Fig. 1. SEM micrographs showing the morphology of the abnormal tertiary dendrite arms in directionally solidified Sn-40 at.%Mn peritectic alloy (41 K/mm) above and below peritectic temperature TP at different growth velocities: (a) v = 5 μm/s above TP; (b) v = 10 μm/s above TP; (c) v = 30 μm/s above TP; (d) v = 50 μm/s above TP; (e) v = 100 μm/s above TP; (f) v = 5 μm/s below TP; (g) v = 10 μm/s below TP; (h) v = 30 μm/s below TP; (i) v = 50 μm/s below TP; (j) v = 100 μm/s below TP.

Fig. 2. The variation of the morphology of the abnormal tertiary dendrite.

Fig. 3. The dependence of the ratio φ=h/w on local solidification time tf at different growth velocities: (a) v = 5 μm/s; (b) v = 10 μm/s; (c) v = 30 μm/s; (d) v = 50 μm/s; (e) v = 100 μm/s.

Fig. 4. Illustration of the formation of the abnormal tertiary dendrite: (a) Gibbs-Thomson effect is more important than the TGZM effect before peritectic reaction in Sn-Mn alloy; (b) TGZM is more important than the Gibbs-Thomson effect after peritectic reaction in Sn-Mn alloy; (c) TGZM is more important than the Gibbs-Thomson effect before (c) and after (d) peritectic reaction in Sn-Ni alloy.

Fig. 5. The investigation of the formation mechanism of the abnormal tertiary dendrite arm: (a) the control area S=Δx·w at the hot side of the liquid pool is chosen; (b) the variation of the solidification velocity vsolid, the advancing velocity vadv and the remelting velocity vremelt with local solidification time tf at the growth velocity of 5 μm/s.