Phase-field simulation of interface and microstructure evolution at high growth velocities during directional solidification of Ti55Al45 alloy

A phase-field model whose free energy of the solidification system is derived from the Calphad thermodynamic modeling of phase diagram is used to simulate the interface and microstructure evolution of Ti55Al45 alloy during directional solidification at high growth velocities (near the absolute stability) when the liquid-solid phase transition happens. The dynamics of the breakdown of initially planar interfaces into cellular structures are shown. When growth velocity is higher than the absolute stability, a planar interface is reestablished after initial breakdown of interface. The solute distributions near the cell tips are investigated at different growth velocities. The increase of solid composition and the reduction of liquid composition with the increase of growth velocities will cause the gradually uniform distribution of solute because of the appearance of solute trapping ahead of the solid-liquid interface.