Grain structure formation of Ti-6Al-4V ingot during VAR process

A finite element-cellular automaton (FE-CA) method is used to simulate the grain structure formation of Ti-6Al-4V ingot during Vacuum Arc Remelting (VAR) process. In this FE-CA model, macroscopic heat conduction differential equation is solved by FE method and moving boundary model is used to get temperature distribution of the whole ingot ; subsequent mesoscopic model of grain nucleation and growth are characterized by the Gaussian distribution continuous nucleation model and the extended KGT model, respectively. Numerical simulation is performed to investigate the effect of melting rate, heat transfer coefficient and nucleation parameters on the distribution, proportion, size of equiaxed grains and columnar grains, together with predicted columnar-to-equiaxed transition (CET). Calculated results reveal that either increasing melting rate or decreasing heat transfer coefficient promotes the CET. Higher mean undercooling and larger nucleation density lead to larger columnar dendrite zone and smaller grain size, respectively. The variation of standard deviation has a minor influence on the grain structure of the ingot.