Effect of Si Alloying on Stability and Fracture Toughness of C15 NbCr2 Laves Phase: First-Principles Study

Based on the first-principles calculation method, the effects of Si alloying on the stability and fracture toughness of the C15 NbCr2 Laves phase were studied by calculating the enthalpy of formation, binding energy, atomic free volume and electronic structure. The site occupation energy indicates that Si tends to occupy the Cr site. The calculation of formation enthalpy and binding energy shows that the formation ability and stability of the Nb8Cr16-xSix(x=0 similar to 5) phase are enhanced with the increase of Si content and maintain a linear correlation with Si content. The atomic free volume calculation shows that the atomic free volume of the Nb8Cr16-xSix phase is higher than that of the NbCr2 matrix phase, and the atomic free volume reaches the maximum when the content of Si is 8.33at% (Nb8Cr14Si2), that is, the fracture toughness is the best. The electronic structure calculation shows that Si alloying makes the DOS curve shift to the right and the Fermi level approaches to the pseudo-energy gap, which stabilizes the NbCr2 matrix phase. Meanwhile, all the bonding peaks decrease and widen, which weakens the bonding strength of Nb-Cr atoms and makes the shear deformation easy to carry out, thus improving the toughness.