Effect of Platform Dimension on the Dendrite Growth and Stray Grain Formation in a Ni-Base Single-Crystal Superalloy

A model of typical turbine blade shape with different platforms was designed to study the nucleation and growth of stray grains in the platforms by both experimental investigation and a ProCAST simulation based on a cellular automaton finite-element model. The results show that at the withdrawal rate of 5 mm/min, no stray grains nucleate in the small dimensional platform. However, the primary grain grows into the inner and outer sections of this platform in different manners due to different thermal conditions in these sections. Furthermore, with the increase of platform dimension, stray grains with random orientations gradually nucleate in the corners of the platforms. It is found that these stray grains tend to nucleate either in the inner corners or at a faster withdrawal rate, which is associated with the corresponding thermal condition. Based on these results, the rule of the critical platform dimension and withdrawal rate without stray grain formation has been proposed. Besides, the simulation results are in accordance with experimental findings.