MODELING OF MACROSEGREGATION AND SOLIDIFICATION GRAIN STRUCTURES WITH A COUPLED CELLULAR AUTOMATON - FINITE ELEMENT MODEL

摘要

Extension of a coupled Cellular Automaton (CA) - Finite Element (FE) model is presented for the prediction of solidification grain structures and macrosegregation. Following the validation procedure proposed by Ahmad et al. [Metallurgical and Materials Transactions 29A (1998) 617-630], applications of the model to the experiments conducted by Hebditch and Hunt are proposed [Metallurgical Transactions 5 (1974) 1557-1564]. The algorithm and the numerical implementation of the coupling between the CA and FE methods are first validated by considering a single grain that develops with almost no undercooling. Such a calculation is shown to retrieve the solution of a purely FE method calculation in which the grain structure is not accounted for. Several applications of the model are then presented in order to quantify the effects of the grain structure on the final macrosegregation map. In particular, the eqffect of the undercooling of the columnar front, the presence of equiaxed grains nucleated in the undercooled liquid, as well as the transport and sedimentation of equiaxed grains are investigated. The differences between the segregation maps predicted with the CAFE model and the purely FE model are presented. Although good validation is reached with the experimental segregation profiles, it is concluded that refined experimental data are required to further validate the predictions.