First-principles calculations for the mechanical properties of Ti-Nb-B2 solid solutions

First-principles calculations based on density functional theory and ultra-soft pseudo-potentials were carried out to investigate electronic, mechanical, and thermodynamic properties of Ti-Nb-B2 solid solutions. The mixing energy is found to be negative for all compositions indicating that formation of the solid solutions is energetically favorable. An analysis of the electronic structure shows that the Ti-Nb interactions are responsible for the stabilization of the solid solutions. A non-monotonic change of the density of states at the Fermi level was revealed. Despite the fact that the bulk modulus of TiB2 is lower compared to that of NbB2, calculated elastic constants, hardness and ideal shear strength gradually decrease on going from TiB2 to NbB2. The correlation between these values and the mixing energy is not observed. The calculated phonon spectra and the thermodynamic characteristics indicate that the thermodynamical properties of the solid solutions will change gradually between TiB2 and NbB2. The results obtained are compared with available experimental data.