Geometrical effect of freckle formation on directionally solidified superalloy CM247 LC components

Abstract

The geometrical effect of freckle formation was investigated on directionally solidified superalloy CM247 LC components. The components with a reduction in the transverse section were favourable to freckle formation whereas those with an enlargement in the cross-section remained freckle-free, clearly revealing a promoting and a suppressing effects on the onset the freckle formation, respectively. Temperature measurements using thermal couples and computer simulations were performed to detect the geometrical effect on the local thermal field. The evaluated local solidification conditions cannot explain the corresponding freckling phenomena, such as why freckling becomes more pronounced in areas where the local thermal gradient is significantly increased. It is indicated that the geometrical feature of the components can strongly change the reservoir and flow condition for thermosolutal convection, which can therefore more effectively affect the freckle formation than the local thermal conditions.