Microstructure and morphology of Si crystals grown in pure Si and Al-Si melts

Microstructure of Al-40 wt%Si samples solidified in electromagnetic levitation furnace is studied at high melt undercooling. Primary Si with feathery and dendritic structures is observed. As this takes place, single Si crystals either contain secondary dendrite arms or represent faceted structures. Our experiments show that at a certain undercooling, there exists the microstructural transition zone of faceted to non-faceted growth. Also, we analyze the shape of dendritic crystals solidifying from liquid Si as well as from hypereutectic Al-Si melts at high growth undercoolings. The shapes of dendrite tips grown at undercoolings >100 K along the surface of levitated Al-40 wt%Si droplets are compared with pure Si dendrite tips from the literature. The dendrite tips are digitized and superimposed with theoretical shape function recently derived by stitching the Ivantsov and Brener solutions. We show that experimental and theoretical dendrite tips are in good agreement for Si and Al-Si samples.

Automated summary

The microstructure of Al-40 wt%Si samples solidified in an electromagnetic levitation furnace under high melt undercooling is studied. Feathery and dendritic structures of primary Si are observed, and the shape of dendritic crystals solidifying from liquid Si and hypereutectic Al-Si melts at high growth undercoolings is analyzed. Experimental and theoretical dendrite tips of Si and Al-Si samples are found to be in good agreement.