Abstract
Studying the microstructure evolution mechanism of directional solidification by numerical simulation has the directive significance in the solidification theory and practical production. Taking account of constitutional undercooling,curvature undercooling,preferred growth orientation coefficient,temperature gradient and pulling velocity,a modified cellular automaton(MCA)model has been developed to simulate the influence of different temperature gradient directions,different preferred growth orientations and different pulling velocities on the morphologies of columnar dendrites. The simulation results well describe the influence of inclination angle between temperature gradient and growth direction on primary dendrite arm spacing(PDAS).Meanwhile the simulation results also reproduce the competitive growth of columnar dendrites with different preferred growth orientations and the splitting of the columnar dendritic tips.For the purpose of verifying this model,the relevant experiments have been carried out on an NH_4Cl-H_2O solution.The experimental results are compared critically with the simulation ones from the MCA model.
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