Effects of transverse magnetic field on the directional solidification structure and segregation behavior of Co-Al-W-based superalloy

Abstract

Directional solidification experiments were conducted on the Co-Al-W-based superalloy under an external magnetic field. The results showed that depression occurred on the right side of the solid-liquid interface at a pulling rate of 5 μm/s, and the Al solute segregated to this side. Spotty segregation also occurred on the sample's right side, and applying an external magnetic field reduced the primary dendrite arm spacing. After the pulling rate reached 50 μm/s, the magnetic field barely had any influence on the solid-liquid interface of the alloy. The primary dendrite arm spacing did not decrease further as the magnetic flux density increased beyond a certain point. This observation could be explained by the shortened action of the thermoelectromagnetic flow in the interdendritic space at an increasing pulling rate under a transverse magnetic field. At a pulling rate of 5 μm/s, the solid-liquid interface and the flow state of the interdendritic melt were altered during the solidification process with an external magnetic field than without one. Moreover, the melt flow had a significant impact on the alloy microstructure, as a result of thermoelectromagnetic convection along the solid-liquid interface induced by the magnetic field. A magnetic field dramatically intensified thermoelectromagnetic convection, facilitating interdendritic melt flow and continuously reducing the primary dendrite arm spacing.