Effect of withdrawal rate on the microsegregation, thermophysical properties and spatial orientation of a Ni₃Al based single crystal superalloy

The effects of withdrawal rate (1-300 μm/s) on microsegregation, solidification characteristic temperature, activation energy of melting and spatial orientation of a Re-containing Ni₃Al based single crystal superalloy were investigated in this study. With increasing withdrawal rate, the as-cast microstructure changed from planar to cellular and then to dendritic, and accordingly the microsegregation degree firstly increased and then decreased. Meanwhile, with transforming the microstructure from cellular to dendritic, the activation energy of melting increased while the liquidus and solidus temperatures decreased, and sample with the severest microsegregation degree possessed the lowest liquidus temperature. In addition, the influence of orientation of the seed on the growth of single crystal became more significant with increasing withdrawal rate, and the spatial orientation of newly growth dendritic single crystal only strictly inherited that of seed at moderate withdrawal rates.