Modeling of percolation of globular-equiaxed grains in Al-Cu alloys

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A new mesoscopic model able to describe percolation of globular-equiaxed grains, highly relevant for hot tearing formation in castings, has been developed. This model is inspired from the granular model of Sistaninia et al. [1-5] that considers polyhedral grains based on a Voronoi tessellation of space. In the new mesoscopic model, the set of tetrahedra that define the grains are further subdivided into smaller tetrahedra called columns and solute diffusion is considered in both the solid and liquid phases. This allows to obtain smoother shapes of the grains and to better describe a progressive coalescence of the grains. In addition, it gives the possibility of having liquid pockets in the last-stage solidification (which is not possible in the case of polyhedral grains) and thus correctly describe the solid fraction at which the grain structure is percolated. The shape of the grains has first been validated with a multiphase-field method. The relevant microstructural features, such as the percolation state of an Al-Cu alloy, were then deduced from the model. This information will then be used to refine the 3D granular models of Sistaninia et al. [1-5] which account for stress development and liquid feeding, in order to create more advanced predictive tools for hot tearing formation.