Metastable phase separation and rapid solidification of undercooled Co₄₀Fe₄₀Cu₂₀ alloy

The metastable liquid phase separation and rapid solidification behaviors of Co₄₀Fe₄₀Cu₂₀ alloy were investigated by using differential thermal analysis (DTA) in combination with glass fluxing and electromagnetic levitation (EML) techniques. The critical liquid phase separation undercooling for this alloy was determined by DTA to be 174 K. Macrosegregation morphologies are formed in the bulk samples processed by both DTA and EML. It is revealed that undercooling level, cooling rate, convection, and surface tension difference between the two separated phases play a dominant role in the coalescence and segregation of the separated phases. The growth velocity of the (Fe,Co) dendrite has been measured as a function of undercooling up to 275 K. The temperature rise resulting from recalescence increases linearly with the increase of undercooling because of the enhancement of recalescence. The slope change of the recalescence temperature rise versus undercooling at the critical undercooling also implies the occurrence of liquid demixing. (special topic)