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 D0(22), cubic L1(2), tetragonal D0(23), trigonal R (3) over bar 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 Pm (3) over bar m> trigonal R (3) over bar m> monoclinic Cm> tetragonal D0(23)> tetragonal D0(22), 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. (C) 2019 Elsevier B.V. All rights reserved.