Abstract
The microstructural evolution of dendrite coarsening during isothermal holding is simulated using a quantitative cellular automaton (CA) model involving the mechanisms of both solidification and melting. The present model encompasses the essential aspects of thermodynamics and kinetics, particularly the evolution/influence of composition, temperature, and curvature, leading to valid simulations of simultaneous solidification and melting. Model validation is performed through a comparison of the CA simulations with analytical predictions for a liquid pool migrating in the mushy zone of a SCN–0.3 wt.% ACE alloy due to temperature gradient zone melting. The model is applied to simulate the microstructural evolution of columnar dendrites of a SCN–2.0 wt.% ACE alloy during isothermal holding in a mushy zone. The simulation results are compared with those of a previous CA model that does not include the melting mechanism under otherwise identical conditions. The role of melting for dendrite coarsening is quantified, showing how the melting influences the coarsening process. The present model effectively reproduces the typical dendrite coarsening features as observed in experiments reported in the literature. The simulations reveal how local solidification and melting stimulate each other through the complicated interactions between phase transformation, interface shape variation, and solute diffusion.
Highlights
Understanding microstructural evolution during solidification is the prerequisite for controlling microstructures and vital for achieving desired properties of castings
Extensive experimental studies have been carried out to investigate the processes of dendrite coarsening by post-mortem analyses of samples quenched from mushy zones[11,12,13,14] or by in situ observations using transparent alloys[15] and synchrotron-based X-ray tomography[9,16,17,18,19,20]
A 2-D cellular automaton (CA) model is proposed for the simulation of microstructural evolution involving both solidification and melting in mushy zones of alloys
Summary
We applied the proposed CA model to simulate liquid pool migration in the mushy zone with different pulling velocities and dendrite arm migration in a temperature gradient. The initial fast drop in SVs is due to the fact that the dendritic microstructure prior to isothermal holding is simulated by the previous CA model This model does not include the effect of melting/remelting and generates some very fine (highly curved) microstructural elements that disappear rapidly. Numerous experimental studies showed that the specific surface area follows approximately a t−1/3 power-law during dendrite coarsening[11,12,13,16,17], even though the solid-liquid mixtures might not be evolving self-[11,12]
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