Unifying mechanics and thermodynamics: The atomic-scale origin of stability in titanium alloys

DY Kim and DH Wang and S Lee and WJ Kim and T Yi, MATERIALS & DESIGN, 260, 115221 (2025).

DOI: 10.1016/j.matdes.2025.115221

The thermomechanical stability of high-performance materials such as titanium alloys is essential to their functional reliability, yet predicting this stability is challenging due to the complex interplay between local stress and thermodynamic driving forces at the atomic scale. Here, using large-scale molecular dynamics simulations, we establish a direct, quantitative correlation between local von Mises stress, configurational entropy, and Helmholtz free energy in representative a-and /3-phase titanium alloys. We reveal that /3-phases exhibit broader stress-entropy distributions, indicating enhanced atomic mobility and reduced thermodynamic stability. Crucially, we resolve a common ambiguity by demonstrating that a-phases, despite having comparable per-atom energies, possess lower free energy per unit volume, which confirms their superior thermodynamic stability at low to moderate temperatures. We further show that the geometric constraints of the HCP a-phase lattice produce a much stronger coupling between local stress and free energy than in the more deformable BCC /3-phase. These insights are integrated into a machine learning model that accurately predicts atomic-scale thermodynamic states of the alloy across a wide temperature range. Our findings provide an interpretable, atomistically resolved framework for predicting stress-driven disorder and phase stability in complex engineering alloys.

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