The freckle formation in specially shaped castings of a single crystal superalloy was investigated under industrial production condition. The results indicate that freckle defects are asymmetrically distributed due to the asymmetrical solidification condition in the ring-likely arranged castings. On the whole

all freckles appear on the inner side of castings with poor heat transfer conditions

while the outside is free of freckle

where the temperature gradient and cooling rate are significantly lower. Locally

all freckles are preferably generated on the convex corners or cambered surface rather than concave

and the reason is that coanda effect of liquid flow in pasty zone are overlapped on the convex site

promoting the formation of freckles. Moreover

the freckles are also observed on the surface

indicating that freckles can lead to an internal defect of single crystal superalloy castings.