Grain structure prediction of Ni-base superalloy castings using the cellular automaton-finite element method

Abstract

A three-dimensional cellular automaton (CA) model has been coupled with finite-element (FE) heat flow calculation to predict the solidification grain structures in a Ni-base superalloy. In the present CA–FE model, Gaussian distribution of nucleation sites was adopted and the Kurz–Giovanola–Trivedi model was extended to multi-component alloys to account for the growth kinetics of the dendrite tip. In particular, for describing the Gaussian distribution of nucleation sites at the mold surface, an empirical relationship between the nucleation density at the surface and the initial cooling time of the melt was proposed and applied to the input parameter in the model. The predicted grain structures were validated at various casting conditions by comparison with the experimental micrographs obtained with cylindrical shaped castings. The CA–FE model was also applied to the complex shaped turbine blade casting and the computed grain structure of turbine blade airfoil was compared with the experimental micrograph.