THE INTERFACIAL UNDERCOOLING IN SOLIDIFICATION

The origin and characteristics of the undercooling at the solid/liquid interface are examined for solidification of metallic alloys in gener al, and of intermetallic compounds in particular. The contributions of the various components of the interfacial undercooling can be clarifi ed using a graphical representation in terms of their corresponding fr ee energies. The interfacial undercooling can consist of up to four di stinct components, excluding the curvature undercooling. The individua l distinct effects of each of these components on the kinetic phase bo undaries (loci on interface condition diagrams) are discussed. The eff ects become apparent for rapid solidification and particular attention is paid to non-equilibrium, solute- and disorder-trapping effects in the case of intermetallic compounds. Even when the overall interfacial undercooling is large, i.e. the interface appears sluggish, the inter facial attachment processes can be collision-limited as expected for m etallic systems.