Paper presents the results of research on modified surface grain refinement method used in investment casting of hollow, thin-walled parts
made of nickel based superalloys. In the current technology, the refining inoculant is applied to the surface of the wax pattern and then, it
is transferred to the ceramic mould surface during dewaxing. Because of its chemical activity the inoculant may react with the liquid metal
which can cause defects on the external surface of the cast part. The method proposed in the paper aims to reduce the risk of external
surface defects by applying the grain refiner only to the ceramic core which shapes the internal surface of the hollow casting. In case of
thin-walled parts the grain refinement effect is visible throughout the thickness of the walls. The method is meant to be used when internal
surface finish is less important, like for example, aircraft engine turbine blades, where the hollowing of the cast is mainly used to lower the
weight and aid in cooling during operation.