Phase and microstructure selection in peritectic alloys close to the limit of constitutional undercooling

Phase and microstructure selection during directional solidification of peritectic alloys has remained unclear for years despite their great technical importance. Taking into account nucleation and growth of the phases, a criterion is proposed in order to determine the phase as a function of alloy composition and growth conditions. A microstructure selection diagram for peritectic alloys close to the limit of constitutional undercooling is developed. This theoretical approach is compared with results from Bridgman experiments using Fe–Ni alloys, and good agreement is obtained. The validity and the limits of this model are also discussed.