Capillary fluctuation method applied to moving solid-liquid interfaces: Temperature dependence of interfacial...

Understanding the solid-liquid interfacial thermodynamics of pure metals under undercooled conditions is essential for predicting microstructure evolution, yet quantitative data on the temperature dependence of interfacial free energy and its anisotropy remain limited. In this study, we extend the capillary fluctuation method (CFM) to moving solid-liquid interfaces obtained from molecular dynamics simulations of solidification in undercooled pure Al. By tracking the instantaneous interface position during steady-state migration and analyzing the fluctuation spectra of the interface height, the average interfacial free energy γ0 and the anisotropy strengths ϵ1 and ϵ2 were determined as functions of temperature. The fluctuation spectra retained a characteristic k-2 dependence even for moving interfaces, demonstrating that the CFM is applicable under non-equilibrium solidification conditions. The results show that γ0 tends to increase with decreasing temperature near the melting point, consistent with theoretical expectations and previous computational studies. The anisotropy parameters exhibit only weak temperature dependence: ϵ1 remains nearly constant over the investigated temperature range, whereas ϵ2 tends to decrease toward zero with increasing undercooling. These trends indicate that the anisotropy of the interfacial free energy at high undercoolings is primarily governed by ϵ1.