Mechanical properties of defective L1₂-Al₃X (X = Sc, Lu) phase: A first-principles study

The mechanical properties of Al₃X (X = Sc, Lu) were studied by density functional theory (DFT). The elastic constants and formation enthalpy indicate that the L1₂-Al₃X (X = Sc and Lu) are mechanically and thermodynamically stable. The bulk moduli and shear moduli show that Al₃Sc has better resistance to volume and shape changes than Al₃Lu. However, the calculated results show that Al₃Lu has better plasticity than Al₃Sc. The properties of structural stability and elastic moduli of the crystal containing four major types of point defects in L1₂-A1₃X (X = Sc and Lu) were calculated. The mechanical properties of point defects show that point defects cause L1₂-Al₃X lattice distortion and change the corresponding elastic constants. Point defects reduce the Young's, shear and bulk moduli but have little effects on the crystal brittleness and toughness of Al₃Sc and Al₃Lu. Therefore, we have found that Lu addition into aluminum alloys is a very good replacement for expensive Sc addition when the L1₂ structures are desired for nucleation or strengthening precipitates in aluminum alloys.