Solidification behaviour of undercooled Co–Cu alloys showing a metastable miscibility gap

Co–Cu exhibits a metastable miscibility gap: Upon undercooling below the binodal the melt separates into the Co-rich L1-phase and the Cu-rich L2-phase. The solidification behaviour and the solidified structure of the Co-rich L1-phase is in the focus of the present work. High values of undercooling are achieved by using the method of containerless processing in an electromagnetic levitation facility (EML), the metastable states are frozen in instantaneously and are studied by scanning electron microscopy. The solidification velocity of the primary solidifying Co-rich L1-phase has been measured. A transition in microstructure of the solidified Co-rich L1-phase has been found, while at lower and intermediate undercooling Co-rich dendrites are formed, an irregular structure is dominating at higher undercooling. The results can be described within the Galenko–Danilov model for dendritic solidification.