Anomalous eutectic morphologies were observed during laser remelting of a Ni-Sn powder bed, where it was sandwiched between a lamellar eutectic at the bottom of melt pool. That is, the anomalous eutectic growth mechanism can be divided into two processes: one is the lamellar to anomalous transition (LAT); the other is the anomalous to lamellar transition (ALT). The thermal distribution at the bottom of melt pool is simulated by the finite difference method. It is found that the cooling rate at the bottom of melt pool is a linear function of time. A cellular automaton (CA) model is developed to simulate the anomalous growth. Simulation results show that the mechanism of the LAT is that one phase overgrows the other followed by subsequent nucleating of the other phase. The mechanism of the ALT is the competitive growth between the anomalous and lamellar eutectic; as the cooling rate increased, the lamellar eutectic is more competitive.

This study investigates eutectic morphology transitions in Ni-Sn alloys using Bridgman directional solidification with a transition variable speed coupled with cellular automaton (CA) simulations. Steady-state solidification (0.1–2000 μm/s) produced only regular lamellar/rod-like eutectics, while velocity jumps triggered anomalous eutectic formation. As the drawing speed increased, the lamellar spacing decreased from ~3 μm to 0.4 μm, while the microhardness increased from ~426 HV to 500 HV. The experiments on Ni-Sn alloys revealed that anomalous eutectic morphologies form specifically at velocity transition interfaces (0.1–1000 μm/s), consistent with CA simulations showing destabilization of the lamellae, epitaxial growth of the Ni₃Sn phase, and decoupled nucleation of the α-Ni phase for the formation. The work defines a processing window for anomalous eutectic formation and provides mechanistic insights bridging undercooling and directional solidification regimes.

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.