Theoretical Study on the Structural, Mechanical, Thermodynamic, and Vibrational Properties of Ti₈Ni_8-xFe_x (X = 0-8) Shape Memory Alloys for Biomedical Applications

Shape Memory Alloys (SMAs) are metal alloys that can return to their original shape after deforming. In this study, Density Functional Theory (DFT) has been employed to study the structural, mechanical, thermodynamic, and vibrational properties of Ti₈Ni_8-xFe_x SMAs, with Fe content varying from x = 0 to 8. Calculated lattice parameters agreed well with the theoretical and experimental data, confirming the validity of this study. The structural analysis revealed a decrease in formation energy with increasing Fe content. These indicated the enhancement of the thermodynamic stability of the alloys. The calculated mechanical property showed a decrease in Poisson’s ratio as the Fe content increased, suggesting that the SMAs transit toward brittle behavior. Similarly, the G/B ratio was found to increase, confirming an improvement in the resistance to plastic deformation. The addition of Fe enhances C′ values and decreases the anisotropy of the alloys. Phonon dispersion calculations were conducted to evaluate the vibrational stability of the alloys. The results indicated that Fe doping modifies the elastic properties and influences the alloy’s mechanical performance. Fe contents changed the phonon frequencies due to bonding characteristics between Ni and Fe. Vibrational instability has been observed for Ti₈Ni_8-xFe_x (x = 0-2), while (x = 3-7) demonstrated the vibrational stability of the alloys. The Ti₈Ni₁Fe₇ alloy is the most thermodynamically stable and is a promising candidate for biomedical applications.