Substituting Ce with La and Nd in Al11Ce3: Effect on microstructure and mechanical properties

Microstructure and mechanical properties are studied for five cast, coarse-grained intermetallic alloys: binary Al ₁₁Ce ₃ and Al ₁₁La ₃, ternary Al ₁₁(Ce _0.75La _0.25) ₃ and Al ₁₁(Ce _0.5La _0.5) ₃, and quaternary Al ₁₁(Ce _0.54La _0.27Nd _0.19) ₃ with mischmetal composition. All compounds exhibit a single phase indicating a solid solution among the three rare-earth elements (RE=Ce, La, and Nd) on the Ce sublattice of Al ₁₁RE ₃ , in disagreement with Thermo-Calc prediction of segregation of Ce and (La, Nd) into two insoluble compounds. The lattice parameters of this orthorhombic Immm-structured α-Al ₁₁RE ₃ phase increase as La concentration increases, while the α-β phase transformation temperature decreases. The five Al ₁₁RE ₃ compounds show very similar (i) propensity for twinning, (ii) high hardness (4.1–4.3 GPa), and (iii) low indentation fracture toughness (0.48–0.65 MPa m ^1/2). The Al-Al ₁₁RE ₃ interface lattice mismatches, as calculated for two stable interface orientations, have comparable values across all examined compounds. These similarities imply that these Al ₁₁RE ₃ compounds will exhibit comparable strengthening and coarsening resistance in Al-RE-based eutectic alloys, thus positioning them as economically- and environmentally-favorable alternatives to the well-developed binary Al ₁₁Ce ₃ compound formed in current eutectic Al-Ce alloys.