First principles study on the phase stability and mechanical properties of MoSi2 alloyed with Al, Mg and Ge

The phase stability, mechanical properties and electronic structure of C11(b) and C40 MoSi2 with alloying elements Al, Mg and Ge were systematically investigated using first principles methods. The calculated lattice constants and elastic constants of C11(b) and C40 MoSi2 are in good agreement with the previous results. It is found that there is a phase transition from C11(b) to C40 when the concentrations of Al and Mg reach similar to 7 at.% and similar to 6 at.%, respectively. Based on the elastic constants, the anisotropy, ductility, hardness and melting temperatures are presented for MoSi2 with alloying elements. For C11(b), the ductility will be enhanced by increasing the concentrations of Al or Mg. Simultaneously, hardness will be reduced by the increasing of Al or Mg. Ge have a reverse effects. For C40, the ductility is reduced weakly by Al or Mg. In addition, the effects of substitution of Mo by Nb with Si substitution of Si by Al, Mg and Ge are also investigated. Nb and Mg codoping can improve the ductility of MoSi2. Finally, the density of states is used to analysis the effects of alloying elements on the mechanical properties, and the results are in consistent with the predictions based on elastic constants. (C) 2015 Elsevier Ltd. All rights reserved.