Effect of Nucleant Particle Agglomeration on Grain Size

Solute accumulation/depletion in the liquid around a growing solid particle during the solidification of metallic melts creates a constitutionally supercooled (CS) zone that has a significant effect on the final solidified grain structure. In this paper, we introduce two mechanisms related to the CS zone that affect grain size: one is the grain initiation free zone (GIFZ) that describes the inability of nucleant particles located in the CS zone for grain initiation and the other is re-melting (RM) of solid particles due to overlap of CS zones. Based on these two mechanisms, we have systematically analysed the effect of nucleant particle agglomeration on grain size. We found that nucleant particle agglomeration has a significant effect on grain size and is responsible for the discrepancy between theoretically predicted grain size and the experimental data. In addition, our numerical analysis suggests that under normal solidification conditions relevant to industrial practice solid particle re-melting has little effect on grain size and thus may be ignored during theoretical analysis. A practical implication from this work is that significant grain refinement can be achieved by dispersing the nucleant particles in the melt prior to solidification.

Automated summary

During the solidification of metallic melts, the accumulation/depletion of solute in the surrounding liquid creates a constitutionally supercooled (CS) zone that significantly affects the final grain structure. Two mechanisms – the grain initiation free zone (GIFZ) and re-melting (RM) of solid particles – related to the CS zone and their impact on grain size were discussed in this paper. The study found that nucleant particle agglomeration has a significant effect on grain size and explains the difference between theoretically predicted grain size and experimental data. Moreover, numerical analysis suggests that solid particle re-melting has little effect on grain size under normal solidification conditions and may be disregarded during theoretical analysis.