The peritectic transformation stage is very slow and seldom reaches completion due to the low diffusion coefficient in the solid phase. During directional solidification, the liquid can only contact at the liquid/interface when the liquid/ interface is planar or cellular, thus the diffusion length of solute in peritectic phase is very long. As a result, the peritectic transformation is more difficult to take place in directional solidification, and this can be approved in Figs. 4, 5 and 7.