Dendrite growth in directional solidification of succinonitrile-5% ethanol alloy was observed to examine effects of temperature and solute distribution.The results reveal that solute concentration in the dendrite interface which is in the middle area of two competitive growth can be increased with the drainage of solute in the process of dendritic growth in both sides

which results in more and more serious solute segregation in the middle dendrite so as to induce the necking effects.That dendrite in the middle area in multi-competitive growth dendrite appears in necking effects as a result of slow growth velocity is attributed to release latent heat from other dendrites growth

resulting in increasing temperature of middle area to form constitutional supercooling.Necking effects can be strengthened with increasing in liquid flow velocity at solid/liquid interface and in heterogeneity of temperature and solute distribution based on theoretical analysis

which is well in agreement with experimental ones.