3-DIMENSIONAL SIMULATION OF THE GRAIN FORMATION IN INVESTMENT CASTINGS

A 3-dimensional (3-D) probabilistic model which has been developed pre viously for the prediction of grain structure formation during solidif ication is applied to thin superalloy plates produced using the invest ment-casting process. This model considers the random nucleation and o rientation of nuclei formed at the mold surface and in the bulk of the liquid, the growth kinetics of the dendrite tips, and the preferentia l growth directions of the dendrite trunks and arms. In the present st udy, the grains are assumed to nucleate at the surface of the mold onl y. The computed grain structures, as observed in 2-dimensional (2-D) s ections made parallel to the mold surface, are compared with experimen tal micrographs. The grain densities are then deduced as a function of the distance from the mold surface for both the experiment and the si mulation. It is shown that these values are in good agreement, thus, p roviding validation of the grain formation mechanisms built into the 3 -D probabilistic model. Finally, this model is further extended to mor e complex geometries and the 3-D computed grain structure of an equiax ed turbine-blade airfoil is compared with the experimental transverse section micrograph.