseudo-lamellar elements each made of odd numbers of alternate Al{sub 11}La{sub 3} and Al{sub 3}Ni fibers usually with Al{sub 11}La{sub 3} as the end member of each element. Formation of {alpha}Al dendrites within this eutectic matrix at V exceeding 2mm/s suggests an asymmetrical zone of coupled eutectic growth similar to Al-Al{sub 11}Ln{sub 3} (Ln = La, Ce or Nd). The eutectic interphase spacing {lambda} is given by {lambda}{radical}V = 8.1 {+-} 1.4 {micro}m{sup 3/2}s{sup {minus}1/2} which is {approximately} 30% smaller than found for the constituent Al-based binary eutectics. Hardness at the same value of {lambda} is larger by some 50% than for either of the constituent binary eutectics.