Effect of Solidification Rate on Microstructure and Solid/Liquid Interface Morphology of Ni-11.5wt% Si Eutectic Alloy

In this study Ni-Ni₃Si eutectic in situ composites are obtained by Bridgman directional solidification technique when the solidification rate varies from 6.0μm/s to 40.0μm/s. At the low solidification rates the lamellar spacing is decreased with increasing the solidification rate. When the solidification rate is higher than 25μm/s, the lamellar spacing tends to be increased, because the higher undercooling makes the mass transport less effective. The adjustments of lamellar spacing are also observed during the directional solidification process, which is consistent with the minimum undercooling criterion. Moreover, the transitions from planar interface to cellular, then to dendritic interface, and finally to cellular interface morphologies with increasing velocity are observed by sudden quenching when the crystal growth tends to be stable.