Microstructure evolution in undercooled Ni-Si melt

Upon non-equilibrium solidification, the intrinsic parameters, such as moving velocity,temperature, solute partition coefficient, and liquid and solid concentrations at the interface, deviatefrom their equilibrium characteristics, and the morphology of the as-solidified structure and the grainsize are influenced by the non-equilibrium liqulid/solid transformation, which further influences thesubquent solid-state transformation. Adopting molten glass purification technology combined withcycle superheating method, the microstructure evolution of Ni-11at.%Si alloy in differentundercooling was investigated. It was found that, with the increase of the initial undercooling, grainrefinement occurred in microstructures of undercooled Ni-11at.%Si alloy. Meanwhile, the NL modelwas used to discuss the two different dendrite morphologies. According to Karma's model fordendrite fragmentation, the grain refinement of undercooled Ni-11at.%Si alloy was in goodagreement with the experimental data, and the grain size was reduced with the increasing ΔT. Theenergy-dispersive spectroscopy (EDS) measurement was applied to analyze the solid solubility of Siatom in α-Ni matrix. It was found that the solid solubility of Si atom in α-Ni matrix increased withundercooling. At the undercooling of ΔT>220K, a complete solute trapping occurred.