Abstract
A phase-field model coupled to the multiphase/multiscale model is used to simulate the microstructural morphology and predict the CET during solidification. The considered mechanism for the CET is based on interactions of solute between the equiaxed grains and the advancing columnar front. The results for the solute concentration in liquid region, dendrite tip velocity, volume fraction of the liquid and solid are presented and discussed. The phase-field model is used to simulate the dendritic morphology of an alloy directionally solidified, by imposing a constant temperature gradient. The simulation of the equiaxed grains growth requires a further important element, the growth of grains with different crystallographic orientations. The grain orientations are generated randomly for each nucleus introduced in computational domain. Finally, the coupling results between the multiphase/multiscale model and phase-field are presented and discussed. For higher nuclei density present in the melt, a shorter distance between mold wall and the equiaxed zone in the solidification process can be observed. A solute concentration boundary layer exists in the liquid along the columnar grain contour. The concentrations in the solid indicate the presence of a microsegregation pattern. The simulated results show that the solidification features are consistent with those observed based on the metallographic examinations of cast microstructures reported in the literature.
Highlights
Solidification is the main phenomenon taking place during casting
The columnar-to-equiaxed transition (CET) will occur, when the solute rejected from the equiaxed grains is sufficient to dissipate the solutal undercooling at the columnar front, such that concentration in extradendritic liquid (Cl) has increased to Cl*
The results show that microstructural morphology depends strongly on said nuclei density (Figure 9 and Figure 10)
Summary
Solidification is the main phenomenon taking place during casting. This, in turn, has long been known as a relatively inexpensive means for producing metal goods. By tracking the columnar front movement and calculating the growth of equiaxed grains in the undercooled liquid in front of it, the CET can be predicted [3] [8]-[15] In both stochastic and deterministic models, the evolution of grain morphology and the competitive growth between columnar and equiaxed grains during the solidification process are not considered. The qualities of aluminum and its alloys are deciding factors for designers, manufacturers and industrial users who are always on the lookout for better-performing materials In this present study, the microstructural evolution and competitive growth from onset of solidification process in Al-0.013 mol% Cu alloy under a constant cooling rate are simulated. It is in this general framework that the present study is developed, with a focus on Al-Cu binary alloy and phase-field model coupled to the multiphase/multiscale model implemented via finite differences method in the explicit form
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