Unraveling Anomalous Eutectic Formation in Ni-Sn Alloys During Directional Solidification with Transition Variable Speed

The transition from regular to anomalous eutectic structures critically impacts the mechanical properties of eutectic alloys. This study investigated the non-equilibrium solidification behavior of Ni-Sn alloys using Bridgman directional solidification coupled with Cellular Automaton (CA) simulations. Unlike deep undercooling methods, this approach can offer a solution by decoupling temperature gradient and growth velocity during the solidification process, revealing that anomalous eutectic formation occurs specifically at growth velocity transition zones, not during steady-state growth (0.1–2000 μm/s). CA simulations confirmed that velocity jumps destabilize regular lamellae, the Ni3Sn phase epitaxially grows along the substrate in a cellular manner, triggering independent α-Ni nucleation followed by Ni₃Sn encapsulation. This work identifies a distinct process window for anomalous eutectic formation and elucidates its decoupled nucleation mechanism, advancing non-equilibrium solidification theory.