Numerical Simulation of Cellular/Dendrite Arm Spacing Selection During Unidirectional Solidification of Ti-Al Alloy

Solute diffusion controlled solidification model was applied to simulate the initial stage cellular to dendrite transition of Ti55Al45 alloys during directional solidification at different velocities.The simulation results show that the dendrite spacing is larger than that of cellular spacing at a given rate,the columnar grain spacing sharply increases to a maximum as solidification advance to coexistence zone.In addition,simulation also revealed the numbers of the seeds also exert an influence on the grain spacing,with increasing the numbers of the seeds;the uniform degree of the columnar grain spacing tends to increase.Lastly the main influence factors of affecting cellular/dendritic transition were analyzed,which could be dendrite growth resulting in slight fluctuations of liquid composition occurred at growth front.The simulation results also are in reasonable agreement with experiment observation at low cooling rates.