The dendritic morphology in Zn-Cd dilute alloys

Abstract

In Zn-Cd dilute alloys the transition from cells to dendrites is analyzed for increasing values of constitutional supercooling. The substructure evolution is through two simultaneous and continuous mechanisms: arm formation as a result of the node mechanism and cell elongation in a direction parallel to the basal plane. For maximum conditions of constitutional supercooling the substructure is composed of dendrites growing cooperatively in a 〈1010〉 direction. The use of epitaxial film techniques shows that the dendrites have a cruciform cross-section with plate-like arms. From these plates, develop uniformly spaced higher order arms which grow either on the basal plane in equivalent 〈1010〉 crystallographic directions or on the (1210) plane in a 〈0001〉 direction. The same technique used near the frozen interface proves that the plates are the result of a coarsening mechanism occuring during solidification. The substructure segregation pattern has, as a fundamental characteristics, a higher segregation in planes parallel to the basal plane than in any other orientation. © 1972.