Solidification mechanism transition of liquid Co-Cu-Ni ternary alloy.

We report a solidification mechanism transition of liquid ternary CoCuNi alloy when it solidifies at a critical undercooling of about 344 K. When undercooling at Δ T<344 K, the solidification process is characterized by primary S (Co) dendritic growth and a subsequent peritectic transition. The dendritic growth velocity of S (Co) dendrite increases with the rise of undercooling. However, once Δ T>344 K, the solidification velocity decreases with the increase of undercooling. In this case, liquid/liquid phase separation takes place prior to solidification. The minor L (Cu) droplets hinder the motion of the solidification front, and a monotectic transition may occur in the major L phase. These facts caused by metastable phase separation are responsible for the slow growth at high undercoolings. [ABSTRACT FROM AUTHOR]