Composition-dependent atomic transport properties of liquid Ti–Al alloys: Correlation between local structure and dynamic behavior

This study investigates the composition-dependent atomic transport properties and structural characteristics of liquid Ti-Al alloys across the entire composition range using ab initio molecular dynamics simulations. We systematically analyze self-diffusion coefficients, inter-diffusion coefficients, and shear viscosity alongside structural features characterized through Honeycutt-Andersen bond-pair analysis and fivefold symmetry parameters. Our results reveal composition-dependent atomic mobility, with Al atoms exhibiting enhanced diffusivity in Al-rich compositions, while Ti atoms show complex non-monotonic behavior influenced by local chemical environments. Inter-diffusion coefficients display a pronounced maximum at the equiatomic composition, coinciding with the peak in the thermodynamic factor, indicating thermodynamically driven diffusion enhancement. Structural analysis demonstrates that chemical short-range order reaches its maximum at the equiatomic composition, where Ti-Al heterogeneous coordination is the strongest. The total fivefold symmetry parameter exhibits nonlinear behavior with a maximum value near the equiatomic composition. We identify two key structure-dynamics correlations: a negative correlation between packing efficiency and self-diffusion coefficients, and a positive correlation between fivefold symmetry and inter-diffusion coefficients.