VOLUME AVERAGING CONCEPT FOR MIXED COLUMNAR-EQUIAXED SOLIDIFICATION

摘要

A 3-phase volume averaging model is developed for mixed columnar-equiaxed solidification. The three phases are the melt, the solidifying columnar dendrites and equiaxed grains. As the numerical method and solution procedure for the multiphase volume averaging approach were presented previously, this paper focuses on the formulations of the model of mixed columnar-equiaxed solidification, and on the algorithm for predicting the CET. Different formulations for the equiaxed and the columnar volume-averaged mass transfer rates based on diffusion controlled growth models are proposed. Dendrite tip growth kinetics is applied to determine the columnar tip position. A new algorithm is developed to track the columnar dendrite tip front. In addition to the competitive growth between equiaxed grains and columnar dendrites, the mechanical interaction between them is simplified: the equiaxed grains are allowed to move freely near the columnar tips, whereas within the interdendrite region they are 'captured' by the growing columnar dendrites. The columnar tip stop mechanism proposed by J.D. Hunt is implemented to predict the CET. A 3D benchmark ingot (Fe-0.34 wt% C) is simulated to show the potentials of the model. 1D simulations with corresponding assumptions were also carried out to evaluate the recent model by comparing it with classical analytical solutions.