The non-dendritic microstructure arising from grain boundary formation and wetting: A phase-field simulation and experimental investigation of semi-solid deformation

Abstract

The semi-solid metal forming process can prevent the formation of unpopular dendritic microstructures but the mechanism remains unclear. To explore the underlying causes, a challenging phase-field simulation was performed, supported by a semi-solid experiment. The simulation managed to couple dendritic growth with melt flow and solid deformation, a process that few existing models or in situ experimental techniques could analyze. This study found that under deformation, grain boundary formation and wetting play a pivotal role in the formation of non-dendritic structures: it is the grain boundary formation and wetting that split the bending side-branch from dendrite trunk; the detached side-branch could then evolve into a non-dendritic morphology. The simulation showed that wetting could finish almost immediately after a moderate bending. This process appears similar to but is essentially distinct from the conventional explanation that describes dendrite fragmentation as mechanical breakage.

Keywords

• Phase-field method
• Semi-solid deformation
• Grain boundary wetting
• Non-dendritic microstructure