Fengyi Yu

The existing theoretical analyses of solidification dynamics lack the insights of historical relevance and transport processes in the whole system. Through the phase-field model, this paper investigates the evolution in the whole domain during entire directional solidification. First, the evolution of characteristic parameters is obtained, including the solute concentration ahead of interface and tip velocity, demonstrating the dissipative features of solidification. Second, by adjusting the diffusion coefficient DL, the dissipation at the interface can be altered. With different DL, different stages during directional solidification are investigated, including planar growth and instability, dendrite growth, and steady-state growth. The results indicate the important role of solute diffusion in alloy solidification. From the viewpoint of the whole domain, smaller DL corresponds to a higher degree of dissipation, forming more interfaces during solidification. Moreover, the competitive influences of tip curvature and velocity are also because of the dissipation, resulting from the friction of atoms.

In alloy solidification, the transport processes of heat and solute result in morphological instability of the interface, forming different patterns of the solidification structure and determining the mechanical properties of components. As the first observable phenomenon of morphological instabilities, planar instability influences the subsequent stages significantly, deserving in-depth investigations. In this paper, the planar instability in alloy solidification under varying conditions is studied. First, the dynamical evolution of the planar instability is performed by the theoretical model and the phase-field model, respectively. Second, to represent the history-dependence of solidification, varying parameters are adopted in the simulations. Then, the criterion of planar instability under varying conditions is discussed. This paper considers that the critical parameters of planar instability are the excess free energy at the interface and the corresponding interfacial energy. Finally, to validate the criterion, comparisons between the phase-field and theoretical models are carried out, showing good consistency. Moreover, solidification processes with different preferred crystallographic orientations are performed, demonstrating the effect mechanism of the excess free energy and interfacial energy on planar instability. The idea of the interfacial energy influencing the planar instability could be applied to investigating other patterns induced by interfacial instability.

In alloy solidification, the transport processes of heat and solute result in morphological instability of the interface, forming different patterns of solidification structure and determining the mechanical properties of components. As the first observable phenomenon of the morphological instabilities, the planar instability influences the subsequent stages significantly, deserving in-depth investigations. In this paper, the planar instability in alloy solidification under varying conditions is studied. Firstly, the dynamical evolution of the planar instability is performed by the theoretical model and phase-field model, respectively. Secondly, to represent the history-dependence of solidification, the varying parameters are adopted in the simulations. Then the criterion of the planar instability under the varying conditions is discussed. This paper considers the critical parameters of the planar instability are the excess free energy at the interface and corresponding interfacial energy. Finally, to validate the criterion, the comparisons between the phase-field model and theoretical model are carried out, showing good consistency. Moreover, solidification processes with different preferred crystallographic orientations are performed, demonstrating the effect mechanism of the excess free energy and interfacial energy on the planar instability. The idea of the interfacial energy influencing the planar instability could be applied to investigating other patterns induced by interfacial instability.