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 general, and of intermetallic compounds in particular. The contributions of the various components of the interfacial undercooling can be clarified using a graphical representation in terms of their corresponding free energies. The interfacial undercooling can consist of up to four distinct components, excluding the curvature undercooling. The individual distinct effects of each of these components on the kinetic phase boundaries (loci on interface condition diagrams) are discussed. The effects 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 interfacial attachment processes can be collision-limited as expected for metallic systems.