Phase stability in metals under electric current: The role of defect-induced charge imbalance

초록

The stability of metallic phases is conventionally explained through thermodynamic free energy governed by temperature, pressure, and composition. Recent studies have shown that applying electric current can alter atomic bonding and accelerate microstructural evolution, implying a substantial modification of the underlying free energy landscape. Yet, attention has primarily focused on kinetically driven microstructural changes, overlooking the electrically induced influence on thermodynamic stability. Here, we show that electric current directly reduces the critical temperature of massive phase transformations in pure metals by modulating their phase stability. The minimal kinetic barriers in these transformations enable direct evaluation of thermodynamic effects of applied electric current in pure metals. Microstructural, calorimetric, dilatometric, and real-time diffraction analyses consistently reveal a significant reduction in transformation temperatures of commercially pure titanium and interstitial-free steel under electrothermal treatment. This temperature drop becomes more pronounced with finer grain sizes and higher current densities. Finite element simulations indicate that electric current concentrates at grain boundaries, inducing localized charge imbalance. Density functional theory-based molecular dynamics simulations further show that this charge accumulation lowers the transformation barrier by enhancing vibrational entropy via phonon softening. These findings position electric current as a decisive external parameter-one that governs phase stability by exerting an electric current-induced driving force alongside temperature, pressure, and composition.

키워드