First-principles investigation of phase stability and effects on ductility for MoSi₂ alloyed by Al and Nb

In this paper, site preference, phase stability and elastic parameters of MoSi2 for Al and Nb addition are studied using first-principles calculation. The results show that alloying elements can cause MoSi2 to change from C11(b) to C40 phase and the phase transition is due to the activated 1/2[ 1 ($) over bar 11](110) slip system for C11(b). G/B ratio reveals that the ductility is enhanced after phase transition. Ductile factor sigma(gamma m) =sigma(c) based on competitive processes between microcrack opening and dislocations emission is defined to assess the ductility of MoSi2. Interestingly, the increased ductility is due to the activated dislocation emission but suppressed crack propagation. Finally, charge density and DOS indicate that the improved ductility is due to the weakened Mo-4d and Si-3p covalent interactions.