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Abstract: Three Co–Sn alloys with compositions around the eutectic point were undercooled to different degrees below the equilibrium liquidus temperature and the solidification behaviors were investigated by monitoring the temperature recalescence and examing the solidification structure. It is revealed that the primary phase during rapid solidification changes complexly with the increasing undercooling in the off-eutectic alloys, while coupled eutectic growth takes place at all undercoolings in the eutectic alloy. Two types of anomalous eutectics form in the alloys: one evolving from coupled eutectics and the other from single phase dendrites or seaweeds. The crystallographic orientation of eutectic phases in the anomalous eutectic is dependent on which type their precursors belong to. [Copyright &y& Elsevier]

Abstract: How to explore an inherent linkage between non-equilibrium liqulid/solid transformation (LST) and subsequent solid-state transition (SST) is becoming more and more important for material preparation. Applying highly undercooled solidification and melting spinning, single-phase supersaturated solid solution (SSSS) was prepared for immiscible Fe–Cu and low-solid-solubility Fe–B alloys, respectively. By performing isothermal annealings at temperatures for the above SSSS, an inherent linkage between non-equilibrium LST and solid-state grain growth has been studied, in terms of an extended dendrite growth model and solute trapping model (for non-equilibrium solidification) and a numerical and an analytical thermo-kinetic model (for solid-state grain growth). For Fe–Cu SSSS, a relation between the metastable equilibrium grain size and the initial melt undercooling was derived, whereas, for Fe–B SSSS, a relation between the metastable equilibrium grain size and the ribbon thickness/rotational speed (in melt spinning) was deduced. The model prediction is consistent with the experimental result, indicating that the solid-state grain growth stops as a result of decrease in GB energy due to solute segregation to GBs. This further certifies that, for the alloys considered, the final microstructure is determined by both the non-equilibrium LST and the solid-state grain growth including GB segregation. [ABSTRACT FROM AUTHOR]

Abstract: Assuming thermal balance and solute conservation, a numerical model has been proposed to describe the recalescence behavior of bulk-undercooled Cu–Ni melts. Applying a finite-difference scheme, the transformed solid fraction upon recalescence is given as a function of the liquid temperature, while the average liquid concentration can be tracked by calculation of the liquid/solid (L/S) Gibbs energy difference, in combination with a dendrite growth model. Accordingly, a transition from non-equilibrium to equilibrium process has been described from the evolution of L/S Gibbs energy difference. Applying the present model, the experimentally observed maximum recalescence temperature can be well predicted. [Copyright &y& Elsevier]