Microstructure of Al 3Sc with ternary rare-earth additions

Abstract

The microstructure of ternary L1 2-Al 3(Sc 1− y RE y ) intermetallics, where RE is one of the rare-earth elements selected from five light (La, Ce, Nd, Sm or Eu) or two heavy lanthanoids (Yb or Lu), was investigated as a function of RE concentration for 0.02 ≤ y ≤ 0.75. Alloys with light RE show two phases: L1 2-Al 3(Sc,RE) and D0 19-Al 3(RE,Sc) (or C11 b-Al 4(Eu,Sc)). Alloys with heavy RE exhibit a single L1 2-Al 3(Sc,RE) phase. The maximum RE solubility in the L1 2 phase is very low (<0.4 at.%) for La, Ce, Nd and Eu, low (3.2 at.%) for Sm and complete solid-solution for Yb and Lu. Both lattice parameter and hardness of the L1 2-Al 3(Sc,RE) phases increase linearly with Sm, Yb or Lu concentration, and the magnitude of both effects correlates with the atomic size mismatch between Sc and RE.