Experimental verification of ribbon formation process in chill-block melt spinning

The rapid solidification process in melt spinning has been empirically deduced from the relationship between the resultant phases/microstructure and the wheel speed, because the melt/substrate interface is difficult to observe directly. The controversy over whether the ribbon solidifies in or outside the melt puddle (thermal or momentum transport control) still remains unresolved. We report the first in situ observation of the melt/substrate interface. The silicon melt was ejected onto a silicon wafer rotated “transversely” by a motor in a chamber. The silicon wafer, which is transparent for wavelengths >1.1 μm, can be used as the chill substrate to simulate rapid solidification on a copper substrate, since the thermal conductivity of silicon is of the same order of magnitude as that of copper. Successive images captured through the silicon wafer by high-speed infrared imaging revealed that the ribbon solidified just at the underside of the melt puddle. It was demonstrated that ribbon formation is controlled by thermal transport.