Microstructural evolution of rapidly solidified Co-Mo and Ni-Mo eutectic alloys

Droplets of Co-37.6 wt pct Mo and Ni-47.7 wt pct Mo eutectic alloys were rapidly solidified during the containerless processing in a 3 m drop tube. A kind of anomalous eutectic appears in these two eutectic alloys when undercooling is beyond 56 K and 61 K, respectively. The two eutectic phases in the anomalous eutectic were observed to grow in the dendrite manner. The formation of the anomalous eutectic is ascribed to the cooperative dendrite growth of the two independently nucleated eutectic phases. Current dendrite and eutectic growth theories are applied to describe the observed processes.