Ab-initio study of electronic, mechanical and thermodynamic properties of -Ti-15Nb-xSi alloys for biomaterials applications

In this paper, we used the first-principles method to investigate the structural, electronic, mechanical and thermodynamic parameters of the ternary beta-Ti-15Nb-xSi alloys with x=0.6,0.8,1,1.2,1.4,1.6wt.%. We have carried out theoretical computations inside the density functional theory (DFT) utilizing the generalized gradient approximation (GGA) with the Perdew-Burke-Ernzerhof (PBE) model. The random distribution of Nb atoms in the alloy was described by using both virtual crystal approximation (VCA), special quasirandom structure (SQS) and the coherent potential approximation (CPA) techniques, in combination with first-principles plane-wave pseudopotential (PW-PP) and exact muffin-tin orbital (EMTO) methods. We determined the elastic constants as well as the bulk, shear, Young's modulus and Poisson's ratio. Our structural results are in good agreement with the available experimental and theoretical results for the pure structure of the titanium. In addition, we have estimated the band structure and the density of state (DOS) for the electronic computations. Our findings demonstrate that all of the compounds are metallic, stable and meet the requirements for stability. Young's modulus of Ti-15Nb-0.6Si and Ti-15Nb-1.6Si is 86.5GPa and 15.11GPa, respectively, which are similar to Young's moduli of human bone (10-30GPa). All calculated parameters of the alloys decreased with increasing of Si concentration except for Poisson's ratio, anisotropy and B/G ratio. Furthermore, all of the materials investigated showed ductile nature, and Young's modulus values are needed for further applications. Excitations from the quasi-harmonic Debye approximation's vibrational part were applied to the 0K free energy calculated via ab-initio calculations. The influence of temperatures up to 800 K on phase stability was investigated. These findings can be utilized to help designers create alternative low-modulus alloys for biomedical applications.