Non-equilibrium kinetic Phase-diagram in undercooling solidification: A case of Pseudo-binary MgTiO3-TiO2 system

Abstract

Extreme solidification processes in advanced manufacturing (e.g., laser additive manufacturing and in space fabrication) amplify challenges in predicting phase selection under severe thermodynamic non-equilibrium. Using aerodynamic levitation containerless processing, we investigate the solidification behavior of pseudo-binary MgTiO₃-TiO₂ system. Our experiments reveal an anomalous trans-phase-regime selection phenomenon in which the thermodynamically stable MgTi₂O₅ phase is kinetically suppressed from precipitation. This selection arises from nucleation kinetic barriers of MgTi₂O₅, where coupled undercooling and compositional fluctuations destabilize critical nuclei formation. By integrating composition- and temperature-dependent interfacial energy dynamics into classical nucleation theory, we develop a predictive framework that quantitatively maps anomalous phase selection regions. This approach establishes the first non-equilibrium kinetic phase diagram of this system with experimental validation, resolving long-standing discrepancies between equilibrium predictions and non-equilibrium experimental outcomes. The proposed methodology establishes a generalized paradigm for phase selection prediction, offering transformative insights into microstructure and phase control under extreme non-equilibrium solidification conditions.