Numerical simulation of solidification structure during electron beam smelting process of superalloy ingots
A cellular automaton–finite element (CAFE) model was developed to simulate the solidification structure evolution of DD98M superalloy ingots during electron beam smelting (EBS). The model couples heat transfer, fluid flow, and solute diffusion. Grain nucleation and growth occur opposite to the heat flow direction. Simulation results show good agreement with experimental observations. The influence of nucleation parameters on solidification structure was systematically examined. Increasing the maximum bulk nucleation density reduces grain size and promotes a larger equiaxed grain region while reducing the columnar grain region. Increasing the mean bulk nucleation undercooling results in a smaller equiaxed region and an expanded columnar grain zone. The standard deviation of bulk nucleation undercooling has a negligible effect on grain morphology. The determined nucleation parameters (ΔTs,max=0.5 K, ΔTs,σ=1 K, ns,max=1×10^7 m−2, ΔTv,max=5 K, ΔTv,σ=1 K, nv,max=5×10^9 m−3) were used to simulate large-scale ingots. EBSD analysis confirmed the model's predictive capability. The solidification sequence begins with fine equiaxed crystals at the bottom and sides, followed by columnar growth that decreases in rate as the billet is pulled out, with sidewall heat dissipation eventually dominating and altering grain growth direction.