Microstructure of Al3Sc with ternary rare-earth additions

The microstructure of ternary L12-Al3(Sc1−yREy) 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: L12-Al3(Sc,RE) and D019-Al3(RE,Sc) (or C11b-Al4(Eu,Sc)). Alloys with heavy RE exhibit a single L12-Al3(Sc,RE) phase. The maximum RE solubility in the L12 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 L12-Al3(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.