The influence of Ti additions on the mechanical and electrochemical behavior of β-Ta₅Si₃ nanocrystalline coating

Highlights: • β-(Ta_0.9Ti_0.1)₅Si₃ was calculated to be optimal composition to improve the ductility of β-Ta₅Si₃. • The addition of a certain amount of Ti has little impact on corrosion resistance of β-Ta₅Si₃. • Ti alloyed β-Ta₅Si₃ coating improve greatly corrosion resistance and hardness of Ti–6Al–4V. - Abstract: In this study, the effects of Ti substitutional additions on the mechanical and electrochemical corrosion behavior of β-Ta₅Si₃ were investigated through both theoretical calculation and experiment. Initially, first-principles calculations, based on density functional theory, were used to guide compositional design, according to the calculation of mechanical parameters (for example, bulk modulus, shear modulus, Young's modulus, the shear modulus/bulk modulus ratio and Poisson's ratio). This analysis showed that optimum mechanical performance may be achieved through Ta atoms in the Ta₂₀Si₁₂ unit cell being replaced by two Ti atoms. Subsequently, both the binary β-Ta₅Si₃ coating and the optimized Ti-alloyed β-Ta₅Si₃ coating (i.e., β-(Ta_0.902Ti_0.098)₅Si₃) were deposited onto Ti–6Al–4V substrates using a double cathode glow discharge plasma method. Both as-deposited coatings exhibited a tetragonal crystal structure with fine equiaxed grains ∼4 nm in diameter. The mechanical properties of the coatings were determined by both nanoindentation and Vickers indentation techniques, and their electrochemical corrosion behavior was examined by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and Mott-Schottky analysis in naturally aerated 0.9 wt.% NaCl solution at 37 °C. These investigations showed that the addition of Ti significantly improved the damage resistance of β-Ta₅Si₃, with little negative impact on its corrosion resistance.