Numerical simulation of microstructure evolution of Ti-6Al-4V alloy in vertical centrifugal casting

A multiscale model is developed for simulating the microstructure evolution during solidification processes of Ti-6Al-4V alloy in vertical centrifugal casting, which combines the 3D finite difference method (FDM) at the macroscale with a 2D cellular automaton (CA) model at the microscale. The macro model is used to simulate the fluid flow, mass, heat and species transfer throughout the casting under centrifugal conditions. The micro model is used to predict the nucleation and growth of microstructures for the vertical central plane. A semi-coupled scheme between the 3D macroscopic and 2D microscopic calculations is adopted. Based on the CA cell, a modified method for simulating the shrinkage cavity is given. With the proposed model, numerical simulations are performed to investigate the influences of mould rotation speed, superheat, and mould material on microstructure formation. Calculated results reveal that the equiaxed zone is found to expand with increasing the mould rotation speed, as well as decreasing melt superheat and heat diffusivity of mould. The role of rotation speed is much greater than that of superheat and mould material in centrifugal casting. The underlying mechanisms responsible for those physical phenomena are discussed.