Simulation of solid deformation during solidification: Shearing and compression of polycrystalline structures

Deformation of the semi-solid mush during solidification is a common phenomenon in metal casting. At relatively high fractions of solid, grain boundaries play a key role in determining the mechanical behavior of solidifying structures, but little is known about the interplay between solidification and deformation. In the present study, a polycrystalline phase-field model is combined with a material point method stress analysis to numerically simulate the coupled solidification and elasto-viscoplastic deformation behavior of a pure substance in two dimensions. It is shown that shearing of a semi-solid structure occurs primarily in relatively narrow bands near or inside the grain boundaries or in the thin junctions between different dendrite arms. The deformations can cause the formation of low-angle tilt grain boundaries inside individual dendrite arms. In addition, grain boundaries form when different arms of a deformed single dendrite impinge. During compression of a high-solid fraction dendritic structure, the deformations are limited to a relatively thin layer along the compressing boundary. The compression causes consolidation of this layer into a fully solid structure that consists of numerous sub-grains. It is recommended that an improved model be developed for the variation of the mechanical properties inside grain boundaries.