Abstract: Solute diffusion controlled solidification model was applied to simulate the columnar to equiaxed transition (CET) during directional solidification of of TiAl alloys. The simulation results showed that the solutal interactions from growing equiaxed grains play an important role on CET, which can render a large fraction of seeds inactive. The effects of the applied temperature gradient and pulling speed, the equiaxed seed spacing and nucleation undercooling on the CET are investigated in present simulation. It indicated that the columnar branch spacing depends not only on the temperature gradient and the pulling speed, but also number of the seeds, a spacing adjustment can occur through initiation of seeds that develop into new columnar grains. The dependence of the CET on the temperature gradient and pulling speed, qualitatively agrees with the analytical CET model of Hunt.

Key words: TiAl alloys, the columnar to equiaxed trans, numerical simulation