Influence of process parameters on CET in Ti-Al alloy ingot with consideration of shrinkage cavity formation: A computer simulation

A macro-micro mathematical model is developed for numerical study of the columnar-to-equiaxed transition (CET) during solidification processes of Ti-Al alloy ingots, which couples the finite difference method (FDM) at the macroscale with a cellular automaton (CA) model at the microscale. The macroscopic model is used to solve the governing equations. The microscopic model is taken to predict the nucleation and growth of grains. The formation of shrinkage cavity during solidification is simulated by a modified method. With the proposed model, numerical simulations are performed to investigate the influences of mold temperature, mold material, superheat and initial alloy composition on CET. Calculated results reveal that the equiaxed zone is found to expand with decreasing the superheat and thermal conductivity of mold, as well as increasing alloy composition and mold temperature. A higher cooling rate can be obtained by decreasing the mold temperature and increasing the alloy composition, superheat and thermal conductivity of mold. The underlying mechanisms responsible for those physical phenomena are discussed. (C) 2006 Elsevier B.V. All rights reserved.