Effects of different phases, compositional change, and doping on ductility improvement of NbAl₃ phases

We use the first-principles calculations based on density functional theory to study how to increase ductility of NbAl₃. Three methods are considered in this study including structural transformation, compositional change and metal substitution. Firstly, the common body-centered tetragonal D0₂₂, cubic L1₂, tetragonal D0₂₃, trigonal R3−m and monoclinic Cm phases of NbAl₃ are investigated. The calculated structural parameters are in agreement with the available data. The order of ductility is cubic Pm3−m> trigonal R3−m> monoclinic Cm> tetragonal D0₂₃> tetragonal D0₂₂, showing that the ductility of NbAl₃ can be effectively improved by structural transformation. The effects of pressure on ductility and phase transition are investigated, indicating that the pressure can induce brittle-ductile transition and structural transition. Secondly, new crystal structures based on Nb and Al are predicted. The obtained NbAl is mechanically stable and shows the characteristic of ductility. Finally, the effects of substitutional doping on ductility are studied. However, both the concentration change and element change have little influence on the improvement of ductility.